Stainless Steel Flange Seal Failure Analysis: Performance of Different Gasket Materials (Graphite/PTFE) Under High Temperature and Pressure

Stainless steel flanges are everywhere in industrial plants—connecting pipes in oil refineries, holding together reaction vessels in chemical factories, and sealing steam lines in power plants. But here’s a quiet problem that costs factories millions every year: seal failure. A single leaky flange can waste 10.000+ gallons of fluid annually, trigger safety shutdowns, or even cause fires if the fluid is flammable. And 9 times out of 10. the failure boils down to one thing: the wrong gasket material for the job.

Two of the most common gasket materials for stainless steel flanges are graphite and PTFE (polytetrafluoroethylene, better known by the brand name Teflon). Both work well in mild conditions, but when temperatures climb above 200°C and pressures exceed 10 MPa (that’s 1450 psi)—the kind of environment you find in a refinery’s distillation tower or a chemical plant’s reactor—their performance diverges sharply.

A maintenance supervisor at a Texas oil refinery summed it up: “We used PTFE gaskets on a steam line that ran at 250°C. Within 3 months, every flange was leaking—we had to shut down the line for 2 days to replace them with graphite. That mistake cost us $80.000 in lost production. Now we never guess which gasket to use; we test first.”

This article breaks down why stainless steel flange seals fail, how graphite and PTFE gaskets perform under high temperature and pressure, and how to pick the right one for your industrial setup. We’ll use real failure cases, lab test data, and simple explanations—no confusing engineering jargon, just what you need to keep your flanges leak-free.

Why Stainless Steel Flange Seals Fail (It’s Rarely the Flange Itself)

Before we compare gaskets, let’s get one thing straight: stainless steel flanges (usually 304 or 316) are tough. They rarely crack or warp under high temp/pressure—most seal failures come from the gasket. Here are the top three gasket-related reasons seals fail:

1. Gasket Material Breaks Down (High Temperature)

When a gasket gets too hot, it can soften, melt, or even burn. A softened gasket can’t hold its shape, so fluid seeps through the gap between the flange and the gasket. A melted gasket leaves a sticky residue that’s impossible to seal—you have to replace the entire gasket.

2. Gasket Compresses Too Much (High Pressure)

Pressure pushes the flange faces together, compressing the gasket. If the gasket is too soft, it compresses beyond its “recovery limit”—meaning when the pressure drops (like during a plant shutdown), the gasket can’t bounce back. This leaves a gap, and the next time the system starts up, it leaks.

3. Gasket Doesn’t Seal Tiny Flange Imperfections

No flange face is perfectly smooth—even brand-new ones have tiny scratches or dents (usually 0.1–0.5mm deep). A good gasket should “flow” into these imperfections to create a tight seal. If the gasket is too hard or brittle, it can’t fill the gaps, and fluid leaks through.

A lab technician who tests gaskets said: “Flange failure is a misnomer. It’s almost always gasket failure. The flange is just the messenger—if the gasket can’t handle the conditions, the seal will break.”

Graphite Gaskets: How They Perform Under High Temp/Pressure

Graphite gaskets (often reinforced with metal mesh or fiber) are the workhorses of high-temperature, high-pressure (HTHP) industrial systems. Here’s how they stack up:

1. Temperature Resistance: Handles Up to 650°C (1200°F)

Graphite’s biggest strength is its ability to stand extreme heat. Unlike PTFE, which starts to soften at 260°C, graphite stays stable up to 650°C (and even higher in inert environments, like nitrogen gas). This makes it perfect for steam lines, boiler systems, and furnace exhaust pipes.

A test by the American Society of Mechanical Engineers (ASME) showed:

Graphite gasket at 300°C: No softening, no leakage under 15 MPa pressure.

Graphite gasket at 500°C: Slight hardening, but still sealed perfectly at 12 MPa.

A chemical plant in Louisiana uses graphite gaskets on a reactor flange that runs at 400°C and 18 MPa. “We check the flanges every 6 months—no leaks, no gasket degradation,” the plant engineer said. “We used to replace gaskets every year; now we go 3+ years.”

2. Pressure Resistance: Up to 35 MPa (5000 psi)

Graphite is rigid enough to handle high pressure without over-compressing. Most graphite gaskets have a “compression rate” of 15–20%—meaning they’ll compress 15% of their thickness under pressure, then bounce back when pressure drops. This keeps the seal tight even during pressure fluctuations (common in batch processing plants).

Compare that to soft rubber gaskets, which can compress 40%+ and never recover. A refinery in Oklahoma tested graphite vs rubber gaskets on a 20 MPa crude oil line: the rubber gaskets leaked after 1 month (from over-compression); the graphite ones lasted 2 years.

3. Sealability: Fills Flange Imperfections

Graphite is slightly malleable—when you tighten the flange bolts, it flows into tiny scratches or dents on the flange face. This creates a “conformable” seal that’s hard to beat. A lab test with a flange that had 0.3mm deep scratches showed:

Graphite gasket: No leakage at 10 MPa.

Rigid metal gasket: Leaked 5 mL/hour at 10 MPa.

The Catch: Graphite Needs Careful Handling

Graphite gaskets are strong, but they’re also brittle. If you drop one or bend it too far, it can crack. Also, they’re not great with strong oxidizing chemicals (like concentrated nitric acid)—the acid can react with graphite and break it down. But for most HTHP industrial applications (steam, oil, natural gas), they’re unbeatable.

PTFE Gaskets: How They Perform Under High Temp/Pressure

PTFE gaskets are popular because they’re cheap, chemical-resistant, and easy to install. But they struggle in HTHP conditions. Here’s the reality:

1. Temperature Resistance: Max 260°C (500°F)—Beyond That, It Fails

PTFE has a “melting point” of 327°C, but it starts to soften and lose strength at just 260°C. Above 260°C, it becomes “creepy”—meaning it slowly flows out from between the flanges, leaving gaps.

A test by a gasket manufacturer showed:

PTFE gasket at 200°C: Sealed perfectly at 10 MPa.

PTFE gasket at 280°C: Started creeping after 4 hours; leaked 10 mL/hour at 10 MPa.

PTFE gasket at 300°C: Melted after 8 hours; complete seal failure.

This is why PTFE is a bad choice for steam lines (which often run at 250–300°C) or high-temperature reactors. A food processing plant in Georgia made this mistake: they used PTFE gaskets on a 270°C oven exhaust flange. The gaskets melted, and the exhaust leaked smoke into the plant—forcing a 1-day shutdown.

2. Pressure Resistance: Max 15 MPa (2175 psi)—Over That, It Compresses Too Much

PTFE is softer than graphite, so it compresses more under pressure. At pressures above 15 MPa, it often compresses beyond its recovery limit—meaning when pressure drops, it can’t bounce back, and the seal leaks.

A brewery in Colorado used PTFE gaskets on a 18 MPa CO₂ line. After the first batch of beer, the gaskets had compressed 30%—they leaked CO₂ so badly, the brewery lost 5% of its CO₂ supply. They switched to graphite, and the leaks stopped.

3. Sealability: Good for Smooth Flanges, Bad for Imperfect Ones

PTFE is stiffer than graphite, so it can’t fill deep scratches or dents on flange faces. If your flange is brand-new and perfectly smooth (0.05mm or less imperfections), PTFE works. But if the flange is old or has been scratched (0.1mm+), it will leak.

A maintenance technician said: “I only use PTFE on new flanges in low-temp, low-pressure lines—like water pipes or mild chemical lines. For anything hot or high-pressure, it’s graphite all the way.”

The Upside: PTFE Is Chemical-Resistant

PTFE can handle almost any chemical—from strong acids (hydrochloric acid) to solvents (acetone)—without breaking down. This makes it ideal for chemical plants that handle corrosive fluids but don’t have HTHP conditions. A pharmaceutical plant in New Jersey uses PTFE gaskets on a 150°C, 8 MPa line that carries hydrochloric acid—they last 2 years with no issues.

Real-World Failure Case: Graphite vs PTFE on a Refinery Steam Line

A refinery in California had a 250°C, 12 MPa steam line that connected its boiler to its distillation tower. The line had 12 stainless steel flanges—6 with PTFE gaskets, 6 with graphite gaskets. Here’s what happened over 6 months:

PTFE Gasket Flanges

After 2 months: 2 flanges started leaking small amounts of steam (1–2 mL/hour).

After 4 months: 4 more flanges leaked; the worst one leaked 10 mL/hour (enough to create a safety hazard from hot steam).

After 6 months: All 6 PTFE gaskets were replaced—cost $12.000 (parts + labor) and 8 hours of line shutdown.

Graphite Gasket Flanges

After 6 months: 0 leaks. The gaskets still looked new when inspected. No replacement needed.

The refinery’s maintenance manager said: “We wanted to save money by using PTFE, but it ended up costing more. Now we use graphite on all steam lines—even if it’s a little more expensive upfront, it’s cheaper long-term.”

How to Choose Between Graphite and PTFE Gaskets

Use this simple checklist to pick the right gasket for your stainless steel flange:

Choose Graphite If:

Temperature >260°C (500°F)

Pressure >15 MPa (2175 psi)

Flange has scratches/dents (0.1mm+ deep)

Fluid is steam, oil, natural gas, or non-oxidizing chemicals

Choose PTFE If:

Temperature ≤260°C (500°F)

Pressure ≤15 MPa (2175 psi)

Flange is new/smooth (≤0.05mm imperfections)

Fluid is corrosive (acids, solvents) or food-grade (PTFE is FDA-approved)

A gasket supplier summed it up: “Graphite is for ‘tough’ conditions—hot, high-pressure, rough flanges. PTFE is for ‘gentle’ conditions—cool, low-pressure, smooth flanges. Mix them up, and you’ll have leaks.”

Common Mistakes That Cause Gasket Failure (Even With the Right Material)

Picking the right gasket is half the battle—installing it wrong can still cause failure. Here are the three most common mistakes:

1. Over-Tightening or Under-Tightening Bolts

Bolts need to be tightened to a specific torque (measured in N·m or ft-lbs) to compress the gasket just enough. Over-tighten, and you’ll crush the gasket (especially PTFE); under-tighten, and the gasket won’t seal.

A chemical plant in Ohio under-tightened graphite gasket bolts: the flanges leaked 5 mL/hour of ammonia gas. A quick torque check (they should have used 80 N·m, but only used 50 N·m) and re-tightening fixed the problem.

2. Reusing Old Gaskets

Gaskets are “one-time use” items. Even if a graphite gasket looks good after removal, it’s lost its ability to recover from compression. Reusing it will almost always cause leaks. A brewery in Oregon reused PTFE gaskets on a CO₂ line—they leaked within a week.

3. Ignoring Flange Face Condition

Before installing a new gasket, clean the flange face and check for scratches. If the face is too rough (0.5mm+ deep scratches), you’ll need to resurface it (with a grinding tool) or use a more conformable gasket (like graphite). A refinery in Texas installed a PTFE gasket on a flange with 0.3mm scratches—it leaked immediately.

Conclusion

Stainless steel flange seal failure is avoidable—you just need to pick the right gasket material for the job. Graphite gaskets are the go-to for high temperature (up to 650°C) and high pressure (up to 35 MPa) conditions; they seal well even on rough flanges and last for years. PTFE gaskets work great for cool, low-pressure, or corrosive environments, but they fail fast when temps or pressures climb too high.

For industrial plants, the key is to stop guessing and start testing. Know your system’s temperature and pressure, check your flange’s condition, and choose a gasket that matches. A 20 grap hit egasket might cost more than a 5 PTFE one, but it will save you thousands in repair costs and lost production.

As one engineer put it: “A good gasket is invisible—you never think about it because it never leaks. A bad gasket is a nightmare—you’re always fixing leaks and shutting down lines. Invest in the right one, and you’ll sleep better at night.”