Evaluation of Basic Sealing Propertiesof the Pipe Flange Connection withMetallic Flat Gasket
1. Introduction

leakage of 1×10−4 Pa･m3/s level due to the limitationsof the measuring functions of evaluation equipment.

flat gaskets and ring joint gaskets are widely used

The objective of this paper is to discuss the leak rate

within the flange connection under high temperatureof 1×10−4 〜 10−7 Pa･m3/s for metallic gaskets. The

and high internal pressure conditions in petroleum

sealing performance of the gaskets under compression

refining, petrochemical, and power plants. However,was measured for two types of gasket materials

the some leakage accidents occur in the connections.

（aluminum and copper）and three types of gasket

The main reasons of those are considered that thewidth using platen by the experiments and the FEM

mechanical characteristics and tightening method ofcalculations. In addition, the mechanical characteristics

the gasketed connection have not been clarified. Manyof pipe flange connection with metallic gasket wereprevious studies for soft gasket such as theevaluated using the ASME/ANSI class 300 2-inch

compressed fiber sheet gaskets, PTFE gaskets, andflange.

High Pressure Institute of Japan（HPI）, universities,and manufacturers. However, there have been few
studies on a flanged connection with the metallicgasket, so their behaviors remain unknown1）,2）.
Kondo et al. reported the plastic strain on the gasket

Leakage volume [Pa･m3/s]

spiral wound gaskets have been performed inAluminum

Chromiummolybdenum steel
Copperface made the sealing performance in metallic flat
gasket improved3）-7）.
The relationship between the leak rate of metallic flat

Mean gasket stress [MPa]（a）The relationship between leak rate and mean contact gasket stressgaskets made by chromium-molybdenum-steel, copperand aluminum and the mean contact gasket stresswere shown in Figure1（a）. It was found the sealing
performances were improved as Young’s modulus andsurface hardness of material decrease. In addition,
when the ratio of mean contact gasket stress for theyield stress was related with leak rate, the leak rate

Leakage volume [Pa･m3/s]

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It is known that the metallic gaskets such as metal

American Society of Mechanical Engineers（ASME）,

No.33of prior studies have been discussed around thedecreased exponentially at the value of ratio is near
1.0 as shown in Figure1（b）. Those data indicated that

Chromiummolybdenum steel

CopperAluminum

Mean gasket stress/yield stress [MPa]the sealing performance of metallic gasket was（b） The relationship between the leak rate and the rationof the mean contact gasket stress for yield stressinfluenced so much by the yield stress. However, mostFigure1

5

The sealing performance of metallic flat gaskets

Technical Papers

2. Experimental Methodwith the axi-symmetric model, however, the 3-D model
was employed to compare with one for the pipe flange

Figure2 showed the experimental setup of platenconnection. The gasket was modeled as elastoplastic

device in which metallic flat gasket was compressed

element, and the Platens were modeled as elastic

for measuring an amount of leakage. The experimental

element. The platen was under compression, then thesetup was consisted of the compression tester（AUTO

gasket stress, compression displacement andGRAPH 500KND; made by Shimadzu Corporation）

corresponding plastic strain were calculated. Here, theconsisted of the platen made of SUS304, a helium gas

corresponding plastic strain is defined as:

cylinder, a pressure gauge, a flow meter for amount ofleakage and the displacement gages. The device formeasuring leak rate could be alternately switchedfunctions between a soap-film flowmeter and helium
leak detector（made by ULVAC）. When the leak rate
was 1×10−4 Pa･m3/s or lower, the measurement wasperformed using the helium leak detector. The
materials of flat metallic gasket were aluminum

Gasket（A1050）and copper（C1020）. The sizes of gasket
were φ25×φ20（outside×inside diameter）,φ30×φ20,Platenchosen as 3.0mm. The helium gas was applied toFigure3FE model for platen testing

4MPa after the platen with gasket is compressed, andthen, the leak rate and displacements of gasket weremeasured. In a test sequence of compression andrecompression, the contact gasket stress was changedin the following stepwise: 0→ 180→ 0 MPa foraluminum, and 0 → 450 → 0 MPa for copper.

4. Results of Experiments and FEM
calculations
Figure4 showed the results of platen test foraluminum and copper gaskets. It was found that thedeformation increased as the outer diameter of gasket

GasketCompression Rubber O-ring Soap-film
flowmeter

decreased（as the gasket width decreased）in bothmaterials. This was resulted in the influence of shapeof gasket.

PlatenFigure5 showed the surface conditions of theSleeve

aluminum flat gasket with a diameter of φ20×φ40 andthe platen after the compression test. It seemed that
there were white discolorations at inner and outer

Illustration of platen test equipment

side positions of gasket on both the gasket face and3. FEM Calculations Method

aluminum gasket would have been deformed to inner

Figure2

the platen faces. Those imply that the compressedand outer diameter and be sharpened by the friction

The FEM calculations were performed for the platenwith the platen faces because of remained small

test shown in section 2, using the numerical code

aluminum particles on the surface.

ABAQUS. Figure3 showed the 3-D FE model of theThe relationship between leakage volume obtained

platen test equipment with metallic flat gasket.

from the platen test and the mean gasket stress was

Originally, an effective evaluation can be calculated

shown in Figure6. Use of a helium leak detector
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φ40×φ20, φ65×φ 55mm, and the gasket thickness wasNo.33

Evaluation of Basic Sealing Properties of the Pipe Flange Connection with Metallic Flat Gasket

allowed the measurement of very small leakage
results for both aluminum and copper gaskets showedthat application of a higher average gasket stress
reduced the leakage volume and that a reduction of
the mean gasket stress increased the leakage volume.
Also, the reduction rate of leakage volume became
more moderate at around 120 MPa for aluminum andGasket stress [MPa]volume of approx. 1×10−7 Pa･m3/s. The measurement

at around 250 MPa for copper.
In general, the relationship between leakage volume

Compression amount [mm]and mean gasket stress is known unchanged even（a）Compression properties of aluminum flat gaskets

when the gasket width is changed. Therefore, theorganized according to the mean gasket stress.
During the unloading process, the leakage volume
rapidly increased at approximately 30 MPa foraluminum gaskets and at approximately 50 MPa forcopper gaskets. This was considered to have beenloading between the flange and gasket surfaces.
Figure7 showed the results of a Finite Element（b）Compression properties of copper flat gaskets

showed the distribution contours of gasket stress andcorresponding plastic strain when the gasket material

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Compression amount [mm]Analysis which replicated the platen test. The figure

Figure4Compression properties of copper flat gaskets

is aluminum and the gasket dimensions are φ20×φ25.
The figure indicated that the corresponding plasticstrain rapidly increased when the mean gasket stressincreased from 100 MPa to 120 MPa. At that time, thegasket might have undergone a marked plastic
deformation to fill the very small roughness on theflange surface to improve sealing properties. This

Figure5

Surfaces of gasket and flanges after compression test

result indicates that plastic strain of a gasket surface
is necessary for metal gaskets to exert their excellent
sealing properties.

Leakage volume [Pa･m3/s]

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caused by the loss of conformability of initial step ofGasket stress [MPa]sealing properties of metal flat gaskets can be

Gasket stress [MPa]（a）Relationship between leak rate and contact gasket
stress for aluminum flat gaskets
7Technical Papers

Leakage volume [Pa･m3/s]

stress was applied to the cross sectional area in thebolt at initial tightening, while the displacements ofthe symmetrical plane were fixed in the axial
direction. In the experiments, each axial bolt force wasmeasured using the strain gauge attached to theshank of each bolt and the outputs are recorded in adata logger. The helium gas 4MPa was applied fromcylinder and the leak rate is measured by pressure
Contact pressure [MPa]（b）Relationship between leak rate and contact gasket
stress for copper flat gaskets
Figure6 Relationship between leak rate and contact gasket stressdrop method.
Figure10 showed the leak rate from aluminum flat
gasket with dimensions of φ65×φ55 for the bolted
flange connection (2inch) with metallic flat gasket
which was described in dotted line and the measured
result in the platen tests was described in line.
Although the value of lower leak rate from pipe flange
connection could not be measured by the pressure（a）Contact gasket stress distributions

drop method, it was found that the leak rate of bolted
flange connection behaved similar with that in thethe bolted flange connection and the plastic
deformation occurred in lower average gasket stress（b）Corresponding plastic strain distributions

region. The leak rate decreased substantially when

Figure7 D istributions of contact gasket stress andcorresponding plastic strain at each step obtained
from FEM calculations

the contact gasket stress was applied 100MPa.

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platen test because it was due to the flange rotation in

Figure11 showed the corresponding plastic strain
distributions at that timing using FEM calculations. It

5. E
 valuations of pipe flanged
connection with the metal gasket

indicated that the corresponding plastic strain was

The previous sections described the evaluation using

100MPa. It was considered that the sealinga platen, which enabled ideal homogeneous compression.

performance increased so much under un-uniform

In this section, the evaluation of characteristics using

stress compression in pipe flange connection because

actual pipe flange connection was discussed.

of increasing of the corresponding plastic strain.

Figure8 showed the test equipment for pipe flange

The method of determining bolt preload for achieving

connection, and figure9 showed the FEA model of theallowable leak rate（less than 1×10−4［Pa･m3/s］）was

pipe flange connection with gasket. The connection

proposed in reference 8）. This equation is described insizes were chosen as ASME/ANSI class 300 2 inch

Eq.（1）.

small when the contact gasket stress was 90MPa,
however rapidly increased at contact gasket stressand bolts were eight M16. Taking into account the（1）symmetry of the connection, a one-thirty two part ofwhere, d2 is the outside diameter and d1 the insideconnection was analyzed. In the FEM model, it wasdiameter of the gasket, N is the bolt number and b isassumed that the nut was connected with a bolt andthe coefficient which indicates the initiation of thethe screw thread of the bolt was not taken into

plastic deformation in the metallic gasket.

account. In addition, for simplicity, the hexagonal nuts

Figure12 showed the leak rate of 2”bolted flange

were replaced with a circle shape. The uniform bolt

connection, the abscissa was bolt preload from8No.33

Evaluation of Basic Sealing Properties of the Pipe Flange Connection with Metallic Flat Gasket

average gasket stress in Figure9 The triangle marks
Eq.（1）. The compressive yield strength of aluminumand copper gaskets were 120 and 250MPa, respectively.
In addition, the factor of better sealing used was 0.8 in
the previous paper 6）. The leak rate less than 1×10−4［Pa･m 3/s］ can be obtained by the bolt preloads

PlatenLeakage volume [Pa･m3/s]（○ , △ , □）showed the bolt preload calculated by

Pipe flanged fastener

calculated by Eq.（1）. Thus, Eq.（1）was verified fordetermining the bolt preload to satisfy the allowableleak rate in bolted flange connection with flat metallicgasket.

Gasket stress [MPa]Figure10 C omparison of leak rate from platen test and pipe
flange connection

StressCorresponding plastic strain

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Leakage volume [Pa･m3/s]

Figure11 T he corresponding plastic strain distributions ofaluminum flat gasket in pipe flange connection

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Figure8

Illustration of pipe flanged connection

Bolt axial tension [kN]

Leakage volume [Pa･m3/s]（a）Aluminum flat gasket

Bolt axial tension [kN]（b）Copper flat gasket
Figure9 F
 EA model of pipe flange connection with metalflat gasket
9Figure12

 easurement results and estimated results ofMleak rate for pipe flanged connection

Technical Papers

Japanese）Vol. 75, 756th issue, pp. 51–56; 2009

6. Conclusion

3）Koji Kondo, Shota Tsubaki, Toshiyuki Sawa, andIn the present paper, the leak rate of 10−7 level for flat

Yuya Omiya. The Sealing Characteristics of Bolted

metallic gaskets which were compressed using theFlanged Connections with Metal Flat Gasket underplaten devise testing machine was measured. In

Internal Pressure, Journal of High Pressure Instituteaddition, the leak rate in the bolted flange connectionof Japan Vol. 52 No. 1, pp. 4–15; 2014

with flat metallic gaskets was also measured. The4）Koji Kondo, Shota Tsubaki, Toshiyuki Sawa, andcontact gasket stress distributions in both platen test

Yuya Omiya. FEM stress analysis and sealing

and bolted flange connection with flat metallic gasket

performance evaluation of bolted flanged connections

were analyzed using FEA calculations. The resultswith ring joint gasket under internal pressure,obtained are as follows.

Transactions of the JSME（in Japanese）Vol. 80,（1） The leak rate of the metallic gaskets which were816th issue, pp. 1–13; 2014

compressed in the platen devices was measured−75）Kondo, K.，
Sawa, T.，
Sato, K.，
T., Kikuchi，and Tsubaki,3in the 1×10 ［Pa･m /s］） level using bothS.，“The sealing characteristics of bolted flange

methods of a soap film flow meter and a helium

connection with metal gasket”，ASME Pressure
Vessels and piping Conference, PVP2012-78413（2012）leak detector.

6）Kondo, K.，
Tsubaki, S.，
Sawa, T.，
Sato, K.，
and Omiya,leak rate was independent of the dimensions ofY.，“Sealing performance evaluation in bolted flangegaskets. In addition, the leak rate decreased withconnections with ring joint gasket subjected to

an increase of the gasket stress linearly to theinternal pressure”, ASME Pressure Vessels andleak rate level of 10−6 which corresponded to thepiping Conference，PVP2013-97173（2013）7）Kondo, K.，
Tsubaki, S.，
Sawa, T.，
Omiya, Y.，
and Sato,

gasket yield strength.
（3） In an ASME/ANSI class 300 2-inch pipe flange

K.，“FEM stress analysis and the sealingconnection, sealing properties were also found toperformance evaluation of bolted flange connections

have been markedly improved when part of thewith metal flat gaskets”，ASME Pressure Vessels

gasket's contact surface had yielded.

and piping Conference，PVP2013-97828（2013）（4） It was provided a method for calculating the axial8）Kondo, K.，and Sawa, T.，“A Determination method

tension required for initial bolt fastening of aof bolt preload for bolted pipe flange connections−6fastener under a basic leakage volume of 1×10

with metal gaskets under internal pressure”，ASME

Pa･m3/s and compared calculated values withPressure Vessels and piping Conference，PVP2015-experimental results to verify the method.

45163（2015）

7. References
1）SAWA, T., HIGURASHI, N., AKAGAWA, H,“StressAnalysis of Pipe Flange Connections”, Transactionsof the ASME, Journal of Pressure Vessel Technology,
Vol.113, No.4, pp.497-503（1991.11）
2）Tadao Fukuta, Koichi Ozaki, Jun Kajiya, and Teiji
Hayakawa. Structural Behavior and Leakage
Characteristics of Pipe Flange Structure under
Bolting up Load and Internal Pressure（In Case ofFlat Metal Gaskets）, Transactions of the JSME（inKouji Satou
Corporate Research andDevelopment GroupDevelopment DivisionYasuharu Kondou SHINKO PLANTECH CO., LTD.
Toshiyuki Sawa Professor Emeritus at the University of Hiroshima
Satomi Takahashi Corporate Research and Development Group
10Summer 2017（2） In the platen device tests, it was found that theNo.33