Investigating the effect of pipe material stiffness on water leakage behaviour through longitudinal cracks in pressurized pipes: An experimental and numerical analysis

This study investigates, both experimentally and numerically, the effect of pipe material stiffness on water leakage behaviour through a longitudinal crack in a pipe, focusing on crack area expansion. Two theoretical equations were derived to estimate the leakage flow rate through longitudinal cracks under uniaxial and biaxial stress conditions. These equations express leakage as a function of pressure, fluid properties, pipe geometry, and mechanical properties, with particular emphasis on mate-rial stiffness. Pipe stiffness was explicitly incorporated as a mechanical property to account for the resistance offered by the material's elastic behaviour against deformation due to pressure variations. This is significant because theoretical orifice equation for flow through openings, as derived by Torricelli does not consider material properties. Experimental results confirmed that the material surrounding a long-itudinal crack undergoes elastic expansion due to hoop stresses induced by internal pressure. The leakage exponent values obtained for Class 6 uPVC pipes were significantly higher than the theoretical value of 0.5, ranging from 1.01 under uniaxial stress conditions to 2.68 under biaxial stress conditions. Moreover, the effect of material stiffness on leakage behaviour was evident, as Class 6 uPVC pipes exhibited higher leakage exponent values (4.42) compared to steel pipes (0.58). In conclusion, pipe material stiffness plays a crucial role in determining the leakage flow rate behaviour in pressurised pipes.