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Connection Design Guide 2
Design Guide 2: Welding in Structural Steel Connections
Level 13, 99 Mount Street, North Sydney. NSW 2060. Phone [phone]. Email [e-mail] Website: www.steel.org.au
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WELDING
Design Guide 2:
Welding in Structural Steel Connections
First Edition 2007
Author T.J. Hogan
Contributing author and editor S.A. Munter
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Design Guide 2.
Welding in structural steel connections
by
T.J.Hogan
contributing author & editor
S.A.Munter
first edition - 2007
AUSTRALIAN STEEL INSTITUTE
(ABN)/ACN (94) 000 973 839
D esign guide 2:
Welding in structural steel connections
C opyright 2007 by AUSTRALIAN STEEL INSTITUTE
Published by: AUSTRALIAN STEEL INSTITUTE
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A ll rights reserved. This book or any part thereof must not be reproduced in any form without
the written permission of Australian Steel Institute.
N ote to commercial software developers: Copyright of the information contained within this publication is
held by Australian Steel Institute (ASI). Written permission must be obtained from ASI for the use of any
information contained herein which is subsequently used in any commercially available software package.
F IRST EDITION 2007 (LIMIT STATES)
National Library of Australia Cataloguing-in-Publication entry:
Hogan, T.J.
Design guide 2. Welding in structural steel connections
st
1 e d.
Bibliography.
ISBN 978 0 909945992
1.
Steel, StructuralStandards - Australia.
2.
Steel, StructuralSpecifications - Australia.
3.
Steel, Structural Welding.
4.
Welded Steel Structures
I.
Munter, S.A.
II.
Australian Steel Institute.
III.
Title
(Series: Structural steel connection series).
This publication originated as part of
Design of structural connections
First edition 1978
Second edition 1981
Third edition 1988
Fourth edition 1994
Also in this series:
Design capacity tables for structural steel, Volume 3: Simple connections open sections
Handbook 1: Design of structural steel connections
Design Guide 1: Bolting in structural steel connections
Design Guide 3: Web side plate connections
Design Guide 4: Flexible end plate connections
Design Guide 5: Angle cleat connections
Design Guide 6: Seated connections
D isclaimer: T he information presented by the Australian Steel Institute in this publication has been
prepared for general information only and does not in any way constitute recommendations or
professional advice. While every effort has been made and all reasonable care taken to ensure the
accuracy of the information contained in this publication, this information should not be used or relied
upon for any specific application without investigation and verification as to its accuracy, suitability and
applicability by a competent professional person in this regard. The Australian Steel Institute, its officers
and employees and the authors and editors of this publication do not give any warranties or make any
representations in relation to the information provided herein and to the extent permitted by law (a) will
not be held liable or responsible in any way; and (b) expressly disclaim any liability or responsibility for
any loss or damage costs or expenses incurred in connection with this publication by any person, whether
that person is the purchaser of this publication or not. Without limitation, this includes loss, damage, costs
and expenses incurred as a result of the negligence of the authors, editors or publishers.
The information in this publication should not be relied upon as a substitute for independent due
diligence, professional or legal advice and in this regards the services of a competent professional person
or persons should be sought.
d esign guide 2:
welding in structural steel connections, first edition
ii
CONTENTS
Page
List of figures
List of tables
Preface
About the author
About the contributing author and editor
Acknowledgements
P age
iv
iv
v
vi
vi
vii
7 WELDING PROCEDURES .......................30
7.1 Qualification of a welding
procedure
30
7.2 Prequalified welding procedure
32
7.3 Qualification by testing
33
7.4 Requalification of welding
procedures
34
8 WORKMANSHIP.......................................35
8.1 Edge preparation
35
8.2 Assembly
35
8.3 Preheat
36
8.4 Tack welds
37
8.5 Distortion and residual stress
38
8.6 Cleaning and dressing welds
39
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1 CONCEPT OF DESIGN GUIDES............... 1
1.1 Background
1
2 INTRODUCTION ........................................ 2
3 TYPES OF WELD ...................................... 3
3.1 Weld types
3
3.2 Fillet welds
5
3.3 Butt welds
8
3.4 Edge preparations
12
3.5 Prequalified joint preparations
13
3.6 Standard weld symbols
14
4 WELDABILITY OF STEEL........................ 17
5 WELDING PROCESSES.......................... 18
5.1 Introduction
18
5.2 Fusion welding process
19
5.3 Terminology
20
5.3.1
Weld metal
20
5.3.2
Partially mixed weld metal
20
5.3.3
Fusion (boundary) line
20
5.3.4
Heat-affected zone
20
5.3.5
Multi-run welds
20
5.4 Manual metal arc welding
21
5.5 Gas metal arc welding and
flux cored arc welding
22
5.6 Summary of characteristics
of welding processes
24
5.7 Welding positions
25
6 WELDING CONSUMABLES .................... 26
6.1 Manual metal arc welding
26
6.2 Gas metal arc welding
27
6.3 Flux cored arc welding
28
6.4 Prequalified welding consumables 29
9 WELD IMPERFECTIONS..........................40
9.1 Weld categories
40
9.2 Levels of inspection
42
9.3 Imperfection levels
43
9.4 Weld defects
46
9.5 Weld repairs
47
10 WELD INSPECTION .................................48
10.1 Introduction
48
10.2 Visual examination
49
10.3 Magnetic particle examination
50
10.4 Liquid penetrant examination
51
10.5 Radiographic examination
52
10.6 Ultrasonic examination
54
11 PRACTICAL CONSIDERATIONS .............55
11.1 Clearances for welding
55
11.2 Site welding
57
11.3 Economical design and detailing
58
12 REFERENCES..........................................59
APPENDIX
A
ASI Design Guide 2
comment form
d esign guide 2
welding in structural steel connections, first edition
61
iii
LIST OF FIGURES
Page
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
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Figure 8
Figure 9
Figure 10
Figure 11
Figure 12
Figure 13
Figure 14
Figure 15
Figure 16
Figure 17
P age
Weld types in AS 4100 ................... 3
Weld use by joint type .................... 4
Typical applications of fillet welds
in steelwork connections ................ 6
Fillet weld size and details .............. 7
Fillet weld size in lapped plates ...... 7
Types of butt welds......................... 8
Typical applications of butt welds
in steelwork connections ................ 9
Examples of use of run-off plate,
backing bar, extension plate ......... 11
Terms applicable to full
penetration butt welds .................. 11
Terms applicable to partial
penetration butt welds .................. 11
Weld edge preparation terms ....... 12
Construction of a welding symbol . 15
Basic welding symbols.................. 16
Supplementary welding symbols .. 16
Structure of a single pass weld..... 20
Manual metal arc welding (MMA) . 21
Schematic diagram gas metal
arc welding ................................... 22
Figure 18 Schematic diagram flux cored
arc welding ....................................22
Figure 19 Welding positions for plate butt
welds .............................................25
Figure 20 Welding positions for plate fillets ...25
Figure 21 Imperfections in butt welds ............44
Figure 22 Imperfections in fillet welds ...........45
Figure 23 Solidification cracks.......................45
Figure 24 Schematic diagram of magnetic
particle examination ......................50
Figure 25 Schematic diagram of liquid
penetrant examination ...................51
Figure 26 Principles of radiographic
examination ...................................52
Figure 27 Examples of imperfection detection
using ultrasonic examination .........54
Figure 28 Angular limits for joint preparations
for various welding techniques ......55
Figure 29 Clearance on an angle cleat
welded to a beam web...................55
Figure 30 Examples of bad accessibility........56
LIST OF TABLES
Page
Table 1
Table 2
Table 3
Minimum size (leg length) of fillet
welds .............................................. 5
Characteristics of welding
processes ..................................... 24
Prequalified welding
consumables ................................ 29
P age
Table 4
Table 5
Levels of non-destructive
examination (NDE) ........................42
Types of imperfection considered
in AS/NZS 1554.1..........................43
d esign guide 2:
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iv
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PREFACE
T his new series of connection publications by the Australian Institute of Steel (ASI) covering
capacity tables, theory and design of individual simple connections will be known as the
Structural Steel Connections Series, Part 1: 1 st ed. 2007 (Connection Series, Part 1). This
Connection Series, Part 1 details the method of design and provides capacity tables and
detailing parameters for a range of simple connections commonly used for structural steelwork
in Australia. Connections have a major engineering and economic importance in steel structures
influencing design, detailing, fabrication and erection costs. Standardisation of design approach
integrated with industry detailing is the key to minimum costs at each stage. This Connections
Series, Part 1 in conjunction with the future Connection Series, Part 2 for rigid connections
(collectively the Structural Steel Connections Series or Connection Series ) replaces and
enhances an ASI flagship publication first released in 1978 at which time connection design
theories were developed for the purpose of generating and releasing connection capacity
tables. The first three editions were released in permissible stress format. The fourth edition
D esign of Structural Connections ( often referred to as the Green Book) was released in 1994 in
limit state format but there was no subsequent release of a limit state companion document
containing connection design capacity tables.
Design Guide 2 W elding in structural steel connections has been introduced into the ASI
Connections Manual as a complementary document to Design Guide 1 Bolting in structural steel
connections . The intention of Design Guide 2 is to act as a basic primer on all aspects of
welding as applied to steelwork connections. Extensive reference is made to sources which can
supply more detailed informationmany of these references are more general and apply to
fabricating in general using welding.
Design Guide 2 addresses the matters covered in Australian Standards with the exception of
weld design which is dealt with in the Handbook 1. The Handbook discusses welding processes,
consumables and procedures in sufficient detail for the structural engineer to understand the
basis of what occurs in a fabrication shop when connections are being fabricated. Welding in
the fabrication shop and bolting on site remain the key to economical structural steelwork.
Design Guide 2 also discusses the issues of workmanship, imperfections in welds, when
imperfections become defects, how welds can be inspected and repair of welds.
An appendix to each publication in the series also contains an ASI comment form. Users of this
Connections Series are encouraged to photocopy this one page form and forward any
suggested improvements which may be incorporated into future editions.
T.J. Hogan
S.A. Munter
d esign guide 2:
welding structural steel connections, first edition
v
ABOUT THE AUTHOR
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T im Hogan is Director of SCP Consulting Pty Ltd. His academic achievements include a
Bachelor of Engineering from the University of NSW with 1st C lass Honours and the University
Medal. Post graduate qualifications include a Master of Engineering Science and a Master of
Business Administration. Tim is a Member of the Institution of Engineers Australia with CPEng
and FIE Aust. status.
His early experience was on bridge design and construction with the NSW Public Works
Department and subsequently as Development Engineer and then Engineering Manager with
the Australian Institute of Steel Construction until 1980. Consulting experience with SCP
Consulting since 1980 has included design and supervision of large steel framed buildings,
industrial buildings, mill buildings, retail developments, defence infrastructure and composite
steel-concrete buildings. His published works deal primarily with the areas of composite
construction, steel connections, fabrication and erection of steel structures and he was a major
contributor and editor of the Commentary to AS 4100. He is a member of a number of
Standards Australia Committees dealing with steel and composite structures and is currently
Chairman of Committee BD-001 Steel Structures and BD-032 Composite Construction. He
received an award from Standards Australia for his contributions to writing of Australian
Standards.
ABOUT THE CONTRIBUTING AUTHOR AND EDITOR
Scott Munter is now the National Structural Decking Manager for BlueScope Lysaght. He was
formerly the National ManagerEngineering & Construction for the Australian Steel Institute
(ASI) and worked in this role from 2000 to 2007. This key role involved setting the technical
leadership of ASI in support of design and construction to enable the efficient specification and
use of steel in construction. Responsibilities included ASI technical publications, advice on
industry best practice, ASI and Code committees, presentations and lecturing.
Scott is a Member of the Institution of Engineers Australia with CP Eng & NPER (Structural)
status. He holds a Bachelor of Structural Engineering from the University of Technology,
Sydney with 1 st C lass Honours and the University Medal. His professional career includes 15
years in consulting civil and structural engineering working for Tim Hogan at SCP Consulting.
His consulting experience includes a strong steel focus with major infrastructure, industrial and
commercial developments plus domestic construction.
d esign guide 2:
welding structural steel connections, first edition
vi
ACKNOWLEDGEMENTS
The authors would like to extend special thanks to:
The ASI Connections steering committee consisting of Richard Collins (Engineering Systems),
Anthony Ng (OneSteel Market Mills), Arun Syam (Smorgon Steel Tube Mills) for their respective
contributions with the development and review of the technical and editorial content of the
revised ASI Connection Publication.
Significant contributions were made by:
Welding Technology Institute of Australia (WTIA) for their expert review and comments.
S tandards Australia for providing their technical typesetting expertise.
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W hizzcad Pty Ltd with drafting and graphics for publishing.
ASI State Engineering & Construction Special
engineering and industry review of manuscripts.
Sub-Committees
for
progressive
Together with support of:
All facets of the ASI membership including design engineers, steelwork detailers and
fabricators in contributing industry best practice and standards through ASI surveys and
direct consultation to establish the theory and geometry in this new ASI Connection
Publication.
d esign guide 2:
welding structural steel connections, first edition
vii
1
CONCEPT OF DESIGN GUIDES
1.1
Background
The ASI was formed in 2002 through the merger of Australian Institute of Steel Construction
(AISC) and Steel Institute of Australia (SIA). The former AISC published a design manual giving
guidance on the design of structural connections in steelwork (Ref. 2).
ASI is updating Reference 2 by way of the Connection Series including design guides, dealing
with connection parts and individual connection types. The overall series of connections
publications will be known as the Connections Series.
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The former AISC also published a manual containing standardised detailing for simple
connections, accompanied by load tables (Ref. 3).
Wherever possible each design guide for individual connection types contains standardised
detailing and design capacity tables for the connection type covered by that design guide
derived using the design models in that design guide.
The Connection Series is a specialist series devoted to the design of connections in structural
steel in accordance with current Australian Standard AS 4100 (Ref 1.), reflecting the current
state of knowledge of connection behaviour from test results. In some instances, the test
evidence is sparse and in other instances the evidence is contradictory or clouded. Each design
guide in the Connection Series has been written by weighing the evidence to provide
recommended design procedures based in part on the design procedures used in equivalent
manuals and/or published papers.
Each design guide is intended to provide a design model which gives a reasonable estimate of
connection design capacity and effort has been expended in researching and developing design
models which can be justified on the basis of the available research and current design
practice. It is to be emphasised that for the connections model presented, the design model is
not the only possible model. I t is therefore not intended to suggest that other models may
not result in adequate connection capacity and further reference is made to the
Disclaimer on page ii of this publication as to the required investigation and verification
by a competent professional person or persons in regards to the accuracy, suitability and
applicability of the materials provided in this Connections Series.
The connections dealt with are those presently in common use in Australia and reflect the types
of connections covered within the earlier AISC Standardized Structural Connections (Ref. 3).
This design guide deals with the welding in steelwork connections and draws on other AISC
publications (Refs 5 and 6).
d esign guide 2
welding in structural steel connections, first edition
1
2
INTRODUCTION
W elds are widely used for making connections in structural steelwork connections, being
executed predominantly in the fabrication shop but occasionally on site. An understanding of all
the aspects of welding that relate to structural steelwork connections is vital to designing,
detailing, fabricating and erecting each type of connection that involve welding.
This Design Gguide is intended to provide a state-of-the-art summary of the following items as
they relate to the use of welds in steel connections:
types of welds that are commonly used in steelwork connections (Section 3);
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weldability of steel (Section 4);
welding processes used (Section 5);
w elding consumables (Section 6);
w elding procedures (Section 7);
workmanship (Section 8);
weld imperfections (Section 9);
w eld inspection (Section 10);
p ractical considerations (Section 11).
The scope of the publication is limited to:
weld types in common use in steelwork connections in Australia
w elding processes in common use in fabricating steel connections in Australia
The design of welded connections and the design capacities of welds are discussed in detail in
Handbook 1.
The use of welds and their design in individual connections is discussed in the Design Guide
relevant to each connection.
d esign guide 2:
welding structural steel connections, first edition
2
3
TYPES OF WELD
3.1
Weld types
Six types of welds are mentioned in AS 4100 (Ref 1) as follows:
Complete penetration butt welda weld where fusion exists between weld metal and the
parent metal throughout the entire depth of the joint. A butt weld is one in which the weld
lies substantially within the extension of the planes of the surfaces of one or more of the
parts joined.
2.
Incomplete penetration butt welda butt weld where, by design, fusion does not extend
throughout the full depth of the joint.
3.
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1.
Fillet welda weld of approximately triangular cross-section which is formed in the corner
between the surfaces of two components.
4.
Plug welda weld made by completely or partially filling a circular hole in one component
with filler metal, with the filler metal fusing to the contiguous component exposed through
the hole.
5.
Slot welda weld made by depositing a fillet weld around the periphery of an elongated
hole in one component so as to join it to the surface of a contiguous component exposed
through the hole.
6.
Compound welda weld comprising a fillet weld superimposed on a butt weld.
AS 4100 restricts the use of plug and slot welds to applications where these welds either
transmit shear in lap joints or where they prevent buckling of lapped parts or where they join
component parts of built-up members. Such welds are not normally used in structural steel
connections and will not be considered further. Almost all the welds used in structural steel
connections are either butt welds or fillet welds as shown in Figure 1.
FIGURE 1 WELD TYPES IN AS 4100
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welding in structural steel connections, first edition
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The four weld types (1, 2, 3 and 6) can be used in five joint types (butt, tee, corner, lap and
edge) as shown in Figure 2. Most structural steel connections involve either:
(welded splices)
lap joint
(splices using splice plates)
tee joint
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butt joint
(many connections)
FIGURE 2 WELD USE BY JOINT TYPE
d esign guide 2:
welding structural steel connections, first edition
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3
TYPES OF WELD
3.2
Fillet welds
Features of fillet welds are:
economic to produce;
ease of fabrication;
adaptability;
less precision in fitting up;
minimum preparation if cutting of edges complies with AS 4100 (Ref. 1).
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Typical applications in structural steel connections are shown in Figure 3.
AS/NZS 1554.1 (Ref. 7) contains the following provisions for fillet welds in Clause 3.3.
Size
Defined by leg length (Figure 4).
Preferred sizes that are used in structural steel connections are: 6, 8, 10 and 12 mm.
M inimum size (Table 1). Minimum sizes are specified in order to avoid internal stresses
due to rapid cooling, such stresses may lead to cracking.
Effective length
Overall length of full-size fillet including end returns. No reduction required for either the
start or end of the weld.
Any segment of intermittent fillet weld shall have an effective length of not less than
40 mm or 4 times the fillet weld size whichever is the greater.
E ffective area
P roduct of effective length and design throat thickness (Figure 4).
Maximum size of fillet along edges
S ince structural steelwork connections where a fillet weld is used along an edge would
involve material of not less than 6 mm in thickness, the maximum size of fillet weld is
equal to the thickness of the material (Figure 4) for steel connections.
Design throat thickness is discussed in Handbook 1.
TABLE 1
MINIMUM SIZE (LEG LENGTH) OF FILLET WELDS
T hickness of thickest part (t)
(millimetres)
Minimum size of fillet weld
(millimetres)
3
2t / 3
>37
3
> 7 10
4
> 10 1 5
5
> 15
6
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welding in structural steel connections, first edition
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FIGURE 3 TYPICAL APPLICATIONS OF FILLET WELDS IN STEELWORK CONNECTIONS
d esign guide 2:
welding structural steel connections, first edition
6
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FIGURE 4 FILLET WELD SIZE AND DETAILS
FIGURE 5 FILLET WELD SIZE IN LAPPED PLATES
The economics of fillet welding should be kept in mind at all times. In the horizontal fillet
positions, single run fillet welds are usually limited to a 6 or 8 mm leg size for most processes
(notably manual metal arc welding), although with other processes under certain conditions, a
10 mm or larger single run fillet is possible. If more than single run welding is required, the cost
of the weld increases significantly (Section 11.3).
Advantage may be taken of the increased penetration achievable with a fully automatic welding
process to reduce the size (but not the design throat thickness) of a fillet weld85% of the
penetration being considered as part of the design throat thickness. The viability of the welding
procedure must be demonstrated by means of a macro test. Such automatic processes are
however not usually used in fabricating steel connections (generally being used to fabricate
sections) so the benefit of this allowance is not usually realised in connections.
d esign guide 2
welding in structural steel connections, first edition
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3
TYPES OF WELD
3.3
Butt welds
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A butt weld is one in which the weld metal lies within the outline in cross section of the part
connected. Butt welds can have a variety of preparations which reflect the shape to which the
plate or element edge is prepared in order to accommodate the weld. Weld preparations
allowed by AS/NZS 1554.1 (Ref. 7) are shown in Figure 6. Butt welds can be made from one
side (single) or both sides (double).
FIGURE 6 TYPES OF BUTT WELDS (after Ref. 9)
Typical applications in structural steel connections are shown in Figure 7.
d esign guide 2:
welding structural steel connections, first edition
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FIGURE 7 TYPICAL APPLICATIONS OF BUTT WELDS
IN STRUCTURAL STEEL CONNECTIONS
d esign guide 2
welding in structural steel connections, first edition
9
Butt welds can be either:
(a)
complete penetration which has weld metal over the full depth of the element being
connected. Such welds usually require access from both sides so that weld metal can be
placed on the back side of the joint which fuses with weld metal deposited from the front
side of the joint; or
(b)
incomplete penetration which has weld metal over only part of the depth of the element
being connected.
Most butt welds in structural steel connections are complete penetration butt welds.
AS/NZS 1554.1 (Ref. 7) contains the following provisions for butt welds in Clause 3.2.
Size
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Complete penetration, butt joint
thickness of thinner part
Complete penetration, tee joint
thickness of part that butts adjacent face of the other part
Incomplete penetration
Minimum depth to which the weld extends from its face
into the joint, exclusive of reinforcement
Effective length
D efined as the length of continuous full size weld, excluding any weld on run-on and run-off
tabs or if tabs are not present any length of weld which is not full size. Extension (run-on/runoff) bars are often provided in order to ensure a sound weld at the ends of the total length of
weld.
E ffective area
Defined as the product of effective length and design throat thickness.
Design throat thickness is defined in Handbook 1.
Figure 8 illustrates the use of extension (run-on/run-off) bars and backing bars in a welded
splice or welded moment connection. Such bars are usually removed once welding is
completed.
Figures 9 and 10 show the terminology commonly used for butt welds.
d esign guide 2:
welding structural steel connections, first edition
10
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FIGURE 8 EXAMPLES OF USE OF RUN-OFF PLATE, BACKING BAR, EXTENSION PLATE
(after Ref. 11)
FIGURE 9 TERMS APPLICABLE TO FULL PENETRATION BUTT WELDS
FIGURE 10 TERMS APPLICABLE TO PARTIAL PENETRATION BUTT WELDS
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welding in structural steel connections, first edition
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3
TYPES OF WELD
3.4
Edge preparations
F illet welds do not require any edge preparation other than that the cut material complies with
Clause 14.3.3 of AS 4100 (Ref. 1).
The reason for having to shape or prepare the plate edge in a butt weld is to enable the welding
arc to access the weld through the thickness of the joint. The depth of plate preparation
depends on the weld used in the joint.
An ideal edge preparation has the following features: (Ref. 9)
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1.
It provides access throughout the depth of the weld to ensure the deposition of sound
weld metal that will be properly fused to the parent metal and to the previously deposited
weld metal. It also allows cleaning of the weld between passes.
2.
It minimises the volume of deposited weld metal so as to achieve economy and reduce
the subsequent joint distortion caused by shrinkage of the cooling metal.
3.
It minimises the cost of edge preparation. Bevel and V edge preparations are
consequently preferred (Figure 6).
4.
It has sufficient tolerance to accommodate the variations in fit that are likely to occur in
practice.
5.
It does not lead to notches or discontinuities in the resulting weld.
The selection of the edge preparations is made by the fabricator to suit the welding equipment,
materials handling methods, access, and welding procedures that are available. The
dimensions of the edge preparation are selected to meet the welding parameters to be used
(electrode, amperage, speed).
The choice between single or double edge preparation depends on:
a ccess;
e ase of turning the structural elements;
plate or element thickness;
distortion control method employed.
Bevel and V edge preparations can be flame cut, plasma cut or (rarely) machined. J and U
preparations are required to be machined but have the advantage of reducing weld volume and
thus reducing distortion. Terms used for a weld edge preparation are shown in Figure 11.
FIGURE 11 WELD EDGE PREPARATION TERMS
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welding structural steel connections, first edition
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3
TYPES OF WELD
3.5
Prequalified joint preparations
AS/NZS 1554.1 (Ref. 7) requires that the welding procedure, which includes the joint
preparations, be qualified before any welding commences, (see Section 7.1 of this Design
Guide).
Joint preparations may be deemed to be prequalifiedmeaning that no testing of the joint
preparation is required. AS/NZS 1554.1 allows certain joint preparations to be deemed
prequalified provided that the welding process and welding consumables used comply with the
recommendations of the consumables manufacturer.
Prequalified joint preparations are specified in AS/NZS 1554.1 as follows:
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complete penetration butt welds, Clause 4.5.2 and Table E1;
incomplete penetration butt welds, Clause 4.5.3 and Table E2;
fillet welds, Clause 4.5.4 and Table E3;
w elds in hollow section members, Clause 4.5.5 and Table E4.
Reference 8 notes that:
p requalified joint preparations can produce satisfactory welded connections even for
comparatively poor workmanship;
prequalified joint preparations do not represent the best that individual welding processes
can achieve. Substantial savings in terms of productivity can be achieved by varying from
the dimensions nominated for the prequalified joint preparations;
a fabricator may well elect to use a non-prequalified joint preparation and qualify the
procedure as discussed in Section 7.1 of this Design Guide.
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welding in structural steel connections, first edition
13
3
TYPES OF WELD
3.6
Standard weld symbols
Standard symbols are used to denote a number of details about a weld on drawings. Such
symbols are described in detail in AS 1101.3 (Ref. 13). The construction of the welding symbols
is summarised in Figure 12.
The following points should be noted in connection with the construction and use of welding
symbols: (Ref. 9)
The reference line is drawn in the horizontal direction, i.e. parallel to the horizontal axis of
the drawing.
2.
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1.
The arrow points to the weld(s) or welded joint being described.
3.
The fillet weld symbol is a small isosceles triangle based on the reference line and having
its vertical side to the left.
4.
The single-bevel weld symbol is a 45 V with its apex to the reference line and its vertical
leg to the left.
5.
The double-bevel and double-V weld symbols have their legs at 60 to each other.
6.
Symbols and notations referring to the arrow side of the joint are placed below the
reference line; those referring to the other side of the joint are placed above. Arrow side is
meant to describe the side of the joint to which the arrow points.
7.
In the case of butt welds where only the one plate edge is prepared and the other is left
square, the symbol arrow is cranked and is made to point towards the plate that has the
bevel.
Basic weld symbols are given in Figure 13, and supplementary welding symbols are given in
Figure 14.
Examples of the use of weld symbols are given in Reference 9.
Weld symbols rarely appear on structural engineering drawings these days but they should
appear on shop detail drawings (Ref. 9).
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FIGURE 12 CONSTRUCTION OF A WELDING SYMBOL (after Ref. 9)
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FIGURE 13 BASIC WELDING SYMBOLS (after Ref. 9)
FIGURE 14 SUPPLEMENTARY WELDING SYMBOLS (after Ref. 9)
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4
WELDABILITY OF STEEL
The weldability of a steel is a measure of the ease of producing a crack-free and sound welded
connection. The selection of an electrode to use in welding should be matched to the chemistry
of the steel.
Steel to be used in welded construction must be able to tolerate the rapid heating and cooling
which accompanies arc welding, without undergoing significant changes in the metallurgical
properties and without allowing cracking to occur.
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As a weld cools, it develops residual shrinkage strains that can approach the yield strain.
Chemical composition, grain size, and thickness of the steel affect both ductility and notch
resistance.
The major influences on weldability are:
(a)
Chemical compositionmeasured through the calculation of a carbon equivalent since
the most important element affecting weldability is carbon. Weldability is enhanced as the
carbon equivalent decreases.
(b)
Grain sizeweldability is enhanced by finer grain size.
(c)
Thicknessweldability is enhanced as thickness decreases because thicker plates
extract heat and quench the weld more rapidly.
Steel weldability is discussed in detail in Reference 14.
Australian standards for structural steels that are weldable specify:
chemistry
s trength
n otch toughness
occurrence of inclusions/laminations
resistance to lamellar tearing
c orrosion resistance (weather-resisting steel)
Steels used in connections and members at connections in Australia are weldable if they
comply with the following Australian Standards:
AS 1163
(Ref. 15)
AS/NZS 3678
(Ref. 16)
AS/NZS 3679.1
(Ref. 17)
AS/NZS 3679.2
(Ref. 18)
These are the standards specified in AS 4100 (Ref. 1) and are among the standards specified in
AS/NZS 1554.1 (Ref. 7).
Chemical analysis of a heat of steel is made during the processing and after the heat has been
tapped into a ladle. The heat analysis is used to compile a mill test report which can be supplied
to a customer upon request by way of a mill certificate. The mill certificate should indicate
compliance with the relevant Standard.
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5
WELDING PROCESSES
5.1
Introduction
W elding in structural steel connections is undertaken mostly by the fusion welding process, the
most common of which are the arc welding processes:
manual metal arc welding
(MMAW)
g as metal arc welding
(GMAW)
f lux cored arc welding
(FCAW)
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Other common fusion welding processes used for general fabrication are submerged arc
welding, stud welding, electro-gas welding, electroslag welding, flash butt welding, thermit
welding.
A fusion weld is one in which the heat of the process produces melting in the joint. Filler metal
may or may not be added. The properties of the weld are controlled by the metallurgical
changes that occur during solidification of the weld metal and during the heating and cooling
cycles in the heat affected zone.
Detailed information on fusion welding and arc welding may be found in References 5, 10 and
12.
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5
WELDING PROCESSES
5.2
Fusion welding process
F usion welding processes have the following features in common (Ref. 19).
The electrode and work piece are connected to opposite sides of the power supply; an arc
is struck between the electrode and the work piece, releasing heat energy.
2)
This heat energy melts the surface of the work piece, the tip of the electrode if it is
consumable and any flux that may be used. The metallic components of these molten
elements form a weld pool, which is held together by electromagnetic and surface tension
forces.
3)
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1)
The edges of this molten weld pool are on the point of solidification. As the electrode is
moved it draws the arc centre and weld pool with it. Semi-solid metal on the boundary of
the weld pool remains behind, fusing with the parent metal and forming a weld bead.
4)
The arc, weld pool and hot weld bead must be protected from the atmosphere to prevent
oxidation of the weld metal. In some processes that is achieved by providing an inert
gaseous atmosphere; in others a flux is used, and this is a mixture of compounds that has
to fulfil several functions. When heated, parts of it form a gaseous envelope to protect the
arc and weld pool; some parts may be drawn into the weld pool to provide necessary
alloying additions and the remainder of the melted components will form a slag over the
deposited weld bead. This serves both to protect the bead and control its shape.
The fusion welding process must supply sufficient heat to effect fusion of the parts to be joined,
must be efficient and able to be used in a variety of welding positions if possible and be able to
effect a weld such that the properties of the weld are adequate in terms of design strength and
fracture toughness (after Ref. 10).
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5
5.3.1
WELDING PROCESSES
5.3
Terminology
Weld metal (based on Ref. 5)
W eld metal is material that has fused and solidified during the welding process. It consists of a
mixture of fused base material and filler metal supplied by the electrode. It will have an as-cast
structure unless subsequently reheated. Its mechanical properties will vary in different
directions due to the solidification process.
5.3.2
Partially mixed weld metal (based on Ref. 5)
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T he mixing of filler and fused base material may be incomplete where melting and solidification
occur rapidly. This usually occurs close to the fusion boundary.
5.3.3
Fusion (boundary) line
Boundary of the weld pool.
5.3.4
Heat-affected zone (based on Ref. 5)
The heat-affected zone (HAZ) is base material which is affected metallurgically by the heat of
the welding process but is beyond the fusion boundary. The size and properties of the HAZ are
related to the size of the weld pool, higher arc energy leading to wider HAZ.
The metallurgical changes that occur in the HAZ depend on the material, the peak temperature
and the cooling rate. The HAZ is usually harder and less ductile than the base material in
structural steel. Cracking in the HAZ is possible.
Material beyond the HAZ is unaffected by welding although it can contain residual stresses.
5.3.5
Multi-run welds (based on Ref. 5)
S ubsequent weld runs modify the HAZ from previously deposited weld runs. Multi-run weld
metal has significantly better toughness and ductility compared to single-run weld metal, due to
the extra heating cycles refining and tempering the grain structure in the previously deposited
weld metal and HAZ zones.
FIGURE 15 STRUCTURE OF A SINGLE PASS WELD (Ref. 5)
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5
WELDING PROCESSES
5.4
Manual metal arc welding
Basic features of the Manual Metal Arc Welding process are (Figure 16):
being a manual process quality is very dependent upon the skill of the operator;
2.
oldest welding process and slowest;
3.
widely used by fabricators for welding connection elements;
4.
electrode consists of a core wire surrounded by flux;
5.
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1.
the arc is struck by scraping the end of the electrode on the earthed work piece and
withdrawing the tip slightly until steady arc conditions of current and arc voltage are
achieved. The electrode needs to be held at this gap while the weld is completed;
6.
electrodes are typically 200 mm to 450 mm long so new electrodes must be fitted at
regular intervals;
7.
flexible welding process able to be used in all welding positions and also used extensively
for field welding because of its low sensitivity to wind.
FIGURE 16 MANUAL METAL ARC WELDING (MMA) (Ref. 23)
This process may also be referred to as stick welding (due to the use of stick electrodes) or
shielded metal arc welding (USA term).
Electrodes for manual metal arc welding are covered by AS/NZS 1553.1 (Ref. 20) and are
discussed in detail in Section 6.1 of this Design Guide. Electrode diameters can vary from
1.6 mm to 10 mm, although 2.4 mm to 6 mm are the most common (Ref. 5).
The flux coating can have a variety of constituents (see Ref. 5), and performs several functions
when it is melted in the arc as follows (after Ref. 10):
(a)
stabilises the arc;
(b)
provides the arc and molten weld pool with a gaseous envelope to prevent the pick-up of
oxygen and nitrogen from the atmosphere;
(c)
produces a slag over the hot deposited weld bead to protect it from the atmosphere;
(d)
produces a slag to form the weld bead shape in the welding position (flat, horizontal,
vertical, overhead) with adequate slag detachability;
(e)
adds alloys where necessary to the weld metal;
(f)
provides the necessary slag/weld metal reactions;
(g)
controls the deposition rate.
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5
WELDING PROCESSES
5.5
Gas metal arc welding and flux
cored arc welding
Both Gas Metal Arc and Flux Cored Arc Welding use a similar principle and equipment but are
usually considered to be separate processes. In both processes, continuously fed wire is melted
in an arc struck between the tip of the wire and the work piece (Ref. 5).
With Gas Metal Arc Welding (GMAW) the weld pool is protected from oxidation by a shielding
gas, which is delivered to the weld through the welding gun which feeds the wire. The wire is
solid and uncoated and is fed from a roll to the gun (Figure 17).
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Flux Cored Arc Welding (FCAW) uses a hollow wire with a flux in the central core that provides
protection to the molten weld metal (Figure 18) . FCAW may or may not use a shielding gas
(gas shielded or self shielded respectively). Self shielded would be used for site welding.
These two processes are usually in semi-automatic mode when used to weld connection
elements whereby the gun is held by a welder and moved along the weld.
Figures 17 and 18 (from Ref. 23) illustrate the principles of the two methods.
FIGURE 17 SCHEMATIC DIAGRAM GAS METAL ARC WELDING (Ref. 23)
FIGURE 18 SCHEMATIC DIAGRAM FLUX CORED ARC WELDING (Ref. 23)
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22
G MAW is also termed metal inert gas welding (MIG) where an inert gas such as argon is used
and CO 2 welding where carbon dioxide is used as the shielding gas.
Both processes eliminate the stop/start problem with MMAW due to the use of a continuous
electrodehence productivity is higher and a potential source of weld discontinuities is
reduced.
Electrodes for GMAW are covered by AS/NZS 2717.1 (Ref. 21) and are discussed in Section
6.2.
Electrodes for FCAW are covered by AS 2203.1 (Ref. 22) and are discussed in Section 6.3.
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Equipment and process variables for these processes are discussed in more detail in
Reference 5.
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23
5
WELDING PROCESSES
5.6
Summary of characteristics of
welding processes
TABLE 2
CHARACTERISTICS OF WELDING PROCESSES (after Ref. 23)
P rocess
Characteristics
S olid wire electrode,
450 mm long approx
F lux coating on
electrode
D eposition rate 0.5
1 kg/hour. Operating
factor 20%. High iron
powder electrodes can
improve deposition rate
Advantages
Disadvantages
F lexible process;
equipment able to get
into difficult spaces;
able to weld in all
positions.
M anual process
S hort length of
electrodefrequent
stopping to change
electrode
S uitable for field
welding
S implicity of equipment
L ow deposition rate
compared to other
processes
S uitable for a wide
range of materials
H ighest likelihood of
minor defects
16
M anual
Metal Arc
Welding
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Fig.
No.
P ortability of equipment
R equires more skilled
welders
H igh deposition rate
D ifficulty in access
O pen arc, easily guided
H ollow metal tube
electrode
O ut of position
capability
S hielding gas (if used)
is wind sensitive
F lux in tube electrode
I mproved penetration
G as (if used) either
carbon dioxide or inert
C ontinuous electrode
feeding
A utomatic/semiautomatic available
A daptable to a wide
variety of applications
17
G as
Shielded
Metal Arc
Welding
M ay or may not be gas
shielded
18
F lux
Cored Arc
Welding
G asless process suited
to site welding
S uitable for welding a
wide variety of steels
S hielding gas is wind
sensitive
H igh deposition rate
D ifficulty in access
I mproved penetration
S emiautomatic hand
held or automatic
L imitations in control of
arc characteristics
V ersatile process
suitable for most
applications
A ble to weld light metal
(dip transfer mode)
N o slag
C an be used on out-ofposition joints
S olid wire electrode
S hielded by gas
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5
WELDING PROCESSES
5.7
Welding positions
FIGURE 19 WELDING POSITIONS FOR PLATE BUTT WELDS (Ref. 5)
FIGURE 20 WELDING POSITIONS FOR PLATE FILLETS (Ref. 5)
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6
WELDING CONSUMABLES
6.1
Manual metal arc welding
C overed electrodes for MMAW are solid or tubular rods 200 mm to 450 mm long with an
extruded or dipped flux coating (Ref. 5). They should comply with AS/NZS 1554.1 (Ref. 20).
Such electrodes are designated as follows in AS/NZS 1553.1 (Ref. 20).
EXXXX
where
E
indicates electrode
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first two digits XX indicates approximately one tenth of the minimum weld metal
tensile strength, as follows:
41410 MPa
48480 MPa
55550 MPa
third digit X
indicates suitable welding positions (Section 5.7)
1all positions
2flat and horizontal positions
4vertical down position
fourth digit X
flux covering type
0, 1 cellulosic type
2, 3 rutile type
4
iron powder type
6, 8 hydrogen controlled
Detailed coverage of the properties of the various types of fluxes
may be found in Reference 5.
The design engineer only needs to specify E41XX, E48XX or E55XX for connection details on
structural drawings, thus leaving the selection of the specific electrode to suit the preferred
welding position and the flux covering to the fabricator.
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6
WELDING CONSUMABLES
6.2
Gas metal arc welding
S olid wires for GMAW are available in diameters from 0.6 mm to 1.6 mm (Ref. 5). For carbonmanganese steels, the wire is often copper-coated in order to provide corrosion protection to
the wire and to improve current pick-up. Copper-free wire is also available. Wires can have a
variety of chemical composition according to the composition of the steel to be welded and the
shielding gas to be used (Ref. 5).
GMAW wire classification to AS/NZS 2717.1, is as follows (Ref. 21):
ESXGC/M WXXX (shortened version)
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where:
ES
electrode solid
X
wire composition term
GC/M torch gas, C = carbon dioxide, M = mixed
W
deposited weld metal
XX
one tenth of the minimum weld metal tensile strength
40400 MPa
50500 MPa
X
charpy impact value
The design engineer only needs to specify the WXXX number required for connection details on
structural drawings, thus leaving the selection of the remainder of the parameters to the
fabricator.
Shielding gases may be
inert
(argon, helium)
active
(oxygen, carbon dioxide)
mixture
(usually argon based)
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6
WELDING CONSUMABLES
6.3
Flux cored arc welding
Cored wire is manufactured from metal strip or tube and filled with dry powder ingredients.
Diameters are 1.2, 1.6, 2.4 and 3.2 mm (Ref. 5).
The core material contains alloying elements, deoxidisers, slag formers and shielding gas
producing compounds (Ref. 5). Most flux-cored wires also require a shielding gas, although selfshielded wires have major advantages (Ref. 5).
There are two main classes of wire (Ref. 5).
r utile
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basic flux
Electrodes for FCAW are designated as follows in AS 2203.1 (Ref. 22) (shortened version).
ETX GXp/n WXXX
where:
ET
electrode, tubular
X
either P all positional
D flat and fillet only
S single pass only
GX
gas
p/n
Polarity/no polarity
XX
one tenth of the minimum weld metal tensile
strength
GC carbon dioxide
GN no gas
GM mixed gas
40400 MPa
50500 MPa
X
charpy impact value
The design engineer only needs to specify the WXXX number required for connection details on
structural drawings, thus leaving the selection of the remainder of the parameters to the
fabricator.
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6
WELDING CONSUMABLES
6.4
Prequalified welding
consumables
Prequalified welding consumables are nominated in AS/NZS 1554.1 (Ref. 7). They are
considered prequalified because they give deposited weld metal that has mechanical properties
equivalent to those of the parent material when using any of the welding procedures permitted
by AS/NZS 1554.1 (Ref. 7).
Mechanical properties matched prequalified by electrodes are:
t ensile strength
yield strength
ductility
h ardness
notch toughness (Ref. 8)
Table 4.6.1 (B) of AS/NZS 1554.1 (Ref. 7) groups steels complying with Australian Standards
into types 1 to 8 depending upon their mechanical properties. Table 4.6.1(A) of AS/NZS 1554.1
lists the welding consumables to Australian Standards that are to be used for each steel type in
order to be considered prequalified.
Table 3 summarises the prequalified welding consumables for the three common welding
processes used in steelwork connections for steel grades to AS/NZS 3678 (Ref. 16) and
AS/NZS 3679 (Ref. 17 and 18).
TABLE 3
PREQUALIFIED WELDING CONSUMABLES
S teel grade in
AS/NZS 3678
(Ref. 16)
AS/NZS 3679
(Ref. 17, 18)
S teel Type
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W eld metal classification
M anual Metal Arc AS/NZS 1553.1
(Ref. 20)
Flux coredAS 2203.1
(Ref. 22)
C lassification
Grade
Gas Metal Arc
AS/NZS 2717.1 (Ref. 21)
2 00, 250, 300
1
E41XX, E48XX
0 and 1
W40X, W50X
250L0
2
E41XX, E48XX
2
W402, W502
250L15, 300L15
3
E41XX, E48XX
3
W403, W503
350, WR350, 400
4
E48XX, E41XX
0 and 1
W50X, W40X
350L0, WR350L0
5
E48XX, E41XX
2
W502, W402
350L15, 400L15
6
E48XX, E41XX
3
W503, W403
N OTE: See expanded version of this table in AS/NZS 1554.1 (Ref. 7).
W here base materials or welding consumables are not to the Australian Standards listed, then
prequalification is not possible and special welding procedures qualification tests are required to
be undertaken using the methods specified in AS/NZS 1554.1 (Ref. 7)see Section 7.3 of this
Design Guide.
Reference 5 (Section 1.3.5) deals at length with the difficulties encountered when imported
steel is used or substitution of grades is envisaged.
More details on this issue may be found in Reference 8.
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7
WELDING PROCEDURES
7.1
Qualification of a welding
procedure
A w elding procedure encompasses the following variables:
P rocess
Electrode specification
Electrode classification
E lectrode diameter
E lectrical characteristics (ac, dc+, dc)
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Base metal specification
M inimum preheat and interpass temperature
W elding current (amperage)/wire-feed speed
A rc voltage
Travel speed
Position of welding
Postweld heat treatment
Shielding gas type and flow rate
Joint configuration
Weld preparation details
S equence of weld passes
Since all these variables can affect the soundness of the resulting weld and its mechanical
properties, it is critical that all the values actually used for a specific weld are appropriate.
AS/NZS 1554.1 (Ref. 7) requires that the welding procedure be qualified before welding
commences (Clause 4.1.1). This Clause also requires that the fabricator establish a welding
procedure and list the applicable parameters on a welding procedure qualification record
(WPQR) which shall be held and shall be available for examination. A suitable form is given in
Appendix C of AS/NZS 1554.1 (Ref. 7).
A welding procedure specification (WPS) is developed from the WPQR and made available to
the welder during fabrication. A suitable form for a WPS is given in Appendix C of
AS/NZS 1554.1 (Ref. 7). Such a form would also be issued to the welding supervisor in the
fabrication shop and to anyone inspecting the weld.
The WPS is the primary means of communicating to all the parties involved how the welding is
to be performed.
The qualification of a welding procedure in conformity with AS/NZS 1554.1 (Ref. 7) involves the
following steps:
(i)
qualification of the joint preparation;
(ii)
qualification of the materials;
(iii)
qualification of the consumables;
(iv)
qualification of the welding parameters.
AS/NZS 1554.1 (Ref. 7) also requires that the welding supervisor and the welder both be
qualified (Clause 4.12). The fabricator remains responsible for ensuring that the correct
procedure is followed and ensuring compliance with AS/NZS 1554.1.
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30
Methods of qualifying a welding procedure are specified in Clause 4.2 of AS/NZS 1554.1
(Ref. 7). These are as follows:
a prequalified procedure (discussed in Section 7.2 of this Design Guide);
(b)
documentary evidence of relevant prior experience by the fabricator. This would be
expected to include a WPQR, records of procedure qualification, records of testing,
records of macro specimens;
(c)
production of a test piece which is tested in accordance with Clause 4.7 of
AS/NZS 1554.1, the welding of the test piece having involved the same parameters that
are to be used for the welding in the project;
(d)
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(a)
preparation of a special test piece which simulates the weld to be made and which is
tested in accordance with Clause 4.7 of AS/NZS 1554.1;
(e)
destructive testing of a prototype joint or component;
(f)
adoption of a welding procedure already qualified by another fabricator, subject to
restrictions specified in Clause 4.4 of AS/NZS 1554.1.
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7
WELDING PROCEDURES
7.2
Prequalified welding procedure
A prequalified welding procedure in terms of AS/NZS 1554.1 involves:
(a)
use of a prequalified joint preparation (see Section 3.5 of this Design Guide);
(b)
use of prequalified materials, comprising:
parent material
AS/NZS 1554.1);
(ii)
backing material complying with Clause 2.2 of AS/NZS 1554.1;
(iii)
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(i)
to
specified
Australian
Standards
(see
Clause
2.1
of
electrodes, filler wires, flux, shielding, gas complying with nominated Australian
Standards (see Clause 2.3 of AS/NZS 1554.1);
(c)
consumables complying with Clause 4.6 of AS/NZS 1554.1 and matched to parent
material as discussed in Section 4.6 of this Design Guide;
(d)
workmanship and welding techniques complying with AS/NZS 1554.1;
(e)
documentary evidence of a macro test of the completed weld, usually obtained from a
run-on or run-off piece.
Hence, a welding procedure can be prequalified by using a number of prequalified parameters,
by making a test weld and by examining a macro specimen of the resulting weld.
The macro test involves taking a transverse slice through the weld and then grinding and
polishing it so that no damage is caused to the sample. The test piece is then acid etched to
reveal the grain structure. The intention is to determine if the weld contains defects but the
macro test will also show up the weld runs used.
Mechanical testing of welds produced by a prequalified welding procedure is not required
because there is very little risk that the procedure will not produce a satisfactory weld.
A prequalified welding procedure may not be the most productive procedure for a particular
application, in which case a fabricator may elect to qualify a more productive procedure.
Some portability of qualified welding procedures between fabricators is permitted by Clause 4.4
of AS/NZS 1554.1 (Ref. 7).
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7
WELDING PROCEDURES
7.3
Qualification by testing
A w elding procedure can be qualified in terms of AS/NZS 1554.1 (Ref. 7) by producing a special
test piece and subjecting the welded test piece to nominated tests. The welding procedure
becomes qualified if it complies with all the requirements of Clause 4.7 of AS/NZS 1554.1
(Ref. 7).
The tests that might be required are:
macro test
transverse butt tensile test
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bend test
c harpy impact test
h ardness comparison test
h ardness test for welded heat-affected zone
All these tests are covered by parts of AS 2205 (Ref. 24). They are described briefly in
References 6 and 8.
Table 4.7.1 of AS/NZS 1554.1 (Ref. 7) nominates which tests are required according to the
following parameters:
w eld category (see Section 9.1 of this Design Guide)
p requalified/not prequalified consumables
p requalified/not prequalified preparations
Where a welding procedure is qualified by testing there is no necessity to employ prequalified
consumables or prequalified materials or prequalified preparations. Thus, a fabricator may
qualify a welding procedure which is directly suited to a particular application in order to
maximise productivity.
The testing is intended to (Ref. 8):
(a)
ensure adequate penetration and freedom from defects when using non-prequalified
preparations and consumables;
(b)
ensure adequate weld metal strength and ductility when using non-prequalified
consumables;
(c)
ensure freedom from excessive HAZ hardness when the heat input/preheat requirements
of AS/NZS 1554.1 (Ref. 7) are not observed.
(d)
Affirm that the notch toughness of the weld metal from non-qualified consumables when
fabricating notch toughness-tested plate is satisfactory.
A full record of the testing should be retained by the fabricator so that it can be referred to if
required. A WPQR should be used for this purpose (Section 7.1).
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7
WELDING PROCEDURES
7.4
Requalification of welding
procedures
Clause 4.11 of AS/NZS 1554.1 (Ref. 7) considers two scenarios for changes in an essential
variable of a welding procedure in assessing what testing is required in order to requalify a
welding procedure.
Where the change is minoras defined by Table 4.11 (C) of AS/NZS 1554.1only a macro test
is required to confirm that the revised welding procedure will still produce a satisfactory weld.
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Where the change is majoras defined by Table 4.11 (A) or (B) of AS/NZS 1554.1
requalification of the welding procedure is required.
A comparatively wide variation in welding parameters is permitted without requalification being
required (Ref. 8). By judicious selection of the parameters which are used for qualification of a
welding procedure, a fabricator can qualify that procedure for a wide range of operations.
A detailed discussion of Tables 4.11 (A) to (C) is contained in Reference 8.
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8
8.1
Edge preparation
8.2
8.1
WORKMANSHIP
Assembly
Edge preparation
Edge preparation is covered by Clause 5.1 of AS/NZS 1554.1 (Ref. 7).
Thermally cut surfaces which are to be incorporated into a weld are required to have a surface
roughness no worse than that given by Class 3 in Reference 25.
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Clause 5.1.1 of AS/NZS 1554.1 requires as follows:
Surfaces and edges to be welded shall be uniform and free from fins, tears, cracks and
other defects that would adversely affect the quality or strength of the weld. Surfaces to
be welded and surfaces adjacent to a weld shall also be free from loose or thick scale,
slag, rust, grease, paint or other foreign matter that could prevent proper welding.
Millscale that withstands vigorous wire brushing, rust-inhibiting coatings, antispatter
compound and weld-through primers that do not interfere with weld quality or the welding
operation may remain.
8.2
Assembly
Assembly is covered by Clause 5.2 of AS/NZS 1554.1 (Ref. 7), wherein requirements for the
alignment of parts to be joined by welding are specified. Alignment requirements may also be
found in Section 14 of AS 4100 (Ref. 1) or on the structural drawings.
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8
WORKMANSHIP
8.3
Preheat
M ost structural steel is thermally cut without preheat, which is usually only used to avoid
quench cracking in the heat affected zone when thermally cutting heavy sections of high
hardenability steels (Ref. 7). Preheat procedures for cutting are contained in Reference 25.
Preheating before welding is required in order to avoid heat affected zone cracking by slowing
the cooling rate. It is only required for certain combinations of steel grade, material thickness
and welding parameters. Clause 5.3 of AS/NZS 1554.1 (Ref. 7) contains the relevant provisions
which are derived from Reference 14.
Generally, the procedure required of the fabricator is as follows (after Ref 8):
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(a)
Identify the steels being welded and the Weldability Group Number from Table 5.3.4 (A)
of AS/NZS 1554.1. The higher the carbon equivalent, the more the steel is prone to
cracking and the higher the group number. If steels of more than one group number are
being welded, choose the highest number. (An alternative is to calculate the carbon
equivalent based on a chemical analysis of the steel being used (Ref. 8)).
(b)
Calculate the combined thickness of the joint. The higher the quench severity of the joint
the more likely cracking will occur, and the higher is the combined thickness.
(c)
Using Figure 5.3.4 (A), of AS/NZS 1554.1, determine the Joint Weldability Index for the
curve closest to the intersection of the combined thickness and Weldability Group
Number.
(d)
Determine whether the welding process is Low hydrogen or not. Choose the relevant
Preheat Determination Diagram 5.3.4 (B) or 5.3.4 (C), from AS/NZS 1554.1.
(e)
Determine the lowest heat input which any pass will be welded at. Preheat temperature
can be determined from the relevant joint weldability curve.
Some HAZ cracking may still occur under conditions of extreme restraint (Ref. 8). Metal
hydrogen cracking in the weld may require additional preheating (Ref. 8).
A lower level of preheat than that calculated can be used if it can be demonstrated by qualifying
the procedure using the lower level of preheat (Ref. 8).
Examples of methods of calculating preheat are given in Reference 8.
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WORKMANSHIP
8.4
Tack welds
T ack welds are used to temporarily hold steel elements in place so that they can be welded in
accordance with the qualified procedure. Both temporary and permanent tack welds must be of
the same quality as the final welds in the structure. Unfortunately, there have been instances
where weld fracture has resulted from cracks originating at tack weld locations (Ref. 8).
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Limitations on tack weld minimum lengths are specified in AS/NZS 1554.1 in order to avoid the
situation where the welder merely applies a dob of weld metal to hold components together
during assembly. These dobs are invariably applied without preheat and are often already
cracked before being incorporated in the final weld (Ref. 8).
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8
WORKMANSHIP
8.5
Distortion and residual stress
Once a weld bead has been deposited and starts to cool, it solidifies and contracts both along
its longitudinal axis and transverse to that axis. This contraction induces residual stresses and
distortion.
Longitudinal shrinkage can cause slender elements to buckle and can cause bowing of the
fabricated element.
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Transverse shrinkage can produce both angular and out-of-plane distortions.
Distortion can be of considerable significance in general fabricationparticularly in the
fabrication of built-up sections or splicing of member lengths. It is generally of less significance
in the fabrication of connections. This is because the weld runs are generally short and
longitudinal shrinkage is rarely a problem.
Distortion in connections can have the following effects:
fit up between parts is not achieved;
local buckling strength may be reduced due to the resulting out-of-straightness;
i ncreased local stresses can reduce design capacity;
appearance may be affected.
In general, the control of distortion is in the hands of the fabricator who can use a number of
techniques to compensate for the distortion. These techniques include:
preset relevant elements;
r estraint during fabrication (use of strongbacks);
m odifying weld sequencing;
p eening;
post weld treatment (mechanical, heating).
There is no real guidance in Clause 5.7 of AS/NZS 1554.1 (Ref. 7) or in AS 4100 (Ref. 1) as to
control of distortion.
AS/NZS 1554.1 (Ref. 7) Clause 5.7.4 permits the following methods for the correction of
distortion:
m echanical means (hydraulic presses, local jacking, local wedging);
heat application;
controlled application of correcting weld runs;
c utting apart and rewelding.
Residual stress and distortion are discussed in more detail in References 6 and 10.
The structural steel connection design engineer can assist in reducing both distortion and
residual stresses by the following means:
u sing as few welds as possible;
u sing the smallest weld size required by the design requirements;
d istributing welds as equally as possible about the connection;
use intermittent fillet welds in lieu of full length fillet welds if possible.
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8
WORKMANSHIP
8.6
Cleaning and dressing welds
AS/NZS 1554.1 Clause 5.11 requires that slag be removed from all completed welds by wire
brushing or other suitable means. Tightly adhering weld spatter can remain unless required to
be removed for surface treatment or to allow non-destructive testing.
AS/NZS 1554.1 Clause 5.12 requires that butt welds that are required to be dressed flush shall
be finished so as to:
n ot reduce the thickness of the thinner base metal or weld metal by more than 0.8 mm or
5% of the thickness, whichever is lesser;
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n ot leave any reinforcement that exceeds 0.8 mm, remove any reinforcement on a contact
surface;
blend smoothly with the plate surfaces.
Dressing is normally only done for architectural reasons in connections rather than for structural
reasons.
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9
WELD IMPERFECTIONS
9.1
Weld categories
AS 4100 permits the use of two weld categories as follows:
SPstructural purpose
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GPgeneral purpose
The difference between these weld categories lies in the level of permissible imperfections
allowed by AS/NZS 1554.1 (Ref. 7). SP weld category has smaller permitted imperfections and
is accordingly more reliable than category GP. Once the permitted level of imperfections is
exceeded, the imperfections are classed as defects. These categories of weld cannot be
accepted under AS/NZS 1554.1 if the level of permitted imperfections is exceeded, unless it can
be demonstrated by a fracture mechanics assessment that the defects will not be injurious to
the performance of the structure (Section 9.4 of this Design guide).
The selection of weld category is at the discretion of the design engineer.
Clause 1.6 of AS/NZS 1554.1 (Ref. 7) contains the following provisions for the two weld
categories of AS/NZS 1554.1:
(a)
GP ( general purpose )GP to be generally selected where:
(i)
(ii)
the weld is stressed to not more than 50% of the relevant maximum permissible
stress as specified in AS 3990 (Ref. 26); or
(iii)
(b)
the weld is essentially statically loaded and designed to meet the appropriate
requirements of AS 4100 (Ref. 1);
the welding application is other than structural.
SP ( structural purpose )SP to be generally selected where:
(i)
the weld is essentially statically loaded and designed to meet the appropriate
requirements of AS 4100 (Ref. 1);
(ii)
the weld is stressed to more than 50% of the relevant maximum permissible stress
as specified in AS 3990 (Ref. 26); or
(iii)
the weld is subject to dynamic loading, within the limits stipulated in Clause 1.1 of
AS/NZS 1554.1.
Welds nominated as Category SP, but not complying with the requirements of that category
when inspected after fabrication, may be considered as Category GP welds, provided the
requirements of AS 4100 or AS 3990 are satisfied and the principal has agreed.
Types of weld imperfections are discussed in Section 9.3 of this Design Guide. Once a
imperfection exceeds a permitted level it becomes a defect and this is discussed in Section 9.4
of this Design Guide.
Reference 8 notes the following in relation to weld categories:
(a)
the level of permitted imperfection is set on the basis that parent materials and weld metal
have been selected to avoid the risk of brittle fracture, such as by using Section 10 of
AS 4100 (Ref. 1) and/or Appendix B of AS/NZS 1554.1 (Ref. 7);
(b)
the failure mechanism is that of ductile failure in tension;
(c)
the influence of any weld defects approximates to a loss of load-bearing cross-sectional
area in the weld of:
(i)
(ii)
(d)
5% category SP
10% category GP
AS/NZS 1554.1 depends on certain levels on inspection of the weld (discussed in
Section 9.2 of this Design Guide), both before and after welding;
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(e)
AS/NZS 1554.1 relies upon adherence to qualified welding procedures (discussed in
Section 7.1 of this Design Guide).
Most welded elements in structural connections will require SP weld category. The structural
drawings and/or specification are required to contain details of the weld size and weld category
(Clause 1.6.2 of AS 4100).
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In general, it is doubtful whether there is any cost saving in specifying GP category welds rather
than SP category welds (Ref. 6).
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WELD IMPERFECTIONS
9.2
Levels of inspection
T he suggested extent of non-destructive examination (NDE) for each weld category is contained
in Table 7.4 of AS/NZS 1554.1 (Ref. 7). A shortened version of this Table is contained in
Table 4.
TABLE 4
LEVELS OF NON-DESTRUCTIVE EXAMINATION (NDE)
E xtent of NDE expressed as a %
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W eld
category
V isual means
Other means
Visual scanning
Visual
examination
Magnetic particle
or liquid penetrant
Radiography or
ultrasonics
GP
100
5 to 25
0 to 2
Nil
SP
100
10 to 50
0 to 10
0 to 10
T he structural drawings and/or specification should contain details of the methods of nondestructive examination to be used and the extent of testing required (Clause 7.4 of
AS/NZS 1554.1).
Reference 6 notes that there can be considerable difference in the cost of non-destructive
examination of category GP and SP welds.
Note that all welds must be 100% visually scanned but that detailed visual examination should
only involve 5 to 50% of all welds while thorough examination by a variety of means may only
be carried out for 0 to 10% of welds. AS/NZS 1554.1 (Ref. 7) places a great deal of reliance on
getting the welding procedure correct as the primary means of producing satisfactory welds.
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WELD IMPERFECTIONS
9.3
Imperfection levels
AS/NZS 1554.1 (Ref 7) deals with imperfectionsbest described as a deviation from perfection.
The term imperfection is not defined in AS/NZS 1554.1. An imperfection only becomes a
defect if the imperfection exceeds the permissible levels of imperfection defined in Table 6.2.1
and 6.2.2 of AS/NZS 1554.1 (Clause 6.7).
The types of imperfections considered in Table 6.2.1 and 6.2.2 of AS/NZS 1554.1 are as
follows:
TABLE 5
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TYPES OF IMPERFECTION CONSIDERED IN AS/NZS 1554.1
T ype of weld
Possible imperfection
B utt weld
Crack
Inclusion
Lack of fusion or incomplete penetration
Undercut
Shrinkage grooves
Root concavity
Reinforcement
Excess penetration
Overlap
Toe shape
Surface porosity and internal porosity
Loss of cross-sectional area
Misalignment
F illet weld
Height of reinforcement
Undersize
Surface imperfections as butt welds
Loss of cross-sectional area
D iagrams illustrating some of these imperfections are shown in Figure 21 and Figure 22.
The permissible levels of imperfection are given in Table 6.2.2 of AS/NZS 1554.1 (Ref. 7) and
are discussed in detail in Reference 8. They are not repeated in this Design Guide.
Table 6.2.1 of AS/NZS 1554.1 deals with permissible levels of imperfections as determined by
Radiographic or Ultrasonic Examinations (see Sections 10.5 and 10.6 of this Design Guide
respectively).
Table 6.2.2 of AS/NZS 1554.1 deals with permissible levels of imperfections as determined by
Visual (Section 10.2), Magnetic Particle (Section 10.3) and Liquid Penetrant (Section 10.4)
Examination.
AS/NZS 1554.1 contained detailed provisions for:
c alculation of loss of cross-sectional area
treatment of aligned imperfections
treatment of overlapping imperfections
A commentary on the provisions of AS/NZS 1554.1 concerning permissible levels of
imperfections may be found at Reference 8.
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FIGURE 21 IMPERFECTIONS IN BUTT WELDS
Reference 5 classifies imperfections into the following categories:
(a)
Fusion flaws
incomplete fusion (sidewall, between weld runs)
incomplete penetration
(b)
Shape flaws
overfill
excessive fillet size
excessive cap height
overroll
undercut
misalignment
spatter
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(c)
Gas and slag entrapment flaws porosity
slag inclusions
(d)
Arc strikes
(e)
Cracking solidification cracks
hydrogen induced cold cracks
lamellar tearing
Solidification crack types include (Ref. 5)Figure 23 from Reference 5:
crater cracks
(ii)
longitudinal cracks
(iii)
narrow bead cracking
(iv)
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(i)
wide bead cracking
Cracking is also discussed in References 10, 12 and 27.
FIGURE 22 IMPERFECTIONS IN FILLET WELDS
FIGURE 23 SOLIDIFICATION CRACKS (from Ref. 5)
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9
WELD IMPERFECTIONS
9.4
Weld defects
I mperfections in excess of the permissible levels specified in Table 6.2.1 and Table 6.2.2 of
AS/NZS 1554.1 constitute defects. These tables should be consulted for details of the
permissible levels of imperfections.
The levels of permissible imperfections are essentially derived from what constitutes good
workmanship and experience of using AS/NZS 1554.1 since first published in 1975. The levels
of imperfection are also related to the restrictions discussed in Section 9.1 of this Design Guide
(Ref. 8) regarding weld categories.
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Reference 6 makes the following pertinent points in relation to the acceptance criteria of
AS/NZS 1554.1.
There are differences in the acceptance criteria for surface flaws between the two weld
categories, but these are only significant to the fabricator if the structure is all Category
GP. Where there is a mixture of SP and GP welds, the fabricator generally works to the
higher standard. Having two standards is confusing to welders. They have to be qualified
to meet the highest standard required for the work. Welders generally try to work to the
highest standard, and do not deliberately try only to just achieve the minimum standard.
The differences in acceptance standard between SP and GP welds are minor and of little
practical significance. Distinguishing between undercut depths of 1 and 1.5 mm is difficult
practically and seems of little significance from a structural viewpoint. Certainly, it is of no
significance when making the weld. Only one difference has practical significance to the
welder and that is the amount of excess weld metal (reinforcement). This is unrestricted
for GP welds and has easily achieved limits for category SP welds. Only poorly skilled
welders cannot achieve the standard. From an engineering viewpoint, excess weld metal
is undesirable only if it causes distortion, or alternatively if the weld bead height is such
that it causes acute notches at the bead toes. Why there is such a difference between the
two categories of welds is questionable.
Full-penetration butt welds have to be backgouged or ground to ensure freedom from root
defects. Because GP welds are not subject to internal inspection techniques, procedures
do not need to assure freedom from internal defects. In particular full-penetration butt
welds can be made without backgouging or back grinding, and this should allow
considerable savings. However, many fabricators do not follow this concept and will back
grind the root run of both SP and GP welds. This avoids the risk of a SP weld being made
to GP category. There is no difference in the procedure for making fillet and partial
penetration welds.
The designer of a structural steel connection will need to rely upon reports produced by a
Welding Inspection Service in order to know if the weld in a connection complies with
AS/NZS 1554.1. The levels of examination undertaken are generally those nominated in Table 4
of this Design Guide, so not every connection is examined except that 100% of all welding at all
connections should be at least visually scanned.
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WELD IMPERFECTIONS
9.5
Weld repairs
A w eld with defects exceeding the permissible levels of imperfections should be considered for
acceptance before a repair is undertaken.
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Clause 6.7 of AS/NZS 1554.1 (Ref. 7) allows that where a defect is not injurious to the
performance of a structure (and by implication a connection) then the defect need not be
repaired provided that the principal and fabricator agree. This would usually involve the
structural steel connection design engineer making an assessment of the design strength of the
weld after allowing for imperfections (usually on the basis of an estimate of the loss of crosssectional area) and/or carrying out a fracture mechanics assessment, using Reference 28 or
similar. Fracture mechanics assessments are best left to a specialist in the field.
Attempts to repair a weld with a defect can be fraught with difficulty and, in some cases, the end
result may be no better than the original defective weld. Repair welds can introduce local
residual stress which can lead to distortion and cracking (Ref. 5). Backgouging and repair of
welds is covered by Clause 5.8 of AS/NZS 1554.1. Under this Clause either part of all of the
weld is removed, the rewelding is carried out in accordance with AS/NZS 1554.1 and the
repaired weld reinspected to the same level as the original (defective) weld.
Clause 5.8 of AS/NZS 1554.1 allows the following repair methods:
m achining
g rinding
c hipping
g ouging (oxygen, air-arc, plasma)
Substantial removal (undefined as to extent) is not permitted by Clause 5.8 of AS/NZS 1554.1.
An alternative to repairing a defective weld is to replace it with a new fabricated piece. This is
often the best course when dealing with a defective weld in a connection as the problem is so
localised and relatively cheap to replace, unlike a weld in a fabricated member of many metres
in length.
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10
WELD INSPECTION
10.1 Introduction
D epending upon the application and the weld category, a weld may be specified to be inspected
by either:
visual examination (Section 10.2)
magnetic particle examination (Section 10.3)
liquid penetrant examination (Section 10.4)
radiographic examination (Section 10.5)
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ultrasonic examination (Section 10.6)
Reference 8 recommends that where only visual, and/or magnetic particle and/or liquid
penetrant examination is undertaken, that this be augmented by examination of the macro test
specimen from the procedure qualification (Section 7 of this Design guide).
Radiographic and ultrasonic examination are only appropriate for weld category SP and can
only be applied to butt welds in order to verify the internal integrity of a weld. The other three
methods can only identify surface imperfections.
Because the techniques involved are specialised, a welding inspection service with qualified
operators should be employed. Many fabricators rely on their own internal quality system to
carry out any welding inspections required.
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10
WELD INSPECTION
10.2 Visual examination
Visual examination is the first step in any weld evaluation process. Such examination is no
substitute for proper supervision of the welding while it is occurring.
Visual examination can be used to detect the following (Ref. 10):
s ize and shape of weld
correct weld preparation
c orrect fit-up
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r oot passes of multi-run welds
s urface cracks
undercut
s urface porosity
a ll welds nominated are actually in place
root concavity
o verlap
e xcess penetration
s hrinkage grooves
misalignment
slag removal
s patter
c leanliness of weld
Ideally, the welding supervisor will make regular visual examination before, during and at the
completion of welding. Either the welding supervisor or the welding inspector or both should
visually examine the completed weld.
There is no Australian Standard describing procedures for visual examination. Reliance is
placed on aids such as:
m irrors
m agnifying glasses
g auges
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WELD INSPECTION
10.3 Magnetic particle examination
M agnetic particle examination (MPE) is covered by Clause 6.5 of AS/NZS 1554.1 (Ref. 7) and is
required by that Clause to be carried out in accordance with one of the techniques specified in
AS 1171 (Ref. 29).
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The following description is taken from Reference 11, Section 8:
For magnetic particle testing, a magnetising current is introduced into the weldment to be
inspected as shown in Figure 24. The magnetic field induced in the work will be distorted
by any cracks, seams, inclusions, etc. located on or within approximately 2 mm of the
surface. A dry magnetic powder spread lightly on the surface will gather at such
discontinuities, leaving a distinct mark. These magnetically held particles then show the
size, location, and shape of the discontinuity. A liquid ink may also be used. This method
will detect surface cracks filled with slag or contaminants which dye penetrant could not
enter. Additionally, the powder may be picked up and preserved with clear tape, providing
accurate and detailed records of inspection results. However, this method requires
relatively smooth surfaces and while cleanup is easy, demagnetisation, when necessary,
may not be.
FIGURE 24 SCHEMATIC DIAGRAM OF MAGNETIC PARTICLE EXAMINATION
(from Ref. 11)
MPE can only be employed to detect imperfections on the surface of a weld or sub-surface
imperfections very close to the surface.
The surfaces need to be clean and free of grease. They are usually sprayed with a white, matt,
quick-drying paint to give contrast so that the magnetic pattern can be seen.
Methods of magnetisation are discussed in detail in Reference 6, as well as its application and
limitations. The technique is quick and sensitive, and relatively economic.
Fully trained technicians are required to carry out the examination.
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WELD INSPECTION
10.4 Liquid penetrant examination
Liquid penetrant examination (LPE) is covered by Clause 6.6 of AS/NZS 1554.1 (Ref. 7) and is
required by that Clause to be carried out in accordance with one of the techniques specified in
AS 2062 (Ref. 30).
The following description is taken from Reference 11, Section 8:
In penetrant testing, a red dye penetrant is applied to the work and penetrates any crack
or crevice open to the surface. After removing excess dye, a white developer is applied.
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'Where cracks are present, the red dye seeps through the developer, producing a visible
red image. This process is summarised in Figure 25.
'LPE may be used to detect tight cracks as long as they are open to the surface.
However, only surface cracks are detectable. Furthermore, deep weld ripples and
scratches may give a false indication when LPE is used.
FIGURE 25 SCHEMATIC DIAGRAM OF LIQUID PENETRANT EXAMINATION
(from Ref. 11)
LPE can only be employed to detect imperfections on the surface of a weld.
LPE is an economical and quick method of examination that does not require highly trained
technicians. The weld surface must be free of grease or oil which should be removed by
solvents.
Wide cracks produce a seepage or spread of the penetrant whilst sharp cracks often appear as
a series of dots in line which in time may link up to give a continuous line. Rounded surface
defects are easily recognisable and they are clearly observed because of the penetrant spread
(Ref. 10). Cracks as small as 0.2 mm can be detected (Ref. 6).
The method is also known as dye penetrant inspection.
More details of the method may be found in Reference 6.
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WELD INSPECTION
10.5 Radiographic examination
R adiographic examination (RE) is covered by Clause 6.3 of AS/NZS 1554.1 (Ref. 7) and is
required by that Clause to be carried out in accordance with AS 2177.1 (Ref. 31). Specific test
methods are prescribed according to whether the material thickness is less than 12 mm or equal
to or greater than 12 mm.
Either X-ray or Gramma-ray technology may be employed. The method uses a radioactive
source and a film process which produces a negative. The negative serves as a record of the
inspection.
RE can detect sub-surface defects such as: (after Ref. 11)
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porosity
s lag inclusions
voids
c racks
lack of fusion
but to be detected, the imperfection must be oriented roughly parallel to the radiation beam and
occupy about 1.5 percent of the metal thickness along the radiation beam.
RE can be difficult to interpret for:
c onnections with varying thicknesses
f illet welds
t ee joints
corner joints
The principle of the method is that where there is an imperfection more radiation passes
through it and affects the photographic film such that the area appears dark after being
developed. The principle of the method is shown in Figure 26.
Interpretation of radiographs requires extensive training, experience, knowledge of welding and
careful interpretation of the film. Access is required to both sides of a weld, the film being
placed on one side and the radiation source on the other side.
FIGURE 26 PRINCIPLES OF RADIOGRAPHIC EXAMINATION
(Ref. 19 and 10)
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It is necessary to check the sensitivity of the procedure during operation. This is carried out by
placing an image quality indicator (IQI) on the surface of the weldment being inspected. A
common type of IQI consists of wires of different diameters mounted side by side in a polythene
tag (Ref. 19). The sensitivity of the particular radiograph is defined as:
Smallest diameter of wire that is visible
100%
Thickness of weldment being radiograph ed
The IQI sensitivity must comply with Table 6.3.2 of AS/NZS 1554.1.
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X-rays have the advantage that the intensity of radiation can be varied, that it is more sensitive
and that, since the source can be switched off, it is only necessary to take safety precautions
during the exposure time rather than be concerned with continuous heavy shielding.
Gamma-rays have the advantage that the equipment is smaller, cheaper and more mobile than
the X-ray unit and that these rays have greater penetration than X-rays and can be used for
thicker sections (Ref. 19).
Detailed information on radiographic examination may be found in References 6 and 10.
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WELD INSPECTION
10.6 Ultrasonic examination
Ultrasonic examination (UE) is covered by Clause 6.4 of AS/NZS 1554.1 (Ref. 7) and is required
by that Clause to be carried out in accordance with AS 2207 (Ref. 32) or by an alternative
method of test acceptable to the principal.
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The following description is taken from Reference 11, Section 8.
Ultrasonic examination is analogous to radar and operates on a principle called pulseecho. A short pulse of high-frequency sound is introduced into the metal. The reflection of
this sound wave from the far end of the member and from any voids encountered along
the way may then be detected. Any reflections are displayed as pips on a cathode display
in which the horizontal grid represents the distance through the metal and the vertical
scale represents the area, and therefore the strength of the reflecting surface. The point
or origin of the sound wave can be readily moved around to check many orientations and
can project the wave into the metal at angles of 90, 70, 60, and 45.
UE can detect favourably oriented flat discontinuities but certain joint configurations limit the
use of UE and it is difficult to inspect component materials less than 8 mm thick. The technique
is not exact and is highly dependent on the skill and training of the operator and frequent
calibration of the equipment.
UE is more versatile, expedient and economical than RE but it does not provide a permanent
record except via a written report. UE can detect tight cracks that RE might not detect and can
provide information on the depth of an imperfection.
Probes can be either:
compression wave (employed normal to a surface)
s hear wave (employed at an angle to the surface)
Figure 27 (from Reference 19) illustrates examples of detection of an imperfection.
Detailed information on ultrasonic examination may be found in References 6, 8 and 10.
FIGURE 27 EXAMPLES OF IMPERFECTION DETECTION USING ULTRASONIC
EXAMINATION (Ref. 19)
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PRACTICAL CONSIDERATIONS
11.1 Clearances for welding
In order to deposit a satisfactory weld complying with AS/NZS 1554.1, the welder must have
sufficient room to manipulate the electrode and must have a clear view of the entire weld.
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There are configurations where although a welding rod or gun can be directed at the joint, the
angle between the parts is so small that the tip of the rod or wire is insufficiently close to the
joint line to allow proper fusion into the root of the joint (Figure 28).
FIGURE 28 ANGULAR LIMITS FOR JOINT PREPARATIONS FOR VARIOUS WELDING
TECHNIQUES
Reference 9 contains the following advice:
(a)
The preferred position of the electrode when welding in the horizontal position would be
one in a plane forming an angle of 30 with the vertical side of the fillet being laid down.
However, little if any difficulty is encountered when, in order to prevent contact with some
projecting part of the work, the angle can be increased.
(b)
A simple rule used by many fabricators to ensure adequate clearance for the passage of
the electrode in horizontal fillet welding is that the root of the weld shall be visible to the
welder. The welds clear distance from a projecting element, which might obstruct the
passage of the electrode, shall be at least one-half the height of the projection.
(c)
One technique used by fabricators might be to cut a component at an angle to improve
accessas in a welded angle cleat fixed to a beam web in Figure 29.
FIGURE 29 CLEARANCE ON AN ANGLE CLEAT WELDED TO A BEAM WEB
(after Ref. 9)
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The examples of bad accessibility for structural steel connections shown in Figure 30 are taken
from Reference 23.
FIGURE 30 EXAMPLES OF BAD ACCESSIBILITY
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PRACTICAL CONSIDERATIONS
11.2 Site welding
The following matters need to be borne in mind when considering using site welding for a
structural steel connection:
labour chargeout rates are higher;
2.
special equipment (cherry pickers, mobile access platforms, scaffolding) may be required;
3.
weather can inhibit when welding can be carried out;
4.
weld quality may be affected and higher defect rates are to be expected;
5.
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1.
self shielded flux cored arc welding and manual metal arc welding are the only processes
commonly used;
6.
risk of fire and electric shock are increased;
7.
lower productivity applies;
8.
access for best results can be difficult to achieve;
9.
site storage of consumables requires a dry warm area;
10.
unless the site has 3-phase power supply, mobile generators are required;
11.
welding cables may get too long from the generator to the weld location;
12.
the earth return may have to pass through several components of the structure and must
be continuouswhich can present difficulties;
13.
welding cable can be easily damaged on a site;
14.
preheat (if required) can be difficult to apply;
15.
the welding area must be correctly screened;
16.
ventilation might be required.
For these reasons, shop welding is preferred to site welding.
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PRACTICAL CONSIDERATIONS
11.3 Economical design and
detailing
T he design and detailing of any structural steel connection should be such that the welding can
be done as economically as possible, while still delivering a weld that complies with AS 4100
(Ref. 1) and AS/NZS 1554.1 (Ref. 7).
References 9 and 23 discuss economical design and detailing in considerable detail. The basic
principles related to economical welding in structural steel connections can be summarised as
follows:
design and detail with welding in mind;
2.
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1.
do not specify oversize or unnecessary welds;
3.
keep the number of elements to be welded to a minimum;
4.
maximise the extent of shop welding, minimise the extent of site welding (Section 11.2 of
this Design guide);
5.
use fillet welds in preference to butt welds wherever possible but remember the economic
limitations on fillet weld size (Section 3.2 of this Design Guide);
6.
ensure adequate access and clearances are available (Section 11.1 of this Design
Guide);
7.
leave the selection of welding procedure and joint preparation to the fabricator wherever
possible;
8.
recognise the value of consultation with the fabricator and be receptive to alternative
proposals suggested;
9.
standardise connection details as much as practical;
10.
allow the use of sub-assemblies wherever practical;
11.
do not overspecify the extent of weld inspection requested;
12.
avoid details which require turning of components during fabrication;
13.
allow for welds to be deposited in the flat position wherever possible as this is more
productive than the vertical or overhead position.
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REFERENCES
1
STANDARDS AUSTRALIA, AS 41001998 Steel structures .
2
AUSTRALIAN INSTITUTE OF STEEL CONSTRUCTION, Design of structural
connections , 4th edition, Authors Hogan, T.J. and Thomas, I.R., Editor Syam, A.A., 1994.
3
AUSTRALIAN INSTITUTE OF
connections , 3rd edition, 1985.
4
STANDARDS
Commentary.
5
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12
AUSTRALIAN INSTITUTE OF STEEL CONSTRUCTION, An engineers guide to
fabricating steel structures , Volume 1: F abrication methods , John Taylor, 2001.
6
AUSTRALIAN STEEL INSTITUTE, An engineers guide to fabricating steel structures,
Volume 2: S uccessful welding of steel structures , John Taylor, 2003.
7
STANDARDS AUSTRALIA/STANDARDS NEW ZEALAND,
Structural steel welding , Part 1: W elding of steel structures .
8
WELDING TECHNOLOGY INSTITUTE OF AUSTRALIA / AUSTRALIAN STEEL
INSTITUTE, WTIA Technical Note No. 11, Commentary on the Standard AS/NZS 1554
Structural steel welding , TN11-04, 2004.
9
AUSTRALIAN INSTITUTE OF STEEL CONSTRUCTION, Australian steel detailers
handbook , 1999.
10
PRATT, J.L. Introduction to the welding of structural steelwork , 3rd rev. edition, 1989.
11
AMERICAN INSTITUTE OF STEEL CONSTRUCTION, Manual of steel construction, load
resistance factor design Volume II: C onnections, 1 999.
12
LINCOLN ELECTRIC COMPANY, The procedure handbook of arc welding , 1973.
13
STANDARDS AUSTRALIA, AS 1101.31987 Graphic symbols for general engineering,
Part 3: W elding and non-destructive examination .
14
AUSTRALIAN WELDING RESEARCH ASSOCIATION, The weldability of steels, AWRA
Technical Note 1, May 1982.
15
STANDARDS AUSTRALIA, AS 11631991, Structural steel hollow sections .
16
STANDARDS AUSTRALIA/STANDARDS NEW ZEALAND, AS/NZS 3678:1996 Structural
steelHot rolled plates, floor plates and slabs .
17
STANDARDS
AUSTRALIA/STANDARDS
NEW
ZEALAND,
Structural Steel, Part 1: H ot rolled bars and sections .
AS/NZS 3679.1:1996
18
STANDARDS
AUSTRALIA/STANDARDS
Structural steel, Part 2: W elded I sections .
AS/NZS 3679.2:1996
19
Owens, G.W. and Cheal, B.D. Structural Steelwork Connections , Chapter 2.
20
STANDARDS AUSTRALIA/STANDARDS NEW ZEALAND, AS/NZS 1553.1:1995 Covered
electrodes for welding, Part 1: L ow carbon steel electrodes for manual metal arc welding
of carbon steels and carbon-manganese steels .
AUSTRALIA,
STEEL
AS 4100
CONSTRUCTION,
Supplement
NEW
Standardized
11999
ZEALAND,
Steel
structural
structures
AS/NZS 1554.1:2004,
N OTE: This reference is expected to be superseded soon, by AS/NZS 4855:2007.
21
STANDARDS
AUSTRALIA/STANDARDS
NEW
ZEALAND,
AS/NZS 2717.1:1996
WeldingElectrodesGas metal arc , Part 1: F erritic steel electrodes .
22
STANDARDS AUSTRALIA, AS 2203.11990
Part 1: F erritic steel electrodes .
23
AUSTRALIAN INSTITUTE OF
steelwork , 4th Edition, 1996.
STEEL
Cored
electrodes
CONSTRUCTION,
d esign guide 2
welding in structural steel connections, first edition
for
Arcwelding,
Economical
structural
59
STANDARDS AUSTRALIA, AS 22052003 Methods for destructive testing of welds in
metal .
25
WELDING TECHNOLOGY INSTITUTE OF AUSTRALIA, WTIA Technical Note 5, Flame
cutting of steels , 1994.
26
STANDARDS AUSTRALIA, AS 39901993 Mechanical equipmentSteelwork .
27
Handbook of structural steel connections design and details , A.R. TamboliEditor,
McGraw-Hill, 1999.
28
WELDING TECHNOLOGY INSTITUTE OF AUSTRALIA, WTIA Technical Note 10,
Fracture Mechanics , 2002.
29
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24
STANDARDS AUSTRALIA, AS 11711998 Non-destructive testingMagnetic particle
testing of ferromagnetic products, components and structures.
30
STANDARDS AUSTRALIA, AS 20621997 Non-destructive testingPenetrant testing of
products and components .
31
STANDARDS AUSTRALIA, AS 2177.11994 Non-destructive testingRadiography of
welded butt joints in metal , Part 1: M ethods of test.
32
STANDARDS AUSTRALIA, AS 22071994 Non-destructive testingUltrasonic testing
of fusionwelded joints in carbon and low alloy steel .
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