5 Types of Stainless Steel used in Process Piping

There are different types of stainless steel used in piping. After carbon steel, Stainless Steel is the second most widely used material in Process industries as it offers excellent corrosion resistance properties.

Stainless steel (SS) is a type of alloy steel with a minimum chromium content of 10.5% or more and maximum carbon content of less than 1.20%.

SS has excellent resistance to corrosion and good ductility. Stainless steel becomes corrosion resistive due to the formation of non-reactive chromium oxide (Cr2O3) film on the surface. This film adheres tightly to the surface of the metal, which acts as a barrier, protecting metal from corrosion.

Types of Stainless Steel

Stainless Steel properties got changed when its microstructure changed. Based on this, SS can be classified as follow;

• Austenitic stainless steel
• Ferritic stainless steel
• Martensitic stainless steel
• Precipitation Hardened stainless steel
• Duplex / Super Duplex stainless steel

Austenitic stainless steel

• Austenitic stainless steel is non-magnetic in nature and has very high corrosion resistance.
• Excellent weldability, formability, fabricability, and ductility.
• High Corrosion resistance at temp up to 1500°F.
• Useful for both low and high-temperature service.
• This type of steel is hardenable by cold working.
• It has a Face centered Cubic –FCC (fine grain structure) structure.
• Possess high impact strength at low temp.
• These types of SS are widely used in the process industry and a variety of industrial applications; cookware is also manufactured from Austenitic stainless steel.
• Type 304, 304L, 316, and 316L are some of the examples of Austenitic stainless steel. Refer to the chart given below.

Ferritic stainless steel

• Ferritic stainless steel is magnetic and contains high carbon; therefore, it is brittle and has relatively poor corrosion resistance as compared to austenitic SS.
• Non-hardenable by heat treatment.
• Body-centered cubic -BCC (coarse grain structure).
• Ferritic stainless steel has a high resistance to chloride stress corrosion cracking, so it is used in marine, petrochemical, heat exchangers, and furnace application, where high chloride content is there.
• Type 409, 430, 439, 444, and 446 are examples of Ferritic stainless steel. Refer to the chart given below.

Martensitic stainless steel

• Martensitic stainless steel has high hardness and poor corrosion resistance than austenitic SS.
• Heat treatable to high hardness level.
• Crystallographic form-distorted structure.
• It is used in the manufacturing of sports knives and multi-purpose tools.
• Type 405, 410, and 420 are examples of Martensitic stainless steel. Refer to the chart given below.

Precipitation Hardened stainless steel

• Precipitation Hardened stainless steel is magnetic and heat treatable to high strength; therefore, it has a very high strength-to-weight ratio with good corrosion resistance.
• It is used in making aerospace components and springs.
• 17-7PH, 17-4PH are examples of Precipitation Hardened stainless steel.

Duplex / Super Duplex stainless steel

• Duplex and Super Duplex stainless steel contain both Austenite and Ferrite in the microstructure.
• Because of its structure, this grade offers benefits of both Austenite & Ferrite stainless steel.
• Good resistance to pitting and crevice corrosion.
• High strength and high resistance to stress corrosion cracking.
• Used in the seawater system, heat exchanger, and structural application
• EX- UNS S32205, S31803, and S32760 are Duplex and Super Duplex stainless steel examples. Refer to the chart given below.

Commonly used stainless Steel ASTM Material Grades

• ASTM A312 Seamless, Welded, and Heavily Cold Worked Austenitic Stainless Steel Pipes
• ASTM A358 Electric-Fusion-Welded Austenitic Chromium-Nickel Alloy Steel Pipe for High-Temperature Service
• ASTM A376 Seamless Austenitic Steel Pipe for High-Temperature Central-Station Service
• ASTM A409 Welded Large Diameter Austenitic Steel Pipe for Corrosive or High-Temperature Service
• ASTM A451 Centrifugally Cast Austenitic Steel Pipe for High-Temperature Service
• ASTM A790 Seamless and Welded Ferritic /Austenitic Stainless Steel Pipe
• ASTM A813 Single- or Double-Welded Austenitic Stainless Steel Pipe
• ASTM A814 Cold-Worked Welded Austenitic Stainless Steel Pipe
• ASTM A872 Centrifugally Cast Ferritic /Austenitic Stainless Steel Pipe for Corrosive Environments
• ASTM A928 Ferritic /Austenitic (Duplex) Stainless Steel Pipe Electric Fusion Welded with Addition of Filler Metal
• ASTM A943 Spray-Formed Seamless Austenitic Stainless Steel Pipe
• ASTM A949 Spray-Formed Seamless Ferritic /Austenitic Stainless Steel Pipe
• ASTM A954 Austenitic Chromium-Nickel-Silicon Alloy Steel Seamless and Welded Pipe
• ASTM A999 General Requirements for Alloy and Stainless Steel Pipe