Austenitic stainless steels are iron-based alloys containing Chromium and Nickel and are widely available in various types having different compositions and material properties. They are the most commonly used material for metal bellows and expansion joints. Stainless steel bellows offer versatility in terms of their ability to withstand high temperature and high pressure and provide good corrosion protection. Types 304/304L, 316/ 316L and 321 are the standard bellows materials and Bellows Systems commonly stocks a wide range of sheet thickness ranging from 0.005″ to 0.062″.
Stainless Steel 302 (UNS: S30200)
| Bellows Materials | SS 302 |
| Description | Austenitic chromium-nickel stainless steel with higher carbon, earlier version of Type 304 stainless steel, and many on legacy parts. |
| Application Notes | 302 applications have switched to Type 304 with the improvements in melting technology. Type 302 is corrosion resistant in many environments, and the corrosion properties are similar to that of 304/304L stainless steel. The susceptibility to carbide precipitation during welding restricts the use of Type 302 in some applications and 304L is used because of its lower carbon content for welded applications. |
| UNS | S30200 |
| Specifications | ASTM A240, ASME SA-240, AMS 5515 |
Material Properties
| Density, ρ, lbs/in^3 | 0.29 |
| Yield Strength, Sy, Psi | 30,000 |
| Tensile Strength, Su, Psi | 75,000 |
| Elongation % | 40 |
| Poisson’s Ratio, ν | 0.30 |
| Youngs Modulus, E psi | 28000000 |
| Creep Temperature, ˚F | 800 |
| Coeff. Thermal Expansion, in/in/˚F | 0.0000092 |
Stainless Steel 304 (UNS: S30400)
| Bellows Materials | SS 304 |
| Trade Name | CRES 304 |
| Description | Standard 18/8 (18% chrome, 8% nickel) austenitic stainless steel and is the most commonly used grade of stainless steels. |
| Application Notes | It is a non-magnetic alloy in the annealed condition but becomes magnetic as it is cold worked. Alloy 304 can be easily welded and is the choice for many deep drawn, spun or formed parts due to its high ductility. |
| UNS | S30400 |
| Specifications | ASTM A240, ASME SA-240, AMS 5513 |
Material Properties
| Density, ρ, lbs/in^3 | 0.29 |
| Yield Strength, Sy, Psi | 30,000 |
| Tensile Strength, Su, Psi | 75,000 |
| Elongation % | 40 |
| Poisson’s Ratio, ν | 0.30 |
| Youngs Modulus, E psi | 28000000 |
| Creep Temperature, ˚F | 800 |
| Coeff. Thermal Expansion, in/in/˚F | 0.0000092 |
| Melting Point, ˚F | 2550 |
Stainless Steel 304L (UNS: S30403)
| Bellows Materials | SS 304L |
| Description | Low-carbon variation of 304 making it useable in the “as-welded” condition (without annealing), even in severe corrosive conditions. |
| Application Notes | The alloy has oxidation resistance to a maximum temperature of 1650°F (899°C) continuously without appreciable scaling. The maximum temperature for intermittent exposure is 1500°F (816°C). |
| UNS | S30403 |
| Specifications | ASTM A240, ASME SA-240, AMS 5513 |
Material Properties
| Density, ρ, lbs/in^3 | 0.29 |
| Yield Strength, Sy, Psi | 30,000 |
| Tensile Strength, Su, Psi | 75,000 |
| Elongation % | 40 |
| Poisson’s Ratio, ν | 0.30 |
| Youngs Modulus, E psi | 28000000 |
| Coeff. Thermal Expansion, in/in/˚F | 0.0000092 |
Stainless Steel 304H (UNS: S30409)
| Bellows Materials | SS 304H |
| Description | A modified version of the widely utilized “18-8” chromium nickel austenitic stainless steel. |
| Application Notes | The carbon content is controlled in the range of 0.04–0.10% for increased strength at temperatures above 800°F (427°C). It is an economical and versatile corrosion resistant alloy suitable for a wide range of general purpose applications. It is common practice for 304H to be dual certified as 304 and 304H. The high carbon chemistry of 304H enables 304 to meet the mechanical properties and grain size requirements of 304H. |
| UNS | S30409 |
| Specifications | ASTM A240, ASME SA-240, AMS 5513 |
Stainless Steel 316 (UNS: S31600)
| Bellows Materials | SS 316 |
| Description | Austenitic chromium-nickel stainless steel alloy containing molybdenum. This addition increases corrosion resistance, improves resistance to pitting chloride ion solutions and provides increased strength at elevated temperatures. |
| Application Notes | Properties of this austenitic stainless steel grade are similar to those of type 304 except that type 316 is somewhat stronger at elevated temperature ranges. 316 alloy may become magnetic when cold worked. Corrosion resistance is improved, particularly against sulfuric, hydrochloric, acetic, formic and tartaric acids, as well as corrosion caused by acid sulfates and alkaline chlorides. |
| UNS | S31600 |
| Specifications | ASTM A240, ASME SA-240 |
Material Properties
| Density, ρ, lbs/in^3 | 0.29 |
| Yield Strength, Sy, Psi | 30,000 |
| Tensile Strength, Su, Psi | 75,000 |
| Elongation % | 40 |
| Poisson’s Ratio, ν | 0.30 |
| Youngs Modulus, E psi | 28000000 |
| Creep Temperature, ˚F | 900 |
| Coeff. Thermal Expansion, in/in/˚F | 0.0000092 |
Post Weld Heat Treatement (PWHT)
| Annealing | Solution anneal at 1900-1950 °F for improved corrosion properties |
Stainless Steel 316L (UNS: S31603)
| Bellows Materials | SS 316L |
| Description | The low carbon version of 316 Stainless is 316L Stainless Steel which has increased resistance to intergranular corrosion. |
| Application Notes | H2S exposure |
| UNS | S31603 |
| Specifications | ASTM A240, ASME SA-240 |
Material Properties
| Density, ρ, lbs/in^3 | 0.29 |
| Yield Strength, Sy, Psi | 30,000 |
| Tensile Strength, Su, Psi | 75,000 |
| Elongation % | 40 |
| Poisson’s Ratio, ν | 0.30 |
| Youngs Modulus, E psi | 28000000 |
| Coeff. Thermal Expansion, in/in/˚F | 0.0000092 |
Stainless Steel 321 (UNS: S32100)
| Bellows Materials | SS 321 |
| Trade Name | CRES 321 |
| Description | Austenitic chromium-nickel stainless steel containing Titanium. The titanium addition stabilizes against carbide precipitation during welding and in 800 – 1500°F (427 – 816°C) service. It also eliminates the need for an anneal after welding. |
| Application Notes | Alloy 321 provides excellent intergrangular corrosion resistance upto 1500 °F and possesses better creep properties than 304/304L. |
| UNS | S32100 |
| Specifications | ASTM A240, ASME SA-240, AMS 5510 |
Material Properties
| Density, ρ, lbs/in^3 | 0.286 |
| Yield Strength, Sy, Psi | 30,000 |
| Tensile Strength, Su, Psi | 75,000 |
| Elongation % | 40 |
| Poisson’s Ratio, ν | 0.30 |
| Youngs Modulus, E psi | 28000000 |
| Coeff. Thermal Expansion, in/in/˚F | 0.0000093 |
| Melting Point, ˚F | 2500 |
Stainless Steel 347 (UNS: S34700)
| Bellows Materials | SS 347 |
| Description | A stabilized austenitic stainless steel similar to type 304 with an addition of Columbium and Tantalum. |
| Application Notes | The columbium serves to produce a stabilized type of stainless steel which is immune to chromium carbide precipitation. Type 347 grades are thus recommended for parts fabricated by welding which cannot be subsequently annealed or for parts which must operate in service between 800 – 1600 °F. |
| Industry Uses /Products | Turbine exhaust Collector, airplane exhaust stacks, jet engine parts, expansion joints, tubing, fasteners, flexible metal hose and bellows |
| UNS | S34700 |
| Specifications | ASTM A240, ASME SA-240, AMS 5512 |
Material Properties
| Density, ρ, lbs/in^3 | 0.288 |
| Yield Strength, Sy, Psi | 30,000 |
| Tensile Strength, Su, Psi | 75,000 |
| Elongation % | 40 |
| Poisson’s Ratio, ν | 0.30 |
| Youngs Modulus, E psi | 28000000 |
| Coeff. Thermal Expansion, in/in/˚F | 0.0000092 |
| Melting Point, ˚F | 2500 – 2550 |
Chemical Compostion, %
| Carbon, C | 0.08 (max) |
| Nickel, Ni | 9.00 – 12.00 |
| Chromium, Cr | 17.00 – 19.00 |
| Manganese, Mg | 2.00 (max) |
Alloy 20 (UNS: N08020)
| Bellows Materials | Alloy 20 |
| Trade Name | INCOLOY® alloy 20, Carpenter® 20 alloy, 20CB-3® |
| Description | An austenitic stainless steel possessing excellent resistance to attack by sulfuric acid and many other aggressive environments. |
| Application Notes | Alloy 20 stainless is also stabilized to limit inter-granular attack, even in the sensitized condition. Important advantages of alloy 20 stainless are its excellent mechanical properties and comparative ease of fabrication. The presence of Columbium in the alloy minimizes the precipitation of carbides during welding. |
| Industry Uses /Products | Components for processing synthetic rubber processing. Components for processing gasoline, solvents, explosives, plastics, synthetic fibers, chemicals Food and dye production. Components for processing pharmaceutical |
| UNS | N08020 |
| Specifications | ASTM A240, ASME SA-240 |
Material Properties
| Density, ρ, lbs/in^3 | 0.292 |
| Yield Strength, Sy, Psi | 35,000 |
| Tensile Strength, Su, Psi | 80,000 |
| Elongation % | 30 |
| Youngs Modulus, E psi | 29000000 |
| Coeff. Thermal Expansion, in/in/˚F | 0.00000816 |