A Probabilistic Safety Factor for Defect Assessment of Water Pipes Subjected to Water Hammer

The aim of this paper is to determine the probabilistic safety factors for water pipes exhibiting surface defects such as gouges. The pipes are located in a water network that consists of a pump, a reservoir, and five pipe sections. Three different materials usually used for water pipes have been studied: cast iron, pipe steel, and polyvinyl chloride (PVC). The water pipes are subjected to the water hammer phenomenon, which is considered to be the loading condition. The overpressure due to water hammer is calculated for each pipe connection with a software program. The circumferential stress induced by the overpressure is then evaluated. Probabilistic safety factors associated with low failure probability are determined using a notch failure assessment diagram (NFAD). Fracture toughness, yield stress, and gouge depth are assumed to be randomly distributed to allow the determination of safety factors by Monte Carlo and FORM/SORM methods. A comparison of pipe material behaviour is then made by means of probabilistic safety factors. For the studied water network it is shown that the probabilistic safety factor is acceptable for steel and cast iron pipes but not acceptable for PVC pipes because its value is lower than 2.