A complete explanation of the sealing mechanism of heat exchanger gaskets: from contact pressure distribution to leakage channel blocking

1. Basic theory of sealing mechanism

Physical basis of sealing mechanism

Contact pressure theory

The essence of gasket sealing is to establish sufficient contact stress to offset the medium pressure

Minimum effective sealing pressure (y coefficient): the minimum compressive stress for the gasket to start to produce a sealing effect

Gasket coefficient (m): the ratio of the contact pressure required to maintain the seal to the medium pressure (ASME PCC-1 standard recommended value)

Surface interaction

The actual contact area accounts for only 5-15% of the apparent contact area (Wickers rough surface theory)

Micro-sealing is achieved by filling the surface troughs through plastic deformation

Surface roughness Ra should be controlled at 3.2-6.3μm (ISO 4288 standard)

Contact pressure distribution characteristics

Three-dimensional pressure field formation

Macroscopic pressure distribution generated by flange bolt load

Local contact pressure peak (up to 2-3 times the average pressure)

Edge effect: 15% area pressure attenuation of flange outer edge reaches 40%

Leakage channel blocking mechanism

Multi-scale sealing principle

Macroscopic scale: Flange-gasket system forms a mechanical barrier

Microscopic scale: Gasket material fills surface defects (＞90% of leakage occurs in surface defects of 10μm level)

Molecular scale: Permeation blocking of polymer chains (especially critical for gas molecules)

Dynamic sealing process

Initial compression stage: Gasket thickness decreases by 20-30%

Stress relaxation stage: 15-25% preload loss in the first 8 hours

Working stage: Need to meet: P_contact ≥ m × P_media + ΔP_thermal

2. Working principle of heat exchanger gasket

Basic sealing principle

Elastic deformation and contact pressure

The gasket undergoes elastic or plastic deformation under the action of bolt preload, filling the microscopic unevenness between flanges or plates (surface roughness usually requires Ra≤3.2μm).

A local high-pressure contact area is formed (metal gaskets can reach 200-500MPa, non-metal gaskets 50-150MPa), blocking the medium penetration path.

Surface bonding mechanism

Microscopic level: The flexibility of gasket materials (such as graphite, PTFE) makes the surface roughness peaks fit together, eliminating leakage channels > 5μm.

Macroscopic level: The gasket structure (such as waveform, tooth shape) compensates for the flange parallelism deviation through geometric deformation (the compensation amount is usually 0.05-0.2mm).

Adaptability under dynamic working conditions

Thermal cycle compensation

The gasket needs to have rebound performance (ASTM F36 standard requires a rebound rate of ≥40%) to compensate for the thermal expansion difference of the flange.

Pressure fluctuation adaptation

When the internal pressure increases, the medium pressure acts on the inner edge of the gasket, forming a self-tightening effect (self-tightening coefficient of metal wound gasket m=2.5-3.0).

Vibration working conditions

Anti-fretting wear design (such as PTFE coating) can reduce the wear of the sealing surface caused by vibration.

3. Heat Exchanger Gasket FAQ

• Q1: What are the main types of heat exchanger gaskets?

Heat exchanger gaskets are mainly divided into three categories:

Non-metallic gaskets: such as nitrile rubber (NBR), EPDM, fluororubber, etc., suitable for medium and low temperature conditions (-50℃~200℃)

Metal gaskets: including copper gaskets, stainless steel toothed gaskets, etc., resistant to high temperature and high pressure (up to 800℃/25MPa)

Semi-metallic gaskets: such as metal wound gaskets (graphite + stainless steel strips), which have both elasticity and strength and are suitable for thermal cycle conditions

• Q2: What role does the gasket play in the heat exchanger?

Gaskets mainly realize four functions:

Sealing: prevent hot and cold fluids from mixing or leaking

Pressure buffering: compensate for the assembly stress between flanges/plates

Medium isolation: extend the leakage path through structural design

Vibration absorption: reduce micro-motion wear during equipment operation

• Q3: How to judge whether the gasket needs to be replaced?

The gasket should be replaced when the following conditions occur:

Compression permanent deformation > 25%

Surface cracks or chemical corrosion pits (depth > 0.2mm)

Rebound rate after thermal cycling < 30%

Measured leakage rate > 3 times the standard value