51313-02684-TEM Investigations into the Effect of a PWHT on IGSCC Susceptibility of Weldable 13Cr Linepipe

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Product Number: 51313-02684-SG

ISBN: 02684 2013 CP

Author: Sytze Huizinga

Publication Date: 2013

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In the past failures have occurred of 13Cr weldable martensitic stainless steels (lean grades) in sweet service as a result of Intergranular Stress Corrosion Cracking in the Heat Affected Zone. Initial lack of understanding of the detailed mechanism has hampered application of the material including the more resistant but not immune higher alloyed grades. A cracking mechanism for the latter grades was proposed recently based on laboratory studies. The present study aims at confirming this mechanism and unambiguously proving the effectiveness of Post Weld Heat Treatment for actual representative field welds.
By performing four point bend stress corrosion cracking tests on welded specimens from several sources both with and without PWHT in representative service conditions and linking the results with detailed Transmission Electron Microscope (element analysis) studies clear evidence was found for the proposed mechanism. In particular PWHT and Molybdenum enrichment along grain boundaries corresponded with the observed resistance against IGSCC.
With the effectiveness of the PWHT unambiguously proven the confidence in application of the weldable 13Cr steels has been restored. There is no longer a need for upfront application specific testing of actual welds as long as normal SCC testing shows resistance in the expected service environment and welding procedures are properly qualified.