Charpy impact properties of stainless steel weldment in liquefied natural gas pipelines: Effect of low temperatures

In this study, an austenitic stainless steel pipe for the transportation of liquefied natural gas (LNG) was gas tungsten arc welded with a wall thickness of 15.1 mm. Low-temperature Charpy V-notch (CVN) impact tests were performed to investigate the effect of low temperatures on the fracture toughness of the welded zone (WZ), heat-affected zone (HAZ), and base metal (BM) of the LNG pipe. For design and safety reasons, it is necessary to investigate the low-temperature impact properties of weld metals, because weld metals have higher susceptibility to embrittlement than their counterpart base metals. In addition, the effects of cubic crystal structures on the CVN impact response were examined to compare the absorbed energy and fracture surfaces of the materials. Charpy impact tests were performed on mild steels with body-centered cubic (BCC) crystal structures for comparison with the test results of welded austenitic stainless steels with face-centered cubic (FCC) crystal structures. The applicable temperatures were examined, and a scanning electron microscope was used to examine the fracture surface morphology of V-notched specimens tested under various temperature conditions. The results revealed that the absorbed energy of the WZ was slightly higher than that of the BM and HAZ in the FCC-crystal-structured welded pipe specimens. In addition, the ductile-to-brittle transition temperature of the BCC-crystal-structured mild steels was examined. (C) 2014 Elsevier Ltd. All rights reserved.