The gasket selection decision seems simple — until a leaking flange causes a chemical plant shutdown, or a prematurely failed seal results in contamination of a pharmaceutical batch. Choosing between PTFE gaskets and metal gaskets is a fundamental engineering decision that depends on the chemical service, temperature, pressure, flange condition, and the sealing reliability requirement of your application. This guide gives you a structured framework to make the right choice.
Head-to-Head Comparison
| Factor | PTFE Gasket | Metal / Spiral Wound Gasket |
|---|---|---|
| Chemical resistance | Excellent — resists virtually all process chemicals | Depends on metal — stainless handles most, but acids attack carbon steel; HF attacks SS |
| Temperature range | –200°C to +260°C (continuous) | Stainless: –100°C to +500°C+; carbon steel: up to 400°C |
| Pressure range | Up to ~100 bar (full face); limited by cold flow | High pressure capable (150+ bar with correct gasket type) |
| Flange face requirements | Low — conforms to imperfect and corroded faces | High — requires smooth, parallel, undamaged faces |
| Bolt load requirement | Low — seals at low bolt load; suitable for glass-lined flanges | High — requires significant bolt torque to seat metal |
| Re-use | Generally single use — replace at each opening | Metal ring gaskets are generally single use; kammprofile may be reused |
| Cost per gasket | Low–moderate | Moderate–high (spiral wound, kammprofile) |
| Available immediately? | Yes — stock sizes available same day | Spiral wound: standard sizes in stock; ring joint: usually to order |
| Cold flow risk | Yes — PTFE creeps under bolt load, especially at elevated temp | No — metal does not creep at normal operating temperatures |
When to Choose PTFE Gaskets
✅ Choose PTFE When…
- Process fluid is corrosive to metals (HCl, HF, H₂SO₄, NaOH, strong organic acids)
- Temperature is below 200°C and pressure is below 40 bar
- Glass-lined or FRP (fibreglass) flanges are involved — cannot tolerate high bolt loads
- Flange faces are old, corroded, or imperfect — PTFE conforms where metal gaskets cannot
- FDA or food compliance is required
- Quick, low-cost replacement at every maintenance turnaround is preferred
- Pharmaceutical / clean process — no metallic contamination risk acceptable
Types of PTFE Gaskets Available
Not all PTFE gaskets are the same — the right type depends on the application:
- Full-face PTFE gaskets — covers the entire flange face including the bolt holes. Standard for glass-lined equipment and FRP piping where high bolt loads must be distributed across the full flange area.
- Raised-face (inner bolt circle) PTFE gaskets — ring gasket seated on the raised face of standard ANSI/ASME flanges. Most common type in chemical plant piping.
- PTFE envelope gaskets — an inner core (rubber, compressed fibre, or spiral wound) wrapped in a PTFE envelope. Combines the conformability of PTFE on the sealing faces with the resilience of the inner filler to resist cold flow under bolt load.
- Chemically modified PTFE (TFM) gaskets — improved resistance to cold flow vs virgin PTFE; recommended for elevated temperature or high bolt-load applications where virgin PTFE would extrude excessively.
- Custom profile gaskets — machined to non-standard flange dimensions, equipment nozzles, or proprietary flange standards per customer drawing.
The Cold Flow Issue — and How to Manage It
PTFE's one significant disadvantage as a gasket material is cold flow (creep) — the tendency of PTFE to continue deforming slowly under sustained compressive load. This means that after the bolts are torqued at installation, PTFE will slowly extrude from the joint over the following days to weeks, losing bolt load and potentially developing a small leak.
This is managed by:
- Retorquing — re-tighten bolts 24 hours after initial assembly, and again after the first thermal cycle, to compensate for PTFE cold flow
- Using thinner gaskets — thinner PTFE sheets (1.5 mm vs 3 mm) have less volume to creep and provide better long-term sealing
- Specify modified PTFE (TFM) — chemically modified PTFE has significantly lower creep than virgin PTFE
- Using PTFE envelope gaskets — the inner core resists extrusion while the PTFE faces provide chemical resistance
Frequently Asked Questions
Can PTFE gaskets be used with steam?
Yes — PTFE is compatible with steam up to its maximum service temperature of 260°C. However, at steam pressures above 20 bar and temperatures above 200°C, virgin PTFE's creep resistance becomes a concern. For high-pressure steam service, specify modified PTFE (TFM) gaskets or PTFE-envelope gaskets with a compressed graphite inner core, which provides better resilience under the high bolt loads needed for high-pressure steam flanges.
How thick should a PTFE flange gasket be?
For standard raised-face flanges in chemical service, 1.5 mm (1/16") is the most common thickness — it provides adequate sealing without excessive cold flow. For glass-lined equipment, 3 mm (1/8") is often used to provide more conformability and protect the glass lining from flange face damage. Thicker gaskets (>3 mm) are generally avoided for process piping as they increase cold flow risk significantly.
PTFE Gaskets — All Standards & Custom Sizes
Full-face and raised-face PTFE gaskets in all ASME, BS, DIN, and IS flange standards. Stock items dispatched same day. Custom sizes manufactured to your drawing.
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