gasket

A gasket is a shaped piece of compressible material placed between two mating surfaces to create a fluid-tight seal under mechanical compression. When bolted or clamped together, the gasket deforms slightly and fills microscopic irregularities in the flanges, preventing leaks of liquids, gases, or steam across the joint. It is one of the most common and cost-effective sealing methods in industrial equipment, from small threaded connections to large pressure vessels and pump casings.

Gasket materials vary widely depending on operating conditions. Cork-rubber compounds work well for moderate temperatures and pressures in automotive and general machinery applications. Nitrile rubber (NBR) seals oils and fuels. Neoprene resists weather and ozone. For high temperatures, manufacturers use graphite-impregnated materials, PTFE (Teflon), or spiral-wound metal-and-elastomer composites rated to 600 degrees Celsius or higher. Gaskets must match the fluid being sealed: a gasket suitable for water may fail against solvents or aggressive chemicals. Pressure rating, temperature range, and chemical compatibility are the three critical selection criteria.

The most common failure mode is creep, in which the gasket material slowly compresses over months or years under constant clamping load, causing the joint to loosen and weep. Thermal cycling accelerates this process by causing the gasket and metal flanges to expand and contract at different rates. Poor flange finish, inadequate bolt tension, or reuse of a single-use gasket will also cause leaks. Conversely, over-tightening bolts can extrude the gasket material or damage the seal faces themselves.

Gasket types and construction

Sheet gaskets are cut from uniform material stock and remain the workhorse for flanged connections. Ring gaskets (such as oval or octagonal cross-sections) are used in pipe fittings and valves where they sit in grooved seats. Spiral-wound gaskets consist of alternating strips of metal (usually stainless steel) and elastomer wrapped in a spiral, offering high reusability and excellent performance in thermal cycling. Semi-metallic gaskets add graphite or PTFE to elastomer for better chemical and temperature resistance. Corrugated gaskets include a metal core to prevent extrusion of softer materials under pressure.

Proper installation requires clean, undamaged flange surfaces and correct bolt tightening sequence, usually a cross-pattern or star pattern to ensure even compression. Bolt preload specifications are critical: insufficient tension leaves gaps; excessive tension damages the gasket or flange. In critical applications such as pressure vessels or chemical reactors, gasket assembly is documented and torque values are recorded to verify joint integrity before service.