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

焊接管道钢由316或316L级不锈钢制成，广泛应用于石油和天然气工业，主要用于输送腐蚀性很强的物质。在焊接这些钢的主要挑战之一是发生变色的焊接区域，这往往导致拒绝的部分。而行业实践则基于AWS D18.2标准；然而，可接受的氧气水平是不确定的，并且通常一个可能是好的焊接，因为明显的变色而被拒绝。在项目的第一阶段，在Engage资助下，开发了一种方法来揭示不同焊接条件下焊接样品的微观结构。具体而言，与AWS D18.2标准相比，评估和量化了50和500ppm氧含量对变色程度的影响。并对不同条件下的微观结构进行了分析。力学和化学的非均质性也被发现和鉴定。根据第一阶段的结果，确定了第二阶段，目的是进一步研究表面处理和氧气含量对其他焊接条件的影响，从而扩大项目第一阶段进行的研究范围。预计该项目的结果将允许提出一种新的标准来量化加工条件对微观结构实际损伤的影响。

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.