Valve parts that can be in contact with the sour service should conform to the following requirements. Valve parts that are not subject to sour service don’t need to comply.
Valve springs should be made of material resistant to corrosion cracking in the presence of H2S. Inconel 718, Alloy 925, or MP35N materials should be used for springs in moderate and severe sour service. Inconel X 750 is acceptable in mild sour services.
- The packing selected should be compatible with the stem material.
- Uninhibited graphite or carbon-type packing should not be used.
- Valves operating in severe sour service should be of low fugitive emission type in accordance with ISO 15848-1. These valves should be tested in accordance with ISO 15848-2 stem tightness class B. The sampling percentage should be 10% with a minimum of one valve per lot, and should be selected at random from each production lot of valves per valve type, pressure class and nominal size. Depending on your requirements, valves operating in moderate sour service may need to follow the requirements above.
Bellow, diaphragms, items that can’t be heat treated after welding, and components that can’t function in the softened condition should be fabricated form material resistant to cracking in the hardened and/or cold worked or non-heat treated condition as defined in NACE MR-0175 / ISO 15156. Material selection should be made in accordance with the process conditions from the following: Alloy 825 and Alloy 625. Monel 400 can be also considered.