PTFE GASKET PERFORMANCE
Figure 6 : Result microscopic glass bubble modified PTFE gasket Figure 7 : Multi-button
Figure 8 : Omega button
Figure 9 : Comparison of the density classes achieved after temperature ageing at -196 ° C followed by helium . The results fell within the mass spectrometer ’ s margin of deviation , indicating that the sequence of test gases does not significantly affect the resulting tightness class . Figure 4 presents an example of a test sequence with documented results . This particular test was conducted at 40 bar test pressure with a 30 MPa initial load on the gasket during assembly . The gasket tested in this sequence was a silica-modified PTFE gasket . The following graphs illustrate the results of leakage testing after cryogenic ageing with hydrogen at -196 ° C :
Sampling results and technical tightness
The testing program was comprehensive , encompassing not only discrete cut gaskets but also ‘ Omega connections ’ and ‘ Multi-button connections ’. Figures 7 and 8 illustrate the achievable tightness classes for these segmented gaskets , demonstrating that high-quality sealing performance can also be achieved with segmented PTFE materials . All the values summarised above and in this report were obtained after assembly in a real flange setup with a surface load of 30 MPa in each case . The values measured after storage in a cryogenic environment at -196 ° C are well below the leakage limit required by TA-Luft . The best performance in this comparison was achieved by a modified PTFE gasket with a patented surface texture , performing two orders of magnitude better ( i . e ., 100 times better ) than gaskets without the innovative surface pattern . Excellent leak tightness can be achieved not only with gaskets made from a single piece . Segmented gaskets also achieve low leakage classes in both gaseous and cryogenic hydrogen environments . As expected , the residual surface load in the cryogenic range was higher than in the gaseous range at + 200 ° C , and all samples were rated as good .
Summary and conclusion
• The results from testing by BAM Berlin ( Federal Institute for Materials Research and Testing ), presented in the May 2024 issue of Valve World Magazine , demonstrate that modified , calendered PTFE gaskets exhibit little or no change in mechanical characteristics under cryogenic and gaseous hydrogen environments .
• Leakage tests with hydrogen , compared to helium tests performed with various modifications of PTFE gaskets , consistently exceed the required tightness class of 1.0x10^-2 mg /( s * m ) under both cryogenic and gaseous conditions at an assembly load of 30 MPa .
• The ‘ worst ’ results achieved in the cryogenic range , at 1.39x10^-5 mg / ( s * m ), are already 1000 times better than the TA-Luft requirements and three orders of magnitude better in the gaseous state .
• The results obtained from helium testing can be used to evaluate the technical tightness of modified , calendered PTFE sealing materials with regard to air pollution legislation requirements such as the German TA- Luft .
Corresponding test reports and certificates in accordance with the new TA-Luft for all results and tests presented in this article are available upon request from the author .
www . valve-world . net Valve World September 2024
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