The maintenance factors (m values) and yield stresses (y values) of four gasket materials at four thicknesses each were determined under water pressures of 2.06 MPa and 0.014 MPa, respectively. The gaskets examined were made of PTFE, graphite, Technograph (trade name), and asbestos, each at thicknesses of 1.0, 1.5, 2.0, and 3.0 mm. The m values of asbestos gaskets decreased from 8.32 to 1.73 as thickness was increased, but values for the non-asbestos materials showed no regular change with thickness. The mean m values for PTFE, graphite, and Technograph gaskets were 0.81, 2.12, and 3.01, respectively. The performance of the non-asbestos gaskets was better than that of asbestos gaskets except 1.73 for the 3.0-mm thickness. The y values were much smaller than the m values, e.g. 2.06 MPa for the 1.0-mm thick asbestos gasket under N
2 gas, and showed no variation with thickness. The mean y values for PTFE, graphite, Technograph, and asbestos gaskets were 0.08. 0.16, 0.36, and 0.34. It is not realistic to use these values as the minimum effective seating stress, replacing design stress for these gaskets on piping. The nonasbestos sheet gaskets can be used in place of asbestos gaskets at normal temperatures.
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