Abstract
Low Carbon-13%Cr martensitic stainless steels have been widely used for line pipe application because of their high strength and excellent corrosion resistance in corrosive conditions. Recently, both laboratory and field experiences related to cracking near fusion line of these steels weld joints in hot acid environments have been published. Electrochemical analysis of weld joints is expected to be effective in understanding the crack mechanism. In this paper, electrochemical behavior of low C – 13%Cr weld joints with and without PWHT was evaluated with the use of a solution flow type micro-droplet cell. In this unique technique, a droplet of around 0.2mm diameter is used as an electrochemical cell and it enables local electrochemical measurements. PWHT leads to more noble and stable potential in HAZ compared to as-welded condition. In the HAZ portion of the as-welded joint, Cr depleted zone was detected under welding scale with the use of GDS (Glow Discharge Spectrometer). This can be an initiation of SCC near girth welded joint in hot acid environment. The reason why a polished specimen did not show any SCC is also given.
