Table Of ContentThe International Institute of Welding
Non-Destructive
Examination of
Underwater Welded
Steel Structures
IIS/IIW Document V-1097-97 (IIS/lIW-1372-97)
V S Davey, 0 Fmli, A Raine and R T Whillock
A B I N G T O N P U B L I S H I N G
\\'oodhcad I'uhlishing Limited in association with l'hc \\!clding Institute
Carnhridge En~land
Published by Abington Publishing, Abington Hall, Abington,
Cambridge CB21 6AH, England
www.wood headpub lishing. com
First published 1999, Woodhead Publishing Limited
0 1999, The International Institute of Welding
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All rights reserved. No part of this publication may be reproduced or
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No responsibility is assumed by the Publisher for any injury and/or damage
to persons or property as a matter of product liability, negligence or
otherwise, or from any use or operation of any methods, products,
instructions or ideas contained in the material herein.
British Library Cataloging in Publication Data
A catalogue record for this book is available from the British Library
ISBN-1 3 978-1 -85573-427-2
ISBN-1 0 1-85573-427-3
Printed by Victoire Press, Cambridge, England
CONTENTS
Preface V
1 Introduction and scope 1
1.1 0b jectives 1
1.2 Scope 2
1.3 Further information 3
2 Definitions and glossary 4
2.1 Definitions 4
2.2 Glossary 5
3 Components of examination 9
4 Personnel, qualifications, and quality assurance 10
4.1 Personn e l 10
4.2 Qualifications 10
4.3 Quality assurance 11
5 Procedures 13
5.1 Principles 13
5.2 Content 13
5.3 Additional requirements 14
6 Pre-inspection activities 15
6.1 Briefing 15
6.2 Location reference marking 15
6.3 Cleaning 15
7 Inspection for flaws 17
7.1 Magnetic particle inspection 17
7.2 Alternating current potential drop 20
7.3 Eddy current and alternating current field measurement 21
7.4 Flooded member detection 22
7.5 Radiographic methods 23
7.6 Ultrasonic inspection methods 23
7.7 Visual inspection 28
8 Inspection for corrosion 30
8.1 Cathodic protection potential measurements 30
8.2 Wall thickness measurement 32
9 Passive NDT methods 33
10 Post-inspection activities 34
10.1 Recording and retention of data 34
10.2 Inspection after repair 34
11 Introduction of new equipment 36
12 Remote operated vehicle deployment 38
12.1 Introduction 38
12.2 Present status 38
12.3 Conclusions 40
Appendix A - Further information 41
-
Appendix B Summary of underwater NDT qualification schemes 66
-
Bibliography Selected reference documents on NDT of offshore
construction 68
1- Government bodies 68
2-Certifying authorities and classification societies 70
3-Advisory bodies and others 73
4-Associated documents 75
iv
This is a revision and replacement of Document IIS/IIW-1033-89,
'Information on Practices for Underwater Non-Destructive Testing' and
was prepared by a task force of Working Group 2, 'Inspection of
Offshore Welded Constructions' of Commission V Quality Control and
Quality Assurance of Welded Products' of the IIW consisting of:
Victor S Davey, (Formerly HSE) UK
Olav Ferrli, Det Norske Veritas , Norway
Alan Raine, Technical Software Consultants Ltd, UK
R Toby Whillock, (Formerly BOMEL) UK
I INTRODUCTION AND SCOPE
This following document has been produced by Working Group 2 of
Commission V of the International Institute of Welding and supersedes
previous versions.
1. I Objectives
The objectives of this document are to give technical guidance and
information on non-destructive testing (NDT) techniques suitable for
use underwater on welded steel constructions.
When properly used, modern underwater NDT techniques are
capable of similar performance to comparable onshore NDT
equipment. However, as with all technologies, the quality of the results
depends on appropriate selection and operation of the equipment. It
is accordingly the primary purpose of this document to assist in the
production of high-quality reliable results from underwater inspection
by promoting what might reasonably be considered good practice
at the time of writing (19 97).
This document is not a code and neither is it a statutory instrument
with legal power, nor does it seek to lay down minimum standards.
Nonetheless, a vital constituent of any inspection practice is to
accomplish the work with minimal risk to personnel, and it is expected
that organisational schedules and procedures will consider this aspect
in adequate detail. Notwithstanding the various notes in this
document concerned with safety, nothing in this text should be taken
as diminishing or removing the onus placed on the individual to adopt
safe working practices and to take the final responsibility for the
consequences of his own actions.
Furthermore, it is not the intention to produce prescriptive
requirements or in any way to restrict underwater inspection by
prohibiting certain practices or by inhibiting the introduction of new
equipment or techniques. However, where in the opinion of the
Working Group, the use of items of equipment in some configurations
may give rise to undesirable consequences, this will be pointed out.
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1.2 Scope
The document is intended for the external inspection of welded steel
constructions used offshore such as oil and gas platforms, pipelines
and risers, harbour installations, ships' hulls, etc, though the practices
discussed should also be suitable for inspection of cast components
with appropriate modifications to reflect the different metallurgical
properties. Testing of parent material as well as welds is covered.
The document applies not only to methods used manually by divers in
water or in a habitat, but also to remotely-controlled or automated
methods used from submersibles, atmospheric chambers, or
remotely-operated vehicles (ROVs) with inspectors remote from the
work site. Only the commonly used NDT methods are described in
detail, with less-commonly used methods being given more superficial
description.
Since this document is concerned with the external inspection of
welded structures underwater, it will not consider inspection in the
splash zone or above water, and it does not cover inspection inside
pipelines by inspection pigs and suchlike. Similarly, information is not
given on diving or operational aspects of underwater inspection
activities. It must, however, be reiterated that, as a minimum, proper
precautions need to be taken with respect to diver safety and
operation, particularly in relation to electrical hazards, implosion of
equipment, and the risk of water penetration into equipment. In
saturation habitats, attention should also be given to helium
penetration into equipment under high external pressure.
The document does not address pre-inspection planning and
scheduling, or the selection of areas for inspection. Reference should
be made to the appropriate company documentation on these
subjects. In addition, the use of inspection results is not covered. Both
these activities are strongly dependent on a host of factors such as:
construction type and environment, consequences of failure, national
regulations, agreement between vendor and purchaser, etc. The
choice of the most suitable NDT methods for an application is also
dependent on similar factors and only broad guidelines will be given.
2
1.3 Further information
Information in the main part of this document may be expanded
upon in the background text given in Appendix A. Reference should
also be made to other IIW documents and to reports such as those
listed in the Bibliography. Particularly recommended are reports
published by the United Kingdom's Marine Technology Directorate
Ltd: 'Underwater inspection of steel offshore installations:
implementation of a new approach; MTD Ltd Publication 89/104.
Publications by the UK Health & Safety Executive (HSE) are also a
good source of information for offshore NDT.
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2
The following terms are defined for use in this document.
2.1 Definitions
Non-des trucf ive testing fNDT), non-destrucf ive examination fNDEJ or
non-destructive inspection - the carrying out of inspection causing
little, if any, damage to the test item, usually by physical test methods
in conjunction with visual assessment, either at the worksite by the
inspector or via a remote telecommunications link. The words testing,
examination and inspection are thoughout this document regarded
synonymous, reflecting the common, and somewhat arbitrary
terminology used in the offshore inspection industry.
Non-destructive evaluation fNDq - the comprehensive assessment of
the results of NDT, including the assessment of any inspection
indications, which may comprise formal fracture mechanics analysis
and other engineering reliability studies. The overall results and
assessment will normally be drawn together in a formal report.
indication - a response from the inspection system suggesting the
existence of a flaw.
Flaw - an indication confirmed by use of two or more different
inspection techniques, including close visual inspection. A flaw is
usually, but not always, a crack. The term is used in preference to
'defect' in accordance with European Standards, the designation
'defect' being considered as connotating 'defective' or 'unfit for
purpose'. A flaw is a departure from perfection that does not
immediately condemn the article as unacceptable but that
nevertheless should be considered in an assessment of reliability.
Further information may be found in IIW documents.
Spuious indication or false call - a plausible, but discounted,
indication that has, on further investigation, been assessed as not
being a flaw. It would normally still be noted in the records of the
inspection.
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Probabfity of detection [POD) - a measure of the performance of an
non-destructive testing (NDT) system intended to detect flaws, in terms
of the chance of finding a flaw. It is a complicated variable,
depending on: NDE technique and equipment: skill of the operator:
the inspection conditions: the definition, nature, location, and size of
flaw and other factors. It is often presented in the form of a curve as a
function of flaw size (usually length). Considerable care should be
taken not to mis-apply such curves as their interpretation is far from
clear-cut and demands some knowledge of statistical methods.
Accuracy of s/ang lA0.J) - a measure of the performance of NDE
equipment in giving an estimate of the size of a flaw. In the important
case of surface-breaking flaws, the depth is quoted as being the
significant variable for causing brittle fracture. Accuracy of sizing is a
complicated concept, being heavily dependent on a number of
factors, some ill-defined. The concept of accuracy of sizing is less well
established than POD but includes systematic and random errors of
size estimates.
2.2 Glossary
Magnetic parfcle inspection fMPIJ or magnetic parfcle testing fMPTj
- a combined visual and electromagnetic technique relying on the
attraction of minute ferromagnetic particles to magnetic flux diverted
from an applied field by a flaw. The particles emphasise the length of
the defect rendering it more visible to the inspector. The method is
suitable for detecting surface-breaking flaws, but may also have a
limited capability for anomalies very near to the surface. The
magnetic field may be applied by permanent magnets or by
electromagnetic induction using coils, a yoke, or prods. In many
ways, MPI can be regarded as a quasi-standard method against
which other NDT methods are often compared, though it is known to
be very sensitive to the skill of the inspector.
Alternating current potential drop [Acpd) - a contacting
electromagnetic technique using the skin effect of the alternating
current from which an assessment of crack depth can be made on
surface breaking defects. ACPD is a sizing technique rather than a
detection method.
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