A Design of the Subsea Manifold Protective Structure against Dropped Objects

Abstract

Subsea structures are always subjected to accidental risks induced by fishing gears, dropped objects, etc. This paper presents a design of the subsea manifold protective structure against dropped objects. Probable dropped object scenarios including masses, sizes and terminal velocity of dropped objects and water depths were established. The annual probabilities for dropped objects hitting the subsea manifold exceeding 10 are determined based on the procedure specified in a reference (DNV, 2010). Structural consequences due to dropped objects are analyzed using the nonlinear finite element method (ABAQUS, 2008), so scantlings and shapes of the protective structure are finalized. A user-subroutine to implement three-dimensional fracture strain surface combined with Abaqus/Explicit is used to judge whether local fractures occurs at impact points of rigid dropped objects. Although local fractures are observed at impact points, it is concluded that the newly designed protective structure has the sufficient global structural integrity against dropped objects