Considerations for Tool Selection
and Installation of Fastening Bolts forFlanges with Large Nominal Diameters
1. Introduction

2. Selection of optimal tools

Various tightening tools are used for fastening bolts.

Firstly, using tools offers the following benefits:

Correctly selecting the optimal tools depending on theBenefits associated with installation quality:

usage environment and required fastening precision

・Correct fastening force can be applied to bolts.

and properly using such tools reduces the workload

・Gaskets, flanges, and bolts are not overloaded.

and improves fastening precision, work efficiency, and・‌Tightening will be consistent if it can be managed

safety.

based on torque values and axial force values.

Bolt fastening is required not only during plant

Winter 2018

construction but also maintenance and inspection.

Benefits associated with operation:

However, bolt fastening is difficult to control and so・‌Work time can be decreased by reducing staff

even now it still depends on the operator’s instincts
and experiences. In addition, as the number of skilled
operators decreases, bolt fastening is becoming amajor cause of leakage accidents and fires at plants.

No.34

Despite this situation, training on bolt tightening,

number and operation time.
・‌Heavy manual work can be eliminated, reducing theburden on operators.
・‌Tightening can be executed even in narrow areas
where there is little space around equipment.

including the systematic selection of fastening tools

To obtain such benefits, it is crucial to select tools thatand their usage, is rarely provided. In recent years, ameet the on-site conditions. Below, we explain the１）certification system for a flange-fastening qualification

important factors for selection.

has been introduced in other countries, and has helped① Fastening-torque value or axial-tension value

to reduce leakage. However, especially in Japan, efforts

When the fastening torque is known, select a tool

to prevent leakage are left to the discretion of facility

which can apply that torque at no more than 70% ofowners and engineering companies.

its maximum output.

Regarding large bolts, which are difficult to fasten by【Point】Consider the tool’s fastening performance.

manpower alone, we sell and rent out tools for suchAs a guide, a tool should be selected from tools

bolts. We also offer on-site supervision on shop floors

which have maximum torque output equal to 1.5

where fastening skills vary among the different

times the target torque. If the axial-tension value

operators who perform fastening.

（bolt elongation）is the target value, the tightening

We have accumulated useful knowledge and information

is managed by using a bolt tensioner or a hydraulicabout fastening from on-site experience, and would liketorque wrench & ultrasonic axial force meter asto share tips on fastening regarding tool selection andshown in Figure1.

considerations for installation.

27

Contribution

nut’s top face, the bolt cannot be fitted with ahexagonal socket. Therefore, center-hole tools andcenter-hole bolt tensioners should be selected.
【Tip】Consider the tool’s operational speed.
Since the operation time per bolt should beshortened, consider selecting a tool with a highFigure1 Measurement‌of bolt elongation value using an
ultrasonic axial force meter

fastening speed, fastening bolts concurrently
using several tools, and other strategies.

②③‌ Clearance around the target bolt and equipment

Shape and number of bolts and nuts
Since the types of tools that can be used are limited

environment

depending on the shapes of bolts and nuts, such as

Check the clearance around bolts to be tightened

all-screw bolts, tap-end bolts, hexagon headed bolts,

and the equipment environment.

and cap nuts, select tools which match such bolts【Tip】‌Check whether there is space in the axial
direction of bolts.

and nuts.

Large spaces in the axial direction are required【Tip】‌Check whether the selected tool matches thefor pistol-type tools including air torque wrenches.

shapes of bolts and nuts.

On the other hand, hydraulic torque wrenches

When the long part of a bolt protrudes from theTable1

Torque range

Booster wrench

Air torque wrench

Hydraulic torque wrench

M16–36

M20–48

M20–56

M30–76

M30 to over M100

1,000–30,000 N・m

Managed using axialtension（kN）
No scoring on screws
Several screws can befastened concurrently.
Highly-precise fastening
No co-rotation
Troublesome setting
Heavy tool

300–2,000 N・m

500–4,000 N・mMajorVery strong torque can be Easy cordless operation
characteristics applied with light force. using a pistol-type tool
Advantages

No need for powersourceDisadvantages

Takes time in fastening.

Power source

Unnecessary（Manpower）

Rechargeable battery○×

Explosion-proof
Condition for
application 1
Condition for
application 2

Handy for anyone
High speed
Regular charging isrequired.

Space of at least 250
Space of at least 500
mm is required in themm is required in theaxial direction of a bolt. axial direction of a bolt.
A reaction-force pointshould be secured on the←neighboring bolt or otherarea.

500–6,000 N・m
Easy operation using apistol-type tool
Handy for anyone
High speed
Need for stable air
supplyCompressed air500 kPa ○Bolt tensioner

Smallest and lightest
among tools with thesame torqueHighly precise torque
Wide torque range
Need for pumps andhydraulic hoses
Compressed air 500 kPa -, Compressed air 500 kPa Power supply 100 V, 200 V○ Depends on pump’s function○Space of at least 500 Space can be minimal in Space of at least 300
mm is required in thethe axial direction of amm is required in theaxial direction of a bolt.
bolt.
axial direction of a bolt.
Bolt’s head should
protrude from nut’s top←←
face by at least 1d（d:diameter）.

Management method

Input torque wrench

Digital pre-setting

Air pressure

Hydraulic power up to 70 MPa Hydraulic power up to 150 MPa

Concurrent
fastening

N/AN/A

N/A（2 bolts to half theAvailable（up to 4 bolts） Best
total number of bolts）

Operator No.

1 operator/tool

1 operator/tool

1 operator/tool

1–2 operators/tool

0.5–1 operator/tool

Nut fitting

SocketSocketSocketSocket or direct fitting

PrybarSpeed

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Concurrent
multiple-bolt
fastening
Applicability tovarious sizes
Introduction cost

28

Winter 2018

Applicable bolt

Characteristics and evaluation of each tool

Battery-type
torque wrench

No.34

Considerations for Tool Selection and Installation of Fastening Bolts for Flanges with Large Nominal Diameters

are compact and can be widely used. Care should

maintenance condition, so maintenance is very

be taken, if space is tight, such as under piping

important, which includes the following:

elbows.

①

Removing rust and scale②

Repairing damaged screw threads③‌Applying lubricant to the nut seat and threaded【Tip】‌Check the orientation in which tools areapplied.

portionWhen tools are heavy, especially when used fromunderneath, workability is greatly affected by thetool’s weight, so the tool’s weight is an important④④‌Smoothing the flange’s surface（when impossible,use a washer）

factor. When a tool weighing over 10 kg is used

We have checked the maintenance conditions at many

upwardly from underneath, some measure tosites and found that although 1）and 2）are conductedsupport the tool or prevent it from falling isproperly, 3）is often inadequate. In the case of torquenecessary.

control, the axial-tension value of the nut seat surface,

Available power source

which is greatly affected by friction, varies

Check the type of power source available.

significantly when a lubricant is applied to the surface.

【Tip】‌Secure a power supply of 200 V or stable

When the surface condition of a flange is poor,

compressed air.

inserting a washer may improve the condition. WeWinter 2018

If there is no power supply, a booster wrench or ahave seen many such cases.

battery-type torque wrench should be selected

In the case of the all-screw bolt, when lubricant is not（the wrench should be charged）. Also, bolt

applied to the fastening side and opposite side of thetensioners can be pressurized using a hand pump.

nut seat surface, co-rotation is less likely to occur.

By considering the above factors and comparing

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them with each tool’s characteristics as shown in3-2）Fastening procedures

Table1, the candidate tool types can be identified.

When fastening a flange’s bolts while uniformly

Especially, the bolt tensioner uses a different

compressing the gasket, fastening should be conducted

fastening mechanism from the torque method: thein a stepwise fashion, as described in JIS B2251２） andbolt tensioner applies axial force to a bolt byJPI-8R-15.３）

directly pulling the bolt. Therefore, the bolt

In practice, these standards are rarely observed, andtensioner is rarely affected by the friction

they show procedures only when using one tool for

coefficient of the contact surface, and so offers

fastening. The proper procedures vary depending on

highly accurate fastening and does not scratch

the number of tools used, so it is desirable to set

the flange’s surface. However, many devices aredesigned without assuming that the bolts arefastened using a bolt tensioner; in some cases,
part of the device must be remodeled, includingchanging the bolts, in order to use a bolttensioner in existing facilities.

3. Considerations of assembly3-1）Maintenance of bolts and nuts
The next important factor is maintenance of bolts andnuts. Especially, in the case of torque fastening, theaxial tension applied to bolts varies depending on the29

Figure2 Parallel fastening using two hydraulic torque wrenches

Contribution

efficient procedures which are tailored to the numberof tools used.
Among the proper procedures, we especially
recommend parallel fastening as shown in Figure2. Inparallel fastening, at least two tools are placed
diagonally for fastening.
This requires less work for one bolt until fastening iscompleted in a shorter time period, and the gasket iscompressed evenly. Therefore, this fastening method
can prevent malfunctions resulting from unevenfastening. Valqua’s Seal Training Center４） has facilities

Figure3

where you can experience parallel fastening of flanges

Backup wrenchwith large nominal diameters, so we encourage you tobackup wrenches are not used, co-rotation must be

take advantage of these facilities.

prevented by using slogging wrenches and chisels,
but it takes longer to remove the wrenches thanwhen fastening nuts.

3-3）Considerations on reaction-force point
In torque fastening, in principle tools should apply②

Hydraulic pump with large discharge volume
The speed of the hydraulic torque wrench and bolt

reaction-force point directly results in accuratetensioner depends on the pump’s discharge volume;

fastening force and safety. Therefore, the following

the discharge volume makes a significant difference

procedures are important when fastening nuts: 1）

especially when a large tool is used. However, large

Draw a horizontal line extended from the center oftools are less portable. Therefore, take on-site

the nut to be fastened. 2）On the horizontal extended

conditions into account when selecting appropriateline, set a position where a reaction-force arm is fixed.

tools.

3）Tightly secure the reaction-point arms on the③Not-too-long hydraulic hose

position in such a manner that the arm is securely

If the hydraulic hose is too long, it is obstructive on

fixed to the position when force is applied to the arm.

the scaffold, and makes tools not only cumbersome
but also slower. The standard length is 5m.

Regarding common flanges, reaction-force points canusually be secured by using the neighboring nut.

④Nut splitter

However, in other cases, it is necessary to carefully

Figure4 shows a hydraulic nut splitter. Although

check in advance whether a reaction-force point canthis phenomenon occurs only when a nut is

be correctly secured.
3-4）Efficient operation
After tool selection, the actual work will start; a little
preparation in advance can reduce the working time,so we recommend preparing the following items.
①Backup wrench
Figure3 shows some backup wrenches. A backup
wrench is set on the nuts on the fastening side andon the opposite side to prevent co-rotation. Inaddition, backup wrenches can be removed easily. If

Figure4

Nut splitter
30

Winter 2018

force from a reaction-force point. Securing a stable

No.34

Considerations for Tool Selection and Installation of Fastening Bolts for Flanges with Large Nominal Diametersloosened, if the nut adheres to a bolt too strongly theof many flanges did not function as intended.

nut does not rotate. In this case, hydraulic power canValqua offers various services at its Seal Training

be used to cut a nut quickly to remove a bolt.

Center, to provide proper knowledge and significantly
reduce the risks stemming from users’ignorance.

4. Conclusion

Leakage at the bolted flange joint is mainly due topoor assembly, which may be due to bolt-tightening

This article introduced considerations for tool selection

problems. We offer products and services for bolt-and installation when fastening the bolts of flanges

tightening, to accumulate on-site experience whichwith large nominal diameters.

cannot be gained from studying theories, and provide

Our first priority is to resolve on-site problems anduseful information for those who need it, ranging fromchallenges in bolt-fastening operations. To achieve thisdesigners to operators. To achieve this goal, we aregoal, we have developed products which are useful on

establishing a system and offering support for all

shop floors; selected tools which meet theprocedures ranging from seal selection to bolt

requirements of each shop floor and promptly

tightening.

procured these tools; created on-site guidance onhandling; and performed fastening management using
an ultrasonic axial force meter.

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Through these experiences, we have encountered１）‌T. Kikuchi and Y. Kondo,“Management Standard

many cases in which ignoring small details resulted in

for Fastening Flanges/Bolts”, The Pipingproblems. Two decades ago, there were many skilledworkers and we witnessed their excellent hammeringworks. However, when an ultrasonic axial force meter
was used to measure the fastening conditions of thebolts which they had fastened, the meter showed thatNo.34

5. References

the bolts had been fastened too strongly. Overfastening was probably performed because the gaskets

Shinichi Kitahara
TORQUE SYSTEM Co.,Ltd.
Managing Director

31

Engineering, November 2017.
２）‌JIS B 2251,“Flange Joint Assembly Guidelines”（2008）.
３）‌Management Standard for Fastening Flanges/Bolts,
JPI-8R-15-2013.
４）‌A. Muramatsu, Valqua Technology News: No. 33,
15–18（2017）.