Leakage Behavior of Gaskets in Flanged Connections M&Y Values vs. PVRC Gasket Factors and the use of Tightness Parameters By Chett Norton, C.E.T. November 17 th, 2014
Biography Chett Norton Applications Engineer at Triangle Fluid Controls Fluid Sealing Association Technical Committee, Vice Chair ASTM F03 Gasket committee, participating member ASME PVP, Associate member Ontario Association of Certified Engineering Technicians and Technologists (OACETT) Certified Engineering Technologist in Mechanical discipline since 2003
Introduction Piping connections and bolted flanges are found everywhere in the world today. These bolted connections are commonly sealed with a gasket by applying a load which is created by turning a bolt to the predetermined torque. The industry standard for many years has used M&Y values to determine torque calculations for flange design; however it should be noted that M&Y values do not directly equate to the minimum required gasket stress and zero leakage.
Introduction - Continued This paper will compare and address leakage rates in various gasket sealing materials for both M&Y and PVRC Gasket Factors using standard assembly methods. By doing so, it is my intention to give the user more information so they he or she can make an educated decision when selecting the required sealing material and to also understand the expected outcome based on the calculation method used.
Gasket Factors Brief History ASME Sec. VIII, Div. 1&2 - M&Y (1937 and discontinued in 1989) Very simple; leakage not taken into consideration DIN V 2505 (1964) General European version of M&Y PVRC G b, a, G s (1974) Accounts for tightness of a joint (leakage) DIN E 2505 (1986, 1990) Improved version with bolt pre-stress
Gasket Factors Brief History Continued DIN 28090 (1995) DIN E 2505 with leakage criteria EN 1591-1 (2001) The general precursor to EN 13555 EN 13555 (2004) Working version of PVRC method
Proposed ASME Gasket Factors New gasket constants to replace the ASME Code m and y are have been developed by the Pressure Vessel Research Council (PVRC) and ASME. Constants are G b, G s & a. Currently m and y are difficult to replicate particularly for non-asbestos gaskets and do not consider joint leakage. Because of the Clean Air Act and environmental considerations in general, it was decided to revisit the design parameters of the bolted joint. The new approach to bolted joint design makes the tightness (or, lack of leakage) of the joint a design parameter.
PVRC Method G b & a both give the gasket seating load, similar to M which is know as the maintenance factor G s is associated with operating stress, similar to Y which is the necessary gasket seating load.
Evaluation Method for Leakage Rates ASTM 2378 test rig with modified test method. Gasket is placed between two steel platens and a predetermined seating stress is placed on the test specimens by a hydraulic press. Test samples are left under compression for 1 hour and 45 minutes while the nitrogen test media is set to 200 psi and run without measurement. Once the 1 hour and 45 minute waiting period is over, the leakage measurement is started. At the end of 15 minutes, the leakage rate for the 3 samples are averaged and recorded.
Testing Rig Steel Platens Gasket Samples Leakage Measurement Orifice Sealing o-ring
Testing Rig Hydraulic Pressure Gauge Leakage Measurement Gauges x 3 Press Frame Nitrogen Supply Line Steel Platens x 3 Hydraulic Ram
Test Model Scenario Application Pressure: 200 psi Temperature: 25 C Gasket size: 50 mm x 90 mm Gasket Thickness: 1.5 mm Leakage Requirement: T3 tightness (For PVRC Method) Bolting material: A193-B7 studs (105ksi yield), 4 bolts 5/8 in diameter with A194 2H nuts and hardened flat washers.
Gasket factors used for test samples PVRC Gasket Factors M&Y Values Test Material Gb (psi) a G b (psi) M Y Compressed Non- Asbestos 650 0.33 200 2.75 3700 Filled PTFE 639 0.22 55 2.2 1937 Flexible Graphite (no insert) 970 0.0384 1 2.0 2500
Calculated torque values and equivalent seating stresses M&Y Values PVRC Gasket Factors Test Material Torque, Ft-lbs (Nm) Equivalent Seating Stress, psi (MPa) Torque, Ft-lbs (Nm) Equivalent Seating Stress, psi (MPa) Compressed Non- Asbestos 28 (38) 1600 (11) 57 (77) 3792 (26.1) Filled PTFE 15 (20) 910 (6.3) 29 (39) 1909 (13.2) Flexible Graphite (no insert) 11 (15) 680 (4.7) 14 (19) 955 (6.6)
Calculated Torque Value - M&Y vs PVRC Gasket Method
Associated Seating Stress - M&Y vs PVRC Gasket Method
Leakage Results Test Data Leakage Testing Data Comparison (3 Sample Average) M&Y Values PVRC Gasket Factors Material Leakage, cc/min Test Duration Leakage, cc/min Test Duration Compressed Non- Asbestos 59.0 2 minutes 1.25 15 minutes Filled PTFE 115.1 10 sec* 1.49 15 minutes Flexible Graphite (no insert) 0.66 2 minutes 0.51 15 minutes * Denotes that results were unobtainable due to very high leakage rates. Results were recalculated based on a 10 second measuring period
Leakage Rates M&Y vs PVRC Gasket Method
Leakage Rates M&Y vs PVRC Gasket Method
Observations Leakage rates for both compressed non-asbestos and PTFE material using M&Y calculated torque values were much higher that those calculated with PVRC gasket factor method. Leakage rates for flexible graphite using both methods were similar and only slightly better using the PVRC gasket factors. Leakage rates for all three types of gasket materials selected using PVRC gasket factors were lower than those using M&Y factors.
Conclusions Based only on test results it appears that M&Y values do not give you the best result for trying to achieve a leak free joint. It is noted that leakage rates are much higher for both compressed non-asbestos and PTFE using M&Y values. It appears that either calculation method would be acceptable with the use of flexible graphite.
Using PVRC Gaskets Factors may benefit you in the following areas: Critical Applications, such as sulfuric acid and other hazardous chemicals. FRP or glass lined piping. Areas of high concern to the public or have a negative public image. Plant safety concerns. Environmentally sensitive areas. Plant areas that have a high frequency of unscheduled down time due to gasket issues.
A Special Thank You! At this time I would like to thank the following people for their help, insight and resources during the writing of this paper. Isabella Anwaryar Lab Technician, Triangle Fluid Controls Mike Shorts Vice President & GM Triangle Fluid Controls Fluid Sealing Association
Questions