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FLEXITALLIC GASKET DESIGN CRITERIA
Introduction
FLEXITALLIC, the world’s leading manufacturer and supplier of static seals and the originator of the Spiral Wound Gasket, is
committed to sealing solutions for today’s industry. With greater emphasis than ever before placed on joint tightness, more atten-
tion is focused toward variables associated with the integrity of the bolted gasketed joint. Flexitallic Gasket Design Criteria man-
ual offers the engineer and end user assistance in meeting the goal of providing fundamentally sound static sealing practice.
Developed and collated by Flexitallic’s worldwide team of engineers, this publication is the “engineer’s handbook” of static seals
technology.
Flexitallic has identified three factors which must be considered to achieve a leaktight joint
• Gasket Selection
• Gasket Design
• Gasket Installation
3 Welcome to the Next Generation of Sealing Technology
Overcoming Flange Imperfections
Distortion
trough
Surface
imperfections
Scorings
Flange
mounted
non-parallel
The Gasket
A gasket is a compressible material, or a combination of materials, which when clamped
between two stationary members prevents the passage of the media across those members.
The gasket material selected must be capable of sealing mating surfaces, resistant to
the medium being sealed, and able to withstand the application temperatures and pressures.
How Does It Work?
A seal is effected by the action of force upon the gasket surface. This force which com-
presses the gasket, causes it to flow into the flange macro and micro imperfections. The
combination of contact stress, generated by the applied force between the gasket and the
flange, and the densification of the gasket material, prevents the escape of the confined fluid
from the assembly.
Flange Imperfections
On seating, the gasket must be capable of overcoming the macro and micro imperfections.
Macro defects are imperfections such as flange distortions, non-parallelism, scoring,
troughs, while superficial imperfections such as minor scratches and minor scores are con-
sidered micro imperfections.
Forces On The Gasket
In order to ensure the maintenance of the seal throughout the life expectancy of the assem-
bly, sufficient stress must remain on the gasket surface to prevent leakage. The residual bolt
load on the gasket should at all times be greater than the hydrostatic end force acting against
it.
The hydrostatic end force is the force produced by the internal pressure which acts
to separate the flanges.
Considerations For Gasket Selections
Many factors should be considered when selecting a gasket to ensure its suitability for the
intended application. Gasket properties as well as flange configuration and application
details are part of the selection process.
Hydrostatic
End Force
Blow Out
Force
Bolt
Load
Gasket
Internal Pressure is exerted
against both the flange and the
gasket.