Raising maintenance standards to extend uptime and avoid maintenance crises
By Ed SullivanEd Sullivan is a technical writer based in Hermosa Beach, CA. He can be reached at email@example.com‘Chronic leaks and blowouts of heat exchanger gaskets, for example, can bring an entire process down.’
SteelTrap gaskets for the main drums. "We're very pleased with the performance of these gaskets,” he says. “We've had no cycling problems and the overall cost savings has been very substantial." Cost is often the issue when gaskets are specified. When compared with spiral wound gaskets, the graphite-stainless technology is similar in cost, but offers substantial savings in other ways. For example, if you live load a SteelTrap gasket, Chesterton and Sealing Corp. will guarantee it for three years of leak-free service. "Whether it's a static application or a temperature cycling application, if it's live loaded, it will be covered by the warranty,” says McCoy. “No one else in the industry will do that," says McCoy. At a Texas refinery, Chesterton installed graphite-stainless gaskets on over 300 valves. Over a three-year period, approximately 20 of those valves required servicing. So, the user not only got years of worry-free service life, but any incidental problems were serviced by the supplier. "The cost of the gasket is not the question," says Vance St. Jean, Sales Manager for Chesterton in Houston, TX. "Your costs aren't really dependent on the sealing device. Your costs are associated with changing it out - the labor, the downtime the process disruptions and the other problems. Once I explain that to one of our refinery customers, they agree with me. Doing it right might be worth thousands of dollars or it might be worth millions of dollars. It depends on the situation." "The graphite-stainless gasket is also much more forgiving in terms of poor bolting procedures and imperfect conditions of flange plate surfaces," McCoy adds. "Unlike other gaskets that creep or cold-flow under load, and you lose gasket volume, the SteelTrap eliminates that problem - takes it to zero. Because of the convolutions of the metal, the sealing material is trapped on all sides by metal. That's where the gasket got its name." McCoy adds that many gaskets can be attacked by the sealing medium. Flexible graphic is a durable sealing medium, but some chemicals will attack it. In those applications, the graphite is replaced with PTFE, as long as the application is within PTFE's temperature limitations. "If you have a chemical application that requires PTFE, then you have always lived with creep relaxation, or cold-flow, and consequential sealing loss," says McCoy. "But with the SteelTrap there is no more concern for cold-flow or creep relaxation." Spiral wound gaskets are designed for use within specified pressure ranges. Since most users have different pressure ranges throughout their plants (e.g. 150, 300, 900, 1200, 1500 PSI) that means you need different gasket for each size of gasket you need within each of those pressure ranges. That's a lot of inventory. Because the equivalent graphite-stainless gasket is self-locating and applicable to pressures ranging from 150 to 2,500 PSI, the inventory requirement is much lower. "A tremendous cost savings to the customer," says McCoy. St. Jean adds that older gasket technologies such as the popular spiral wound gaskets are still appropriate for a lot of routine applications. "The graphite-stainless gasket is a superior one for many applications," he says. "You can live load a SteelTrap gasket, put springs on both sides of the stud, and you're done. The heat exchangers I've put them in - they were all high temperature applications running at 1,000-1,100°, and they seem to perform well." Heat exchangers may be the quintessential test for gasket technology, with opposing temperature zones, and differing loads on both sides the gasket. The resulting stresses translate into a "live load" requirement that too often results in frequent service, including gasket changes that are cumbersome and time-consuming. "Heat exchangers are engineered-to-order equipment," says Ron Shipman, Chief Engineer at Fabsco Sheet & Tube, Tulsa, OK. "At one time we had some leaks in our exchangers, but they have been mainly high temperature, high pressure, and a cycling service. That's where we elected to use the Selco SteelTrap gaskets, and they have worked well for us. Very seldom do I have to a case that that won't fix. If I have severe cycling, like in power plants, there's nothing short of welding that can solve their needs, but we do the next best thing with SteelTrap gaskets." George Pyros, an engineer with Siemens Westinghouse agrees. "These gaskets have proven to be a successful solution to preventing leaks in several heat exchangers," he says. "They prevent leakage whether of the gas or the water from the heat exchangers, which are typically used on combined cycle power plants." While reasonably priced in comparison with spiral wound gaskets, the graphite-stainless ones are considerably more expensive than standard compression gasket material. "But that requires cutting," McCoy says, "and perhaps 60 percent of the material is wasted. Also, you have all the added labor time and cost. Plus, many of the compression gasket materials that are manufactured today have binders in them, and the binders can be attacked by the sealing media. When that happens, the gaskets lose volume and the ability to hold the seal. So, the price difference has little to do with the outcome." "One application we had was constantly leaking," says Jim Lawrence of Sealing Resources, Sylvania, OH. "It was a flange on a valve sealing nitric acid at about 130°F at a major chemical processing plant. For this application, anything they tried failed immediately. The current solution for this application was a spiral wound PTFE gasket and it was constantly leaking. We've had great results with the graphite-stainless gasket, so we made the change to that. We also live-loaded them with Chesterton 5500 flange disc springs. Now they've gone through two thermal cycles with no failure. They're running 24/7, and now we're looking at converting the entire plant to that sealing solution." Offering an advanced gasket that provides low seating stress and a thermally stable seal that is fire safe, blowout safe and requires no re-torquing would appear to be a slam-dunk solution at most industrial plants. "A gasket purchasing decision may come down to ‘Is the problem bad enough? Are they leaking enough?’ But the real question is, ‘Do they want the problem to go away?’" says St. Jean. "We've had a lot of success with the SteelTrap at refineries that do a lot of hot oil pump suction and discharge valves, where they have a lot of cycling. Unlike some customers, those guys are aware of problems - when there is oil dripping on the ground, or when there are fugitive emissions problems. So maybe they're more likely to want to fix it right."
Imperfect Mating Surfaces
Another important advantage of advanced graphite-stainless gaskets is the ability to deal with imperfect mating surfaces. "This is particularly true when you're dealing with hot surfaces," says Greg Gravenmeir at Sealing Specialists, MO. "The graphite-stainless design is one of the better gaskets you can use. With the corrosion and pitting that can damage flange surfaces, and Selco's ability to move the sealing ring to different positions on the gasket face, enables you to put that ring into a position that may be more advantageous. In some instances that might allow you to use a heat exchanger that is not in the best condition." Bolting, including proper torquing is extremely important to the success of any gasket. Proper bolting techniques are sometimes overlooked in industry today, which has resulted in poor gasket sealing. "That is another benefit of the graphite-stainless gasket technology - the gasket is much more forgiving for poor bolting procedures," says McCoy. "Thicker standard gaskets are more susceptible to blowing out if they are not bolted down correctly."