A numerical investigation into the effect of pressure on holes and cracks in water supply pipes

Abstract

The effect of water pressure in a pipe on the rate of leakage from leak openings in the pipe is one of the main factors influencing leakage that is still not understood sufficiently. In this study, the behaviours of different types of leak openings (round holes and longitudinal and circumferential cracks) on pressurized pipes were investigated for different pipe materials (uPVC, steel, cast iron and asbestos cement) using finite element analysis. Linear elastic behaviour was assumed. The study found that (1) pipe stresses are significantly affected by a leak opening, and can easily exceed the material's yield strength in the vicinity of the opening; (2) round holes show the smallest expansion with pressure, followed by circumferential cracks and then longitudinal cracks; (3) the areas of all leak openings increase linearly with pressure; (4) longitudinal pipe stresses affect the behaviours of round holes and circumferential cracks, but not that of longitudinal cracks; and (5) the effect of pressure on a leak opening increases exponentially with increasing hole diameter or crack length. An equation is proposed for modelling the effect of pressure on individual leaks.

Keywords:

• pipe failures
• leakage
• pressurized systems
• stress concentration
• finite element analysis
• water distribution networks

Acknowledgements

This study wishes to gratefully acknowledge the financial support from Rand Water, VGC Consulting Engineers, Infraconsult and the NRF THRIP programme.