Selection of the correct bellows material is a very important detail to consider when designing an expansion joint. Some of the factors that influence the material selection process are given here:

Problem
Cause
Solution
  • Joint Corrosion
    Galvanic reaction causing holes in a bellows. Common in acidic medium.
    Use A240-316, B443-625 or B424-825. Any other material that contains molybdenum will also help.
  • Chloride Stress Corrosion Cracking
    Chlorides attacking austenitic stainless steel bellows (A240-304, A240-316, A240-321).
    Use a high nickel alloy (B168-600, B443-625, B409-800).
  • Carbide Precipitation
    At temperatures over 700 deg F, chromium carbides form in unstabilized grades of stainless steel (A240-304, A240-316). Corrosion occurs in the grain boundaries.
    Use a stabilized grade of stainless steel (A240-321, A240-347), low carbon materials (A240-304L, A240-316L) or carbide precipitation resistant high alloy.

 

Stainless Steel - Type 300 Austenitic Series

304SS (ASTM A240-304)

Services a wide range of applications. It resists organic chemicals, dye stuff, and a wide variety of inorganic chemicals. Type 304 resists nitric acid and sulfuric acids at moderate temperatures and concentrations. It is used extensively in piping systems conveying petroleum products, compressed air, steam, flue gas, and liquefied gases at cryogenic temperatures. The temperature range varies from -270 °C to 650 °C.

304LSS (ASTM A240-304L)

Has a maximum carbon content of 0.03% versus 0.08% for type 304. This lower carbon content eliminates the problem of chromium carbide precipitation and makes it more resistant to intergranular corrosion. It is preferred over 304 for nitric acid service.

316SS (ASTM A240-316)

This alloy contains more nickel than the 304 types. The addition of 2% to 3% molybdenum gives it improved corrosion resistance compared to 304 especially in chloride environments that tend to cause pitting. Some typical uses are flue gas ducts, marine service, crude oil systems high in sulfur, heat exchangers, and other critical applications in the chemical and petrochemical industries.

316LSS (ASTM A240-316L)

With its low carbon content of 0.03% maximum, it lends itself to highly corrosive applications where intergranular corrosion is a hazard.

321SS (ASTM A240-321)

The addition of titanium to this stainless steel acts as a carbide stabilising element that prevents carbide precipitation when the material is heated and cooled through the temperature range of 400°C to 800 °C. 321 finds uses in many of the same applications as type 304, where the added safeguard from intergranular corrosion is desired. The standard catalog exhaust joints are made from this material because of the high operating temperatures they withstand.

High Nickel Alloys

Nickel 200 (ASTM B162-200)

A commercially pure nickel (99.5% Ni), nickel 200 has good mechanical properties and excellent corrosion resistance to salt water attack and chloride cracking.

Monel 400 (ASTM B127-400)

This copper-nickel alloy (66.5% Ni, 31.5% Cu) is a higher strength material than Nickel 200 with excellent corrosion resistance over a wider range of temperatures and operating conditions.

Inconel 600 (ASTM B168-600)

This nickel-chromium alloy (76% Ni, 15.5% Cr) has very desirable properties for the manufacture of expansion joints. It has a very high strength over a wide range of temperatures and a good resistance to a variety of corrosive environments. It finds wide use in steam and salt water services where it is virtually immune to chloride stress corrosion.

Inconel 625 Gr.1 (ASTM B443-625)

This alloy contains a higher chromium content (21.5%) than alloy 600. With the addition of 9% molybdenum, it produces an alloy of superior strength and corrosion resistance over a wider range of temperatures and environments. It is used on many critical applications such as heat exchangers and catalytic cracker expansion joints. When exposed to temperatures above 540 °C for prolonged periods, it may become embrittled.

Inconel 625 LCF (ASTM B443-625 LCF)

Similar to straight grade 625, this alloy has a slight change in material composition to enhance low-cyclic fatigue properties at elevated temperatures.

Incoloy 800 (ASTM B409-800)

This nickel-iron-chrome alloy is less expensive than alloy 600. It has good corrosion resistance properties and high temperature strength over a wide variety of difficult service conditions.

Incoloy 825 (ASTM B424-825)

This is a copper-chrome nickel alloy that exhibits excellent corrosion resistance to the most severe acids, in particular hot concentrated sulfuric acid and sulfur bearing environments.

Other Materials

In addition to the materials listed above, Axial Dynamics has successfully manufactured bellows from Hastelloy C22 and C276, duplex 2205, alloys 253 MA, 800H/HT, 3CR12, and many others. Please consult Axial Dynamics for any material not listed or for ordering catalogue parts with alternate materials.