🔧 GASKETS — TYPES, MATERIALS, SELECTION & INDUSTRIAL APPLICATIONS

 🔧 GASKETS — TYPES, MATERIALS, SELECTION & INDUSTRIAL APPLICATIONS

1. What is a gasket?

A gasket is a sealing element installed between two mating surfaces—normally flanges—to prevent leakage of:

• Liquids
• Gases
• Steam
• Refrigerants
• Hydraulic fluids
• Chemicals
• Hydrocarbons
• Compressed air
• Vacuum

A gasket works by being compressed between the sealing surfaces, filling surface imperfections and maintaining a seal while the joint experiences pressure, temperature, vibration and thermal expansion.

Basic sealing principle

Flange → Gasket → Flange

The bolts generate a clamping force, which compresses the gasket and creates the sealing contact.

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2. Main Types of Gaskets

A. Rubber / Elastomeric Gaskets

Common materials include:

• EPDM
• NBR / Buna-N
• Neoprene
• Silicone
• FKM / Viton
• Natural rubber

Applications

• Water pipelines
• HVAC
• Chilled-water systems
• Cooling towers
• Compressed air
• Hydraulic systems
• Low-pressure piping

Example

EPDM is commonly suitable for water, hot water and many HVAC applications.

NBR is often preferred where oil/hydrocarbon resistance is important.

⚠️ Important: EPDM and petroleum oils are generally a poor combination; material compatibility must always be checked.

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3. Silicone Gaskets

Silicone has excellent flexibility and performs well across a relatively wide temperature range.

Applications

• HVAC equipment
• Food processing
• Electrical enclosures
• Doors and access panels
• Low-pressure equipment
• High/low-temperature applications depending on grade

Advantages

✔ Flexible
✔ Good weather resistance
✔ Good temperature capability
✔ Good aging resistance

Limitation

Silicone is not automatically suitable for every chemical, hydrocarbon or high-pressure flange service.

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4. PTFE Gaskets

PTFE — Polytetrafluoroethylene

PTFE is particularly valuable because of its excellent chemical resistance.

Applications

• Chemical plants
• Acid/alkali service
• Petrochemical systems
• Pharmaceutical plants
• Aggressive chemical services

Advantages

✔ Excellent chemical resistance
✔ Low friction
✔ Good corrosion resistance
✔ Suitable for many aggressive fluids

Limitation

PTFE can exhibit creep/relaxation, particularly under elevated temperature and load.

Modified PTFE grades can improve performance in demanding services.

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5. Non-Asbestos Compressed Fiber Gaskets

These are manufactured from combinations of:

• Aramid fibers
• Mineral fibers
• Elastomers
• Fillers
• Other reinforcing materials

They replaced many traditional asbestos-containing gasket materials.

Applications

• Water
• Oil
• Steam
• Air
• Hydrocarbon services
• General industrial piping

Advantages

✔ Good general-purpose performance
✔ Economical
✔ Available in many thicknesses
✔ Suitable for many moderate-pressure applications

Selection must be based on the manufacturer's pressure-temperature rating and fluid compatibility.

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6. Graphite Gaskets

Flexible graphite is widely used for high-temperature and demanding services.

Applications

• Steam
• Boilers
• Heat exchangers
• Refineries
• Petrochemical plants
• High-temperature piping
• Valves

Advantages

✔ Excellent temperature resistance
✔ Good chemical resistance
✔ Good sealing characteristics
✔ Useful in thermal cycling

Graphite can oxidize at elevated temperatures in the presence of oxygen, so service conditions matter.

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7. Cork Gaskets

Cork is compressible and has good sealing characteristics for relatively low-pressure applications.

Applications

• Oil pans
• Gearboxes
• Covers
• Engines
• Low-pressure equipment

Advantages

✔ Highly compressible
✔ Good vibration absorption
✔ Economical

Not normally selected for high-pressure/high-temperature process flange service.

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8. Spiral-Wound Gaskets

One of the most important industrial gasket types.

A spiral-wound gasket is constructed by winding:

Metal strip + filler material

Typical metal materials include:

• Stainless steel
• Carbon steel
• Alloy materials

Common fillers include:

• Graphite
• PTFE
• Other engineered fillers

Applications

• Refineries
• Petrochemical plants
• Power plants
• Steam systems
• Heat exchangers
• Process piping

Advantages

✔ Excellent pressure capability
✔ Good temperature resistance
✔ Handles thermal cycling
✔ Suitable for demanding flange services

Important

Correct centering, flange condition and bolt tightening are essential.

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9. Metal-Jacketed Gaskets

A soft filler material is enclosed within a metallic jacket.

Typical construction:

Metal jacket → soft filler → metal jacket

Applications

• Heat exchangers
• Boilers
• High-temperature equipment
• Flue gas systems
• Process equipment

Advantages

✔ Good temperature resistance
✔ Strong mechanical construction
✔ Suitable for heat exchanger applications

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10. RTJ — Ring Type Joint Gaskets

RTJ gaskets are precision-machined metallic rings used primarily with specially designed RTJ flanges.

Common profiles include:

• Oval
• Octagonal

Applications

Especially common in:

• Oil & gas
• Refineries
• Wellhead equipment
• High-pressure process piping
• High-pressure/high-temperature services

Key feature

The gasket seals through metal-to-metal contact and controlled deformation within the RTJ groove.

⚠️ RTJ gaskets must match the correct:

Ring number + flange groove + pressure class + material

They should not simply be substituted with a flat gasket.

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11. Kamm profile Gaskets

A Kamm profile gasket consists of a metal core with concentric serrations, normally with a sealing layer such as graphite.

Applications

• Heat exchangers
• Pressure vessels
• Steam systems
• Petrochemical equipment
• High-temperature services

Advantages

✔ Excellent sealing
✔ Good resistance to thermal cycling
✔ Suitable for high-temperature applications
✔ Can perform well with relatively low gasket thickness

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12. Corrugated Metal Gaskets

These use a corrugated metallic core with a sealing layer or facing.

Applications

• Heat exchangers
• Exhaust systems
• High-temperature equipment
• Petrochemical plants
• Steam systems

The corrugations provide flexibility while the facing provides the sealing surface.

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13. Composite Gaskets

Composite gaskets combine multiple materials to achieve improved performance.

Examples include:

• Metal + graphite
• Metal + PTFE
• Fiber + elastomer
• Metal + soft filler

They are useful when one material alone cannot meet all requirements.

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14. O-Rings

O-rings are different from conventional flange gaskets.

They are circular elastomeric seals with a round cross-section.

Materials

• NBR
• EPDM
• FKM
• Silicone
• FFKM
• PTFE-based designs

Applications

• Hydraulic cylinders
• Pumps
• Valves
• Compressors
• Refrigeration
• HVAC
• Pneumatic systems
• Medical equipment

Example

A hydraulic cylinder may use an NBR or polyurethane sealing system, depending on pressure, temperature and hydraulic fluid.

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15. Gasket Selection — 8 Critical Factors

Never select a gasket only by its diameter.

1. Pressure

Determine:

Operating pressure + design pressure

High-pressure services generally require more robust gasket systems.

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2. Temperature

Check:

Normal operating temperature + maximum temperature

A gasket suitable for chilled water may be completely unsuitable for high-pressure steam.

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3. Fluid Compatibility

Ask:

What exactly is inside the pipe?

Examples:

Fluid	Possible gasket considerations
Chilled water	EPDM
Hot water	EPDM / suitable fiber
Oil	NBR / FKM
Steam	Graphite / spiral wound
Aggressive chemicals	PTFE
Hydrocarbons	NBR/FKM/appropriate engineered gasket
Oxygen service	Special oxygen-compatible materials and procedures

These are examples, not universal selections; manufacturer compatibility data must govern.

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16. Flange Design

The gasket must match the flange arrangement.

Consider:

• Flat face
• Raised face
• RTJ
• Male/female
• Tongue-and-groove
• Flange pressure class
• Flange dimensions
• Surface finish

A gasket designed for one flange configuration should not automatically be installed on another.

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17. Bolt Load — Extremely Important

A gasket needs sufficient compression to seal.

But:

More bolt torque does NOT always mean a better seal.

Excessive bolt load can cause:

• Gasket crushing
• Flange deformation
• Bolt yielding
• Loss of flange integrity
• Leakage after thermal cycling

Insufficient bolt load can cause:

• Leakage
• Blowout risk
• Gasket movement
• Loss of sealing

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18. Proper Gasket Installation

A good installation procedure should include:

Step 1 — Isolate the system

Close valves and establish positive isolation as required.

Step 2 — Depressurize

Confirm:

Pressure = zero

Do not rely only on a pressure gauge.

Step 3 — Drain / vent

Remove trapped:

• Pressure
• Liquid
• Gas
• Steam
• Chemical

Step 4 — Remove old gasket

Never reuse a gasket unless specifically designed and approved for reuse.

Step 5 — Inspect flange

Check for:

• Corrosion
• Pitting
• Scratches
• Warping
• Cracks
• Excessive surface damage
• Incorrect flange alignment

Step 6 — Clean surfaces

Remove:

• Old gasket material
• Dirt
• Rust
• Oil
• Scale

Step 7 — Install correct gasket

Confirm:

Size + material + rating + flange type + service compatibility

Step 8 — Align flanges

Avoid forcing the flange into alignment using excessive bolt tightening.

Step 9 — Tighten bolts correctly

Use the manufacturer's recommended torque or tensioning procedure.

Typical sequence:

Cross / star pattern → multiple stages → final verification

Step 10 — Leak test

Where required, conduct the applicable pressure/leak test before returning the system to service.

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19. Common Causes of Gasket Failure

❌ Wrong gasket material

Chemical attack or temperature degradation.

❌ Wrong gasket size

Poor seating or leakage path.

❌ Excessive bolt torque

Gasket crushing or flange distortion.

❌ Insufficient torque

Insufficient gasket compression.

❌ Uneven tightening

Uneven gasket stress.

❌ Poor flange alignment

Creates uneven compression.

❌ Damaged flange face

Prevents proper sealing.

❌ Reusing old gasket

Loss of original sealing capability.

❌ Incorrect surface finish

Gasket cannot properly conform to the flange.

❌ Thermal cycling

Repeated expansion/contraction can relax the joint.

❌ Vibration

Can contribute to bolt preload loss and joint leakage.

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20. Gasket Failure Analysis

When a gasket leaks, don't immediately replace it.

Inspect the failed gasket.

If gasket is crushed:

Possible causes:

• Excessive bolt load
• Incorrect gasket thickness
• Incorrect installation

If gasket is burned:

Possible causes:

• Excessive temperature
• Wrong material
• Fire/thermal exposure

If gasket is chemically deteriorated:

Possible causes:

• Incorrect material compatibility
• Contaminated process
• Unexpected chemical concentration

If gasket is blown out:

Possible causes:

• Insufficient compression
• Incorrect gasket
• Excessive pressure
• Flange damage
• Poor installation

If only one side is damaged:

Possible causes:

• Flange misalignment
• Uneven bolt loading
• Surface damage

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21. Gaskets in HVAC & Building Services

Gaskets are extensively used in:

Chilled-water systems

• Flanged valves
• Pumps
• Strainers
• Heat exchangers
• Chillers

Steam systems

• Boilers
• Steam valves
• PRV stations
• Heat exchangers

Cooling towers

• Flanges
• Pumps
• Piping connections

HVAC equipment

• AHUs
• FCUs
• Heat exchangers
• Condenser-water systems

Medical gases

Special attention is required for:

• Oxygen
• Medical air
• Vacuum
• Nitrous oxide

For oxygen service, materials, cleanliness and installation procedures must be specifically suitable for oxygen service.

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22. Gasket Selection Matrix

Fluid Possible gasket considerations Chilled water EPDM Hot water EPDM / suitable fiber Oil NBR / FKM Steam Graphite / spiral wound Aggressive chemicals PTFE Hydrocarbons NBR/FKM/appropriate engineered gasket Oxygen service Special oxygen-compatible materials and procedures

23. Gasket vs O-Ring

Feature Gasket O-Ring Shape Usually flat/profiled Circular Main use Flange joints Static/dynamic seals Material Fiber, graphite, PTFE, metal Elastomer Applications Piping/equipment Pumps, valves, hydraulics Reuse Normally no Normally replace when disturbed Pressure capability Depends on design Depends on groove/material

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🛡️ Critical HSE Rule

Before opening any flanged joint:

STOP → ISOLATE → LOCKOUT/TAGOUT → DEPRESSURIZE → DRAIN/VENT → VERIFY ZERO ENERGY → OPEN SAFELY

For hazardous services, also consider:

• Permit to Work
• Gas testing
• PPE
• Chemical exposure
• Line breaking procedure
• Blind/spade installation
• Double block and bleed where required
• Barricading
• Emergency response arrangements

The most important engineering principle:

A gasket is not selected by size alone. It is selected by pressure, temperature, fluid compatibility, flange design, surface condition, bolt loading and installation requirements.

A small gasket failure can cause loss of product, environmental release, equipment damage, fire, personnel injury and significant plant downtime.

Good gasket selection + correct flange preparation + controlled bolt loading = reliable joint integrity.