SERVICE QUALITY PERFORMANCE Leakage Behavior of Gaskets in...

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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)


28 (38) 1600 (11) 57 (77) 3792 (26.1)

Filled PTFE 15 (20) 910 (6.3) 29 (39) 1909 (13.2)


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


59.0 2 minutes 1.25 15 minutes

Filled PTFE 115.1 10 sec* 1.49 15 minutes


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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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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