SCC resistance of UNS S31603 line pipe lining in mildly sour service under plastic strain

摘要

To achieve corrosion resistance in wet gas and condensate production, use of UNS S31603 clad (metallurgically bonded) carbon steel or UNS S31603 lined (mechanically bonded) carbon steel as line pipe material are two of the options. The success of this application depends on the actual exposure conditions in terms of H_2S level, temperature, pH and salt content but also on the straining the stainless steel will undergo. To demonstrate SCC resistance of UNS S31603 liner material in a mildly sour but relatively elevated temperature application in which a strain based pipeline design was applied a series of tests was performed, taking account of both straining that would occur in reeling and in service. Test specimens were taken from shop welds, representative of the welding on the pipeline liner, and from actual liner removed from a test section of the lined pipe. Specimens were tested as tensile bars, which for the actual liner were of flat dog bone shape, in Ripple Strain Rate Tests as noted in ANSI/NACE MR0175/ ISO 15156-3. The results showed that, for the exposure conditions simulated, in situ strains up to 1% did not cause SCC. Hence the resistance of the lined pipe against SCC was considered demonstrated up to the strain limit in the pipeline design.