Potential risk of vapour cloud explosion in FLNG liquefaction modules

Floating Production Storage and Offloading vessels have been in operation for four decades and there are now well over 250 vessels in existence, but their gas equivalent floating liquid natural gas plants kwon as FLNGs are still very new. Consequently designs and arrangement of top-side process units are still evolving and their safety has yet to be fully and objectively evaluated. This paper explores the probability of occurrence of accidents leading to vapour cloud explosion at one of the topside liquefaction modules of an FLNG. The worst possible scenario with the maximum tolerable probability is identified and the impact of the corresponding vapour cloud explosion is estimated. The strength of the structures supporting the neighbouring modules was examined using finite element analysis to determine if the accident has a potential of escalating to neighbouring modules.
It is found that the current levels of safety gaps between the liquefaction modules may be insufficient for the structural arrangement in place. It is thought that a new structural design using circular pipes as the structural elements instead of the I-beams may enhance the integrity of the top-side supporting structures against the impact of potential vapour cloud explosion. The effectiveness of the new structure is demonstrated by comparing it to the conventional supporting structure using I-beam members. This also implies that, by using pipe elements, the safety gaps can be reduced, thus making it possible to optimise the topside arrangement more easily.