Common Classifications of Gasket Materials and Comparison of Sealing Performance

1. Non-Metallic Gaskets: Flexible and Versatile

Non-metallic gaskets are the go-to for low to medium pressure systems, thanks to their flexibility and ability to conform to uneven flange surfaces. They're usually made from materials like rubber, fiber, or polymers—let's break down the most common types.

Rubber Gaskets

Rubber is a classic for a reason: it's elastic, cheap, and easy to work with. You'll find rubber gaskets in everything from household plumbing to industrial valves. But not all rubber is the same—here are the key varieties:

• Nitrile (Buna-N): Great for oil and fuel systems (think petrochemical facilities). It stands up to mineral oils, gasoline, and hydraulic fluids but struggles with high temperatures (max around 120°C).
• EPDM (Ethylene Propylene Diene Monomer): The champion of weather and chemical resistance. EPDM handles water, steam, acids, and alkalis, making it ideal for outdoor pipeline works or water treatment plants. It can take temperatures up to 150°C (sometimes higher with special formulations).
• Love high heat? Silicone gaskets work well up to 200°C (even 300°C for short periods) and are resistant to ozone and UV light. But they're not great with oils or fuels—stick to water or air systems here.
• A good all-rounder. Neoprene resists oils, chemicals, and abrasion, plus it's weatherproof. You'll see it in marine applications (like ship-building) or where the gasket might be exposed to saltwater.

Compressed Fiber Gaskets

These are made from plant fibers (like cellulose) or synthetic fibers (aramid, glass) mixed with a binder (rubber or resin). They're thicker than rubber gaskets and often used in low-pressure, low-temperature systems—think HVAC ducts or plumbing for structure works.

One thing to note: traditional asbestos fiber gaskets were once popular for their heat resistance, but they're now banned in most countries due to health risks (asbestos fibers can cause lung diseases). Today, you'll find asbestos-free alternatives like aramid fiber gaskets, which offer similar heat resistance without the hazards.

PTFE (Teflon) Gaskets

PTFE—you know, the stuff on non-stick pans—might be the most chemically resistant material out there. It can handle almost any fluid: acids, bases, solvents, even molten salts. That's why it's a staple in chemical processing plants. But there's a catch: PTFE is stiff, so it doesn't conform to flange surfaces as easily as rubber. It also has poor thermal conductivity, which can be an issue in heat efficiency tube systems where heat transfer matters. And while it handles high temperatures (up to 260°C), it starts to degrade above 300°C.

Graphite Gaskets

Graphite gaskets are like the non-metallic heavyweights. Made from pure graphite or graphite-impregnated fibers, they handle extreme temperatures (up to 650°C in oxidizing environments, 3000°C in non-oxidizing!) and high pressures (up to 200 bar). They're also chemically inert, so they work with acids, alkalis, and hydrocarbons. The downside? They're brittle and can't handle much flexing, so they need smooth flange surfaces and careful installation.

2. Metallic Gaskets: Built for High Pressure and Temperature

When the going gets tough—think high-pressure pipeline works, power plant boilers, or marine engines—metallic gaskets take over. They're rigid, strong, and designed to withstand the harshest conditions. Here are the main types:

Solid Metal Gaskets

These are exactly what they sound like: a solid piece of metal (usually copper, aluminum, steel, or nickel alloys). They're used in ultra-high pressure systems, like those found in oil and gas pipelines or nuclear facilities (ever heard of RCC-M Section II nuclear tubes? Yeah, those need serious gaskets).

Copper and aluminum gaskets are soft, so they conform well to flanges but can't handle as much pressure as steel. Steel gaskets (carbon or stainless steel) are tough but require perfectly smooth flanges—even a small scratch can cause a leak. Nickel alloy gaskets (like Monel or Incoloy) are the top tier, resisting corrosion and high temps (up to 1000°C+) for aerospace or petrochemical applications.

Ring-Type Joint (RTJ) Gaskets

RTJ gaskets are the rock stars of high-pressure sealing. They're circular metal rings with a cross-section that's either oval or octagonal, designed to fit into a groove on the flange. When tightened, the metal deforms slightly, creating a metal-to-metal seal that can handle pressures up to 15,000 psi (that's over 1000 bar!). You'll see them in offshore oil rigs, refineries, and any system where failure isn't an option.

3. Composite Gaskets: The Best of Both Worlds

Why choose between non-metallic and metallic when you can have both? Composite gaskets combine the flexibility of non-metallic materials with the strength of metal, making them perfect for medium to high pressure systems.

Spiral Wound Gaskets

These are probably the most common composite gaskets. They're made by winding a thin metal strip (usually stainless steel) and a filler material (like graphite or PTFE) together, forming a spiral. The metal provides strength and resilience, while the filler handles the sealing. Spiral wound gaskets work in a huge range of conditions: pressures up to 420 bar and temperatures from -200°C to 1000°C. They're used everywhere from chemical plants to power stations—basically, any system where you need a reliable seal under stress.

Metal-Clad Gaskets

Imagine a non-metallic core (like asbestos-free fiber or graphite) wrapped in a thin metal sheet (aluminum, copper, or stainless steel). That's a metal-clad gasket. The metal shell protects the core from damage and improves handling, while the core provides flexibility. They're great for high-temperature systems with moderate pressure, like in boiler tubing or heat exchanger tubes.

Flange Surface Finish

Ever tried to seal a leak with a rough, pitted flange? It's like trying to stack blocks on a bumpy table—no matter how hard you press, there will be gaps. Non-metallic gaskets (like rubber or PTFE) need smoother surfaces (Ra 1.6-3.2 μm) to conform, while metallic gaskets can handle slightly rougher finishes but still require precision.

Bolt Tension (Stud Bolt & Nut Torque)

Too loose, and the gasket won't compress enough to seal; too tight, and you'll crush the gasket or warp the flange. Getting the right torque on the stud bolt & nut is crucial. Most manufacturers provide torque charts based on gasket material and flange size—always follow those!

Flange Alignment

Misaligned flanges put uneven pressure on the gasket, leading to leaks. Even a small offset can cause the gasket to compress more on one side than the other. Take the time to align flanges properly before tightening the bolts—it'll save you headaches later.

Power Plants & Aerospace

In power plants, boilers and heat exchangers deal with superheated steam (temperatures over 500°C, pressures over 100 bar). Here, spiral wound gaskets with graphite filler or solid metal gaskets (like nickel alloys) are the norm. They can handle the extreme conditions without degrading. Aerospace applications (think jet engines) use similar high-performance materials, often nickel-cr-fe alloy gaskets, to seal fuel and hydraulic lines in tight, high-vibration spaces.

Marine & Ship-Building

Saltwater is brutal on materials, so marine gaskets need to resist corrosion. EPDM rubber gaskets work well for freshwater systems, while copper-nickel flanges paired with PTFE or graphite gaskets are common for seawater lines. For high-pressure fuel or hydraulic systems on ships, spiral wound gaskets with stainless steel windings are the go-to.

Petrochemical Facilities

Petrochemical plants handle everything from crude oil to corrosive solvents. PTFE gaskets are ideal for chemical lines, while nitrile rubber works for oil and fuel systems. For high-pressure distillation columns or reactor vessels, RTJ gaskets ensure no leaks—critical when dealing with flammable or toxic chemicals.