Non-destructive evaluation of brittle fracture resistance of operated gas pipeline steel using electrochemical fracture surface analysis

Abstract

The use of effective non-destructive evaluation techniques for assessing degradation degree of pipeline steel would allow planning actions in order to correctly manage required emergency response at gas pipeline incident. In this paper, a new non-destructive evaluation technique based on electrochemical analysis of fracture surface for assessing in-service degradation degree of operated pipeline steels was developed. A significant difference between open-circuit potentials of the fracture surface (brittle fracture) and the polished surface of specimens made of operated pipeline steels observed after their long-term operation was associated with increased content of carbon compounds on the fracture surface. Embrittlement mechanism of ferrite-pearlite pipeline steels under operation was explained by carbides enrichment both grain boundaries and intragranular defects. The correlation dependence between operational changes in brittle fracture resistance of a metal and in open-circuit potential of its fracture surface being the basis of the developed electrochemical method for evaluation of operational degradation of pipeline steels was determined.