13Cr weldable supermartensitic stainless steels (WSMSS) find increasing application as line pipe materials. Before a decision for application is taken, the corrosion resistance and mechanical properties of the material are assessed via a qualification process. In the context of this process, sensitivity for elevated
temperature stress corrosion cracking (in the absence of H2S) has been found. The cracking is intergranular in nature and occurs in the heat affected zone. The phenomenon has been demonstrated on several grades of weldable supermartensitic stainless steels, in most cases associated with girth welding and in one case with seam welding. As yet, the results do not allow a detailed description of the mechanism. Application boundaries for safe use of the material, for instance in terms of temperature and chloride content, are not yet known. As long as the weldable supermartensitic stainless steels are not a fully developed material with associated welding materials and procedures, “new” phenomena may turn up and testing procedures need to be adapted accordingly. Testing for elevated temperature stress corrosion cracking has therefore been included in the pre-qualification procedure. Such testing is also a necessity in qualification for specific applications of the material; account should then be taken of actual service conditions.
Keywords: weldable, supermartensitic, 13Cr, line pipe, qualification, corrosion, cracking