Recent Experience from Field Application and Laboratory Testing on the Corrosion Risk of Stainless Steel UNS S82551 in Water Alternating Gas Service

Abstract Duplex stainless steel UNS1 S82551 tubing has been used since 2017 in Water Alternating Gas (WAG) injection wells on the Norwegian continental shelf. After approximately five years of operation, leaks were reported in two wells. Investigations were performed to determine the root cause of these failures, including a review of the metallurgy and fluids used during well construction and operation phases. The metallurgy included, amongst others, the following alloys: UNS S82551, UNS S39274 and UNS N09925. Inspection of the retrieved well components revealed that the leaks were caused by crevice corrosion to the tubing threaded connections. UNS S82551 is expected to be corrosion resistant in WAG service utilizing treated seawater and dried gas. However, earlier extensive laboratory testing showed that this alloy can be sensitive to crevice corrosion under seawater treatment deviations. Subsequent laboratory corrosion testing including all fluids in contact with the well materials during construction showed no impact on crevice corrosion. The root cause analysis revealed that the operating treatment procedure allowed residual chlorine in the injected seawater. Immersion and electrochemical testing confirmed that the conditions of exposure induced by the operation procedure led to crevice corrosion of alloy UNS S82551, and this was the root cause of the tubing leaks.