There are many different types of grey cast iron pipe failures, with the variations caused by both the size of the pipe and the type of loading it experienced.
Large-diameter grey cast iron pipes are normally too thick to experience circumferential cracking when they experience high bending loads. However, they can fail by an alternative mechanism, where a wedge of pipe at the bell is split off to relieve the bending stresses. Corrosion pitting or manufacturing defects may also be associated with this type of failure, but further research is needed to completely understand how wedge splitting occurs.
This type of failure appears to be common in medium-sized pipes (approximately 400-500 mm diameter). The failure started as a circumferential crack, but then a section of the pipe
broke and the crack propagated down the pipe barrel in a spiral.
The above picture shows a section taken out of the pipe, with the right edge of the section showing the rusty fracture surface. The spiral fracture appears to take place as a form of transition between the circumferential cracking of small pipes loaded in bending and the longitudinal cracking seen in large-diameter pipes. While some spiral fractures have been associated with pressure surges, the pipe shown here failed in normal service due to manufacturing defects.