Compression test The tests were carried out at -50 , -100 and -150 ° C . Based on the test standard , intermediate reliefs were also recorded to determine the elasticity of the gasket . π www . valve-world . net Valve World February 2024 37
Gaskets
then kept constant for 4 hours and the relaxation behavior of the seal is determined . For this purpose , after setting the initial gasket stress , the stiffness of a flange connection is simulated by regulating the gasket stress in a displacement-controlled manner . The ratio of the residual gasket stress at the end of the test to the initial gasket stress results in the creep relaxation factor PQR , which is given as a function of the initial gasket stress , the test temperature and the system stiffness .
Figure 3 . Compression test at -50 , -100 and -150 ° C of TF .
The modulus of elasticity EG of the gasket material can be determined from the compression curve at alternating between loading and unloading the gasket with defined stresses .
Creep relaxation test In the creep relaxation test , the gasket is pressed to the initial gasket stress before the test gasket is cooled to the test temperature . The temperature is
Leakage test In the leakage test , the gasket is loaded to a predefined assembly gasket stress of 30 MPa before the test item is cooled to a test temperature of -150 ° C . The gasket is then unloaded and loaded again in several steps , with the leakage rate determination for each load step . In addition to the loads of 30 and 40 MPa , unloading curves are also drawn up . The smallest load level is 5 MPa . The test medium for these leakage tests is helium and test pressure is 40 bar . The required minimum gasket stresses
Q min ( L ) and Q smin ( L ) can be determined from the leakage curve for the various tightness classes L , depending on the previously applied initial gasket stress QA .
Results and discussion
• Maximum permissible gasket stress
Q smax
( -50 , -100 , -150 ° C ) at operating temperature ,
• Modulus of elasticity EG ( -50 , -100 , -150 ° C ), which describes the deformation behaviour of the gasket ,
• Creep relaxation factor PQR , which describes the decrease in gasket stress due to creep of the gasket under load and temperature ,
• Required minimum gasket stress Q min ( L ) for tightness class L ,
• Required minimum gasket stress
Q smin ( L ) for tightness class L depending on the initial gasket stress QA .
Compression test The tests were carried out at -50 , -100 and -150 ° C . Based on the test standard , intermediate reliefs were also recorded to determine the elasticity of the gasket . π www . valve-world . net Valve World February 2024 37