Valve Materials for Sour Gas Service (H2S)

The Challenge of Hydrogen Sulfide

Hydrogen sulfide (H2S) causes sulfide stress cracking (SSC) and hydrogen-induced cracking (HIC) in susceptible steel alloys. Valves in sour service must meet NACE MR0175/ISO 15156 to prevent catastrophic brittle failure.

NACE MR0175 Material Requirements

• Carbon and low-alloy steels: hardness must not exceed 22 HRC (250 HBW)

• Austenitic stainless steels: generally acceptable but cold-work limits apply

• Nickel alloys: Alloy 718 and similar must be qualified by testing

• Avoid 17-4 PH, 13Cr in H2S above certain partial pressures without qualification

Key Sour Service Valve Features

• All pressure-containing parts and bolting compliant with NACE MR0175

• Body and trim hardness verification by PMI and hardness survey

• Elastomers resistant to H2S permeation (HNBR, FKM selected for H2S)

• SSC-resistant packing: PTFE, graphite, PEEK-reinforced options

Testing for Sour Service

NACE TM0177 and TM0284 define laboratory testing methods to qualify materials for SSC and HIC resistance. Valve manufacturers providing NACE-compliant valves maintain mill certificates and hardness records for each heat of material used.

Inspection During Fabrication

Weld heat-affected zones (HAZ) are particularly vulnerable to SSC due to hardening during welding. Post-weld heat treatment (PWHT) and hardness surveys of welds are mandatory for sour service valves to verify compliance.