Chloride seawater with cyclic wet-dry exposure, biofouling and crevice conditions, often with stagnant zones.
Almost every alloy decision comes back to these. Get them right and the grade usually picks itself.
General corrosion, pitting, crevice, stress-corrosion cracking, oxidation, creep. Each one excludes different alloys. Deciding which mechanism governs removes most of the shortlist immediately.
Nominal conditions are not design conditions. Peak temperature, peak concentration, upset conditions and shutdown states are what actually consume the material.
The same grade carries different ASTM specifications for bar, plate, pipe and forgings. Name the form with the grade, or accept whatever the mill has in stock.
The grades that suit this service, with their UNS numbers and the specifications they are supplied to.
254 SMO is a high performance austenitic stainless steel. Its high alloying elements content imparts excellent resistance to uniform, pitting and crevice corrosion, and stress corrosion cracking.
2507 is a super duplex stainless steel with higher alloy content, thus making it superior to 2205 in corrosion resistance and strength. It has excellent resistance to uniform, pitting, crevice corrosion and chloride stress corrosion cracking.
2205 is a duplex stainless steel with nearly equal proportions of austenite and ferrite when properly heat treated. This microstructure makes it much more resistant to stress corrosion cracking than stainless steel 304 and 316L.
Inconel 625 has excellent strength at temperatures up to 816℃. At higher temperatures, its strength is generally lower than that of other solid solution strengthened alloys.
Monel 400 has excellent resistance to corrosion by many reducing media such as sulfuric and hydrochloric acids. It is generally more resistant to corrosion by oxidizing media than higher copper alloys. Monel 400 resists pitting and stress corrosion cracking in most fresh and industrial waters.
Hastelloy C-276 has excellent resistance to localized corrosion, stress corrosion cracking, and to both oxidizing and reducing media, thus making it suitable for a wide variety of chemical process environments, including ferric and cupric chlorides, hot contaminated media (organic and inorganic),…
The wrong grade in the right service fails quietly for a long time and then all at once. These are the pairings that go wrong most often.
304 and 316 suffer chloride pitting and crevice corrosion in seawater. They are not marine materials, even though they are often the first thing offered.
2205 is limited to around 300 °C for chloride service because of its ferrite content. Above that, 2507 or a nickel alloy.
