Material selection guide for corrosive service
Which alloys are usually chosen for common corrosive media, and the reason. A starting point for discussion with your materials engineer.
Media and typical alloys
| Service | Alloys often specified | Why |
|---|---|---|
| Dilute and intermediate sulphuric acid | 904L, Alloy 20 | Copper and high nickel keep the alloy passive where 316L corrodes |
| Seawater and brine | Super duplex 2507, 254 SMO, titanium Gr 2, Cu-Ni 90/10 | High PREN or a stable oxide film resists chloride pitting and crevice attack |
| Chlorides with stress (chloride SCC risk) | Duplex 2205, super duplex | The two-phase structure resists chloride stress-corrosion cracking |
| Wet chlorine and hypochlorite | Titanium Gr 2, 7, 12 | Titanium's oxide film is stable in oxidising chlorides |
| Hydrochloric acid and mixed acids | Hastelloy C276 | High molybdenum and tungsten in a nickel base |
| High-temperature steam | A335 P11, P22, P91 with matching forgings | Chrome-moly steels keep creep strength at temperature |
Corrosion depends on concentration, temperature, velocity and impurities. Use this table for orientation, not as a design basis.
Detailed grade data
Specifications, chemistry and strength for each alloy are in the material guides on Teshi Fittings.
Questions buyers ask
What is PREN?
Pitting Resistance Equivalent Number, usually Cr + 3.3 Mo + 16 N. It ranks stainless steels by resistance to chloride pitting. Higher is better, but it does not predict behaviour in acids.
Send us your BOQ
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Drawings, BOQ spreadsheets and QAPs are easiest by email. Attach them to a message to info@teshigroup.com and mention your project name.