Stress intensity factors for external corrosions and cracking of buried cast iron pipes

Abstract

The municipal water distribution systems across the world include a significant amount of cast-iron pipes. Many of the buried cast-iron pipes are over fifty years old and require rehabilitation. Municipalities decide on a rehabilitation solution between the replacement and re-use of the existing pipes based on the remaining strengths of the pipes. Fracture mechanics has appeared as the most viable tool for remaining strength assessment of the deteriorating pipes. However, a method of assessing the stress intensity factor (SIF) is often not available to municipal engineers to apply fracture mechanics. This paper presents a method for calculating the SIFs of buried cast iron pipes subjected to corrosion and crack on the exterior surface. Different semi-elliptical-shaped defects were characterized using various aspect ratios (crack-depth to crack-length ratio) and relative depths (crack-depth to pipe thickness ratio). The SIFs were assessed for invert/crown and springline position cracks under internal pressure and vertical surface loads. A simplified method is proposed for evaluating the SIFs of buried pipes subjected to the exterior surface defects.