Leak-before-break (LBB) analysis and failure processes for small-diameter cast iron pipes

Cast iron water pipes have high failure rates in Australia, and these pipes were generally buried in reactive soils without effective coatings. As the majority of the water network consists of small-diameter (< 150 mm) pipes, circumferential fractures are the predominant failure mode, and the failure was considered as brittle fracture without warning. However, recent failure analyses indicate that multiple failure processes occur and leaks are frequently observed before breaks. Liner Elastic Fracture Mechanics (LEFM) is used to evaluate the remaining strength of cracked pipes. Leaks are normally caused by soil bending stress in deep corrosion patches. The cracks can stably grow through 20–60% of the entire perimeter, which allows the installation of tightened clamps to stop leakages. Cracks may propagate over a long period until the leak becomes detectable. Therefore, it is argued that the leak-before-break concept developed for large-diameter pipes may be applicable to small-diameter pipes.