Stainless steel tubes are often manufactured in compliance with ASTM A269/A213, the American Society for Testing and Materials standard. The ASTM A269 standard specifies austenitic stainless steel tubing for general duty, both seamless and welded. While ASTM A213 is a standard specification for seamless ferritic and austenitic alloy-steel boiler, superheater, and heat-exchanger tubes, it is a standard specification for seamless ferritic and austenitic alloy-steel boiler, superheater, and heat-exchanger tubes. They're also frequently built of dual-grade stainless steel SS 316H with a seamless finish.

Finishing of Stainless Steel Tubes

Stainless steel 316H Tubes are typically supplied annealed and pickled. Annealing is a thermal treatment that changes the material's physical and chemical properties. It improves the flexibility of stainless steel tubes while lowering their hardness. Pickling is a metal surface treatment that uses a strong acid to remove contaminants from the surface of the tube. Polished 320 Grit is made for applications that demand a smoother finish for aesthetic purposes. Bright Steel is heat-treated (annealed) in a controlled atmosphere to create annealed.

The steel has a reflective, mirror-like look after heat treatment. Flaring and cold bending are also possible with stainless steel tubes. With tube benders or by hand, a bend radius of 3x the exterior tube diameter is recommended for cold bending. Arc welding is possible with SS 316H tubes using standard procedures. The welding filler should be chosen in line with DIN EN 1600 and DIN EN 12072 part 1, with the kind of application and welding process in mind.

Characteristics of Stainless Steel Tubes

Stainless steel 316H Tubes have minimum yield strength of 515 N/mm2 and a maximum hardness of 90 HRB. Compression fittings must be able to work with the tubes at a maximum of 80 HRB. The chromium in stainless steel tubes is at least 10.5 percent, and it reacts with oxygen to generate an undetectable chrome-oxide coating. The layer is thick enough to keep oxygen from rusting the surface further.

SS 316H Tubes is a molybdenum-bearing austenitic stainless steel that contains between 2.0 and 3.0% molybdenum. The high nickel and molybdenum concentration gives resistance to corrosive conditions such as saltwater and chlorine. Furthermore, SS 316H has an exceptional tensile strength at elevated temperatures, as well as great formability and weldability.

The carbon content is regulated to a maximum of 0.03 percent by the "H" designation after the grade number, although the standard amount of carbon content in stainless steel is 0.08 percent. Where welding will be done, stainless steel tubes with a lower carbon content are used. Because of the decreased carbon concentration, the chromium is not exhausted, and the chrome-oxide layer on the tube surface can still form.