An evaluation and estimation of stresses on a vessel's side plate and its capacity

Abstract

History shows that the combination of stresses and pressure in a vessel can cause failure and lead to huge losses, examples of this are the ‘Prestige accident’ (November 2002) and the ‘Energy Concentration accident’ (July 1980). In the oil and gas industry structures are often mobilized on the deck of a vessel, transported to a specific location offshore and installed on the seabed. Occasionally these structures are quite large, resulting in their sticking out from the deck. A side plate in the sheer strake area needs to be evaluated, as stresses from the protruding structure, and stresses and pressure from the vessel’s global loads, gives in-plane stresses and out-of-plane pressure. In this study, the aim is to establish a simplified approach for estimating stresses that arise from a vessels global loads, evaluate how much these stresses might influence the plate capacity and conclude whether these stresses should be included in a plate capacity check in Subsea 7. At this time, researchers such as Paik, Owen and Mansour are considered as wellestablished researchers in naval society, and their studies will be used to reach a method for finding the arising stresses on plate that occur because of the global vessel loads. The stresses will be estimated by idealizing the vessel as a hull girder and applying beam theory combined with recommendations from Det Norske Veritas. The study shows that there are several key factors to establish these stresses and these factors will be estimated numerically and by computer software. The study shows that a stiffened side plate that is subjected to in-plane and out-ofplane stresses and pressure can experience failure modes when the structure on deck results in large stresses. In this study a stiffened plate capacity checks will be evaluated based on Det Norske Veritas (DNV) and NORSOK standards and recommended practices, and are considered as state-of-the-art approaches. The study concludes that both the magnitude of the global stresses and the stiffened plate’s characteristics are key factors in determining how much the global stresses influence the capacity of a specified plate.