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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 17th, 2014
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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
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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.
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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.
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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 Gb, a, Gs (1974)
– Accounts for tightness of a joint (leakage)
DIN E 2505 (1986, 1990)
– Improved version with bolt pre-stress
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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
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Proposed ASME Gasket FactorsNew 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 Gb, Gs & “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.
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PVRC Method Gb & a both give the gasket seating load, similar to M
which is know as the “maintenance” factor
Gs is associated with operating stress, similar to Y which is
the necessary gasket seating load.
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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.
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Testing Rig – Steel Platens
Gasket Samples
Leakage Measurement Sealing o-ring
Orifice
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Testing Rig
Hydraulic Pressure
Gauge
Press Frame
Nitrogen Supply
Line
Hydraulic Ram
Leakage
Measurement
Gauges x 3
Steel Platens x 3
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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.
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Gasket factors used for test samples
PVRC Gasket Factors M&Y Values
Test Material Gb (psi) a Gb (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
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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)
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Calculated Torque Value - M&Y vs PVRC
Gasket Method
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Associated Seating Stress - M&Y vs
PVRC Gasket Method
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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
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Leakage Rates – M&Y vs PVRC Gasket
Method
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Leakage Rates – M&Y vs PVRC Gasket
Method
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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.
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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.
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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”.
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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
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Questions