Stainless steel is a versatile material comprised of a steel alloy and a small percentage of chromium — the addition of chromium adds to the material’s corrosion resistance, a trait that earned stainless steel its name. Because stainless steel is also low-maintenance, oxidation resistant, and doesn’t affect other metals it comes in contact with, it is frequently used in a large array of applications, especially in piping and tubing manufacturing. Based on the end use of the pipe, stainless steel piping is broken down into several categories.
Pipes and tubes are sometimes difficult to classify, and tend to be distinguished based on function. In addition to these classifications, stainless steel is also distinguished by type and grade.
For tubing and piping applications, type 304 stainless steel is a common selection because it is highly chemical- and corrosion-resistant. However, type 304 stainless steel is not compatible with applications where temperatures fall between 800 and 1640 degrees Fahrenheit (F) because it is prone to carbide precipitation, a result of the material’s .08 percent carbon content limit. Stainless steel type 304L circumvents this problem because it has a lower carbon content limit, and therefore can be subjected to welding and higher temperature applications. Other types of stainless steel often possess additives (such as nickel or molybdenum) which strengthen traits that are desirable in particular applications.
This general category of steel is appropriate for applications that require corrosion resistance above other traits. Ferritic or martensitic types of steel (those made with the most chromium) are manufactured to be either heat-treated or annealed. Austenitic Stainless steels (those with high chromium and nickel contents) offer even more resistance, and can be used under the same general conditions as ferritic and martensitic types.
This type of stainless steel pipe is made from either solid chromium or a chromium and nickel combination. Types of stainless steel pressure pipe include seamless and welded pipe, electric fusion welded pipe for high-pressure applications, large diameter welded pipe for corrosive or high-temperature applications, and seamless and welded ferritic and austenitic stainless steel pipe.
For applications where stainless steel tubing or piping must come into contact with food and other sensitive products, sanitation is a high priority. Stainless steel sanitary tubing is used in such applications because it has high corrosion-resistance, doesn’t tarnish, and is easy to keep clean. For specific applications, different tolerances can be achieved. The grade typically used for these applications is ASTMA270.
In applications such as cylinders, bearings, and other hollow formed parts, stainless steel mechanical tubing is typically used. Tubing can manipulated to have a variety of cross-sectional shapes, such as square and rectangular, in addition to the more traditional, round tubing cross-section. Typically, ASTMA 511 and A554 grades are employed for mechanical tubing applications.
In highly-specific aircraft applications, chromium and nickel type stainless steel is used because of their heat and corrosion-resistance. Found in applications that require high-strength, stainless steel aircraft tubing can be work-hardened or welded, although work-hardened pieces shouldn’t be used with some kinds of corrosive substances. Low-carbon types of stainless steel are a common choice for welded parts.
For applications that require seamless and welded tubing in larger sizes (1.6 to 125 mm in outside diameter), aircraft structural tubing is used—this type of stainless steel is manufactured according to Aerospace Material Specifications (AMS) or Military Specifications (MIL Specs).
Another type of aircraft tubing, aircraft hydraulic-line tubing is used in aerospace applications as fuel-injection lines and hydraulic systems, and tends to be small. It is often manufactured from types 304 or 304 L stainless steel because of the steel’s high-strength, corrosion-resistance, and ductility.