Understanding the Hydrogen Embrittlement Behavior of Welded High Strength Low Alloy Steels

Abstract

Moving towards a Hydrogen Economy has attracted a lot of attention as they are a pivotal strategy for their sustainable development. However, the use of the available pipeline infrastructure to administer them for the purpose of transporting hydrogen is quite unknown. Pipelines do not exist as standalone structures and require joining techniques such as welds for longer distances. The thermodynamic nature of welding creates heterogeneous microstructures at the weld interface, increasing their susceptibility to hydrogen embrittlement. This research aims to investigate the diverse microstructures in various zones of the welding resulting from gas metal arc welding. The diverse microstructures obtained after welding were characterized using electron back scatter diffraction (EBSD). EBSD mapping showed the presence of smaller grains for base metal that has crystal orientation in all directions of body centered cubic (BCC) or body centered tetragonal (BCT) structure, whereas for weld nugget, longer grains are observed that are mainly oriented in <001> and <111> crystal orientation. To identify the susceptibility of material towards hydrogen embrittlement slow strain rate testing under cathodic polarization was conducted. Our preliminary investigation shows that the weld nugget of the material structure has a higher susceptibility to Hydrogen Embrittlement (HE) than the base metal. However, their susceptibility to HE is within acceptable limits, indicating appropriate welding method will be able to reduce the HE relatively less, retaining the structure for better performance.