Prediction of remaining strength of corroded pressurised pipelines

In this paper a deterministic model is developed which can be used to evaluate the remaining strength of corroded steel pipeline over time. This model also can be used to evaluate the maximum allowable failure pressure of corroded pipelines. The motivation for the development of the model is that during in-service conditions the strength of pressurised pipelines may be impaired, for example, from the failure of the protective coatings, paint surfaces or cathodic protection or as a result of externally applied mechanical damage or as a result of ageing (e.g. fatigue). Any of these may lead to the initiation of corrosion at the damaged area if it is not repaired. Once initiated, corrosion increases gradually both in extent and depth with increased exposure period. This results in the reduction of the remaining strength and hence a reduction in the carrying capacity of a pipeline. It also creates uncertainty about the future capacity. The proposed model is related to accepted methods for estimating the remaining strength of pipelines, but uses a simple corrosion model to estimate future remaining life. A sensitivity analysis can be used to investigate the effect of corrosion parameters on the pipeline carrying capacity. A simple example is given to illustrate the approach.