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

Abstract

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.

On the assessment of U-shaped notches using Failure Assessment Diagrams and the Line Method: Experimental overview and validation

“…Moreover, regardless of the specific CFF obtained in each specimen, the average value observed in Figure 1 is around 2.5. This reveals a high degree of (over)conservatism when treating notches as if they were cracks [50,51], and justifies the need for more accurate structural integrity assessment methodologies for notch-type defects. (between the FAL and the coordinate axes).…”

Optimal boundary control for water hammer suppression in fluid transmission pipelines

“…Problem P 0 . Given the system (1) with boundary conditions (2) and initial conditions (6), choose the boundary control u : [0, T ] → R to minimize the objective function (7) subject to the bound constraints ( 3) and ( 4) and the terminal control constraint (5).…”

“…In severe cases, water hammer may even cause the pipeline to rupture, resulting in slurry and water leakage (examples of pipeline rupture are shown in Figure 1) [4]. Fluid pipeline failures due to water hammer effects are described in detail in [5,6].…”

Master and Auxiliary Compound Control for Multi-Channel Confluent Water Supply Switching Control Based on Variable Universe Fuzzy PID

“…The common manifestation of pipeline pressure changes is water hammer, which can cause major damage to the water supply system. For example, references [1][2][3] describe in detail the failure of water supply pipes due to the water hammer effect. Reference [4] analyzes the factors that affect pressure variation in the water supply system, such as power outages, pump shut-downs, valve operation, flushing, fire-fighting and main breaks.…”