Offshore Structures: Fire-Based Structural Design Criteria

Offshore Structures: Fire-Based Structural Design Criteria

Mavis Sika Okyere (Ghana National Gas Company, Ghana)
Copyright: © 2019 |Pages: 59
DOI: 10.4018/978-1-5225-7059-2.ch004

Abstract

Fire will always be a major threat to the offshore structure as oil and gas always passes through the installation. The design against accidental fire situation should be included in the structural design of offshore structures in collaboration with safety engineers. The design of offshore structures for fire safety involves considering fire as a load condition, assessment of fire resistance, use of fire protection materials, and so on. This chapter presents a methodology that will enable an engineer to design an offshore structure to resist fire. It aims to highlight the major requirements of design and to establish a common approach in carrying out the design.
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Introduction

During a major fire incident, it is our aim to be able to sustain the integrity of the offshore structure for an ample period to perform critical task such as platform shutdown, fire-fighting response, disembarkation, etc, whiles permitting evacuation of operation and maintenance personnel.

The offshore structure must be able to maintain its safety functions for a required performance time, if subjected to fire and explosion damage. Therefore, there is a need to design the offshore structure to have redundant elements appropriately placed, be able to withstand increased loadings, and have the ability to redistribute loadings.

Offshore structural engineers concerning structural fire endurance use the slenderness ratio and the wall thickness modulus. Protecting people from injuries is therefore linked to designing structures. Structures should be designed to withstand loads without creating dangerous fragments or falling down.

According to Design Buildings Ltd (2018), the key design options to ensure fire safety are:

  • Prevention: Controlling ignition and fuel sources so that fires do not start.

  • Communications: If ignition occurs, ensuring occupants are informed and any active fire systems are triggered.

  • Escape: Ensuring that occupants and surrounding areas are able to move to places of safety.

  • Containment: Fire should be contained to the smallest possible area, limiting the amount of property likely to be damaged and the threat to life safety.

  • Extinguishment: Ensuring that fire can be extinguished quickly and with minimum consequential damage.

This chapter describes the major items that need to be incorporated in the structural design of an offshore structure for fire resistance. Structural engineers in collaboration with safety engineers should perform the structural fire design of offshore structures.

Objective

  • The main objective is to reduce to within standard limits the possibility for death or injury to the occupants of the offshore structure and others who may become involved, such as maintenance and operation personnel, fire and rescue team, as well as to protect contents and ensure that the structure can continue to function after a fire and that it can be repaired.

  • To characterize the offshore fire problem and develop an engineering methodology to improve the offshore platform fire resistance by extending structural fire endurance.

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Design Load

The offshore structure design must account for a variety of loads demands including, dead and live loads, environmental loads (ie. Wind, wave, ice and current loads), seismic loads, operational loads (such as drilling) and transportation and construction loads, accidental loads such as collision, fire, hydrocarbon explosion should also be accounted for during the design process (Bea, Williamson & Gale, 1991).

The structure must be adequately robust in terms of capacity, redundancy, and ductility, to transfer the environmental and deck loads to the pile foundation without loss of serviceability over a wide range of conditions.

Key Terms in this Chapter

Deflection: Is the degree to which a structural element is displaced under a load. It may refer to an angle or a distance.

Fire Resistant Material: Is one that is designed to resist burning and withstand heat.

Slenderness Ratio: Is the ratio of the effective length of a column (L) and the least radius of gyration (r) about the axis under consideration. It is given by the symbol “?” (lambda).

Fire Resistance: Is the ability of construction or its element to satisfy for a stated period of time load bearing capacity, integrity, and insulation when exposed to fire.

Design Optimization: Is the process of finding the best design parameters that satisfy project requirements. Engineers typically use design of experiments (DOE), statistics, and optimization techniques to evaluate trade-offs and determine the best design.

Explosion: Is a sudden and violent release of energy the violence of which depends on the rate at which the energy is released.

Fire: Is the rapid oxidation of a material in the exothermic chemical process of combustion, releasing heat, light, and various reaction products.

Fixed Offshore Platform: Is a type of offshore platform used for the production of oil or gas in shallow waters. It extends above the water surface and supported at the seabed by means of piling or shallow foundation with the intended purpose of remaining stationary over an extended period.

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