Hastelloy C22 Diaphragm enhanced resistance to pitting, crevice corrosion and stress corrosion cracking

Diaphragm
Diaphragm seals utilize a thin, highly compliant or flexible diaphragm between the process medium and the pressure containing internals of the pressure instrument. Hastelloy C22 is a reasonable diaphragm materials.

Given that the customer has the final word materials such as Hastelloy C276, Hastelloy C22, Monel 400, and tantalum are materials commonly used in diaphragm seals for chemical and petrochemical applications. In some cases, the entire diaphragm seal is constructed of the special material. For a more economical alternative, a layer of a corrosion-resistant material is attached to the surface of a steel diaphragm seal with a metallic bonding process. Hastelloy C22 and C276 alloys are frequently used for wetted parts in chemical process technology and equipment. These alloys have excellent corrosion resistance against acids at high temperatures, various solvents, chlorine-based media, formic and acetic acid, or brine/salt solutions, and can be used in a broad range of applications. Diaphragm seals and other equipment made of Monel 400 are also relatively common in the chemical industry. This alloy is highly resistant to organic and inorganic acids, caustic alkali solutions, and salts in a variety of operating conditions. Monel 400 offers better protection from reduction reactions than it does from oxidation reactions. Tantalum is highly resistant to corrosion, roughly equivalent to glass or platinum, but it is quite expensive. Very few organic or inorganic materials will corrode this rare metal at room temperature. The reason tantalum is so resistant to corrosion is that a layer of tough tantalum pentoxide that inhibits chemical reactions forms quickly on surfaces exposed to air. The goal with specialty material diaphragm seals is to help the customer select the most economical material for the seal to get the job done. For example, there’s probably no need to pay for an expensive tantalum diaphragm seal if a relatively inexpensive Hastelloy C276 seal will work just as well.

HASTELLOY Alloy C-22 is a nickel-chromium-molybdenum alloy with enhanced resistance to pitting, crevice corrosion and stress corrosion cracking. It resists the formation of grain boundary precipitates in the weld-heat affected zone making it suitable for use in the as-welded condition. C-22 has outstanding resistance to both reducing and oxidizing media and because of its resistibility can be used where "upset" conditions are likely to occur. It is proven to possess excellent weldability and high corrosion resistance as consumable filler wires and electrodes. The alloy has proven results as a filler wire in many applications. As filler wire use when other corrosion resistant wires have failed.

C-22 can easily be cold-worked because of its ductility and cold-forming is the preferred method of forming. More energy is required because the alloy is generally stiffer than austenitic stainless steels. 0.28" thick sheet in the heat-treated at 2050°F, rapid quenched condition, has an average olsen cup depth of 0.49".