The design and testing of gaskets for severe, possibly life threatening, liquid media, like hydrofluoric acid, is critical and difficult. This paper shows the relationship between basic gasket stress calculations, of applied load over the gasket sealing area, actual gasket stress test results, and dye penetrant test results. The gasket designs evaluated will be from across the industry and follow the typical design of having expanded PTFE (ePTFE) as the inner sealing element for the harsh media and a redundant flexible graphite sealing element that will seal the media as well as give an expected fire test rating.
The gaskets tested had different structural designs for sealing the media as well as providing corrosive protection for the clamping flanges. There was both supported and unsupported ePTFE sealing elements. Some designs are new, and one has been in service for years. The basic calculations typically used to determine adequate gasket stress showed that all the gaskets should seal effectively. The question is: Would they all equally help protect the flange face from corrosive damage?
The data from the actual applied gasket stress correlates nearly perfectly to the dye penetrant results but varies from expected stress distribution of the typical gasket stress calculation. The paper will cover the theoretical calculation approach, the test methodology for the actual applied gasket stress, the methods for ensuring applicable dye penetrant testing and comparing the results to each other. The results show that under equal clamping loads, the different structural designs directly impact the ability for fluid to penetrate the ePTFE section of the gaskets.