316 STAINLESS STEEL INSTRUMENT TUBING IN MARINE APPLICATIONS - LOCALIZED CORROSION PROBLEMS AND SOLUTIONS

Localized corrosion of 316 stainless steel instrument and chemical injection tubing in marine environment has been an old and widespread problem for the offshore operations in the oil and gas industry. To identify the best solutions to this problem the field experience was studied, and laboratory tests and exposure in marine environment of samples have been used to study possible alternative materials and protective chemicals. Testing was performed in a salt fog chamber with one hour long subsequent wet and dry periods. 316 stainless steel tubing samples sprayed with six commercially available chemicals were used. Furthermore, UNS C69100, Alloy 625, 317LMN, 254SMO, and Alloy 825 were also exposed in the same environment and conditions. In a second phase, two racks, each containing samples of 316 stainless steel tubing sprayed with the above chemicals and samples of the materials listed above plus super duplex stainless steel and Monel 400, were prepared. One rack was installed in an offshore platform in the Gulf of Mexico and the other in Trinidad. After one year exposure the samples were analyzed to evaluate their corrosion performance. The test results and the field exposure showed that protective chemicals are a viable method but only as a temporarily solution. The different chemicals tested could be ranked based on their performance. This evaluation protocol was also effective for assessing the corrosion resistance and applicability of the different alloys tested.