Structural integrity of corrosion-affected cast iron water pipes using a reliability-based stochastic analysis method

A significant proportion of current water networks are composed of cast iron pipes. The occurrence of failures of this type of pipe is increasing due to ageing and progressive deterioration (i.e. corrosion). This necessitates the completion of structural integrity assessment and reliability analysis of in-service cast iron water pipes. The failure of a cast iron pipe can be characterised by fracture, when the stress intensity factor exceeds the toughness of the pipe material. In this research, a stochastic model for the stress intensity factor is developed and a time-dependent analysis method is employed to quantify the failure probability so that the time for the pipe to be failed and, hence, requiring repairs or replacement is determined with confidence. For a comprehensive structural assessment, two types of stresses (hoop and axial) are considered for two cases of corrosion (external and internal). A case study is provided to illustrate the application of the proposed method. In the system failure analysis, it is found that hoop stress is the dominant stress, since it can result in external corrosion, the effects of which are known to be of greater significance than those caused by internal corrosion.