Cracking of underground welded steel pipes caused by HAZ sensitization

(in lingua inglese)

The failure of a galvanized welded 27 mm 3 mm steel pipe was investigated. The findings ofthe present evaluation have led to the following conclusions: cracking initiated prior to galvanizing and has led to brittle fracture adjacent to the weld area in the HAZ. No static tensile overload during service is considered as primary failure mechanism. Strong microstructural heterogeneity is evident in HAZ, while the failure is most probably attributed to sensitization and intergranular embrittlement. The sensitization could be probably attributed to the segregation of harmful impurities or hot shortness constituents (such as Cu, CuS) to the grain boundaries, while the contribution of hydrogen and Zn-liquid metal assisted cracking to the intergranular failure cannot be discounted.