Experimental Study on Girth Welds of X80 High Deformability Pipeline

Abstract

Girth welds of X80 high deformability pipeline were welded by self-shield flux-cored arc weld (FCAW) and manual shield-metal arc weld (SMAW). The FCAW used E9018-G electrode to weld root and under-matched flux-cored wires to fill welding and cap welding. The SMAW also used the same welding consumable to weld root, but the metal of the filler welding and cap welding is overmatched electrodes. The mechanical properties testing and metallography testing of girth welded joints were carried out. It was found that the qualifications of two welding procedures met the requirements of API Std. 1104. The test results of Charpy impact (CVN) and crack-tip opening displacement (CTOD) of welded joints for FCAW were higher than that of welded joints for SMAW. The microstructures of FCAW welds were polygonal ferrite (PF) and pearlite (P). But the microstructures of SMAW welds were polygonal ferrite (PF), intra-granular nucleated acicular ferrite (IAF) and pearlite (P). The microstructures of fusion zones are granular bainitic ferrite (GBF), and that there is no martensite in coarse grain heat affected zone (CGHAZ) and fine grain heat affected zone (FGHAZ). So heat affected zone (HAZ) exhibited excellent fracture toughness.