Evaluation of the Mechanical Behaviors
of Pipe Flange Connections with PTFE
Gaskets Subjected to Bending Moment
1. Introduction

behaviors of pipe flange connections with PTFE

The pipe flange connection with gasket is widely usedgasket are not well defined: gasket contact stressat petroleum-refining, chemical, and power-generating

distribution, sealing performance, changes in hub

plants. In Japan, asbestos gaskets were widely usedstress and axial bolt force, and other behaviors.

and intensively researched, since those were low-cost

The authors previously studied the abovementioned

and offered excellent heat resistance, sealingmechanical behaviors of pipe flange connections withperformance, durability, and ease of handling. １）- ３）

PTFE gasket at room temperature and high４）

However, a regulation

Winter 2018
No.34

connecting parts.5） However, the following mechanicalon the use of asbestos wastemperature and found that the connections with

implemented in 2008 due to its effects on human

PTFE gasket are superior to the compressed asbestos

health.

fiber sheet gasket. ６）, 7）

Asbestos gaskets can be categorized into two major

Japan is prone to earthquakes: recent ones include thetypes: the spiral-wound gasket containing asbestos

Hyogo-ken Nanbu Earthquake in 1995, the Niigata-ken

filler, and the compressed asbestos fiber sheet gasket.

Chuetsu-oki Earthquake in 2007, the Tohoku Pacific

When the asbestos regulation was introduced,

Offshore Earthquake in 2011, and the Kumamoto

replacing the asbestos of the spiral-wound gasket with

Earthquake in 2016. In addition, according to some,flexible graphite filler did not cause any major

the Nankai Megathrust Earthquake is expected toproblem. However, regarding compressed sheet

occur within the next 10 years. There are manygaskets, it was difficult to replace the material forplants and buildings located near the postulated

several reasons, and so the compressed aramid-fiber

seismic center, which would likely suffer serious

sheet gasket was developed as an alternative to thedamage. In the Hyogo-ken Nanbu Earthquake,compressed asbestos fiber sheet gasket. However, itliquefaction caused bending on pipe flange

required a higher rubber content, which caused

connections, resulting in leakage of LP gas and thechallenges for heat resistance. While the flexible

issuance of an evacuation advisory to 70,000 people.

graphite sheet gasket had no problems in heat

Therefore, countermeasures against earthquakes areresistance, the gasket surface is vulnerable toessential for plants. Sawa et al. studied the mechanicalscratches because the material is brittle. Therefore,

behaviors of the flange connection with spiral-wound

the improved polytetrafluoroethylene （PTFE）

gasket when subjected to bending moment.８）-10） At theblended gasket came to be widely used. This gasket

Tightness Testing and Research Laboratory of Ecolehas excellent chemical resistance as well as heat

Polytechnique de Montreal（Canada）, the characteristics

resistance, and the conventional problems of creepof change in axial bolt force when flange connections

characteristics were overcome by devising formulation

with expanded PTFE gasket are subjected to bending

and production methods. Therefore, the improved

moment were studied. 11） Meanwhile, Koves et al.

PTFE blended gasket came to be used in many

described a method to evaluate the effects of bending

7

Technical Papers

moment using equivalent internal pressure.12）-16）

nominal diameter of the gasket was ASME/ANSI

However, there have been no studies on the pipeclass 300 4-inch with a thickness of 1.5 mm.

flange connection with PTFE gasket subjected toFlange hub stress and axial bolt forces werebending moment and internal pressure. As PTFE-

measured using the strain gauges; the leak rate wasblended gaskets are widely used, countermeasures formeasured with a helium leak detector according to thedisasters including earthquakes are required, and so it

sniffer method. The initial bolt tightening was

is important to evaluate the mechanical behavior of

conducted according to JIS B 2251“Bolt tightening

pipe flange connections with PTFE gasket.

procedure for pressure boundary flanged joint

This study aimed to determine the mechanicalassembly.”18） After bolt tightening, four-point bending

behaviors of the pipe flange connection with PTFE

moment and inner pressure were applied and thengasket subjected to bending moment and internalflange hub stress, change in axial bolt force and leakpressure using FEM stress analyses and experiments.

rate were measured. M, which is the bending moment

Firstly, the fundamental characteristics of a gasket

acting on the connection, was calculated using thewere measured according to JIS B 2490. In finite

equation M = W/2 ×α, where α is the effective pipe

element method（FEM）stress analyses, axial bolt

length（= 1.6 m）. The initial axial bolt force was 11.1

force, hub stress, and the gasket contact stresskN per bolt to give an average gasket stress 10 MPa;

distribution were calculated. In addition, leak rate was

the internal pressure applied on the connection was 2

estimated based on the gasket contact stress

MPa.

Winter 2018

distribution and fundamental characteristics. To verify
the method of FEM stress analyses, the FEM results
were compared with those from experiments on axial
bolt force and hub stress. In the experiments, leakrate from connections, axial bolt force, and hub stresswere measured.The connection size was ASME/ANSI
class 300 4-inch. The gasket used was the No. GF300,

No.34（a）Equipment

which contains no rubber and so suffers no chemicaldegradation due to heat and deterioration over time.
Accordingly, it is possible to conduct a precise
mechanical evaluation with the No. GF300.

2. Experimental method
Figure1（a）shows the experiment equipment used to
study the effects of bending moment on the pipe
flange connection; Figure1（b）outlines the equipment.
Through four-point bending, bending moment wasapplied to the pipe flange connection. In addition,internal pressure could be applied to the piping（b）Outline of the equipment
Figure1Experiment equipment used to measure themechanical behaviors of a pipe flange
connection subjected to four-point bending
moment3. Gasket characteristics

through a connected helium gas cylinder. The

For FEM stress analyses, compression and sealing

connection size was ASME/ANSI class 300 4-inch; thecharacteristics of gaskets were evaluated.

flange and pipe material was SUS304.

17）

Each pipe

was 2 m long, and the total length of the equipment

3-1）Compression characteristics

was approximately 4 m. To match the connection, theThe stress–strain curve of gasket at room8

Evaluation of the Mechanical Behaviors of Pipe Flange Connections with PTFE Gaskets Subjected to Bending Moment

temperature was evaluated. Figure2 shows an outline of
the experimental equipment used for the evaluation.19）
The size of the flange raised face is equivalent to thecompressed in a compression tester. Figure3 shows
the stress–strain curve of No. GF300 gaskets obtained
from the experiments. The strain value was calculated

leak rate

size stipulated in JIS 10K 50A; the raised face wasby averaging the indicated values of three displacementgauges to obtain the amount of compression, and thendividing the compression amount by the initial

Gasket contact stress
Figure4 Relationship between leakrate and gasket contact stressthickness to obtain the strain value.
Even though the gasket contact stress was increased3-2）Sealing performance

to approximately 40 MPa, the leak rate was too small

The sealing performance of gasket was evaluatedto be measured when the contact stress exceeded 20

using the equipment shown in Figure2 according toMPa, so no data is shown in the graph.

JIS B 2490. The pressure of the helium gas supplied
from the cylinder was increased to 2 MPa, then theleak rate from the gasket, which was collected using a

4. FEM stress analysis

Winter 2018sleeve, was measured with a soap-film flowmeter.

Figure5 shows the FEM model of the pipe flange

Figure4 indicates the relationship between the leakconnection with gasket subjected to four-point

rate and gasket contact stress obtained from thebending and internal pressure as shown in Figure1. In

experiment.

consideration of symmetry, the model was arranged
at 1/4 scale（axial direction = 1/2, circumferential

GasketNo.34

Compression

O-ringdirection = 1/2）. The threads of bolts and nuts were
Soap-film
flowmeter

Platenomitted, and the nut shape was simplified fromhexagonal to circular having the same cross sectional
area. Figure 6 shows a boundary condition for the

Sleeve

FEM stress analyses. In the illustration, the condition
was replicated in the following manner: 1）Symmetricfaces were fixed, and 2）Regarding bolt tightening,
tension equivalent to the axial force was applied to

Figure2 O utline of test equipment used to evaluate gasket
characteristics

each bolt model. Regarding four-point bending aftertightening the piping ends, a load of W/2 was applied
to jigs located around flanges. The effects of internalpressure were replicated by applying pressure to theinternal side of the pipe flange vessel. Flanges andbolts were modeled using elastoplasticity elements;

Stressgaskets were modeled using ABAQUS gasket
elements. In the FEM analyses, axial bolt force, flange
hub stress, and the gasket contact stress distribution
were calculated.
StrainFigure39Stress–strain curves of No. GF300 gasket

Technical Papers

the bolts, resulting in increased axial force. The
increased tension on the side of bolt #1 and #2 is dueto this increased axial force. On the other hand, thecontact surface of the flange closes. The closing
compresses bolts, reducing axial force on the side ofbolt #3 and #4. The results of the FEM analyses andW/2experiments matched well, verifying the robustness ofthe FEM stress analyses.

Axial bolt force

Tension side

Pipe flange
GasketBolt
Figure5

FEM model of a pipe flange connection

Compression
sideBolt #3

Bending moment
Figure7 C hanges in axial bolt force when bending moment is applied
to the pipe flange connection（The bending moment wascalculated from FEM stress analyses and experiments.)5-2）Gasket Contact stress distribution
Figure8 shows contour figures of the gasket contact
stress distribution at the following timings: when theflange was initially tightened; when a bending momentof 3500 N/m was applied to the pipe flange connection;

Bolt #2
Bolt #1
At tightening
Figure6Winter 2018

W/2

Bolt #4

Compression
side

Tensionside
At bending is applied

Boundary conditions in FEM stress analyses

5. Results‌of FEM stressanalyses and experiments

and when a bending moment of 3500 N/m and internalpressure were applied to the pipe flange connection.
The contact gasket stress is found to be zero at the
non-contacted gasket area, that is, at the most outerradius part of the gasket. The gasket contact stress
distribution at initial tightening indicates increasing
contact stress in the radius direction of the outside5-1）Change in Axial bolt force

diameter due to flange rotation. In the circumferential

Figure7 shows changes in axial force for the four bolts

direction, the contact-stress gradient is negligible.

shown in Figure6. The values were obtained by FEM

When a bending moment of 3500 N/m was applied,stress analyses and experiments. The abscissapart of the gasket’s contact stress significantly

represents the bending moment M ; the ordinate

decreased（left figure）; when internal pressure wasrepresents axial bolt force; the solid line represents theapplied, the gasket’s contact stress decreased further.

results of experiments; the dashed line represents the

Figure9 shows the gasket contact stress distribution in

results of FEM stress analyses. The axial force values

the outermost diameter contact area（r = 46.05 mm）inof bolt #1 and #2 increase with increasing bending

the circumferential direction at each step. The graphmoment, whereas those of bolt #3 and #4 decrease.

indicates marked changes in contact stress distribution

The contact surface of the flange opens due to bending

due to opening of the flange’s contact surface; themoment on the piping. The opening applies tension to

opening was caused by the bending moment applied
10

No.34

Evaluation of the Mechanical Behaviors of Pipe Flange Connections with PTFE Gaskets Subjected to Bending Momentto the flange.

exceeds approximately 3000N/m, the leak rate

Next, The leak rate from the connection is estimatedsubstantially increases. As Figure8 shows, part of theusing the contact gasket stress distribution obtained

gasket’s contact stress became zero due to bending

from the FEM and the fundamental leakage

moment; this zero stress appears to have caused the

20）
−21）

. Figure10 shows

substantial increase. The estimated leak rate and thethe estimated leak rate and the experimental results.

experimental results matched well, indicating the

As the bending moment increases, the leak ratevalidity of the FEM analyses and the method of

gradually increases; when the bending moment

estimating leak rate.

performance shown in Figure4

Gasketcontact
stressFigure11 shows the relationship between the
maximum principal stress in the axial direction, which
occurs at the flange hub, and bending moment. The

At initial tightening
Tension side5-3）Flange Hub stressgraph also shows values calculated using an ASME

Compression side

Boiler & Pressure Vessel Code Section Ⅷ Division 1“Rules for construction of Pressure Vessels”App.2,（2004）.（in this case, ASME values were calculated
under the condition of zero bending moment）.22） This

Winter 2018

when bending moment of3500 N/mwhen internal bending
pressure of 3500 N/m

Figure8 Gasket‌Contact stress distribution obtained from
FEM stress analyses

graph indicates that as the bending moment increases,
hub stress, which was evaluated from the experiments
and FEM stress analyses, increases. The results of theexperiments and FEM stress analyses matched well,indicating the validity of the analyses.

Step 1: Tightening
Step 2: Bending moment is applied
Step 3: ‌Bending moment and internalpressure are applied
Angle in the circumferential direction

Figure9Flange hub stress

Gasket contact stress

No.34

Gasket Contact stress distribution at each step

Bending moment
Figure11

Effects of bending moment on hub stress

6. Discussion
leak rate

6-1）‌Effects of nominal diameter ofconnection on axial bolt force behavior
The effects of nominal diameter on the axial force
behavior of the bolts in the connection were studied
Bending moment

by FEM stress analysis. Figure12 shows the greatest

Figure10 Comparison‌of leak rate from connection whenbending moment is appliedchanges in the increase and decrease of axial bolt force

11Technical Papers

when bending moment was applied to a pipe flange

application（solid blue line）. The ordinate represents

connection with a No. GF300 gasket. The nominal

the leak rate and the abscissa represents the bending

diameters were chosen as 4, 8, 12, 16, 20, 24 inches andmoment. When the bending moment exceeds 3000 N/

internal pressure was not applied. The ordinatem, the order of“Step 2: internal pressure application,

represents the axial bolt force ratio（=（Ff+Ft）/

Step 3: bending moment application”is associated withFf）,where Ff is bolt preload and Ft is an increment inslightly larger leak rate; however, the difference in leakaxial bolt force; the abscissa represents the bending

rate was small and almost at the level of error. In the

moment per bolt. the initial mean gasket contact stressexperiments, the order in which bending moment andwas 10 MPa; the maximum bending moment M, whichinternal pressure were applied showed no substantial

was applied to the flange, was 3500 N/m, indicating

effects on leak rate.

the following: the bolt number N increases whennominal diameter is greater, reducing the maximum
M/N. The solid line represents data for bolts subjected
to tension by bending moment; the dashed line
（contraction）by bending moment The figure indicates
the trend that the smaller the nominal diameter, thegreater the effects of bending moment on axial bolt

leak rate

represents the data for bolts subjected to compression

applied to the flange, the sealing properties are safer
when the nominal diameter is greater.

Bending moment
Figure13 Effects‌
on sealing performance of the order in which
bending moment and inner pressure are applied

Changes in axial bolt force

6-3）‌Effects of action point of bending
moment on leakage volume
As sown in Figure14, the effects of applying bending
moment at different points of bolt configuration werestudied. In Figure14（a）the bolts were arranged in a
vertically symmetrical manner; this configuration is
widely used（pattern A）. In Figure14（b）, two bolts
Bending moment per bolt

Figure12 E
 ffects of nominal diameter on behaviors of change
in axial bolt force in pipe flange connections
subjected to bending moment

are placed on the vertical line（pattern B）. Figure15
shows the relationship between leak rate and bending
moment for each pattern.
The results show that pattern A was associated with

6-2）‌Effects of the order in which bending
moment and inner pressure are applied

smaller leak rate than pattern B. Placing bolts at the

Figure13 shows the effects on the leak rate of thealleviate the reduction in contact pressure and sealingorder in which bending moment and inner pressure

performance; however, the commonly-used pattern A

are applied. The graph shows the results of leakage

was associated with greater sealing performance. In

tests which were conducted in the following two

pattern A, four bolts resist the opening force, whereasorders: Step 1: tightening, Step 2: bending-momentin pattern B, only three bolts resist the opening force.

application, Step 3: internal pressure application（solid

Therefore, in total, the opening appeared to be greater

red line）; and Step 1: tightening, Step 2: internalin pattern B.

position where the opening is largest was thought topressure application, Step 3: bending moment
12

Winter 2018

force. Thus, for the equivalent bending moment

No.34

Evaluation of the Mechanical Behaviors of Pipe Flange Connections with PTFE Gaskets Subjected to Bending Moment

Bending load

Bending load

bending moment per bolt as M/N, the evaluation
revealed the trend that the greater the nominal
diameter, the stronger the resistance to bending
moment.
（3） The gasket contact stress distributions wereobtained from the FEM stress analyses; therelationship between the leak rate and contact

Pattern A
Figure14

Pattern B

where bending moment is appliedstresswas obtained from the experiments.

Using the two results, leak rate was estimated.
The estimated and experimental values matched
relatively well, indicating the validity of both themethods of analyzing FEM stress andestimating leak rate.

leak rate（4） The effects on sealing performance of the orderin which bending moment and internal pressure
are applied were studied. The results indicatedBending moment

Winter 2018
No.34

Figure15 Effects‌of where bending moment on sealing
performance

7. Conclusions

that the order does not significantly affect leakrate.
（5） The effects of the action point of bending moment
on sealing performance were studied. The results
indicated that the common bolt arrangement（pattern A）is associated with greater resistanceIn this study, experiments and FEM stress analyses

to bending moment on the piping than is thewere used to study the mechanical behaviors of axial

arrangement in which two bolts are arranged onbolt force, hub stress, and sealing performance of thethe vertical line（pattern B）.

pipe flange connection with PTFE gasket subjected tobending moment. The following conclusions wereobtained.

8. References（1） FEM stress analyses were used to calculate the１）T. TAKAKI, K. SATO, Y. YAMANAKA, T. FUKUOKA,

gasket contact stress of a 4-inch pipe flange“Effects of Flange Rotation on the Sealing

connection subjected to bending moment andPerformance of Pipe Flange Connections”, ASME

internal pressure. When bending moment was

PVP Vol.478,（2004）,pp.121-128.

applied, the contact stress decreased on part of２）T . SAWA, N. OGATA, T. NISHIDA,“Stressthe gasket contact surface. When the bending

Analysis and Determination of Bolted Preload in

moment reached approximately 3500 N/m, thePipe Flange Connections with Gasket undercontact stress became zero, causing a rapid

Internal pressure”, Transactions of the ASME,

increase in leak rate.

Journal of Pressure Vessel Technology, Vol.124,（2） The results of the experiments and FEM stress３）T. KOBAYASHI, T. NISHIDA, Y. YAMANAKA,

force when bending moment was applied to the“Effect of Creep-Relaxation Characteristics offlange. The evaluation results indicated that theGaskets on the Bolt Loads of Gasketed Joints”,

results of the FEM stress analyses andexperiments matched well. In addition, when
13

（2002）,pp.22-27.

analyses were used to evaluate the axial bolt

ASME PVP Vol.457,（2003）, pp.111-118.
４）Ministry of Health, Labour, and Welfare, Cabinet

Technical Papers

Order on the Partial Revision of the Order for
Enforcement of the Industrial Safety and Health
Act, Cabinet Order No. 349（2008）.
５）Nippon Valqua Industries, Ltd., Gasket Catalogue,
Catalogue No. YC08（2016）.
６）K. SATO, A. MURAMATSU, T. KOBAYASHI, T.
SAWA, “FEM Stress Analysis and Sealing

316SS/GORE-TEX gasket style”, 1996.
12）W . J. Koves,“Analysis of Flange Joints Under
External loads”, Journal of Pressure Vessel
Technology, Vol.118, pp59-63,（1996）.
13）W. J. Koves,“Design for Leakage in Flange Joints
under External Loads”PVP2005-71254, Proceedingof ASME PVP 2005 Conference,（2005）.

Performance of Bolted Flanged Connections using14）E. C. Rodabaugh, S. E. Moore,“Evaluation of thePTFE Blended Gaskets under Internal Pressure”,

Bolting and Flanges of ANSI B16.5 Flanged Joints –PVP2015-45268, Proceeding of ASME PVP 2015

ASME Part A Design Rules”（1976）,.

Conference,（2015）.
７）K. SATO, T. SAWA, T. KOBAYASHI,“FEM STRESSANALYSIS of Long-term Sealing Performance for15）C. J. Dekker, H. J. Brink,“External flange loads and‘Koves’-method”, International Journal of Pressure
Vessels and Piping, Vol.79, pp145-155,（2002）.

Bolted Pipe Flange Connections with PTFE

16）W. Brown,“Improved Analysis of External Loads on

Blended Gaskets under Elevated Temperature”,

Flanged Joints”PVP2013-97814, Proceeding of

PVP2016-63372, Proceeding of ASME PVP 2016

ASME PVP 2013 Conference,（2013）.

Conference,（2016）.
８）T. SAWA, Y. TAKAGI, K. SATO, Y. OMIYA, H.
performance of pipe flange connection with gaskets

Fittings”,（1996）.
18）Japanese Industrial Standards JIS B 2251“Flange
Joint Assembly Guidelines”（2008）.

under external bending moment and internal19）Japanese Industrial Standards. JIS B 2490“Testpressure”, PVP2012-78411, Proceeding of ASME PVP

method for sealing behavior of gaskets for pipe

2012 Conference,（2012）.

flanges”,（2008）.

９）Y. Takagi, H. Torii, T. Sawa, K. Funada,“Evaluation20）Y. OMIYA, T. SAWA, Y. TAKAGI,“Stress Analysis

of Sealing Performance of Pipe Flange Connection

and Design of Bolted Flange Connections under

Subjected to External Bending Moments”,

Internal Pressure”, PVP2014-28606, Proceeding of

PVP2009-77494, Proceeding of ASME PVP 2009

ASME PVP 2014 Conference,（2014）.

Conference,（2009）.

21）Y. OMIYA, T. SAWA,“Stress Analysis and Sealing10）F . Ando, T. Sawa, M. Ikeda, and T. Furuya,

Performance Evaluation of Bolted Pipe Flange“Assessing Leakage of Bolted Flanged Joints under

Connections with Smaller and Larger NominalInternal Pressure and External Bending Moment”,

Diameter under Repeated Temperature Changes”,

Proceeding of ASME PVP 1998 Conference, 376,

PVP2014-28730, Proceeding of ASME PVP 2014
Conference,（2014）.

pp.39-44,（1998）.
11）TTRL Tightness Testing and Research Laboratory,22）ASME Boiler & Pressure Vessel Code Section Ⅷ“Room temperature external bending moment

Division 1“Rules for construction of Pressuretightness test（ROBT）on the selco seal 4”cl 150 lb

Vessels”App.2,（2004）.

Koji Sato
Corporate Research andDevelopment Group
Product Development DivisionⅠ

Toshiyuki Sawa University of Hiroshima
Riichi Morimoto Mitsubishi Chemical Corporation
Takashi Kobayashi Numazu College
Yuta Motono
Corporate Research and Development Group
Product Development Division Ⅰ
14Winter 2018

DOI,“Effects of scattered bolt preload on the sealing17）ANSI/ASME B 16.5,“Pipe Flanges and Flanged

No.34