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

点击翻译按钮获取中文摘要

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.