Comparative study of corrosion and environmental cracking properties of 316L and lean duplex alloys

摘要

Alloy S31603 (316L) is a widely used corrosion resistant alloy with a Ions experience record in offshore oil & gas applications. With recent price fluctuations in metals' prices, many alternatives to Alloy S31603, specifically 'lean duplex' alloys, have risen in popularity. Lean duplex alloys may offer two cost advantages to Alloy S31603: lower or more stable materials prices (depending on the commodity price of nickel), and less material (wall thickness) required due to the higher strength of lean duplex alloys compared to Alloy S31603. In this investigation, a comparative test plan was developed to determine how some common lean duplex alloys would perform in offshore environments relative to Alloy S31603. The comparative test plan included salt water immersion, salt fog testing, pitting corrosion evaluation, and chloride stress corrosion cracking resistance testing on welded and non-welded samples. The chloride stress corrosion cracking test was a four-point bend test across a welded sample. Three different lean duplex alloys were tested. Each alloy was compared against Alloy S31603 in each of the tests to determine if the lean duplex alloys may be used in place of Alloy S31603 in some offshore applications without sacrificing corrosion performance. Sour service applications were not investigated as part of this study. The results of the study showed that the corrosion resistance of the lean duplex alloys was comparable to Alloy S31603.