Design and Application of Passive Fire Protection for the Deck of the Mars Tension Leg Platform

Abstract

Abstract As an integral part of the Mars Tension Leg Platform's emergency response procedures, passive fire protection (pfp) has been designed for the Deck primary steel. The area and thickness requirements for the pfp coating of the primary steel are developed. The design process is described in detail, from the definition of the fire scenario, to the treatment of the fire's heat flow characteristics and the application of data representing steel properties at elevatedtemperatures. The design process described serves as an illustrated example of the treatment of fire as a load condition as set out in Supplement 1 of the API RP 2A document (Recommended Practice for the Planning, Design AndConstruction of Fixed Offshore Platforms) Section 18 that describes fire, blast and accidental load. Optimization of the area of primary steel requiring protection is discussed with reference to ultimate strength analysis whichis used to ensure that the pfp coating is applied for maximum effect. The quality of the application achieved at the fabrication facility is a key component in achieving the specified level of protection. Criteria established to aid the selection offireproofing material for the Mars TLP project are presented. The application of the pfp coating represents a substantial amount of work in the fabrication process and as such has the potential to significantly effect the fabrication schedule. Details of experience gained from the successful application of the fireproofing material are presented. 1.0 Introduction The Mars Tension Leg Platform (TLP) was installed in the Gulf of Mexico in 1996 in 2,940 feet of water (Figure 1). The TLP is composed of a deck structure, a hull structure, amooring system, production risers and export risers. Passive fire protection (pfp) material is applied to structural members of the TLP deck (Figure 2) to ensure that, in the event of a fire, escape routes and safe areas are maintained for sufficient time to allow platform evacuation and emergency response procedures to be implemented. Additionally, the tension support to the production risers is to be maintained for the same duration. This time requirementwill typically range from 4 hours to 30 minutes and is directly related to the fire fighting philosophy which in tum must be consistent with the facility design concept andmanning levels. For Mars the 30 minute time period was selected, based on the assumption that this is sufficient time for the 10 minute blowdown cycle to be completed, for the tubing volume between the surface controlled subsurface safety valve and the bottom master to deplete and for firewaterpumps to be started up. Forming as much as 10% of the Deck fabrication budget, pfp material is expensive to purchase and requires special work-site conditions that have the potential to severely disrupt the fabrication schedule. The platform's detection, warning and shutdown systems will protect the Deck structure duringits service life, but in the event that fire does occur, it is vital that the pfp material performs as expected. The design and specification of this pfp material is the subject of this paper.