Corrosion of welded joints of bimetallic composite tube in simulated offshore gas field environment

Purpose – The purpose of this investigation was to research the corrosion behavior of welded joints of bimetallic composite tube (X65/316L) welded with Inconel 625 in simulated sea water and in simulated production water, respectively. Design/methodology/approach – The different electrochemical corrosion and galvanic corrosion behaviors of different welded zones were identified using the dynamic potential scan method and galvanic corrosion technique. Findings – The heat-affected zone (HAZ) of welded joints was the most critical zone for corrosion. The closer to the welding line, more severe was the corrosion that was evident in the HAZ at room temperature. In welded joints of X65 tested in simulated seawater, tremendous corrosion occurred in the HAZ, followed by the base metal, and finally the welding line. However, there were few differences in corrosion of the different zones of welded joints in 316L in simulated production water. In such joints of 316L, corrosion comparatively attacked more easily to the HAZ. In galvanic corrosion tests, tremendous galvanic corrosion was evident on welded joints on X65, but comparatively slight gavanic corrosion appeared at welded joints in 316L. With the increased temperature, galvanic corrosion of welded joints was enhanced. Originality/value – The results can provide reference for reducing the gavalic corrosion of welded bimetallic composite tube metal in the actual operation.