Effect of viscoelasticity on the hold pressure of plastic pipe reinforced by cross helically wound steel wires in leak test

Abstract

Leak test is required in a number of standards to verify the leak tightness of pipelines based on the pressure drop in the pressure-hold period. However, the viscoelasticity of the matrix material polythene in plastic pipe reinforced by cross helically wound steel wires (PSP) would cause an evident pressure drop in leak test. In this study, a theoretical model was proposed to investigate the effect of viscoelasticity on the hold pressure through combining a long-term mechanical model of PSP and water state equation. Leak tests were conducted to validate the model, and a good agreement was obtained. Results showed that the pressure rapidly declined initially, and then the decreasing rate slowed until the pressure was almost stable. Finally, the principal mechanical performance of PSP was further explored, and the effects of pressurization rate and temperature on the pressure drop were also investigated.