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Comment Processing & Handling

Seals and gaskets, at your service

By Chemical Engineering |

In today’s global marketplace, multinational companies are almost expected to manufacture products at different sites around the world. Try as they might to build plants that are identical and employ the same procedures, there are no guarantees the results will be the same. Regional differences in the water supply, or seasonal changes in temperature and humidity, can affect process parameters. Variations in the feedstock can wreak havoc on seals and gaskets.

Just ask any petroleum refiner. Typically, sour crude sells for a lower price than sweet crude, but is more difficult to process due to its higher solids content and acidic nature. To achieve the desired reliability and control emissions, mechanical seals designed for more aggressive service may have to be employed.

Whatever companies in the chemical process industries (CPI) need in the way of sealing solutions — from mechanical seals and exotic elastomers, to universal gaskets and specialized fittings — you can be sure that somewhere, somehow, there is supplier who will deliver it off the shelf or made to order.

“Developments in seal compounding technology make it easier than ever to produce customized seals,” says Darryl Turland, materials technologist for Precision Polymer Engineering Ltd. (PPE; Blackburn, U.K.). There are many types of elastomers and an infinite number of performance enhancements that can be realized by changes in the compounding, allowing seals to be fine-tuned to the needs of specific applications, he explains. “It should be possible to find a good match for any process condition.”

Courting customers

Chemical engineers can save money in their processes by using elastomer seals, according to DuPont Performance Elastomers (Wilmington, Del.). Depending on the equipment, chemical environment and seal material previously used, the savings can range from 10 to 200% in total system running costs. The caveat, of course, is that the engineers would have to specify DuPont’s perfluoroelastomer seals.

To be closer to customers, wherever they are, seal manufacturers are stepping up maintenance programs and forming new alliances. In 2004, Parker Hannifin Corp. acquired Acadia Elastomers and Advanced Products Co., a maker of metallic and polymer spring-energized seals. The moves, says Dale Ashby, vice-president of innovation and technology for the Parker Seal Group, have increased the company’s presence in the CPI and its capability to engineer innovative sealing solutions to meet customers’ most sophisticated applications demands.

As to programs, Bill Root, district sales manager for seal manufacturer John Crane (Morton Grove, Ill.), says the company is proud of the results achieved through a Managed Reliability Program (MRP) at Valero Energy Corp.’s (San Antonio, Tex.) refinery in Paulsboro, N.J. Since 1995, when the program was implemented, the refinery has increased the average service life of its sealed pumps to about five years, reduced seal failures by half, and reduced inventory by more than 80%.

John Crane has achieved similar results at other refineries, using an MRP customized for each facility. As part of the program, one of the company’s technicians works fulltime at the customer’s site. “Unlike customers’ maintenance or reliability staffs, we have opportunity to focus primarily on pumping equipment, seals and seal support equipment,” says Root. “This focus delivers increased reliability and lower cost of ownership for the customer.”

Industrial operators in the European Union are racing against an October 30, 2007 deadline to comply with the IPPC Directive. The directive, whose acronym stands for Integrated Pollution Prevention and Control, aims to minimize pollution from industrial installations in the EU. All installations covered under Annex 1 of the directive must get operating permits based on the Best Available Techniques (BAT). Installations that do not secure permits will be shut down.

Aware of Germany’s TA-Luft directives on volatile emissions, Burgmann Industries GmbH (Wolfratshausen, Germany) introduced the Corratherm gasket. Made of corrugated stainless steel and coated on both sides with flexible graphite foil, the gasket is resistant to practically all media, including aggressive types, says the company.

“Many people are worried about IPPC, but in fact, we have a great number of products,” says Peter Plaisier, sales and marketing director for Garlock EMIA (Neuss, Germany). Some of Garlock’s new products will be introduced next month at the Achema 2006 trade show in Frankfurt, Germany. He is excited about the prospects for a new sealing system and its potential for the next generation of sealing technology. Originally developed for France’s nuclear industry, Helicoflex is now being prepped for general industry applications, particularly those involving high temperatures. The material sells for a premium, but if purchased in large quantities, it could be very efficient to use. Plaisier also claims that Helicoflex will last more than 1,000 years.

 

All pumped up

Some equipment manufacturers are finding their own fixes for sealing problems and, like Garlock, will unveil them at Achema. Tuthill Pump Group (Alsip, Ill.) will be at the show with a new seal for its GlobalGear line of positive-displacement gear pumps. Essentially, the TuffSeall device accomplishes mechanical sealing with shaft packing, says Kevin Delaney, Tuthill’s director of product marketing.

The seal has a silicon carbide sleeve with a rotating metal-filled sealing element made of polytetrafluoroethylene (PTFE). Like shaft packing, Tuffseall tolerates intermittent periods of run dry, and when Tuffseall fails, it gradually weeps — as opposed to leaking like mechanical seals. The weeping is an indication that the Tuffseall needs to be repaired, which it can be, using an insert that is field-replaceable. Suitable for applications involving paints and coatings, glues, polymers and greases, Tuffseall handles viscosities to 150,000 cP, differential pressures to 300 psi and continuous operating temperatures to 375ËšF.

Many pumps have stuffing boxes that are designed to accept packing, single mechanical seals or double mechanical seals. While the packing and double mechanical seals are large enough to completely fill up the stuffing box, single mechanical seals have room to spare. They are secured so that the seal faces are recessed farther back in the stuffing box, outside the flow stream. While heat is generated by the friction of the moving, contacting faces, lubrication is limited because there is little or no product movement in the back of the stuffing box. As the product heats up and its liquid is evaporated, the lubricating properties are lost, creating more friction and causing the seal to fail.

Moyno, Inc. (Springfield, Ohio) believes it has solved this problem with its PowerSeal. To provide a better fit for mechanical seals, Moyno machined the casting to open up the stuffing box and provide a longer gland to position seal faces in the flow stream. A continuous flow of product over the seal faces keeps the seal cool and prevents concentration of the product, says Dave Doty, Moyno’s technical sales engineer. The PowerSeal features a thick cross section for long service life and more-effective handling of the high starting torques often encountered with solids-laden slurries.

At Woodex Bearing (Georgetown, Me.), Meco single-face seals, originally designed as replacements for troublesome double-face seals in high-temperature and high-speed applications, are being used for vapor containment in process vessels. The outside face seal (OFS) is well suited for top-entry agitator shafts, where long, cantilevered shafts can exhibit high runout and angular misalignment. The seal can be constructed without elastomers, for use with aggressive chemistries.

Last summer, John Crane introduced a live-loaded, mechanical packing-cartridge seal for static or dynamic sealing applications. The Type LMPC seal is designed for use in all types of process equipment, including mixers, agitators, pumps, valves and cylinders. “In the past, there was no standalone unit for these kinds of sealing applications,” says Alfred Cooper, the company’s engineering supervisor. “Users had to assemble a lot of pieces, costing time and money.”

Viking Pump (Cedar Falls, Iowa) has added customizable shaft seals to the list of sealing systems available for its pump products, including a series of gear pumps that is widely used for rubber and polymer processes with viscosities from water thin to 500,000 cP. Seal options range from multiple-lip seal designs to flushed or quenched double mechanical seals. The company also makes sealless magnetic drives. Customizable seals allow pump configurations to be tailored for maximum performance and lower operating costs.

At Achema, Flowserve Flow Solutions will exhibit its GCX single mechanical-cartridge pump seal. This system is designed for applications where the operator may want to put different chemicals though an ANSI or DIN pump, and run cleanout processes in between changeovers, but doesn’t want to change the seal, says product manager Thomas Bennett.

Offered as an alternative sealing system for industrial and petrochemical applications where elastomers are likely to fail, GCX is constructed of grafoil, a graphite foil that withstands temperatures from –40 to 400Ëš F (204 ËšC). Installed in an amines plant in Louisiana, where prior seal life was six weeks, the GCX operated the full year, until the plant’s annually scheduled shutdown for maintenance and repair.

Bennett is careful to make the point that GCX does not compete with elastomers. To the contrary, he says, elastomers are preferable for service involving oxidizers, such as bromine and chlorine, which are incompatible with grafoil.

A proprietary elastomer is the backing for a non-rotating PTFE seal featured on Chemineer’s (Dayton, Ohio) new Clean Sweep sanitary mixer. A replacement for conventional mechanical seals, this diaphragm seal provides hermetic sealing and eliminates the particle shedding associated with mechanical seals. “Changeout is easier, and costs absolutely are more economical” says Jason Hora, a Chemineer applications engineer.

Typically, mechanical seal components, including the mounting flange, have to be polished. In contrast, only Clean Sweep’s mounting flange has to be polished, not the seal itself. And because the seal is made of PTFE, it doesn’t require any special treatment. The mixer does not rotate; instead, the pendulum motion of the shaft causes the mixer to gently flex back and forth.

Global gaskets

According to Garlock’s Plaisier, 60% of fugitive emissions are caused by valves. To achieve further emissions reductions, the company has developed a special valve stem packing, EVSP9001M.

Gaskets will guide Teadit N.A., Inc.’s (Houston) next drive into the U.S. market. Already commercialized in Europe, this firm’s reinforced PTFE gasket will be targeted for chlorine or other aggressive chemical service, says Doug Wade, Teadit’s U.S. sales manager. Called a kammprofile gasket, it can be customized for applications ranging from pipelines to pressure vessels, and for operation at high temperatures and pressures.

A.W. Chesterton (Stoneham, Mass.) is calling on customers with a new valve sealing system. KVSP valve packing combines Kalrec perfluoroelasotomer V-rings and Vespel backup components. Because the V-rings have very low frictional characteristics, low loading forces are sufficient to activate and seal them, while backup components support the sealer rings.

So customer-centric are some seal and gasket marketers that they may be missing out on bigger opportunities. W.L. Gore & Associates (Elkton, Md.), for example, reports that its Universal Pipe Gasket, introduced in early 2005, is finding widespread acceptance in process piping applications. Apparently, the prospect of standardizing gaskets across steel, glass-lined steel and fiber-reinforced plastic systems could realize significant savings in overall sealing costs, and inventory management is worth a try.

PPE’s Turland expects the sealing industry will turn its interests to composites that accommodate broader and more-universal types of products. For example, PPE has developed Perlast G75S, a perfluoroelastomer reinforced with nanofillers, that matches the traditionally better physical performance of perfluoroelastomers reinforced with carbon black. Like most sanitary seals, Perlast G75S is compliant with the pharmaceutical standards of the U.S. Food and Drug Administration (Washington, D.C.). Thermally stable at temperatures to 260Ëš (500Ëš F), G75S can withstand aggressive chemicals, making the seal available for a wider range of applications. For example, processors have the option of standardizing with a single perfluoroelastomer, reducing inventory.

Innovations in nanotechnology, Turland believes, will drive this trend. “In fluoroelastomers, we have 60 grades of products to match physical properties with exactly what customers want,” he says. “In a few years, as we move to nanotechnology, the number of grades will be fewer than 10.”

 

Deborah Hairston

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