abter steel pipe manufacturer, natural gas casing and tubing,seamless steel pipe,OCTG, http://www.abtersteel.com OCTG pipe,carbon steel pipe,seamless steel pipe ,erw pipe Thu, 21 Feb 2019 09:48:37 +0000 en-US hourly 1 https://wordpress.org/?v=4.9.8 Galvanized steel pipe specification, size theoretical weight table http://www.abtersteel.com/structural-pipe/galvanized-steel-pipe-specification-size-theoretical-weight-table/ Thu, 14 Feb 2019 03:15:21 +0000 http://www.abtersteel.com/?p=4686 China standard hot-dip galvanized steel pipe|cold galvanized steel pipe specification, size theoretical weight table regulation grid OD mm Wall thickness mm Minimum wall Welded pipe ( 6 m fixed length) Galvanized pipe ( 6 m fixed length) Nominal inner diameter inch   Thick mm Meter weight kg Root weight kg Meter weight kg Root weight kg DN15 1/2 21.3 2.8 2.45 1.28 7.68 1.357 8.14 DN20 3/4 26.9 2.8 2.45 1.66 9.96 1.76 10.56 DN25 1 33.7 3.2 2.8 2.41 14.46 2.554 15.32 DN32 1.25 42.4 3.5 3.06 3.36 20.16 3.56 21.36 DN40 1.5 48.3 3.5 3.06 3.87 23.22 4.1 24.6 DN50 2 60.3 3.8 3.325 5.29 31.74 5.607 33.64 […]

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China standard hot-dip galvanized steel pipe|cold galvanized steel pipe specification, size theoretical weight table

regulation

grid

OD

mm

Wall thickness mm

Minimum wall

Welded pipe

( 6 m fixed length)

Galvanized pipe

( 6 m fixed length)

Nominal inner diameter

inch

 

Thick mm

Meter weight kg

Root weight kg

Meter weight kg

Root weight kg

DN15

1/2

21.3

2.8

2.45

1.28

7.68

1.357

8.14

DN20

3/4

26.9

2.8

2.45

1.66

9.96

1.76

10.56

DN25

1

33.7

3.2

2.8

2.41

14.46

2.554

15.32

DN32

1.25

42.4

3.5

3.06

3.36

20.16

3.56

21.36

DN40

1.5

48.3

3.5

3.06

3.87

23.22

4.1

24.6

DN50

2

60.3

3.8

3.325

5.29

31.74

5.607

33.64

DN65

2.5

76.1

4

3.5

7.11

42.66

7.536

45.21

DN80

3

88.9

4

 

8.38

50.28

8.88

53.28

DN100

4

114.3

4

 

10.88

65.28

11.53

69.18

DN125

5

140

4.5

 

15.04

90.24

15.942

98.65

DN150

6

168.3

4.5

 

18.18

109.08

19.27

115.62

DN200

8

219.1

6 (welded pipe)

 

31.53

189.18

   

DN200

8

219.1

6.5 hot-dip galvanizing

     

36.12

216.72

GB / T 3091-2001 hot-dip galvanized pipe wall thickness deviation

name

Weigh

Chinese standard

Enterprise standard

Contrast conclusion

Low pressure fluid conveying welded steel pipe

Welded steel pipe

GB/T3091-2001

Q/YF01-2002

1

Steel pipe outer diameter

Steel pipe outer diameter,

outer diameter allowable deviation

Better than Chinese standards

Outer diameter D/mm

Tube outer diameter deviation mm

Tube outer diameter

Deviation mm

Outer diameter D

8″

± 0.60mm

D< 48.3

± 0.5mm

 

5″-6″

± 0.50mm

48.3<D <

168.3

± 1.0%

 

4″

± 0.40mm

168.3<D <

508

± 0.75%

+2.4 -0.8

3″-“

± 0.30mm

D>508

± 1.0%

+3.0 -0.8

2″ or less

± 0.20mm

Wall thickness deviation

± 12.5%

Wall thickness S

1.8

5.75mm

5%

2

Usual length

Allowable deviation

length

Usual length

Allowable deviation

Better than Chinese standards

4M-12M

+20 -0

2 inches or less

5-0

Double length: 5-10mn ® should be

left for each double in the usual length

Margin

+20 -0

2.5 inches – 4 inches

5-0

5 inches or more

15-0

Special length

20-0

China standard hot-dip galvanized (welded) steel pipe price

Product name

Material

specification

Wall thickness ( mr )

Unit (ton / yuan)

Theoretical weight (m / kg )

Unit (m / yuan)

Hot dip galvanized steel

235

DN 15

(1/2)

2.8

6300

1.357

8.549

Hot dip galvanized steel

235

DN 20

(3/4)

2.8

6300

1.760

11.088

Hot dip galvanized steel

235

DN 25 (1.0)

3.2

6300

2.554

16.090

Hot dip galvanized steel

235

DN 32

(1.25)

3.5

6100

3.560

21.716

Hot dip galvanized steel

235

DN 40

(1.5)

3.5

6100

4.100

25.010

Hot dip galvanized steel

235

DN 50

(2.0)

3.5

6000

5.607

33.642

Hot dip galvanized steel

235

DN 65

(2.5)

4.0

6000

7.536

45.216

Hot dip galvanized steel

235

DN 80

(3.0)

4.0

6000

8.880

53.28

Hot dip galvanized steel

235

DN 100

(4.0)

4.0

6000

11.530

69.18

Hot dip galvanized steel

235

DN 125

(5.0)

4.5

6200

15.942

98.84

Hot dip galvanized steel

235

DN 150

(6.0)

4.5

6200

19.270

119.474

Hot dip galvanized steel

235

DN 200

(8.0)

6.5

6300

36.120

227.556

Welded steel pipe

235

DN 15

(1/2)

2.8

6500

1.357

8.8205

Welded steel pipe

235

DN 20

(3/4)

2.8

6500

1.760

11.44

Welded steel pipe

235

DN 25

(1.0)

3.2

6500

2.554

16.601

Welded steel pipe

235

DN 32

(125)

3.5

6500

3.560

23.140

Welded steel pipe

235

DN 40

(1.5)

3.5

6500

4.100

26.650

Welded steel pipe

235

DN 50

(2.0)

3.5

6500

5.607

36.4455

Welded steel pipe

235

DN 65

(2 5)

4.0

6500

7.536

48.984

Welded steel pipe

235

DN 80

(3.0)

4.0

5500

8.880

48.84

Welded steel pipe

235

DN 100

(4 0)

4.0

5500

11.530

63.415

Welded steel pipe

235

DN 125

(5 0)

4.5

5700

15.942

90.869

Welded steel pipe

235

DN 150

(6 0)

4.5

5700

19.270

109.839

Welded steel pipe

235

DN 200

(8.0)

6.0

5900

36.120

213.108

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STEEL PLATE AND STEEL PIPE FOR LINE PIPES http://www.abtersteel.com/line-pipe/steel-plate-and-steel-pipe-for-line-pipes/ Sat, 12 Jan 2019 14:23:57 +0000 http://www.abtersteel.com/?p=4634 This is a §371 of International Application No. PCT/ JP2008/070726, with an international filing date of Nov. 7, 2008 (WO 2009/061006 Al, published May 14,2009), which is based on Japanese Patent Application No. 2007-290220, filed Nov. 7,2007, the subject matter of which is incorporated by reference. TECHNICAL FIELD This disclosure relates to a high-strength steel plate for line pipes, which is used for transportation of crude oil, natural gas or the like and which is excellent in anti hydrogen induced cracking (hereinafter referred to as HIC resistance), and to a steel pipe for line pipes produced by the use of […]

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This is a §371 of International Application No. PCT/ JP2008/070726, with an international filing date of Nov. 7, 2008 (WO 2009/061006 Al, published May 14,2009), which is based on Japanese Patent Application No. 2007-290220, filed Nov. 7,2007, the subject matter of which is incorporated by reference.

TECHNICAL FIELD

This disclosure relates to a high-strength steel plate for line pipes, which is used for transportation of crude oil, natural gas or the like and which is excellent in anti hydrogen induced cracking (hereinafter referred to as HIC resistance), and to a steel pipe for line pipes produced by the use of the steel plate; and relates to a steel plate and a steel pipe for line pipes especially favorable for line pipes having a pipe thickness of at least 20 mm and required to have an excellent HIC resis­ tance.

BACKGROUND

In general, line pipes are produced by forming a steel plate produced in a plate mill ora hot-rolling mill, by UOE forming process, press bend forming process, roll forming or the like. Line pipes for use for transportation of hydrogen sulfide- containing crude oil or natural gas (hereinafter this may be referred to as “line pipes for sour gas service”) are required to satisfy so-called “sour resistance” such as resistance to hydrogen induced cracking (HIC resistance), resistance to anti-stress corrosion cracking (SCC resistance) and the like, in addition to strength, toughness and weldability. Hydrogen induced cracking (hereinafter referred to as HIC) of steel is said as follows: Hydrogen ions from corrosion reaction adhere to the surface of steel and permeate into the inside of steel as atomic hydrogens, then diffuse and accumulate around the non-metal inclusions such as MnS and the like or hard second phase in steel and then form hydrogen gas thereby cracking the steel owing to the inner pressure thereof.

Heretofore, for preventing such hydrogen induced crack­ ing, some methods have been proposed. For example, JP-A 54-110119 proposes a technique of reducing the S content of steel and adding a suitable amount of Ca, REM (rare-earth metal) or the like to steel to thereby prevent the formation of long-extending MnS and convert the shape into a finely dis­ persed spherical CaS inclusion. Accordingly, the stress con­ centration by the sulfide inclusion is reduced and cracking is therefore prevented from initiation and propagation to thereby improve the HIC resistance of steel.

JP-A 61-60866 and JP-A 61-165207 propose a technique of reducing center segregation through reduction in elements having a high tendency toward segregation (C, Mn, P,etc.) or through soaking heat treatment in a slab heating process, and changing the microstructure of steel in to bainite phase by accelerated cooling after hot rolling. Accordingly, formation  of an island martensite (M-A constituent) to be a initiation point of cracking in the center segregation area, as well as formation of a hardened structure such as martensite or the like to be a propagation path of cracking can be prevented. JP-A 5-255747 proposes a carbon equivalent formula based on a segregation coefficient, and proposes a method of pre­ venting cracking in the center segregation area by controlling it to a predetermined level or less.

Further, as countermeasures to the cracking in the center segregation area, JP-A 2002-363689 proposes a method of defining the segregation degree of Nb and Mn in the center segregation area to be not over a predetermined level, and JP-A 2006-63351 proposes a method of defining the size of the inclusion to be the initiation point of HIC and the hardness of the center segregation area.

However, heavy wall pipes having a wall thickness of at least 20 mm are increasing for recent line pipes for sour gas service; and in such heavy wall pipes, the amount of alloying elements to be added must be increased for securing the strength thereof. In that case, even when the MnS formation is prevented or the micro structure of the center segregation area is improved according to the above-mentioned prior-art methods, the hardness of the center segregation area may increase and HIC may occur from Nb carbonitride. Cracking from Nb carbonitride has a small crack length ratio, and therefore it has heretofore not been specially taken as a prob­ lem in the conventional requirement for HIC resistance. How­ ever, recently, further higher HIC resistance is required, and it has become necessary to prevent HIC from Nb carbonitride.

The method of reducing the size of an Nb-containing car­ bonitride to an extremely small size of 5 jimor smaller, as in JP-A 2006-63351, maybe effective for preventing the occur­ rence of HIC in the center segregation area. In fact, however, coarse Nb carbonitride may often form in the finally-solidi­ fied zone in ingot casting or continuous casting; and for the above-mentioned severer request for HIC resistance, the material of the center segregation zone must be extremely strictly controlled for preventing initiation of HIC and for preventing the propagation of cracking from the Nb carboni- tride that may form at some frequency. As the method of controlling the material of the center segregation area, there is mentioned the carbon equivalent formula proposed by JP-A 5-255747 in which a segregation coefficient is taken into consideration. However, since the segregation coefficient is experimentally obtained through analysis with an electron probe micro analyzer, it can be obtained only as a mean value within the measurement range of the spot size of, for example, around 10 |im or so. Also, this is not a method capable of strictly estimating the concentration of the center segregation area.

Accordingly, it could be helpful to provide a steel plate for high-strength line pipes excellent in HIC resistance, in par­ ticular, a steel plate for high-strength line pipes for sour gas service that has excellent HIC resistance capable of suffi­ ciently satisfying the severe requirement for HIC resistance necessary for line pipes for sour gas service having a pipe thickness of 20 mm or more.
It could also be helpful to provide a steel pipe for line pipes, which is formed of the high-strength steel plate for line pipes having such excellent capabilities.

SUMMARY

The steel pipes to which this disclosure is directed is a steel pipe having API grade ofX65 or higher (having an yield stress of at least 65 ksi and at least 450 MPa), and is a high-strength steel pipe having a tensile strength of at least 535 MPa.

We thus provide:

A steel plate for line pipes containing, in terms of% by weight, C: 0.02 to 0.06%, Si: 0.5% or less, Mn: 0.8 to
1.6%, P: 0.008% or less, S: 0.0008% or less, Al: 0.08%
or less, Nb: 0.005 to 0.035%, Ti: 0.005 to 0.025%, and
Ca: 0.0005 to 0.0035%, with a balance of Fe and inevi­

table impurities, which has, as represented by the fol­ lowing formula, a CP value of 0.95 or less and a Ceq value of 0.30 or more:
CP=4.46C(%)+2.37Mk(%)/6+{1.18Cr(%)+1.95
M?(%)+1.74r(%)}/5+{1.74C«(%)+l .7M(%)}/
15+22.36P(%),
Ce^=C(%)+MK(%)/6+{Cr(%)+Mo(%)+r(%)}/5+
{C«(%)+M(%)}/15.

2. The steel plate for line pipes of the above

1, which further contains, in terms of % by weight, one or more of Cu: 0.5% or less, Ni: 1% or less, Cr: 0.5% or less, Mo: 0.5% or less and V: 0.1% or less.
3. The steel plate for line pipes of the above 1 or 2, wherein the hardness of the center segregation area is HV 250 or lower, and the length of the Nb carbonitride in the center segregation area is at most 20 [m or less. 

4. The steel plate for line pipes of any of the above 1 to 3, wherein the microstructure of the steel plate has a bainite phase of 75% or more as the volume fraction thereof
5. A steel pipe for line pipes, produced by shaping the steel  plate of any of the above 1 to 4 into a tubular form by cold forming, followed by seam-welding the butting parts thereof.
The steel plate and the steel pipe for line pipes have excel­ lent HIC resistance and can sufficiently satisfy the require­ ment of severe HIC resistance especially needed for line pipes having a pipe thickness of 20 mm or more.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: A graph showing the relationship between the hardness of the center segregation area and the crack area ratio in a HIC test of a steel plate having MnS or Nb carbo­ nitride formed in the center segregation area thereof.
FIG. 2: A graph showing the relationship between the CP value of a steel plate and the crack area ratio thereof in a HIS test.
DETAILED DESCRIPTION
We investigated in detail the occurrence of cracking and propagation behavior thereof in a HIC test from the viewpoint of the initiation of cracking and the microstructure of the center segregation area and, as a result, have obtained the following findings.
First, for preventing cracking in the center segregation area, a appropriate material property of the center segregation area is necessary in accordance with the type of the inclusion that is to be the initiation point of cracking FIG. 1 shows one example of the result of a HIC test (the test method is the same as in Examples given below) of a steel plate having MnS or Nb carbonitride formed in the center segregation area thereof. According to this, it is known that, in the case where MnS exists in the center segregation area, the crack area ratio increases even the hardness is low and, therefore, controlling the growth of MnS is extremely important. However, even when the formation of MnS could be prevented, in the case where the center segregation area contains an Nb carbonitride and when the hardness thereof is over a predetermined level (in this, Vickers hardness, HV 250), then cracking occurs in the HIC test.
To solve this problem, it is necessary to strictly control the chemical compositions of the steel plate and control the hard­ ness of the center segregation area to be not higher than a predetermined level (preferably at most HV 250). We ther­ modynamically analyzed the distribution behavior (or incras- sate behavior) of the chemical composition in the center segregation area and have derived the segregation coefficient of the individual alloy elements. The segregation coefficient derivation is according to the following process. First, in the  finally-solidified zone in casting, there are formed cavity (or voids) owing to solidification shrinkage or bulging; and the peripheral enriched molten steel flows into the cavity to form segregation spots of enriched constituent. Next, the process of solidifying the segregated spots includes constituent change in the solidification boundary based on the thermodynamic equilibrium distribution coefficient, and therefore, the con­ centration of the finally formed segregation area can be ther­ modynamically determined. Using the segregation coeffi- cient obtained through the above-mentioned thermodynamic analysis, the CP value is obtained, corresponding to the car­ bon equivalent formula in the center segregation area repre­ sented by the following formula. We found that, when the CP value is controlled to be not larger than a predetermined level,  then the hardness of the center segregation area can be thereby controlled to be not larger than the critical hardness to cause cracking FIG. 2 shows the relationship between the CP value represented by the following formula and the crack area ratio thereof in a HIS test (the test method is the same as in the
25 Examples given below). According to this, when the CP value increases, then the crack area ratio rapidly increases, but cracking of HIC can be reduced by controlling the CP value to be not larger than a predetermined level.

CP=4.46C(%)+2.37Mk(%)/6+{ 1.18Cr(%)+l .95
M?(%)+1.74 F(%)}/5+{ 1.74C«(%)+1.7M(%)}/
15+22.36尸(%).
In addition, when the size of the Nb carbonitride to be the initiation point of cracking in a HIC testis controlled to be not larger than a predetermined level, and fiirther when the micro- structure is mainly consisting fine bainite, then the cracking propagation can be prevented. Also, when combined with the above-mentioned countermeasures, more excellent HIC 

40 resistance can be attained stably.
The details of the steel plate for line pipes are described below.
First, the reason for defining the chemical compositions is described as below. % indicating the amount of the constitu-
45 ent is all “% by weight.”
C: 0.02 to 0.06%:
C is the most effective element for increasing the strength of the steel plate to be produced through accelerated cooling. However, when the C amount is less than 0.02%, then a
50 sufficient strength could not be secured; but on the other hand, when more than 0.06%, then the toughness and the HIC resistance may deteriorate. Accordingly, the C amount is from 0.02 to 0.06%.
Si: 0.5% or less:
55 Si is added for deoxidation in the steel making process. However, when the Si amount is more than 0.5%, then the toughness and the weldability may deteriorate. Accordingly, the Si amount is 0.5% or less. From the above-mentioned viewpoint, the amount of Si is more preferably 0.3% or less.
60 Mn: 0.8 to 1.6%:
Mn is added for enhancing the strength and the toughness of steel; but when the Mn amount is less than 0.8%, then its effect is insufficient. However, when more than 1.6&, then the weldability and the anti-HIC property may deteriorate.
65 Accordingly, the Mn amount is within a range of from 0.8 to 1.6%. From the above-mentioned viewpoint, the Mn amount is more preferably from 0.8 to 1.3%.

P: 0.008% or less:
Pisan inevitable impurity element, and increases the hard­ ness of the center segregation area to deteriorate the HIC resistance. This tendency is remarkable when the amount is more than 0.008%. Accordingly, the P amount is 0.008% or less. From the above-mentioned viewpoint, the P amount is more preferably at most 0.006% or less.
S: 0.0008% or less:
S generally forms an MnS inclusion in steel, but Ca addi­ tion brings about inclusion morphology control to a CaS inclusion from the MnS inclusion. However, when the S amount is too much, then the amount of the CaS inclusion may increase, and in a high-strength material, it may be a starting point of cracking. This tendency is remarkable when the S amount is more than 0.008%. Accordingly, the S amount is 0.0008% or less.
Al: 0.08% or Less:
Alis added as a deoxidizing agent in steel making process. When theAl amount is more than 0.08%, then the cleanliness may lower to deteriorate the ductility. Accordingly, the A1 amount is 0.08% or less. More preferably, it is or less 0.06%. Nb: 0.005 to 0.035%

 

Nb is an element to prevent the grain growth in plate rolling, therefore enhancing the toughness owing to the for­ mation of fine grains, and it enhances the hardenability of steel to increase the strength after accelerated cooling. How­ ever, when the Nb amount is less than 0.005%, then the effect is insufficient. On the other hand, when more than 0.035%, not only the toughness of the welded heat affected zone may deteriorate but also a coarse Nb carbonitride may be formed to thereby deteriorate the HIC resistance. In particular, in the finally-solidified zone in the casting process, the alloying elements are enriched and the cooling speed is slow and, therefore, Nb carbonitride may readily form in the center segregation area. The Nb carbonitride still remains as such even in the rolled steel plate, and in an HIC test, the steel plate may crack from the Nb carbonitride. The size of the Nb carbonitride in the center segregation area is influenced by the Nb amount added and, therefore, when the uppermost limit of the Nb amount to be added is defined to be at most 0.035%, then the size may be controlled to be at most 20 jim. Accord­ ingly, the Nb amount is from 0.005 to 0.035%. From the above-mentioned viewpoint, the Nb amount is more prefer­ ably from 0.010 to 0.030%.
Ti: 0.005 to 0.025%:
Ti forms TiN and therefore prevents the grain growth in slab heating and, in addition, it prevents the grain growth in the welded heat affected zone to thereby enhance the tough­ ness owing to fine microstructure of base metal and the welded heat affected zone. However, when the Ti amount is less than 0.005%, then the effect is insufficient. On the other hand, when more than 0.025%, then the toughness may dete­ riorate. Accordingly, the Ti amount is from 0.005 to 0.025%. From the above-mentioned viewpoint, the Ti amount is more preferably from 0.005 to 0.018%.
Ca: 0.0005 to 0.0035%:
Ca is an element effective for sulfide inclusion morphology control to thereby improve the ductility and the HIC resis­ tance. When the Ca amount is less than 0.0005%, then the effect is insufficient. However, on the other hand, even when Ca is added in an amount of more than 0.0035%, its effect maybe saturated but rather the toughness may lower owing to the reduction in the cleanliness and, if so, in addition, the Ca-based oxide amount in steel may increase and the steel may crack from it with the result that the HIC resistance may also deteriorate. Accordingly, the Ca amount is from 0.0005 to 0.0035%. From the above-mentioned viewpoint, the Ca amount is preferably from 0.0010 to 0.030%.
The steel plate may iurther contain one or more selected from Cu, Ni, Cr, Mo and V in a range mentioned below.
5 Cu: 0.5% or less:
Cu is an element effective for improving the toughness and increasing the strength. To obtain the effect, the amount is preferably at least 0.02%. However, when the Cu amount is more than 0.5%, then the weldability may deteriorate.
10 Accordingly, in the case where Cu is added, its amount is
0.5% or less. From the above-mentioned viewpoint, the Cu amount is more preferably 0.3% or less.
Ni: 1% or less:
Ni is an element effective for improving the toughness and 15 for increasing the strength; but for obtaining the effect, the
amount is preferably 0.02% or more. However, when the Ni amount is more than 1.0%, then the weldability may deterio­ rate. Accordingly, in the case where Ni is added, its amount is 1.0% or less. From the above-mentioned viewpoint, the Ni
20 amount is more preferably 0.5% or less.
Cr: 0.5% or less:
Cr is an element effective for improving the hardenability to thereby increase the strength. To obtain the effect, the amount is preferably 0.02% or more. However, when the Cr
25 amount is more than 0.5%, then the weldability may deterio­ rate. Accordingly, in the case where Cr is added, its amount is 0.5% or less. From the above-mentioned viewpoint, the Cr amount is more preferably 0.3% or less.
Mo: 0.5% or less:
30 Mo is an element effective for improving the toughness and increasing the strength; but for obtaining the effect, the amount is preferably 0.02% or more. However, when the Mo amount is more than 0.5%, then the weldability may deterio­ rate. Accordingly, in the case where Mo is added, its amount
35 is 0.5% or less. From the above-mentioned viewpoint, the Mo amount is more preferably 0.3% or less.
V: 0.1% or less:
Vis an element of increasing the strength not deteriorating the toughness. To obtain the effect, the amount is preferably
40 0.01% or more. However, when the V amount is more than 0.1%, then the weldability may greatly deteriorate. Accord­ ingly, in the case where V is added, its amount is 0.1% or less. From the above-mentioned viewpoint, the V amount is more preferably 0.05% or less.
45 The balance of the steel plate is Fe and inevitable impuri­
ties.
The CP value and the Ceq value represented by the follow­ ing formulae are defined.
CP value: 0.95 or less:
50
CP=4.46C(%)+2.37Mk(%)/6+{1.18Cr(%)+1.95
M?(%)+1.74 F(%)}/5+{ 1.74C«(%)+1.7M(%)}/
15+22.36尸(%)_
In this, C(%), Mn(%)5 Cr(%), Mo(%),V(%), Cu(%), Ni(%)
55 and P(%) each are the content of the respective elements.
The above-mentioned formula relating to the CP value is a formula formulated for estimating the material of the center
segregation area from the content of the respective alloy elements. When the CP value is higher, the concentration of
60 the center segregation area is higher, and the hardness of the center segregation area increases. As shown in FIG. 2, when
the CP value is 0.95 or less, then the hardness of the center segregation area could be sufficiently small (preferably HV
250 or lower) and cracking in a HIC test can be thereby 65 prevented. Accordingly, the CP value is defined to be 0.95 or
less. In addition, when the CP value is smaller, then the hardness of the center segregation area is lower. Therefore, in the case where a further higher HIC resistance is desired, the CP value is preferably 0.92 or less. Further, when the CP value is smaller, then the hardness of the center segregation area is lower and the HIC resistance increases and, therefore, the lowermost limit of the CP value is not defined. However, to obtain a suitable strength, the CP value is preferably 0.60 or more.
Ceq Value: 0.30 or more:
Ce^=C(%)+MK(%)/6+{Cr(%)+Mo(%)+r(%)}/5+
{Ctt(%)+M(%)}/15.
Ceq is a carbon equivalent of steel, and this is a harden- ability index. When the Ceq value is higher, then the strength of steel is higher.
Our approach improves the HIC resistance of heavy-wall line pipes for sour gas service having a heavy wall thickness of 20 mm or more, and to obtain heavy wall pipes having a sufficient strength, the Ceq value must be 0.30 or more. Accordingly, the Ceq value is 0.30 or more. When the Ceq value is higher, then the strength can be higher and therefore steel pipes having a larger pipe thickness can be produced. However, when the alloy element concentration is too high, then the hardness of the center segregation area may also increase and the HIC resistance may deteriorate. Therefore, the uppermost limit of the Ceq value is preferably 0.42%.
The steel plate and the steel pipe preferably satisfy the following conditions in regard to the hardness of the center segregation area and the Nb carbonitride to be an initiation point of HIC.
Hardness of Center Segregation Area: Vickers Hardness, HV 250 or Lower:
As described in the above, the mechanism of crack growth in HIC is that hydrogen accumulates around the inclusion and the like in steel to cause cracking, and the cracking propagates around the inclusion thereby bringing about large cracks. In this, the center segregation area is a site to be most readily cracked, cracking readily propagates. Therefore, when the hardness of the center segregation area is lai^er, then the cracking occurs more readily. In the case where the hardness of the center segregation area is HV 250 or lower, and even when small Nb carbonitride may remain in the center segre­ gation area, the cracking would hardly propagate and, there­ fore, the crack area ratio in the HIC test may be reduced. However, when the hardness of the center segregation area is higher than HV 250, the cracking may readily propagate and, in particular, the cracks generated in the Nb carbonitride readily propagate. Accordingly, the hardness of the center segregation area is preferably HV 250 or lower and, in the case where severe HIC resistance is required, the hardness of the center segregation area must be ilirther reduced and, in such a case, the hardness of the center segregation area is preferably HV 230 or lower.
Length of Nb Carbonitride in Center Segregation Area: 20 \im or Less:
The Nb carbonitride formed in the center segregation area is a hydrogen accumulation point in the HIC test, and cracks may occur initiating from the point. When the size of the Nb carbonitride is larger, then the cracks may readily propagate and, even though the hardness of the center segregation area is not more than HV 250, the cracks may propagate. In the case where the length of the Nb carbonitride is 20 jimor less, then the cracks maybe prevented from propagating when the hardness of the center segregation area is not more than HV 250. Accordingly, the length of the Nb carbonitride is 20 jim or less, preferably lOfxmor less. The length of the Nb carbo­ nitride means the maximum length of the grain.

 Our approach is favorable especially for steel plates for line pipes for sour gas service having a wall thickness of 20 mm or more. This is because, in general, when the plate thickness (pipe wall thickness) is less than 20 mm, then the amount of the alloying element added is small and, therefore, the hard­ ness of the center segregation area could be low and, in such a case, the steel plate could readily have a good HIC resis­ tance. In the case where steel plates are thicker, the amount of the alloying element therein increases and, therefore, it becomes difficult to reduce the hardness of the center segre­ gation area in such thick plates. Especially for such thick steel plates having a plate thickness of more than 25 mm, our approach can more effectively exhibit the advantages thereof.
The steel pipes are all steel pipes having API grade X65 or higher (yield stress of at least 65 ksi and at least 450 MPa), and are high-strength steel pipes having a tensile strength of at least 535 MPa.
The metal structure of the steel plate (and the steel pipe) preferably has a bainite phase of 75% or more as the volume fraction thereof, more preferably 90% or more. The bainite phase is a microstructure excellent in strength and toughness, and in the case where the volume fraction thereof is 75% or more, then cracking propagation maybe prevented in the steel plate, and the steel plate can have a high strength and a high HIC resistance. On the other hand, in a microstructure in which the volume fraction of a bainite phase is low, for example, in a mixed structure of a ferrite, pearlite, MA (island martensite), martensite or the like microstructure and a bain­ ite phase, the cracking propagation in the phase interface may be promoted and the HIC resistance may be thereby deterio­ rated. In the case where the volume fraction of the micro struc­ ture (ferrite, pearlite, martensite or the like) except a bainite phase is less than 25%, then the deterioration of HIC resis­ tance may be small and, therefore, the volume fraction of the bainite phase is preferably 75% or more. From the same viewpoint, the volume fraction of the bainite phase is more preferably 90% or more.
The steel plate is defined in point of the chemical compo­ sition, the hardness of the center segregation area and the size of the Nb carbonitride as above, and further its microstructure is defined to be a structure of mainly bainite and, accordingly, the steel plate can have an excellent -HIC resistance even when its plate thickness is large. Therefore, the steel plate can be produced basically according to the same production method as before. However, to obtain not only the HIC resis­ tance, but also the optimum strength and toughness, the steel plate is preferably produced under the condition mentioned below.
Slab Heating Temperature: 1000 to 1200° C.:
In the case where the slab heating temperature in hot rolling a slab is lower than 1000° C., then a sufficient strength could not be obtained. On the other hand, when higher than 1200° C., then the toughness and the DWTT property (drop weight tear test property) may deteriorate. Accordingly, the slab heating temperature is preferably from 1000 to 1200° C.
To obtain a high base metal toughness in the hot rolling process, the hot rolling finish temperature is preferably lower, but on the contrary, the rolling efficiency may lower. There­ fore, the hot rolling finish temperature maybe defined to be a suitable temperature in consideration of the necessary base metal toughness and the rolling efficiency. For obtaining a high base metal toughness, the reduction ratio in the non­ recrystallization temperature zone is preferably at least 60% or more.
After the hot rolling, accelerated cooling is preferably applied under the following condition. Steel Plate Temperature at the Start of Accelerated Cooling: not Lower than (Ar3-10° C.):
The Ar3 is a ferrite transformation temperature that is given Ar3(° C.)=910-310C(%)-80Mn(%)-20Cu(%)-15Cr(%) 55Ni(%)-80Mo(%), from the steel chemical compositions. In the case where the steel plate temperature at the start of
the accelerated cooling is low, then the ferrite volume fraction before accelerated cooling is large and, in particular, in the case where the temperature is lower than Ar3 temperature by more than 10° C., then the HIC resistance may deteriorate. In addition, the micro structure of the steel plate could not secure a sufficient volume fraction of the bainite phase (preferably 75% or more). Accordingly, the steel plate temperature at the start of the accelerated cooling is preferably not lower than Ar3-10° C.).  Cooling Speed in Accelerated Cooling: not Lower than 5° C./Sec:
The cooling speed in accelerated cooling is preferably not lower than 5° C./sec for stably obtaining the sufficient strength.
Steel Plate Temperature at the Stop of Accelerated Cooling:  The accelerated cooling is an important process for obtain­ ing a high strength through bainite transformation. However, when the steel plate temperature at the time of stopping the accelerated cooling is over 600° C., then the bainite transfor­ mation maybe incomplete and a sufficient strength could not be obtained. On the other hand, when the steel temperature at the time of stopping the accelerated cooling is lower than 250° C., then a hard structure such as MA (island martensite) or the like may be formed and, if so, not only the HIC resis­ tance may readily deteriorate but also the hardness of the surface of the steel plate may be too high, and the flatness of the steel plate may be readily deteriorated and the formability thereof may deteriorate. Accordingly, the steel temperature at the stop of the accelerated cooling is from 250 to 600° C.
Regarding the steel plate temperature mentioned above, in the case where the steel plate has a temperature distribution in the plate thickness direction, then the steel plate temperature is the mean temperature in the plate thickness direction. How­ ever, in the case where the temperature distribution in the plate thickness direction is relatively small, then the tempera­ ture of the surface of the steel plate could be the steel plate temperature. Immediately after the accelerated cooling, there may be a temperature difference between the surface and the inside of the steel plate. However, the temperature difference may be soon decreased through thermal conduction, and the steel plate could have a uniform temperature distribution in the plate thickness direction. Accordingly, based on the sur­ face temperature of the steel plate after homogenizing in thickness direction, the steel plate temperature at the stop of the accelerated cooling maybe determined.
After the accelerated cooling, the steel plate may be kept cooled in air, but for the purpose of homogenizing the mate­ rial property inside the steel plate, it my be re-heated in a gas combustion furnace or by induction heating.
Next, the steel pipe for line pipes is described. The steel pipe for line pipes is a steel pipe produced by forming the steel plate as described above, into a tubular form by cold forming, followed by seam-welding the butting parts thereof.
The cold forming method maybe any method, in which, in general, the steel plate is shaped into a tubular form according to a UOE process or through press bending or the like. The method of seam-welding the butting parts is not specifically defined and maybe any method capable of attaining sufficient joint strength and joint toughness. However, from the view­ point of the welding quality and the production efficiency, especially preferred is submerged arc welding. After seam welding of the jointing parts, the pipe is processed for mechanical expansion for the purpose of removing the weld­ ing residual stress and improving the steel pipe roundness. In
5 this, the mechanical expansion ratio is preferably from 0.5 to 1.5% under the condition that a predetermined steel pipe roundness can be obtained and the residual stress can be removed.

EXAMPLES

Steel slubs having the chemical compositions shown in Table 1 (Steels A to V) were produced by a continuous casting process and, using these, thick steel plates having a plate
15 thickness of 25.4 mm and 33 mm were produced.
A heated slab was hot-rolled, and then accelerated cooled to have a predetermined strength. In this, the slab heating temperature was 1050。C” the rolling finish temperature was 840 to 800° C., and the accelerated cooling start temperature
20 was 800 to 760° C. The accelerated cooling stop temperature was 450 to 550。C. All the obtained steel plates satisfied a strength of API X65, and the tensile strength thereof was from 570 to 630 MPa. Regarding the tensile property of the steel plates, a iull thickness test specimen in the transverse direc-
25 tion to rolling was used in a tensile test to determine the tensile strength thereof.
From 6 to 9 HIC test pieces were taken from the steel plate at different positions thereof, and tested for the HIC resis­ tance thereof. The HIC resistance was determined as follows:
30 The test piece was dipped in an aqueous solution of 5% NaCl+0.5% CH3COOH saturated with hydrogen sulfide hav­ ing a pH of around 3 (ordinary NACE solution) for 96 hours, and then the entire surface of the test piece was checked for cracks through ultrasonic flaw detection, and the test piece
35 was evaluated based on the crack area ratio (CAR) thereof. One of 6 to 9 test pieces of the steel plate having the largest crack area ratio is taken as the typical crack area ratio of the steel plate, and those having a crack area ratio of at most 6% are good.
40 The hardness of the center segregation area was deter­ mined as follows: The cross sections cut in the plate thickness direction of plural samples taken from the steel plate were polished, then lightly etched, and the part where the segrega­ tion lines were seen was tested with a Vickers hardness meter
45 under a load of 50 g, and the maximum value was taken as the hardness of the center segregation area.
The length of the Nb carbonitride in the center segregation area was determined as follows: The fracture surface of the part where the sample was cracked in the HIC test was
50 observed with an electron microscope, and the maximum length of the Nb carbonitride grains in the fracture surface was measured, and this is the length of the Nb carbonitride in the center segregation area. Those hardly cracked in the HIC test were processed as follows: Plural cross sections of the
55 HIC test pieces were polished, then lightly etched, and the part where the segregation lines were seen was analyzed for elemental mapping with an electron probe micro analyzer (EPMA) to identify the Nb carbonitride, and the maximum length of the grains was measured to be the length of the Nb
60 carbonitride in the center segregation area. Regarding the microstructure, the samples were observed with an optical microscope at the center part of the plate thickness thereof and at the position of t/4 thereof, and the thus-taken photo­ graphic pictures were image-processed to measure the area
65 fraction of the bainite phase. The bainite area fraction was measured in 3 to 5 views, and the data were averaged to be the volume fraction of the bainite phase.

11
The above-mentioned test and measurement results are shown in Table 2.
In Table 1 and Table 2, the steel plates (steels) of Nos. A to K andU andV that are examples all have a small crack area ratio in the HIC test, and have extremely good HIC resistance.
As opposed to these, the steel plates (steels) L to O that are comparative samples have a CP value of more than 0.95, or that is, the hardness of the center segregation area thereof is high, and they have a high crack area ratio in the HIC test, and have a poor HIC property. Similarly, in the steel plates (steels) P and Q, the Mn amount or the S amount is larger than our range of, and therefore MnS formed in the center segregation area of those steel plates. Accordingly, the steel plates cracked from MnS and their HIC resistance is low. Also similarly, in the steel plate (steel) R, the Nb amount is laigerthan our range and, therefore, coarse Nb carbonitride formed in the center segregation area of the steel plate and, accordingly, the HIC resistance thereof is low through the CP value thereof falls within our range. Similarly, no Ca was added to the steel plate (steel) S, which therefore did not undergo morphology con­ trol of sulfide inclusion by Ca and, accordingly, the HIC resistance of the steel plate is low. Similarly, in the steel plate (steel) T, the Ca amount is larger than our range and, there­ fore, the Ca oxide amount increased in the steel. Accordingly, the steel plate cracked from the starting point of the oxide, and the HIC resistance of the steel plate is low.
Some steel plates shown in Table 2 were formed into steel pipes. Concretely, the steel plate was cold-rolled according to a UOE process to give a tubular form, and the butting parts

12
thereof were welded by submeiged arc welding (seam weld­ ing) of each one layer of the inner and outer faces, then these were processed for mechanical expansion of 1% in terms of the outer periphery change of the steel pipe, thereby produc-
5 ing steel pipes having an external diameter of 711 mm.
The produced steel pipes were tested in the same HIC test as that for the steel plates mentioned above. The results are shown in Table 3. The HIC resistance was determined as follows: One test piece is cut into quarters in the length
10 direction, and the cross section is observed, and the sample is evaluated based on the crack length ratio (CLR) (mean value of [total of crack length/width (20 mm) of test piece]).
In Table 3, Nos. 1 to 10 and 18 and 19 are our steel pipes, and the crack length ratio in the HIC test thereof is not higher
15 than 10%, and the steel pipes have an excellent HIC resis­ tance. On the other hand, the steel pipes of comparative examples, Nos. 11 to 17 all have a low HIC resistance. Industrial Applicability
Thick steel plates having a plate thickness of 20 mm or
20 more have an extremely excellent HIC resistance. They are applicable to line pipes that are required to satisfy the recent, severer HIC resistance.
Our approach is effective when applied to heavy wall pipes having a wall thickness of 20 mm or more; and steel pipes
25 having a larger wall thickness require addition of alloy ele­ ments, and it may be difficult to reduce the hardness of the center segregation area thereof. Accordingly, our steels can exhibit its effect when applied to thick steel plates of more than 25 mm in thickness.

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What Is Black Steel Pipe ? http://www.abtersteel.com/octg-2/what-is-black-steel-pipe-the-definition-of-black-pipe/ Thu, 10 Jan 2019 03:06:57 +0000 http://www.abtersteel.com/?p=4614 Black steel pipe is used in applications that do not require the pipe to be galvanized. This non galvanized black steel pipe acquired its name because of its dark coloured iron oxide coating on its surface. Because of the strength of black steel pipe , it is used for transporting gas and water to rural areas and for conduits that protect electrical wiring and deliver high pressure steam and air. The oil field industry also uses black pipes for piping large quantities of oil through remote areas.   erw black carbon iron schedule 40 steel pipe  Product Name:   astm a53 […]

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Black steel pipe is used in applications that do not require the pipe to be galvanized. This non galvanized black steel pipe acquired its name because of its dark coloured iron oxide coating on its surface.

Because of the strength of black steel pipe , it is used for transporting gas and water to rural areas and for conduits that protect electrical wiring and deliver high pressure steam and air. The oil field industry also uses black pipes for piping large quantities of oil through remote areas.

 

erw black carbon iron schedule 40 steel pipe

 Product Name:

  astm a53 gr.b erw black carbon iron schedule 40 steel pipe

  Size

  OD  (mm)

 21.3mm-355.6mm

 

  Wall Thickness (mm)

 SCH 10,SCH 20………..SCH80

 

  Steel material

Gr A,Gr B

  Standard

 ASTM A53

  Section shape

  Round

  Type

  ERW Pipe

  Length

  5.8M, 6M, 11.8M, 12M or customized length

Article

ASTM106 black steel pipe 

Surface

according to the customer’s acquirement

Length

1m – 6m or as your requirement

W.T.

2-30mm

O.D.

30-250mm

Application

Vehicles, engineering machinery hydraulic chassis, air piping system, etc

Packing

We usually bundle with steel strips ,branding parcel ,wooden box

Terms conditions

CIF,CFR,FOB

Payment

should be 30% in advance by T/T and the balance upon B/L copy or L/C.

Delivery Time

25 days after received the deposit by T/T

Note

we can produce other standard as the customers’ requirement

 ABOUT THE TOLERANCE

 

Size of I.D

I.D Tolerance

Tolerance of wall thickness

H8

H9

H10

 

 

±7.5%

>210mm ±10%

30

+0.0330

+0.0520

+0.0840

>30-50

+0.0390

+0.0620

+0.1000

>50-80

+0.0460

+0.0740

+0.1200

>80-120

+0.0540

+0.0870

+0.1400

>120-180

+0.0630

+0.1000

+0.1600

>180-250

+0.0720

+0.1150

+0.1850

>250-315

+0.0810

+0.1300

+0.2100

Mechanical Property of Material:

Delivery 
condition

cold finished(hard)(BK)

Cold drawn and stress-relieved(BK+S)

Steel grade

Rm MPa

Elongation
A5(%)

Rm MPa

ReH MPa

Elonggation
A5(%)

St45

≥550

≥5

≥520

≥375

≥15

20#

≥550

≥8

≥520

≥375

≥15

St52 (E355)

≥640

≥5

≥600

≥520

≥14

SAE1026

≥640

≥5

≥600

≥510

≥15

STKM 13C

≥550

≥8

≥520

≥375

≥15

Q345B

≥640

≥5

≥600

≥520

≥14

CK45

≥640

≥5

≥600

≥520

≥10

 CHEMICAL COMPOSITION OF MATERIAL

Steel grade

Chemical composition,%

 

C

Si

Mn

P

S

Cr

 
 

 

St45 (20#)

0.17-0.24

0.17-0.37

0.35-0.65

0.035

0.035

0.25

 

ST52(E355)

≤0.22

≤0.55

≤1.6

0.025

0.025

0.25

 

SAE1026

0.22-0.28

0.15-0.35

0.6-0.9

0.04

0.05

/

 

STKM 13C

≤0.25

≤0.35

0.3-0.9

0.04

0.04

/

 

Q345B

≤0.2

≤0.5

1.0-1.6

0.03

0.03

0.30

 

CK45

0.42-0.50

0.17-0.37

0.5-0.8

0.035

0.035

0.25

 

 

Black steel pipes and tubes can be cut and threaded. Fittings for this type of pipe are of black malleable (soft) cast iron. They connected by screwing onto the threaded pipe, after applying a small amount of pipe joint compound on the threads. Larger diameter pipe is welded on rather than threaded. Black steel pipe is cut either with a heavy-duty tube cutter, cut-off saw or by a hacksaw. It can also get Mild Steel ERW Black Pipes that are extensively used for gas distribution inside & outside of the home, and for hot water circulation in boiler systems. Can also be used in usage in potable water or drains waste or vent lines. 


Difference Between Black and Galvanized Pipe

Galvanized Pipe

Galvanized pipe is covered with a zinc material to make the steel pipe more resistant to corrosion. The primary use of galvanized pipe is to carry water to homes and commercial buildings. The zinc also prevents the buildup of mineral deposits that can clog the water line. Galvanized pipe is commonly used as scaffolding frames because of its resistance to corrosion.

Black Steel Pipe

Black steel pipe is different from galvanized pipe because it is uncoated. The dark color comes from the iron-oxide formed on its surface during manufacturing. The primary purpose of black steel pipe is to carry propane or natural gas into residential homes and commercial buildings. The pipe is manufactured without a seam, making it a better pipe to carry gas. The black steel pipe is also used for fire sprinkler systems because it is more fire-resistant than galvanized pipe.


Developments of black steel pipe

Whitehouse’s method was improved upon in 1911 by John Moon. His technique allowed manufacturers to create continuous streams of pipe. He built machinery that employed his technique and many manufacturing plants adopted it. Then the need arose for seamless metal pipes. Seamless pipe was initially formed by drilling a hole through the center of a cylinder. However, it was difficult to drill holes with the precision needed to ensure uniformity in wall thickness. An 1888 improvement allowed for greater efficiency by casting the billet around a fire-proof brick core. After cooling, the brick was removed, leaving a hole in the middle.

Quality Control of black steel pipe

The development of modern manufacturing equipment and inventions in electronics allowed for marked increases in efficiency and quality control. Modern manufacturers employ special X-ray gauges to ensure uniformity in wall thickness. The strength of the pipe is tested with a machine that fills the pipe with water under high pressure to make sure the pipe holds. Pipes that fail are scrapped.

Applications of black steel pipe

Black steel pipe’s strength makes it ideal for transporting water and gas in rural and urban areas and for conduits that protect electrical wiring and for delivering high pressure steam and air. The oil and petroleum industries use black steel pipe for moving large quantities of oil through remote areas. This is beneficial, since black steel pipe requires very little maintenance. Other uses for black steel pipes include gas distribution inside and outside homes, water wells and sewage systems. Black steel pipes are never used for transporting potable water.

History of black steel pipe

William Murdock made the breakthrough leading to the modern process of pipe welding. In 1815 he invented a coal burning lamp system and wanted to make it available to all of London. Using barrels from discarded muskets he formed a continuous pipe delivering the coal gas to the lamps. In 1824 James Russell patented a method for making metal tubes that was fast and inexpensive. He joined the ends of flat iron pieces together to make a tube then welded the joints with heat. In 1825 Comelius Whitehouse developed the “butt-weld” process, the basis for modern pipe making.

Modern Techniques of black steel pipe

Scientific advancement has greatly improved on the butt-weld method of pipe making invented by Whitehouse. His technique is still the primary method used in making pipes, but modern manufacturing equipment that can produce extremely high temperatures and pressure has made pipe making far more efficient. Depending upon its diameter, some processes can produce welded seam pipe at the incredible rate of 1,100 feet per minute. Along with this tremendous increase in the rate of production of steel pipes came improvements in the quality of the final product.

 

 

 

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How is the theoretical weight of spiral steel pipe calculated? http://www.abtersteel.com/news/how-is-the-theoretical-weight-of-spiral-steel-pipe-calculated/ Tue, 08 Jan 2019 02:01:50 +0000 http://www.abtersteel.com/?p=4609   The theoretical weight of steels is obtained by calculating nominal dimensions and density (which is called specific weight in the past). This is directly related with the steel length, the cross section area, and the allowable size deviation. Because of the allowable deviation in the process of manufacturing, the calculated theoretical weight is somehow different from the actual value, and the theoretical value is only for reference while estimating. The fundamental equation is as follows: Steel pipe single meter weight calculation (kg / m): W = (outer diameter – wall thickness) * wall thickness * 0.02466 = 2408 * 12 * 0.02466 […]

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The theoretical weight of steels is obtained by calculating nominal dimensions and density (which is called specific weight in the past). This is directly related with the steel length, the cross section area, and the allowable size deviation.

Because of the allowable deviation in the process of manufacturing, the calculated theoretical weight is somehow different from the actual value, and the theoretical value is only for reference while estimating.

The fundamental equation is as follows:

Steel pipe single meter weight calculation (kg / m):

W = (outer diameter – wall thickness) * wall thickness * 0.02466 = 2408 * 12 * 0.02466 = 712.57 kg / m

The unit for the calculated theoretical weight of steel is kilo grams (kg).

 

 

 

 

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Corrosion Resistance of API 5L Pipeline Steel with Coating Protection http://www.abtersteel.com/news/corrosion-resistance-of-api-5l-pipeline-steel-with-coating-protection/ Mon, 07 Jan 2019 02:36:45 +0000 http://www.abtersteel.com/?p=4598 ABSTRACT The corrosion resistances of enamel-coated steel pipe in  3.5 wt% NaCl solution was evaluated and compared with those of epoxy-coated pipe using open-circuit potential, linear po- larization resistance, and electrochemical impedance spectros- copy tests. T-001c enamel slurry and GP2118 enamel powder were sprayed to steel pipe in wet and electrostatic processes, respectively. The phase composition and microstructures of the two enamels were characterized with x-ray diffraction and scanning electron microscopy (SEM). The surface roughness of enamels and their bond strength with steel substrates were quantified to understand coating quality. SEM images revealed that both types of enamel coatings have […]

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ABSTRACT

The corrosion resistances of enamel-coated steel pipe in  3.5 wt% NaCl solution was evaluated and compared with those of epoxy-coated pipe using open-circuit potential, linear po- larization resistance, and electrochemical impedance spectros- copy tests. T-001c enamel slurry and GP2118 enamel powder were sprayed to steel pipe in wet and electrostatic processes, respectively. The phase composition and microstructures of the two enamels were characterized with x-ray diffraction and scanning electron microscopy (SEM). The surface roughness of enamels and their bond strength with steel substrates were quantified to understand coating quality. SEM images revealed that both types of enamel coatings have a solid structure with isolated bubbles. Electrochemical tests showed a high corrosion resistance of the enamel coatings as verified in visual inspection on the tested samples. In particular, the GP2118 enamel-coated samples consistently outperformed the epoxy-coated samples.

KEY WORDS: corrosion, electrochemical impedance spectroscopy, enamel coating, pipeline steel, scanning electron microscopy

INTRODUCTION

Natural gas, oil, and hazardous liquid transmission and gathering pipelines have reached 484,000 miles in the U.S.1 Aging pipelines are faced with reduced
service life and reliability as a result of corrosion. They can be protected from corrosion by protective coating, cathodic protection, and use of corrosion inhibitors. Coating as a physical barrier to electrolyte penetra- tion is one of the most effective and efficient methods in corrosion mitigation.
When internally applied to steel pipelines, coat- ing has several advantages. First, the internal coating can prevent fluid or gas from interacting and reacting with underlying steel. Second, coated steel pipe reduces microbiological deposits and bacteria biofilm forma- tions because the higher surface roughness of uncoated pipe helps shield the bacteria and provide growth conditions for bacterial colonies.2 Third and last, the
internal coating can reduce pressure drop over a long distance of a pipeline and thus power required to transmit oil and gas. The pressure drop in coated pipe was experimentally demonstrated to be 35% lower than that in bare steel pipe at a Reynolds number of
1 × 107.3
Today, two-part solvent based epoxy coatings, solvent free and fusion bonded coatings, and polyamide coatings are widely used in crude oil and natural gas pipelines.4-6 These coatings are weakly bonded with
their steel substrate and thus prone to under-film corrosion.7
Porcelain enamel, as an inorganic material, is chemically bonded to substrate metals at a temperature of 750°C to ∼850°C. It can not only be finished with a smooth and aesthetical surface, but also provide ex- cellent chemical stability, good corrosion resistance, and durability in various harsh environments.8 Unlike

 

epoxy coating, enamel coating has no under-film corrosion when locally breached because of its chemical bond with metal substrates.9 It has been widely used  for household cooking utensil protection or steel container protection in industries. Its corrosion re- sistance as a protective coating for steel reinforcement in concrete structures has been investigated in pre- vious studies and demonstrated to be satisfactory in general.10-11

In this study, the corrosion behavior of steel pipe internally coated with two types of enamel (T-001 slurry and GP2118 powder) was examined in 3.5 wt% NaCl solution. The phase composition and microstructure of enamels were characterized with x-ray diffraction
(XRD) and scanning electron microscopy (SEM), respectively. The surface roughness of enamel coating and its bond strength over steel pipe substrates were determined. The electrochemical behaviors were studied with open-circuit potential (OCP), linear polar- ization resistance (LPR), and electrochemical imped- ance spectroscopy (EIS) tests. Visual inspections were made on tested samples for any obvious signs of corrosion. The corrosion resistance of enamel-coated steel is compared with that of epoxy-coated steel.

EXPERIMENTAL PROCEDURES

Enameling and Specimens

An API 5L X65 steel pipe (MRC Global) with 323.85 mm in outer diameter and 9.53 mm in wall thickness was used as substrate metal in this study. The chemical composition of the steel provided by the vendor is presented in Table 1. The steel pipe was first cut into 18 25 mm × 50 mm coupon specimens. The cut specimens were then steel blasted for 1 min to get rid of mill scale and rusts, and finally cleansed with
a commercially available cleansing solvent.
Two types of enamel were applied on the steel coupons: T-001 slurry and GP2118 powder. The chemical compositions of T-001 glass frits and GP2118 enamel powder were determined by x-ray fluorescence (XRF) as presented in Table 2. The enamel slurry was prepared by first milling glass frits, clay, and certain electrolytes, and then mixing them with water until the mixture was in a stable suspension state. The enamel slurry was manually sprayed on coupon specimens using a spray gun, which was powered by a jet of compressed air as specified in Table 3. The specimens were heated at 150°C for 10 min to drive off moisture, fired at 815°C for 10 min, and finally cooled to room temperature. For electrostatic spraying, the GP2118 enamel powder with an average particle size of 32.8 μm was used. An electric field was formed between a nozzle electrode and the sample. Enamel particles, propelled out of the spray gun by a stream of air, became negatively charged, migrated toward the sample (positive electrode) and were de- posited. After power spraying, the steel coupons were moved into a furnace and fired at 843°C for 10 min, and then moved out and cooled to room temperature. The thickness of the T-001 coating was controlled by the spraying time, while the thickness of the GP2118 coating was controlled by the number of spray guns. For comparison, epoxy-coated steel samples were pre- pared and tested. In this case, 3M Scotchkote 323† epoxy, which was applied in pipeline industry, was used to coat the samples. Steel coupons were coated by brushing epoxy at room temperature and then dried in air for 3 d prior to electrochemical tests.

 

Characterization of Enamel Coatings

The coating thickness and roughness were measured with a coating thickness gauge MiniTest 6008† and optical microscope Hirox†, respectively.

The bond strength between the coating and its substrate steel were determined using PosiTest† following ASTM  D4541-09.12 To enhance its bond with the coating, a  20 mm diameter dolly at the base was roughened with abrasive papers, and cleansed with alcohol to remove oxidation and contaminants. The base of the dolly was adhered with a uniform layer of glue to the test coating surface. After curing for 24 h, the coating around the dolly was removed using a 20 mm cutting tool in order to isolate the dolly on a specific test area. The dolly was finally pulled off the sample surface perpendicularly at a stress rate of 0.4 MPa/s. The maximum strength of each coated sample was recorded.
At the completion of corrosion tests, the phases in coating were examined directly on the surface of coated steel samples by XRD (Philip X’Pert†) with diffraction angle (2θ) varied between 10° and 55°. Cross sections of the enamel-coated samples were prepared for microstructure analysis with SEM (Hitachi S4700†). Each enamel-coated sample was first cold mounted in epoxy resin (EpoxyMount†, Allied High Tech Products,  Inc.) and cut into a 10 mm thick cross section using a diamond saw. Then, the cross section was abraded with carbide papers to 1200 grit, rinsed with deionized water, and finally dried in air at room temperature prior to examination. SEM images were analyzed with ImageJ† software for porosity evaluation.

Electrochemical Tests

Each sample was soldered with a copper wire for electrochemical measurements as illustrated in Figure 1. All sides of the sample except the enamel- or epoxy-coated face were covered with Marine epoxy.

The exposed enamel or epoxy area was 30 mm × 20 mm in size.
All samples were immersed in 3.5 wt% NaCl solution with the pH of 7 and tested at room tempera- ture for 69 d. The solution was prepared by adding purified sodium chloride (Fisher Scientific, Inc.) into distilled water.

At the time of 1, 3, 6, 13, 27, 41, 55, and 69 d, OCP, LPR, and EIS tests were performed to monitor the corrosion evolution of the enamel- and epoxy-coated steel samples. A standard three-electrode system was used for electrochemical tests, including a 25.4 mm × 25.4 mm × 0.254 mm platinum sheet as a counter electrode, saturated calomel electrode  (SCE) as a reference electrode, and the coated sample as a working electrode. All three electrodes were connected to a Gamry 1000E Potentiostat/Galvanostat† for data acquisition.

After each stable OCP (lasting for 1 h) was recorded, an EIS test was performed with a sinusoidal potential wave of 10 mV in amplitude around the OCP and a frequency of 100 kHz to 5 mHz. The LPR test was conducted by scanning a range of ±15 mV around the OCP at a scan rate of 0.167 mV/s. The LPR curves are used to determine the polarization resistance Rp, which is equal to the slope of the linear region of a polarization curve around zero current:13

Rp =ΔE=Δi

where ΔE and Δi represent the voltage and current increments, respectively, in the linear portion of a polarization curve at i = 0. LPR measurements were used to calculate the corrosion current density by the Stern-Geary equation:13

icorr =βaβc=½2.303ðβa + βcÞRp (2)

where βa and βc represent the anodic Tafel constant (0.12) and the cathodic Tafel constant (0.12), respectively, and icorr is the corrosion current.

RESULTS AND DISCUSSION
Coating Characterization
Phases in Enamel — XRD patterns on the surface of GP2118 and T-001 enamel-coated samples after immersion in 3.5 wt% NaCl solution for 69 d are identified and displayed in Figure 2. Quartz SiO2 is present in both types of enamel coatings. The highest intensity peaks of quartz SiO2 were at 26° and 26.5°  for GP2118 and T-001 enamels, respectively.

Microstructure at Enamel/Substrate Interface —  Cross-sectional SEM images at the steel/coating interface with different magnifications are presented in Figure 3. The enamel coatings have a solid structure with disconnected air bubbles through the coating thickness (Figures 3[a1] and [b1]). The air bubbles were formed during the high-temperature chemical

reaction of the enamel glass frit with the steel during firing process.14-15 The enamel coatings have numerous
isolated small pores with the exception of GP2118 enamel that has a few large pores with a diameter of approximately 105 μm. The porosity content of T-001 enamel was measured to be 4.26%, which is lower than 12.72% for the GP2118 enamel. Figures 3(a2) and (b2) show the magnified enamel/steel interfaces at which small-Fe protrusions grow into the enamel coating to form various anchor points. These epitaxial spinel particles improve the bonding between the enamel and its steel substrate.16

Pull-Off Strength — The measured thickness, surface roughness, and bond strength of three types of coatings are summarized in Table 4. The average and the standard deviation of the thickness and surface roughness of each coating were calculated from
27 measurements taken from three different samples that were polished to have a flat surface for the pull-off test. The average and the standard deviation of the bond strength of each coating were calculated from the three pull-off tests conducted. It can be seen from Table 4 that epoxy coating is the thickest (396 μm) and T-001 enamel is the thinnest (230 μm). The

 

roughness of the three coatings is around 1 μm, indicating smooth surfaces in all specimens.

At the completion of pull-off tests, the dolly and substrate fracture surfaces are shown in Figure 4. In a pull-off bond test, four possible failure modes include: (1) adhesion break between the coating and its steel substrate, (2) cohesion break within the coating layer, (3) glue break, and (4) mixed break or a combi- nation of the above breaks at multiple locations.17

Enamel coatings have a mixed failure mode in- volving a break inside the coating (cohesive break) and a break in glue used to bond the dolly to the specimen. Epoxy coating also has a mixed failure mode involving a break inside the coating (cohesive break), a break between the coating and the substrate steel (adhesive break), and a glue break. There are no adhesive breaks for enamel coatings because the anchor points on the interface increase the bonding between an enamel coating and its substrate steel as shown in Figure 3. Specifically, GP2118 enamel coating has the highest bond strength with an average value of 17.89 MPa, epoxy coating has the lowest bond strength of 8.01 MPa, and T-001 enamel coating has a bond strength of 16.85 MPa.

Figures 5(a) and (b) represent the magnified fracture surface morphologies as shown in Figures 4(a2) and (b2), respectively. When the dolly was pulled off the coated specimen at right angle, a crack initiated and ProPaGaTEd acroSS larGE aIr bubblES wIThIn ThE coaT- InG undEr IncrEaSInG loadS. FIGurES 6(a) and (b) Show SEM IMaGES For ThE croSS SEcTIonS oF ThE TESTEd SPE- cIMEnS In rEcTanGular arEaS oF FIGurES 4(a2) and (b2), rESPEcTIvEly. ThE FracTurE SurFacES oF ThE SPEcIMEnS arE GEnErally SMooTh wITh ThE MInIMuM rEMaInEd coaTInG ThIcknESSES oF aPProxIMaTEly 70 μM and
40 μM For GP2118 and T-001 EnaMElS, rESPEcTIvEly. In coMParISon wITh FIGurE 3, FIGurES 6(a) and (b) IndIcaTE ThaT ThE FracTurE SurFacES arE Far away FroM ThEIr corrESPondInG bondInG layErS aT ThE EnaMEl/ SubSTraTE InTErFacES and PaSS ThrouGh ThE wEakEST layEr connEcTInG larGE aIr bubblES In ThE coaTInG bEcauSE ThE adhErEncE oF EnaMEl on STEEl SurFacES IS chEMIcally STrEnGThEnEd wITh ThE GrowTh oF EPITaxIal SPInEl ParTIclES In ThE EnaMEl durInG chEMIcal rEacTIon In ThE firInG ProcESS.16

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Casing pipe application in high-temperature gas wells http://www.abtersteel.com/news/casing-pipe-application-in-high-temperature-gas-wells/ Fri, 04 Jan 2019 15:01:55 +0000 http://www.abtersteel.com/?p=4594 In recent years, with the decreasing number of easily exploitable oil and gas wells, it has become necessary for oil and gas wells to go deeper on both underground and underwater. And, tubing and casing strings are subjected to higher temperature and higher pressure in these wells, which would probably cause casing failure or gas leakage in the high-pressure/high-temperature (HPHT) wells. Hence, more attention has been paid to wellbore integrity in oil and gas industry in recent years.1,2 The key factor of wellbore integrity is casing string connections, which are expected to provide both structural and leakage integrity under severe environment. […]

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In recent years, with the decreasing number of easily exploitable oil and gas wells, it has become necessary for oil and gas wells to go deeper on both underground and underwater. And, tubing and casing strings are subjected to higher temperature and higher pressure in these wells, which would probably cause casing failure or gas leakage in the high-pressure/high-temperature (HPHT) wells. Hence, more attention has been paid to wellbore integrity in oil and gas industry in recent years.1,2 The key factor of wellbore integrity is casing string connections, which are expected to provide both structural and leakage integrity under severe environment. As loading conditions are associated with deeper, higher temperature and pressure gas wells, many operators switched from using standard American Petroleum Institute (API) connections to the premium connections.Figure 1 shows the casing of premium connections and its gas sealing mechanism. The sealing surface is also called metal-to-metal seals, which provide contact pressure through the interference fit. What is more, the contact pressure on the sealing surface is higher than the gas well pressure, and the casing connections could prevent the gas leakage efficiently.3,4

Figure 1. Gas sealing mechanism of premium connection.

In recent years, the gas sealing connection failed in some extra-high temperature gas well, although the designing contact pressure on the sealing surface was higher than the gas pressure. In the South China Sea, the temperature in some exploratory gas wells can reach up to 240°C.5 The well-designed premium connections could bear high-pressure gas in the downhole at early stage. However, the gas leakage problem could be detected after 2 years of gas production in some wells, which is far less than the expected service life of gas wells. At the extra-high temperatures, the sealing surface of casing connections will experience creep strain, which will lead to the reduction in the sealing surface’s contact pressure. When the contact pressure is lower than the gas well pressure, the gas will leak from the casing connection, which will reduce the service life of the gas well. Furthermore, it would bring a sustained casing gas pressure, casing collapse, or abandonment well, causing a huge economic loss. Therefore, it is significant to study the viscoelasticity of the casing connection’s material and find out the relaxation of contact pressure on sealing surface, which could be helpful for the exploration and development of high-temperature gas wells.

Research studies on the casing connections have been mainly focused on the thread connection structure design and safety evaluation in the past years. Analytical method,6,7 finite element (FE) method,8,9 and experimental method10,11 were commonly adopted in the research works. Some researchers have investigated the sealing mechanism of the premium connections,12,13 and some researchers developed high-performance premium connection in the high-temperature/high-pressure (HTHP) gas well.14,15However, these research works are all conducted in the steady state, not considering the time changing. And, the sealing mechanism of the premium connections in the high-temperature gas well has not been completely investigated, especially the viscoelastic behavior of the casing material.

In this article, a creep experiment of casing material was conducted under the same tension stress but different temperatures. And then, the viscoelastic behavior of the casing material is studied. Furthermore, the WLF (William–Landel–Ferry) equation for the casing material is derived. Finally, a FE model is used to study the relaxation of sealing surface’s contact pressure of the casing connection, which can predict its service life in the high-temperature gas well.

Experimental material tests

Experimental apparatus and procedure

According to ISO 204:2009, metallic materials’ uniaxial creep testing in tension method of test, creep experiments are performed under different high temperatures to estimate the material relaxation mechanical property based on the theory of viscoelasticity.16 As shown in Figure 2, the creep experiment apparatus is composed of oven, temperature sensor, displacement senor, tension tester, and specimen. The experiment principle is shown in Figure 2(b). The bottom of specimen is fixed, and the top is loaded. Experimental temperature is controlled by oven and temperature sensor. Meanwhile, the creep strain is recorded by displacement sensor. The specimen casing material is P110T and its chemical composition is listed in Table 1. As the metal creep experiment is time-consuming, a set of constant tension load tests are carried out at 120°C, 200°C, and 300°C, respectively.

Figure 2. (a) Creep experiment apparatus and (b) experimental principle.

Experimental result

Table 2 shows the creep experimental conditions, which include a constant tension load of 680 MPa, three different temperatures, and consuming experimental time. Moreover, the loaded tensile stress is under the elastic limit of the P110T material. In test #1, the specimen was broken after 570 h experiment under 300°C, as shown in Figure 3. It shows that the fracture of specimen belongs to the necking phenomena. However, at a lower temperature and after 630 h of creep testing, the specimen did not fracture. It proves that the material creep behavior at 300°C is more obvious than at lower temperatures. The creep experiment results are shown in Figure 4. The strain–time curve at the 300°C consists of the whole three creep stages: primary, secondary, and tertiary. And, the strain rate is defined as the ratio of strain to the time. In the primary stage, the strain rate is relatively high, but slows with time. Then, the strain rate eventually reaches a minimum value and becomes a constant at the secondary stage, as the strain–time curve is a straight line at this stage. Finally, in the tertiary stage, the strain rate exponentially increases with time until the specimen fractures, which is mainly caused by necking phenomena in the specimen. However, for the specimen at 120°C and 200°C creep experiment, there were only two stages during the 630 testing hours: primary stage and secondary stage.

Figure 4. Creep experiment results under different temperature.

Viscoelastic constitutive model

In this article, the casing material is selected as linear viscoelastic. The constitutive relations can be expressed by the linear viscoelasticity superposition principle and the use of the relaxation and the creep modulus function.17,18 Starting from the generalized Maxwell model and adding one more spring term leads to a model known as Wiechert model, according to Figure 5. Using the Wiechert model, the creep and relaxation of viscoelastic material could be described well, and this model could be represented by the relaxation modulus function E(t) as follows

E(t)=E+i=1nEiexp(tτi)E(t)=E∞+∑i=1nEiexp(−tτi)
(1)

where τiτi is the relaxation time, EiEi is the relaxation modulus, EE∞ is the equilibrium modulus, and n is the total number of Prony series terms. Equation (1) represents the sum of a series of exponential terms and could be interpreted as a mechanical element model, also known as Prony series.

Figure 5. Wiechert material mode.

Note that, from equation (1), if t = 0

E(0)=E0=E+EiE(0)=E0=E∞+∑Ei
(2)

where E0 is instantaneous relaxation modulus. And, equation (1) can be rewritten as follows

E(t)=E+i=1nmiE0exp(tτi)E(t)=E∞+∑i=1nmiE0exp(−tτi)
(3)

where mi=Ei/E0mi=Ei/E0 is defined as Prony series parameter.

P110T material characterization

As for the creep experiment, the application tension load is a constant, and the relaxation modulus can be represented by another form

E(t)=σ[ε]E(t)=σ[ε]
(4)

where σσ is the application tension load; [ε][ε] is a strain matrix for the creep experiment, [ε1,ε2,ε3,][ε1,ε2,ε3,…], corresponding to the experiment time matrix [t][t] or [t1,t2,t3,][t1,t2,t3,…]. So the relaxation modulus E(t) in the matrix form is

E(t)=E0+i=1nmiE0[1exp([t]τi)]E(t)=E0+∑i=1nmiE0[1−exp([t]τi)]
(5)

Combining equation (4) with equation (5), the relationship between the time and the strain is established, as shown in equation (6)

i=1nmiE0[1exp([t]τi)]=E0σ[ε]∑i=1nmiE0[1−exp(−[t]τi)]=E0−σ[ε]
(6)

By solving equation (6) by the method of linear matrix equation and substituting the time matrix [t][t] and the strain matrix [ε][ε] using the creep experimental data, the Prony series parameter mi can be obtained.

As for the computing complexity of the Prony series function, the MATLAB software is applied to find the Prony series parameter. For the 200°C environmental temperature, the Prony series parameter of the P110T casing material is listed in Table 3, and its relaxation modulus equation can be obtained as follows

E(t)=79,827+61,991[1et10]+7367[1et100]+49,615[1et1000]E(t)=79,827+61,991[1−e−t10]+7367[1−e−t100]+49,615[1−e−t1000]
 

According to the Hooke law theory, the creep strain is the ratio of the constant tension stress to the relaxation modulus E(t). Moreover, the relationship curve of the creep strain versus time is plotted in Figure 6. Compared with strain–time curve in the experiment result at 200°C, as shown in Figure 6, the Prony series model curve fits well with the creep experimental data, which validate the constitutive model of the P110T material. Therefore, the Prony series equation of the casing material P110T at 120°C and 300°C can be also derived in the same way, as shown in equations (8) and (9), respectively

E(t)=125,986+875[1et]+43,314[1et12]+2956[1et100]+38,942[1et1000]E(t)=125,986+875[1−e−t]+43,314[1−e−t12]+2956[1−e−t100]+38,942[1−e−t1000]
(8)
E(t)=53,560+66,362[1et5]+6985[1et10]+4802[1et200]+30,015[1et800]E(t)=53,560+66,362[1−e−t5]+6985[1−e−t10]+4802[1−e−t200]+30,015[1−e−t800]
(9)
 

Figure 6. Creep experimental data and Prony series tensile versus at 200°C.

Thermo-rheological behavior of casing material

The relaxation modulus is temperature dependent.19,20 At lower temperatures, the material’s relaxation rate is very slow, which can be modeled as elastic behavior. At higher temperatures, the material’s relaxation rate becomes much faster, which is the pure viscous behavior. The relaxation modulus, obtained by the Prony series method, is plotted on a log time scale under the three different temperatures, as shown in Figure 7. It can be found that all the plots have almost the same shape but are only shifted horizontally. This is a property of the casing material and is called thermo-rheological behavior. The average of horizontal distance between two curves, at the top, middle, and bottom, is defined as shift factor, αTαT, and the relationship between the curves can be described by the following equation

E(log(t),T)=E(log(t)logαT,T1)E(log(t),T)=E(log(t)−logαT,T1)
(10)

where E(t, T) is the relaxation modulus at temperature T and time t.

Figure 7. Thermo-rheological behavior of casing material P110T.

Equation (10) can be rewritten as follows

E(t,T)=E(tαT,T1)E(t,T)=E(tαT,T1)
(11)

The shift factor αTαT can be obtained by the WLF equation

logαT=C1(TT0)C2+(TT0)logαT=−C1(T−T0)C2+(T−T0)
(12)

where T is the temperature at which the relaxation modulus is calculated, T0T0 is the reference temperature. C1 and C2 are constants of the WLF equation.

Based on the creep experimental data and Prony series method in Figure 6, and setting 200°C as the reference temperature, the shift factors, from 200°C to 120°C and 200°C to 300°C, can be scaled in the plot. By substituting the shift factors in the WLF equation, the constants C1 and C2 can be solved: C1 = 45.03 and C2 = 4640. Therefore, the WLF equation for the casing material P110T is

logαT=45.03(T200)4640+(T200)logαT=−45.03(T−200)4640+(T−200)
(13)

FE simulation and its application

FE model

The numerical simulation of the specimen tension creep test was performed using the commercial FE software ABAQUS. Basing on the casing material P110T creep experiment loading, the FE mechanical model was established, as shown in Figure 8. The elastic properties, including elastic modulus and Poisson’s ratio, 1.99 × 105 MPa and 0.3, respectively, are defined in ABAQUS. Besides, the viscous properties, including the relaxation time and Prony series, as shown in Table 3, are also defined in ABAQUS. What is more, the thermo-rheological simple (TRS) parameters, C1 and C2, obtained by the WLF equation, are also included in this simulation, and *VISCO type of analysis was applied for the viscoelastic behavior.

Figure 8. FE mechanical model used for simulation of the tension creep test.

The comparison between the creep experimental data and the simulation results at three different temperatures is shown in Figure 9(a)–(c), respectively. At temperature 200°C, the simulation result matches the creep experimental data well. This is because temperature 200°C was set as reference temperature in equation (13). But for the temperatures 120°C and 300°C, as thermo-rheological behavior, there are small differences between the experimental and the simulated results, and the biggest difference is less than 8%. The reason for this difference is because that, for the FE analysis, the thermo-rheological parameters are applied into the simulation, which is obtained from the WLF equation. In the WLF equation, the 200°C is taken as the reference temperature, so that, in Figure 7, the red curve is shifted to the position of the blue curve and black curve. And, the new shifted curves represent the thermo-rheological behavior of the casing material and is used to solve the WLF equation. Because the shifted curves cannot 100% match well with the original one, which is obtained by the experimental results, the deviation exists between experimental and simulation. Moreover, as the 200°C is taken as a reference temperature, the simulation result is more accurate than others, as shown in Figure 9. Therefore, the simulation results show the validity of the viscoelastic theory and TRs method in this article. In addition, the FE model can be used to estimate the viscoelastic behavior of casing material P110T at different mechanical and thermal conditions.

Figure 9. Comparison of experimental data and simulation result under different temperatures: (a) 120°C, (b) 200°C, and (c) 300°C.

Contact pressure on the sealing surface

Based on the geometry of 5.5″ SL-APOX joint connection type, an axial symmetry FE model for the sealing surface was built in ABAQUS, as shown in Figure 10. The inner wall is under the applied gas pressure. The red line in the figure represents the sealing surface. If the gas pressure is higher than the contact pressure on the sealing surface, the joint connection will be more likely to leak.

Figure 10. Finite element model of the sealing surface from the SL-APOX joint connection.

At high-temperature environment, the contact pressure on the sealing surface will decrease with time due to the material viscoelasticity. The gas pressure on the inner wall is set to 75 MPa. The simulation result of the averaged contact pressure relaxation on the sealing surface versus time is shown in Figure 11. Simulation results show that the initial average contact pressure is 116 MPa at 160°C and 230°C. Then, the average contact pressure decreases with time. The average contact pressure drops to 76 MPa. Furthermore, the rate of decreasing pressure at 230°C is faster than the one at 160°C environment. It is shown that within 4000 h (166 days), the contact pressure drops to 76 MPa at 230°C. However, at a lower temperature environment, it will take 9000 h (375 days) to drop to 76 MPa.

 

Figure 11. Relaxation of contact pressure on the sealing surface varying with time.

According to the simulation result, the ratio of the initial contact pressure and the finial contact pressure is 1.56, which means, at high-temperature environment, the final contact pressure on the sealing surface will drop by almost a third. Based on the safety factor equation

n=[σ]σgpn=[σ]σgp
(14)

where n is the safety factor, [σ][σ] is the designing contact pressure, σgpσgp is the intending sealing gas pressure. The safety factor n must be more than 2 for the safety consideration.

Conclusion

  1. The relaxation of the contact pressure on the sealing surface of the premium connection is the main reason for the gas leakage from the casing at high-temperature natural gas well.

  2. At high temperatures, creep tension experiment was employed to study the viscoelastic behavior of the casing material P110T. The mechanical behavior of the casing material is strongly temperature dependent. The higher the temperature environment is, the faster the creep rate is.

  3. The constitutive model for the casing material P110T was derived through creep experimental data, and the Prony series parameter was calculated. The thermo-rheological behavior was also investigated, and the shift factors of the material between environmental temperatures of 120°C to 300°C are obtained.

  4. A viscoelastic FE model for the material P110T was established, and the simulation results fit well with the experimental data.

  5. The FE model of a sealing surface in the premium connections was built in ABAQUS, and its contact pressure relaxation was investigated. It is recommended that the designing contact pressure on the sealing surface should be twice as much as the intending gas sealing pressure at high-temperature natural gas wells.

Handling Editor: Michal Kuciej

Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

 

References

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Ong, G, Nizam Ramli, M, Ahmad, H. Evaluation of fatigue performance on semi premium connection for casing drilling application to prevent connection fatigue failure. In: Proceedings of the off shore technology conference Asia, Kuala Lumpur, Malaysia, 22–25 March 2016, https://www.onepetro.org/conference-paper/OTC-26807-MS 

Sugino, M, Yamaguchi, S, Ugai, S. VAM 21, an innovative high-performance premium threaded connection for OCTG. Nippon Steel & Sumitomo Metal technical report no. 107, February 2015, pp.10–17, http://www.nssmc.com/en/tech/report/nssmc/pdf/107-03.pdf 

Takano, J, Yamaguchi, M, Kunishige, H. Development of premium connection “KSBEAR” for withstanding high compression, high external pressure, and sever bending. Kawasaki Steel technical report no. 47, 2002, http://www.jfe-steel.co.jp/archives/en/ksc_giho/no.47/e47-014-022.pdf 

Kim, J, Lee, HS, Kim, N. Determination of shear and bulk moduli of viscoelastic solids from the indirect tension creep test. J Eng Mech 2010; 136: 1067–1075. 3

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Properties of Galvanized Steel Pipe Welds http://www.abtersteel.com/structural-pipe/galvanized-steel-pipe-welds/ Fri, 04 Jan 2019 02:20:34 +0000 http://www.abtersteel.com/?p=4574 Properties of Galvanized Steel Pipe Welds Galvanizing has been used to protect iron and steel from rusting for over a hundred years in places as diverse as the wire rope used for the suspension cables on the Brooklyn Bridge to gutters on houses. Galvanizing is simply coating of zinc over steel. Like paint, galvanizing protects steel from rusting by forming a barrier between the steel and the environment, but galvanizing goes one giant step further than paint — it also provides electrochemical protection of the steel. Since zinc is electrochemically more reactive than steel, it oxidizes to protect the steel […]

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Properties of Galvanized Steel Pipe Welds

Galvanizing has been used to protect iron and steel from rusting for over a hundred years in places as diverse as the wire rope used for the suspension cables on the Brooklyn Bridge to gutters on houses. Galvanizing is simply coating of zinc over steel. Like paint, galvanizing protects steel from rusting by forming a barrier between the steel and the environment, but galvanizing goes one giant step further than paint — it also provides electrochemical protection of the steel. Since zinc is electrochemically more reactive than steel, it oxidizes to protect the steel near it; as a result, even if a galvanized steel surface is scratched down to the bare steel, the galvanizing coating will prevent the steel from rusting. Galvanized steel is, therefore, a superior product to steel with any other type of coating on it since it protects the steel even when the coating is damaged in handling or in service.

The successful welding of Galvanized Steel Pipe is so widely accepted that there is very little recently-published mechanical property data comparing uncoated versus galvanized weld properties. The welding industry recognized fifty years ago that welds on Galvanized Steel Pipe and welds on uncoated steel are of comparable strength if the quality of the welds is comparable. Recent publications on welding Galvanized Steel Pipes deal with weld toughness, porosity control, weld appearance, restoring corrosion resistance and other issues that are much more complex than the strength of the weld.

When using SMAW (“stick”) welding, Galvanized Steel Pipe can be welded in the same manner as uncoated steel. When using MIG or flux cored welding, one may have to adjust the voltage slightly to control spatter, and one may have to clean the welding gun of spatter and zinc oxide deposits more frequently that when welding uncoated steel. Hobart makes a flux cored wire called “Galvacore” that some users have had good success with when welding Galvanized Steel Pipe.
When difficulty is encountered welding Galvanized Steel Pipe that was not encountered during welding uncoated steel, it is usually because the Welding Engineer has not accounted for the volume of gas that is evolved by the vaporization of zinc during welding. The thicker the zinc coating, the more fumes are generated, and those fumes have to be able to escape easily into the atmosphere and not be forced through the liquid weld metal.

For example, welding galvanized plates to form a T-joint is a commonly troublesome situation. Since the galvanized edge of one plate is butted against another galvanized surface, the zinc vapors that are formed at the abutting surfaces will not be able to escape to atmosphere easily as the zinc is vaporized. Instead, they will blow into the weld pool, creating porosity or a poor weld surface. This is aggravated when welding conventionally hot-dipped products, since the edges frequently have excessively heavy zinc coatings. One solution is to separate the parts by 1/16 inch using wire spacers or fixtures which will leave a gap for the zinc vapors to escape easily. Other approaches are to use a slight (15˚) bevel on one member (Figure 1), to remove the zinc from the faying surfaces by shearing or mechanically cuting the plate where the faying surfaces will meet, and to abrasively remove most of the zinc from one or both of the faying surfaces (Figure 2). Any of these methods will significantly reduce the amount of zinc between the parts, and this will reduce the volume of gas evolved, improving weld quality.

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Why not galvanizing after welding for steel pipe http://www.abtersteel.com/news/galvanize-welding-steel-pipe/ Wed, 02 Jan 2019 02:17:53 +0000 http://www.abtersteel.com/?p=4571 Why not galvanizing after welding Why not avoid the whole problem of welding galvanized steel pipe sheets after galvanizing? After all, steel products are always galvanized after manufacture, because there has been no practical way to restore the galvanizing effect after welding. Zinc plating after manufacture is still conventional, but must be done with great care. The manufacturing must be cleaned in acid, the acid must be neutralized, and then made into a liquid zinc can that must be immersed in excess of 900 °F. People must be very careful to make it dry when it is put into zinc, […]

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Why not galvanizing after welding

Why not avoid the whole problem of welding galvanized steel pipe sheets after galvanizing? After all, steel products are always galvanized after manufacture, because there has been no practical way to restore the galvanizing effect after welding.

Zinc plating after manufacture is still conventional, but must be done with great care. The manufacturing must be cleaned in acid, the acid must be neutralized, and then made into a liquid zinc can that must be immersed in excess of 900 °F. People must be very careful to make it dry when it is put into zinc, because any trapped water will flash into steam, and zinc is everywhere. It must also be noted that zinc can easily flow into and out of any corners and gaps to achieve complete coverage; this is particularly difficult if the manufacture is made of tubes, since the tubes must be open at both ends to allow the zinc to flow properly. In addition to the simplest manufacturing, achieving uniform coverage is very difficult. Finally, the manufactured product must be able to fit into a molten zinc can – this is a problem with large structures.

Sheets, sheets, wires, structural shapes, especially tubing, are easily galvanized before they are made because they are very simple in shape – no corners or gaps, no hidden cavities, no water trapped.

Ordinary hot dip galvanizing, rather than “online” galvanized products, present particular problems during welding, primarily due to coating non-uniformity. Edges and corners – usually where welding is taking place – usually have very thick heavy zinc deposits, which may interfere more than the evenly applied weld of zinc. In addition, hot dip products typically have a rough Finshes that does not perform topcoating well, and the top coat, especially the powder topcoat, must be completed within 48 hours to avoid white rust formation difficulties.

1) galvanized steel pipe can be welded using the same arc welding processes that are being used for fabrication today.
2) galvanized steel pipe can be arc welded safely with little increase in cost or welder discomfort.
3) Corrosion resistance at welds can be effectively restored by application of paint coatings which are high in elemental zinc or by thermal spraying zinc over the weld areas.
4) Galvanizing simple shapes can be controlled better than psot-fabrication galvanizing, resulting in smoother surfaces and a more uniform top coating appearance.

Restoring Corrosion Resistance

The heat from welding vaporizes the protective zinc coating near the weld. Even though the remaining zinc continues to provide some protection to the zinc-free areas, the appearance is poor, and the zinc-free areas will rust when exposed to the environment. Paints which are high in elemental zinc (i.e., “Zinc-rich”), properly applied, will effectively restore full corrosion protection to the weld areas. These paints are available in either spray cans or in containers suitable for brush or spray application. This paint can be applied to the weld after sand blasting or wire brushing to remove all welding slag followed by wiping the weld clean with a rag. Thermal- sprayed zinc is also effective in restoring corrosion resistance, but the surface has to be sufficiently roughened, usually by sand blasting or coarse abrasive conditioning to enable thermal- sprayed zinc to stick properly.

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Black and Galvanized Steel Pipe For Water Transmission & Scaffolding http://www.abtersteel.com/structural-pipe/black-and-galvanized-steel-pipe/ Sun, 30 Dec 2018 02:30:44 +0000 http://www.abtersteel.com/?p=4561 Carbon Steel Pipe (Black and Galvanized) Water Transmission Pipe Pipe Standard : ASTM A53 Grade A – Sch 40 NOMINAL SIZE OUTSIDE DIAMETER WALL THICKNESS LENGTH WEIGHT BUNDLING     maximum minimum inch inch mm inch mm inch mm inch mm meter ft kg/m kg/ft lb/ft pieces 1 1.315 33.4 1.331 33.7 1.299 33.1 0.133 3.38 6 20 2.50 0.76 1.68 91 1¼ 1.660 42.2 1.676 42.5 1.644 41.9 0.140 3.56 6 20 3.39 1.03 2.28 44 1½ 1.900 48.3 1.916 48.7 1.884 47.9 0.145 3.68 6 20 4.05 1.23 2.72 44 2 2.375 60.3 2.399 60.8 2.351 59.8 0.154 3.91 6 […]

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Carbon Steel Pipe
(Black and Galvanized)
Water Transmission Pipe

Pipe Standard : ASTM A53 Grade A – Sch 40

NOMINAL

SIZE

OUTSIDE DIAMETER

WALL THICKNESS

LENGTH

WEIGHT

BUNDLING

 

 

maximum

minimum

inch

inch

mm

inch

mm

inch

mm

inch

mm

meter

ft

kg/m

kg/ft

lb/ft

pieces

1

1.315

33.4

1.331

33.7

1.299

33.1

0.133

3.38

6

20

2.50

0.76

1.68

91

1.660

42.2

1.676

42.5

1.644

41.9

0.140

3.56

6

20

3.39

1.03

2.28

44

1.900

48.3

1.916

48.7

1.884

47.9

0.145

3.68

6

20

4.05

1.23

2.72

44

2

2.375

60.3

2.399

60.8

2.351

59.8

0.154

3.91

6

20

5.44

1.66

3.66

44

2.875

73.0

2.904

73.6

2.846

72.4

0.203

5.16

6

20

8.63

2.63

5.80

19

3

3.500

88.9

3.535

89.6

3.465

88.2

0.216

5.49

6

20

11.29

3.44

7.59

19

4.000

101.6

4.040

102.4

3.960

100.8

0.226

5.74

6

20

13.57

4.14

9.12

19

4

4.500

114.3

4.545

115.1

4.455

113.5

0.237

6.02

6

20

16.07

4.90

10.80

10

5

5.563

141.3

5.619

142.3

5.507

140.3

0.258

6.55

6

20

21.77

6.64

14.63

10

6

6.625

168.3

6.691

169.9

6.559

166.6

0.280

7.11

6

20

28.26

8.61

18.99

10

8

8.625

219.1

8.711

220.9

8.539

217.3

0.322

8.18

6

20

42.55

12.97

28.59

5

   
Carbon Steel Pipe
(Black and Galvanized)
Water Transmission Pipe / Structural Pipe
Pipe Standard : JIS G 3452

NOMINAL

SIZE

OUTSIDE DIAMETER

WALL

THICKNESS

LENGTH

WEIGHT

BUNDLING

maximum

minimum

inch

mm

inch

mm

inch

mm

inch

mm

meter

ft

kg/m

kg/ft

lb/ft

pieces

7

175

7.571

192.30

7.445

189.10

0.209

5.30

6

20

24.20

7.38

16.27

7

8

200

8.584

218.03

8.448

214.57

0.228

5.80

6

20

30.10

9.17

20.20

5


Carbon Steel Pipe

(Black and Galvanized)

Structural Pipe / Scaffolding

Pipe Standard : JIS G 3444

NOMINAL

SIZE

OUTSIDE

DIAMETER

WALL

THICKNESS

WEIGHT

REFERENCE

BUNDLING

 

Cross

SectionalArea

Geometric

Moment of Inertia

Modulus of

Section

Radius of

Gyration of Area

maximum

minimum

mm

mm

mm

mm

kg/m

2

cm

4

cm

3

cm

cm

pieces

 

 

21.7

 

21.95

 

21.45

1.2

0.61

0.773

0.407

0.375

0.726

217

 

1.5

0.75

0.952

0.488

0.450

0.716

217

 

1.6

0.79

1.010

0.513

0.473

0.713

217

 

2.0

0.97

1.238

0.607

0.560

0.700

217

 

34.0

34.25

33.75

2.0

0.95

2.011

2.580

1.520

1.130

91

 

35.0

35.25

34.75

1.6

1.32

1.679

2.350

1.340

1.400

217

 

36.0

36.25

35.75

1.6

1.36

1.729

2.560

1.420

1.480

127

 

2.0

1.68

2.136

3.100

1.720

1.450

127

 

2.4

1.99

2.533

3.590

2.000

1.420

127

 

 

42.7

 

42.95

 

42.45

2.0

2.01

2.557

5.310

2.490

1.440

91

 

2.3

2.29

2.919

5.970

2.800

1.430

91

 

2.5

2.49

3.157

6.400

3.000

1.420

91

 

2.8

2.76

3.510

7.020

3.290

1.410

91

 

 

48.6

 

48.85

 

48.35

2.3

2.63

3.345

8.990

3.700

1.640

91

 

2.5

2.84

3.621

9.650

3.970

1.630

91

 

2.8

3.16

4.029

10.600

4.360

1.620

91

 

3.2

3.58

4.564

11.800

4.860

1.610

91

 

Carbon Steel Pipe
(Black and Galvanized)
Scaffolding
Pipe Standard : BS 1139

NOMINA

SIZE

LOUTSIDE DIAMETER

WALL

THICKNESS

WEIGHT

BUNDLING

maximum

minimum

mm

mm

mm

mm

kg/m

kg/ft

lb/ft

pieces

48.3

48.8

47.8

4.0

4.37

1.33

2.94

91

Carbon Steel Pipe
(Black and Galvanized)
Water Transmission Pipe

Pipe Standard : BS1387:1985 ,AS1074 ,SS17:1996

Tensile Strength : 320 to 460 N/mm²
Yield Strength (min) : 195 N/mm²
Length Tolerance : -0, +30 mm
Thickness Tolerance : – 10%, + not specified

BS1387 ASTM A53 Galvanized Steel Pipe

CLASS

NORMINAL

SIZE

OUTSIDE DIAMETER

WALL THICKNESS

LENGTH

WEIGHT

BUNDLING

maximum

minimum

plain end

inch

mm

inch

mm

inch

mm

inch

mm

meter

ft

kg/m

kg/ft

lb/ft

pieces

 

1

25

1.346

34.2

1.315

33.4

0.126

3.2

6

20

2.410

0.735

1.620

91

1 ¼

32

1.689

42.9

1.657

42.1

0.126

3.2

6

20

3.100

0.945

2.083

44

1 ½

40

1.921

48.8

1.890

48.0

0.126

3.2

6

20

3.570

1.088

2.399

44

2

50

2.394

60.8

2.354

59.8

0.142

3.6

6

20

5.030

1.533

3.380

44

2 ½

65

3.016

76.6

2.969

75.4

0.142

3.6

6

20

6.430

1.963

4.328

19

3

80

3.524

89.5

3.469

88.1

0.157

4.0

6

20

8.370

2.551

5.625

19

4

100

4.524

114.9

4.461

113.3

0.177

4.5

6

20

12.200

3.718

8.199

10

5

125

5.535

140.6

5.461

138.7

0.197

5.0

6

20

16.600

5.095

11.156

10

6

150

6.539

166.1

6.461

164.1

0.197

5.0

6

20

19.700

6.004

13.239

10

 

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API 5L Grade-B ERW Line Pipe Technical Specifications , 20″DN (508.0 mm)×WT 7.9 mm http://www.abtersteel.com/line-pipe/api-5l-grade-b-erw-line-pipe/ Sat, 29 Dec 2018 08:42:43 +0000 http://www.abtersteel.com/?p=4554 Schedule of Requirements IFT NO. PD.2312/397-MECD/MEZ/PIPE.Materials: Line Pipe. Item No. Description of Goods Qnty Unit A. Line Pipe. As per detailed technical specifications at Section 7. Size and quantity are as follows:     A.1 DN 20″ x WT 7.9 mm API 5L Grade B, ERW 450 Meter. A.2 DN 16″ x WT 7.9 mm API 5L Grade B, ERW 5,600 Meter. Technical Specifications       IFT NO. PD.2312/397-MECD/MEZ/PIPE. API 5L Grade-B ERW Line Pipe 20″DN (508.0 mm)×WT 7.9 mm This Specification covers the manufacturer, acceptance and delivery of steel pipes with Electric Resistance Welded Longitudinal seam for gas line pipe. Said […]

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Schedule of Requirements

IFT NO. PD.2312/397-MECD/MEZ/PIPE.Materials: Line Pipe.

Item

No.

Description of Goods

Qnty

Unit

A.

Line Pipe.

As per detailed technical specifications at Section 7.

Size and quantity are as follows:

 

 

A.1

DN 20″ x WT 7.9 mm API 5L Grade B, ERW

450

Meter.

A.2

DN 16″ x WT 7.9 mm API 5L Grade B, ERW

5,600

Meter.

Technical Specifications

      IFT NO. PD.2312/397-MECD/MEZ/PIPE.

API 5L Grade-B ERW Line Pipe 20″DN (508.0 mm)×WT 7.9 mm

This Specification covers the manufacturer, acceptance and delivery of steel pipes with Electric Resistance Welded Longitudinal seam for gas line pipe. Said pipes shall be manufactured in accordance with the following listed in the order of precedence:

         (a)     This specification

         (b)     API 5L Spec. (Latest edition)

         (c)     ASME Guides for Transmission and Distribution Piping System (Latest edition)

  1. MATERIAL:

Steel of Grade-B, PSL-1in accordance with API 5L shall be used. The steel shall be fully- killed, fine grained steel and shall comply with the following Heat Analysis requirements at maximum:

         C       = 0.26%

         Mn    = 1.20%

         P       = 0.030%

         S       = 0.030%

         Heat analysis shall be made and the results of the analysis shall be recorded in the inspection certificate.

  1. METHOD OF MANUFACTURING:

         Electric Resistance Welding: Longitudinal welding without filler metal.

  1. DELIVERY ALLOWANCE AND PIPE LENGT:

         The pipe shall not have any girth welds. The length of each batch of pipe shall be 12m±50mm.

         Delivery Allowance : +Nil, -(minus) 1%, Delivery Allowance and Pipe length beyond this shall not be acceptable.          

  1. HYDROSTATIC TESTING:

         Each length of pipe shall be tested hydrostatically in accordance with API 5L Spec. PSL-1.

  1. LONGITUDINAL WELD:

         The hardness of the longitudinal weld and the heat affected zone shall not exceed 250 HV 10. Complete penetration shall be warranted and NON-Destructive Inspection shall be carried as per API 5L Spec.

 

  1. TOLERANCES:

         6.1    Diameter Tolerance

                  The tolerance for diameter of pipe body shall be +/- 3.2mm

                  The tolerance for diameter at Pipe Ends (within 100.0mm of the pipe end) shall be:

                  Plus Tolerance = 1.60mm, Minus Tolerance = 1.60mm.

         6.2    Thickness (Wall) Tolerance

                  Wall thickness tolerance shall be ±0.79mm.

  1. PREPARATION OF PIPE ENDS:

         Pipe shall be furnished with both the ends beveled to an angle of 30o, +5o, -0o, measured from line drawn perpendicular to the axis of the pipe and with a root of 1/16″ +/- 1/32″ (1.59 +/- 0.79mm). The bevel ends of each pipe shall be protected by suitable plastic bevel protectors.

         The internal weld bead of each pipe shall be ground flush with the parent material over a length of 150 mm from each end of pipe.

         The finished pipe ends shall be free of lamination and other defects Ends shall be checked for such defects by ultrasonic testing of 25mm from each end of each pipe.

  1. COATING:

         The pipes shall be cleaned and be given a mill coating on external surface to protect it from rusting during transit/transportation.

         The individual pipe numbers shall be selected consecutively. In case of pipe manufactured by more than one Manufacture, the individual pipe number shall be on the basis of individual mill with a three letters abbreviation of the mill identifying the Manufacturer to be followed by pipe number starting with 1(one).

         Heat number shall be traceable by means of pipe number and vice versa. The pipe length (in meter with two decimals) shall be painted in white color on the surface of the each pipe at one end.

  1. MARKING:

         The identification markings shall be in accordance with API. The following identification markings shall paint stencil on one end of each pipe length approximately 140mm from the pipe end:

         –        API Monogram;

         –        Manufacturer’s mark;

         –        Material grade;

         –        Outside diameter times specified wall thickness;

         –        Pipe number;

         –        Process of manufacturing;

         –        Test pressure;

         –        Weight per meter;

         –        Country of origin;

         –        Contract Number

         –        Destination.

 

         The pipe length (in meter with two decimals) shall be painted in white color on the surface of each pipe at one end.

  1. CERTIFICATE(S):

         The Manufacturer must have valid API Monogram Certificate of authority issued in favour the manufacturer to use API official Monogram and the accreditation by recognized authority to issue ISO 9001:2008/ BS 5750: Part-1  EN 29001/ EN 29002 must be submitted with the tender. Tender submitted without these certificate(s) shall be treated as technically non-responsive.

 

  1. In addition to the warranty certificate required under clause-6 of the tender document, the supplier shall have to furnish the following special warranty certificate with the shipping document:

       “purchaser is to be reimbursed for direct replacement costs of any Pipe furnished that falls under field Hydrostatic Tests due to defect of materials, workmanship, or lack of compliance with all aspects of the specifications agreed upon. Such tests shall be applied at the time of construction of the pipeline and before the pipe line is placed in service. The test pressure shall not exceed the one with which the pipes are tested in mill(s) in accordance with the specifications agreed upon. These replacement costs shall include and be limited to Pipe, Labour & Equipment Rental for locating, cutting out and replacing defective Pipe. Suppliers/Manufacturer shall be responsible only for the failures which are proved to be attributable to his own responsibility and Supplier’s/Manufacturer’s liability shall be in any case not more than 5% of the contract amount. Supplier’s/Manufacturer’s liability shall be, in any case limited to the above and shall terminate after 12 months of delivery of the pipes at Chittagong Port or after 18 months of final shipment whichever date comes earlier”.

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