Probabilistic Corrosion Modelling to Estimate the Design Life of Pipes

The paper outlines a process undertaken to determine the need for cathodic protection (CP) on a new pipe installation. Coating breakdown over time was predicted based on CP design codes. Published data on corrosion of buried or immersed metal samples was reviewed to provide a correlation between ground water chemistry and mass lost. This was combined with probability distributions of corrosion rates used in other corrosion modelling work to produce distributions of corrosion rates for buried metal. The probability that wall thickness would be reduced below that required within the design life of the pipe was calculated and compared with acceptable probabilities of failure contained within design codes. This demonstrated that CP was not necessary on this project, saving both initial capital cost and the associated maintenance liability. An example is also presented showing how this approach can be easily adapted to provide a design life for CP that could feasibly be significantly shorter than the design life of the pipe.