Pressure control
Choosing API 6A Material Class (AA–HH) for Sour Service | Riis Energy Services
Ingrid Solheim, Chief Engineer, Pressure Control · Опубликовано · Обновлено
Короткий ответ
Pick the API 6A material class from the partial pressure of H2S and the CO2 corrosivity: AA/BB/CC for non-sour (sweet) service with increasing CO2, and DD/EE/FF/HH for sour service (NACE MR0175/ISO 15156), with HH being corrosion-resistant alloy throughout for the most severe conditions.
Step 1: Is it sour?
If H2S partial pressure is at or above 0.05 psia (0.0003 MPa), NACE MR0175/ISO 15156 applies and you need a sour class (suffix -NL, -1.5 and so on indicate the H2S limit).
Step 2: How corrosive is the CO2?
Rising CO2 partial pressure moves you from carbon/low-alloy steel (AA, DD) to stainless trims (BB, EE) and fully stainless bodies (CC, FF).
Step 3: Extreme cases
HH uses CRA or CRA-clad bodies and trims for highly corrosive, high-H2S wells.