Guidelines for the management of
the integrity of bolted joints
for pressurised systems
2nd edition
An IP Publication
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GUIDELINES FOR THE
MANAGEMENT OF THE INTEGRITY OF BOLTED JOINTS
FOR PRESSURISED SYSTEMS
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GUIDELINES FOR THE
MANAGEMENT OF THE INTEGRITY OF BOLTED JOINTS
FOR PRESSURISED SYSTEMS
May 2007
Second edition
Published by
ENERGY INSTITUTE, LONDON
The Energy Institute is a professional membership body incorporated by Royal Charter 2003
Registered charity number 1097899
Endorsed by
Oil & Gas UK, HSE OSD and the ECITB
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The Energy Institute gratefully acknowledges the financial contributions towards the scientific and
technical programme from the following companies:
BG Group
BHP Billiton Limited
BP Exploration Operating Co Ltd
BP Oil UK Ltd
Chevron
ConocoPhillips Ltd
ENI
ExxonMobil International Ltd
Kuwait Petroleum International Ltd
Maersk Oil North Sea UK Limited
Murco Petroleum Ltd
Nexen
Saudi Aramco
Shell UK Oil Products Limited
Shell U.K. Exploration and Production Ltd
Statoil (U.K.) Limited
Talisman Energy (UK) Ltd
Total E&P UK plc
Total UK Limited
Copyright © 2007 by the Energy Institute, London:
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damage which may arise from the use of any of the information contained in any of its publications.
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CONTENTS
Page
Foreword ............................................................................................................................................................. vii
Acknowledgements .............................................................................................................................................. ix
1
Introduction ................................................................................................................................................... 1
2
Bolted joint technology and practice ............................................................................................................ 3
2.1 Overview .................................................................................................................................................. 3
2.2 Types of bolted joints ............................................................................................................................... 3
2.3 Bolted pipe joint components ................................................................................................................... 4
2.4 Principles of joint assembly and disassembly ........................................................................................... 6
2.5 Controlled tightening of joints .................................................................................................................. 8
2.6 Bolted joint reliability ............................................................................................................................. 10
2.7 Integrity testing....................................................................................................................................... 14
3
Criticality assessment .................................................................................................................................. 17
3.1 Introduction ............................................................................................................................................ 17
3.2 Assessing the risks with bolted joints ..................................................................................................... 17
4
Training and competence ............................................................................................................................ 21
4.1 Introduction ............................................................................................................................................ 21
4.2 Competence management ....................................................................................................................... 21
4.3 Training .................................................................................................................................................. 21
4.4 Ongoing competence .............................................................................................................................. 22
4.5 Training in engineering construction skills (TECSkills) ........................................................................ 22
4.6 Vocational qualifications ........................................................................................................................ 22
4.7 Independent accreditation organisations ................................................................................................. 22
5
Records, data management and tagging .................................................................................................... 27
5.1 Joint identification .................................................................................................................................. 27
5.2 Records and data management ............................................................................................................... 28
5.3 Review.................................................................................................................................................... 29
v
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Contents Cont....
Page
6
Management of leaks ................................................................................................................................... 31
6.1 Introduction ............................................................................................................................................ 31
6.2 Engineering risk assessment of leaks ..................................................................................................... 31
6.3 Stages at which leaks occur .................................................................................................................... 32
6.4 Corrective actions ................................................................................................................................... 32
6.5 Definition and detection of leaks ............................................................................................................ 32
6.6 Managing leaks and repairs .................................................................................................................... 34
6.7 Learning from leaks................................................................................................................................ 34
7
In-service inspection .................................................................................................................................... 37
7.1 Introduction ............................................................................................................................................ 37
7.2 Risk assessment ...................................................................................................................................... 37
7.3 Degradation mechanisms ....................................................................................................................... 37
7.4 Inspection techniques ............................................................................................................................. 37
7.5 Defect mitigation measures .................................................................................................................... 38
vi
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FOREWORD
The first Issue version of this document has its roots set in the upstream oil and gas industry being part of the
HSE/industry drive to reduce the incidence of hydrocarbon leaks on offshore installations. Leaking joints have been
the main cause of hydrocarbon releases on the UKCS offshore sites and there exists similar concern for the vast
number of facilities handling petrochemical and other hazardous material on main land sites.
In 2005, the UKOOA (now Oil & Gas UK) led Installation Integrity Working Group (IIWG) requested that the
Energy Institute manage the review and revision of the Joint UKOOA/IP Guidelines for the management of the
integrity of bolted pipe joints first issued in June, 2002. This project required the formation of a cross-industry Work
Group (WG) many of whom were from that used to compile Issue One. Others included those from the parent IIWG
members, consultants and representation from the industry training organisation, ECITB.
The revision exercise was part of the programme of work undertaken by the IIWG which included development and
promotion of industry good practices and suitable performance measures. The principal deliverables of this Work
Group were an Asset Integrity Tool Kit and review and revision of guideline documents one of which was for the
management of integrity of bolted pipe joints. It is therefore considered that this Guideline will provide valuable
advice to assist operators manage plant integrity for any installation employing bolted joints.
During the review process, the WG elected to widen the scope to include bolted joints used within pressurised
systems and not just pipe joints as is the case for Issue One, and to ensure that the document is applicable to onshore
industries as well as offshore oil and gas.
This document has been compiled as guidance only and is intended to provide knowledge of good practice to assist
operators develop their own management systems. While every reasonable care has been taken to ensure the
accuracy and relevance of its contents, the Energy Institute, its sponsoring companies, section writers and the Work
Group members listed in the Acknowledgements who have contributed to its preparation, cannot accept any
responsibility for any action taken, or not taken, on the basis of this information. The Energy Institute shall not be
liable to any person for any loss or damage which may arise from the use of any of the information contained in any
of its publications.
This Guideline will be reviewed in the future and it would be of considerable assistance for any subsequent revision
if users would send comments or suggestions for improvements to:
The Technical Department,
Energy Institute,
61 New Cavendish Street,
London
W1G 7AR
e: technical@energyinst.org.uk
vii
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viii
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ACKNOWLEDGEMENTS
As Work Group members, the Institute wishes to record its appreciation of the work carried out by the following:
Sub Group Champions, who have managed the coordination and compilation of designated sections through
leadership of their respective volunteer sub-groups and through providing authorship expertise:
Stuart Brooks
Rod Corbet
Anderson Foster
Jim MacRae
Robert Noble
BP Exploration Operating Company Ltd.
Rotabolt
Total E&P UK plc
Nexen Petroleum UK Ltd.
Hydratight
Sub Group members, who have provided valued input into their designated sections:
Blair Barclay
Keith Dunnett
Bill Eccles
Alan Gardner
Tim Jervis
Gary Milne
Phillip Roberts
Ravi Sharma
Mike Shearer
Lawrence Turner
Mark Williams
Pat Wright
ECITB
CNR International
Bolt Science (Hytorc)
Consultant
Shell Exploration & Production
Hydratight
Shell Exploration & Production
HSE
Lloyds Register EMEA
Shell Exploration & Production
Klinger UK Ltd
RGB Ltd.
Assistance was also provided by the following other Work Group members:
Gwyn Ashby
Peter Barker
Arunesh Bose
Martin Carter
Kevin Fraser
Norrie Hewie
Gavin Smith
Roy Smith
Jan Webjorn
Mitsui Babcock
Marathon Oil
Lloyds Register EMEA
BHP Billiton
IMES
Hess Corporation
Novus Sealing
Hytorc
Verax
ix
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Liaison with other organisations was provided by:
EEMUUA
IMechE Pressure Systems Group
Oil & Gas UK (formerly UKOOA)
Andrew Pearson
Chris Boocock
Bob Kyle
Technical authorship and editing:
Phil Smith
ODL
The revision/review project was coordinated and managed by Keith Hart FEI, Energy Institute, Upstream Technical
Manager.
The Institute also wishes to recognise the contribution made by those who have provided comments on the Draft
document which was issued during an industry consultation period.
x
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1
INTRODUCTION
A bolted joint is one of many critical components of a
pressurised system. Dependent upon the contents and
pressure of the system, leakage or failure of a bolted
joint can have potentially catastrophic consequences. To
meet this challenge, every operator of pressurised
systems should have in place a system to positively and
actively manage the integrity of bolted joints. It is
expected that such a system will be built around the
principle of continuous improvement (see Figure 1.1).
This document describes the principles and good
practice for the establishment of a management system
for bolted joints in pressurised systems. Individually the
sections of this document provide details of what is
considered good practice in the key areas of ensuring
joint integrity. Together they provide the framework for
a management system.
This document is not intended as a design guide for
bolted joints, but as a guide to how to manage joints
during construction and commissioning phases and
through their operational life. It provides a framework
to achieve this based on working with a correctly
designed joint.
ANALYSIS,
LEARNING AND
IMPROVEMENT
OWNERSHIP
MANAGEMENT
OF LEAKS
TECHNOLOGY
AND PRACTICE
IN-SERVICE
INSPECTION
CRITICALITY
ASSESSMENT
RECORDS, DATA
MANAGEMENT
AND TAGGING
TRAINING AND
COMPETENCE
Figure 1.1: Essential elements of a management system
1
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GUIDELINES FOR THE MANAGEMENT OF THE INTEGRITY OF BOLTED JOINTS FOR PRESSURISED SYSTEMS
The following are considered essential elements of
a management system which must be applied to ensure
that the system is implemented and remains effective:
in the past, ideally from original construction of the
joint, linked to the design specification of the joint.
Providing and recording traceable data encourages
best practice at the time of the activity, and will
provide useful planning data for the next time the
joint is disturbed.
— Ownership
There should be an identified owner of the
management system, responsible not only for its
implementation and ongoing maintenance, but also
for communicating its aims and objectives
throughout the organisation. The owner should
state the expectations for the system and monitor its
effectiveness.
— In-service Inspection
Learning from both positive performance and
incidents is important. A management system
should include the means for gathering relevant
data on joints which are successful and those that
have incidents or leakage issues. These should be
collected by everyone involved in bolted joints, and
periodically reviewed and analysed to establish
trends, issues and improvement opportunities.
— Technology and Practice
Good practice with regard to selection and control
of assembly, tightening and assurance of bolted
joints should be applied. Understanding of the
theory and practice of bolted joints and
development of appropriate procedures should be
encouraged throughout the organisation.
— Management of Leaks
The objective of a correctly designed and installed
bolted joint is to provide a long-term tight seal and
prevent ingress or egress of fluids through the joint.
However, leaks can occur and managing the
investigation and repair of the leak is essential to
avoid recurrence. It can also provide useful data for
prevention on other projects.
— Criticality Assessment
The range of services, pressures and conditions
which bolted joints experience varies considerably.
Each joint should undergo a criticality assessment
which will determine the levels of inspection,
assembly control, tightening technique, testing,
assurance and in-service inspection relevant to the
joint.
— Analysis, Learning and Improvement
Analysis of leakage and inspection data coupled
with formal reviews of the management system
should occur at agreed intervals by the owner and
users. Results obtained from commissioning,
incident analysis and in-service inspections should
be used to generate ideas for continuous
improvement.
Easily monitored but meaningful performance
standards should be put in place at launch to
quantify the contribution being made by the
management system and evaluate user satisfaction.
Feedback on good practice in integrity issues and
causes and solutions to incidents should be
provided both internally and to industry to
contribute to continuous improvement.
— Training and Competence
Everyone with an influence on joint integrity in the
organisation should be aware of the management
system, its objectives, expectations and effects on
project planning and day-to-day working. Good
awareness needs to be maintained. Any staff
working on bolted joints should be appropriately
trained and competent.
— Records, Data Management and Tagging
The certainty of achieving joint integrity increases
if historical data exist on the activities carried out
2
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2
BOLTED JOINT TECHNOLOGY
AND PRACTICE
Pipework and pressure systems are designed to
meet varying operational conditions. In order to avoid
failure, it is very important that the relevant piping
specifications for materials and components are adhered
to in full.
There are many types of bolted joint and only some
of the more commonly used are mentioned here but as
mentioned previously, the basic reliability parameters
and procedures applied are the same for all.
2.1 OVERVIEW
This section gives a brief outline of how joints work and
provides guidance on the safe and efficient assembly
and disassembly of flanged joints and clamps. It also
discusses basic proposals for integrity testing. The
scope of these Guidelines covers all pressure-containing
joints including pipelines, pressure vessels such as
reactors and heat exchangers, associated valves and
other pressure-containing equipment. Due to operating
conditions with heat exchangers and reactors,
particularly temperature gradients, different metal joint
components and thermal and pressure cycling, a higher
level of control and assurance of bolt load is generally
required compared to, for example, piping joints
subjected to static pressure only. The principles set out
are generic in nature and not exclusive to pressure
containment applications; they can be applied to bolted
joints subjected to other service conditions such as
fatigue, vibration and structural loading.
The flanged joint is deceptively simple yet, in
common with the welded joint, its integrity relies on a
number of parameters including the basic design,
structural and metallurgical quality of its components
and achieving the required design clamp force on
assembly. Important to meeting these assembled design
objectives is the selection of suitable installation
procedures and tools that are applied by competent
operators.
The importance of planning the joint assembly,
preparation of all components, procedures, tooling and
ensuring application of the correct methodology is
essential.
2.2 TYPES OF BOLTED JOINTS
2.2.1
Flange joints
The most common type of joint is made up of two pipe
flanges to ASME B16.5 design code, between which a
gasket is compressed by the installed bolting. Similar
arrangements are used for other codes such as API 6A,
BS 1560 and MSS SP 44. The piping material
specification will detail the codes and materials to
construct the facility.
The principle of a bolted joint is based on the
bolting delivering sufficient joint compression and
gasket seating stress to withstand maximum service
pressure and forces. This is when the bolting is under
tensile load as illustrated in Figure 2.1. For integrity a
minimum level of operational gasket seating stress must
be maintained throughout joint service, therefore the
design bolt load/compression target on installation
should allow for creep, relaxation, uncertainty over
service loadings and the tolerances of components and
tools used.
3
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GUIDELINES FOR THE MANAGEMENT OF THE INTEGRITY OF BOLTED JOINTS FOR PRESSURISED SYSTEMS
Figure 2.1: Working principle of bolted flange joints
2.2.2
Compact flanges
2.2.3
Various types of compact flanges have been developed
by specialist manufacturers. Some use gasket
arrangements similar to the metallic ring joint whereas
others use metal to metal, gasketless contact and the
joint becomes a static entity with minimal flange
rotation potential. Such compact flanges tend to be
characterised by the sealing area being positioned closer
to the pipe bore thereby reducing bolt and working load
eccentricity and subsequent end load on the bolts. This
is a preferred bolted joint design feature and can result
in smaller, lighter flange sizes and a reduction in bolt
diameter, quantity or strength grade. The design
philosophy can vary from type to type so the
manufacturer should always be consulted for advice on
joint sealing, design bolt tension and installation
procedures.
Clamped connectors
Clamped connectors (see Figure 2.2) use a split clamp
to join the pipe. Hubs at the ends of the pipe have
tapered shoulders sloping towards the joint and the
clamps have tapered faces, which form a wedging
action to close the two hubs together. The hubs have
internal sloping faces which bear on taper ring gaskets,
causing them to be distorted elastically and form a seal.
2.3 BOLTED PIPE JOINT COMPONENTS
2.3.1
Flanges and clamped connectors
Like pipes, flanges and clamped connectors operate
under varying conditions of temperature and pressure.
The most critical area on a flange or clamped connector
is its sealing face, on which the gasket or seal ring seats
to form a pressure retaining seal (see Figure 2.3 on
page 7). It is therefore imperative that the sealing face’s
surface finish complies with the design specification or
the manufacturer’s recommendations. It must be
protected at all times and free from damage, grease and
protective coatings.
On ASME B16.5 type flanges, the nut seating area
at the back of the flange must be clean and of a smooth
finish to reduce friction unless stated in the
manufacturer’s specification. Flanges, blinds and flange
facings should be in accordance with the relevant flange
code or manufacturer’s proprietary requirements.
Flanges are marked to identify the size, pressure
rating and flange material, as shown in Figure 2.4 on
page 7. The pipe schedule used with the flange should
Hub
Clamp
Seal
ring
Figure 2.2: Clamped connector
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BOLTED JOINT TECHNOLOGY AND PRACTICE
also be marked. Corresponding bolts and nuts also carry
material identification marking. These should conform
to the relevant fastener specification.
2.3.2
the double jacketed gasket is intended to go against
this face; this is an important assembly feature.
— Kammprofile
This is a solid metal ring having a serrated tooth
form profile on both faces. A covering layer of
graphite or PTFE is applied which compresses into
the serrated surface as the gasket is loaded. These
are used increasingly for heat exchanger flanges
(see Figure 2.5 on page 7).
Gaskets and seal rings
Correct gasket or seal ring selection and installation are
important and only those specified in the piping material
specification should be installed. The gasket creates the
seal between the two flange faces and contains the
internal pressure of the joint.
As with flanges, gaskets and seals can be marked to
identify principal characteristics, as shown in Figure 2.5
on Page 7.
There are three main types of gasket: non-metallic,
semi-metallic and metallic. Application selection is
dependent on service conditions.
2.3.2.3 Metallic
These are made from one or a combination of metals in
a variety of shapes and sizes for high temperature and
pressure usage. The metal ring fits into grooves that
have been machined into the flange faces. Due to the
high application pressures, the seating stresses and
corresponding bolt tension are necessarily large to give
sufficient deformation to overcome flange surface
imperfections and distort against the groove surfaces so
as to overcome high service pressures. Oval and
octagonal types (see Figure 2.7 on page 7) are
commonly used in oil and gas applications under ASME
B16.20 and API 6A. RX rings are perceived to be selfenergising whilst the BX type are designed to fit into a
recess that allows metal to metal contact when the
flanges are tightened.
2.3.2.1 Non-metallic
These are made from elastomers, cork, compressed
fibres, plate minerals and PTFE. Usually the material
sheet is cut to the shape of the flange sealing face. They
are generally used for low to moderate pressures and
temperatures and see wide chemical service including
acid and alkaline applications.
2.3.2.2. Semi-metallic
These combine a combination of non-metallic filler for
compressibility and metal for strength. They are
typically used for higher temperature and pressure
applications compared to the non-metallic types.
Common types include:
2.3.2.4 Specific seal rings
These will be found on proprietary equipment
manufacturers’ joints and should be assembled and
tightened in accordance with the manufacturer’s
specification.
— Spiral wound
These gaskets are constructed with spirally wound
metal and soft filler (see Figure 2.6 on page 7). A
wide range of metals can be used for the winding
strip and support rings as well as various filler
materials. On raised face flanges, the gaskets have
an outer support ring which locates inside the bolt
PCD. They can also be supplied with an inner ring
for higher pressure system usage. The inner ring is
also used where high process flow rates or abrasive
media are found; the inner ring reduces turbulence
at the pipe bore. On spigot or recess flanges a
simple sealing element gasket is used with no
additional support rings.
2.3.2.5 All gaskets
Gaskets and seal rings should be suitable for their
intended operating conditions and be capable of
providing a seal under the varying loads imposed by
fluctuations in pressure and temperature. Depending
upon the application, the main requirements are any or
all of the following:
—
—
—
—
—
— Metal jacketed
These clad gaskets have been traditionally used on
heat exchangers. A variety of metals can be used to
encase a soft filler material. It should be noted that
some heat exchanger flanges have stress raising
'nubbins' on one face and the non-seamed face of
Hardness and compressibility.
Flexibility.
Resistance to heat.
Resistance to pressure.
Resistance to corrosive action.
Under no circumstances should gasket compound or
grease be applied to the gasket or flange faces. Note that
for some clamp connectors, the manufacturers
recommend that the seal ring be lubricated.
Gaskets and seal rings should be:
— Stored in their original packing until required.
5
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GUIDELINES FOR THE MANAGEMENT OF THE INTEGRITY OF BOLTED JOINTS FOR PRESSURISED SYSTEMS
— Kept horizontal and flat.
— Where applicable, left on their individual backing
boards until immediately prior to fitting.
The number of reuses and subsequent life of the
bolt should be based on the level of assurance provided
by the tightening methodology selected. Greater
reusability and longest service life will be provided
where the bolt tension requirement is assured by using
a load control measurement system with the selected
tightening tool. If the bolt is suspected of being
overloaded or yielded during a previous installation, it
should never be reused.
Specific difficulties can arise with insulating gasket sets
and appropriate precautions should be taken if these are
to be used.
2.3.3
Bolting
Correct bolt selection, procurement and installation are
crucial and only the bolt type as specified in the
equipment material specification should be installed.
On ASME B16.5 type flanges, for example, the
bolts are designed to carry pressure end load at the
gasket and also provide the load required to compress
the gasket into the flange face in order to effect a seal.
Bolt diameters and lengths are specified in the
relevant flange code and should also be stated on the
fabrication/erection detail drawing. Bolt lengths may
have been increased to allow for bolt tensioning
equipment, or spades, spacers, drip rings and wafer
valves, and the associated extra gaskets. Although the
amount of specified bolt protrusion may vary there must
be sufficient protrusion for full thread engagement.
Many specifications call for a protrusion length of three
thread pitches through the nut. Where hydraulic
tensioners are used a minimum of one bolt diameter
must protrude through the nut to enable safe and
effective tensioner operation.
The bolt and nut grades and manufacturer’s
identification should be stamped on both and should be
correctly identified before they are used (see Figure 2.8
on page 7). They should both be in compliance with the
equipment material specification. The selected fastener
material and diameter must provide sufficient elastic or
yield strength capacity to safely sustain the design load
requirement, service bolt loads and any compensatory
overloads needed from the tightening method.
Coatings such as hot dipped galvanising and PTFE
should also comply with the appropriate coating
standard. Bolts with different coatings should not be
used on the same flange joint.
Bolts, nuts and washers used for joint make-up
should be clean, rust free and undamaged. Fasteners can
be considered for reuse after considering their service
history, operating environment and original risk
assessment. Any service coating must be in good
condition and still provide 100% fastener surface
coverage. This is especially important for
PTFE/Organic barrier coatings. Section 7 provides
guidance on in-service inspection.
2.4 PRINCIPLES OF JOINT ASSEMBLY AND
DISASSEMBLY
2.4.1
Identification of joint and selection of
correct components
Ensure the correct materials are available, matching
those detailed in the piping specification, including:
— Flanges of correct size, type, material and rating.
— Bolts of correct size, material, and length for
flange and tightening method.
— Nuts of correct grade and size.
— Correct thread lubricant.
— Correct gasket is available.
2.4.2
Inspect the components and flange faces
Ensure that:
— Components and flange faces are clean and
undamaged and of the correct surface finish.
— Nuts and bolts are clean and free running but not
sloppy on threads.
— Gaskets are clean and free of damage.
2.4.3
Assemble the components
Components should be assembled in accordance with
the procedure relevant to the joint type and
specification, and the tightening method to be used.
Ensure that:
— Bolts are lubricated on threads.
— Nuts to be tightened are lubricated on the spot
faces.
— Bolts are set correctly in the flange to allow for the
correct thread protrusion and fitting of tools.
— Gasket is centred correctly.
6
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BOLTED JOINT TECHNOLOGY AND PRACTICE
Figure 2.3: Example of flange face configuration
Figure 2.4: Flange identification markings
Figure 2.5: Kammprofile gasket with
Ident and class marking
Figure 2.6: Schematic of typical spiral
wound gasket
Figure 2.7: Type R octagonal ring type joint
Figure 2.8: Stud point and nut showing
identification markings
7
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the licence terms and conditions. It must not be forwarded to, or stored or accessed by, any unauthorised user. Enquiries: e: pubs@energyinst.org.uk t: +44 (0)207 467 7100
GUIDELINES FOR THE MANAGEMENT OF THE INTEGRITY OF BOLTED JOINTS FOR PRESSURISED SYSTEMS
2.4.4
The following precautions should be taken when
breaking a joint:
Alignment
Flanges should align initially in the un-stressed
condition without any external forces applied unless
stipulated within the design (e.g. cold spring). ASME
Piping Code B31.3 (1999 Edition) 335.1.1(c) stipulates
that flange faces shall be aligned within 1 mm in 200
mm measured across any diameter, and flange bolt
holes should be aligned within 3 mm maximum offset
(see Figure 2.9). However, this is considered to be a
maximum and best practice is to use half this tolerance,
thereby making the alignment tolerance 0,5 mm in 200
mm. In general, because of the many variables involved,
company standards should be set as to allowable
misalignment, but large forces should be avoided. It is
recognised that misalignment greater than that specified
here, particularly on pipework connected to non-loadsensitive equipment, may be acceptable.
However, pulling the flanges into position could
cause unacceptable loads and deflections in other parts
of the system, and means that bolt load is being used to
pull the flanges together instead of to compress the
gasket. If additional force greater than can be applied by
a single person is required, where flange misalignment
or pulling together is excessive or outside the company
standards, or where considerable loads are required to
correct the misalignment, then the appointed Technical
Authority should be consulted and the outcome
recorded.
2.4.5
1.
2.
3.
4.
Ensure beyond all doubt that the line or piece of
equipment being worked upon has been correctly
isolated and vented to atmospheric pressure, and
flushed and purged if appropriate.
Ensure that all safety precautions and work permit
instructions are in place and are strictly adhered to.
Take a position upwind of the flange whenever
possible. Never stand in line radially with the
flange face. Release the bolt furthest away,
allowing any residual pressure of gas or liquid to
blow away from you. Do not remove the nut and
bolt at this stage.
Continue to release the remaining flange nuts, but
do not separate them from the bolts until the flange
joint has been fully broken.
Note: It could be the fifth or sixth bolt to be released
before the seal is broken.
CAUTION: For pressure energised seals on compact
flanges or hub connectors, care must be taken that the
joint is released before removing the bolts. Personnel
should also be aware of the risk of pipe spring or sudden
movement as bolt loads are released.
2.5 CONTROLLED TIGHTENING
OF JOINTS
Breakout
Before tightening of the joint is considered, it is
necessary to consider breakout. It may be that the joint
has already been assembled and tightened before, for
example as part of a test programme during
construction, or the joint is being opened as part of a
maintenance programme after a period in service.
The objective of any tightening is to achieve a correct
and uniform clamping force in the joint. The operator
needs to know the bolt load or bolt stress value required
irrespective of what parameter he will be measuring
during the tightening cycle. He also needs to know the
tightening methodology selected.
1 mm
3 mm
1 mm
Angular offset
Centre-line offset
Figure 2.9: Alignment tolerances
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BOLTED JOINT TECHNOLOGY AND PRACTICE
The bolt load or stress will have been calculated to
be suitable for the joint and its service conditions. These
details should be obtained from the record and data
management system for the site (see Section 5). Any
changes in the flange system such as its size, type and
material could change the bolt stress requirement and
subsequent selection fastener material/diameter
selection. Similarly any gasket change could also
change the design bolt load. Any such changes must be
checked with a Technical Authority.
Hot dip galvanised bolting could change the thread
dimensions and this should be considered when
selecting the correct tensioner or torque tool.
On completion of tightening, the joint should be
tagged and details recorded in accordance with the site’s
records and data management system.
The following points are specific to the relevant
tightening technique.
2.5.1
Lubricant must be properly applied to 'working'
surfaces only. This includes the bolt threads and the
bearing faces of the nuts.
2.5.1.2 Tightening
Torque tightening should be carried out sequentially, in
stages to 100% of specified full torque, using the crossbolt tightening method. Typically three stages of 30%,
60% and 100% are used. It is important that the flange
is brought together evenly to prevent overloading of the
gasket at any point and this should be monitored at all
times during the process. Once the first 100% level has
been achieved a check pass should then be carried out
on all bolts using a clockwise pass to ensure all bolts are
at the final torque level. If a bolt load assurance system
is used then the final tightening cycle or check is
measured by bolt load. It is possible that the use of a
bolt load assurance method can reduce the number of
intermediate, pre-torque cycles.
The joint will continue to settle under load and
the number of passes at 100% will be influenced by the
type of joint and its gasket type. For example, cut
gaskets and most ring type joints can be considered as
'soft' joints whereas metallic gaskets such as spiral
wound types can be considered as 'hard' joints. A soft
joint may require more torque passes to reach the
required bolt load in all bolts.
Figure 2.10 shows cross bolt torque tightening
sequences from ASME PCC1.
Torquing specific considerations
2.5.1.1 Lubricant
Regardless of the torque tool used, lubricant has a
significant effect on the achieved bolt load or stress for
a given torque. A known good quality lubricant, suitable
for service and of proven coefficient of friction must be
used. It is recommended that where possible sites adopt
a single lubricant policy; this avoids the opportunity for
confusion.
Extra care needs to be taken with high friction
surface coatings.
1
8
8
1
4
1
9
12
5
5
4
4 Bolt
Flange
4
8 Bolt
Flange
3
2
16 Bolt
Flange
14
3
6
2
16
7
13
3
6
11
10
2
7
15
Figure 2.10: Cross bolt torque tightening sequence
9
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GUIDELINES FOR THE MANAGEMENT OF THE INTEGRITY OF BOLTED JOINTS FOR PRESSURISED SYSTEMS
2.5.2
Hydraulic tensioning specific considerations
2.5.2.1 Key requirements
Hydraulic tensioning involves the use of a number of
tensioners simultaneously to tighten a joint. The number
of tensioners and passes must be known to determine
operating pressures. When tensioning, it is important to
ensure that the correct bolt tensioning procedure is used
in order to obtain a secure and long-lasting leak-free
joint. Usually bolts are tensioned in alternate phases
using specified hydraulic pressures, taking into account
the load loss factor. In high risk joints where a load
control system is used a more streamlined procedure is
possible.
Flanges should be checked for squareness after
each tensioning phase. Confirm the bolt load with a
break loose/check pass. Where load control systems are
used this basic check is not required.
Bolt lengths need to be increased by one bolt
diameter distance to accommodate the hydraulic jack.
Hot dip galvanised bolting could change the thread
dimensions and this should be considered when
selecting the correct tensioning tool. This should be
notified to the tensioning company at an early stage.
Figure 2.11: Use of multiple torque tools
2.5.1.3 Use of multiple torque tools
Multiple torque tools can be used on a joint to help
flange faces keep parallel during the tightening process.
As with hydraulic tensioners, the use of multiple tools
can also reduce the effects of elastic interaction causing
variation in the residual bolt load achieved. The use of
multiple tools can also increase joint assembly speed.
In a typical application four torque tools are
connected to a hydraulic pump and arranged evenly
spaced around the joint as shown in Figure 2.11. When
these bolts are tightened, the tools are then moved to the
bolts that lie equidistant between the previous tool
positions, should there be an odd number of bolts
between the tools. When there is an even number of
bolts between the tools, the bolts that are nearest the
equidistant location are tightened next. On the first pass,
typically 30% of the final torque is applied to the bolts.
This first cycle is important in pulling flange faces
parallel and achieving satisfactory gasket seating.
The tightening procedures are dependent upon the
individual supplier of the equipment. An example of a
procedure is for 50% of the bolts to be tightened in the
first pass followed by a second pass in which all the
bolts are tightened to full torque. A third checking pass
is then made to ensure that the effects of elastic
interaction are minimised. However the methodology
may vary for differing vendors and therefore the
procedures must be checked with the supplier.
Where space permits and when there are sufficient
tools and equipment available, it is possible for all bolts
to be tightened simultaneously to their final torque value
thereby eliminating the need for intermediate steps.
2.5.2.2 Tensioning pattern or cover
Ideally tensioning should be applied simultaneously to
all studs in one operation. Where this is not possible,
tensioning should be applied in phases using two
different pressures, followed by a break loose/check
pass, as shown in Figure 2.12. Where a load assurance
system is used the break loose/check pass is not
necessary.
2.6 BOLTED JOINT RELIABILITY
2.6.1
Reliability factors
The reliability of a bolted joint is dependent on three
key factors:
— Joint/flange design and calculated bolt load.
— Joint component quality.
— Correctly assembled and installed design bolt load.
These three factors are critical to joint reliability.
Measure and control these factors and bolted joint
reliability is assured.
Once the bolt design load objective has been
established the operator needs to consider the criticality
of the joint in terms of operating pressures, process
fluids and health and safety. This will determine the
level of assurance required on installed bolt load, and
10
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BOLTED JOINT TECHNOLOGY AND PRACTICE
A
B
A
B
A
B
B
A
1st Pass at Pressure ‘A’
2nd Pass at Pressure ‘B’
Figure 2.12: Tension tightening sequence
capacity of all joint components – bolt, gasket and
flange – is also an important assessment to avoid
overloading and damage from the tightening forces used
in achieving the residual design load and subsequent
service loads. Calculation methods based on VDI 2230
(Systematic calculation of high duty bolted joints) take
into account these different loading conditions. One
such design code, EN1591 (Flanges and their joints.
Design rules for gasketed circular flange connections.
Calculation method), is specific to pressure-containing
flanged joints but certain gasket performance data are
required from the gasket manufacturers for the
calculation. Gasket manufacturers also provide design
bolt loads for various standard flange ratings based on
the gasket performance data.
selection of tightening control methodology to achieve
the design objective.
The design of the joint is outside the remit of this
document; however, it is intended to provide a
management system that can gather the correct
information from the design specification and apply
techniques, procedures and systems, to manage the joint
in line with design objectives. The following notes are
provided for information on that basis.
2.6.2
Bolt load calculations
It is crucial that the design bolt load required to seal the
joint has been calculated using an approved method and
is known prior to joint installation. The value for each
joint and the source of the value should be recorded in
the site’s record and data management system. This
facilitates consistency and traceability and allows
conscious decisions to be made regarding bolt load
should an issue arise with a joint.
The recognised codes generally provide a method
for calculation based on operating conditions such as
pressure and temperature. The most frequently used
code is the ASME Boiler and Pressure Vessel Code. It
is relatively simplistic in predicting gasket performance.
The latter is an important factor and it has been
recognised that more realistic and definitive gasket
performance data are required. Both in USA and Europe
gasket testing is being conducted, the results of which
will be incorporated into an updated ASME code in the
future.
There are other service loads acting upon the joint
which can be just as significant as the internal pressure.
Transverse vibration, axial cyclic fatigue and structural
loading all come into play. The joint can also suffer
relaxation or increase in compression dependent on
component materials and temperature. The strength
2.6.3
Bolt tightening
The purpose of tightening a bolt is to stretch the bolt
(like a spring) within its elastic limit such that in trying
to return to its original size it imparts a clamping force
on the flange.
Bolted joints can be tightened by a number of
techniques. Torsional based methods range from the
simplest low cost spanners through to impact, manual
and hydraulic wrenches. These apply a torsional force
to generate tensile loading in the bolt. Bolt tensioners
are different in that the bolt is loaded by applying a
direct axial tensile force with hydraulic jacks to stretch
the bolt. Some of this stretch is then captured by the
turning down of the permanent nut. A mechanical
variation on this method uses torque tightened small
diameter screws going through the flange’s load bearing
nut and reacting against a jacking washer, thereby
tensioning the bolt.
None of these systems directly measures the
achieved bolt load. However steps can be taken to
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GUIDELINES FOR THE MANAGEMENT OF THE INTEGRITY OF BOLTED JOINTS FOR PRESSURISED SYSTEMS
improve correlation between actual residual bolt load
achieved and the tightening system’s power input of
torque or initial hydraulic pressure. Robust procedures,
well maintained, calibrated tooling and the use of
competent operating personnel help improve the
correlation.
Totally uncontrolled tightening with spanners is not
a preferred option for tightening any size of bolt.
However, where a risk assessment identifies a
significant risk and where a superior tightening method
is not possible, e.g. in a space too restricted for torque
or tensioning equipment, spanners can be used with a
load control system.
system. Torque values for particular bolt sizes can be
found within specific operators’ standards or, in the case
of proprietary manufacturers’ connectors, from their
catalogue or from approved bolting service providers.
When selecting values great care must be taken to
ensure that the same lubricant or anti-seize compound
is used as stated in the data sheet from the management
system. The actual lubricant friction factor must be
recorded. Many sites find it advantageous to specify one
lubricant for all bolt torquing operations. Elastic
interactions in the joint can significantly affect the
residual bolt load achieved through torque tightening.
These effects can be reduced by simultaneously
tightening a number of bolts in the joint with multiple
torque tools similar to hydraulic tensioning
methodology. This procedure is detailed in 2.5.1.3.
2.6.3.1 Torque tightening
Torque control methods such as impact wrenches have
far less load control than hydraulic wrenches. For the
smaller bolts (< 1", M24) calibrated and maintained
hand torque wrenches will generally provide good
practice for controlled torque tightening.
The variation in a torque reading and the resultant
bolt load is dependent on many factors e.g:
2.6.3.3 Hydraulic tensioners
When joint conditions are favourable and all bolts in a
joint are tightened simultaneously, hydraulic tensioners
can provide a consistent bolt tension. Whilst the bolt
tension, or preload, is known through the hydraulic
pressure applied, the residual bolt load at the end of the
tightening cycle is subject to the amount of relaxation
that occurs on load transfer. The latter depends on a
number of factors, some joint related, some tool related
and others 'fitter' related, e.g:
— Friction in the fastener mating interfaces.
— Fastener quality e.g. nicks, thread laps, general
damage etc.
— Tolerances in bolt, nut and flange dimensions.
— Tolerances in bolt, nut and flange material and
mechanical properties.
— Operator competence.
— Accuracy of the torque application device.
— Bolt diameter.
— Surface coatings and lubrication.
— Tolerances in bolt, nut, flange and gasket material
properties.
— Tolerances in bolt, nut, flange and gasket
dimensions.
— Operator skill and control of technique.
— Load loss factors during the process.
— Calibration of pressure gauges.
— Correctly maintained tensioning system.
Great care has to be taken in evaluating the frictional
conditions and resultant friction factor used in the
torque tension equation to improve the reliability in
correlation between torque and bolt load. The choice of
lubricant, surface coating and fastener quality can
improve the torque/ bolt load variation. One new
hydraulic torque system uses a hardened washer
introduced under the load bearing nut such that its
design provides system reaction and reduces bending
stresses associated with traditional torque reaction
against the adjacent bolt or joint structure. The washer
has a specially prepared bearing surface that is intended
to improve friction consistency, in the nut bearing
interface face, and bolt load variation.
Two specific types of load loss factors to be considered
when calculating the required level of compensatory
hydraulic overload pressurisation are Tool Load Loss
Factor (TLLF) and Flange Load Loss Factor (FLLF).
TLLF occurs in all tensioning cases, whereas FLLF
does not occur in 100% tensioning.
— Tool Load Loss Factor
When the load is applied to the tensioner it stretches the
bolt and lifts the permanent nut clear of the surface.
Whilst the load is held by the tensioner the nut is then
turned back against the flange surface. When the
tensioner pressure is released the load transfers from the
tensioner to the threads of the nut. In taking up the load
the threads deflect resulting in a loss of load. This factor
is allowed for in the calculation of applied load.
2.6.3.2 Torquing process
It is vital to ensure that the correct bolt torque figures
are available prior to making up a flange joint. These
should be stored along with the source of the bolt load
calculation in the site’s record and data management
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BOLTED JOINT TECHNOLOGY AND PRACTICE
Note: This means that with hydraulic tensioning a
higher load than the residual design load should always
be applied.
and for ensuring that tools are used by personnel
competent and trained in their use. Such procedures
should be specific to the equipment employed.
— Flange Load Loss Factor
2.6.5
Flange Load Loss Factor only occurs when less than
100% tensioner coverage is used.
When using only 50% cover (e.g. eight tensioners
on a 16 bolt flange) when the second pass is applied, the
gasket undergoes further compression, effectively
relieving some of the load in the bolts tightened by the
first pass. By tightening the first pass to a higher load,
i.e. adding on FLLF, the need for more than one pass at
the second pass pressure can be avoided.
It should be noted that when two passes are used
the combination of FLLF and TLLF may mean that the
applied bolt stress is greater than the yield stress of the
bolt. An alternative technique such as multiple passes at
the second pass or pass B pressures may then be
required.
Careful use of load factor curves to predict the
above factors and realistic selection of the system for
short, medium and long grip length joints can improve
the correlation between compensatory overload
pressurisation and the residual design load target. As
indicated above, the number of jacks selected for the
tightening can improve the load transfer relaxation
situation, particularly with respect to joint elasticity
effects.
The selection of control of installed bolt load through
torque, hydraulic pressure or direct through a load
control system, should be dependent on the risk
assessment. Assured bolt load provides assured joint
reliability assuming the design and component quality
and assembly are also assured.
Selection of an appropriate tightening methodology
with bolt load assurance will provide the minimum risk.
Risk increases if bolt load assurance is not provided.
It is recommended that any load control system is
100% load test calibrated to ensure all bolts tightened in
the joint are loaded correctly and to the system’s
assured accuracy tolerance.
Several techniques are commercially available to
control and assure bolt load, as set out below.
2.6.5.1 Direct length measurement
This method uses mechanical extensometry to measure
the bolt extension. Accuracy is dependent on the level
of physical load test calibration carried out. A readily
available technique is the indicating rod bolt type. A rod
is inserted into a drill hole in the bolt that runs the
fastener’s complete length. The rod is anchored at the
opposite end to where the measurement takes place. At
the measuring end a precise datum face is machined
leaving the rod end flush with the bolt face. Relative
displacement of the rod compared to the bolt face is
measured and calibrated against bolt load by physical
load test.
2.6.3.4 Tensioning process
The hydraulic tensioning values needed to achieve the
residual design load derived from 2.6.2 should be
obtained from the record and data management system.
Tool pressures must be specific to the tool used. The
bolt tensioning operation must be carried out in
accordance with the tension equipment manufacturer’s
specified procedure and the load loss factors should be
recorded. Ideally tensioning should be applied
simultaneously to all studs in one operation. Where this
is not possible, tensioning should be applied in phases
using two different pressures as described 2.5.2.2.
2.6.4
Load control systems – Assured bolt load
2.6.5.2 Ultrasonic direct length measurement
This method determines the stress by measuring the
time of flight of an acoustic pulse travelling from one
end of the stud or bolt to the other. The time will vary
depending on the extension and the stress in the stud or
bolt. The monitored time is proportional to the bolt
extension and stress and can be converted to provide an
output as a bolt tension or stress as required. The pulse
is generated by a hand-held processing unit and is
independent of the tightening method.
Accuracy is dependent on precise datum faces
machined at each end of the fastener, the level of
physical bolt load/extension load testing carried out and
operator skill. It is recommended that only skilled
operatives are used to carry out this technique. 100%
load test calibration can provide accuracy results similar
to mechanical methods. Calibration by calculation only
provides the least degree of accuracy.
Equipment and tools
In order to improve flange integrity and safety in
operation, it is important that pneumatic and hydraulic
torque/tensioning equipment meets the required
specification and is maintained and calibrated as a
minimum on an annual basis or more often if
circumstances warrant it. Gauges should be calibrated
prior to extended use.
There should be clearly defined procedures stating
who is responsible for ensuring that tools are calibrated
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GUIDELINES FOR THE MANAGEMENT OF THE INTEGRITY OF BOLTED JOINTS FOR PRESSURISED SYSTEMS
Pressure testing should be carried out to a documented
procedure which complies with the HSE Guidance Note
GS4 'Safety in pressure testing'. Additional guidance
can be found in the OCA 'Guidance Notes of Good
Contracting Practice – Pressure Testing'.
2.6.5.3 Load monitoring sensors
There are several load monitoring sensors commercially
available. These include capacitance, fibre optic and
strain gauge techniques that take the form of sensor
inserts placed into a converted bolt. Another type is the
compression load cell that fits like a washer under the
nut or bolt head. One load cell monitors any change in
the nut face stress using an amorphous material. Other
types use strain gauges in the cell structure.
Signals from all types of sensors can be read by a
hand-held device or hard-wired logging systems; they
have future potential for remote signal monitoring. The
sensors are particularly useful where there is a need to
continuously monitor bolt load in service.
2.7.1.1 Standard pressure (strength) test
On newly constructed or installed pipework and
pressure equipment, company standards will normally
conform to a relevant design code such as ASME
B31.3. The objective of a strength test is to prove the
quality of materials and construction of the equipment
before it enters service or re-enters service following
significant repair. This test is carried out at a specified
pressure above the design pressure – detailed within the
relevant design code.
Pressures are typically 1,25 to 1,5 times the design
pressure for hydrostatic tests or 1,1 times for pneumatic
testing.
This is a strength test of the system and whilst it
will indicate some issues with joints it does not provide
assurance of the integrity or in-service reliability of the
bolted joint.
2.6.5.4 Mechanical load indicating bolts
These comprise standard bolts converted to monitor bolt
load. The bolt has a pin with a rotor attached, anchored
in an axial drill hole. The rotor air gap is set to rotate
freely until a specified bolt load is achieved. The
indicator is enclosed in a protective cap. Simple finger
feel of this cap determines bolt load status. Tension is
indicated at make-up and throughout the life of the joint.
Variations of this technique include a dual indicating
maximum/minimum load range system as well as a
visual indication system.
2.7.1.2 Leak test
Leak testing may be carried out on equipment prior to
strength testing. In this case, testing should be limited
to a pressure not exceeding:
— 10% of design pressure.
2.7 INTEGRITY TESTING
The combination of the procedures and processes
recommended in this document together with
appropriate testing prior to going on line and in-service
inspection programmes described in Section 7 will
provide the highest level of assurance. Testing is not a
substitute for correct assembly and controlled
tightening. It should be standard practice to assemble
and control-tighten joints correctly the first time to
eliminate rework and minimise downtime.
2.7.1
Leak testing is normally carried out on equipment in
order to prove the integrity of joints disturbed after a
strength test has been successfully completed or during
subsequent maintenance work. In this case, testing
should be limited to a pressure not exceeding:
— 110% of design pressure, or
— 90% of relief valve set pressure if still in place and
un-gagged.
NB – on older equipment, the strength test is likely to
have been carried out several years earlier.
Levels of pressure testing
Once the joint has been tightened and certified, and
details recorded in the record and data management
system, the joint should be subject to an integrity test
prior to going into service. The level of testing is
determined by the operator and will normally comprise
one or more of the following:
—
—
—
—
2.7.1.3 Service test
A service test is one which is normally carried out on a
joint where it has not been possible or practicable to
carry out a leak test first. Service tests are carried out
with the pressure system in service, normally during
start-up. The test is normally carried out (but not
necessarily always) at maximum normal operating
pressure using the process fluid as the test medium,
supplemented by water or inert gas from an external
source if necessary. The scope of service testing is to
demonstrate joint integrity for any joints where leak
Standard pressure (strength) test.
Leak test.
Service test.
Functional test.
14
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BOLTED JOINT TECHNOLOGY AND PRACTICE
configuration of the system, and the hazards associated
with the introduction of high pressure testing equipment
would be greater than the hazards associated with
service testing.
Where this method is proposed it should only be
carried out in accordance with a company procedure for
service testing and a written justification must be
recorded and a risk assessment carried out.
testing is not reasonably practicable, i.e. witness joints.
2.7.1.4 Functional test
This test is normally carried out at the working pressure
using a suitable test medium. Its objective is to ensure
that the equipment and its components function properly
e.g. valve cycling.
2.7.1.5 Testing mediums
Hydraulic test mediums (incompressible fluids) are
commonly treated water, glycol or diesel. These have
low stored energy; however, there can be material
compatibility issues which require consideration e.g.
chlorides on stainless steel.
Pneumatic test mediums (compressible fluids) are
commonly nitrogen with a helium trace, air or steam.
2.7.2
Test recording
The type of test, specification and acceptable leakage
rate criteria should be determined and documented by
the operator based on the criticality assessment already
carried out on the joint to determine the assembly and
tightening assurance specification.
Results of tests should be recorded in the record
and data management system.
Safety Note
Strength testing is almost always carried out using
liquids (hydrostatic or hydraulic testing). Although
pressure testing using a liquid is not without risk, it is
by far the safer method and should be used wherever
practicable. Pressure testing using air, steam or gas
(pneumatic testing) is more dangerous because of the
higher energy levels involved.
The energy released during a total failure of
equipment containing compressed air can be up to 200
times the energy released by the same test if water was
used as the test medium. Pneumatic strength testing
should never be carried out using flammable gas.
Pneumatic leak testing to 10% of design pressure
can be used to find small but significant leaks in
equipment which will contain flammable gases and/or
liquids.
Caution should also be taken when carrying out
hydrostatic testing at low ambient temperatures (<7°C)
to avoid the risk of brittle fracture.
Refer to the HSE Guidance Note GS4 'Safety in
pressure testing' and the associated research report for
further details.
2.7.3
Witnessed joints and reverse integrity
testing
Where joints have no means of isolation to allow leak
testing of the installed joint, such as the last connection
on an open flare line, or where a large number of joints
makes it impracticable or unreliable to conduct a leak
test, the operator should regard this as a higher risk joint
in his criticality assessment and therefore consider a
number of additional steps including:
— Witnessing assembly of the joint.
— Witnessing controlled tightening of the joint.
— Applying a load assurance system to assure the
required bolt tension has been achieved.
— Using a reverse integrity test using a proprietary
gasket. This is based on the principle of
pressurising the annular space above and below the
seal ring using a test gas, usually nitrogen.
Witnessed joints should be highlighted in the record and
data management system, including the results of any
tests or witness inspections.
2.7.1.6 Testing using process fluid or gas
For process hydrocarbons systems, although it is not the
preferred means of testing, under certain conditions it
may be considered appropriate to carry out testing with
the service fluid rather than with water, nitrogen or
some other medium. This should only be considered
where it can be clearly demonstrated that it is
impractical to carry out leak testing due to the
2.7.4
Joint failure during integrity testing
Where a joint fails an integrity test, then applying more
bolt load alone is not the answer. Investigation and
analysis in accordance with the measures described in
Section 6 should be carried out.
15
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GUIDELINES FOR THE MANAGEMENT OF THE INTEGRITY OF BOLTED JOINTS FOR PRESSURISED SYSTEMS
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3
CRITICALITY ASSESSMENT
safety and environmental aspects of the local and distant
environment.
For onshore, this will often be part of the Control of
Major Accident Hazard (COMAH) assessment for the
site.
For offshore, Safety Case, PFEER and Pipeline
Safety Regulations will apply. The UK Health and
Safety Executive OIR/12 database contains useful
information to enable offshore industry operators to
develop their risk assessment.
Risk may also occur with joints containing
harmless fluids e.g. water, which would damage
building fabric or product, or risk interaction with
electrical installations if they leaked.
There are a number of areas which will affect the
criticality of the joint. These can be grouped as follows:
3.1 INTRODUCTION
There is a variety of bolted joints involved in
pressurised systems, ranging from low pressure joints
containing water or compressed air to high pressure
joints containing steam, hydrocarbons or explosive or
poisonous gases. Although every joint should be
designed and installed to safely contain the pressure and
contents specified, it is logical that joints at higher
pressure or with hazardous contents will require
additional vigilance due to the potential consequences
of failure.
The criticality of a joint may have an effect on a
number of areas addressed in the management system
including:
— Choice of tightening method.
— Choice of personnel assembling and tightening the
joint.
— Level of bolt load assurance.
— Level of records and data stored against the joint.
— Level of inspection and testing prior to entering
into service.
— Level of testing and inspection in service.
3.2.1
Leak potential
One method of determining the criticality of a joint is to
consider the potential for a leak. The potential for a leak
will increase with:
—
—
—
—
—
—
—
—
—
3.2 ASSESSING THE RISKS WITH
BOLTED JOINTS
The level of risk will primarily be based on the service
conditions the bolted joint is exposed to, along with the
impact any release would have on the operational,
Process and test pressures.
Cyclical load.
Vibration load.
Low temperature.
High process temperature.
Structural load.
Corrosive environment.
Aggressive environment.
Unknown conditions of any sort.
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GUIDELINES FOR THE MANAGEMENT OF THE INTEGRITY OF BOLTED JOINTS FOR PRESSURISED SYSTEMS
3.2.2
Service fluid
3.2.4
The contents of the pressure system have a major effect
on the criticality of the joint and should be considered
in determining the level of inspection, control and
testing applied to the joint. A joint’s criticality will
increase if the contained service is:
—
—
—
—
—
—
—
—
Local factors must always be considered when assessing
a joint’s criticality. Table 3.1 describes some of the
factors which may occur at individual joint level.
3.2.5
Hydrocarbon.
Corrosive.
Explosive.
Poisonous or noxious.
Radioactive.
High temperature.
Environmental contaminant.
Expensive.
Joint criticality rating
The criticality of the joint is shown in Table 3.2. The
criticality level can be determined by considering all of
the factors identified in 3.2.1 to 3.2.4. The operator
should use the level of criticality to set standards and
specifications for:
— Joints which will be included in the management
system.
— The level of inspection and assurance at assembly
stage.
— The level of personnel who will control tighten the
joints.
— The control tightening method.
— The level and method of bolt load assurance.
— The level of inspection during the controlled
tightening stage.
— The type and level of integrity test prior to entering
into service.
— The type and level of in-service inspection.
Such joints would often be viewed as at least of medium
criticality.
3.2.3
Local factors
Loss potential
The criticality may also increase if loss of the service
would render the plant inoperable. For example a fire
service line, although having safe contents, would cause
a plant shutdown if inoperable. Similarly a cooling
water system for a computer plant could be highly
critical.
The loss potential may also increase with pipe size
and the area through which it runs.
Table 3.1: Local factors
Factor
Problem
Vibration or slug flow
If severe may cause joint to loosen
Cyclic temperature
If severe may cause joint to loosen
Substitute materials to those in
Piping Specification
Compatibility not guaranteed
Local joint history
If this individual joint is misaligned or difficult to close, or if this type of
joint is problematic on this site
Untested joints
Cannot be leak tested prior to start-up (e.g. tie-in points)
Vendor package joints
Often assembled and tightened to vendor’s system, outside of asset
system
Exception on joint
Flange face marked, piping load, history of leakage with root cause
unidentified
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CRITICALITY ASSESSMENT
Table 3.2: Joint criticality – Examples of criteria used and controls applied
Joint Criticality
Low
3.2.6
Controls
— Joint identified and recorded in database
— Assembly not witnessed but carried out to a procedure by trained and competent
contractor
— Bolt loads taken from database
— Controlled tightening applied by use of hand torque wrench or torque wrench
— Tightening carried out by competent personnel (see Section 4)
— Integrity test by local arrangement
— In-service testing includes visual inspection
Medium
— Joint identified and recorded in database
— Assembly witnessed or a sample of joints witnessed and carried out to a procedure
by trained and competent personnel
— Bolt loads taken from database
— Controlled tightening applied by use of hand or hydraulic torque wrench or tensioner
by competent personnel
— A sample of joints witnessed by specialist personnel
— Integrity test may include nitrogen helium or similar
— In-service testing in accordance with the techniques described in
Section 7
— Consider use of load assurance
High
— Joints uniquely identified in database and identified as High criticality
— Assembly by specialist contractor or witnessed by specialist contractor
— Controlled tightening using hydraulic tensioner or hydraulic wrench with load
assurance system by specialist personnel
— Integrity test using nitrogen helium or similar prior to entering into service
— In-service inspection at higher level in accordance with the techniques described in
Section 7
effective procedure than tensioning. The shorter grip
length joint also makes the tensioner less reliable as a
control system. By thoroughly researching the friction
factor for the preferred lubricant and taking into account
the surface coating and bolt quality, torque tension
variations may be reduced.
Sample risk assessment selections
Assured design bolt load on installation by measuring
with a load control system provides assured joint
reliability or minimum risk with any tightening
technique. Under the same joint conditions reliability
will be less assured and risk will increase by using only
the tightening technique. Selection is down to the
operator’s risk assessment, past history of the joint and
associated life cost of the techniques available to him.
These examples are not intended to be prescriptive but
show possible methodology selection subject to an
operator’s individual situation.
ANSI B.16.5 600LB 10 INCH; HAZARDOUS FLUID.
1,1/4 in. Hydraulic tensioner tightening
Whilst the 1.1/4 in dia bolt could be tightened using a
hydraulic wrench, it may have insufficient control to
provide a reliable level of bolt load. The service
conditions in terms of pressure, temperature and
contained fluid provided intermediate risk. The bolt
diameter and grip length were such that the hydraulic
tensioner could provide sufficient bolt load for joint
reliability under service conditions.
We could have this same 600 lb flange but service
temperatures could be high (350°C plus) and/or cycling.
This could present an increased risk such that assurance
ANSI B.16.5 150 LB 5 INCH; HAZARDOUS FLUID.
¾ in. bolt Torque tightening; torque control; known low
friction lubricant for friction factor control.
The operator may decide this application does not
warrant the use of a load control system. The smaller
diameter means that torque tightening is a more cost
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GUIDELINES FOR THE MANAGEMENT OF THE INTEGRITY OF BOLTED JOINTS FOR PRESSURISED SYSTEMS
is needed on installed bolt load. For this a load control
system is used with hydraulic tensioner tightening to
minimise the risk of a leak.
3.2.7
Record the criticality assessment
The joint risk criticality should be recorded in the
records and data management system (see Section 5).
Before work on any joint (e.g. design, modification
or maintenance) the risk criticality should be identified
and recorded. If the risk criticality has not already been
identified and recorded, a criticality assessment should
be performed and recorded in the records and data
management system.
ANSI B.16.5 900LB 16IN, HAZARDOUS FLUID.
1,5/8 in. Hydraulic tensioner tightening; load control
system.
Some operators link tightening method selection to bolt
diameter. For example, hydraulic tensioners are usually
specified for diameters 1,1/8 or 1,1/4 diameter and
above. The larger the diameter, the more effective
tensioners become compared to torque in terms of
providing tightening power with variation in bolt load.
The higher pressure, pipe diameter and process gas in
this situation results in the operator regarding risk as
'high'. Therefore assurance on installed bolt load is
necessary and a load control system is required to
ensure design objectives are achieved on installation. It
would be quite feasible however to select a hydraulic
torque wrench with a load control system for this
application.
Tightening method selection based on bolt
diameter; whilst satisfactory for general 'rule of thumb'
on low and some intermediate risk standard ANSI
flanges, the policy could be problematic for non
standard joints especially those where the bolt diameter
to clamp length ratio is relatively small (less than four
to one for example). Where one would normally
nominate tensioning for a larger bolt diameter, the latter
situation could result in the target bolt load being
practically unreachable due to joint elasticity. The
higher compensatory hydraulic overload may be outside
the elastic capacity of the bolt or even the capacity of
the hydraulic jack itself.
3.2.8
Risks to personnel
It is important to note that assembly of flanged
connections involving the use of high pressure hydraulic
tools and systems will present a level of inherent risk to
the operator which if not assessed, controlled and if
possible mitigated, may result in a serious incident. For
all flange assembly operations the risks during assembly
should be fully and formally assessed, the selection of
methods and tooling reviewed, hazards identified and
where possible, the risks mitigated on the basis of the
ALARP (As Low As Reasonably Practical) principle.
All personnel involved should be made fully aware of
the potential dangers of accidental leakage of high
pressure hydraulic fluid from the tools and systems
deployed.
During training of personnel, it should be
emphasised that the risks from high pressure fluid
systems are constantly present during the tightening/
loosening procedures. The need for constant observation
and inspection of the equipment throughout the whole
operation should also be stressed.
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4
TRAINING AND COMPETENCE
maintain joints, or to supervise or assess such
work.
— Includes a process to assure that third party vendors
and contractors can demonstrate that their
personnel are managed using equivalent systems to
equivalent competence standards.
4.1 INTRODUCTION
All personnel carrying out work on bolted joints should
be trained and competent to a level appropriate to the
required technical skills and failure risks of the joint
involved. Similarly, supervisory personnel and assessors
should also be trained and competent to ensure they are
aware of the issues involved in achieving a leak-free
joint.
4.3 TRAINING
The skill levels that individual companies use will
depend on a number of variables. For example, a
company with a large number of personnel may decide
on a number of skill levels appropriate to the type of
work an individual may perform. Other companies may
decide to train all their personnel to a higher level as a
matter of course. This approach is particularly relevant
to remote sites where it is imperative to have personnel
with the necessary skills available at all times. As such,
the training specifications for the following Engineering
Construction Industry Training Board (ECITB)
TECSkills units have become the benchmark standards
for the UK offshore oil and gas industry:
4.2 COMPETENCE MANAGEMENT
Control of the competence of people working on bolted
pipe joints is a critical factor in achieving joint integrity.
Hydrocarbon release incident data for the UK offshore
oil and gas industry indicate that poor bolted pipe joint
make-up is a major cause of leaks, and a review of
historical causes confirms that the skills and practices
used have not given leak-free joints. Therefore an
important element of a management system is to ensure
that any person working on a given joint has been
trained and assessed as competent to perform the task.
Fundamental to the demonstration of personnel
competence is the provision of a documented
competence management system that:
PF010 Jointing Pipework using Flanged Joints (Hand
Torque Tightening).
PF015* Assembling and Tightening Bolted Flanged
Connections.
PF018 Assembling
and Tensioning
Bolted
Connections.
PF019 Assembling
and Tightening
Bolted
Connections (Hydraulic Torque Tightening).
— Contains clear standards for recruitment, training,
development and ongoing competence assessment.
— Is based upon, equivalent to or better than a
nationally or industry-recognised technical
standard.
— Provides demonstrable capability for all staff
personnel who might be expected to make, break or
*superseded
by PF018 and PF019
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GUIDELINES FOR THE MANAGEMENT OF THE INTEGRITY OF BOLTED JOINTS FOR PRESSURISED SYSTEMS
Schemes operated by individual companies should be
aligned with these or equivalent specifications. Such
schemes should also address those individuals used
during turnarounds and periods of high activity whose
core function is not assembly and tightening of bolted
joints.
training. It is rooted in the Engineering Competence
Standards (ECS) based on national occupational
standards for the engineering construction industry.
Successful completion of TECSkills On-the-Job
Performance Units or equivalent units from other
Independent Accreditation Organizations (IAOs) (see
4.7) can contribute to the evidence requirements of
vocational qualifications. An occupationally competent
coach and IAO representative support the learner in the
attainment of new skills and knowledge when
undertaking training or performing these units.
In response to the UK oil and gas industry, the
ECITB developed training and performance units
PF010, PF018 and PF019 for assembling and tightening
bolted flanged connections. These units form part of the
TECSkills training programmed for training pipe and
mechanical fitters, hence the PF title.
4.4 ONGOING COMPETENCE
Successful completion of an appropriate training course
is only the first step towards gaining and demonstrating
competence. The course should be followed up by an
agreed training and assessment plan between the coach
and learner, which will establish whether the training
has been effective and identify gaps in the learner’s
skills and knowledge. Together with a logged record of
experience and a site assessment, this can lead to a
recognized qualification such as the ECITB’s TEC Skills
units PF010, PF018 and PF019 (see 4.5). These units,
with supporting material, may contribute as evidence
towards obtaining a vocational qualification unit (see
4.6).
An example of the competence requirements for
authorized bolt tightening personnel is given in Table
4.1.
To assist in demonstrating ongoing competence, a
record should be maintained of each individual’s
mechanical jointing performance. This should comprise
details of the types of joints the individual has worked
on (including evidence that a representative sample of
joints have been made up in the presence of a competent
assessor), whether the joints have performed
satisfactorily, and details of any further training
required. It is the responsibility of the individual to
maintain this certified history and to have it formally
validated by an approved assessor. If there is no record
of successful past work within a 12-month period it is
recommended that an assessment is performed to
identify any re-training requirements.
An example of a mechanical jointing performance
record is shown in Figure 4.1.
4.6 VOCATIONAL
QUALIFICATIONS
A vocational qualification (e.g. National or Scottish
Vocational Qualification – N/SVQ) is effectively a
portfolio-based validation process that will include
onsite assessment by an occupationally competent
assessor. No training is necessarily required to take a
vocational qualification. The qualification is based on
evidence of competence by a variety of techniques,
including documentary evidence, questioning, site
observation and testimonials. A competent assessor will
easily identify weak candidates.
The standard of candidate able to pass a vocational
qualification is controlled by the awarding body in line
with national guidelines.
4.7 INDEPENDENT ACCREDITATION
ORGANISATIONS
Examples of bodies who can be contacted for advice are
given below. There are many other agencies and
individual companies which are available to provide
training. However, it is essential to ensure that the
training they provide is to a recognized standard.
4.5 TRAINING IN ENGINEERING
CONSTRUCTION SKILLS (TECSKILLS)
ECITB (Engineering Construction Industry Training
Board)
SEMTA (Science, Engineering and Manufacturing
Technologies Alliance)
API
(American Petroleum Institute)
The ECITB’s Training in Engineering Construction
Skills training program (TECSkills) is an example of a
flexible training scheme for craft and other site
operatives to cater for both initial and skill enhancement
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TRAINING AND COMPETENCE
Table 4.1: Competence requirements for authorized bolt tightening personnel
Key Requirement
Training provided should include knowledge of the specific joint types employed at the worksite. Operators
should ensure that any training carried out on their behalf meets with this requirement.
Knowledge Base
Awareness of:
— Health and safety precautions
— Pressure, temperature and hostile environmental factors (such as corrosion and vibration) on the
degradation of bolted assemblies
— Factors which result in bolt load variation
— Applied and residual loads
— The effect of different lubricants on friction losses
— The relative accuracy of different methods of tightening
— The techniques for application of tensioned bolt loading
— Joint assembly methods and tightening procedures
— The need to check gaskets, nuts and stud bolts against specification
— Safety precautions when handling and removing Compressed Asbestos Fibre (CAF) gaskets
— The requirement to tag and complete records for assembled joints
— The need to:
- Check the compatibility of the selected torque tools and equipment capacity prior to use
- Top up oil levels in hydraulic pumps
- Clean and protect tools and equipment from corrosion
Understanding of:
— The principles of joint component sealing action
— The principles of bolt elongation and tensile stress
— The function of gasket or seal types
— The importance of correct bolt loading
— The effect on bolt load and seal compression using different methods of tightening
— The importance of using the correct lubricant
— The importance of the correct selection of joint components to comply with the design specification
— The correct sequence and number of tightening passes required for torque and tensioned bolts
— The principles and techniques used for direct bolt length measurement
— The need for and using reporting procedures when defects or faults in bolt tightening equipment or its
assembly are identified
— The principles of preparing bolted joint connections for assembly
— The need for seal face cleanliness and for nuts to be free-running
— The effect of joint alignment and gap uniformity on residual bolt loading
— The importance of gasket storage, handling, preparation and installation
— Good installation practice for bolting, washers and nut orientation for tightening method and equipment
to be used
— The need to report variances from design specifications and tightening procedures
— The principles and requirements for the safe selection, calibration, installation and use of hydraulic
torque and bolt tensioning equipment
— The principles of carrying out bolt de-tensioning and joint breakout safely and correctly
— The importance of attending product-specific training and following the manufacturer’s procedures for
proprietary joint types
— Why mixing components from different equipment manufacturers is prohibited
— The principles of inspection after tightening and the procedures and techniques to be used such as 'break
loose' tests (check passes) and bolt tightness 'tap-test'
— The requirements for the storage, preparation, maintenance and calibration of torque tools and bolt
tensioning equipment for its safe use
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GUIDELINES FOR THE MANAGEMENT OF THE INTEGRITY OF BOLTED JOINTS FOR PRESSURISED SYSTEMS
Table 4.1: Competence requirements for authorised bolt tightening personnel (cont’d)
Ability to:
— Recognise and rectify faults with torque or tensioning equipment
— Interpret joint or flange manufacturer identifying marks
— Identify defects, distortion and surface irregularities on flange sealing faces and threads
Demonstrated Application of Knowledge
Demonstrate ability in:
— Preparation of all joint components
— Correct selection and assembly of joint components
— Diagnosis and rectification of problems with hydraulic equipment
— Selection and correct installation of hydraulic torque or tensioning equipment
— Correct application of the various tightening techniques
— Carrying out specified tightening sequence and subsequent tightening passes to ensure axial alignment
and squareness of joint assembly
— Carrying out joint breakout safely and correctly
— Carrying out bolt 'break loose' tests (check passes) to check integrity of assembled tensioned assembly
— Completion of a joint record sheet
— Integrity and inspection checks of completed joint assembly
— Maintaining a personal portfolio of joint assembly
Demonstrate awareness of:
— The health and safety precautions at the worksite
— Hot bolting and live plant procedures and risk assessments
24
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TRAINING AND COMPETENCE
JOINTING PERFORMANCE RECORD
Name
ID No
Installation
Date
This is to certify that the Technician named above has produced satisfactory leak-free mechanical joints of
the types indicated below within the past 12 months.
Joint Type
Satisfactory
Performance
Requires Training
Date
Signature
Comments
RTJ
Raised face
Insulating gasket
Compact
Clamp connector
Taper-Lok
Kidney
Other (installationspecific)
Note:
1. This record does not replace a recognised NVQ but certifies a Technician’s ongoing competence in
making a specified mechanical joint.
2. It is recognised that certain installations do not have all types of joints.
Supervisor
(Position)
Verified
(Position)
Name:
Name:
Signature:
Signature:
Date:
Date:
Figure 4.1: Example jointing performance record
25
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GUIDELINES FOR THE MANAGEMENT OF THE INTEGRITY OF BOLTED JOINTS FOR PRESSURISED SYSTEMS
26
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the licence terms and conditions. It must not be forwarded to, or stored or accessed by, any unauthorised user. Enquiries: e: pubs@energyinst.org.uk t: +44 (0)207 467 7100
5
RECORDS, DATA MANAGEMENT AND
TAGGING
The certainty of a successful joint being made up
increases if data are controlled and historical data exist
on the activities carried out in the past. Recording
traceable data encourages best practice at the time of the
activity, and will provide useful planning data for the
next time the joint is disturbed.
Learning from incidents is important. A
management system should include the means for
gathering relevant data, which should be collected by
everyone involved in bolted joints and periodically
reviewed to establish trends, performance and
improvements. This can be achieved if records and data
are kept for each joint as part of a management control
process.
should be securely attached to the joint and may hold no
other data than the unique tag number. In selecting a
permanent tag, consideration needs to be given to the
attachment method, the temperature of the flange and
tag and security device material, the permanence of the
tag markings, and avoidance of corrosion spots due to
dissimilar metals or water traps.
5.1.2
Temporary tags
The purpose of a temporary tag is to uniquely identify
a joint during a work scope and to indicate the status of
the joint during the work scope. The tag will normally
hold a unique ID number for the joint which is
traceable; it may also hold a small amount of
information such as tightening method and date, person
who assembled the joint, person who tightened the joint
and person who tested the joint. A common method is
to use multipart tags where the status is indicated by the
colour of the portions remaining on the tag.
Common status conditions are:
5.1 JOINT IDENTIFICATION
In order to record data and plan activities - each joint
needs to be clearly and uniquely identified.
This requires the joint to be physically tagged so
that its identity is clear and visible at the joint location
including a unique Joint ID number in order that it can
be recognised in a joint database or other record system.
All joints should be tagged, there are also
advantages to having both permanent and temporary
tags assigned to joints.
—
—
—
—
Joint to be broken out/Joint broken out.
Joint to be assembled/ Joint assembled.
Joint to be controlled tightened/Joint tightened.
Joint to be tested./Joint tested.
Joint tagging can bring a number of benefits:
5.1.1
Permanent tag
—
—
—
—
The purpose of a permanent tag is to uniquely identify
a joint throughout its life cycle, enabling all activities
and data on that joint to be recorded. Permanent tags
Control competence.
Assist in the preparation of work permits.
Provide cross-shift communication of job status.
Assist job completion confirmation.
27
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GUIDELINES FOR THE MANAGEMENT OF THE INTEGRITY OF BOLTED JOINTS FOR PRESSURISED SYSTEMS
— Aid leak and seep searches by identifying disturbed
items (which have a higher probability of leaking).
— Support a record and data management system.
5.1.3
Example tagging procedure
The following is an example tagging procedure.
Individual operators’ schemes will depend upon a
variety of issues including the number of joints to be
tagged and the size of local organisation.
All joints that are to be made or disturbed during
construction or maintenance work should be identified,
recorded and tagged. The tag should be fitted using a
suitable tie and in a position adjacent to or on the joint.
The person who breaks the joint(s) should mark up
the tag identification numbers on a copy of the relevant
Isometric or P&ID and its corresponding register. The
Isometric or P&ID and register should be controlled by
the relevant designated person. These records
complement the leak test certificate and provide an
audit trail.
At the completion of each stage of the job
(inspection, assembly, tightening and testing) the
responsible person should record their name against that
stage. This could be done directly on the tag or the
relevant task could be crossed off on the tag and the
name recorded in the work pack.
Once testing has been satisfactorily completed, the
removable insert of the tag should be returned to the job
co-ordinator. The task completion should be recorded in
the work pack when all joint tag bodies are returned,
indicating that all work has been completed. This can be
checked against the permissions required for restarting
the plant.
Plant start-up should be prevented until all the tag
inserts are signed off and returned to allow sign-off of
the job.
After start-up and while the root of the tag remains
attached, search teams should patrol the disturbed area
and inspect tagged joints for leaks and seeps. Any leaks
or seeps should be reported to a nominated supervisor.
The root of the tag should be left on the joint until
the operation is satisfied that the joint is not likely to
leak (normally 48 hours after start-up.) During that
period the tag makes leak searches more effective.
An example of a multipart tag is shown in Figure
5.1.
Figure 5.1: Example of a multi part tag
5.2 RECORDS AND DATA MANAGEMENT
A successful record and data management system will
aid and provide information during the work planning
and execution process.
Once unique joint IDs have been established then
useful and essential data can be recorded against them.
As work is carried out and recorded the status of the
disturbed joints should be updated to reflect the status of
all joints including temporary blinds. This process
should be carefully controlled and reported as laid down
by the management process.
The preparation and collection of data by
competent personnel will assist in ensuring all joints are
assembled, tightened during construction or reinstated
during maintenance and ready for leak-free service.
Additionally, as the status of all pipework has been
carefully monitored, it should not be possible to
introduce pressure into any joint before all joints have
been reinstated.
28
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RECORDS, DATA MANAGEMENT AND TAGGING
5.2.1
and maintenance of the asset.
— Records of any modification, exceptions or
deviation from standards with the joint.
Recommended data
The following data are recommended as a minimum for
bolted joints on critical services:
Whilst this data can be kept in hard copy format, a
database system is recommended due to the high
volume of data required and the ease of searching and
retrieving data that computerised systems offer.
5.2.1.1 Joint details
— Identity of joint.
— Joint location.
— Drawing references.
— Size, type, class.
— Flange and bolt material.
— Gasket specification.
— Approved bolt stress and source.
— Approved tightening method and settings/tools to
achieve approved bolt stress.
— Lubricant used.
5.2.1.4 Joints included in the database
It is recommended that the operator as a minimum
keeps records for all joints on critical services and those
on other services which have a history of leakage, or
potential to leak, and that this is kept with any relevant
procedures for monitoring the specific joint. To
minimise the possibility of the problem resurfacing,
methods for countering the leak should be included
within the individual joint records.
There are however benefits in maintaining a system
for all joints, in terms of safety, efficiency and
traceability. Statistics show that using a system to
control joint integrity will reduce the effort required to
achieve a successful integrity test.
5.2.1.2 Additional data
Additional data can be recorded to make the system
more user friendly and effective as a planning tool, such
as:
— Status of the joint.
— Any exceptions or anomalies regarding the joint.
— Location description of the joint.
5.3 REVIEW
5.2.1.3 Joint history
— Starting at the construction stage: Records of
assembly, break out, reassembly, inspections and
controlled tightening. Including personnel
involved, equipment and procedures used. Results
and measurements taken where appropriate.
— Records of inspection and testing of the joint.
— Records of subsequent disassembly, inspection,
assembly, tightening and testing during operation
The entire process and outcome should be reviewed by
managers and members of the work team. Identified
improvements to the activities, work scopes and
procedures should be recorded and retained for when
the work is next repeated.
Information of performance and good practice
should be shared with industry.
29
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GUIDELINES FOR THE MANAGEMENT OF THE INTEGRITY OF BOLTED JOINTS FOR PRESSURISED SYSTEMS
30
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6
MANAGEMENT OF LEAKS
However, there are a significant number of industries
where good business practice or regulatory requirements
make it essential to formally assess loss of containment
events and determine root cause and measures to
prevent recurrence.
When a leak or incident occurs, a common
approach to manage such situations is an engineering
risk assessment which utilises the collective skills
within the organisation to address three fundamental
questions:
6.1 INTRODUCTION
The objective of a correctly designed and installed
bolted joint is to provide a long-term tight seal and
prevent ingress or egress of fluids through the joint.
However, leaks can occur and the Duty Holder or
operator has overall responsibility to manage this
situation. This section introduces some important
features that may be required of the management system
for pressurised systems after joint make-up. These
include:
— Safety impact to ongoing operations – is it safe to
continue to operate the plant?
— Environmental impact – what is the environmental
impact of continued operations?
— Economic cost – what is the business cost?
— Management of leaks and releases and the
appropriate engineering risk assessments that might
be required.
— Definition of leaks.
— Integrity testing of joints as an assurance measure
of joint tightness.
— Potential options for repair or replacement of
leaking joints.
An engineering risk assessment should be performed to
establish whether it is acceptable to continue operations.
The assessment should also identify control or hazard
mitigation measures required such as increased
surveillance or plant de-rating. Alternatively, the
outcome of the assessment might indicate that there is
significant hazard with continued operation and that
immediate shutdown, repair or replacement is required.
It should be noted that most companies have some
form of environmental policy which requires recording
emissions from process systems. In the UK statutory
rules require reporting of leaks and emissions depending
upon the fluid and the magnitude of the leak.
6.2 ENGINEERING RISK ASSESSMENT
OF LEAKS
The degree of review or assessment of leaks will depend
upon the industry, the nature of the process fluid and
pressure and temperature conditions; all factors
affecting the criticality of the joint (see Section 3). In
some situations, it may be acceptable for joints to
leak.
31
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GUIDELINES FOR THE MANAGEMENT OF THE INTEGRITY OF BOLTED JOINTS FOR PRESSURISED SYSTEMS
6.3 STAGES AT WHICH LEAKS OCCUR
6.4 CORRECTIVE ACTIONS
Leaks often occur when the joint is under test, as
described below. However, regardless of when a leak
occurs, it should always be investigated and recorded in
the records and data management system (see Section
5). This will not only store useful data against the joint
and assist in preventing the same issue arising on the
same joint in future, but will also enable trend analysis
to prevent leakage on other joints. A leak decision and
analysis tree, such as the example illustrated in Figure
6.1, can assist in determining an appropriate course of
action and also provides input to the data management
system.
Where a release is identified, a corrective action must
be carried out to secure a tight joint. Some measures
include:
6.3.1
— Depressurize the system, and check load on bolts.
— Identify root cause of the problem (and notify
appropriate authorities).
— Depressurize and completely remake the joint after
component inspection.
Other measures such as hot bolting and tightening of
live joints are not recommended.
Standard pressure (strength) test
6.5 DEFINITION AND DETECTION OF LEAKS
A leak occurring during a strength test is an indication
that there is a major issue in the installation of the
bolted joint. Although the joint is subject to a higher
than working pressure at this stage, it is not subject to
temperature or cyclic loading and therefore leakage
during this activity suggests poor assembly or applied
bolt load. Identifying and correcting the cause is
essential for reliable operation of the plant.
6.3.2
The following definition of a leak is widely used in the
upstream oil and gas industries:
A release of hydrocarbon or other hazardous fluid
should be recorded as a leak when the release rate is
equal to or greater than:
— Liquid leaks:
A release rate of one drop per 15 seconds (four
drops per minute).
Leak test
A leak test is not a replacement for correct joint makeup and tightening; rather, it is merely part of the
assurance process. Where a joint is just failing a leak
test it is tempting to increase bolt load. However, if
thebolt load was correctly applied in the first instance,
increasing the bolt load could be hiding a problem,
e.g., a nipped gasket or grit on the gasket, which will
manifest as a service leak later.
6.3.3
— Gas leaks:
A release that will cause a hand-held gas detector
10cm 'downwind' of the release source to indicate
20% Lower Explosive Limit (LEL).
The most likely method of detecting a leaking bolted
joint is observation by operations and maintenance
personnel or inspection personnel during routine
operation in the plant. There is no substitute for 'line
walking' as most leaks are of relatively small
magnitude. The more significant leaks may also be
detected by plant safety systems such as gas detectors
or, in extreme cases, by the process control system.
All leaks should be tagged and entered in the
maintenance system for repair and the record and data
management system as soon as is reasonably practical.
It may also be reportable.
An emission from a joint with a lower release rate
than a leak is described as a seep. These too should be
tagged and periodically checked to ensure they have not
worsened, and be entered into the maintenance system
for repair at the next scheduled service for that item. It
should also be recorded in the records and data
management system.
Service testing
Where the service test identifies a slight leak, there will
be a temptation to apply more bolt load to seal the leak.
This may be successful, but if the load was correct in
the first place, then consideration must be given to
identifying why the joint leaked (see also 6.3.2 above).
6.3.4
Leaks occurring
operation
during
start-up
or
These leaks potentially have the greatest impact not
only for safety but also commercially as they will either
delay start-up or stop production.
32
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MANAGEMENT OF LEAKS
START
PASS
PASS OR FAIL?
FAIL
Joint failure leakage
rate above the target
acceptance criteria
Is this
a single failure
or are there numerous
failures in the
system?
SINGLE
NUMEROUS
TIME OUT
YES
Technical review
required
Is there a
common style of joint that
is failing?
NO
YES
Is the
leakage rate above
the maximum acceptance
criteria?
NO
NO
Update workpack with
new torque/tension
figures
Is the technical
authority willing to approve
the leakage result?
Is the
torque/tension
applied to the joint
correct for this application?
(Check procedure and all
assumptions made)
NO
YES
YES
Correctly apply
the torque/tension
in the field
NO
Has the
torque/tension
been correctly applied
in the field?
YES
Break the joint and
investigate failure mode.
Apply rigorous checks.
Reassemble and retighten
joint to approved method.
SUCCESS
Figure 6.1: Example leak decision and analysis process
33
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GUIDELINES FOR THE MANAGEMENT OF THE INTEGRITY OF BOLTED JOINTS FOR PRESSURISED SYSTEMS
Leaks may pose special risks in confined spaces
such as pits, trenches, buildings and modules. Examples
include concentration of toxic or poisonous gases or
heavier than air asphyxiates such as argon or carbon
dioxide gas.
Fugitive emissions as described in the IPPC regulations
are beyond the scope of this section. It is assumed that
issues such as Best Available Techniques (BAT) for
sealing have been addressed by the specifiers and
designers of joint systems.
achieved, the only option may be to shut down the
plant to carry out the repair. An example of such a
situation is given in Figure 6.2 which shows a
flange with gasket seating face pitting. Corrosion at
the bottom of the pipe has caused metal loss of the
entire gasket seating width and resulted in a leak. In
this case a unit shutdown was undertaken to replace
a pipe spool.
— Carry out on-line repair
On-line repairs to live plant have been carried out
using techniques such as encasement clamps and
various forms of glass and carbon fibre wraps.
These are considered to be engineering repairs and
need appropriate technical skills and installation
competences. Specialist service companies can
provide this type of product on a world-wide basis.
Some high level guidelines on safety considerations
are presented in EEMUA publication 199.
Guidelines on requirements and qualification of
repairs to corroded or damaged piping using
composite wraps are presented in ISO document
ISO/PDTS 24817. A typical clamp type repair is
illustrated in Figure 6.3.
6.6 MANAGING LEAKS AND REPAIRS
An engineering risk assessment will provide a technical
basis for reviewing repair options which can range from
shutdown and repair/replace to continued operation with
no intervention. The choice of options may be further
restricted by Company policy depending upon the type
of facility. In many industries, unplanned shutdown for
repairs is normally avoided wherever possible.
Whatever the planned course of action, it should be
formally documented before work begins and carried
out in a safe, managed and controlled manner. No
matter what the circumstances, the temptation to tighten
up the joint beyond design parameters should be
resisted.
There are a number of candidate repair and
replacement strategies. These include:
Detail design considerations include:
– Definition of the expected design/operating
life of the repair.
– Impact of fluid on bolting, e.g. exposure of
some bolting to fluids with H2S or chlorides.
– Pressure end cap forces.
– Site constraints such as insufficient space to
install a clamp.
— Continued service accepting the joint leakage:
It may be acceptable to permit continued leakage
from the joint based upon the engineering risk
assessment and environmental impact until a
planned shutdown.
6.7 LEARNING FROM LEAKS
— Continued service operating with de-rating:
It may be acceptable to permit continued joint
service by imposing a control measure such as derated duty point or downgrade condition. This may
be appropriate where the leak rate is pressure or
temperature activated.
In order to prevent future leaks lessons should be learnt
from past incidents. Operators should develop a process
to capture data in a form that can be readily reviewed
and analysed. The process should aim to:
— Isolate and repair the leaking joint (line isolation):
There may be sufficient valves to isolate the
leaking flange and allow maintenance to be carried
out. This may prove difficult in some plants where
the valves do not provide tight shut-off or the
required level of isolation as required by the
company’s safety policy cannot be achieved.
— Improve the quality of information gathered on
joint leaks.
— Identify and better understand the causes of
failure(s).
— Provide data for the hydrocarbon leaks database.
— Provide data for long-term learning on leak
occurrence.
— Ensure periodic review and learning.
— Shutdown unit, isolate and repair joint:
In some instances, where safe isolation cannot be
These details should be recorded in a data management
system.
34
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the licence terms and conditions. It must not be forwarded to, or stored or accessed by, any unauthorised user. Enquiries: e: pubs@energyinst.org.uk t: +44 (0)207 467 7100
MANAGEMENT OF LEAKS
Figure 6.2: Flange with gasket seating face pitting
Figure 6.3: Encasement clamp repair on a 24 in. seawater line to stop leak on stub of composite flange
35
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GUIDELINES FOR THE MANAGEMENT OF THE INTEGRITY OF BOLTED JOINTS FOR PRESSURISED SYSTEMS
36
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7
IN-SERVICE INSPECTION
— Flange orientation, particularly blind flanges
installed horizontally, allowing water to collect in
the holes. Stud bolts in blind flanges in firewater
mains have suffered this form of damage.
7.1 INTRODUCTION
In-service inspection of bolted joints is an integral
activity to ensure the continued integrity of the joints
and as such should be built in to all relevant inspection
programmed. This section looks at the possible
damage that can occur, the inspection methods
available for detection of defects and the mitigation
measures that can be put in place to minimize such
degradation.
A summary of the key issues addressed in this
section is included in Table 7.1.
7.3 DEGRADATION MECHANISMS
A number of degradation mechanisms can contribute to
the failure of a bolted joint, most of which are corrosion
related. Figures 7.1 – 7.11 (see pages 39-41) illustrate
the most common problems found.
7.2 RISK ASSESSMENT
7.4 INSPECTION TECHNIQUES
For high-risk joints it is recommended that methods are
implemented for monitoring bolt stress to ensure that
pre-load is maintained. Generally, a risk assessment
should be carried out to determine the inspection
requirements.
The following factors should be considered for
specific joints:
7.4.1
Non-destructive testing
The most common method of in-service non-destructive
inspection is visual inspection, normally carried out as
part of general visual inspections of pipework or
structures as opposed to specific bolt inspections. The
limitations of this method are that only the external
parts of the joint are visible which will detect loose
bolts and corrosion; however the extent of surface
degradation on the strength of the joint is difficult to
measure.
Where bolt threads or nuts show the effects of
significant corrosion then further investigation should
be undertaken to ensure that the joint is still fit for
purpose. Some Operators use a Performance Standard
to quantify the extent of bolt degradation. An example
of a PS for low alloy steel bolting material is shown
below:
Bolts shall be visually examined for evidence of
corrosion and other defects (mechanical damage or
— High temperature pipework may cause bolts to
creep and cause leakage.
— Large numbers of temperature cycles can cause the
bolts to loosen.
— Mechanical vibration or shock loading may cause
the flange bolts to loosen.
— Areas of high external corrosion may cause the
bolts to lose integrity. Susceptible locations include
insulated pipework, bolts open to harsh
environments or those subject to deluge system
tests.
— Internal corrosion can cause flange faces to lose
material.
37
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GUIDELINES FOR THE MANAGEMENT OF THE INTEGRITY OF BOLTED JOINTS FOR PRESSURISED SYSTEMS
Table 7.1: Summary of key issues
Damage
type
General corrosion
Typical
conditions
Exposed areas
Galvanic corrosion
Dissimilar metals –
flanges, bolts, gaskets
Localised bolt
corrosion
Crevice corrosion
Fatigue
Dissimilar metals, exposed
areas
Exposed areas
Joints subject to vibration,
cyclic loading
High temperature
applications
A combination of a
chloride-containing
environment, susceptible
material and tensile stress
Hydrogen can form on
surface during manufacture
or be caused by Cathodic
Protection
Sample removal, visual,
Phased Array UT, CGWT
Visual, sample removal
Visual, Phased Array UT
Pipework containing a
corrosive medium,
dissimilar materials
Intrusive visual, UT
Creep
Stress corrosion
cracking
Hydrogen
embrittlement
Flange face
corrosion
Inspection
technique
Visual, sample removal,
Cylindrical Guided Wave
Technique
Visual
Time-of-flight UT
Phased Array UT
Visual, highlighting any
corroded High Strength
Fasteners for replacement
Mitigation
measures
Material selection, thread
protectors, coatings
Material selection, gaskets,
bolt/flange insulating kits,
weld overlay
Material selection
Material selection
Pipework design
Material selection, ASME
SA-453
Material selection
Material selection – most
common in High Strength
Steels e.g. ASTM
Standards A345 Gr BD,
A490
and A547 Thread
protectors and coatings
Material selection, gasket
selection, weld overlay
— Ultrasonic inspection of flange faces using shear
wave transducers – detects flange face corrosion
and erosion.
— Black light NDT of threads and body on bolts that
are to be re-used on high critical joints – detects
stress cracking.
cracking). Bolting showing signs of mechanical damage
to plain shanks or threaded portions within the stressed
portion or any cracking shall be replaced with new
bolting.
Bolts, studs and screwed fasteners that have
corroded such that the diameter of the smooth shank or
the major thread diameter is less than 90% (i.e. 10%
loss in diameter) of the nominal size, after removal of
the corrosion product, shall be replaced with new
bolting.
A number of more specialised techniques are
available which can be used to check for specific
conditions; these include:
7.4.2
Destructive testing
Where degradation is thought to have occurred and
assessment is not possible through non-destructive
techniques, sample removal of bolts for destructive
testing can be carried out to estimate if joints are still fit
for purpose. Finite element analysis has also been used
to model the effects of progressive removal of layers of
bolt material.
— Phased Array Ultrasonics – detects thread wear and
cracking from the bottom of the threads, as
illustrated in Figure 7.11 (see page 41).
— Time of Flight (TOF) UT – measures bolt
elongation.
— Cylindrically Guided Wave Technique (CGWT) –
detects corrosion wastage.
7.5 DEFECT MITIGATION MEASURES
In-service inspection requirements can be greatly
reduced by designing the bolted joint to include
38
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IMPORTANT: This file is subject to a licence agreement issued by the Energy Institute, London, UK. All rights reserved. It may only be used in accordance with
the licence terms and conditions. It must not be forwarded to, or stored or accessed by, any unauthorised user. Enquiries: e: pubs@energyinst.org.uk t: +44 (0)207 467 7100
IN-SERVICE INSPECTION
— Coatings
Bolts can be supplied with a variety of life
extending surface treatments such as hot dip spun
galvanising, which research shows offers the best
long term protection. Zinc, PFTE or electroless
nickel are also used.
measures which will reduce the risk of degradation due
to mechanical damage and corrosion. The following are
some commonly used measures:
— Material selection
Corrosion-resistant alloys e.g. stainless steel,
duplex and cupro-nickel alloys are used. However,
they can suffer specific rapid failure mechanisms
such as stress corrosion cracking. In addition, the
high costs of these materials restricts widespread
use.
— Cathodic protection
Used for underwater applications. However, there
is usually a need to apply coating to the pipework
and flange joints to minimise the risk of hydrogen
embrittlement.
— Thread protectors
Neoprene, polyethene and aluminium are common.
However, the potential for loss of thread
engagement strength needs to be assessed.
— Flange protection
Gaskets (material selection is important to avoid
galvanic corrosion), flange protectors, coatings.
Figure 7.1: General corrosion
(General corrosion of flanges and bolts.)
Figure 7.2: Galvanic corrosion (1)
(Galvanic corrosion where dissimilar materials
have been used for the bolts and one flange.)
Figure 7.3: Galvanic corrosion (2)
(Galvanic corrosion where dissimilar
materials of bolts only has been used.)
Figure 7.4: Localised corrosion
(Severe localised corrosion of bolt body.)
39
Issued under licence to BP employees only.
IMPORTANT: This file is subject to a licence agreement issued by the Energy Institute, London, UK. All rights reserved. It may only be used in accordance with
the licence terms and conditions. It must not be forwarded to, or stored or accessed by, any unauthorised user. Enquiries: e: pubs@energyinst.org.uk t: +44 (0)207 467 7100
GUIDELINES FOR THE MANAGEMENT OF THE INTEGRITY OF BOLTED JOINTS FOR PRESSURISED SYSTEMS
Figure 7.6: Fatigue
(Failed bolt displaying typical
fatigue failure characteristics.)
Figure 7.5: Crevice corrosion
(Advanced crevice corrosion of a stainless steel bolt.)
Figure 7.7: Stress corrosion cracking
(Failure surface of bolt which had been subject to the
combined influence of tensile stress and a corrosive
environment – a typical example would be austenitic
stainless steel in high chloride conditions.)
Figure 7.9: Flange face corrosion
(Flange face corrosion in seawater pipework.)
Figure 7.8: Hydrogen embrittlement
(Fracture surface of a bolt that resulted
from hydrogen embrittlement cracking.)
Figure 7.10: Galvanic corrosion
(Galvanic corrosion of clamped assembly seal ring.)
40
Issued under licence to BP employees only.
IMPORTANT: This file is subject to a licence agreement issued by the Energy Institute, London, UK. All rights reserved. It may only be used in accordance with
the licence terms and conditions. It must not be forwarded to, or stored or accessed by, any unauthorised user. Enquiries: e: pubs@energyinst.org.uk t: +44 (0)207 467 7100
IN-SERVICE INSPECTION
Figure 7.11: Phased array ultrasonics
41
Issued under licence to BP employees only.
IMPORTANT: This file is subject to a licence agreement issued by the Energy Institute, London, UK. All rights reserved. It may only be used in accordance with
the licence terms and conditions. It must not be forwarded to, or stored or accessed by, any unauthorised user. Enquiries: e: pubs@energyinst.org.uk t: +44 (0)207 467 7100
GUIDELINES FOR THE MANAGEMENT OF THE INTEGRITY OF BOLTED JOINTS FOR PRESSURISED SYSTEMS
42
Issued under licence to BP employees only.
IMPORTANT: This file is subject to a licence agreement issued by the Energy Institute, London, UK. All rights reserved. It may only be used in accordance with
the licence terms and conditions. It must not be forwarded to, or stored or accessed by, any unauthorised user. Enquiries: e: pubs@energyinst.org.uk t: +44 (0)207 467 7100