gAskets or elastomer-based gaskets should be checked in additional tests at cryogenic conditions .
Leakage test In these tests , the tightness class L0.001 was already achieved at a surface pressure of 30 MPa . If the seal is further stressed to 40 MPa , the leakage rate continues to drop . The unloading steps were carried out up to a gasket stress of 5 MPa and show only a slight increase in the leakage rate . The following leakage result , fits to the typical leakage performance of this gasket material , as shown in Figure 9 . Unfortunately , there are no further results for the other sealing materials available so that comparisons can ’ t be made .
Summary and conclusion
The results clearly show that tests based on EN 13555 are possible up to -150 ° C . The first EN 1591-1 calculations have already been carried out with good results using the available gasket parameters for TF .
Polytetrafluorethylen ( PTFE )
Polytetrafluorethylen ( PTFE ) Figure 7 . Temperature effect at a 2 mm thick PTFE gasket .
1
0,5
0
0
D e f o r |
-0.01
-0.02
|
m |
|
a ti
o n 1 in
|
-0.03
-0.04
-0.05
|
mm |
-0.06 -150. 0 -133. 0 -116. 0 -99. 0 |
-82. 0 |
-65. 0 -48. 0 |
-31. 0 |
-14. 0 |
3 . 0 |
20 . 0 |
0,68
Temperature in ° C
Creep relaxation [ PQR ]
0,89 strukt . PTFE ePTFE NA
Figure 8 . Creep relaxation comparison for different materials at -150 ° C .
0,93
E-Modulus and Q smax The tests to determine the maximum gasket stress have so far only been carried out on TF up to 100 MPa . No damage was found on the gaskets . The maximum gasket stress on the TF material is therefore > 100 MPa . The lower the temperature , the higher the modulus of elasticity . As it is well known , plastics become stiffer , harder and more brittle at lower temperature .
Fiber gaskets in particular requires further investigations for safety reasons due to their significantly higher E-modulus . We classify the measured modulus of elasticity as alarmingly high .
Creep relaxation “ PQR ” The PQR value of the TF gasket decrease with lower temperature .
If you compare the creep relaxation of ePTFE and NA gaskets with characteristic published values , you can also see smaller PQR values at cryogenic temperature . With ePTFE and NA , this effect is smaller than with TF .
Leakage performance As expected , the tightness class of L0.001 was reached below 30 MPa . Comparable values are obtained with the results at RT .
T i g t
h n es
s C la
s s
i1 n
1.00E + 00
1.00E-01
1.00E-02
1.00E-03
1.00E-04
4 .
3 . 2 . 1 . p = 40 bar T = -150 ° C He
6 . 5 .
m |
1.00E-05 |
g |
|
|
|
|
|
|
|
|
|
/ m / s
1
|
1.00E-06
0
|
5 |
10 |
15
20
25
Gasket Stress in MPa
|
30 |
35 |
40 |
45 |
Figure 9 . Leakage curve at -150 ° C and initial gasket stress of 30 MPa . |
About the author Florian Werner , MSc , graduated at the University of applied science in Austria in his studies about Material and Process Sciences . Now , he is the Head of Application Engineering for TEADIT International in Austria , overseeing its team of Applications Engineers . Together with his team , he is responsible for gasket selection , flange calculation , installation training , product presentations and many more actions related to customer service . Additionally , he participates as a voting member of a myriad of industrial committees related to bolted flanged joints like CEN , DIN , ASI and ESA .
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