Reason Analysis on Unqualified Root Bend of SAWL Pipe

The unqualified reason in root bend test for SAWL pipe was analyzed by means of chemical composition analysis, mechanical property testing, metallographic examination and fracture analysis. The results showed that heat affected zone crack in SAWL pipe formed because of the inclusions of calcium aluminum silicate in plate edge subsurface during the rolling process for steel plate. In the welding process, the cracks initiated from inclusions and grew under thermal stress, at last the intermittent stress cracks occurred.