Transient Hydraulic Analysis for Pressure Surge Mitigation in Offshore Firewater Distribution Systems

Hydraulic transients induced by rapid changes in operating conditions represent a major challenge in the design and safe operation of offshore Firewater systems. During emergency events, such as fire pump start-up or rapid valve operations, pressure waves may propagate throughout the distribution network, generating water hammer effects capable of compromising the integrity and reliability of critical safety equipment. This study investigates the transient hydraulic response of an offshore Firewater ring-main system installed on a Floating Production Storage and Offloading (FPSO) unit using a detailed numerical model developed in PIPENET Transient. Three representative emergency operating scenarios were analysed, including fire pump start-up, deluge valve closure, and monitor valve closure. For each scenario, the hydraulic response of the original system configuration was compared with a modified pressure-protection arrangement involving relocation of the check valve immediately downstream of the fire-pump discharge flange and reduction of the pressure safety valve (PSV) set pressure from 17.5 barg to 16.5 barg. The simulations enabled the identification of critical pressure locations, evaluation of transient pressure propagation, and assessment of the effectiveness of the proposed mitigation strategy. The results demonstrate that the modified pressure-protection arrangement reduces the governing system-level pressure peaks and attenuates transient pressure oscillations under the investigated operating conditions. The proposed engineering methodology provides practical support for the design verification and optimization of offshore Firewater systems and contributes to improving the operational safety and reliability of safety-critical piping networks.