Abstract:

This paper presents a summary of the structural design work against explosion loads on the "Sleipner A" topside. The defined and applied design philosophy is discussed and analysis results are presented. The "Sleipner A" topside was initially designed to withstand a general overpressure of 0.15 bar. However, this pressure was for some specific areas increased up to 0.70 bar after thourough safety studies. In order to achieve a reasonable structural design, ductile behavior of structures were taken into account. Thus, nonlinear structural analyses had to be performed. The results from these calculations showed lack of capacity for several blast walls and decks. Suggested reinforcements were found to be very effective and were subsequently verified.

Introduction

Explosion is one of the major accidental events to be considered in the design of offshore topsides. Since the loss of Piper Alpha, much effort has been given to determine quantitatively the effect of blast on platform topsides. The following effects have been considered in the design against explosions:

  • direct blast pressure wave on a structure,

  • fire after the blast.

The current philosophy in the design against explosion is (1) event control, (2) indirect design and (3) direct design. The event control is to reduce the probability and the consequences of explosions. Indirect design means use of energy absorption capacity. In the direct design, a characteristic blast wave is estimated and the dimensions are checked to satisfy certain criteria /1/. It is economically unacceptable to obtain the above goals by designing blast walls, pipe systems and decks without considering the ductile behavior of steel components. Thus, under explosion loads, it is expected that a properly designed structure will suffer damage, but will not collapse, cause loss of human life or pollution due to ductile behaviour of its members.

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