Numerical Analysis for Cutting a Subsea Bundle

Abstract

The decommissioning of subsea bundles presents a significant challenge to the industry. Bundles are unique to the North Sea with more than 70 bundles currently in use with diameters reaching 1400 mm. The 1992 Convention for the Protection of the Marine Environment of the North East Atlantic, which is the international treaty governing offshore decommissioning in the North East Atlantic, presumes that all installations will be removed and the London Convention prohibits dumping at sea so the decommissioning of subsea bundles is a legal requirement. This study identifies that cutting and lifting subsea bundles is the best option for decommissioning bundles and is the first use of finite element analysis to design such a tool to cut bundles and determine the forces required. This modeling of the hydraulic shear indicates that the required shearing force is 18.65 MN when using a blade with a 60-deg cutting angle and a 180-deg shape angle. The modeling further demonstrates that the shearing force varies with the cutting and shape angles. On the other hand, the modeling for the guillotine cutter indicates a required shearing force of 19 MN. This analysis demonstrates the parameters required to design a subsea bundle-cutting tool and is the first step toward developing a practical tool for decommissioning subsea bundles.