Collapse of thick-walled subsea pipelines with imperfections subjected to external pressure

In this study, the collapse responses of thick-walled subsea pipelines with imperfections subjected to external pressure are studied using finite element (FE) method. First, the FE model of the imperfect thick-walled pipe is built and validated by experimental results from other publications. Then, different collapse responses are obtained by using the validated FE model. The collapse modes are analyzed and the interaction mechanism of the ovality and the thickness eccentricity affecting the collapse response is proposed. The effects of the ovality and the thickness eccentricity on the collapse pressure are discussed. Finally, a new collapse pressure formula which includes both the ovality and thickness variation is presented. The comparisons of collapse pressures from the proposed formula, FE model, and DNVGL-ST-F101 are performed. It is found DNVGL-ST-F101 underestimates the collapse pressure when the diameter-to-thickness ratio (DTR) is less than 20. In addition, the errors of collapse pressures predicted by DNVGL-ST-F101 are unstable. While the proposed formula can provide a pretty well prediction of collapse pressure for thick-walled subsea pipelines and the error is stable.