Abstract
Higher grade alloys such as super-duplex stainless steels have been the conventional choice when selecting corrosion resistant alloys (CRAs) for seawater or water-alternative gas (WAG) injection service. However, the use of less costly, leaner alloyed stainless steels has recently been given greater consideration in treated seawater systems where the dissolved oxygen concentration (DOC) is better controlled. Crevice corrosion exposure tests were conducted on nine (9) stainless steel alloys in synthetic seawater containing controlled DOC levels (100 ppb to 500 ppb range). The alloys ranged from a martensitic (13-Cr) stainless steel to higher alloyed duplex and super-duplex stainless steels (25-Cr). The stainless steel specimens were creviced using the CREVCORR configuration to produce tight and reproducible crevice geometries. The exposure tests were carried out in a stepwise process in which increasingly harsher test conditions (higher temperature, higher DOC) were applied after certain periods. The open circuit potentials of the specimens were monitored during the tests to indicate the onset of crevice attack as the conditions were altered. The results of this testing revealed that stainless steels containing 17-Cr or higher are not susceptible to crevice corrosion in synthetic seawater, even for dissolved oxygen levels as high as 500 ppb.
