-
Visual Inspection Works hop
R E F E R E N C E M A N U A L c
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Visual Inspect ion Workshop
Reference Manual
Second Edition
Published by American Welding Society
Education Department
American Welding Society e Copyright American Welding Society
Provided by IHS under license with AWS Licensee=IHS Subs and Mgrs
/IHSINTL003, User=Plata, Rodrigo
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networking permitted without license from IHS
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The American Welding Society Inc. assumes no responsibility for
the information contained in this publication. An independent
substantiating investigation should be made prior to reliance on or
use of such information.
International Standard Book Number: 0-87171 -483-3
Amencan Welding Society, 550 N.W. LeJeune Road, Miami, FL
33126
O 1997 by American Welding Society Printed in the United States
of America
All rights reserved. No part of this book may be reproduced in
any form or by any means, electronic or mechanical, including
photocopying, recording, or by any information storage or retrieval
system without permission in writing from the publisher.
I
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Table of Contents
Module Page
Introduction to the Works hop
1 . Module#l- Visual Inspection of Welding
2 . Nondestructive Examina ti on (NDE) of Welds and Welding
3 . Weld Discontinuities
4 . Welding Codes and Specifications
1 .o 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9
Rationale
.................................................................................................
1 Workshop Aims
......................................................................................
1 Quality
....................................................................................................
2 Terms and Definitions
.............................................................................
2 Certified Welding Inspectors
..................................................................
3 Visual Inspection
.....................................................................................
3
Aims of Module #1
..............................................................................
1-1 Weldment and Joint Design
.................................................................
1-1 Materiais of Construction
....................................................................
1-2 Procedures of Welding
.........................................................................
1-3 Manner of Weld Application ........i...
................................................... 1-3 Inspection
Program
..............................................................................
1-4 Inspection Program-Phase A
............................................................. 1-6
Inspection Program-Phase B
.............................................................
1-8
Inspection Program-Phase D
............................................................. 1-23
Inspection Program-Phase C
.............................................................
1-16
2.0 Aims of Module #2
..............................................................................
2-1 2.1 Introduction to Module #2
...................................................................
2-1 2.2 Liquid Penetrant Examination (PT')
..................................................... 2-3 2.3
Magnetic Particle Examination (MT)
.................................................. 2-7 2.4
Radiographic Examination (RT)
.......................................................... 2-12 2.5
Ultrasonic Examination (UT)
.............................................................. 2-17
2.6 Summary of Weld NDE Methods
........................................................ 2-21
3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8
Aims of Module #3
..............................................................................
3-1 Introduction to Module #3
...................................................................
3-1 Cracks and Cracking
............................................................................
3-2 Incomplete Fusion
................................................................................
3-7 Incomplete Joint Penetration
............................................................... 3-9
Solid Inclusions
....................................................................................
3-10
Shape Discontinuities
..........................................................................
3-12 Miscellaneous Discontinuities
.............................................................
3-15
Gaseous Inclusions (Porosity)
.............................................................
3-11
4.0 Aims of Module #4
..............................................................................
4-1 4.1 Introduction to Module #4
...................................................................
4-1 4.2 Finding Code References ( I )
............................................................... 4-1
4.3 Part B, Examination Book of Specifications
....................................... 4-2 4.4 Part B, Appendix I
and II
.....................................................................
4-6 4.5 Prequalified CJP Groove Welded Joints-Appendix III
..................... 4-7
... 111
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Module Page
4.6 4.7 4.8 4.9 4.10 Matching Filler Metals and
Strengths-Appendix IV ......................... 4-19
4.12 Finding Code References (2)
...............................................................
4-27
WeldrTest Criteria-Appendix V. VI. VII. and VI11
............................ 4-9 Weld Metal-Appendix IX and
Electrode Groups-Appendix X ...... 4-12 Welder Qualification
Requirements-Appendix XI ............................ 4-14 Welding
Procedure Qualification-Appendix XII and XII1 ................
4-18
4.11 Minimum Reheat and Interpass Temperatures-Appendix XV
......... 4-26
5 . Measurements 5.0 of Welding 5.1
5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9
Aims of Module #5
..............................................................................
5-1 Introduction to Module #5
...................................................................
5-1 Inspection Instruments and Gauges
..................................................... 5-2 Undercut
Gauge
...................................................................................
5-2 Machinists Rule
..................................................................................
5-4 Micrometer
...........................................................................................
5-5 Dial Caliper
..........................................................................................
5-8 Measurement Conversions
...................................................................
5-12 Magnifier
.............................................................................................
5-12 Linear Measuring Instrument Comparisons
........................................ 5-12 .
5.10 Special Welding Gauges
......................................................................
5-14 5.1 1 Welding Math
.......................................................................................
5-17
Exercise Questions EQ-1
..............................................................................
iv
.
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List of Figures
Module
1 . Module#1- Visual Inspection of Welding
2 .
Figure Page
1 . 1.Indication of Welded Joint Design
............................................................... 1-2
1.2-Joint Tolerances: With and Without Backing
............................................... 1-4 1 -3-Ioint for
Welder Qualification Test
.............................................................. 1-5
1 .&Using a Temperature Indicating Crayon
...................................................... 1-9
1.6-Presetting of Joint Members
.........................................................................
1-12 1 . 7-Significance of Weld Preparation Elements
................................................. 1-13
1.8-Regularizing Joint Members Gaps
............................................................... 1 .
14 1.9-Surface Contact Thermometer
......................................................................
1-15 1.10-Using a Tong Test Ammeter
.......................................................................
1-17 1.11-Significance of Weld Bead Size, Shape
...................................................... 1-18
1.12-Welding Sequence Techniques
...................................................................
1-20 1.13-Effect of Bead Placement on Weld Quality
................................................ 1-21 1.14-Effect
of Order of Weld Bead Placement
................................................... 1-21
1.15-Discontinuities in Intermediate Passes
....................................................... 1-22 1.1
&Backgouging Method, Accessibility
.......................................................... 1-22
1.17-Groove Weld Reinforcement
......................................................................
1-23 1.18-Excessive Fillet Convexity and Concavity
................................................. 1-24
1.19-Weld-Associated Surface Cracks
...............................................................
1-25 1.20-Overlap and Undercut
................................................................................
1-26 1.21-Undercut Gauge and Calibration Block
..................................................... 1-26
1.22-Incomplete Joint Penetration
......................................................................
1-26
1.5-Examples of Unweldable Joints Due to Access Problems
........................... 1-11
Nondestructive Exam i nation (NDE) of Welds and Welding
2 . l-Optical Borescope with Extensions
.............................................................. 2-2
2.2-Sub-surface Crack Undetectable by VT
...................................................... 2-3
2.3-Liquid Penetrant Examination Process
......................................................... 2-3
2.4-Visible Dye Penetrant Kit
.............................................................................
2-4 2.5-l? Indications
...............................................................................................
2-6 2.6-Florescent F?
................................................................................................
2-6 2.7-Magnetic Force Lines in a Permeable Body
................................................ 2-7
2.9-MT Equipment (Circular Magnetism)
.......................................................... 2-8
2.10-Longitudinal Magnetic Field
......................................................................
2-9 2.1 1-MT Examination Using Prods
....................................................................
2-10 2.12-Magnetic Yoke (Electromagnet)
.................................................................
2-11 2.13-MT Indications in Shaft
..............................................................................
2-11 2.14-Principles of Radiographic Examination
.................................................... 2-13
2.15-Effect of Radiation Beam Orientation
........................................................ 2-14
2.1-Viewing a Radiographic Film
.....................................................................
2-15 2.17-Film? Identification, and Macrosection of
Longitudinal
Toe/HAZ Crack
...............................................................................
2-16
2.8-Current-Carrying Conductor?s Magnetic Field
............................................ 2-8
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3 .
2.18-Normal Radiation Beam Orientation
.......................................................... 2-17
2.19-Sound Reflection in Ultrasonic Testing
...................................................... 2-18
2.22-Angle Transducer in Use
............................................................................
2-20
2.20-Diagram of a Pulse-Echo Raw Detector
.................................................... 2-19 2.21-UT
Cathode Display Tube Display
............................................................
2-20
2.23-Search Patterns, UT Weld Examinations
.................................................... 2-21
Weld Discontinuities
3.1-Weld and Weld-Related Discontinuities
....................................................... 3-2
3.2-Weld Area at Time of Weld Formation
........................................................ 3-3 3 .34
racks in Weld Metal
...................................................................................
3-5 3.4-Weld and Base Metal Crack
.........................................................................
3-6 3.5-Cold Cracks
..................................................................................................
3-7 3.-Incomplete Fusion in Various Locations
...................................................... 3-8
3.7-Incomplete Joint Penetration
........................................................................
3-9 3.8-Slag Inclusions
.............................................................................................
3-10 3.9-Porosity Types
..............................................................................................
3-13
3.1 1-Examples of Underfill and Undercut
.......................................................... 3-15
3.12-Acceptable (Conforming) and Unacceptable (Nonconforming)
3.10-Reinforcement Effect
.................................................................................
3-14
Weld Shapes (AWS D1.1)
...............................................................
3-16 3.13-Lamination and Delamination
....................................................................
3-18 3.14-Examples of Lamellar Tearing
...................................................................
3-19
4 . Welding 4.1-Calculation of Weld Metal Dilution
............................................................. 4-12
4.2-Fillet Weld Procedure Test Specimen
........................................................... 4-18
Codes and
Specifications
5 . Measurements 5.1-Typical Instruments. Tools. and Gauges Used
in Weld Inspection .............. 5-3 of Welding 5.2-Undercut Gauge
............................................................................................
5-3
5.3-Machinists Rule (Scale) Graduations
.......................................................... 5-4
5.5-Micrometer Zeroed
.......................................................................................
5-7 5.-Micrometer Readings
...................................................................................
5-8
5.8-Dial Caliper (Metric)
....................................................................................
5-10 5.9-Measuring with the Dial Caliper
..................................................................
5-10 5.10-Reading the Dial Caliper
............................................................................
5-11 5.1 1-Using the Extension Rod
............................................................................
5-11 5.12-Magnifier
....................................................................................................
5-13 5.13-The Palmgren Gauge
..................................................................................
5-14
5.15-Fillet Weld Profiles
.....................................................................................
5-17 5.1-Fillet Gauge
................................................................................................
5-17 5.17-Convex and Concave Fillet Weld Sizes
...................................................... 5-17
5.18-FibreMetal Fillet Weld Gauge
....................................................................
5-18
5.4-0 to 1 in . Micrometer and its Components
................................................... 5-6
5.7-Reading the O to 1 in . Micrometer
................................................................
5-9
5.14-Fillet Weld Profiles and Dimensions
.......................................................... 5-16
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VISUAL INSPECTION OF WELDING
INTRODUCTION TO THE WORKSHOP
Rationale Inspection is traditionally considered a
post-processing activity. A machine com- ponent may be turned to
finished form and size-then inspected for conformance to the
applicable drawing or specification. A gannent is inspected after
sewing and all the buttons and other features are in place. In
these and similar instances, visual inspection is carried out after
the production activities have been completed.
In the case of weldments, experience has shown that
post-processing inspection, even when supplemented with
nondestmctive examination (NDE), gives no guar- antee of
suitability for intended service. However, consistent results over
a con- siderable period of time have demonstrated the effectiveness
of a pre-planned sequence of visual inspections. If canied out at
specific stages of weldment production, such programs give a high
degree of assurance of meeting quality expectations-frequently
without recourse to NDE.
With welding, the factors infiuencing quality may manifest
themselves at any stage of the production operation. In many
instances, quality is compromised even before welding commences. In
most such circumstances, suitably timed visual inspection would
have revealed the shortcoming at a stage when corrective action
would be simple to implement and inexpensive to carry out.
Weld and weldment quality are determined by:
Weldment and joint design
Materials of construction
Procedure of welding
Manner of weld application
Inspection program
Visual welding inspection provides the basis for the effective
control of these determinants.
Workshop Aims The aims of this workshop are to:
Provide a basic understanding of the circumstances under which
weld and weldment quality, or both, may or will be compromised.
Offer a 24-point program of weld inspection that gives a high
degree of assur- ance of meeting weld quality requirements for most
fabricated products.
Show how to develop and implement specific quality plans to meet
ail normal requirements for weld and weldment quality.
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AWS Visual Inspection Workshop Introduction
Quality
Terms and Definitions
Demonstrate and practice the techniques of visual inspection
required to cary out effective weld quality control.
The term quality is widely used and applied. However, many
times, the general concept of quality is misunderstood.
Quality is conformance to the applicable specification.
The required level of quality for a product or service is
typically determined by the designer, based on suitability for
service over the intended life span. All prod- uct variables must
be specified in a manner that is capable of being measured.
Dimensions are readily verified. Attributes such as surface finish,
if significant, must be specified in terms allowing for precise
determination or measurement.
In carrying out an inspection, the inspectors task is to compare
the actual with the required or specified product dimensions.
Appearance alone is rarely the determi- nant of product
quality.
Certain important terms are used in the inspection of welding
that may or may not apply in other industries. These include:
Discontinuity-any interruption in the uniformity of an
object.
Defect-a discontinuity that does not meet the required product
specification.
While all defects are discontinuities, only certain
discontinuities are defects. The reinforcement and penetration
beads of butt welds are discontinuities because they represent an
interruption in the surface of the weldment. Only if outside the
provi- sions of the code or specification governing the welding
concerned however, would they represent defects.
The term specification is used to describe the all-important
information used by inspectors to determine quality of the item
under consideration. As a general prin- ciple, the purchaser and
the manufacturer agree to all the quality criteria applica- ble in
any given situation. Purchasers may nominate a given code or
standard or write their own specification of what is required.
Whichever way the quality requirements are specified, the agreed
criteria become the inspectors specifica- tion to be used for the
job concerned.
The term code describes a systematically arranged, comprehensive
set of rules and standards for welding applications, mandatory
where the public interest is involved.
A review of the 24-point Welding Inspection Program presented in
Table 1.2 clearly shows that welding inspectors require specific
knowledge and experience. To advance the application and
utilization of welding, the American Welding
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AWS Visual Inspection Workshop Introduction
Society (AWS) has standardized requirements for welding
inspectors. Certifica- tion of eligible persons is based on
documented evidence of appropriate experi- ence along with the
achievement of a certain minimum level of competence in a 3-part
examination.
Certified Welding Inspectors
An Inspector meeting AWS standards is designated a Certified
Welding Inspec- tor (CWI). CWIs are employed in a wide spectrum of
industry and carry out a variety of tasks. While certain CWIs will
have a wide range of situations with which to deal, others work in
more specific areas of inspection. However, a knowledge of all
facets of welding quality is required of CWIs to determine how the
variables interact.
Visual Inspection Key points about the visual inspection of
welding should be recognized. These include:
No inspection program will give an absolute guarantee as to weid
and weld-. ment suitability for intended service over the life of a
product. However, by structuring an appropriate inspection plan,
commercially realistic degrees of confidence in a welded product
can be achieved.
While visual inspection is highly effective in the control and
assessment of weld and weldment quality, there is one obvious
limiting factor. Visual inspec- tions are confined to exposed
surfaces-so subsurface discontinuities may not be detected. This is
offset by structuring welding inspection programs to examine the
minimum number of surfaces that will give the required degree of
assurance.
Nondestructive testing of welds and welding is an adjunct to the
visual inspec- tion program, not a substitute for it. The four NDE
methods used in connection with welding each have their own areas
of best application-along with limita- tions. Penetrant and
magnetic testing are surface techniques, with the latter limited to
ferro-magnetic materials. Radiography is directional, ultrasonic
examinations require smooth surfaces for transducer contact.
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1. MODULE # I V I S U A L INSPECTION OF WELDING
1.0 Aims of The aims of Module #1 are: Module #1
To consider the circumstances under which a weld and/or weld
quality may or will be compromised.
To detail the elements of a 4-phase, 24-point program of weld
inspection that will give any required level of assurance required
of the fabrication to meet weld quality requirements.
To review the individual elements of such a program to show the
basis for each and its scope so appropriate weight may be given in
specific cases.
1.1 Weldment and Without question, the most significant factor
in the quality of a welded product is the mangement of parts to be
welded. The relationship of members and the manT ner in which the
loads are handled determines the local stresses. Likewise, the
placement of joints has great significance. However, these last two
matters are the designers responsibility and are not the
responsibility of the welding inspector.
Joint Design
Joint design is another matter, one in which the welding
inspector is vitally con- cerned. In one sense, joint design, along
with the procedure of welding, could be identified as the most
significant factors in weld and weldment quality.
The most significant factors include but are not limited to
those shown in Table 1.1.
Table 1 .l-Welded Joint Design Determinants
DESIGN OF WELDED JOINTS
1. Welding and inspection access 2. Most cost-effective form 3.
Minimize residual stresses
Ideally, joint design is proposed by the manufacturer and
approved by the designer. Inappropriate joint designs are
frequently imposed on manufacturers. In such instances, the welding
inspector has a vital role to play in identifying poten- tial
problem areas. The initiation of the required corrective action
through the appropriate channels should automatically follow.
Joint designs are specified in the applicable welding procedure
specifications (WPS). The practice of making pictorial joint
representations on drawings is costly, counterproductive and
inaccurate. Compare the diagrams in Figure 1.1.
Inspectors initially consider joint design in Phase A (Initial
Review) of the Weld- ing Inspection Program (see Table 1.2) when
the applicability of the WPS is
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AWS Visual Inspection Workshop Module #1-Visual inspection of
Welding
1.2 Materials of Construction
NOTE OVERLAP
WEU) CROSS S E M O N SYMBOL
NOTE: TOTAL GROOVE WELD SIZE CANNOT EXCEED 1.
Figure 1 .l-Indication of Welded Joint Design
reviewed. At this stage, joint design and its form and
configuration will have been decided. Conformance of joint shape,
form, and dimensions to applicable criteria are to be checked.
in Phase B (Pre-welding Checks), the actual dimensions of joint
form and fit-up are to be verified to again establish conformance.
Once welding commences, only in exceptional circumstances can
meaningful changes to joint type and dimen- sions be made. Only
certain elements of a joint configuration may be altered with- out
engineer approval.
While welding can be successfully used to make a wide range of
welded joints in many materials, there are certain limitations.
These include:
1. Not all metals are weldable. Of those that are, not all can
be welded with the same degree of ease or using similar methods and
procedures.
2. Welding has the potential to cause significant physical and
metallurgical changes that may adversely affect the suitability for
intended service of the welded product.
Material specifiers are generally aware of these limitations and
call for the use of materials considered weldable. However, many
fully weldable materials react dif- ferently to certain welding
processes and procedures of welding. As with design, this leaves
the welding inspector with two important determinations to
make.
In Phase A, the compatibility of the base metal with the filler
metals to be used and the welding process to be employed are
verified. These are the essential vari- ables of the welding
procedure and must be established by test. Where previously
qualified welding procedures have been specified, only verification
checks are necessary. In other circumstances, more comprehensive
action will be required. The extent and scope of such action will
be dictated by the prevailing situation.
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AWS Visual Inspection Workshop Module #i-Visual Inspection o
Welding
During Phase B, it is necessary to verify that all materials to
be welded satisfy the established base metal requirements.
Inadvertent changes of material can have far- reaching
consequences. Protection against this possibility by building in
adequate checks is required by many Codes of Practice. In Section 8
of the ASME Boiler & Pressure Vessel Code, positive and
verifiable identification of all parts to be welded is a
requirement.
1.3 Procedures of Welding Procedure Specifications (WPSs) are a
breakdown of the welding vari- ables to be used to make one or more
joints under certain circumstances. In a general sense, there can
be a limitless number of such combinations. In practice, by using
care and attention, it is possible for a relatively small number of
WPSs to cover ail the diverse situations that arise even when
making complex weldments.
Welding
Over time, manufacturers of welded products build up a library
of qualified weld- ing procedures from which unique WPSs can be
generated. In the event that there are no suitable qualified (or,
if appropriate, prequaified) procedures available, it is necessary
to carry out further qualification testing. The significant point
is that this possibility allows time for appropriate action,
together with the qualification of welding personnel if
necessary.
The WPS fields set out the welding parameters, known as
essential vuriables. Change outside a certain code-specified range
requires the development and/or qualification of a new welding
procedure. Figure 1.2 shows a range of joint edge preparation
variables, with machining and assembly tolerances.
1.4 Manner of Weld Application
Welders are responsible for the application of welding. However,
welders do not act in isolation. Welder certification attests to
the skiU and ability of a welder to weld spec- Zied types of joints
in certain materiais under a range of restricted conditions. These
conditions typically include the welding process, type(s) and
form(s) of base metal, and joint position dong with the technique
and progression of welding.
In Phase A, welding inspectors verify that the welders, welding
operators or tackers are certified to weld with the procedures to
be used during production. This gives warning of any additional
requirements as far as welding personnel are concerned. It should
be kept in mind that welder certification tests may or may not
duplicate joints to be made in production. The test coupon joint
shown in Figure 1.3 may well be used to qualify welders for welding
plate, The purpose of the restricting ring is to limit access to
the joint to prove welder capability to weld, even on awkward
joints.
During Phase B, the welding inspector checks the condition of
the welding equip- ment and suitability of the base and filler
metals. The inspector checks joint fit-up and preheat
condition.
During Phase C, welding inspectors are required to assure that
welder skill is maintained throughout. Where there is evidence of
reduced skill, requaiification or even retraining, may be necessary
if substandard work persists.
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AWS Visual Inspection Workshop Module #l-Visual Inspection of
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1.5 Inspection Program
R i 1116 in.+ + (1.6 m)
(A) GROOVE WELD WilHOUT BACKIN- ROOT NOT BACKGOUGED
f i1/16in.7 +I+) /:+ (1.6 mm)
7-
4 I- +1/4 in. (6 mm) R -1/16 in. (1.6 mm) (B) GROOVE WELD WITH
BACKING-
ROOT NOT BACKGOUGED
+1/16 in. (1.6 mm) -1/8 in. (3 mm)
t
(C) GROOVE WELD WITHOUT BACKING- ROOT BACKGOUGED
Figure 1.2-Joint Tolerances: With and Without Backing
While the specific details of any given welding program will
differ in detail, the basic requirements remain the same. Three
phases have already been identified. As enumerated below, there is
a fourth phase which follows the completion of welding. The four
phases of a welding inspection program are set out in Table
1.2.
The abbreviated form of identification given in Table 1.2 will
be used to outline each of the required inspection activities.
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AWS Visual Inspection Workshop Module #1-Visual inspection of
Welding
Phase A-Initial Review 1. Review purchase order, all codes and
drawings 2. Develop all necessary inspection plans 3. Check welding
procedures; welder status 4. Establish inspection documentation
system 5. Publish non-conforming product ID system 6. Create a
corrective action program
Phase B-Pre-welding Checks 1. Check suitability, condition of
welding equipment 2. Check conformance of base and filler materials
3. Check the positioning of members and of joints 4. Check joint
preparation, fit-up, cleanliness 5. Check adequacy of alignment
maintenance 6. Check preheat (or initial) temperature
12.7
150
SAME O.D. AS TEST PIPE OR SAME SIZE AS TEST BQX TUBING
Phase C-In-process Inspections 1. Check compliance with WPS
provisions 2. Check quality, placement of key weld passes 3. Check
weld bead sequencing and placement 4. Check interpass temperature
and cleaning 5. Check adequacy of backgouging 6. Monitor any
specified in-process NDE
Phase -Postwelding Activities 1. Check finished weld appearance,
soundness 2. Check weld sizes and dimensions 3. Check dimensional
accuracy of weldment 4. Carry out or monitor/evaluate specified NDE
5. Monitor any PWHT or other postweld work 6. Finalize and collate
inspection documentation
Figure i .3-Joint for Welder Qualification Test
The AWS publication devoted to visual inspection of welding is
ANSIAWS BZ.12, Guide for the Ksual Inspection of Welds. It fonns
the basis for the informa- tion that follows and should be
available for reference at ail stages of the detailed consideration
of each item of the 24-step program given in Table 1.2.
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AWS Visual Inspection Workshop Module #l-Visual Inspection of
Welding
1.6 Inspection Program- Phase A
The purpose of any inspection is to establish conformance to
specification. It is self-evident that the very first inspection
task will be to find out what is required. The first activity
is:
Al-Review Purchase Documents and Specifications
Depending on a large number of significant factors, the scope
and detail given will vary over a wide range. Structural work is
different from process piping; pressure vessel work and tankage are
not the same. Each will have their own specifics. However, there
are certain common factors and these should be ascertained at the
earliest possible stage. If errors, omissions or incomplete data
are uncovered at this point, prompt corrective action should be
initiated.
The minimum data to be obtained include:
1. Code(s) of construction
2. Materials of construction
3. Applicable standards and specifications
4. Drawings showing weld locations and types'
5. Inspection frequency, techniques, criteria
ASDevelop an Inspection Pian
As the name implies, an inspection plan is a detailed list of
all inspection activities to take place before, during and after
welding. For Phase A activities, a single inspection plan will
suffice as these are one-time, up-front requirements. Input data
are obtained during purchase order review and from applicable
specifica- tions, augmented by any other requirements covering the
job as a whole.
Inspection plans typically are in the form of a check isr.
Column headings cover, as a minimum, such items as the Activity,
Applicable Specification, Date, Inspection Report No., and
Signature. Each specific inspection activity is listed
separately.
Except for very small jobs with few activities to be covered,
multi-level inspec- tion plans are necessary and usual. The first
level typically covers a job as a whole. As such. it acts as a
control document to monitor and direct the more
- 'Two types of drawings are usually used. Detail drawings show
job form, dimensions, member size and position. Weld location, form
(butt,fillet, or other) and extent are given, but not joint type or
size. Working drawings show consauction detail, including joint
type and other applicable weld data, communicated by symbols or
other means.
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AWC Visual Inspection Workshop Module #l-Visual Inspection of
Welding
specific activities of the second level of inspection plans.
This means the column headings of each level of the inspection plan
may change to embody different roles.
Most second-level inspection plans contain those items listed in
Phases B, C and D of the inspection program set out in Table 1.2.
Second-level inspection plans may, in turn, be used as control
documents to cover specific sections of a job.
Third-level inspection plans are used to control the activities
taking place with respect to individual joints, which may be within
a component within a section of a job. The number of levels will be
governed, in part, by the degree of confidence required for the job
in part and as a whole.
It is desirable that inspections take place as a part of the
production process. Hold Points, where production is halted to
await inspection clearance, should be kept to a code-mandated
minimum.
A3-Check Welding Procedures and Welder Status
Most contractors, fabricators and manufacturers have a number of
welding proce- dures, qualified either by test or with prequalified
status. In any given situation, existing procedures may or may not
cover ail the required welding to be carried out. In the event of
deficiencies, it takes some time to have new procedures devel- oped
and qualified. Taking action on this matter at the earliest
possible stage is prudent. All necessary welding procedure
specifications can be developed once the supporting procedures are
qualified.
Similar remarks apply to welder status. The limitations on
welder qualification include the form of items to be welded (plate,
pipe), the welding process or pro- cesses, electrode
classifications, the welding positions, member thickness, and pipe
diameter. Prompt action to have suitably qualified welders on the
roster is a self-evident requirement. In the event that new
procedures have to be qualified, existing welder certifications may
or may not be sufficient.
There is a provision in some codes that permits welders to
qualify during produc- tion. This possibility should be viewed with
restraint. Usually, radiographic exam- ination of a certain length
or number of joints is required. If the film images conform to
specification, the scope of the qualification is typically much
narrower than normal welder tests. If the test welds do not
conform, then removal of all the subject welds, not just repair, is
typically required.
Usually, welding procedures are not time constrained. Once
qualified, procedures remain current indefinitely. Welder
qualifications, on the other hand, are often for a specified time.
The duration of currency may be 6 months or a year. Renewal by
evidence of use of the process is frequently automatic. In other
cases, retesting after a specified period of time is required.
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AWS Visual Inspection Workshop Module #l-Visual Inspection of
Welding
1.7 Inspection Program- Phase B
AAEstablish Inspection Documentation System
Most organizations operating in the field of welded fabrication
will have inspec- tion documentation such as Inspection and
Non-conformance Reports. With these and other required documents
however, it should be verified that the form of the documents
satisfies the requirements of the applicable codes or
specifications.
Some companies require special documentation in addition to
requirements speci- fied by code. Today, with the widespread use of
computers, producing specialized forms is a simple matter. The time
to identify and respond to special requirements is before the job
commences.
ALPublish Non-conforming Product ID System
Most firms have a means of identifying and handling
non-conforming product. It should be verified that the system meets
the purchasers requirements, with changes made as required. Any
such changes must be communicated to all con- cerned with the job.
Incorporating non-conforming product into an assembly is one of the
most common problems associated with welded fabrication. It is usu-
ally brought about by ignorance of the system.
ACMaintain a Corrective Action Program to Eliminate Defects
Corrective action to eliminate defects should be an organized
activity, carried out in accordance with a formal procedure, and
approved for use by the competent authority-typically, the
engineer. It should not be a surreptitious activity, carried out
when no one in authority is present. While under-the-table repairs
may smooth feelings, it overlooks the basic aim of quality systems
to identify causes of non- conformance. By so doing, system
problems, rather than just symptoms, can be addressed and prompt
corrective action implemented, the most common being:
1. Improved communication
2. Job training
Phase A activities have the effect of laying the foundation upon
which a Welding Inspection Program is based. The actions required
represent what are generally considered normal to most persons
expected to execute them. However, it is desir- able, where
possible. to have written procedures to stmcture and standardize
action as per the program procedure. For instance, in reviewing rhe
purchase doc- uments and specifications, what information is being
sought? Certainly, a check- list or similar document will be useful
when checking welding procedures and welder status.
While industry is not unanimous on the need for formal
procedures for Phase A, there is no doubt that Phase B, C, and D
activities should be governed by formal
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AWS Visual inspection Workshop Module #l-Visual Inspection of
Welding
procedures. For example, in Figure 1.4, where should the
temperature indicating be applied in relation to the joint? Should
it be 1 in., 2 in., or just what distance from the joint?
Figure i .4-Using a Temperature Indicating Crayon
B1-Check Suitability, Condition of Welding Equipment
The suitability of the welding equipment refers to its
capability to produce sound welds using the applicable welding
procedures. It is unlikely that a 150 amp, AC welding machine would
be capable of successfully running 118 in. E7018 elec- trodes;
notwithstanding a maximum current requirement of say 120 to 130
amps.
A 600 A, 60% duty cycle machine would not be suitable for
submerged arc weld- ing (SMAW) a circumferential seam of a 6 foot
diameter vessel at 500 amps. The same machine may well be capable
of welding longitudinal seams on the same vessel if the seam length
is not more than 5 or 6 feet.
Additionally, secondary equipment must also be checked for
suitability. For example, storage ovens for low-hydrogen SMAW
electrodes, e.g., E7018, must be capable of maintaining a
temperatue of at least 250F. These electrodes are limited in terms
of how long they are permitted to be exposed to the atmosphere
without adversely affecting their low-moisture content.
Welding accessories such as cables and workpiece leads,
electrode holders and workpiece lead clamps ail carry the full
welding current. Are the connections suf- ficiently tight and
secure to avoid overheating and consequent loss of current and
possible variation in electrical output? The heating effect of
electrical current is a function of circuit resistance (12R). These
and similar questions are to be addressed and resolved before
welding commences.
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AWC Visual Inspection Workshop Module #1-Visual Inspection of
Welding
B2-Check Conformance of Base and Filler Metais
While it is an evident requirement that base and filler metals
must conform to the WPS requirements, it may take foresight to
ensure that it is possible to make this verification. Material Test
Reports (MTRs), even Certified Material Test Reports (CMTRs) are
fine; but how is the metal to be welded identified as being that
referred to in the Test Reports? Material traceability is a must
for all metals to be welded.
B 1 C h e c k the Positioning of Members and Joints
This is the appropriate time to verify that accessfor welding
has been allowed. Dur- ing the review of drawings in Phase A of the
Welding Inspection Program, the ini- tiai activity involves a
documentation review. At that time, any potential access problems
will have been identified. Simple examples are shown in Figure
1.5.
An inspection carried out at this stage will possibly be the
first opportunity the inspector has to see that changes were made
to correct any design shortcomings. This example also illustrates
the need for effective communication. When initially identified and
the matter drawn to the attention of the relevant parties, circum-
stances may dictate that the inspector who carried out the initial
phase of the weld- ing inspection program is not the same person
involved with the later phases. It is thus vital to have a record
of the initiai finding flagged for later attention and
Verification.
Of course, it is always possible that access problems were not
identified from the drawings. While the problems shown in Figure
1.5 are obvious, potential dificul- ties of this type are not
always readily discernible. This check provides an ideal
opportunity to verify this important point.
Presetting of members to be welded is a prudent and effective
way in which to offset, or at least reduce the effects of weld
shrinkage. Some examples of preset- ting are shown in Figure
1.6.
Where presetting is involved, there are 3 important accompanying
factors to be considered. as follows:
Amount of presetting
The existence of non-uniform restraint
The sequence of welding
It is also appropriate at this time to again review the scope of
qualifications of the welder(s) concerned with making the joint(s)
under consideration. In Phase A of the Welding Inspection Program,
the welders qualifications are required to be verified.
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AWS Visual Inspection Workshop Module #l-Visual Inspection of
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ELECTRODE MUST BE HELD CLOSE MAKING THESE FILLEiS.
EAsv TO DRAW, BT THE 2ND WELD WILL BE HARD TO MAKE.
/ E4SY VEAY DIFFICULT
TO
9
EASY TO SPECIFY WELDALL
TRY To AVOID PLACING PIPE JOINTS NEAR WAU SO THAT ONE OR TWO
SIDES ARE INACCESSIBLE THESE WEU)S MUST BE MADE WITH BEM ELECTRODES
AND MIRROR.
4 AROUND, BUT... I I
/ /
I
TOO CLOSE INSIDE TO ALLOW PROPER ELECTRODE POSmONING. MAY BE OK
FOR AVERAGE WORK, BUT BAD FOR LEW-PROOF WELDING.
Figure 1.5-Examples of Unweldable Joints Due to Access
Problems
Welders are qualified to weld in one or more joint positions, on
a range of metals in terms of composition, form (plate, pipe) and
dimensions.
Additionally, certain codes (including, for instance, AWS DI. I
) impose positional restraints on the scope of welding procedures.
WPSs supported by procedures qualified on pipe butts usually have a
wider scope of positional capability than procedures qualified on
plate. Welder qualification is generally similar.
B4-Check Joint Preparation, Fit-up, and Cleanliness
The term joint preparation covers a wide range of combinations
of plate edge treat- ment. On working drawings, the dimensional
requirements for joint preparations should be shown by the use of
the appropriate welding symbol(s). The purpose of
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AWC Visual Inspection Workshop Module #l-Visual Inspection of
Welding
A F E R WEDING
E 3 BEFORE WELDING
Figure 1 .+Presetting of Joint Members
edge preparation is to allow the electrode access to the joint
root. The arc must be able to impinge on all surfaces to be melted.
This means there is no universal edge prep because there are many
electrode sizes in use. It also means the dimensions of a weld
preparation are important. Consider the joints in Figure 1.7.
While the examples in Figure 1.7 may represent extreme cases, it
is evident that the tolerances applicable to weld edge preparations
and to joint fit-up are signifi- cant and must be observed. In the
absence of anything to the contrary, it is sug- gested that the
tolerances shown in Figure 1.2 be adopted.
The examination of weld edge preparation and fit-up is
considered to be the most important of the Welding Inspection
Program steps. Inaccuracies at this point pre- destine a weld to
almost certain non-cocformance. Use of suitable instruments to
check each part of the weld preparation and fit-up is vital.
The assembly of T-joints deserves particular attention. Most
T-joints are fillet welded, generally from both sides. Separation
between the members acts to
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AWC Visual Inspection Workshop Module #l-Visual Inspection of
Welding
n
Figure 1.7-Significance of Weld Preparation Elements
reduce the effective weld size. With double-welded joints,
separation cannot nor- mally be seen after welding. Generally,
specified weld sizes are required to be increased by the amount of
separation to restore the specified weld size.
A second consideration in this connection stems from the way in
which fillet welds perform their function. By definition, the weld
root of a sound fillet weld intersects the joint members at one
point only. In other words, there will be a sin- gle point of
stress concentration at the joint root. Where there is separation
between the joint members, there will be two weld roots and thus
two points of stress concentration; at best, an undesirable
situation.
If from some prior event there is an excessive gap between
members of a butt joint, there are several possible remedies short
of member replacement. For small additions, joint edge(s) can be
built up by welding. Alternatively, consider the use of a backing
bar. After welding, the backing bar can be removed if
necessary.
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AWS Visual inspection Workshop Module #i-Visual inspection of
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Another possibility is to use a spacer which is gouged out after
welding from the first side is completed. See Figure 1.8. e
:.:.:.:.:.:.:. m
Figure 1 .&-Regularizing Joint Members Gaps
B4-Check Joint Preparation, Fit-up, and Cleanliness (Contd)
Cleanliness of the joint area is a general requirement. Arc heat
melts and vapor- izes everything in its vicinity. Cleanliness of
the joint area is a general require- ment and must be verified
prior to welding. Loose scaie, rust, oil, grease, cutting fluid
residues, paint and other surface contaminants should not be
present for at least 2 in. on either side of the weld center line
nor on the other side of joint members.
If the area to be welded is pitted with rust, it is highly
desirable to grind the area to shiny metal. For new material,
vigorous brushing should suffice. For steel no longer showing
tightly adhering blue mill scale, grinding is preferred.
Particular attention needs to be paid to pipe joints, especially
if gas backing is to be used. Under the heat of welding, many
surface contaminants are vaporized-
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AWS Visual Inspection Workshop Module #1-Visual Inspection of
Welding
generally into hydrogen-rich substances which have potentially
unsatisfactory effects on molten weld metal and base metais at the
elevated temperatures associ- ated with welding.
BS-Check Adequacy of Alignment Maintenance
During welding, forces of considerable magnitude act on joint
members. It is nec- essary to establish that the means of holding
joint members is adequate to ensure that members are held in proper
alignment throughout welding. Where members are tacked, verify that
tack length and the number of tacks are sufficient to main- tain
alignment.
When joint alignment is to be maintained by use of clamps,
pressure is at right angles to the forces involved in weld-caused
expansion and contraction. The reac- tion to transverse expansion
and contraction is a function of welding speed. Rapid welding tends
to open seams in front of the arc. Slow welding, such as with GTAW
or gas welding tend to cause closing of members, or scissoring.
B-Check Preheat or Initial Job Temperature
It is the responsibility of the welding inspector to verify that
the workpiece has been heated to the specified preheat temperature.
The workpiece may have been heated to the required temperature, but
in such a localized area that workpiece temperature has fallen by
the time welding commences. Preferred practice is to apply the
heating medium in a band of 2 in. width centered 2 in. away from
the edges of the joint members. The joint itself and adjacent metal
for at least 3 in. on either side of the joint should be raised to
the specified preheat temperature.
Temperature checks should be made 2 in. away from the joint
(some specifica- tions call for 3 in.) on both sides of the joint
and on both front and back. Means to verify job temperature include
temperature indicating crayons (immediate) and a number of
pyrometers, most of which require little time to give the correct
job temperature. A surface contact thermometer is shown in Figure
1.9.
Figure 1 .%Surface Contact Thermometer
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AWS Visual Inspection Workshop Module #1-Visual Inspection of
Welding
1.8 Inspection Program- Phase C
For site work or work being carried out in low-temperature
environments, special conditions may apply. AWS D1.1, for instance,
mandates that no welding is to be carried out when the ambient
temperature in the work area is
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AWS Visual Inspection Workshop Module #l-Visual Inspection of
Welding
direct current and must be matched to the current being tested.
In operation, the movable jaw is opened to encircle the
current-carrying welding or workpiece lead at any convenient point,
such as near the workpiece lead clamp where the likeli- hood of
interfering with the welder is minimized.
Figure 1 .lO-Using a long Test Ammeter
C2-Check Quality, Placement of Key Weld Passes
Without a doubt, the most critical stage of welding is the root
puss. As with any operation, good work is based on a sound
foundation. The root pass is the founda- tion of every welded
joint. The function of the root pass is to provide a sound tie
between members at the joint root. This applies to both unbacked
and backed joints. With unbacked joints, the root pass must be a
compromise between apply- ing sufficient heat to melt joint member
edges but not so much as to give exces- sive penetration. With
backed joints, the root pass must tie member edges and the backing
together with a single bead. Using more than one edge-to-backing
bar pass is not a good welding practice, as incomplete fusion
almost always results.
A second consideration at this time is the shape of the root
pass. This is desirably flat to slightly convex. While in a
multipass joint, a concave profile may appear desirable, the
shrinkage stresses may give rise to cracking, as in Figure
1.11.
At the other extreme, excessive bead convexity can lead to
incomplete fusion. High beads prevent access of the arc to all
areas of the partially filled joint, as shown in Figure 1.1 1.
As the root pass is being made, it is prudent to check if the
means of joint assembly, such as tacking or clamping, is holding
joint members in the correct
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AWS Visual Inspection Workshop Module #1-Visual Inspection of
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U U
Figure 1.11-Significance of Weld Bead Size, Shape
relationship. Depending on the welding process, there will be a
tendency for the root to open or close. If corrective action is
necessary, other joints that are simi- larly assembled should also
reflect the changes.
The toes of root beads should be checked perbdically to ensure
that sidewall under- cutting is not taking place. To make sound
root passes, a common practice is to increase the welding current
and to offset the additional heat availability by increas- ing the
travel speed of the arc along the seam being welded. Undercut
results when the amount of weld metal available is insufficient to
fill the area of metal melted. With slag-shielded welding
processes, sidewall undercut may be indicated by difficult slag
removal, but this will need to be confirmed by examination.
Corrective action for sidewall undercut is to grind the joint
edges back to elimi- nate the grooving effect. If not done, it is
unlikely that arc impingement during subsequent weld passes will
reach the bottom of the undercut grooves. This is the primary
source of wagon tracks, a linear slag inclusion. In the case of
non-slag processes, sidewall undercut is usually identified on
radiographs as a slag inclu- sion. Notwithstanding the absence of
slag, the image shape is the same as in the case of slag-shielded
processes.
Porosity in the root pass will tend, if left untreated, to
persist in subsequent passes. A pore may produce a vertical pipe in
a multipass weld. The heat of welding expands air in existing
pores, the pressure of which causes the entrapped gases to rise
through the molten metal as it is deposited in subsequent
overlaying beads. Complete removal of any pore from the first pass
in which it is detected is the only effective corrective
action.
C3-Check Weld Bead Sequencing and Placement
The sequence in which weld beads are deposited exercises a
significant effect on the dimensions and shape of a weldment. Where
distortion caused by shrinkage is likely to be a problem, it is
prudent to require that a weld sequence program be
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AWS Visual Inspection Workshop Module #l-Visual Inspection of
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developed and observed during welding. Such a program would
appear as an addendum to the applicable wPS(s).
Even when a welding sequence is not specified, it is desirable
that the usual niles to minimize distortion are followed. These
include, but are not limited to:
1. Welding from areas of greatest restraint towards areas of
least restraint
2. Welding long weld joints from the center outward
3. Balancing welding on either side of joints, of welded
assemblies and of weld- ments as a whole
Some common techniques for sequencing weld beads include (a)
buckstepping, (b) skip welding, and (c) an offset method for
T-joints using double fillet welds, as shown in Figure 1.12.
In backstep welding, while individual weld passes are made from
the outside towards the center, the general direction of welding is
from the joint center line outward. This technique is used for both
thick and thin base metal and for groove and fillet welds made on
one side of T-joints. Skip welding is a variation of back step
welding, but primarily for groove welds in thinner base metals. The
technique shown in Figure 1.12 for fillet welded joints is based on
limiting longitudinal shrinkage and, at the same time, offsetting
angular rotation.
The placement of individual weld passes within a joint can
exercise a significant effect on joint quality and alignment.
Consider the last completed weld pass on the left in Figure 1.13.
In making the next pass (dotted) the arc may be unable to melt the
sidewall, resulting in incomplete fusion.
The order in which weld beads are placed on one side of a joint
or the other is important. As Figure 1.14 shows, the effect of
making a second weld bead on the same side as the first was made
(2nd down) is dramatic. Instead of being "pulled" almost straight,
the net effect is to make it impossible for all the weld beads
placed on the opposite side of the joint to pull the joint into the
correct alignment.
CACheck Interpass Temperature and Cleaning
For joints where preheat and interpass temperature are
specified, it is intended that the joint area will be kept within
the required temperature range throughout weld- ing. For work
extending over a work break, the best practice is to determine
whether the job can be allowed to cool or if the minimum specified
temperature must be preserved in the joint until welding has been
completed. Irrespective of the specifics, the welding inspector
should take an active role to ensure proper temperature
control.
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AWS Visual Inspection Workshop Module #1-Visual inspection of
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4
I bl+ DIRECTION OF DEPOSITION OF EACH ELECTRODE
I GENERAL DIRECTION OF WEDING *
b I I I
(A) BACKSTEPPING I \ I I I 7 1 2 1 8 1 3 1 9 1 4 1 1 0 1 5 1 1 1
1 6 1
I I I
X in.
h 6 1 2 1 7
I A I
Figure 1.1 2-Welding Sequence Techniques
Finally, with respect to interpass temperature, where there is a
maximum speci- fied-as may be the case where toughness is
critical-the weld area should be checked with sufficient frequency
to be certain that there is no excessive heat buildup. If this does
occur, no attempt to accelerate cooling should be allowed. A basic
purpose of preheat and interpass temperature control is to retard
the cooling rate in the joint area. Forced cooling or accelerated
cooling will not cor- rect the situation.
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AWS Visual Inspection Workshop Module #1-Visual Inspection of
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Figure 1.1 &Effect of Bead Placement on Weld Quality
,$fi Pa ........ ........ ....... QQ .:., ....... ..:.:i.
....... :.: .;.: < ........ :.:.: x i ......... .:.:.:..::. :..
..;:.>:.:.:.: ..... ............... ? .......... * .: .*.
.,.:.:.: .... .... :.:.:.:...,: pJ,$g .. ........ :.:..
.,.:.:.:.: .,., ..:.:.:.:.:.: ,
... ,.:.:.:., ... % ..:$::p. Figure 1 .l&Effect of Order of
Weld Bead Placement
Interpass cleaning is needed to ensure that subsequent weld
passes will be made on clean metal. It also allows the welder to
carry out a visual examination of the work just completed. Apart
from the obvious, it is useful to look for surface dis-
continuities such as those shown in Figure 1.15.
While the removal of slag is the primary aim of weld pass
cleaning, other surface contaminants may be present to a greater or
lesser degree. Spatter in front of the advancing arc may create
problems in regard to fusion, and should be removed from the joint
area after each weld pass. Small globules of loosely adhering spat-
ter are normal. Large globules and tightly adhering spatter are
not. The smoke that accompanies welding-which is primarily the
oxide of the base meta-does not interfere with welding but if left
on a job to be painted will cause discoloration of the dried
paint.
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AWS Visual Inspection Workshop Module #l-Visual Inspection of
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Figure 1.1 5-Discontinuities in Intermediate Passes
CS-Check the Adequacy of Backgouging
Backgouging-the removal of base or weld metal from the weld root
side of a joint to sound metal-is used to ensure complete fusion
and joint penetration and to avoid gaseous and solid inclusions.
Typically carried out by grinding or by arc- air gouging,
backgouging is required by many codes when unbacked Complete Joint
Penetration (CJP) welds are specified. Figure 1.16 shows, in the
upper dia- gram, the principle involved.
Figure 1.1 &Backgouging Method, Accessibility
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AWS Visual inspection Workshop Module #1-Visual Inspection of
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1.9 Inspection Program- Phase D
The depth of backgouging must be such that there is sound metal
exposed over the whole of the joint length. The angle of the groove
must allow full access for the electrode. In Figure 1.16, the lower
diagram at left shows a groove typical of arc- air gouging when the
electrode diameter is too small for the depth of gouging required.
The lower diagram at right shows the usual groove produced by
grind- ing. In both cases, the groove angle must be increased to
that specified in the WPS for the first side welded. Welding
inspectors must be satisfied that backgouging is complete,
including the use of NDE, if considered necessary.
CLMonitor Any Specified In-process NDE
Apart from the NDE noted above in connection with backgouging,
there are cir- cumstances where in-process NDE is specified.
Magnetic particle inspection, even radiography of root passes on
heavy-wailed pipe, is not uncommon. in all such instances the role
of the welding inspector will vary, but basic to all situa- tions
is that these activities are carried out under proper control.
Further, that appropriate records are furnished and maintained.
The final phase of the welding inspection program embodies the
postwelding activities necessary to ensure that the finished
weldment meets the applicable requirements in all relevant
respects. This should not be confused, at least in prin- ciple,
with the final job inspection. The object is to establish weld and
weldment quality conformance within the overall job context. This
involves the following activities:
D1-Check Finished Weld Appearance and Soundness
Weld faces should display uniform ripples with no significant
variations in shape or form. Bumps and depressions indicating
starts or stops should be minimal. Groove weld reinforcement should
be evident, without underfill or excess. See Figure 1.17 for
examples of each of the foregoing.
NOT ENOUGH 0000 TOO MUCH
Figure 1 .i7-Groove Weld Reinforcement
This similarly applies to fillet welds, where minimum ratio of
width to depth (W:D) should be 1.25 to one. Excessive convexity or
concavity are equally unde- sirable. Possibilities include those
shown in Figure 1.18.
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AWS Visual Inspection Workshop Module #1-Visual Inspection of
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Figure 1.1 8-Excessive Fillet Convexity and Concavity
Wetting-in at the toes of both groove and fillet welds without
undercut is desirable with all welds. Welds with excessive
convexity or reinforcement increase the stress concentration,
sometimes to unacceptable values.
weld width weld depth Form factor =
Following the check of the general appearance of all welds, a
detailed examina- tion should be carried out to establish freedom
from nonconforming surface dis- continuities. In the absence of
other indications, this will represent the final visual inspection.
Accordingly, it needs to be detailed and thorough. As will be noted
later in this text, a flashlight is a most important aid in
carrying out this examina- tion. Surface discontinuities not
considered above include, but are not limited to:
Cracks
Incomplete fusion, on the sidewall, between weid passes or as
overlap
Incomplete joint penetration of one sided butts
Slag inclusions
Porosity, and other gaseous inclusions
Undercut
Arc strike
Common surface cracks are shown in Figure 1.19. Sometimes
overlapping tenni- nology is used for cracks. It may be based on
time of occurrence, site, direction or other determinants. The
throat crack, as shown in Figure 1.19, may also be known as a hot
crack, a center line crack or a longitudinal crack.
Incomplete fusion may appear as cavities between weld passes or
between the weld sidewall and an adjacent weld bead. A third form
of this discontinuity is
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AWS Visual Inspection Workshop Module #1-Visual Inspection of
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I CRATER\
THROATA CRACK
Figure 1 .l&Weld-Associated Surface Cracks
overlap, where molten filler metal has rolled over unmelted base
metal. a charac- teristic is a distinct re-entrant angle at the
weld toe. Examples of overlap are shown in Figure 1.20.
Undercut may be considered as the opposite of overlap. In the
case of undercut, the cause is the melting of a greater amount of
base metal than there is available molten weld metal to fill. This
results in the characteristic groove at the weld toes. While the
severity of undercut is redly the sharpness of the angle made by
the sides of the undercut groove, in practice, acceptability is
based on depth. A gauge for measuring undercut to AWS DI. 1-96
Section 4.8.1 requirements, along with its calibration block, is
shown in Figure 1.21. The gauge shown is applicable to dynamically
loaded structures built in accordance with AWS D1.l.
With joints welded from one side only, with access to the back
of the joint, incom- plete joint penetration may generally be
detected. An exception is when weld shrinkage has pulled the
members together so there is no evident separation. How- ever, the
absence of a penetration bead should indicate the need for further
exami- nation. Readily apparent incomplete penetration is seen in
Figure 1.22.
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AWS Visual Inspection Workshop Module #l-Visual Inspection of
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Figure 1.20-Overlap and Undercut
~~~
W.T.P.S. .O10 CALIBRATION BLOCK TOLERANCES i .o005 in.
Figure 1.21-Undercut Gauge and Calibration Block
Figure 1.22-Incomplete Joint Penetration
Surface slag discontinuities will typically appear as elongated
cavities, in which slag may or may not remain. Surface slag
cavities should be investigated for depth. If the weld cross
section is not reduced beyond the applicable tolerance, corrective
action is usually to grind the area to a slight concavity to remove
any tendency to stress concentration.
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AWS Visual Inspection Workshop Module #l-Visual Inspection of
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Porosity is the term covering discontinuities caused by trapped
gases. During welding, atmospheric and other gases are drawn into
the weld pool because they are soluble in molten metal. Normally,
this gas escapes as the weld puddle cools. However, there are
circumstances when the gas remains in the solidified puddle, mainly
as a result of incorrect electrode manipulation. Gases may be
wholly entrapped in the weld or have sufficient pressure to break
the weld surface to appear as sulface porosity.
Porosity tends to be round or nearly so; with little ability to
concentrate stress. Most codes allow some pores, up to a specified
diameter, in a unit length of weld. Individual pore diameters are
measured to determine conformance or otherwise, based on the
applicable criteria.
Arc strike shows as a scar on the base metal surface and must be
investigated. Corrective action includes grinding the affected area
to a shallow dish, ensuring that the thickness tolerance is not
exceeded. Testing with magnetic particle testing (MT) or dye
penetrant testing (E') or both, as applicable, is usually
mandatory.
D2-Check Weid Sizes and Dimensions
The size of fillet welds should be verified as meeting the
specified requirements- with due consideration of any weid size
under-run provisions. Some codes allow all or portions of a weld to
under-run the weld size specified. Although not a cause for
rejection, consistently oversized welds should be drawn to the
attention of the welding supervisor. Increasing the size of a 114
in. fillet weld to 5/16 in. involves an increase of more than 50%
in weld metal, heat input and distortion potential. This is
significant especially in terms of job cost.
Weld lengths, where specified, must be verified. Again, this
provision IargeIy applies to fillet welds and in situations where
the required weld length is less than the length of the joint. The
increments and pitch (center-to-center distances) of intermittent
fillet welds are required to be checked.
DLCheck Dimensional Accuracy of the Weldment
The term weldment is used to denote a welded product, be it a
simple assembly of two pieces joined by welding, as in a test
coupon, or a complex finished product made up of subassemblies and
other components. Depending on the nature of the work, the scope
and extent of dimensional checking will vary from a few simple
measurements of flatness, straightness and overall dimensions to a
complex sur- vey involving instruments outside the range normally
associated with welding inspection.
D4-Carry Out or Monitor and Evaluate Specified "DE
Suitably qualified welding inspectors may carry out specified
postwelding NDE. Alternatively, such work is performed by
specialists. In the latter case, the welding
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AWS Visual Inspection Workshop Module #1-Visual Inspection of
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inspectors role is evaluating the reports produced thereby.
These reports will become part of the job records and are to be
retained.
For activities D4 and D5, specialists may be involved so the
welding inspectors role changes to one of monitoring rather than
active inspection. In broad terms, monitoring involves verifying
conformance of the service to both the overall job requirements and
the specifics of the type of service being supplied. Qualification
and calibrations are important factors as is reporting accuracy. It
is important that suitable evidence of certification of NDE
operators who sign conformance reports be produced.
The types of consumables used in the various examinations may be
specified or left to the discretion of the service agency. It is
usual to require some level of Cer- tification. For P,
chloride-free penetrant may be required-particularly in the case of
stainless steel weldments. For RT, the film speed may be specified.
Slower speed films are finer grained, given finer definition but
increase exposure time. For UT, type of couplant to be used may be
specified. AWS D1.l calls for either glycerine or a cellulose-water
gel type product.
In terms of NDE procedures, variables include:
For MT-magnetizing medium, particle type For F-penetrant type
and removal system For RT-radiation source, film type For
UT-transducer types, scanning patterns
DS-Monitor PWHT or Other Postweld Activities
When postweld heat treatment (PWHT) is required, the welding
inspectors roIe is to monitor the overall activities to ensure a
suitable outcome. This activity fails into 4 sections-initial
review, before HT commences, during the HT cycle, and post- HT.
An initial review must be made to see that the weldment will
remain dimension- ally stable during heat treatment. Any enclosed
space must be vented-fully welded doubling plates and double-welded
flanges must have one or more holes drilled to avoid pressure
buildup. Horizontal surfaces must be supported either by the
structure itself or by temporary braces. Irrespective of the type
of heat treat- ment involved, the yield strength of the metal will
be reduced.
Before heat treatment, the number and positioning of
thermocouple leads must be adjusted to give an accurate reflection
of the current temperatures. Thermocouples in the roof are not
likely to give meaningful readings of the job temperature. Dur- ing
PWHT, thermocouples should be mounted on or below the
workpiece.
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AWS Visual Inspection Workshop Module #l-Visual Inspection of
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Heat treatment is typically carried out using a programmed
controller. After charging (or the fitting of thermal mats for
in-situ work) the preset cycle of heat- ing (at a specified rate),
holding for the required time at temperature, and con- trolled
cooling (again at a specified rate) to a certain temperature, is
monitored by a recorder, which plots time against temperature on
either a circular or strip chart. Each thermocouple is connected to
a pen so the temperature at any time can be determined. If the heat
treatment is being physically monitored, it is customary for
welding inspectors to sign the chart at the time of their visit to
the work site.
Upon completion of the heat treatment and the removal of
thermocouple leads and temporary supports, a visual inspection
should be made to ensure that no prob- lems have arisen during
treatment.
In particular, the maintenance of dimensions should be
established.
A further visual examination of all welds should be made after
PWHT. While the effect of most postweld heat treatment is to temper
any hardening in the heat affected zone, any differential stresses
developed during welding may have been sufficient to cause
problems. Likely sites are at positions where a number of mem- bers
meet on differing planes such as comer joints, particularly if
gussetted or stiffened. In these locations, multi-axial stresses
which affect the base metals duc- tility may have developed.
With certain types of metais, particularly micro-alloyed and
chrome-moly steels, there is a degree of risk of liquation
cracking, or reheat cracking. The pres- ence of low-melting
temperature phases within a metal can lead to this problem. For
such cases, an NDE examination is frequently required. For
ferromagnetic materials, this is typically MT.
An essential activity that will follow PWHT is a full
dimensional check, with such corrections as necessary. As mentioned
previously, this may or may not be the responsibility of the
welding inspector. If appropriate, it will also be necessary to
plug vent holes. It is usual to have all such holes threaded so
that they may be plugged by the use of set screws.
As a principle, welding should not take place on work that has
undergone postweld heat treatment. Welding will induce further
residual stress in the prod- uct, which was the reason PWHT was
specified in the first instance. If welding is used to carry out a
repair, specific approval should be obtained from the Engineer of
Record beforehand.
Other finishing operations, such as painting, are normally not
part of the welding inspectors work.
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AWS Visual Inspection Workshop Module #l-Visual Inspection of
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D-Finalize and Collate Inspection Documentation
It is the responsibility of the welding inspector to keep
originals (or copies, as appropriate) of all inspection-related
documents. With this aspect in mind, prudent welding inspectors
make timely preparation. One method is to draw up a list of all the
expected activities and open a file with some or all of the
following lis