Gaskets
Determination of gasket characteristics at cryogenic temperature
EN 13555 includes tests for tightness , creep relaxation ,
Q smax and E-Modulus of gasket materials excluding tests at cryogenic conditions . Cryogenic temperatures significantly influence the characteristics of the sealing materials . It is known that at -40 ° C binders in elastomer bonded sheet gasket materials are getting brittle .
By Florian Werner , TEADIT International Produktions GmbH
Subject of investigations
Three different gasket materials , cut out of sheets , were tested for this :
• Structured PTFE with hollow glass microspheres ( TF 1570 )
• 100 % expanded PTFE ( ePTFE 24 SH )
• Compressed non asbestos fiber gasket ( CNAF )
The aim of the investigation is to determine the following gasket parameters based on the test procedures of EN 13555 :
• Maximum permissible gasket stress Q smax
( -50 ,
-100 , -150 ° C ),
• Modulus of elasticity EG ( -50 , -100 , -150 ° C ),
• Creep relaxation factor PQR ( -50 , -100 , -150 ° C ),
• Minimum gasket stress at assembly Q min ( L ) ( 40 bar / -150 ° C ) and
• Minimum gasket stress at operating condition
Q smin ( L )
( 40 bar / -150 ° C ).
Testing
The tested gaskets have the standard dimension DN40 / PN40 . The gasket thickness is 3 mm for structured PTFE ( TF ) and 2 mm for expanded PTFE ( ePTFE ) and fiber gasket ( NA ). The tests were carried out on the equipment shown in Figure 2 in the laboratory of AMTEC Messtechnischer Service GmbH .
Compression test In this compression test , the gasket is cooled down to the test temperature at a low gasket stress before the test gasket is then subjected to increasingly higher loads in loading and unloading cycles until the gasket fails . The result in this test is used to determine the maximum permissible gasket stress at operating conditions Q smax ( T ) for the gasket .
Durchmesser / Diameter [ mm ] 100 80 60 40 20 0 20 40 60 80 100 |
Durchmesser / Diameter [ mm ]
100 80 60 40 20 0 20 40 60 80 100
|
Durchmesser / Diameter [ mm ]
100 80 60 40 20 0 20 40 60 80 100
|
4 3 2 1 0 1 2 3 4 |
4 3 2 1 0 1 2 3 4 |
4 3 2 1 0 1 2 3 4 |
Durchmesser / Diameter [ inch ]
Durchmesser / Diameter [ inch ]
Durchmesser / Diameter [ inch ]
Figure 1 . Test samples TF , ePTFE and NA .
Figure 2 . Equipment for cryogenic tests .
36 Valve World February 2024 www . valve-world . net