Influence of purge quality and surface preparation on weld microstructure and degradation of austenitic stainless steel pressure piping

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。焊接这些钢的主要挑战之一是发生变色，也称为热着色，焊接区域，这往往导致拒绝的部分。变色现象的起因与焊接根道及随后的填充和盖道时氧化铬的形成有关。最近的研究表明，融合区的氧捕获也可能是变色现象发生的一个可能来源。然而，在焊接过程中存在的氧气水平对变色程度和对组织和腐蚀性能的破坏程度的影响尚未量化。除了氧含量外，表面处理也是一个非常重要的工艺参数，它会影响到接头的质量及其在使用条件下的耐久性。因此，本研究的主要目的是通过确定控制机制，研究起始母材、焊接工艺参数和表面处理对变色程度和严重程度的影响，以及变色与接头结构和性能的关系。工业合作伙伴的项目结果将是实施改进的表面准备和焊接程序，作为选定材料的功能，以达到可接受的变色水平。

Welded pipeline steels made of 316 or 316L grade stainless steels are widely used in oil and gas industry mainly for the transportation of very corrosive substances. One of the main challenges in welding of these steels is the occurrence of discoloration, also called heat tinting, of the weld region which results often in the rejection of the part. The origin of the discoloration phenomenon has been related to the formation of chromium oxides during the welding of the root pass and subsequent fill and cap passes. Recent research has indicated that oxygen trapping in the fusion zone could also be a probable source for the occurrence of the discoloration phenomenon. However, the influence of the oxygen level present during welding on the extent of discoloration and level of damage to the microstructure and corrosion properties has not been quantified yet. In addition to the oxygen level, surface preparation has been identified as a very important process parameter that could affect the quality of the joint and its durability under service conditions. The main objective of the present research is therefore to investigate the influence of starting base material, weld process parameters, and surface preparation on the extent and severity of the discoloration and its correlation with joint structure and properties through the identification of the governing mechanisms. The outcome of the project for the industrial partner will be to implement improved surface preparations and welding procedures as a function of the selected material in order to achieve acceptable discoloration levels.