Probabilistic design method (PDM) for composite overwrap repair system of corroded steel pipelines

Issue of corrosion in oil and gas pipelines is a serious matter. More than 60 percent of the world's oil and gas transmission pipelines are more than 40 years old and for the most part in urgent need of rehabilitation in order to re-establish the original operating capacity. A promising advanced repair method used for the repair of deteriorated pipelines is based on utilizing fibre reinforced polymer (FRP) composites. This involves wrapping the corroded part of the pipe with this material. Many laboratory tests and field experiments have been performed and documented in the past few years, which have proven the viability of this method. World standards of structural design are moving away from deterministic methods towards probability based design. This is to reflect the fact that loads applied to a structure and resistance from the structure against the loads are of random nature and hence probabilistic. Such transition that has already occurred in many structural design codes provides rather more efficient repair designs, improves safety and lowers the costs associated with the repair and maintenance. When it comes to the repair design of the vitally important, critical infrastructure of corroded oil and gas pipelines, however, the major standards are deterministic; hence inefficient and very much outdated. This research aimed to introduce an innovative probabilistic design method that will improve design efficiency by incorporating the random nature of influencing load and resistance parameters into the design of FRP overwrap repairs. The method developed through performing of comprehensive experimental study in two different environmental conditions to replicate onshore and offshore pipelines. Performing statistical analysis and choosing the best-fit statistical model to the experimental data obtained were the next steps to develop the new design method.The end product of this research was a probabilistic design method for the overwrap repair of corroded onshore and offshore pipelines. The proposed method allows the design of FRP overwrap repair consistently and It is anticipated that the developed method would significantly improve the design, reducing the time and cost of repair leading to added safety and longevity of repair.