51312-01245-Corrosion Testing of Weldable 13%Cr Supermartensitic Stainless Steel for Weld Procedure Qualificatio

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Product Number: 51312-01245-SG

ISBN: 01245 2012 CP

Author: Chi-Ming Lee

Publication Date: 2012

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The use of weldable 13%Cr supermartensitic stainless steel (SMSS) for flowlines is becoming more widespread largely due to its lower cost high strength and good corrosion resistance in oxygen-free high CO2 brine environments. However the sensitivity of this material to stress corrosion cracking (SCC) when H2S is present precludes its use in all but very mild sour environments. This paper presents results from the corrosion qualification testing of butt welded DNV SML 13CR-2.5MO grade 13%Cr steel pipes for use in a subsea flowline project. Welds were manufactured using a manual GTAW process and a superduplex stainless steel consumable and subjected to a plastic straining cycle to simulate reeling; the preferred method of pipe laying. Stress corrosion cracking (SCC) and electrochemical polarisation tests were carried out on the welds in simulated formation water service environments with 178000mg/l and 235000mg/l chloride at pH4.5. The results showed no failures in four-point bend SCC tests at stress of 550MPa which was 100% of the SYMS of the parent material tested at 130°C in two simulated formation waters environments. Supplementary tests using electrochemical cyclic polarisation scans were also conducted on the parent material and HAZ of the welds in the same environments.