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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.

rott graphic

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 Gb a Gs
5X00 Series 1/16" 474 0.256 48
5X00 Series 1/8" 902 0.253 4
7000 Series 1/16" 497 0.226 3
7000 Series 1/8" 486 0.276 0.4
7760 (DuraSwell) 1/16" 95 0.609 0.4
7910 1/16" 502 0.289 0.001
7910 1/8" 736 0.237 9.1
8300 1/16" 512 0.355 13
8300 1/8" 460 0.313 0.427
8400 1/16" 380 0.311 0.01
8400 1/8" 391 0.321 0.014
8500 1/32" 410 0.25 190
8500 1/16" 650 0.33 200
8500 1/8" 400 0.35 20
8600 1/16" 343 0.325 0.3
8600 1/8" 866 0.273 37
8700 1/16" 546 0.455 12
8700 1/8" 758 0.34 0.01
8900 1/16" 915 0.428 0.02
8900 1/8" 567 0.556 0.26
9000 1/16" 639 0.22 55
9000 1/8" 495 0.262 65
9200W 1/16" 153 0.36 15
9200W 1/8" 96 0.437 14
9400 1/16" 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" 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
CFG 3/32" 557 0.325 2.21
DURTEC (FG) 1/8" 187 0.467 0.5
DURTEC (ePTFE) 1/8" 204 0.316 1.00E-07
SWG/FG 0.175" 86 0.594 0.1
SWG/Mica-FG 0.175" 90 0.59 0.1
SWG/PTFE 0.175" 173 0.405 1
KAMMPROFILE 1/8" 368 0.4 0.28
ETG-SWG 0.175" 90 0.59 0.1
ETG-DURTEC 1/8" 187 0.467 0.5
ETG-KAMMPROFILE 1/8" 368 0.4 0.28