Structural Analysis of 18¾-in. Drilling Connector
Authors: Kandoker S. , Bunch P.D. 
Published: October 2008

A two-dimensional finite element analysis (FEA) of an 18%" bore 15,000 psi working pressure hydraulically operated connector assembly has been completed to determine maximum operating limits for bending moment, tension, and pressure load capacities. Simulation of the connector locking action was analyzed using axisymmetric elements for individual components and intetiace elements with a large sliding option for component interaction. Loading of pressure and tension were applied directly to the model as axisymmetric forces, where non symmetric bending moments were applied as equivalent tension loads. The operating limits are defined for stress and displacement limiting conditions, where stress allowable are based on ASME Pressure Vessel Code [1], Section Vlll, Div. 2, and displacement limits are based on hub separation and gasket leakage. This analysis provides an evaluation of the suitability of the hydraulic connector for deep water drilling, and addresses the concerns of the United Kingdom Offshore Operators Association [21 for connector operating capabilities. The analysis also provides an improved technique simulating the connector locking action, gasket loading and subsequent external loading.

INTRODUCTION

Most high pressure drilling connectors are actuated by a hydraulically operated pistons [21 to lock and unlock the riser and the BOP stack on the wellhead. These hydraulically operated segmented connectors use metal to metal gaskets to form a tight seal which will withstand the separation forces and moments caused by well pressure, riser tension, ocean wave and current and essel motion.

The connectors are initially guided into position on the wellhead hub by a funnel formed by the open collet segments or outer frame structure. The connector locks to the mating hubby pivoting individual tapered finger like collet segments. The locking force is generated by sliding the actuator piston while locking pressure is applied on the outer annular cylinder of the connector. Once in locked position the pressure on the actuator piston is released. This is the final make-up or pre-load condition. The active loads on the connector consist of the tension, bending moment, and bore pressure with its associated pressure end load.

A finite element method based analysis of such a connector is presented in this paper. The connector was analyzed using ABAQUS [31, with axisymmetric elements and sliding interface elements between the center body section, the collet segments, the outer actuator ring, and the mating hub, reference Figure 1. This model simulated the true make-up loading condition (with friction incorporated), due to 3,000 psi locking pressure, by large relative sliding of the actuator piston with respect to thecollet segments. in addition, internal pressure and tension loads were applied. The non-axisymmetric bending moment was simulated using the equivalent tensiongenerated on the component at the maximum value of the hub tension side, This produced the highest combined stress condition as well as the highest separation loads for the connector assembly,