Appropriate Tightening Method ofGaskets
Training Center are gathering attention.

1. Introduction

This report will introduce a summary of items that

Appropriate maintenance of high pressure vessels isrequire careful attention for gasket tightening based on

indispensable for safe operation of the plant. The fluids

trouble caused by flange tightening.

handled may have flammable, flammable, explosive,
toxic, and other properties so leaks can lead to disasters

the numerous flange tightening sites within the plant.

Winter 2022

However, the current situation is that the number ofharmful accidents caused by flange tightening has notdecreased. Table1 and Figure1 show the analysis ofhigh-pressure gas accidents in Japan. As these statistics
indicate, the total number of accidents due to poor
maintenance of facilities is not showing a decreasing

No.42

Ratio

daily management to ensure appropriate tightening of

No. of cases

and accidents. Therefore, plant operators are conducting

Figure1 No. of cases and ratio of flange tightening related accidents

trend, and about 30% of that constituent factor is due to“flange tightening causes”. Therefore, appropriate flangetightening is one of the major issues for the safe

2. Troubles related to gasket tightening

operation of a plant.

Analysis of the cause of trouble that occurred in actual

To increase the skills and knowledge related to flange

gasket work cases found that the major causes weretightening, establishing standards regarding gasket

insufficient tightening, excessive tightening, and uneven1）

fitting represented by ASME PCC-1 and training

tightening.

programs for gasket tightening tasks like the Seal

Insufficient tightening is the state where the appropriate

Table1 No. of cases of accidents due to poor maintenance of facilities

surface pressure is not on the entire gasket. It isInsufficient Flange
Test
Vesselcorrosion tightening control Inspection control
failurecontrolcausesfailurefailure
104
72
2237
14

common in flat face flanges or when flange or bolt

Year
2020

Total
249

strength is insufficient. In addition, a decrease in gasket
surface pressure due to stress relaxation may lead to2019

155

84

133510297

2018

124

99

193513290

leakage and damage due to the gasket being unable to2017

1139729308277

2016

109

109

20

4210290

resist internal pressure and being pushed out by the2015

9360

31

1721222

2014

7855

191116179

of a blowout gasket.

2013

80

56

28

1620200

2012

65

5965

811208

Conversely, gasket destruction may occur if gaskets are

2011

67

66

66

820

227

Source: METI“Summary of High Pressure Related Accidents”

7fluid（blow out）
. Figure2 shows the external appearance

tightened excessively. This is especially common influorocarbon resin envelope gaskets. As shown inCustomer Solutions

Figure3, many circumferential cracks are generated anddestroyed, leading to leakage.

3. Standards for the tightening procedures

Uneven t tightening refers to a state in which the gasket

In general, multiple bolts of pipe flanges are tightened,surface pressure becomes uneven. If sections of thebut the tightening task is normally conducted one-by-gasket are insufficiently tightened or excessively

one. The axial force of a bolt of the tightened flanges

tightened, this causes partial leakage, ruptures, andchanges upon the tightening of other bolts, and the axial

deformities. Figure4 shows uneven tightening. In thisforce decreases in many cases. This phenomenon iscase, tightening strength was low in some sections, andcalled elastic interaction. The effect of elastic interaction

friction between the flange and gasket decreased,is minimized by repeated multiple tightening to adjust

causing leakage by being pushed out with internal

the target bolt tightening load.

pressure.

ASME PCC-11） and JIS B 22512） are introduced as

These failures are all caused by Inappropriate

standards that show multiple tightening procedures.

tightening and highlight the importance of tightening

ASME PCC-11）and JIS B 22512）standards perform diagonalmanagement. Therefore, we will introduce basic

tightening after circular tightening. Diagonal tightening

tightening procedures and control methods to conduct

effectively prevents uneven tightening of the gasket byappropriate tightening tasks.

increasing the tightening torque in stages. Tightening ina circular pattern reduces the inconsistent tightening
load due to elastic interactions in adjacent bolts.
2251 is a standard that enables even more efficient andaccurate tightening than the ASME PCC-11） establishedearlier. In ASME, all bolts are tightened during diagonaltightening, but in JIS, only 4 to 8 bolts are tightened. It is

Figure2 Case of gasket blowout due to insufficient tightening

more efficient when the number of bolts is large.
Regarding the circular tightening at the target torque,
ASME is until the nut stops rotating, but JIS sets anupper limit on the number of times. Furthermore,setting in JIS the target torque to 110% when thenumber of bolts is 12 or more is also a technique forquickly achieving the target bolt axial force. The JIS B
2251’s applicable range is joint sheet gaskets and spiral
Table2 Tightening procedures in JIS B 2251 and ASME PCC-1

Figure3 Case of compression failure due to excessive tightening

JIS B 2251
StagesProcedures

Preliminary
Only 4 or 8 target bolts
tightening Stage-wise, diagonal tightening
All bolts tightened in acircular pattern 100％
Target torque is 110%
Mainfor over 12 bolts
tightening

Figure4 C ase of deformity due to uneven tightening（insufficient tightening in a section）

Winter 2022

Table2 compares ASME PCC-11）and JIS B 22512）. JIS B

ASME PCC-1
StagesProcedures

Preliminarytightening
Rounds1 to 3All bolts
Snag torque（≤20%）
All bolts are tightened in a
step-wise diagonal pattern

All bolts tightened in aRound 4 circular pattern 100％
No. of times going（Until the nut does not rotate）
around: 4 to 6 cycles
After 4 hours passes,
same of tightening as theAfter 4 hours passes,
Additional
main tightening
Round 5same tightening astightening
No. of times going
Round 4around: 1 to 2 cycles
Snag torque: Necessary torque to firmly attach the bolt seating surface

8No.42

Appropriate Tightening Method of Gaskets

wound gaskets. However, our in-house experimental

friction with the seating, and axial force of the bolt isresults confirmed that this is also applicable for High

controlled using devices such as ultrasonic axial force

Performance Non-asbestos Sheet by No.GF300 andmeters and bolt tensioners.

fluorocarbon resin sheet gaskets.

Ultrasonic axial force meters are a method thatmeasures the length of the bolt and obtains the axial

Winter 2022
No.42

4. Tightening control method

force from the difference in bolt length before and after

Quantitative tightening management methods forwhere the axial force and bolt elongation are in agaskets include a torque method, a rotation angle

proportional relationship. The method has high precision,method, a torque gradient method, an axial force

and the measurement itself is simple, but it is necessary

management method using an ultrasonic axial force

to keep the surfaces of both ends of the bolt smooth.

meter, and a bolt tensioner. Each method has

Bolt tensioners are a method that pulls the bolt withadvantages and disadvantages, and it is necessary tohydraulic pressure until the pre-designated target axial

select a method by comprehensively determining theforce. The nut is tightened, and the hydraulic pressure isbalance among workability, construction accuracy, etc.

released to give the designated axial force. Extra bolt

Table3 shows a comparison of various control methods.

length and space are required for attaching the bolt

JIS B 1083 Rules for Bolt Tightening3） proposes thetensioner. Both ultrasonic axial force meter and bolt

torque method, rotation angle method, and torquetensioner have high precision but require time and cost.

gradient method. The torque method only controls

They are often used in important sections such as high-tightening torque using a torque wrench. It is usedpressure pipes and large diameter flanges.

widely as a simple and conventional control method.

For non-quantitative tightening, hand wrenches are used

However, about 90% of tightening torque is consumed

for small diameter flanges, and impact wrenches areby the friction of the bolt face and seating, and therefore,

used for large diameter flanges. However, experience isvariation is likely to occur depending on the frictional

required for even tightening because variation is high,properties of each material.

and it isn’t easy to control tightening strength.

The rotation angle method is a method that controls theAs a sealing manufacturer, we recommend therotation angle of the bolt by tightening. When tightening

quantitative tightening control methods shown inat the elastic region of bolts, the variation becomes more

Table3.

tightening. It is applicable only in the elastic region

significant if the rigidity of the bolts is high. Conversely,

Table3

when tightening at the plastic region, it is less likely toTightening control
methodbe affected by rotation angle error. Still, there is an issue
that bolts become plastically deformed and cannot bereused.

Quantitative tightening control method
Tightening indicator

Tightening region

Torque method

Tightening torque

Elastic region

Angle rotation
methodTightening rotation
angle
Tightening torquegradient of tightening
rotation angle

Elastic region
Plastic region

The torque gradient method uses the tightening rotation

Torque gradientmethodangle and tightening torque gradient as tightening

Ultrasonic axial force
meterBolt elongation

Elastic region

Bolt tensioner

Bolt axial force

Elastic region

indicators, and the yield load of bolts is the target value.
It is used to keep the variation in initial tightening small
and maximally utilize the elastic region of the bolt. Aswith the rotation angle method of the plastic region, it isnecessary to take care not to exceed the yield point andElastic limit

5. Effect of tightening procedureon bolt axial force

proof load.

We will introduce the results evaluating bolt axial force

Axial force control of the bolt is possible with high-and gap between the flange faces with the tightening

precision tightening control because it is not affected bymethods of ASME PCC-1 and JIS B 2251４）. Tables4 and9

Customer Solutions

5 show the test methods, Figure5 shows themeasurement results of bolt axial force, and Figure6
shows the measurement results between flange faces.
Gaskets were spiral wound gaskets（No.6596V）with
expanded graphite filler and joint sheet gaskets（No.6500）, dimensions are JPI Class 300 24 inch.
Figure5 shows that for No.6596V, the mean value washigher in bolt axial force and the variation was lower.
for JIS B 2251 than ASME PCC-1. This is because in JIS
B 2251 stipulates that“for spiral wound gasket, perform
circular tightening with a tightening torque of 50% after
the preliminary tightening,”and set the target torqueas110%. The gasket width of spiral wound gaskets is[kN]○No.6596V
No.1[kN]○No.6596V
No.1○JPI Class300 24inch
No.24150
No.2○JPI Class300 24inch
No.24150
No.2
No.23
No.3
No.23
No.3
No.22
No.4
No.22
No.4
100
100
No.21
No.5
No.21
No.550No.20
No.650No.20
No.6
No.19
No.19

0

No.18
No.18

No.8

No.20
No.20No.20

50tightening because the compression amount is high. InNo.19
No.19No.19

00

ASME PCC-1, circular tightening is until the nut does

No.18
No.18No.18

of going around is higher for JIS B 2251.
as shown in the results for bolt axial force, for No.6596V,
the tightening procedures for JIS B 2251 had a smaller
gap between faces. In addition, regarding the variation ofthe gap between flange faces, the tightening proceduresfor ASME PCC-1 did not show a variation as large asthat for bolt axial force.
Table4Gasket

Spiral wound gasket
No.6596V

Joint sheet gasket
No.6500

Dimensions

JPI Class300 24inch
t4.5

JPI Class300 24inch
t3.0

Diameter offlange seatφ692.2

φ692.2

Bolt

M39, 24 bolts

M39, 24 bolts

Target gasket
face pressure

40MPa

40MPa

Table5Tightening procedures
JIS B 2251

Tightening stages
until target value
Tightening
procedures

Target bolts

4 stages
At preliminary tightening:
Diagonal tightening
At main tightening:
Circular tightening
At preliminary tightening:
4 bolts
At main tightening:
All bolts

Total number of stages
until completion oftightening

11 stages

Notes

Tightening at
110％ of target torque50No.6
No.6 No.6

0

No.7
No.7 No.7
No.8
No.8 No.8

No.17
No.9
No.17No.17
No.9
No.9
No.16
No.10
No.16No.16
No.10 No.10
Target surface pressure:No.15
No.11
No.11
目標面圧：40MPa40MPaNo.15No.15
No.11
目標面圧：40MPa
No.14
No.12
目標面圧：40MPa
No.14No.14
No.12
No.12
No.13
目標軸力
:
150.6[kN]No.13
Targetaxialforce:
目標軸力: 108.2[kN]
No.13
目標軸力
: 150.6[kN]
N…
150.6
［kN］
N…
N…
N…
N…
6N…
JISB 2251
ASME
PCC-1
[kN] No.1○No.6500
N…
N…
N…
N…
N…
JIS
B 2251 No.24 200ASME PCC-1
N…
N…
N…6N…
No.2
○JPI Class300 N…
24inch No.23
No.3
ボルト軸力の分布
Figure5Figure5Distribution
ofbolt axial
150 ボルト軸力の分布
Figure5No.4force
No.22
No.21
100 [mm] No.1
○No.6596V
No.24 8.0
○JPI Class300 24inch No.23
No.20
50
No.22
7.5
No.190
No.21
No.18

Test conditions

No.2

No.5
No.3 No.6
No.4
No.7
No.5

7.0

No.20

No.8[mm] No.1
○No.6500
No.24 6.4
○JPI Class300 24inch No.23
No.22No.2No.3
No.4

6.2

No.21

3 stages

No.5
6.0

No.20

Diagonal tightening
Circular tightening

No.19

No.6
No.7

5.8

No.18

No.8

No.17

All bolts

At circular tightening, tightening
until nuts do not rotate

No.42

No.6

No.17
No.9
No.19
No.7
6.5
No.16
No.10
No.18
No.8
No.15
No.11
目標面圧：40MPa
No.14
No.12
No.17
No.9
No.13
目標軸力 : 150.6[kN]
N…
N…
N…
No.16
No.10
N…
6N…
JIS
B 2251
ASME PCC-1
N…
N…
N…
No.15
No.11
Mean gap between flange
締付け前のNo.14
No.12
faces before tightening:
Figure5 ボルト軸力の分布No.13フランジ面間平均：約8.7mm
Approximately
8.7 mmASME PCC-18 stages

No.8

Winter 2022

Next, Figure6 shows the gap between flange faces, andNo.7

No.17
No.9
No.17
No.9
No.16
No.10
No.16
No.10
Target surface pressure:No.15
No.11
目標面圧：40MPa40MPa
No.15
No.11
No.14
No.12
目標面圧：40MPa
No.14
No.12
No.13
Target axialforce:
目標軸力: 108.2[kN]
No.13
目標軸力:
108.2[kN]108.2［kN］[kN] No.1○No.6500[kN]○No.6596V[kN] No.1○No.6500
No.24 200No.1
No.2○JPI Class300
Class300 24inch
24inch No.23No.24No.24
No.2
○JPI
○JPI Class300 24inch No.23150 200 No.2 No.3 No.3
No.23
No.3150
No.22
No.4150
No.22No.22
No.4 No.4100
No.21
No.5100
No.21No.21
No.5 No.5
100narrow, and there is a tendency toward uneven

not rotate and as shown in Table5, the number of times

No.70

No.9

No.16

No.10

Mean gap between flange No.15
締付け前のNo.14
faces before tightening:
フランジ面間平均：約7.4mm
Approximately 7.4 mm

6JIS B 2251

Figure6No.13

No.11
No.12

ASME PCC-1Gap between flange faces
Figure6 フランジ面間距離10

Appropriate Tightening Method of Gaskets

6. Conclusions
The equipment of domestic plants is aging, and by2025, most of the equipment will be in operation for
more than 40 years. Therefore, an“increased risk for
accident occurrence”and“decreased profitability due

7. Reference1）ASME PCC–1, Guidelines for pressure boundary
bolted flange joint assembly（2010）2）Japanese Industrial Standards. JIS B 2251“Flangeconnection tightening method”（2008）

to decreased operating rate”is anticipated. This

3）JIS B 1083, Rules for Bolt Tightening（2008）

report introduced several cases of gasket trouble,4）Takahiro Fujiwara,“Effect of tightening procedures

basic procedures for tightening, and methods toon sealing properties”, Valqua Technology News

control tightening. Our company will continue toVol. 37（2019）provide seal engineering services as a sealing
manufacturer and contribute to eradicating accidents
due to leakage.

Winter 2022

Kenshiro Nakade
H&S Sales GroupNo.42

11Satomi Takahashi
Corporate Research andDevelopment Group