Stainless Steel Tubing and Piping Standards

Stainless steel is typically comprised of a basic iron-derived steel alloy and approximately 11 percent chromium. Additives, such as nickel, can be added to help enhance or manipulate chromium’s characteristics. Said to be “stainless” because it resists corrosion, stainless steel’s resistance to wear and oxidation increases with the amount of chromium present in the metal. Additionally, stainless steel is relatively low-maintenance and clean, and does not compromise the purity or integrity of metals that it encounters. This is pertinent information to those working in the deep drawing process.

Stainless Steel Grades for Tubing and Piping

Because of its desirable traits, stainless steel is often used in piping and tubing applications. Not all grades of stainless steel serve the same function, so it is important to become familiar with differences between grades before selecting stainless steel for a specific application. In piping applications, type 304 stainless steel is the most commonly used alloy because of its corrosion resistance and suitability for use in chemical applications. Type 304 stainless steel is also used in food and beverage applications and paper mills. Because this type of steel has a maximum carbon content of .08 percent, it is subject to carbide precipitation at certain temperatures, which can result in failure. Therefore, 304 should not be used in applications where temperatures fall between 800 and 1640 degrees Fahrenheit.

Another type of stainless steel, type 304L, has a lower maximum carbon content (.03 percent), and is therefore able to withstand higher temperatures and can be welded—a quality that allows pipes to be interconnected without threading. In tubing and piping applications where acids and salts are encountered, type 318 is well-equipped because it contains a small amount (2 to 3 percent) molybdenum. For tubes and pipes involved in plastic manufacturing, type 316 is the preferable type of stainless steel.

Pipe and Tubing Standards and Specifications

Austenitic stainless steel, as used for tubing and piping, is produced according to these standards:

• ASTM A249 / ASME SA249

This specification is the standard for welded austenitic stainless steel for high temperature applications, such as boiler, heat-exchanger, and condenser tubes. Typically, the tubes are produced with 1/8 inch inside diameters and up to 5 inch outside diameters. To manufacture this grade of steel (which can include types 304, 304L, and 316, as well as types 316L, 317, and 321), there are three procedural steps: automatic welding (without any filler metal), testing each tube (hydrostatic or non-destructive electric testing), and then testing each tube for reverse-bend and hardness.

• ASTM A269

This standard specification applies to seamless and welded austenitic stainless steel tubing for general applications, including those that require general corrosion resistance and low and high temperature usage,  and can include types 304, 304 L, 316L and 321.Tubes are usually ¼ inch in inside diameter and more than .020’ in nominal wall thickness. Mechanical procedures are the same as for ASTM A249.

• ASTM A270

As the specification for seamless and welded austenitic stainless steel sanitary tubing, applications include tubes designated for food and beverage industry use, as well as those with special finishes. Because the tolerances are tighter for this standard, tube to tube fitting is more closing aligned. Tubes are made with inside diameters up to 6 inches.

• ASTM A312/ ASME SA312

For high temperature and general carrion resistance this specification for seamless and straight-seam welded stainless steel pipe applies. Appropriate grades include 304, 304L 316, 316L, 317, and 321. The manufacturing process lends itself to high-production runs because of the basic nature of the techniques and design. As a result, ASTM A312 is not appropriate for use as sanitary tubing, and is subject to size limitations—industrial piping of nominal pipe size (NPS) should instead be used for pharmaceutical facilities or other sensitive large-scale applications.

Other specifications, such as ASTM A358 (which designates the standards for chromium-nickel alloy stainless steel pipe for high temperature service), address other sizes, diameters, and temperature ranges for stainless steel piping and tubing. The specifications discussed above only address several common specifications and are do not constitute an exhaustive list.