A study on methods for fire load application with passive fire protection effects
Introduction
Hydrocarbon explosions and fires in FPSO installations are extremely hazardous. They involve extreme explosion actions and heat, which can have serious consequences for health, safety, and the surrounding environment as can be evidenced by the Piper Alpha accident, which occurred on 6 July, 1988 (Cullen, 1990) and Deepwater Horizon accident, which occurred on 20 April, 2010.
A total number of 26 joint industry projects have been undertaken worldwide in the area of fire or explosion engineering since the Piper Alpha incident as shown in Fig. 1 (Paik and Czujko, 2009). The objectives of the EFEF JIP, which constitutes the 27th such joint industry project, are to bridge the gaps that exist between academic developments and engineering practice and to develop pertinent guidelines for the Quantitative Risk Assessment (QRA) of FPSO installations, with a focus on topsides and equipment that are subject to fires (Paik, 2009, Paik and Czujko, 2010). Its more specific objective is to produce documented procedures and guidelines for use in the assessment of fire actions (loads), their consequences (e.g., structural damage) for FPSO topside structures and equipment, and their associated risk levels. The acceptance risk criteria are also addressed. The overall EFEF JIP comprises the following three phases:
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Phase I: This phase includes a literature survey, identification of resources, and a detailed definition of the scope of work for the entire project in terms of fire and gas explosion events in FPSO installations.
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Phase II: In this phase the procedures used to identify the design loads for hydrocarbon fires and explosions on FPSO topsides and equipment are developed. The design loads for gas explosions are equivalent to overpressure, drag forces, and pressure impulses, and those for fire are equivalent to temperature and heat doses. Probabilistic approaches in association with the exceedance curves of design loads are applied.
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Phase III: The final phase establishes the NLFEM-based consequence analysis procedures. Guidelines and a handbook for the analysis, design, risk assessment and management, and risk acceptance criteria of FPSO topsides and equipment subject to gas explosion and fire events are developed.
The following figure shows the quantitative risk assessment (QRA) procedure for fires developed by the EFEF JIP (Fig. 2).
The final phase of EFEF JIP concludes with the establishment of NLFEM based consequence analysis procedure. NLFEM is of course necessary and cost effective for enhancing fire risk evaluations of steel structures (Reed and Peterson, 2012). The following figure shows the nonlinear structural consequence analysis procedure under fire load (Fig. 3).
This paper is a part of the report of EFEF JIP phase III. It is very important to determine the actual fire load profile of structure for performing nonlinear structural consequence analysis under fire load. The gas temperature profile and the steel temperature profile are not same. The gas temperature profile can be found by performing fire simulation or from standard fire curve. But, to find the actual response of structure under fire load, it is necessary to calculate the steel temperature. Again some structures are provided with passive fire protective materials.
In the present study, a method for calculating steel temperature profile was developed considering the PFP effects. The main objectives of the study were as follows:
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To develop a numerical method for modeling of PFP materials.
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To introduce the fire load application methods for steel structures.
Section snippets
Nonlinear material modeling of steel
To perform the thermal and structural response analysis of steel structures due to fire, material properties should be known properly. This section describes the thermal properties of carbon steel according to EN 1993-1-2 (European standard [Eurocode 3], 2005, FABIG, 2001).
Methods for fire load application
The increase in steel temperature depends on the temperature of the fire compartment, the area of steel exposed to the fire and the amount of the applied fire protection. This chapter will focus on the transfer of the heat from the fire compartment to structural elements and method of fire load application for thermal and structural response analysis.
The heat transfer from the hot gases into the surface of the structural elements by a combination of convection and radiation is normally treated
Validation of fire load application methods
To validate the fire load application methods, fire simulations were performed to get the realistic gas temperature profile. A simple model consisting of FPSO topsides structures was used for fire CFD simulation using Kameleon FireEx code (KFX, 2010). In the model, the thickness of the two vessels are 7 mm. Fig. 16 shows the steel temperature distribution and also the checking points for the temperature profile in case of without PFP. Fig. 17 illustrates the gas temperature profile and the
Conclusions
This paper is a part of the report of phase III, EFEF JIP which deals with the NLFEM-based structural consequence analysis of offshore structure. In this paper, nonlinear material modeling technique of steel and PFP materials is developed. PFP material modeling technique is validated with experimental results. The modeling method of PFP using temperature dependent thermal conductivity and specific heat is very useful in prediction of temperature development through insulation materials. Fire
Acknowledgments
The present work was undertaken at the Research Institute for Ship and Offshore Structural Design Innovation at Pusan National University (PNU), Korea. The leading investigator of the EFEF JIP (Jeom Kee Paik) is pleased to acknowledge the support of a number of partners, including the American Bureau of Shipping, Busan Metropolitan City Government, the Daewoo Shipbuilding and Marine Engineering, the Korean Register of Shipping, and The Lloyd's Register Educational Trust as funding sponsors in
References (13)
User's Manual, Version 13.0
(2011)The Public Inquiry into the Piper Alpha Disaster
(1990)- European standard [Eurocode 3], 2005. Design of Steel Structures—Part 1–2: General Rules—Structural Fire Design (CEN...
- FABIG, 1993. Technical Note 1: Fire Resistant Design of Offshore Topside Structures. Fire and Blast Information Group,...
- FABIG, 1995. Technical Note 3: Use of Ultimate Strength Techniques for Fire Resistant Design of Offshore Structures....
- FABIG, 2001. Technical Note 6: Design Guide for Steel at Elevated Temperatures and High Strain Rates. Fire and Blast...