OCTG is the abbreviation of Oil Country Tubular Goods, it mainly refers to the piping products that applied in the oil and gas production (drilling activities). OCTG pipe normally is manufactured based on API or related standard specifications. It also could be taken as a collective name of Drill pipe, Steel Casing Pipe and Tubing pipe, Couplings, Connections and Accessories, used in petroleum industries that onshore and offshore.
According to the API (American Petroleum Institute) standardized specifications, through the control on the chemical properties and adopts different heat treatment, OCTG pipe is classified into different performances material more than ten grades.
There are three main types of Oil Country Tubular Goods, which includes Drill pipe, Casing pipe and Tubing pipe.
Drill pipe is a heavy, seamless tube that rotates the drill bit and circulates drilling fluid. It allows the drilling fluid to be pumped through the bit and back up the annulus. The pipe is subject to axial tension, extremely high torque and high internal pressure. That is why the pipe is extremely strong and vital in OCTG endeavour.
Drill Pipe normally mean for the Durable steel pipe used in drilling, standards in API 5DP and API SPEC 7-1.
Steel casing pipe is used to line the borehole that is being dug into the ground to get oil. Just like the drill pipe, the steel pipe casing is also subject to axial tension. This is the large diameter pipe inserted into a drilled borehole and held into place with cement. The casing is subject to axial tension by its dead weight, external pressure by the rock surrounding it and internal pressure by the fluid purging
The casing is extremely heavy duty pipe which is vital to OCTG.
OCTG Tubing pipe goes inside the casing pipe because it is the pipe through which oil makes its way out. Tubing is the simplest part of OCTG and it is normally found in the segment of 30 ft (9 m), with threaded connection at both ends. The pipe is either used to transport natural gas or crude oil from the producing formation to the facilities where it will be processed after drilling is complete.
This tubing must be able to withstand pressure during the extraction process and adequately resist loads and deformations that have to do with production and workovers. Just like casing is manufactured, tubing is also manufactured the same way but the additional upsetting process is applied to make it thicker.