Carbon steel (A106 B, A105, A234 WPB) covers most water, steam, oil and gas service from about −29 °C to 425 °C.
Low-temperature carbon steel (A333 Gr 6, A350 LF2, A420 WPL6) is impact tested at −45/−46 °C for cold service.
Chrome-moly alloys (P11, P22, P91) handle high-temperature steam and hydrogen service and need PWHT.
Austenitic stainless (304/316 and L grades) resists corrosion; L grades avoid sensitisation after welding. Duplex and super duplex add strength and chloride resistance for seawater and offshore.
