Evaluation of the Bolted Flange Connection
with PTFE-blended Gasket under Hightemperature and Long-term condition
characteristics（JIS B 2490）,and creep characteristics

1. Introduction

for these gaskets have not been available. In addition,

The bolted flange connections with gasket have been

there has been insufficient verification as to whether

used under high temperature and long-term conditions

thisin oil plant, chemical plant, power plant and so on. In

superior sealing performance compared with theJapan, various asbestos gaskets used to be widely

conventional connection with asbestos gasket.

used because of excellent heat resistance, sealing

Previous studies have investigated the connection

performance, strength, ease of use, and low cost tillwith PTFE-blended gasket for its sealing performance

2008. The many studies for asbestos gaskets

haveat room temperature, flange hub stress, change in axial

been conducted, clarifying the characteristics of thebolt force（load factor）, and the contact gasket stressconnection with asbestos gasket such as sealing

distribution. The results showed that the sealing

performance. In Japan, the use of asbestos products

performance of the PTFE-blended gasket is quite

was restricted in 2008, requiring non-asbestos products

superior to that of connections with the compressed

to be used.

asbestos fiber sheet gasket.８）However, its performance

１-５）

Spring 2017
No.32６）

As a result, non-asbestos gaskets haveconnection

with

PTFE-blended

gaskethasbeen developed and improved.

at high temperatures is not well known.８） Therefore,

The asbestos gaskets are categorized into two major

research on the mechanical properties of the connection

types: the spiral wound gasket containing asbestos

including creep characteristics and sealing performance

filler and the compressed asbestos fiber sheet gasket.

under high temperatures and long-term condition are

For the substitution of asbestos, asbestos for spiralrequired.

wound gaskets was replaced with flexible graphite,

The objective of the present paper is to examine theand it caused no major problems. On the other hand,mechanical characteristics of bolted pipe flange

the compressed aramid fiber sheet gasket, the flexible

connections

graphite sheet gasket and the PTFE-blended gasket

elevated temperature using FEM calculations andwithPTFE-blendedgaskets

underhave been developed . The compressed sheet gaskets

experiments. Firstly, the fundamental characteristics

containing aramid fibers shows low resistant to heatof the PTFE-blended gasket such as stress–strain

because they contained a lot of rubber, and the flexible

curves, thermal expansion coefficient, and fundamental

graphite sheet gaskets are so fragile and easy toleakage characteristics are measured. In addition, thescratch. Therefore, in Japan, the PTFE-blended gasket

creep

was improved further and is now widely used. Themeasured. In FEM calculations, the change in axial

former PTFE-blended gaskets showed poor creep

bolt force, the flange hub stress and the contact gasket

characteristics, whereas the newly developed PTFE-stress distribution of bolted pipe flange connection

blended gasket offers improved creep characteristics.

with PTFE-blended gasket at some temperature are

However, the mechanical characteristics including thecalculated. And then, the leak rates ware estimatedstress–strain curve of gasket, fundamental leakage

from the contact gasket stress distribution and7）

47

characteristics

athightemperaturesareTechnical Papers

relationship between the leak rate and contact gasket
stress. For verification of the FEM method, theexperiments to measure the change in axial bolt force,the flange hub stress and the leak rate at eachtemperature are carried out.
In this study, the test gasket is No.GF300 in Nippon
Valqua Industries, ltd.. The No.GF300 includes norubber and no material degradation occurs in hightemperature and long-term conditions.
Figure1

2. Experiment set up
Figure 1 shows the experimental setup for connection.

experimental set up for connection

3.Gasket property measurement

The change in axial bolt force, the flange hub stressand the leak rate are measured using this set up. The

Prior to FEM calculations, the gasket properties such as

nominal size of pipe flange is ASME/ANSI class300

stress-strain curve, fundamental leak rate, thermal

2inch and the flange material is Stainless Steel 304 .

expansion coefficient and creep are measured.

9）

cartridge heaters. The flange temperature is measured３-1）Stress–Strain curveand controlled using the thermocouple and the flange

Figure2 shows the schematic of experimental setup forhub stress is measured using the strain gage. The

measuring the sealing performance of the gasket（JISaxial bolt force was measured using the strain gages

B 2490）.It can be heated by electric cartridge heaters.

attached to shank of bolt. The tightening is performed

Figure3 shows the stress-strain curve at room

according to JIS B 2251:2008“Bolt tightening procedure

temperature, 50℃, 100℃, 200℃ and 300℃ measured.

for pressure boundary flanged joint assembly”.

The strain increases as test temperature increases andLeak rate was measured using the pressure dropit can be seen the temperature dependency. It is

method and calculated by equation（1）because that the gasket material was softened in hightemperature.
⑴

where, L is leak rate（Pa･m3/s）,M is molar mass（kg）,
V is volume within equipment（mm3）,t is measurement
time （s）, R is gas constant （J/kg･K）, T1 is initialtemperature（℃）, T2 is measurement temperature（℃）,
P1 is initial internal pressure（MPa）and P2 is measurement
internal pressure（MPa）.The nominal size of gasket isASME/ANSI class 300 2 inch with thickness of 1.5mm.
The internal pressure is 2MPa, the flange temperatures

Figure2 S chematic of experimental setup for measuring
the sealing behavior of the gaskets（JIS B 2490）

are chosen as room temperature, 100℃ and 200℃. The
initial axial bolt force is 16.4kN correspond to meancontact gasket stress 35MPa.

48

Spring 2017

The connection is heated 3℃/min using electric

No.32

Evaluation of the Bolted Flange Connection with PTFE-blended Gasket under High-temperature and Long-term condition

Figure3

Stress–strain curves of gasket３-2）Sealing performance

Figure5 M easured relationship between the fundamental leakrate and the contact gasket stress in unloading step
at RT and 200℃

The relationship between the fundamental leak rate
and the contact gasket stress at room temperature３-3）Thermal expansion coefficientand only re-load step at 200℃. The experimental setup

Figure6 shows thermal expansion coefficient measured

was shown in Figure2 and the test gas is helium gas

by thermal mechanical analysis（TMA）.It can be said

2MPa.

that the thermal expansion coefficient increases withFigure4 shows fundamental leak rate at room

higher temperature.

temperature obtained from the experiment. When theSpring 2017contact gasket stress is 20MPa or greater, it can bemeasured because that the value was less than lower
limit of 5 x 10−5 Pa･m3/s.

No.32
Figure6

Thermal expansion coefficient of gasket３-4）Creep
Figure4 R elationship of gaskets between leak rate andcontact gasket stress at room temperature in aplaten test

The creep characteristics of gasket are measured by
the setup shown in Figure7, for evaluation of gasketed
connection in long-term condition. The dimensions ofFigure5 shows the leak rate in unloading process attest gasket are φ22mm and φ58mm, test gasket

200℃, the initial contact gasket stresses are chosen as

stresses are chosen as 12.5MPa, 25.0MPa, 35MPa, and19.8MPa, 25.5MPa and 35.0MPa. From comparison

the temperature is 200℃. Figure8 shows the measured

between results of Figure4 and Figure5, it can be seen

creep strain behaviors of the gasket. The abscissa isthat the sealing performance at high temperature iselapsed time, and the ordinate is creep strain. Thisbetter than at room temperature. The result indicatesfigure indicates that the creep strain increased overthat sealing performance increases as the temperature

time. So creep strain increases as gasket stressincreases. This is suggested that because the softened

increases and it show the stress dependency. This

gasket material is able to fill the micro gaps of flange

behavior was formulated to equation 2 and inputted tofaces at high temperature.

FEM calculations.

49Technical Papers

bolt at initial tightening. In Step 2, heat and internalpressure are applied to the inside of the connection.
Flanges and bolts/nuts are modeled with elasticityheat transfer elements. The gasket is modeled withelasticity-plasticity-heattransfer-viscosity

elements.

Table 1 shows the characteristics of each material.

Figure7Equipment for testing the creep of gaskets

Figure8

FE model for pipe flange connection with gasket

Measured creep strains of gaskets（2）
whereNo.32

is creep strain rate（/s）;σ is stress（MPa）;t

is measurement time（s）;and a, n, and j are constants
obtained by experiment（a = 1.61×10−5（/MPa）, n =1.25, j = −0.915）.

Initial state of tightened bolt

Figure10

4. FEM calculations

Table1The FEM calculations are conducted using ABAQUS.
Figure9 shows the FE model for bolted flange
connection with gasket. Taking into account thesymmetry of the connection, 1/32 part（1/2 in axialdirection,1/16incircumferentialdirection） ofconnection is analyzed. Bolts and nuts are united, andscrews are omitted. Also, nut shape is simplified fromSpring 2017

Figure9Internal pressure and heatapplication

Boundary conditions

The characteristics of each material

Modulus of longitudinalelasticity [GPa]FlangeBoltGasket

200200Fig.3
0.45

Poisson’s ratio

0.3

0.3

Linear expansion
coefficient [/K]
Heat transfer
coefficient [W/m･K]

1.12
E-05
4.4
E-02

1.09
E-05
1.1
E-02

Specific heat [J/kg･K]

5005001000

Density (roomtemperature) [kg/m3]

7800

7800

2.3

Fig.6
2.5
E-05

hexagonal to circular.
Figure10 shows the boundary conditions. The uniform
bolt stress is applied to the cross sectional area in the50

Evaluation of the Bolted Flange Connection with PTFE-blended Gasket under High-temperature and Long-term condition

5. Experiments and Results of  FEM Analysis５-1）Changes in Axial Bolt Force
Figure11 and 12 show the changes in axial bolt force
obtained by FEM calculations and experiments at100°
C and 200°
C respectively. The solid lines show theFEM results, the dotted lines show experimentalresults. And the change in flange temperature isshown in same figure. The initial axial bolt force isFigure12

Changes in axial bolt force at 200℃

chosen as 16.4kN. The flange is heated, kept for 24

Spring 2017

hours, cooled to room temperature. The heated and５-2）Hub Stress of Flanges

cooled cycles are 4 times.

Figure13 shows the flange hub stress at initial

From figure 11 and 12, it can be seen that the changetightening and under high temperature. The figure

in axial bolt force are influenced from temperature ofalso shows value calculated according to the Boiler &the connection. In initial heating, the axial bolt force

Pressure Vessel Code, Section VIII, Division 1.14） The

decreases substantially, because the gasket strain

measured results are fairly good agreement with theincreases due to the temperature dependency ofFEM results, the method of FEM calculations arestress-strain curve of gasket material, that is, theverified.

gasket thickness decreases. Axial bolt force increased
and decreased in accordance with increasing anddecreasing temperature due to the difference inthermal expansion coefficient between each component.
In heating at 200℃, the change in the axial bolt force isNo.32

larger than that at 100℃ and also the reduction in theaxial bolt force is larger in cooling. In cooling, the axial
bolt force is reduced to 2kN, by which the averagegasket stress is 4.3MPa. However, no leakage isobserved.

Figure13

Flange hub stress５-3）Contact Gasket Stress Distribution andLeak Rates
Figure14 shows the obtained contour figure of contact
gasket stress distribution for the gasket in initial bolt
tightening, and the cases where the connection isheated to 100 and 200℃, respectively. The aroundoutside of gasket did not contact the flange face. So thecontact gasket stress is zero.
In these figures, it can be said that the change inFigure11 C hanges in axial bolt force at 100℃

contact gasket stress distribution in the circumferential
direction is negligible. As the result, the contact gasket
stress increases at the outer edge of the gasket because
the flange rotation occurs. The results at the elevated51

Technical Papers

temperature, show that the outside of gasket is35MPa, the contact gasket stress keep over leakage

deformed by compression due to the heating and astress, it can be considered that the sealing is kept.

contact force by a bolt.
Figure15 shows the leak rate from the gasket interfaces
is estimated using the contact gasket stress distribution
obtain from the FEM and the fundamental leak rate
shown in Figure4 and 5 12）13）. The abscissa is contact
gasket stress, the ordinate is the amount of gas leakage
per unit contact diameter. A fairly good agreement
between the estimated results and the experimental
results is observed. This confirms the validity of themethod for estimating the amount of leakage from theFEM calculations and the fundamental leak rate.

Figure15 C omparison of leak rates of connections between
the experimental results and estimated results.

５-4）Estimation of the sealing performance inlong-term condition
The bolted connection with gasket is used in hightemperature and long-term condition, so it is important toand long-term condition. Figure16 shows the change incontact gasket stress in ten years estimated from resultsof FEM calculations. The leak stress（when allowableleakage is 1.7×10−4 Pa･m3/s）is also shown in same figure,the leakage occurs when the contact gasket stressdecreases less than that value. The connection size isASME/ANSI class 300 2inch, the fluid temperature isFigure16

Change in contact gasket stress of connection inten years estimated by FEM calculations

6. Conclusion

No.32

200℃ as above evaluations. The shutdown is every two

In this present paper, it is shown that bolted pipeyears, so it is considered in FEM calculations. When theflange connection with PTFE gasket（No.GF300）keep

initial contact gasket stress is chosen as 25MPa, thegood sealing performance in high temperature andcontact gasket stress fall down less than leak stress, andlong-term condition by using experiments and FEM

then it is estimated that the leakage occur. On the othercalculations. The results obtained are as follows.

hand, when the initial contact gasket stress is chosen as（1）The fundamental characteristics of PTFE-blended
gasket were measured experimentally such as therelationship between gasket stress and displacement andits temperature dependency, the relationship between
the leak rate and contact gasket stress, thermal expansion
coefficient and creep property.
（2）The change in axial bolt force of bolted connection
with PTFE-blended gasket is effected substantially byheat cycle and the connection with No.GF300 gasket
shows the good sealing performance in 200℃ heatFigure14 C ontact gasket stress distributions obtained byFEM calculations

Spring 2017

evaluate the sealing performance in high temperature

cycle condition. In addition, the flange hub stress waslower than the value calculated using ASME code.
52Evaluation of the Bolted Flange Connection with PTFE-blended Gasket under High-temperature and Long-term condition（3）The leak rate from the connection with PTFE-5）Kobayashi, T., Nishida, T., Yamanaka, Y.:“Consideration

blended gasket was estimated from the contact gasket

on the Representations of Sealing Behavior of Gaskets:stress distribution obtained by FEM calculations andEffects of the Internal Pressure and the Gasket

the relationship between leak rate and contact gasket

Width,”ASME PVP Vol. 457（2003）,pp. 133–138

stress obtained by experiments, and compared with6）Industrial Safety and Health Law No. 318（2008）

the experimental value to verify the robustness of our7）Nippon Valqua Industries, Ltd. Non-Asbestos Gasket,
Catalogue No. ZY03（2011）

prediction method.
（4）It is proposed the method to estimate the long-8）Sato, K., Muramatsu, A., Kobayashi, T., Sawa, T.:

term behavior of bolted flange connection with PTFE-“FEM Stress Analysis and Sealing Performance of

blended gasket（No.GF300）under high temperature.

Bolted Flanged Connections using PTFE Blended

And it is shown that the connection with No.GF300

Gaskets under Internal Pressure,”PVP 2015-45268,

gasket keeps safety for 10 years when the initial

Proceedings of ASME PVP 2015 Conference（2015）

contact gasket stress is 35MPa, and also that re-9）ANSI/ASME B 16.5, “Pipe Flanges and Flanged

tightening resulted in additional safe.

Fittings”（1996）
10）Japanese Industrial Standards: JIS B 2251 “Bolt

7. References

joint assembly”（2008）

Spring 2017

１）Takaki, T., Satou, K., Yamanaka, Y., Fukuoka T.:“Effects11）Japanese Industrial Standards: JIS B 2490“Testof Flange Rotation on the Sealing Performance of Pipe

Method for Sealing Behavior of Gaskets for Pipe

Flange Connections,”ASME PVP Vol. 478（2004）pp.

Flanges”（2008）
12）Omiya, Y., Sawa, T., Takagi, Y.:“Stress Analysis and121–128
２）Takaki, T., Fukuoka, T., Yamanaka, Y.:“Finite Element

Design of Bolted Flange Connections under Internal

Simulation of Bolt-Up Process of Pipe Flange

Pressure,”PVP 2014-28606, Proceedings of ASME

Connections,”Valqua Technology News, No. 2（2002）,No.32tightening procedure for pressure boundary flanged

PVP 2014 Conference（2014）13）Omiya, Y., Sawa, T.:“Stress Analysis and Sealing

pp. 5–13３）Sawa, T., Ogata, N., Nishida, T.:“Stress Analyses

Performance Evaluation of Bolted Pipe Flange

and a Sealing Performance Evaluation of Pipe

Connections with Smaller and Larger Nominal

Flange Connections with Spiral Wound Gaskets

Diameter under Repeated Temperature Changes,”

under Internal Pressure,”Proceedings of the JapanPVP 2014-28730, Proceedings of ASME PVP 2014Society of Mechanical Engineers （Ver. A）, IssueConference（2014）

671 of Vol. 68（2002）,pp. 1120–11284）Kobayashi, T., Nishida, T., Yamanaka, Y.:“Effect ofCreep-Relaxation Characteristics of Gaskets on theBolt Loads of Gasketed Joints,”ASME PVP Vol. 457（2003）,pp. 111–118

Kouji Satou
Corporate Research andDevelopment Group
Development Division5314）ASME Boiler & Pressure Vessel Code Section VIII,Division 1: “Rules for Construction of Pressure
Vessels”App. 2（2004）