Fiberglass Firewater Systems for Offshore Platforms

Abstract

ABSTRACT An analysis was made by Amoco Norway Oil Company on methods to improve the on-line availability of deluge firewater systems on the offshore platforms at the Valhall Field. It was concluded that a major change in materials for firewater system construction was required. Fiberglass reinforced plastic (FRP) piping components were proposed asan alternative to existing carbon-steel dry deluge firewater systems. Advantages of FRP include enhanced safety through superior corrosion resistance and consequent improved system availability. Additional benefits are anticipated reduced installation and maintenance cost. A program was developed in cooperation with the Norwegian Petroleum Directorate (NPD) todemonstrate suitability of the material. To verify survivability of FRP under various worst case accident scenarios, the following tasks were identified: a risk assessment study to establish functional requirements and acceptance criteria; a verification explosion and fire testing program, and the development of detailed specifications and quality assurance systems. Performance of these tasks clearly demonstrated the acceptability of fire protected, insulated FRP piping for dry deluge firewater systems at Valhall. Based on this work, Amoco Norway obtained NPD consent to install fire insulated FRP piping in this service. Complete system retrofit has been preceded by offshore installation of a prototype dry deluge system. Experiences to date indicate the approach is an effective method of reducing costs while enhancing offshore safety. INTRODUCTION Deluge firewater systems are an important type offire protection used on wellhead and process areas of offshore platforms. For operational reasons, the majority of piping in these systems are maintained dry, with open spray nozzles and sprinkler heads. The dry systems are separated from pressurized wet systems by deluge valves (often in duplicate), which open to flood dry systems and create deluge upon detection of fire and/or high gas levels. As shown in Figure 1, the amounts of water released by deluge are impressive. Dry deluge firewater systems are found throughoutnearly all platform areas, with many kilometers of piping used for typical offshore platforms. Dry piping sizes are predominantly less than 200 mm (8 inch) in nominal diameter, with smaller sizes suchas 50 mm (2 inch) representing the majority of piping. Materials of construction have traditionally been carbon-steels. Because the systems often utilize seawater and are continuously exposed to the hostile offshore environment, internal corrosion of piping is common. This leads not only to loss of wall thickness, but to blocking of spray nozzles and sprinkler heads by corrosion products and scales. Amoco Norway Oil Company began operations at theValhall Field in the southwest Norwegian sector of the North Sea in 1982. Deluge firewater systems on drilling and process platforms of the type described above had been installed. Since field start-up, significant plugging of nozzles and sprinkler heads by internal corrosion products has been observed about every two years.