Metamodeling of structural failure: Case study of API S-135 steel tube cut in BOP

Abstract

In offshore oil exploration, the use of a Dynamic Positioning System (DPS) is necessary to maintain the platform at a fixed point regardless the influence of the environment. In an event of DPS failure, however, a drill string inside BOP (BlowOut Preventer) must be cut and disconnected from the well. The required force to cut the string is traditionally determined by analytical models and commissioning tests, which can be far from the real situations. Depending on geometry and loading conditions of this tubular, the BOP may fail to cut it, which can lead to catastrophic events. Numerical analysis can not only bring more accurate and realistic results of the failure process but also it is an alternative to the expensive and complex experimental tests. Moreover, through post-processing tools, numerical models provide a more detailed understanding of the failure mechanism. However, due to the variety of geometric and loading conditions, a metamodel is proposed to predict required forces for BOP to cut API S-135 6.63″ 40.87ppf drill pipes. A calibrated and validated material model for API S-135 steel was applied to simulate the pipe cutting process in BOP at different combined conditions, including initial normal longitudinal load, torque, internal and external pressure, pipe decentralization and indenter offsetting. The predicted forces from numerical analysis were used to feed a machine learning algorithm, particularly a regression technique, providing the metamodel parameters. The conclusion is that current BOP cutting models may underestimate the required force to cut pipe in realistic conditions.