Proposed ASME Gasket Factors

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New gasket constants to replace the ASME Code m and y are currently being developed by the Pressure Vessel Research Council (PVRC) and ASME. The current m and y are difficult to replicate 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.

In a manner similar to the traditional ASME Code method, the design bolt load for a joint is calculated for operating and seating requirements from the new constants Gb, a and Gs and the required tightness class associated with the minimum tightness. Gb and a, gives the gasket seating load and are similar to y in the present Code. Gs is associated with the operating stress and is similar to the m value in the Code.

The proposed ASME constants Gb, a, and Gs give a design bolt load obtained by interpretation of leakage test data as plots of gasket stress Sg, vs. a tightness parameter, Tp. Tp is the pressure (in atmospheres) normalized to the atmospheric pressure required to cause a helium leak rate of 1 mg/sec for a 150 mm OD gasket in a joint. Since this is about the same as the OD of an NPS 4 joint, the pressure to cause a leak of 1 mg/sec of helium for that joint is its tightness. A standard test procedure, the PVRC Room Temperature Tightness Test (ROTT) has been designed to produce the constants Gb, a and Gs. Low values for Gb, a and Gs are desirable while a higher value of Tp means a tighter joint.

The new gasket factors Gb, a and Gs, are available for for Durlon® gasket materials. While the torque tables for Durlon® gasketing use these new gasket constants as a guide, generally the recommended bolt stress range of 40% to 60% of bolt yield is higher and takes precedence for our recommended torque values.

Durlon® Style Thickness m y Gb a Gs
5X00 Series 1/16″ 1.5 1855 474 0.256 48
5X00 Series 1/8″ 2.5 2619 902 0.253 4
7000 Series 1/16″ 3 3347 497 0.226 3
7000 Series 1/8″ 3.2 3385 486 0.276 0.4
7760 (DuraSwell) 1/16″ 6.9 2412 95 0.609 0.4
7910 1/16″ 1.5 2416 502 0.289 0.001
7910 1/8″ 1.5 3576 736 0.237 9.1
8300 1/16″ 3.7 3515 512 0.355 13
8300 1/8″ 3 4014 460 0.313 0.427
8400 1/16″ 2.9 2410 380 0.311 0.01
8400 1/8″ 4.5 3967 391 0.321 0.014
8500 1/32″     410 0.25 190
8500 1/16″ 2.7 2359 650 0.33 200
8500 1/8″ 4.2 2931 400 0.35 20
8600 1/16″ 2.9 2540 343 0.325 0.3
8600 1/8″     866 0.273 37
8700 1/16″ 3.1 3127 546 0.455 12
8700 1/8″ 5 4000 758 0.34 0.01
8900 1/16″ 4.8 4851 915 0.428 0.02
8900 1/8″ 7.3 3730 567 0.556 0.26
9000 1/16″ 2.2 1937 639 0.22 55
9000 1/8″ 4.6 1639 495 0.262 65
9200W 1/16″ 1.5 952 153 0.36 15
9200W 1/8″ 4.2 827 96 0.437 14
9400 1/16″ 6.8 2765 1701 0.173 99
9400 1/8″     1412 0.164 248
9600 1/16″     1200 0.2 3.5
9600 1/8″     1400 0.19 1.5
9600 w/ DurCore 1/8″ 1.5 833 204 0.316 1.00E-07
FGS95 1/16″     970 0.038 1
FGS95 1/8″     970 0.038 1
FGL316 1/16″     816 0.38 1
FGL316 1/8″     816 0.38 1
FGT316 1/16″     1400 0.33 1
FGT316 1/8″     1400 0.33 1
FGM316 1/8″ 2.5 4000      
CFG 3/32″     557 0.325 2.21
DURTEC (FG) 1/8″ 1.5 833 187 0.467 0.5
DURTEC (ePTFE) 1/8″ 1.5 833 204 0.316 1.00E-07
SWG/FG 0.175″ 2.8 6500 86 0.594 0.1
SWG/Mica-FG 0.175″ 2.8 6500 90 0.59 0.1
SWG/PTFE 0.175″ 2.8 6500 173 0.405 1
KAMMPROFILE 1/8″ 4 1000 368 0.4 0.28
ETG-HT1000™ 1/16”          
ETG-SWG 0.175″ 2.8 6500 90 0.59 0.1
ETG-DURTEC 1/8″ 1.5 833 187 0.467 0.5
ETG-KAMMPROFILE 1/8″ 4 1000 368 0.4 0.28