Part 1: Leakage and Emission Characteristics of Sheet Gaskets: Fugitive Emission Characteristics of Gaskets

The fugitive emission characteristics of two sheet gasket materials, an NBR/asbestos sheet and a metal-reinforced flexible graphite sheet, were investigated with four different fluids: helium, methane, propane and sulfur hexafluoride. The effect of a moderate temperature exposure (5 days at 350°F) on the gasket tightness was also studied. The tests were conducted on 4-inch NPS gaskets using the room temperature tightness test (ROTT) procedure and the newly developed emission hot operating tightness test (EHOT) procedure. During the tests, gasket leak rates were measured using either the pressure decay or the pressure rise methods. To improve the precision of the leak rate calculations, a correction for deviation from the ideal gas law was developed and applied.

Part 2: Leakage and Emission Characteristics of Sheet Gaskets: Exploratory Investigation of the Leakage Stabilization Time at Room Temperature for Flexible Graphite and PTFE-Based Sheet Gaskets

The dwell time effect on the room temperature leakage behavior of one typical flexible graphite material and one expanded PTFE-based product was investigated by performing exploratory leakage tests on the ROTT test rig available at TTRL (RH Rig). Leak rates over time have been measured at eight different gasket stress levels between 1025 and 15,160 psi, and for two gas pressures (400 and 800 psig) as recommended in the proposed ASTM Method Draft No 8 of the "Standard Test Method for Gasket Constants for Bolted Joint Design." The helium mass spectrometer leak detector has been used for all leak measurements. Leak measurements have been recorded every 15 minutes during a maximum time of 5 hours for each combination of stress/pressure. The minimum time allowed for leakage measurement has been set to 2 hours. A leakage stabilization criterion was defined on the basis of the last three leak measurements: the leak is assumed to be stabilized when the calculated standard deviation is less than 2% of the average of these measurements. Longer-term leakage measurements were preformed to better examine the effect of stress and gas pressure changes on the leak stabilization time.