Outdoor enclosures are evolving
Published on : Monday 30-11--0001
We see plenty of news about field equipment enclosures, but what are the key underlying forces driving development? At the heart of many developments is an increased focus on human safety and risk, and the need to extend lifecycles. This article looks at a few key trends from the perspective of a specialist in outdoor enclosures for process instrumentation and control equipment, Intertec Instrumentation.
The most significant of trends is buying systems that are assembled in the factory and delivered ready for hook-up to the process (Photo 1). Supplying turnkey outdoor instrumentation systems – enclosures fitted with process transmitters, valves, tubing, heating, etc – is not new. Intertec has been doing it for decades. However, the main clients have typically been the high volume buyers: EPC (engineering, procurement and construction) companies and large plants working on projects such as process upgrades or new plants and offshore platforms. The enclosure quantities for such projects often run into hundreds. But something interesting has happened over the last few years. We now regularly see orders for assembled systems in much smaller quantities – down to quantities of just one.
Why is this happening? Labour in the factory costs significantly less than in the field – and much less than labour in remote locations such as offshore – so there can be a strong economic case. Self assembly also requires careful storage, gathering and transport to the location for installation.
The quality of assembly and inspection/testing in a workshop with its superior tools and facilities is also invariably higher than in the field. And there is a single point of responsibility for the design – making sure it integrates without problem, meets the specification and has the right certification.
However, there are some less obvious reasons for the rise of turnkey solutions. One is cost of procurement. For an engineering house with a term contract for an offshore platform for instance, it can cost a lot to raise an order (and dozens of orders might be needed for a complete enclosure assembly). So it becomes much simpler and cheaper to deal with a turnkey solution supplier.
Another reason is the ability to more easily perform added value services to the factory-assembled enclosure system. One example is high quality machine bending of tubing for compact and ergonomic layouts. Another service and one which is becoming a trend is leak testing, particularly for systems destined for high pressure applications. Testing can be done more easily and economically in the factory, but also more safely. High pressure requirements are a particular requirement offshore, where wells in deeper water are starting to raise instrumentation tubing pressure levels beyond the 6,000 PSI rating of conventional compression tube fittings, up to 10,000 or 15,000 PSI.
The general shortage of skilled engineers and technicians is one more factor. By and large, many plants have trimmed their skilled workforces down to a minimum, and it is common today to rely heavily on outside contractors for services and support.
An aspect of the growth in custom services for engineers specifying field instrumentation enclosures is a trend to exploit manufacturers' abilities to produce custom size and shape enclosures. The availability of sophisticated CNC machinery for cutting, routing and drilling enclosures – such as the machines Intertec uses to customise GRP sheets for larger cabinets and shelters – represents a minor revolution for some segments of the field enclosure market. Typical applications for this service include offshore platforms – where the ability to make a cabinet/shelter to fit available space has significant advantages (GRP's much lower weight compared with steel is also a major benefit driving offshore use). However, there are onshore applications as well, particularly for larger cabinets and shelters, for instance because of the trend to move analyzers closer to the process, which means they must fit in cramped areas, on top of piping/flanges, on process columns etc.
One shift in specifying and configuring outdoor enclosure solutions also worth mentioning is the much greater focus on the materials used – both for the structure of the enclosure itself, as well as the metal components inside. The greatest driver in this situation is the threat of corrosion, and the associated safety risks. Again, offshore applications are at the forefront of the trend. This is because of the need to minimise risk to human life and the environment, but also because many offshore operators are trying to specify systems that have much longer lifetimes.
For applications in harsh environments, the virtues of GRP (glass reinforced polyester) as a structural material for enclosures have become a preferred and standard solution compared with traditional bent-metal constructions. It's now common for EPCs and large users to nominate acceptable materials such as GRP and 316 stainless steel on their field instrumentation specifications. Intertec has documented examples of its GRP enclosures surviving in harsh environments for 40 years (Photo 2). This kind of long-term reliability is achieved through the use of proprietary composite constructions of GRP/insulation/GRP – with thick gelcoat surface coatings for UV and scratch protection (Photo 3).
Inside the enclosure, it is also now commonplace to specify tubing and valve assemblies made from high performance alloys such as 6Mo and Super Duplex. This is prevalent in oil and gas applications dealing with sour gas.
One final trend worth highlighting is the increasing number of requests for cabinets and shelters with fire resistance, for housing critical resources in plants, parts of emergency shutdown systems etc. There is no global standard in the instrumentation industry for fire resistance, so at the moment Intertec is tending to see requests from large users and processing companies asking for conformance to fire resistance classifications such as F60 or F120. These specifications come from fire regulations designed to protect buildings (and call for things like fire doors to be able to withstand fire for durations such as 30, 60 or 120 minutes). Intertec has transferred this kind of specification to the outdoor enclosure world by producing special composite constructions. These can keep the control and instrumentation equipment inside an enclosure - such as an actuated shutdown valve – below 60°C for periods of up to two hours, even in the presence of a high temperature hydrocarbon fire (Photo 4).
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Assembling outdoor enclosures at the factory, and providing them ready for connection to the process is a key trend.
Despite 40 years’ exposure to an atmosphere containing sulphuric acid, after cleaning (bottom right) this Intertec GRP enclosure's surface is unblemished.
Intertec utilises multi-layer 'sandwich' materials to build protective enclosures. This composite construction shows two GRP sheets with insulation between – plus a thick gelcoat surface coating for UV and scratch protection.