Hydrogen sulphide embrittlement combined with chloride stress-corrosion cracking in a wet, high-pressure environment.
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.
Incoloy 925 is a precipitation-hardenable nickel-iron-chromium alloy. It combines high strength with Incoloy 825’s excellent corrosion resistance. Incoloy 925 is particularly resistant to sulfide-induced stress cracking and stress-corrosion cracking.
Incoloy 825 has excellent resistance to chloride-ion-induced stress corrosion cracking, reducing environments containing phosphoric and sulfuric acids, oxidizing environments containing nitric acid and nitrates, and pitting, crevice corrosion and intergranular corrosion.
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 K-500 combines Monel 400’s excellent corrosion resistance with greater strength and hardness as a result of adding aluminum and titanium and proper heat treatment to cause precipitation hardening. It is nonmagnetic at temperatures as low as -101℃.
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.
Type 304 and 316 have no molybdenum and no resistance to hydrogen embrittlement. They are not candidates for sour service, however well they perform in benign chloride service.
A hardened condition with high hardness and a high yield strength is exactly what NACE MR0175 warns about. If sour service is possible, the hardness limit must be demonstrated, not assumed.
