Effect of PWHT on Electrochemical Behavior of Low C - 13%Cr Welded Joints with The Use of A Solution Flow Type Micro-Droplet Cell

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 has been published.  Electrochemical analysis of weld joints are expected to be effective to understanding crack mechanism.  In this paper, electrochemical behavior of low C – 13%Cr welded joints with and without PWHT was measured by using solution flow type micro-droplet cell.  In this unique technique, a droplet with a diameter of hundreds of micrometers is used as an electrochemical cell and this technique enables local electrochemical measurements.
PWHT leads to more noble and stable potential in HAZ compared to as-welded condition.  In HAZ portion of as-welded joint, Cr depleted zone was detected under welding scale by using GDS(Glow Discharge Spectrometer).  This can be an initiation of SCC near girth welded joint in hot acid environment.  Explanation why polished specimen did not show any SCC was also done.