Residual Strength Analysis of Diagonally Aligned Interacting Corrosion Defects Subjected to Internal Pressure and Longitudinal Compressive Stress

Corrosion defects are bound to occur externally or internally on the surfaces of pipeline wall. It is unavoidable whereby it causes the pipeline to burst or leak which endangers the safety of people, decreases the rate of production and affects the environment as well. Although countless studies have been conducted to assess the residual strength of a corroded pipeline, there are only a few researches conducted on pipeline burst strength with multiple defects under combined loading which are internal pressure and compressive stress. Additionally, the present assessment involves high conservatism compared to the finite element method and the effect of combined loading involving pipeline with multiple defects has not been vastly explored. Therefore, in this study finite element analysis model will be employed to investigate the failure pressure of pipeline subjected to internal pressure and compressive stress. The results from the simulations are compared with DNV RP-F101 code as the base reference solution. In order to assist extensive use in the pipeline integrity assessment in the future, a correlation factor was established from the failure pressure acquired from the FE analysis. The results obtained from FEA and DNV showed a maximum of 23% in percentage increment of the failure pressure as the depth of defects increases linearly with increasing normalized spacing between diagonal defects and increasing longitudinal compressive stress. Generally, the results obtained showed that FEA results had higher failure pressure when compared to DNV code. It can be justified that the reason for this outcome is the conservatism element in DNV code. Nevertheless, correlation factors were developed based on the results obtained from the ratio of FEA results compared to DNV code results to establish a more accurate failure pressure prediction when normalized spacing between defect, defect depth and longitudinal compressive is involved.