DAMAGE ASSESSMENT OF OFFSHORE RISER-GUARDS UNDER IMPACT LOADING

Steel riser-guards are installed on the offshore platforms to protect the risers against accidental vessel collisions. Offshore riser protection is important due to the flammable content it carries. In the absence of riser-guards, vessel collision can damage risers and hence leads to platform explosion. The conventional riser guards are designed to resist static force equivalent to vessel collision on any part of steel frame. Vessel collision with offshore structure has been highlighted in many design standards. However, those studies only limit to the structural response of the whole platform. In depth, investigation on the structural response and performance of riser guard has not been carried out. Therefore, this project was carried out to have better understanding on structural response of conventional riser guard in order to provide more economic and effective design of riser guard. In this project, finite element modelling of conventional riser guard under impact loading was performed using different Structural Analysis Computer System (SACS) modules to study its structural behavior. Different types of vessel collision scenario were studied in this research to understand the structural response and damage of steel riser-guards under different accidental vessel impacts. The riser-guards were modelled under impact load equivalent to vessel collision using SACS. The deformation, stress, strain and unity check values were analyzed to investigate the structural response and resulting damage to the riser-guards. Different magnitude of vessel impact loads were applied to the riser guard till its maximum capacity. The simulation shows that the maximum deformation occurs at the center of the riser guard. Collapse analysis was performed to study the plastic deformation of riser-guard and its plasticity. The structural response of offshore riser guard for different vessel collision scenarios was studied and presented in this paper.