Structural Response of Offshore Plants to Risk-Based Blast Load Heo, YeongAe;
Offshore oil and gas process plants are exposed to hazardous accidents such as explosion and fire, so that the structural components should resist such accidental loads. Given the possibilities of thousands of different scenarios for the occurrence of an accidental hazard, the best way to predict a reasonable size of a specific accidental load would be the employment of a probabilistic approach. Having the fact that a specific procedure for probabilistic accidental hazard analysis has not yet been established especially for explosion and fire hazards, it is widely accepted that engineers usually take simple and conservative figures in assuming uncertainties inherent in the procedure, resulting either in underestimation or more likely in overestimation in the topside structural design for offshore plants. The variation in the results of a probabilistic approach is determined by the assumptions accepted in the procedures of explosion probability computation, explosion analysis, and structural analysis. A design overpressure load for a sample offshore plant is determined according to the proposed probabilistic approach in this study. CFD analysis results using a Flame Acceleration Simulator, FLACS_v9.1, are utilized to create an overpressure hazard curve. Moreover, the negative impulse and frequency contents of a blast wave are considerably influencing structural responses, but those are completely ignored in a widely used triangular form of blast wave. An idealistic blast wave profile deploying both negative and positive pulses is proposed in this study. A topside process module and piperack with blast wall are 3D FE modeled for structural analysis using LS-DYNA. Three different types of blast wave profiles are applied, two of typical triangular forms having different impulse and the proposed load profile. In conclusion, it is found that a typical triangular blast load leads to overestimation in structural design.
British Standards Institution. (2002) Petroleum and natural gas industries-Offshore production installations-Guidelines on tools and techniques for hazard identification and risk assessment. BS EN ISO 17776.
British Standards Institution. (2005) Petroleum and natural gas industries - Specific requirements for offshore structures - Part1 : Metocean design and operating considerations. BS EN ISO 19901-1.
British Standards Institution. (2007) Petroleum and natural gas industries - Fixed steel offshore structures. BS EN ISO 19902.
Hydrocarbon Releases System. (1992-2012) Offshore Division of Health and Safety Executive. https://www.hse.gov.uk/hcr3/
International Organization for Standardization. (2010) Petroleum and natural gas industries - Specific requirements for offshore structures - Part3 : Topsides structure. ISO/FDIS 19901-3.
IP Research Report. (2006). Ignition Probability Review, Model Development and Look-up Correlations. Energy Institute, London
Norsok Standard Z-013. (2010). Risk and emergency preparedness assessment. Edition 3.
UKOOA. (2003) Fire and Explosion Guidance Part 1: Avoidance and Mitigation of Explosions. Issue 1.UK Offshore Operators Association, London.