Corroded bellow surface Bellows in normal condition
How to choose the material of the expansion joint is a very important factor to be considered in the design of an expansion joint. The common materials used in the construction of metal bellows are usually Stainless steel series, Incoloy series and Inconel series. However, the most common available on the market is the stainless steel expansion joint, the bellow elements of which can be designed as either single ply or multi-plied.
Stainless Steel - Type 300 austenitic series
304 (ASTM A240-304)
It is the most common grade and services a wide range of applications, with the characters of thermal resistance, corrosion resistance, nicer cold crushing strength and mechanical properties. Type 304 resists nitric acid and sulfuric acids at moderate temperatures and concentrations. Bellows supplied in this grade are usually used on water or steam applications. When the material of the bellow elements is Type 304, but the End pipes or Flanges is Carbon steel, the temperature of expansion joints will range varies from -20℃to 400℃. If bellow element, end pipes and flanges are all stainless steel, then the temperature of expansion joints will range from -40℃to 600℃.
321 (ASTM A240-321)
Similar to 304 but lower risk of Weld Decay due to addition of titanium, the addition of titanium also make it have better ability to prevent Intergranular corrosion and high temperature resistance and prevent the forming of Chrome carbide. The temperature of Type 321 is range from 427℃to 816℃. In respect of High temperature, Type 321 even better than Type 316L. The expansion joints for Engine exhaust pipe are made from this material because of the high operating temperatures they can withstand.
316L (ASTM A240-316L)
Extra low carbon content of 316L, its ability of Intergranular corrosion resistance is much better than grade 321, generally used in Chemical industry and marine applications due to its high resistance to corrosion.
309S (ASTM A240-309S)
Type 309S mainly be used in High temperature environment, its higher Chromium content and Nickel content ensure its superior corrosion resistance ability and antioxidant ability, compare with Type 304, its intensity will be much higher under room temperature.
310S (ASTM A240-310S)
The Antioxidant ability of Type 310S is better than Type 309S, it was mainly be used as Heat resistant steel.
Nickel alloys
Alloy 800/800H ( N08800 / N08810 )
The application temperature of Alloy 800 is about 590℃. It has nicer ability of Creep resistant, corrosion resistance and stress resistant properties. No matter sub - zero, indoor temperature or high temperature which below 600℃, it always has better mechanical properties which widely used in variety of difficult service conditions.