Investigation into the Impact Toughness of API 5L X80 Steel Weldments and its Relationship with Safe Welding Procedures

API 5L X80 steels are widely used in welded pipes in the petroleum industry. However, microstructural changes in the heat affected zone are a concern when welding such pipes due to the potential formation of regions with low toughness. Despite all the research concerning mechanical properties of welded joints, the acceptance criteria for the qualification of welding procedures are still limited. Welded joints do not always guarantee the safe operation of industrial equipment, because the current Standards adopted are not able to evaluate the properties at some critical regions of the welded joint. This work studied the characteristics of a girth welded joint and showed evidences of low toughness at 0.5 mm from the fusion line due to the micro-phases necklacing the prior austenite grain boundaries. As this feature is not considered by the current Standards for approval of welding procedures, this work proposes an alternative approach to improve the safety of welded structures.

API 5L X80钢（API 5L X80 steels）广泛应用于石油工业的焊接钢管制造中。然而，在焊接此类钢管时，热影响区（heat affected zone）的微观组织变化是广受关注的问题，因为该区域可能形成韧性偏低的组织区域。尽管目前已有大量针对焊接接头力学性能的研究，但焊接工艺评定的验收准则仍相对有限。焊接接头无法始终保障工业设备的安全运行，这是因为现行采用的标准无法对焊接接头的部分关键区域的性能进行有效评估。本研究针对环向焊接接头（girth welded joint）的特性展开了系统分析，并证实了在距熔合线（fusion line）0.5 mm处，由于原奥氏体晶界（prior austenite grain boundaries）被微相环绕，该区域存在韧性不足的现象。由于现行焊接工艺评定标准未纳入该特征考量，本研究提出了一种可提升焊接结构安全性的替代方案。