Influence of Oxygen content and surface condition on weld quality of pipeline steels

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Welded pipeline steels made of 316 or 316L grade stainless steels are widely used in oil and gas industrymainly for the transportation of very corrosive substances. One of the main challenges in welding of thesesteels is the occurrence of discoloration of the weld region which results often in the rejection of the part.While the industrial practice is based on AWS D18.2 standard; however, the acceptable level of oxygen is notidentified and often a weld, which might be good, is rejected because of apparent discoloration. In the firstphase of the project carried out under the Engage Grant a methodology was developed to reveal themicrostructure of the samples welded under different welding conditions. Specifically, the influences of 50 and500ppm of oxygen content on the discoloration level in comparison with the AWS D18.2 standard wasassessed and quantified. The microstructure under each specific condition was revealed and examined. Themechanical and chemical heterogeneities were also revealed and identified. Based on the results of the firstphase, the second phase was defined with the objective to further study the influence of surface preparation andoxygen content for other welding conditions and therefore to widen the scope of the study carried out in thefirst phase of the project. It is expected that the results of this project will allow proposing a new criteria forquantifying the influence of processing conditions on the actual damage to the microstructure.