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Visual Inspection Works hop

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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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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 component 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 guarantee of suitability for intended service. However, consistent results over a considerable 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 assurance 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 product 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 provisions 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 principle, the purchaser and the manufacturer agree to all the quality criteria applicable 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 specification 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 experience 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 inspections 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 inspection 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 limitations. 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 concerned. 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 potential 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 dimensions be made. Only certain elements of a joint configuration may be altered without 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 variables 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 variables 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 welding 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 equipment 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 Welding

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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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 information 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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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 specifications, 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 inspection 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 procedures, 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 developed 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 processes, 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 production. This possibility should be viewed with restraint. Usually, radiographic examination 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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1.7 Inspection Program- Phase B

AAEstablish Inspection Documentation System

Most organizations operating in the field of welded fabrication will have inspection 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 specified 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 concerned with the job. Incorporating non-conforming product into an assembly is one of the most common problems associated with welded fabrication. It is usually 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 desirable, where possible. to have written procedures to stmcture and standardize action as per the program procedure. For instance, in reviewing rhe purchase documents 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 electrodes; 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 welding (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 initiai 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, circumstances may dictate that the inspector who carried out the initial phase of the welding 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 presetting 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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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 treatment. On working drawings, the dimensional requirements for joint preparations should be shown by the use of the appropriate welding symbol(s). The purpose of

1-1 1 Copyright American Welding Society Provided by IHS under license with AWS Licensee=IHS Subs and Mgrs /IHSINTL003, User=Plata, Rodrigo


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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 significant 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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n

Figure 1.7-Significance of Weld Preparation Elements

reduce the effective weld size. With double-welded joints, separation cannot normally 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 single 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 Welding

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 requirement 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 associated with welding.

BS-Check Adequacy of Alignment Maintenance

During welding, forces of considerable magnitude act on joint members. It is necessary 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 specifications 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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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


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 foundation 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 excessive 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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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 similarly 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 increasing 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 eliminate 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 inclusion. 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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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 weldments 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 welding. 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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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 specified-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 correct the situation.



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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 discontinuities 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 spatter 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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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 diagram, the principle involved.

Figure 1.1 &Backgouging Method, Accessibility



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AWS Visual inspection Workshop Module #1-Visual Inspection of Welding

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 grinding. 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 circumstances 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 situations 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 principle, 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 undesirable. Possibilities include those shown in Figure 1.18.



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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 examination should be carried out to establish freedom from nonconforming surface discontinuities. 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 examination. 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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I CRATER\

THROATA CRACK

Figure 1 .l&Weld-Associated Surface Cracks

overlap, where molten filler metal has rolled over unmelted base metal. a characteristic 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, incomplete 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 examination. Readily apparent incomplete penetration is seen in Figure 1.22.



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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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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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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 treatment 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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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 heating (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 problems 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 members 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 product, 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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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