Appendix Crack Propagation

A recent analysis has investigated the possibility of crack propagation in the pipeline, with special reference to the sea outfall. 

In a pressurized pipe there is a probability that fracture may occur locally because of unforseen circumstances. If this occurs it is important that the damage is confined locally and that the fracture does not propagate rapidly along the whole length of the pipeline. There has been at least one instance of a running crack destroying several miles of PVC pipe. 

In order for the crack to propagate the energy available at the crack tip must be greater than the energy required to produce crack extension. 

The energy, U, stored in unit length of a pressurized pipe of wall thickness, s, and mean diameter, D, is given by  

The energy required to fracture unit length is equal to G s, where G is the fracture energy per unit area. 

---

Appendix 16) indicates that the propagation of crack is negligible under the load cycles involving plant shutdowns, hot shocks and seismic events. 

---