Influence of Bolt Tightening Methods on theSealing Performance of Large Diameter Bolted
Pipe Flange Connections
specification”was published in China. However, the1. Introduction

index used in these standards is the final bolt axial

Gasketed pipe flange connections are used in large

force and does not deal with the actually required

numbers in pressure vessels and pipe connections insealing performance of the flange connections.

various industries. It is known that the sealing

In Valqua Technology News Vol.37 in the previous

performance of the pipe flange connections depends

report, the effect of tightening methods of ASME PCC-

not only on the gasket characteristics but also on the16）and JIS B 22517） using ASME class 150 4 inches

tightening method. According to The High Pressure

small diameter and ASME class 300 24 inches large

1）

Winter 2020
No.38

Gas Safety Institute of Japan（KHK） , it is reported

diameter flange connections sealing performance wasthat about 67% of leakage accidents from gasketed

examined and it was clarified that both of them arepipe flange connections are caused by improper bolt

appropriate methods to exhibit adequate sealing

tightening method. One of the factors of tightening

perfromance 8）. However, although ASME PCC-1 6）

failure is the elastic interaction occurring during bolt

shows several bolt tightening methods, the effects oftightening. This is a phenomenon that affects eachthese tightening methods on the sealing performanceother when a large number of bolts are tightened.

of the connections have not been studied.

Each axial bolt force falls below the target bolt axial

This reportaims to investigate the effects of theforce, and individual bolt axial forces vary. As a result,tightening methods combined with Alternative #1, #2,

an appropriate bolt axial force cannot be achieved, theand #3, which are newly added to ASME PCC-16） bygasket compressive force required for sealing cannot

using ASME class 300 24-inch flange connections, onbe obtained and leakage may occur. It is difficult tothe variation of bolt axial force, sealing performances,

reduce the effects of this elastic interaction to zero,bolt tightening times, and wrench moving distances.

and measures are being taken to reduce the effects,

In this report, the test was conducted using our high-such as increasing the number of circular tightening

performance gasket No. GF300 and expanded graphite

cycles or performing cross-tightening. However, all offiller spiral gasket No. 6596V.

them are based on experience and it is hard to saythat sufficient technical studies have been done2）-5）.
Under these circumstances, various standards have

2. Test method

recently proposed bolt tightening methods for2-1）Test equipment

achieving an appropriate bolt axial force. In the UnitedFigure1 shows the pipe flange connection with aStates, ASME PCC-1 6） Guidelines for Pressuregasket used in this paper. The dimensions are 24

Boundary Bolted Flange Joint Assembly was proposed

inches, which is the largest nominal diameter in thein 2000 and revised in 2013 and 2019. In Japan, JIS B

ASME standard, the pressure rate is class 300, the7）2251 “Flange joint tightening method”was issued inshape is W/N, the seat is RF, and the material is2008, and in 2018,“Flange method mounting technical

SUS304. It is known that the mechanical behavior of3

Technical Papers

the flanged connections changes depending on theσgT＝K N Agd （2）presence or absence of the pipe. In thisreport, we usedequipment with a pipe of about 800 mm to study

whereunder conditions close to the actual equipment.

T：Torque,［N・m］

The bolts are made of SNB7, and 24 hexagon bolts of

K：Nut factor,（=0.135）

size M39 are used. Two strain gauges are attached toσg：Target contact gasket stress,［MPa］

each bolt body so that the axial force of all bolts can be

Ag：Contact gasket area,［mm2］measured. The strain gauge of each bolt has been

N：Number of bolts,［pcs］

calibrated in advance, and molybdenum disulfide has

d：Bolt nominal diameter,［m］

been applied to the thread and seat of the bolt and nut.
Helium gas was used as the test gas, and the internal

In the experiment, the bolt axial force and the flangepressure was 2 MPa. The leakage amount of the flange

clearance are measured for each tightening cycle.

connection was measured by a pressure drop method.
We measured the change in pressure with a pressuregauge and calculate using the following equation（1）.
MVT1
L=1atm×ρtRT c P1− T P 2 （1）12（）

whereWinter 2020L：L
 eakage per outer circumference of gasket,［Pa·m3/（s·m）］
M：Molar mass,［mg/mol］
V：Inner volume of pipe flange connections,［ml］
ρ：Density of test gas,［mg/ml］
t ：Measurement time，［s］
R：Gas constant （=8.314）,［J/mol·k］，

Figure1

Experimental setup of 24”pipe flange connection

No.38

T1：Absolute temperature at the start of test,［K］
T2：Absolute temperature at the end of the test,［K］
P1：Absolute internal pressure at the start of the test,［MPa］
P2：Absolute internal pressure at the end of the test,［MPa］c：Gasket contact outer circumference,［m］
atm：Standard atmospheric pressure（=0.101325），［MPa］
Figure2 shows an image of the work of tightening thepipe flange connection body. Bolt tightening isperformed using a torque wrench with the targettorque. Target gasket surface pressure was 40 MPa

Figure2

Image of tightening

Table1 Target torque, target axial bolt force and contact gasket stress
Size of pipe flange connection

Class300 24B

GasketNo.6596V

No.GF300

and the target torque value T was determined fromSuggested contact gasket stress［MPa］

5035Target contact gasket stress［MPa］

40

25

the following equation（2）. Table 1 shows the target

Target axial bolt force［kN］

98.4

85.6

gasket stress and torque.

Target torque［N·m］

520451for gasket No. 6596V and 25 MPa for gasket No.GF300

4Influence of Bolt Tightening Methods on the Sealing Performance of Large Diameter Bolted Pipe Flange Connections

2-2）Test gasket

3-1）Tightening method JIS B 22517）

The gasket dimensions used in this paper φ612×φ772

In JIS B 2251 flange joint tightening method 7）,×t3.0 for No.GF300 and φ603.2×φ628.6×φ685.8×φ717.6

paragraph 4b）states that "if the number of flange

×t4.5 for No.6596V. Both are ASME class 300 24-inch

bolts is 12 or more, 110% of the specified tightening

diameter dimensions.

torque shall be the target tightening torque. In thisstudy, the measurement and examination are
performed when the target torque is set to 110% in

3. Tightening method

addition to 100%. 5.3b）Section 4）states that when aIn this paper, we compared the variation of bolt axial

spiral-wound gasket is used, the gasket width is soforce, sealing performance, and tightening time of thenarrow that one-sided tightening is likely to occur. To

flange connection under seven types of bolt tightening

prevent this, tighten all bolts at the end of star pattern

methods.

by 50% of the target tightening torque, and one round

Table2 shows each tightening method, and the outlineof tightening is performed by clockwise orof each tightening method is described below.

counterclockwise tightening methods. For this reason,

Table2Tightening methods

Target Torque

Winter 2020

No.6596V
JIS B 2251 110%

110%
No.GF300

No.38

No.6596VJIS B 2251 100%

100%
No.GF300

ASME
Legacy5100%

ASME
Alt.#1100%

ASME
Alt.#2

100%

ASME
Alt.#3100%

3 Rounds

100%

Bolt tightening methods

Gaskets

Step 1

Step 2

Step 3

Step 4

Number of bolts

4242424

Rounds4162

PatternStar

Circular

Circular

Circular

Number of bolts

42424

Rounds462

PatternStar

Circular

Circular─

Number of bolts

4242424

Rounds

4162
CircularPatternStar

Circular

Circular

Number of bolts

42424

Rounds462

PatternStar

Circular

Circular

Total232bolts

208bolts

232bolts

─208bolts

─216bolts

Number of bolts

242424Rounds

333PatternStar

Circular

CircularNo.6596V
No.GF300

Number of bolts

4162424Rounds

2113PatternStar

Star

Star

CircularNo.6596V
No.GF300

Number of bolts

4162424Rounds

2113Star

Circular──108bolts──72bolts

No.6596V
No.GF300

No.6596V
No.GF300

No.6596V
No.GF300

PatternStar

Star

Number of bolts

424Rounds

34PatternStar

Circular

Number of bolts

24Rounds

3PatternStar─120bolts

120bolts

Technical Papers

the tightening method of No.6596V is different fromsheet gasket of No.GF300. In addition, in JIS B 22517）,

4. Experimental results

additional tightening was proposed in some cases, and4-1）Gap distribution between flange faces

the retightening was also carried out in this study.

Figure3 shows the gap distribution between the7）A major feature of the tightening method according

flange when tightening by seven methods. The results

to JIS B 2251 is that only four bolts（when the numberfor the installed gasket No.GF300 are shown by solidof bolts is 24 or less）are temporarily tightened first,lines, and those for No.6596V are shown by broken

and in the final tightening, all bolts arelines. When the gasket was No.GF300, the effect of thecircumferentially tightened. Since the final tightening

tightening method was minor. On the other hand, inis a simple circular tightening, it can be expected tothe case of No. 6596V, almost the same results werereduce time and prevent mistakes such as forgetting

obtained with the methods based on the standards ofto tighten.

JIS B 22517） and ASME PCC-16）, but with the 3 rounds
method, the gap was slightly large and the compression3-2）Tightening method ASME PCC-1

6）6）amount was small.

7）

In ASME PCC-1 , unlike JIS B 2251 , the tightening
method does not change depending on the gasket type.
This study covers Legacy, which has been proposed
previously, and Alternatives #1, #2, and #3, which

Winter 2020

have been newly added since 2013.
Legacy is a method of diagonally tightening all bolts
and is the most widely used tightening method, but it
has been pointed out that it takes a lot of time.
Alternative #1 and #2 are methods to reduce thenumber of tightening bolts in the first step byincreasing the torque stepwise for four different bolts

No.38

in Step 1 and Step 2.
Alternative #3 is a simple tightening method similar toJIS B 22517） where only four bolts are temporarily
tightened and then circumferentially tightened.
The final steps of the four tightening methods
described in ASME PCC-16）are "until the nut no longer
turns," and the number of tightening times describedin Table 2 is the result of the number of times the nut
no longer turns in this test.

Figure3

Distribution of the flange gap3-3）Tightening method 3 Rounds

4-2）Bolt axial force distribution

In addition to JIS B 2251 and ASME PCC-1 tightening

Figure4 and 5 show the final bolt axial force distribution

methods, a convenient way to make three cycles ofand the variation in axial force, respectively when thecross tightening in stepwise is also examined.

gasket was No.GF300. Regardless of the tightening
method, variations in axial force are observed due toelastic interaction. In particular, the variation was large
in the 3 Rounds method, and the tightening coefficient Q（=Fmax/Fmin）was 2.62. Regarding the minimum bolt
6Influence of Bolt Tightening Methods on the Sealing Performance of Large Diameter Bolted Pipe Flange Connections

axial force Fmin, the target bolt axial force of 85.6 kN

Q=1.47 in JIS 110%, showing the smallest value. In

could not be achieved with all tightening methods dueaddition, the value of Q indicates that the tightening

to the influence of elastic interaction. According toof No.6596V is larger than that of No.GF300.

this, the value of Q in JIS 110%
（Table2）
is 1.31, and thevalue of Q in Alt#3 is 1.33, indicating the smallest4-3）Sealing performancevalue.

Figure8 shows the measurement results of the leakFigures6 and 7 show the final bolt axial force

rate of the pipe flange connection tightened by each

distribution and the results of variation in axial force,method. Regardless of the tightening method, therespectively when the gasket was No. 6596V. As inamount of leakage was smaller in the case where thethe case of No.GF300, the variation was remarkablegasket was No.GF300 than in the case where theby 3 Rounds method and one of the three bolts hadgasket was No.6596V. The figure also shows thezero axial force. In Figure 7, the value of Q becomes

smallest bolt axial force Fmin of 24 bolts. Comparing

Winter 2020
No.38

Distribution of final axial bolt force（No.GF300）

Figure6

Distribution of final axial bolt force（No.6596V）

Figure7

Variation of final axial bolt forces（No.6596V）

Axial Bolt Force［kN］

Axial Bolt Force［kN］

Figure4

Tightening methods

Tightening methods

Figure57

Variation of final axial bolt forces（No.GF300）

Technical Papers

understood that the leakage amount decreases as theminimum bolt axial force increases. Conversely, thesmaller the minimum bolt axial force, the smaller thegasket contact stress locally and the larger theleakage amount. In other words, the minimum gasket

Moving Distance［m］

the leak rate by each tightening method, it iscontact stress has a large effect on the leakage. In thecase of a pipe flanged joint with a gasket, if the bolt
axial force is low in some parts, it is considered thatTightening methods

leakage is likely to occur from the gasket contact

Figure9

surface in the vicinity. It has been shown that it is

Wrench’s Moving distanceimportant to increase the minimum bolt axial force asmuch as possible to improve the sealing performance.

4-5）Tightening time
Figure10 shows the tightening time required for eachof the six tightening methods. In this experiment, thegap between the flange faces was measured during

Leak Rate［Pa.m3/s.m］

the tightening, but the results in Figure 10 do notinclude the gap measurement time. JIS B 22517） andtightening bolts, have a longer tightening time, andthe 3 Rounds tightening method with a smaller
number of tightening bolts has the shortest tighteningtime. Although a torque wrench was used in thisTightening methods

Winter 2020

ASME PCC-16） Legacy, which has a large number ofstudy, the tightening time may greatly varydepending on tools such as a hydraulic wrench andtorque tensioner and the environment at the site.

Sealing Performance4-4）Moving distance of wrench
Figure9 shows the moving distances of the wrenches
when tightening in six different tightening methods.
The moving distance is calculated not by the straightline distance between the bolt holes but by theTightening Time［min］

Figure8

shortest distance along the circumference. JIS B 2251
and ASME Alt#3 had relatively shortmovingdistances. 3 Rounds method has a long moving
distance in spite of the least number of tightening
bolts. It can be said that the moving distance becomes

Tightening methods

Figure10

Tightening timeshorter in the tightening method in which there aremany circumferential tightening, and it can be said
that the moving distance becomes longer in thetightening method in which there are many crosstightening.
8No.38

Influence of Bolt Tightening Methods on the Sealing Performance of Large Diameter Bolted Pipe Flange Connections

5. Summaryby 1/η.（JIS B 22517））The basic idea of 110% is totighten 10% larger. However, this is based on the bolt

In this paper, sealing performance, flange gap, bolt

axial force and is not always appropriate, and it hasaxial force, moving distance of torque wrench andbeen proposed to use the assembly efficiency based ontightening time of two gaskets of No.GF300 andtightness parameter9）. It seems that there is room for

No.6596V were used when tightened by seven

improvement to a more efficient tightening method todifferent tightening methods, were measured using a

improve the sealing performance required for thelarge- diameter pipe flange connection, and the following

gasketed flange connection. We hope that thisresults were obtained.

research will help the plant tightening work.

（1）‌No significant difference was found in the flange

We were advised by Mr. Koichi Morimoto of Mitsubishi

gap distribution according to these tightening

Chemical Co., Ltd. about this experiment. We wouldmethods.

like to express my gratitude by noting.

（2）‌The sealing performance of pipe flange fasteners isaffected by the tightening method and JIS B22517）110% tightening method has the least leakrate. Then, JIS B 22517）was 100%.

Winter 2020
No.38

7. References

Although it

1）‌A. Muramatsu，“ Seal Training Center （STC）

was observed that the 3 rounds tightening-Interactive Training for Sealing Operation”，

method was simple but the sealing performance

Valqua Technology News Vol.33，（2017）

was inferior.

2）‌H. Lejeunt, Y. Birembaut, Alexander Riedl, Arne（3）‌It was observed that the sealing performance ofSchunemann," Investigation on Different Tightening

pipe flange joints are affected by the minimum

Methods on Several Bolted Flange Types,bolt axial force and it is important to increase thedimensions and Their Associated Gasket Types",

minimum bolt axial force as much as possible toPVP2011-57525, Proceeding of ASME PVP 2011

improve the sealing performance.

Conference,（2011）（4）‌As for the tightening method, the moving distance3）‌H. Gong, Russell R. Flocken", Study of Bolt Tighteningof the torque wrench tends to lengthen when theMethods Using Load Indicating Bolts", PVP2016-

cross tightening is large, and as for the tightening

63723, Proceeding of ASME PVP 2016 Conference,

method with a large number of tightening times,（2016）

the tightening time tends to longer.

4）‌H. Gong, Wesley Pudwill, Elysia J. Sheu," Study of（5）‌JIS B 22517）and ASME PCC-16）Legacy and Alt

Alternative Assembly Patterns Using Finite#1 have relatively small leaks but require a longer

Element Analysis and Lab Tests", PVP2018-84465,

tightening time. The 3 Rounds method has aProceeding of ASME PVP 2018 Conference,（2018）

relatively large leakage but the tightening time is5）‌W. Brown," Efficient Assembly of Pressure Vessel

less than half of JIS B 22517）.

Bolted Joints", PVP2004-2635, PVP-Vol.478,
Analysis of Bolted Joints,（2004）

6. Conclusion

6）‌ASME PCC-1," Guidelines for Pressure Boundary
Bolted Flange Joint Assembly",（2013）

The American Society of Mechanical Engineers

7）‌Japanese Industrial Standards. JIS B 2251“ Bolt（ASME）has introduced a factor called assembly

Tightening Method for Pressure Boundary

efficiency η. η is the ratio of the final axial bolt force toFlanged Joint Assembly”,（2008）.

the target axial bolt force, and the value is less than 1.

8）‌T. Fujihara,“Effects on Sealing Performance of Pipe

In other words, in actual design and construction, theFlange Connections Tightened by Different

target value of the bolt axial force is further increased

Tightening Methods”，Valqua Technology News

9Technical Papers

Performance of Bolted Gasketed Pipe Flange

Vol.37,（2019）.
9）‌X. Zheng, K. Sato, T. Fujihara, Y. Akamatsu, T.Sawa,"Effect of Tightening Method on the Sealing

Xing Zheng
China Research Institute
Seal Engineering
Development GroupConnections", PVP2019-93497, Proceedings of ASME
PVP 2019 Conference,（2019）

Kouji Satou
Corporate Research andDevelopment Group
Product Development
Division

Takahiro Fujihara
Toshiyuki Sawa
Hiroshima University,
Professor Emeritus

Winter 2020

Corporate Research andDevelopment Group
Product Development
Division

No.38

10