Guidelines for use of welded stainless steel in corrosive environments (JOINOX) : final report

During welding of stainless steels thermal oxides form and may, unless removed, cause severe reduction in corrosion resistance. They are often the underlying cause behind structural failures and in many applications it is necessary to remove them through combination of cleaning operations. JOINOX deals with the relationship between welded joints oxides, corrosion resistance of welded joints and appropriate post-weld cleaning strategies. The project, with starting date September 1st 2012 and final date February 2016 28th, was coordinated by Swerea KIMAB with the participation of voestalpine Böhler Welding, TWI Limited, Fundació CTM Centre Tecnològic, Outokumpu Stainless, Sandvik Materials Technology and Max-Planck- Institut für Eisenforschung. A wide range of stainless steel welded joints were manufactured in the project including austenitic, ferritic and duplex stainless steels welded by Gas Tungsten Arc Welding, Gas Metal Arc Welding, Flux Core Arc Welding, Submerged Arc welding and Laser Beam Welding. The corrosion resistance and the efficiency of post-weld cleaning techniques were evaluated by immersion testing, exposures at end-users sites, Scanning Vibrating Electrode Technique testing and Critical Pitting Temperature testing. Oxide properties, such as thickness, composition and discoloration, were correlated to the corrosion resistance of the welded joints and evaluated by visual inspection, X-ray Photoelectron Spectroscopy, Scanning Kelvin Probe microscopy and Electrochemical Impedance Spectroscopy. The results showed that heat tins are detrimental for corrosion resistance of welded joints and should be removed by a combination of brushing followed by pickling. The mechanical post-weld cleaning methods proved to be insufficient to remove the anodic activity in the heat tint.