Two outdoor shelters fabricated from glassfibre-reinforced polyester (GRP) – supplied by Intertec Instrumentation – provide lightweight and corrosion-resistant protection for gas chromatograph analysers and process transmitters mounted above new natural gas export pipelines connecting the platform to an onshore UK terminal. The instrumentation provides critical monitoring data on gas quality as part of the custody transfer metering system.

This particular platform upgrade project presented a number of challenges, including the harsh operating environment of the southern North Sea, and the space and weight restrictions of adding the new facilities onto a working platform.

OGS’s gas chromatograph quality measurement system inside the Intertec GRP shelter

Glassfibre-reinforced polyester (GRP) materials were specified to protect the instrumentation. GRP construction also provided excellent protection against both the harsh weather in the offshore location, and the local environmental conditions.

Intertec was selected to build the custom GRP shelters because of previous good experience of working with the company.

The GRP material used by Intertec is protected by an advanced gel-coat, which incorporates a unique nanotechnology treatment that employs single-wall carbon nanotubes (SWCNTs) to provide conductivity. Because the SWCNTs are only around 1-2 nanometres in diameter, they enhance surface smoothness.

The lightness of GRP compared to steel helped to reduce the size and weight of the metalwork structure that mounts the shelters directly above the export pipelines. So, natural ventilation according to IEC EN DIN 61285 was specified. This eliminates routine maintenance visits that would be required with other shelter ventilation approaches such as fans or an HVAC system.

To support natural ventilation for safe operation in the hazardous environment, Intertec supplied explosion-proof heaters and installed louvre panels at the top and bottom of shelter walls. All of the shelter fittings, apart from the finned aluminium bodies of the heaters, are fabricated from 316 stainless steel for corrosion resistance – including the panic bar door opening mechanism.

The Intertec GRP shelters installed above the offshore platform’s gas export pipelines

In total, two walk-in shelters and two large cabinets were built by Intertec to meet the custom shape, size and weight constraints. Each shelter houses an identical instrumentation system including pressure reduction sample conditioning equipment, a Danalyzer gas chromatograph, Rosemount pressure transmitters, calibration facilities and various safety devices and accessories. The two cabinets house cylinders to supply the required gas for calibration purposes, along with associated pressure regulation, measurement instruments, tubing connection and flow control components.

The GRP material used by Intertec to build the shelters and cabinets is a proprietary multi-layer composite with moulded GRP panels enclosing polyurethane foam insulation, protected by gel-coated surfaces.

This composite material has a very high thermal resistance, reducing the amount of energy required to heat equipment. A further benefit of Intertec’s approach to shelter fabrication is an advanced gel-coat, which is applied in a much thicker layer than alternatives such as paint. It protects against ultraviolet (UV), and is highly effective against abrasion. It offers exceptional environmental protection and resistance to `corrosion’, allowing maintenance-free lifecycles of 30-40 years – more than enough to meet the anticipated cease of production date for the platform.

The gel-coat also incorporates a unique nanotechnology treatment that provides conductivity to dissipate static electric charges safely to ground – protecting against sparking in hazardous areas. Developed for Intertec by BUFA, the coating employs single-wall carbon nanotubes (SWCNTs) to provide conductivity. Because the SWCNTs are only around 1-2 nanometres in diameter, they enhance surface smoothness. The gloss retention after accelerated weathering tests of this surface is some 50 per cent better than the previous coating technologies used.

This technology is behind the significant improvement in resistance to UV of Intertec’s shelters. Previously, exposure to high UV levels over the long term could lead to surface roughening – which is sometimes referred to as ‘chalking’ or ‘frosting’. Intertec’s weathering tests have demonstrated that the new coating will withstand extended exposure to very high UV levels – providing hitherto unachievable protection for GRP field enclosures destined for ultra-harsh environments such as offshore platforms, deserts and Arctic environments.