TECHNICAL ARTICLE—PEER-REVIEWED Evaluation of Failure Capacity of Offshore Riser Protectors Under Vessel Impact Zubair I. Syed . Mohd S. Liew . Shaikh A. Rahman . Dinesh K. Palaniandy Submitted: 10 August 2017 / in revised form: 13 October 2017 Ó ASM International 2018 Abstract Conventional riser protectors, also known as riser-guards, are installed on fixed offshore platforms to protect risers from vessel impact. These space frame structures made of hollow mild steel tubular sections are mainly designed using the approach of boat fenders which may result in over- or under-protection provided to risers. Lack of in-depth study on the dynamic behavior and capacity of conventional riser-guards is considered to be the primary challenge for creative and efficient design of conventional riser protectors. This paper presents a detailed numerical investigation on the dynamic response, damage and failure mechanics of conventional steel riser-guards during accidental vessel collision using nonlinear finite element analysis. Collision forces equivalent to vessel collision with riser-guards for different spans were esti- mated to provide information for load-based design. Variation in damage patterns for broadside and bow impacts is presented for riser protectors with different spans. The actual capacity of a typical riser-guard in terms of maximum impact energy sustainable prior to failure was also determined from dynamic pushover analysis. The structural response and damage parameters presented in this study can be used for better understanding of damage mechanism and failure capacity of riser protectors which can act as a baseline for further design optimization, as well as the development of other alternative riser protection systems. Keywords Riser protector Á Vessel impact Á Damage assessment Á Nonlinear analysis Introduction A large number of fixed offshore platforms are located in the South China Sea and the Gulf of Mexico where over- hanging pipelines known as risers are used to transport oil and gas from a reservoir to processing facilities on topside of platforms. A review on collision incidents between vessels and fixed platforms in UK Continental Shelf over a 16-year period shows that 83% of collision incidents caused damage to offshore structures [1]. Similar concerns have been highlighted by major design standards and rec- ommended practices [2–4]. Protection for the risers is extremely crucial as they carry high volumes of extremely flammable fluids. The significant loss in the Mumbai High North platform disaster clearly demonstrated the conse- quence of failure to protect risers from impact and explosion [5]. Typical riser protectors used in the fixed platforms located in the South China Sea consist of welded steel tubular members forming a mesh-like structure, shielding the riser against vessel impact. Vessel collisions with fixed offshore platforms have been well studied [6–8], and the required preventive ini- tiatives are incorporated in many design manuals for offshore structures [9]. Wei-liang et al. [10] successfully used the impulse–momentum approach to simulate the damage on offshore jacket brace members due to barge impact. Jebaraj et al. [11] analyzed the responses of a boat landing system (BLS), typically installed on jacket plat- forms, by performing nonlinear transient dynamic analysis using finite element analysis. In this study 10% of the Z. I. Syed (&) Department of Civil Engineering, Abu Dhabi University, P.O. Box 59911, Abu Dhabi, UAE e-mail: szimam@yahoo.com; zubair.syed@adu.ac.ae M. S. Liew Á S. A. Rahman Á D. K. Palaniandy Offshore Engineering Centre, Universiti Teknologi PETRONAS, 31750 Tronoh, Malaysia 123 J Fail. Anal. and Preven. https://doi.org/10.1007/s11668-018-0407-7