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.
“How much pressure can this seal handle?”
The answer to this question depends on a number of parameters and conditions. But the principle limiting factor in the pressure handling of any seal system is the extrusion gap.
Commonly referred to as the “E-Gap,” the extrusion gap is one of the most critical design aspects in any high-pressure application. Seal design, type, and material are all influenced by the extrusion gap and the desired pressure handling capability.
What exactly is an extrusion gap, and why is it so important in the successful design of a sealing system? Let’s find out.
In terms of sealing systems, the extrusion gap is defined as the clearance between the hardware components.
In a piston configuration, this would be the clearance between the piston and bore. In a rod configuration, this is the clearance between the rod and housing it’s passing through.
The extrusion gap can be expressed in terms of radial or diametral clearance, which can lead to some confusion. Our partners at Eclipse define the E-Gap by stating it as the radial clearance. The radial clearance is equal to the diametral clearance divided by two.
It’s important to note that while hardware components might be machined to have a specified clearance, this gap might not be perfectly realized or maintained.
Moves away from bronze and rubber bearings have boosted the expansion and usage of Vesconite Hilube across the world. Vesconite lasts longer, wears less, requires less maintenance, and doesn’t require lubrication. This makes it suitable for different applications, in different industries, and on different continents.
Take the U.S. market for example.
“A state like California has banned lead so you cannot sell a bronze product. People have to find an alternative,” says Vesconite Bearings’ technical representative, Charlie Simpson. “Vesconite is getting more and more business as people move away from bronze and rubber bearings.”
Simpson says Vesconite has seen steady growth in sales from the US over the last two years. Some of this is due to the need for an alternative product; much is due to the benefits of the product, such as increased efficiency.
Simpson says the companies in the US are willing to test and try new things. “If they can get five percent more efficiency they will go for it.”
Because Vesconite doesn’t need lubrication, bearings last longer. That means less downtime, less maintenance and fewer stoppages. The end result is increased efficiency.
Amine treatment is a process typically used for Hydrogen Sulfide removal from natural gas (sour gas). This operation is commonly referred to as gas “sweetening," acid gas removal, or amine scrubbing
Amine units are used all over the world in oil refineries and gas plants to remove hydrogen sulfide (H2S) from a product stream. New environmental standards are more strict and require ever-decreasing contents of H2S in clean natural gas. Most of the new sources of oil and gas discovered today have high contents of H2S which demand more efficient removal technologies (the Shah Gas field in the United Arab Emirates for example has up to 30% H2S).
Amine units operate under harsh chemical environments. H
Article re-posted with permission from Parker Hannifin Sealing & Shielding Team.
Original content can be found on Parker’s Website and was written by Vivek Sarasam, heavy duty mobile Sr. application engineer, and Jeffrey Labonte, market manager.
Parker Hannifin Engineered Materials Group has developed a wide variety of metal seals which can be formed or machined. A metal seal is a highly engineered sealing solution which provides elastic recovery or spring back to maintain good sealing, despite separation of mating surfaces due to effects of thermal cycling, flange rotation, applied mechanical or hydrostatic loads or creep.
A metal seal is used when the application conditions are outside the specification limits of a polymer. For example, when:
Metal Seals are primarily used in static applications for temperatures as high as 1000°C/1832°F and pressures as high as 6825 bar/99000 psi for select applications. At low cryogenic temperatures and low pressures, such as vacuum seal applications, metal seals are far better than polymers since they do not become brittle and lose elasticity. Metal seals also have a low leakage rate down to 1 x 10-12 cc/sec per mm circumference which in comparison to high load O-rings is almost 100x better.
Unlike elastomer seals, metal seals are very highly resilient to corrosive chemicals and even intense levels of radiation. With this resilience coupled with the right material selection/coating for an application, a metal seal can be a very durable seal performing dependably year after year.
Parker has a variety of in-house developed coatings which are used based on the application conditions and base material. The chart on page D-59 of the Metal Seal Design Guide (shown below) shows examples of some of the coatings based on the base material.
Metal seal x-sections can vary from a solid O to a Hollow O and from a C Ring to an E Ring depending on the application load and allowable leakage rate as shown in the figure below. Each x-section has benefits based on the application use and cost as indicated in the chart below.
Page A-10 of the Metal Seal Design Guide (shown below) shows some common applications in the industry and the type of metal seal used in those applications. These are examples of applications where the application conditions exceed beyond what an elastomer is capable of handling.
Garlock Style 215 Expansion Joints are PTFE concentric spool-type flexible couplings that are designed to reduce noise and compensate for expansion, contraction, and minor piping misalignment in chemical processing, air conditioning, and heating systems.
The complete assembly includes a fluorocarbon resin PTFE body, electroless nickle-plated ductile iron flanges, polyethylene-covered restriction zinc plated bolts, and stainless steel corrosion-resistant reinforcing rings.
Primary Metals
South American manufacturer of flat and long steel products
Construction of two new facilities including a hot rolling mill.
The plant was in need of expansion joints that could handle chemicals on their pickling lines. Pickling is a metal surface treatment used to remove impurities, such as stains, inorganic contaminants, rust or scale from ferrous metals. A solution called pickle liquor, which contains strong acids, is used to remove the surface impurities. It is commonly used to clean steel in various steel making processes. The line required an expansion joint with a PTFE tube to handle the pickle liquor which included hydrochloric and sulfuric acid, but a very short overall length for installation.
Fiber Reinforced Plastic (FRP) pipes and flanges are increasingly used in the oil and gas industry where metal is simply too heavy and expensive. In addition to cost pressure, the need for lightweight chemically resistant materials are also driving the use of fiberglass pipes and flanges. Innovations in FRP flange design coupled with improvements in manufacturing technology have allowed FRP piping to be used in even more demanding applications. However, these demanding applications have added challenges for sealing the bolted flange connections.
More aggressive media and higher internal pressures have pushed the limits of the commonly used rubber gasketing materials, such as Nitrile Butadiene Rubber (NBR), Ethylene Propylene Diene Monomer (EPDM), or neoprene. Obtaining a reliable seal in FRP flanges using conventional gasketing materials has become more difficult.
Fiberglass pipes are generally known to have strength limits and a lower pressure resistance, making sealing fiberglass flanges difficult. Gore solved this problem with its patented expanded polytetrafluoroethylene (ePTFE) gasket, specifically designed to seal flanges at low stresses. This solution was successfully demonstrated in a multistage testing procedure conducted in cooperation with a globally leading manufacturer of anti-corrosive fiberglass pipe systems.
When it comes to maintaining a high-functioning rotary shaft, you need to select the appropriate lip seal.
The shaft seal protects the rotary shaft from contaminants such as dust and dirt, and it keeps water out and lubricant in.
A rotary seal, also known as a radial shaft seal, typically sits between a rotary shaft and a fixed housing — such as a cylinder wall — to stop fluid leaking along the shaft. The rotary seal’s outside surface is fixed to the housing, while the seal’s inner lip presses against the rotating shaft.
Common applications for shaft seals include motors, gear boxes, pumps and axles. They’re also increasingly used for food and chemical processing, as well in pressurized gas applications.
Three of the most important considerations when the choosing the best lip seal for a rotary shaft are:
Here’s your quick go-to guide on how to achieve optimum performance and longevity for your seals and shafts, ultimately minimizing the risk of seal failure. Presented by our partners at Eclipse Engineering: