Project Description
Submerged Christmas trees are used to control flow into and out of oil, gas, and water wells. They play the role of a pressure-containing interface through mechanisms of potential energy storage. However, these energy storage systems can become safety hazards during decommissioning.
This study investigated the behaviour of Belleville springs used in subsea tree valves. The study included (i) a survey of the literature
on the modelling of springs; (ii) mathematical and numerical models that predict the behaviour of Belleville springs in terms of force-deflection of springs, critical stresses, and stored energy; and (iii) the use of locking substances to freeze the potential energy in deformed springs. The mathematical and numerical models proved to give excellent agreement and predicted the field data (provided by Woodside) accurately. This allowed the reliable selection of appropriate substances that can freeze the potential energy of deformed springs. High performance concrete and high strength resin proved to perform well as locking substances. However, this study proved that ordinary concrete, self-compacting concrete and low-range resin are insufficient to contain the spring of a 5” valve.