Limits of Use of Low Alloy and Stainless Steels in Upstream Sour Environments

Abstract Currently the use of sour service metallic materials is guided by ISO 15156/NACE MR0175 standard and guideline documents such EFC N°16 and 17. Carbon and low alloy steels are used according to the sulfide stress cracking (SSC) severity diagram in ISO 15156-2. However, there is a zone in the lower left hand corner which is undefined so far. Hence, the severity is unknown and qualification may need to be specifically carried out for using steels under these conditions. Work has been undertaken to test several steels of known sour service resistance to better assess the severity in this area of the diagram. For corrosion resistant alloys such as stainless steels the limits of use are still under investigation and so far only limited data is available in the open literature. The work reported here has been carried out to test the resistance of UNS S31603 (AISI 316L) stainless steel in a number of sour service media. The data obtained has been compared with published data to better assess the limits of use of this alloy and extend its use in upstream sour service. The first part of the paper deals with the resistance of carbon and low alloy steels and the limits of use of UNS S31603 stainless steel are addressed in the second part. Both topics are important to optimise the use of these steels in sour service conditions.