Production equipment shielding deployed on FPSO units

Operators are striving to meet oil and gas demands by advancing into ever more hostile and deeper waters. At the same time, these operators are endeavoring to cut construction and operational costs while increasing safety awareness.

Bill Oliver
Darchem Engineering
Operators are striving to meet oil and gas demands by advancing into ever more hostile and deeper waters. At the same time, these operators are endeavoring to cut construction and operational costs while increasing safety awareness.

That awareness has been bolstered by considerable innovation of late in the design of super performance, passive fire protection, and radiant heat shield systems which can survive an offshore installation's harsh regime during its planned operating lifetime. Regulation and industrial requirements demand ever higher standards in passive fire protection and also related systems, such as those involving high levels of radiant heat from operational flares or from predicted incidental fire sources.

As production switches increasingly from traditional large fixed platforms to mobile floating production, storage, and offloading systems (FPSOs) more appropriate for marginal reservoirs, a further demand is arising for lightweight facilities and safety systems. The requirement for long life and durable systems, however, remains a key priority since the nature of an FPSO allows for relocation of the vessels over a new field once the old one is depleted.

The offshore industry has been vigilant in maintaining and improving safety measures such as passive fire and blast protection, in conjunction with active fire protection systems, since the Piper Alpha incident in 1988. All types of offshore installations are now designed to minimize the effect of explosive overpressure, hydrocarbon jet and engulfment fire conditions. Moreover, it has been recognized that as production moves from oil to gas on mature fields, as was the case with Shell UK's Brent redevelopment, the chances of large-scale releases of high pressure velocity gas increases.

In recent years this has led to switching from hydrocarbon engulfment fire scenarios to jet fire situations. The interim jet fire test procedure developed by the industry in conjunction with certifying authorities and test centers has now been adopted as the formal system to which suppliers must submit samples for testing, in order to prove the resistance of their materials to the increasingly onerous conditions.

In parallel with these trends, the continuing need to reduce construction costs when developing new fields has led oil and gas companies to form alliances with the major fabricators and design houses. Their risk/revenue sharing agreement can give these teams a competitive edge. But the drive to cut costs also has to be carefully balanced so that safety standards are not jeopardized and that imposed conditions, as defined in the associated HAZOP studies, are implemented.

It is against this background that passive fire protection products can offer some of the more cost-effective and innovative solutions to the industry's needs. Modern offshore production often still necessitates burning of gas via high level flares. The need to provide suitable radiant heat shielding close to the flare tip, capable of withstanding severe thermal cycling for long periods, has led Darchem Engineering based near Billingham, UK to engineer an all-metallic heat shield system called Darmet.

Flare shielding

By using high nickel alloys and thin foil technology, which allows a constant flow of cooling air from below the shield to permutate to the top surface, a stable consition can be achieved equating to heat flux reductions of up to 95%. The shield can withstand flame impingement and other extreme environmental conditions while providing a platform during flare tip changeovers and maintenance operations. The modular design of the panel shield clamps allow for severe thermal cycling during prolonged and short duration flaring operations. The product is designed for the full life of an offshore instalation.

Other typical offshore production requirements mean that critical items such as emergency shutdown valves, pipelines, process vessels and instrumentation need to be fire proofed against jet fire and blast overpressure scenarios. Here passive fire protection products offer state of the art solutions in the form of removable or spray-on products.

Spray applied and coating systems, however, are not always practical due to the need to access the protected items periodically for inspection, maintenance or replacement purposes. Furthermore, in the case of process vessels operating at high temperatures, a thermal insulation has to be installed prior to the spray applied fire protection, which is time consuming and less cost effective.

Fire blanket

In response, Darchem produced a unique compressed flexible thermal composite fire protection blanket system, called Darmatt. This can withstand blast overpressure up to 1.5 bar and jet fires up to 120 minutes duration, and can be retrofitted to existing equipment. The system is lightweight, requires no equipment preparation and is totally removable.

R & D will continue into solutions for offshore fire protection needs, but knowledge transferred from other industries can also be applied.

A recent example involved using thin foil technology originally developed for the nuclear power industry. It was used in the supply of lightweight radiant heat shields to protect critical deck level cables on Navion's Munin FPSO for Statoil's Lufeng Field offshore China.

Through using the highly reflective foils encapsulated in sheet metal, radiated heat was reflected away from the cables, convected heat was reduced to zero by the air flow through the shield, and conducted heat was minimized by the stainless steel foils' extreme thinness (0.05 mm).

The need to further reduce the physical size of the passive fireproofing, while at the same time increasing performance, is leading to the development of new super-performance endothermic materials which, in the fullness of time, will be used in future generations of offshore installations.

Copyright 1998 Oil & Gas Journal. All Rights Reserved.

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