Damage assessment of offshore riser-guards under accidental vessel impact

Steel riser-guards are installed on offshore jacket platforms to provide protection to risers against vessel collision. As risers transport the crude oil which is highly flammable, a collision between vessel and risers has the potential of causing severe structural damage to the platform and injuries to on-board service personnel. Due to lack of in-depth investigation on the response and damage of conventional riser-guards under an accidental vessel collision, the current practice of design of steel riser-guards is open to further improvement in terms of level of protection and economy. This paper presents a new approach in assessing the level of damage on conventional steel riser-guards, in the event of a collision with offshore supply vessels. Systematic numerical investigations were performed using non-linear finite element analysis to explore the structural response and damage under accidental vessel impact. This investigation was aimed to assess the adequacy of the protection provided by the conventional riser-guard and to ascertain the damage level under its maximum capacity in energy dissipation. The results from this investigation show that the conventional riserguard does not only provide sufficient protection under accidental vessel impacts, but also indicates toward an overly-designed protection system which possesses much higher capacity than the design requirements for offshore oil producing regions.