Modification of Existing Pipeline Corrosion Assessment Methods for Combined Internal Pressure and Compressive Loading - An Update

Abstract

Corrosion anomalies in pipelines are typically assessed using methods such as ASME B31G. These methods were developed to consider the axial extent and depth of the anomaly in relation to internal pressure loading only. For the majority of pipelines internal pressure will be the primary loading; however, pipelines can also be subject to additional axial compressive stresses (e.g. thermal stresses). When these additional axial compressive stresses become significant, they can interact with the applied internal pressure to lower the failure pressure of the anomaly. ASME B31G, which now incorporates Modified B31G and Detailed RStreng, acknowledges the need to account for significant axial compressive stresses but it does not include a codified procedure to account for combined loading. This paper considers an approach to modify these widely used existing assessment methods in order to account for the potential effects of combined loading. The approach used to modify the methods was based on the global collapse method developed for DNVGL-RP-F101, which uses the Tresca yield criterion. To validate that the modified assessment methods would provide safe failure pressure predictions, the results were compared against existing full-scale test data. This was further supported by carrying out finite element analysis (FEA) simulations to estimate plastic collapse and local failure pressures, in order to consider the impact of different corrosion profiles on predictions using effective area calculations. This work follows on from a previous paper and includes additional FEA simulations to consider the influence of the loading order on the failure pressure. In addition, a case study is presented showing the potential benefit of using an effective area method when compressive loading is significant.