Failure analysis of buried cast iron water main using fracture mechanics

ABSTRACT: Water main failure, particularly for cast iron pipes, has been identified as a major concern for municipalities, as a number of water main breaks occur every year. Despite numerous past studies, pipe failure mechanisms observed in the field are not well understood. Conventional analyses using continuum based and Winkler spring based finite element methods calculate higher circumferential stress on the pipe wall which might lead to longitudinal wall cracking. However, circumferential cracking is the most commonly observed failure mode in water mains. In this paper, fracture mechanics is applied to study the stress concentrations in the buried pipe and offer new insights into the failure mechanisms of buried pipelines. Stress intensity factors for cast iron water mains with different shapes of corrosion defects are investigated using finite element analysis for crack assessment of the pipelines. The stress intensity factors are compared with the fracture toughness determined from laboratory tests.