WRC BUL 427
LEAKAGE AND EMISSION CHARACTERISTICS OF SHEET GASKETS: I) FUGITIVE EMISSION CHARACTERISTICS OF GASKETS; II) EXPLORATORY INVESTIGATION OF THE LEAKAGE STABILIZATION TIME AT ROOM TEMPERATURE FOR FLEXIBLE
|Publication Date:||1 December 1997|
This project provides baseline leak rate data for four fluids and two gasket materials under conditions of known compression and for moderate operating temperatures most frequently encountered in process plants. 1. 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 350EF) on the gasket tightness was also studied. The analysis of the test results indicate that gasket mass leak rate depends on both the fluid and the gasket material. The fluid can also change the tightness behavior of a gasket as indicated, for instance, by the tightness hardening phenomena displayed with sulfur hexafluoride. After the 5-day exposure at a moderate temperature, the gasket tightness was found to be either the same or improved and, consequently, the hot Gs, constants of the two gasket materials are equal or smaller than their room temperature Gs constants. 2. Exploratory Investigation of the Leakage Stabilization Time at Room Temperature for Flexible Graphite and PTFE-Baseed 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. The analysis of the test results indicates that leakage can take a long time to reach a stable value and that at high leakage levels, the gasket leakage dwell time appears to be much shorter than at very low leakage levels. The report concludes that the level of leak rate changes of compressive stress and gas pressure, gasket creep, all appear to impact the leakage stabilization period. A leak stabilization check algorithm has been implemented for each leakage measurement step of the load-pressure sequence of the PVRC ROTT procedure, and a revised draft of the ROTT test procedure is proposed as it was recommended to the ASTM gasket committee in the form of Draft No. 9 of the AStandard Test Method for Gasket Constants for Bolted Joint Design@ together with Draft No. 1 for the APractice for Measuring Gas Leakage Through Gaskets.@ Publication of this document - WRC Bulletin No. 427 was sponsored by the Pressure Vessel Research Council of the Welding Research Council.