Failure Analysis of Type 316L SS Drain Nozzle Elbow in H_2S Service

摘要

Austenitic stainless steels (SS), such as AISI Type 304 (UNS S30400) and 316 (UNS S31600) are used in the annealed condition for hydrogen sulfide (H_2S) service. ASTM A403 Type 316L SS (UNS S31603) is normally suitable for H_2S service in non-sensitized condition.1 If, however, the material undergoes prior sensitization or in situ sensitization, it becomes susceptible to sulfide stress corrosion cracking (SSG).~2 The austenitic SS are used to a maximum Rockwell C hardness of 22 HRC.~3 The factors that influence the SSC susceptibility include the H S concentration, pH, temperature, strength level, and cold work. The present case study is related to such a phenomenon. A detailed investigation was made to ascertain the cause of failure of an elbow used in H_2S service. The Type 316L SS pipeline system elbow was carrying water saturated with H_2S at a maximum temperature of 130 °G and pressure of 25 kg/cm~2.