Stainless steels have a great variety of potential applications in the petroleum industry, mainly as an alternative to carbon steel in corrosive environments. Within a number of media that can cause corrosion problems with these materials, only chloride solutions and hydrogen sulfide are of importance in oilfield service.
A reliable tool that permits the proper selection of stainless steels has yet been missing. In order to provide engineering diagrams for this purpose, pitting and stress corrosion cracking (SCC) tests were performed. Specimens were exposed to NaCl solutions containing from 3 to 100,000 ppm Cl- at temperatures from 40 to 200 °C. This test configuration was chosen to give a better representation of actual service conditions than accelerated standard test procedures do.
Tested materials were the austenitic stainless steel grades 321, 316Ti (API LC30–1812) and 254 SMO, and 22Cr duplex (austenitic-ferritic) steel (API LC65–2205). Based on an optical examination of the specimens, no-risk regions of chloride concentration vs. temperature have been identified. Subsequently, service temperature limits have been deduced for each tested material.
Thus, material failures by pitting and SCC can be prevented without overdesigning. The results of the testing series are applicable to all chloride environments without presence of H2S, as they have to be handled by primary production equipment, as well as transportation and gas processing facilities.