Structural Capacity Analysis of Subsea Equipment

Abstract

Abstract Subsea oil and gas production equipment such as risers, manifolds, trees, wellheads, tubing hangers, tubing heads, blow out preventers, etc., are predominantly designed to criteria of API 6X, API 6A, API 16A, API 17D, API 17G, ASME VIII-2, ASME VIII-3, and NORSOK U-001 design codes. These industry codes provide design criteria to verify failure modes such as plastic collapse, fatigue failure, ratcheting, local strain failure, brittle failure, etc. Among these failure modes, plastic collapse and fatigue failure can be considered as the primary failure modes. A detailed review of plastic collapse design criteria from these codes and standards is discussed in this paper. These codes allow elastic (linear), limit load (elastic perfectly plastic), and elastic-plastic finite element analysis (FEA) to estimate the structural capacity. Some of these codes allow geometric nonlinearity in limit load FEA and some are not. All elastic-plastic analyses are solved with geometric nonlinearity. For this study, four components are considered which represent many subsea equipment. A pressure vessel (cylindrical shell) with internal pressure, open-end vessel (cylindrical shell) with external pressure, load shoulder, and pipe (cylindrical shell) bending are considered. Three materials with yield to tensile strength ratio of 0.53, 0.79, and 0.89 are considered in this study. A detailed review of plastic collapse criteria design criteria from these codes and standards is discussed in this paper for the four cases above.