In a typical oil refinery or chemical processing plant, 60% of fugitive emissions are attributable to leaking valves. Of these, nearly 80% are released at valve stems. Also contributing to valve failures, are leaks at the bonnet, flanges and seats. As operating conditions in these and other industries continue to subject valves to ever more extreme temperatures and pressures, sealing them effectively poses a challenge that cannot be met with traditional materials and methods. Soft, compressible elastomers provide good sealing performance, but they are porous and cannot withstand temperatures in excess of 482°F (250°C). They also become hard and brittle in cryogenic service. Metal seals have much greater temperature capabilities, high mechanical properties, lack of porosity and long shelf life. Ductility and elasticity are typically the limiting factors.

Today more resilient, metal-to-metal seals are available and being used in valves operating under extreme conditions. Spring- and pressure-energized metal seals function much like a gasket between two flanges with little or no relative motion between them.

The sealing principle of spring-energized seals is based on plastic deformation of a jacket that is more ductile than the mating surface. This deformation occurs between the sealing face and an elastic core composed of a closely wound helical spring. The spring provides specific resistance to compression, during which the resulting pressure forces the jacket to yield and fill flange imperfections. Each coil of the helical spring acts independently, allowing the seal to conform to any surface irregularities. This combination of elasticity and plasticity provides an extremely effective seal even under the decompression cycles.

Spring-energized metal seals provide numerous advantages in oil and gas applications, including but not limited to MWD and LWD tools, couplings, subsea compressors, enclosures/vessels, christmas trees, electronic submersible pumps and flowmeters. Extreme operating pressures and temperatures, together with more difficult resource recovery, zero tolerance for failure and environmental concerns, are placing unprecedented demands on this equipment.

Traditionally this industry has used solid machined seals that provide high compression loads but lack resilience. They also tend to have relatively high rates of leakage over time as flanges deteriorate. Recent advances in metal seal technology provide controlled compression, high resilience and reduced leakage.

Background

Designing with inflatable seals for the medical industry

Seals are central parts of the design of medical equipment with moveable, interlocking parts that must be secured for sanitary, thermal, or radioactive reasons.

Designing with inflatable seals requires the inclusion of a source of compressed gas, which is used to inflate seals in the medical device industry and it is often already available on the plant floor, in a laboratory, or medical environment. It is also possible to inflate with liquids rather than gas in demanding applications, and water would be an acceptable inflation media in this sector, although not common. For some low-temperature applications, a seal may be inflated with a blend of glycerine and water.

Designing with inflatable seals

Seals used on doors and openings should be part of the early phases of product design. In some cases, contact seals may be effective, but they often require substantial force be applied to load the seal, which impacts product design and increases manufacturing cost. Inflatable seals enable more cost-effective machinery fabrication for two reasons:

1. Inflatable seals are more forgiving because the seal can inflate to close a gap between structural members and achieve equal sealing pressure around the flange as long if the gap falls within a broad tolerance. An inflatable seal will work whether the gap spans 3mm or 10mm, for instance. A compression seal or other contact seal will not be effective unless the seal and flange contact each other with great precision, which can be difficult to achieve on new equipment. Even a robust and precision-manufactured machine with well-designed flanges will lose some of its geometric integrity as hinges and other components deform or bend over years of use. Throughout the course of the equipment lifecycle, a contact seal may become problematic and exhibit leakage.
2. Inflatable seals enable lighter and more affordable methods of equipment fabrication. The force exerted on the chassis of a piece of equipment means doors and related components must be thicker, and perhaps machined instead of welded. These components are typically made of stainless steel, and inflatable seals might be attractive due to lowered material costs.

Which equipment needs inflatable seals?

• Isolators — where a leak-tight enclosure can be critical for environmental health protection due to hazardous substances or processes. — can secure glove boxes, access gates, transfer systems and filtration systems that handle toxic or sterile components.
• Sterilizers — which may rely on heat, chemicals, irradiation, or filtration — may be suitable for desktop autoclave sterilizers, sterilizing tabletop autoclaves and static air depyrogenation sterilizers.
• Dryers and freeze dryers - used to sterilize everything from machine components to glassware.
• Material handling functions - to raise, lower, or grasp objects.

Innovative Subsea Processing Technologies

The Aasgard oil and gas field in the North Sea has been operating since 1999. Innovative subsea processing technologies were used to compress the oil and gas on the site’s seabed to improve recovery rates as the field ages and as equipment begins to draw from increasingly deeper subsea reservoirs. The operator required seals for the lid and body of the control power distribution unit in order to protect its vital electronics in the harsh, unforgiving subsea environment.

As a globally trusted source for engineered components, seals, assemblies, and sub-systems for demanding environments, Technetics was uniquely positioned to evaluate and specify a sealing solution for this application. The system designer and Technetics engineers subsequently underwent a two-year testing phase to examine the performance of a variety of sealing options.

Demanding Subsea Environment

Due to the extremely demanding environment in