Session: CT-03-01 Leak Tightness and Fugitive Emissions

Paper Number: 151452

151452 - A Study on the Thighness Parameter Used in the Evaluation of the Pvrc Gasket Constants 

Abstract: 

The tightness parameter is a relatively new concept being adopted by the ASME Sub-Working Group on Bolted Flange Connections for flange design based on leakage performance. Originally developed in the late 1980s under the Committee on Bolted Flange Connections of the PVRC, this parameter was designed to replace the outdated gasket constants m and y from the 1940s with leakage-based constants (Gb, a, and Gs) for a new ASME procedure. This new design method focuses on tightness in bolted flange joints. A key advantage of the tightness parameter is its ability to link leakage and pressure through a simple expression, eliminating the need to account for the complex flow regimes present in porous gasket materials. Furthermore, it circumvents the need for standard leak tests, such as ASTM F2836 – 18 Standard Practice for Gasket Constants for Bolted Joint Design or the Room Tightness Test, to be conducted at varying pressures to determine leakage-based gasket constants and save the cost of additional testing.

However, the value of the tightness exponent used in the leakage-to-pressure relationship has faced significant criticism. It was developed during a time when fiber gaskets were the standard, prior to the introduction of more advanced gasket materials like flexible graphite and PTFE in the early 1990s which are much tighter and require less load to seal.  To account for the diverse flow regimes that may occur in modern gasket materials, a reevaluation of the pressure-tightness relationship is necessary. This is achieved by an evaluation of the slope of the leak rates plotted against a wide range of fluid pressures and repeated at different gasket stress levels.  

Therefore, a comprehensive study involving leak tests conducted on various gasket materials and fluid media, subjected to different internal pressures and contact stresses, has been conducted to adjust this correlation. The findings indicate that a tightness exponent of ¾, rather than the current ½, more accurately reflects real-world conditions. For a comparison purpose, the gasket constants calculated with tightness parameter based on both exponents were used to predict leak rates. It was found that the revised constant produces more accurate predictions, better aligning with measured leak rates. The presence of the different types of flows including porous and surface leaks, laminar and molecular that can be present individually or combined in any given gasket are better described. The required gasket contact stresses to achieve target leak rates were found to be lower. This version enhances readability, ensures technical clarity, and improves the overall predictions.

Presenting Author: Hakim Bouzid École de Technologie Supérieure

Presenting Author Biography: Hakim Bouzid is a full professor at Ecole de Technologie Supérieure of Montreal Canada. He graduated from mechanical engineering Department of Nottingham University, UK, 1981. He holds a master Degree in Tribology from Leeds University, UK in 1982. He has a Ph.D in bolted joints received from École Polytechnique, Montreal, Canada, 1995. He worked in the nuclear industries for 8 years specializing in pressure vessels and piping before joining the Tightness Testing Research Laboratory at Ecole Polytechnique in 1990 as a research scientist. In 2000, he became a professor at Ecole de Technologie Superieure in Montreal. He is currently the director the Static and Dynamic Sealing Laboratory of ÉTS. Prof. Bouzid has authored or co-authored over 200 technical papers on different subjects including stress analysis, bolted joints, valves, polymers and biomechanics.
Dr. Bouzid is a fellow of ASME. He is a member of the Pressure Vessel ad Piping Division Executive committee and a member of the Fellow Review Committee. He served as a member of the Pressure Vessel Research Council, ASME subworking Group on Bolted Flange Connections and PCC-1 and ASTM F03 committee on gaskets.

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