What Are Gaskets?

Gaskets are mechanical sealing elements placed between two mating surfaces to prevent the leakage of fluids, gases, or contaminants under conditions of pressure, temperature, and vibration. They work by conforming to surface irregularities when compressed by bolts or clamping forces, filling microscopic gaps that would otherwise allow leakage paths. Gaskets are found in virtually every industry that involves contained fluid systems, from automotive powertrains and chemical processing plants to aerospace assemblies and power generation equipment.

The design of a gasket involves balancing three competing requirements: sufficient compressibility to conform to mating surfaces, adequate strength to resist blowout under internal pressure, and chemical compatibility with the fluid being sealed. Material selection, contact stress distribution, and surface finish of the mating flanges all influence sealing performance. Standards governing gasket dimensions and materials for piping systems include ASME B16.20, which specifies ring-joint, spiral-wound, and metal-jacketed gasket types for use with flanges defined in ASME B16.5 and API-6A.

Materials and Construction

Gasket materials span a wide range, from soft nonmetallics to solid metals, and selection depends on the process temperature, pressure, and chemical environment. Rubber and elastomeric gaskets serve in low-pressure water and HVAC systems. Compressed fiber sheet gaskets, made from aramid fibers, glass, or cellulose bound with rubber or resin, are used in general industrial service. Polytetrafluoroethylene (PTFE) gaskets offer excellent resistance to corrosive chemicals and are common in pharmaceutical and chemical processing applications.

For higher pressures and temperatures, spiral-wound gaskets alternate thin metal strips, typically stainless steel, with soft filler materials such as flexible graphite or PTFE. This construction combines metal strength with filler conformability and can handle temperatures above 850°F and pressures exceeding 1,500 psi. Solid metal ring-joint gaskets, machined from soft iron, steel, or Monel, seat against precision-machined grooves in the flange face and are used in high-pressure oil and gas wellhead equipment where blowout consequences are severe.

Sealing Mechanisms and Performance

A gasket seals by developing a contact stress, expressed in pounds per square inch or megapascals, that exceeds the fluid pressure seeking to escape. Standards define a seating stress, the minimum bolt load per unit of gasket contact area required to achieve initial seating, and a maintenance stress, the minimum load that must remain after all relaxation losses to sustain the seal. Relaxation occurs because gasket materials creep under sustained compressive load, and bolts also relax through thermal cycling and vibration. The Fluid Sealing Association's industry standards resources document the test methods and performance criteria used to characterize these behaviors.

Blowout resistance depends on the ratio of the sealing force to the hydrostatic end force trying to separate the flanges. Proper bolt loading, as specified in ASME PCC-1 guidelines for pressure boundary bolted flange joint assembly, is critical to ensuring that the gasket remains in compression throughout the operating cycle.

Applications

Gaskets have applications in a wide range of disciplines, including:

• Engine cylinders and exhaust manifold sealing in internal combustion and diesel engines
• Pipe flange connections in oil refineries, chemical plants, and water treatment facilities
• Pressure vessel and heat exchanger assembly in power generation and petrochemical processing
• Aerospace fuel system and hydraulic line sealing under extreme temperature ranges
• Pharmaceutical and food processing equipment requiring cleanable, chemical-resistant joints
• Valve bodies and pump housings in fluid-handling systems