Response of Topside Structures to Fires and Explosions: Design Considerations

Abstract

Abstract The design of topside structures to resist hydrocarbon fires and explosions necessitates consideration of a range of issues not normally addressed by the designer. This paper gives an overview of the key issues that have been studied in several sponsored R&D projects and by the Fire and Blast Information Group (FABIG). The results are presented in a form that is usable by designers. The main areas covered are:Elevated temperature material property design data for use in fire engineeringHigh strain rate material property design data for use in explosion resistant designAnalysis techniques for fire and explosion designDesign methods based on codified rules (i.e. covered by design standards) and advanced techniques Introduction The design of North Sea topside structures to resist fire and explosion scenarios received greater prominence since the late 1980's. Numerous joint industry projects were undertaken to better understand the characteristics of hydrocarbon fires and explosions, and the way topside structures respond to such events. In 1992, the Fire and Blast Information Group (FABIG) issued the 'Interim Guidance Notes for the Design and Protection of Topside Structures' (IGN's) [1], the first comprehensive design document to deal with these issues, and this subsequently became the de facto design standard. Since then, FABIG has issued 7 Technical Notes to supplement the IGN's. These have been distilled from the large number of joint industry projects completed in the 1990's. This work continues with plans now in place for a number of future Technical Notes and new projects identified to generate the background work for other Technical Notes. This paper draws on the work of FABIG to give an overview of the technical issues that need to be considered by a structural engineer when designing topside structures to resist fires and explosions. In particular, the paper considers the role of advanced and simplified methods, and discusses the input requirements for these methods, especially with respect to appropriate material data. Design Considerations for Topside Structures Subjected to Fire The design of topside structures to resist hydrocarbon fires necessitates an understanding of the following issues:Nature of the fire load and how it impacts on the structure (i.e. identification of the nature of the fire, where it will burn, the thermal load generated by the fire and the temperature rise in time of the affected structural members)The performance requirements of the structure (e.g. strength, deformation limits, load shedding, etc.)The response of the structure when subjected to the received heat loading. Fire Load Characteristics A number of researchers have studied the nature and evolution of hydrocarbon fires [2,3,4,5,6]. Methods for converting the thermal loading from the fire into a received thermal load acting on the structural members, and subsequently into a time-temperature curve for each member are also available in the literature [7,8] in a form suitable for use in design.