Give gaskets a squeeze

Sept. 16, 2004
Reevaluate gasket use when operating conditions or maintenance procedures change.
Gaskets are critical but often-neglected components of plant piping systems. They may be unimposing and modest-cost items, but they play an important role by keeping process fluids inside pipes and equipment. Misapplied gaskets lead to leaking flanges — and potentially severe safety, environmental, operating and product-quality consequences.The most common types of gaskets in process plants include solid-composition (polymer, fiber or other material), ring-joint, O-ring, spiral-wound and solid-metal designs. All have suitable applications.However, as the following example highlights, a gasket that might have been suitable in initial conditions may not continue to be the right choice as plant operations evolve.The damaged gasket shown at the top of the article is made of polytetrafluoroethylene (PTFE). Such gaskets were installed in numerous raised-face and slip-jointed flanges. However, during a 20-year span, the plant’s product slate completely changed, requiring much higher operating temperatures. Yet, the gasket material and type were never reviewed. Since the gaskets no longer sealed, the unit “steamed” with a mixture of water and solvent escaping from nearly all its major flanges.As part of resolving various operating problems, new gaskets were chosen. You must consider flange details, process fluid and operating conditions when selecting a gasket. For this process, the best choices were spiral-wound or solid-metal gaskets. Spiral-wound designs have layers of V-shaped metal and gasket material wound to create a gasket. They also have a centering ring on either the inside diameter or outside diameter of the gasket, or both. Under load, the V-shaped metal in the spiral compresses, sealing the process. Maintenance procedures must account for the gasket types in use. Because the flange load permanently compresses the metal in the gasket, a second use often leads to process leaks. Treat spiral-wound gaskets as single-use items; procedures to prevent reuse must be in place.Solid metal gaskets are more expensive. This type of gasket consists of a grooved metal plate with a process-compatible sealer filling the groove. Under load, the material in the groove compresses and seals the process. With proper maintenance, which includes sealer reapplication, these gaskets can be reused.In this plant, the PTFE gaskets were replaced with solid metal ones. These gaskets were a better choice than spiral-wound designs due to the relatively short run length of the unit (less than six months between cleanings for product changeover). Product leaks stopped immediately and unit control and product quality improved dramatically. Gaskets may be humble, but don’t let them humble you. Andrew Sloley is contributing editor for Chemical Processing magazine.

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