Valve Material Grades for Harsh Service: Sour, Cryogenic and High-Temperature
Quick Answer
Harsh-service material selection matches the failure mode to the grade. Sour (H2S) service follows NACE MR0175/ISO 15156, which limits hardness and mandates H2S-resistant steels. Cryogenic duty uses carbon or low-alloy steel with verified low-temperature impact toughness and extended bonnets. High temperature calls for Cr-Mo or austenitic grades for creep and oxidation resistance.
Sour (H2S) Service - NACE MR0175
Hydrogen sulfide can cause sulfide stress cracking (SSC) and hydrogen-induced cracking (HIC) in susceptible steels. NACE MR0175/ISO 15156 limits hardness, requires controlled-yield carbon/low-alloy steels, and mandates heat-treatment and HIC/SSC testing for the duty.
Cryogenic Service
Below about -29 C (and especially for LNG at -162 C), use carbon or low-alloy steel with Charpy impact testing at the design temperature. Extended bonnets keep the stem packing above the ice point, and the seat/trim must retain toughness when cold.
High Temperature
Above roughly 425 C, carbon steel loses strength and oxidizes. Cr-Mo grades (1.25Cr-0.5Mo, 2.25Cr-1Mo) and, at higher temperatures, austenitic stainless steels provide creep and oxidation resistance.
Trim Is Separate
The trim (seat, ball, plug, disc) is usually upgraded independently of the body - Stellite or tungsten-carbide facing extends life against erosion, galling and wire drawing.
See NACE MR0175 sour service, high-temperature selection and the materials & flanges hub.
Frequently Asked Questions
What does NACE MR0175 require for sour service?
It limits material hardness, requires H2S-resistant carbon or low-alloy steels with controlled heat treatment, and mandates HIC/SSC testing appropriate to the partial pressure of H2S.
Why are extended bonnets used on cryogenic valves?
They keep the stem packing and gland above the ice point so the packing stays functional and does not freeze, while the cold service stays at the body.
Which materials suit high-temperature valves?
Cr-Mo grades such as 1.25Cr-0.5Mo and 2.25Cr-1Mo for moderate high temperature, and austenitic stainless steels where creep and oxidation resistance are needed.