|Content Type||Conference Paper|
|Title||316 STAINLESS STEEL INSTRUMENT TUBING IN MARINE APPLICATIONS - LOCALIZED CORROSION PROBLEMS AND SOLUTIONS|
|Authors||Ardjan Kopliku, BP America Inc.; Conchita Mendez, DNV-Columbus|
|Source||CORROSION 2010, March 14 - 18, 2010 , San Antonio, TX|
|Copyright||2010. NACE International|
|Keywords||localized corrosion, stainless steel, marine corrosion, protective sprayed coatings, cyclic salt fog, field exposure|
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 field experience was studied, and laboratory tests and exposure in marine environment of samples have been used to evaluate possible alternative materials and protective chemicals. Testing was performed in a salt fog chamber with subsequent periods of one hour wet and one hour dry. 316L stainless steel tubing samples sprayed with six commercially available chemicals were used. Furthermore, UNS C69100, Alloy 625 (UNS N06625), 317LMN (UNS S31726), 6Mo stainless steel (UNS S31254), and Alloy 825 (UNS N08825) were also exposed in the same environment and conditions. In a second phase of the study, 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 Alloy 400 (UNS N04400), 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 temporary 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.
Miles of small diameter instrument and chemical injection tubing are used in each offshore platform and similar quantities are used in plants located near the sea in onshore locations. The most used material for the manufacturing of this type of tubing has been 316L austenitic stainless steel. In the recent years the oil and gas industry and other industries1,2 are becoming more and more aware of the corrosion damage that tubing in 316L is subject to in marine environment even if this is not at all a new problem. Crevice and pitting corrosion are the main forms of corrosion damage experienced followed by much less frequent cases of stress corrosion cracking.
In the last decade there has been an increase in the reported cases of corrosion damage. There are two main explanations offered. The first, and most frequent, is that the steel manufacturers are now able to better control the 316L chemical composition and have reduced the chromium and molybdenum concentrations near the minimum of the acceptable range for this material. In particular a minimal Molybdenum content very close to the lower limit of 2.0% has been observed and it is well established that Mo plays a key role in providing resistance to localized corrosion. The second explanation is that the industry is doing a better job in the recent years in capturing, recording and sharing the corrosion cases inside each company as well as industry wide.
|File Size||1098 KB||20|