ANALYSIS FOR CAUSE OF CRACKS IN HAZ OF X52 ERW PIPELINE

Adopting metalloscope and SEM to inspect the fracture and inclusions in the cracks of X52 experimental-welded-pipe steel,the composition of the inclusions was analyzed.The results show that the mass dense RE-sulphide and RE-sulphide-oxide laminated zonal inclusions are the main causes of the cracks. With high temperature and welding pressure,the severance of inclusions forms crack.