A new cast Ni-base alloy suitable for severe sour service

This paper reports the recent findings on corrosion resistance of a new centrifugally cast austenitic corrosion resistant alloy (CRA), 46Ni-35Cr-9Mo, against severe sour gas environment. The sour service corrosion validation was carried out by sulphide stress cracking (SSC) using autoclaves with four point bend (4PB) samples. The specimens were deflected (stressed) to 100% of the actual yield strength (AYS) at 205 °C, and the condition used was as per NACE (1) MR0175/ISO (2) 15156-3/Level VII with a pH of 5 and with a total exposure time of 720 h. The samples were taken from commercially centrifugally cast tubes. Two types of non-passivated surface finish conditions were exposed (pulled bored and ground). The post-test examination did not reveal any cracking or corrosion, i.e. the tested alloy fulfills the requirements of NACE MR0175/ISO 15156-3/Level VII. Consequently both the base material and the pull bored surfaces withstand the test conditions.