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Intertec

Environmental Protection for Field Instrumentation

More info about Intertec

GRP Enclosures Extend Fire Survival Time for Critical Equipment

CASE STUDIES
By Intertec

The potentially catastrophic results of fires at oil and gas processing facilities - such as on the Deepwater Horizon or at the Buncefield terminal - has led to a much greater focus on improving emergency management systems and related plant infrastructure.

By Klaus-Dieter Meyer, Vice President of INTERTEC.

Glass reinforced polyester (GRP) has been exploited in special-purpose enclosure designs made by INTERTEC to offer fire protection solutions for oil, gas, chemical and other processing companies. This valuable property is well known as a material for constructing robust and long-life outdoor equipment shelters. GRP also offers significant benefits in this area because of its intrinsic resistance to fire.

One area of safety that is receiving particular attention is the protection of critical safety equipment against high temperature hydrocarbon fires, such as emergency shut-down valves and actuators, or control and fire-fighting systems. The longer that critical emergency resources remain operational in the event of a fire, the greater the likelihood of averting disaster. However, the ferocity of hydrocarbon fires poses major design challenges. These types of fires are often characterised by a very rapid rise in temperature, typically reaching about 1100°C within five minutes.

Passive fire protection offers the simplest and most inherently reliable means of guarding against premature equipment failure due to fire. For smaller-scale applications like protecting valves and actuators, various forms of close-fitting passive protection such as flexible fire-resistant bags and blankets and intumescent coatings have been on the market for years. However, these can have disadvantages when used with field equipment in hostile environments. Tailored fittings can be susceptible to weather damage. Over time they can absorb moisture and sag, making them difficult to reseal properly after maintenance of the valve or actuator. And thick film intumescent coatings generally need to be applied to equipment at the factory. These types of coatings can hinder maintenance access and can require periodic repainting to prevent them becoming hygroscopic when exposed to weather.

Rigid Enclosures Simplify Access

For smaller-scale applications, rigid passive fire protection cabinets overcome these disadvantages by providing maintenance-free solutions that can be retrofitted to existing process equipment in the field and which do not restrict service access. For larger requirements, such as protecting complete control and communications electronics and systems, walk-in style shelters provide versatile protection solutions.

However, the choice of construction materials is key. Some manufacturers use metal for the outer walls of the enclosures and shelters, which can corrode due to the presence of salt or other aggressive chemicals in the atmosphere. Furthermore, the weight of such enclosures can preclude direct mounting on process pipes, making installation more difficult by demanding use of load-bearing support brackets.

Glass reinforced polyester or GRP is well known as a material for constructing robust and long-life outdoor equipment shelters. GRP also offers significant benefits in this area because of its intrinsic resistance to fire. This valuable property has been exploited in special-purpose enclosure designs made by INTERTEC to offer fire protection solutions for oil, gas, chemical and other processing companies.

GRP’s Natural Fire Resistance

Before looking at the enclosure construction techniques used, and the kind of fire resistant properties they make possible, it’s worth emphasising the basic fire retardant capability of GRP.

Steel might seem an obvious choice for enclosure materials, but in fact it will rapidly conduct the heat to the inside of the enclosure, leading to earlier failure of contained equipment. The type of GRP sheet materials used by INTERTEC to build enclosures has a very high thermal resistance compared to metal, with an efficiency of some 1000 times better. It is also naturally fire retardant and self-extinguishing. The material is classified to UL 94 V-0 and is self-extinguishing without leaving burning droplets.

The natural resistance of GRP to fire is readily apparent in Figure 1. This photo shows a small-scale outdoor enclosure following a fire at a polyolefin plant. This familiar type of enclosure – which is widely used for housing one or more field-based process instruments – is often constructed from just single-thickness sheets of GRP (using the sheet moulded compound or SMC hot-pressing process). The GRP enclosure retained complete structural integrity throughout the fire with the only damage being the loss of its acrylic inspection window which melted in the heat – a failure that can be remedied by specifying safety glass.

Intertec Hess GRP

INTERTEC uses GRP materials in a number of ways depending on the application. The applications range from small-scale moulded enclosures (typically two-part enclosures for housing process instruments which open for easy access), to larger cabinets (suitable for enclosing process valves and actuators for example), and walk-in shelters for housing large-scale equipment.

Composite Techniques
One of the major attributes of building enclosures using GRP sheet materials is the ease with which sheets can be fabricated into composite material forms using ‘sandwich’ style layered constructions. This is most commonly employed by INTERTEC to embed a foam core within inner and outer GRP sheets – to provide a high degree of thermal insulation from external environmental conditions. However, these composite fabrication techniques can also be used to enhance fire resistance, by embedding one or more layers of materials such as fire-resistant Gypsum board, or mineral wool (Figure 2).

Composite Techniques

One of the major attributes of building enclosures using GRP sheet materials is the ease with which sheets can be fabricated into composite material forms using ‘sandwich’ style layered constructions. This is most commonly employed by INTERTEC to embed a foam core within inner and outer GRP sheets – to provide a high degree of thermal insulation from external environmental conditions. However, these composite fabrication techniques can also be used to enhance fire resistance, by embedding one or more layers of materials such as fire-resistant Gypsum board, or mineral wool (Figure 2).

INTERTEC hess grp

The composite panels used to build cabinets and smaller shelters are produced using a vacuum moulding process, using a special polyester resin and additives to achieve ‘not easily inflammable’ properties according to ASTM D635-63 or DIN 53438 test procedures, to be classified according to DIN 4102 B1. INTERTEC’s GRP materials are also available with a low smoke generating resin – which can be important in some applications such as tunnels and railways.

Proprietary jointing and bonding techniques help the enclosures to resist the damaging effects of the fire, and to ensure that degradation happens in a slow and predictable manner.

The resulting composite GRP materials are so good at insulating enclosed equipment against the heat of fires that INTERTEC is able to build cabinets that will keep internal temperatures below 60°C for periods of up to 30 or 60 minutes in the event of a fire. Moreover, this level of protection is even possible when exposed to high-temperature, hydrocarbon-fuelled fires. This is ideal for engineers and safety specialists designing fire protection systems for processing plants (Figure 3).

intertec hess grp

INTERTEC produces two types of fire cabinets and shelters. The regular version is designed to withstand ‘normal’ fires with a standard temperature/time curve such as that defined in the ISO 834 fire resistance tests, for buildings designed for residential or business purposes. A more advanced version called ‘1709’ is designed to withstand hydrocarbon fires with a rapid-rise temperature/time curve (as specified in the ANSI/UL 1709 standard).

The 1709 standard covers the protection of structural steel and has a permissible temperature of 550°C for the specified protection time. However, thanks to proprietary design techniques, INTERTEC’s 1709 fire cabinets and shelters meet the much more stringent requirement that the internal temperature must not exceed 60°C for a duration of 30 minutes.

Independently Tested

There are no specific standards in the process control arena for protective fire cabinets and shelters, so INTERTEC commissions its own testing to verify performance.

The independent test house, MPA Dresden has carried out significant tests to verify this capability. It subjected a typical process valve/actuator sized cabinet, with an interior space of around a cubic metre, to a hydrocarbon-based fire (Figure 4). After a period of 60 minutes, the body temperature of an electrical actuator mounted inside the cabinet was still less than 60°C. The cabinet also retained its structural integrity, suggesting that it could survive even longer. To discover more on the subject, explore a video of this fire test

intertec hess grp

Protection Combined With Walk-In Access

For larger scale applications, such as housing emergency shut-down control or telecommunications systems, larger shelters with walk-in access may be required. Such applications pose additional challenges.

Conventional fire safe buildings can be constructed from concrete or steel and covered with fire resistant ceramic tiles, or they can be more traditional field shelters covered with intumescent materials – which might hinder access.

INTERTEC recently produced some walk-in fire shelters for an offshore platform with a specification of two-hours of fire resistance while keeping internal wall temperatures below a maximum of 140°C – an exceptionally difficult challenge. Large shelters are needed because they house the offshore platforms’ ESD and fire suppression systems. These electronics systems need to be adequately insulated, but also have to be readily accessible for routine testing and maintenance. The shelter itself also needed to have a long service life, demanding structural robustness and high corrosion resistance, yet weigh as little as possible – as each additional kilo has a significant knock-on effect on the cost of the supporting offshore platform. Ideally the shelters also needed to be entirely passive and require no electrical power or other services for their fire protection capabilities.

INTERTEC’s unique fire-resistant GRP techniques proved ideal for this application, because of low weight (the GRP materials that INTERTEC uses weigh around 75 percent less than steel – yet offer a similar structural strength) as well the superb performance and longevity of GRP materials in harsh environments.

The shelters that INTERTEC developed for this particular offshore application (Figure 5) employ a thick double-sandwich design with two layers of a special certified mineral wool insulation to withstand fire for 120 minutes while maintaining structural integrity. This performance stems from a proprietary composite wall structure with two layers of mineral wool sandwiched between special-grade GRP sheets. The fire resistance of this composite material has also been verified by the independent test house MPA Dresden.

intertec hess grp

Large outward-opening doors provide personnel with instant access for routine equipment inspection and maintenance. However, for air conditioning purposes of the electronics systems, the shelters also needed to be equipped with ventilation. The fire-resistant air transfer grilles that perform this function contain special intumescent damper slats that are expressly designed for use in harsh environments. Under normal conditions the grilles allow an unrestricted flow of air into and out of the shelter. However, in the event of a fire, the heat activates the intumescent material, which then creates a very durable and insulating barrier against the ingress of flames and hot gases.

intertec hess grp