Fitness-for-Purpose Material Testing for Sour Gas Service—An Overview

Sour environments differ significantly in their aggressiveness toward materials, depending on such factors as total system pressure, partial pressures of hydrogen sulfide (H2S) and carbon dioxide (CO2), pH of the aqueous phase, temperature, chloride ion (Cl–) concentration, etc. Materials that perform poorly in standard laboratory sulfide stress cracking and hydrogen-induced cracking tests and some field environments may give acceptable performance under other sour service conditions. This paper provides some additional guidance on the manner in which standard sour service testing methods should be selected and performed, and on the interpretation and application of the results. The relevant recommendations and requirements of NACE International, the European Federation of Corrosion (EFC), and the American Petroleum Institute (API) are reviewed. The recommendations of NACE, EFC, and API for the selection of the most appropriate test method(s), test frequency, and acceptance criteria for particular components and services are listed. Some alternative tests being used to qualify materials for general and specific sour gas service conditions are described and reviewed.