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SENIOR WELDING INSPECTION
CONTENTS
Section Subject
1.0 Duties of the Senior Welding Inspector
2.0 Terms and Defin itions
3.0 Planning
4.0 Codes and Standards
5.0 Calibration of Welding Equipment
6.0 Destructive Testing
7.0 Heat Treatment
8.0 WPS and Welder Qualifications
9.0 Materials Inspection
10.0 Residual Stress and Distor tion
11.0 Weldabil ity of Steels
12.0 Weld Fractures
13.0 Welding Symbols
14.0 NDT
15.0 Welding Consumables
16.0 GMAW
17.0 SMAW
18.0 SAW
19.0 GTAW
20.0 Weld Imperfections
21.0 Weld Repairs
22.0 Welding Safety
23.0 Appendices
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Section 1
Duties of the Senior Welding Inspector
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1 General
The Senior Welding Inspector has primarily a
supervisory/managerial role,which could encompass the management
and control of an inspectioncontract. The role would certainly
include leading a team of Welding
Inspectors, who will look to the Senior Welding Inspector for
guidance,especially on technical subjects. The Senior Welding
Inspector will beexpected to give advice, resolve problems, take
decisions and generallylead from the front, sometimes in difficult
situations.
The attributes required by the Senior Welding Inspector are
varied and theemphasis on certain attributes and skills may differ
from project to project.Essentially though the Senior Welding
Inspector will require leadershipskills, technical skills and
experience.
2 Leadership Skills
Some aspects on the theory of leadership may be taught in the
classroom,but leadership is an inherent part of the character and
temperament of anindividual. Practical application and experience
play a major part in thedevelopment of leadership skills and the
Senior Welding Inspector shouldstrive to improve and fine tune
these skills at every opportunity.
The skills required for the development of leadership
include:
A willingness and ability to accept instructions or orders from
senior staffand to act in the manner prescribed.
A willingness and ability to give orders in a clear and concise
manner,whether verbal or written, which will leave the recipient in
no doubt as towhat action or actions are required.
A willingness to take responsibility, particularly when things
go wrong,perhaps due to the Senior Welding Inspectors direction, or
lack of it.
A capacity to listen (the basis for good communication skills)
if and whenexplanations are necessary, and to provide constructive
reasoning andadvice.
A willingness to delegate responsibility to allow staff to get
on with thejob and to trust them to act in a professional manner.
The SeniorWelding Inspector should, wherever possible, stay in the
background,managing.
A willingness and ability to support members of the team on
technicaland administrative issues.
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3 Technical Skills
A number of factors make up the technical skills required by the
SeniorWelding Inspector and these are a knowledge of:
Technology; Normative documents;
Planning;
Organisation;
Auditing;
4 Knowledge of Technology
Welding technology knowledge required by the Senior Welding
Inspector isvery similar to that required by the Welding Inspector,
but with someadditional scope and depth.
Certain areas where additional knowledge is required are:
A knowledge of quality assurance and quality control.
A sound appreciation of the four commonly used non-destructive
testingmethods.
A basic understanding of steel metallurgy for commonly
weldedmaterials and the application of this understanding to the
assessment offracture surfaces.
Assessment of non-destructive test reports, particularly the
interpretationof radiographs.
5 Knowledge of Normative Documents
It is not a requirement for Inspectors at any level to memorise
the content ofrelevant normative documents, except possibly with
the exception of takingexaminations.
Specified normative documents (specifications, standards, codes
ofpractice, etc) should be available at the workplace and the
Senior WeldingInspector would be expected to read, understand and
apply therequirements with the necessary level of precision and
direction required.
The Senior Welding Inspector should be aware of the more widely
usedstandards as applied in welding and fabrication. For
example:
BS EN ISO 15614 / ASME IX Standards for welding
procedureapproval
BS 4872, BS EN 287 / ASME IX Standards for welder approval.
PED BS 5500 / ASME VIII Standards for quality of
fabrication.
BS EN ISO 9000 2000 Standards for quality management.
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6 Knowledge of Planning
Any project or contract will require some planning if inspection
is to becarried out effectively and within budget.
See unit: Planning for more detailed information.
7 Knowledge of Organisation
The Senior Welding Inspector must have good organisational
skills in orderto ensure that the inspection requirements of any
quality/inspection plan canbe met, within the allocated time,
budget and using the most suitablepersonnel for the activity.
Assessment of suitable personnel may requireconsideration of their
technical, physical and mental abilities in order toensure that
they are able to perform the tasks required of them.
Otherconsiderations would include availability of inspection
personnel at the time
required, levels of supervision and the monitoring of the
inspectors activitiesform start to contract completion.
8 Knowledge of Quality/Auditing
There are many situations in manufacturing or on a project where
the SeniorWelding Inspector may be required to carry out
audits.
See section on: Quality Assurance/Quality Control and Inspection
for moredetailed information.
9 Man ManagementAs mentioned above, the Senior Welding Inspector
will have to direct andwork with a team of Inspection personnel
which he may well have to pick.He will have to liaise with Customer
representatives, sub-contractors andthird party Inspectors. He may
have to investigate non-compliances, dealwith matters of discipline
as well as personal matters of his staff.
To do this effectively he needs skills in man management.
10 Recruitment
When recruiting an individual or a team the SWI will first have
to establishthe requirements of the work. Among them would be:
What skills are definitely required for the work and what
additional oneswould be desirable?
Are particular qualifications needed?
Is experience of similar work desirable?
What physical attributes are needed?
Is the work local, in-shop, on-site, in a third world
country?
Does the job require working unsociable hours being away from
home
for long periods?
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Is the job for permanent staff or for a fixed term?
If overseas what are the leave and travel arrangements?
What is the likely salary?
During subsequent interviews the SWI will need to assess other
aspects of
the candidates suitability:
Has he the ability to work on his own initiative?
Can he work as part of a team?
If overseas has the person been to a similar location?
What is his marital/home situation?
Are there any Passport/Visa problems likely?
11 Morale and Motivation
The morale of a workforce has a significant effect on its
performance so theSWI must strive to keep the personnel happy and
motivated and be able todetect signs of low morale.
Low morale can lead to among other things:
Poor productivity, less good workmanship, lack of diligence,
taking shortcuts, ignoring safety procedures and higher levels of
absenteeism.
The SWI needs to be able to recognise these signs and others
such aspersonnel not starting work promptly, taking longer breaks,
talking in groups
and grumbling about minor matters.
A good supervisor should not allow his workforce to get into
such a state.
He must keep them motivated by:
His own demeanour does he have drive and enthusiasm or is heseen
to have no energy and generally depressed. The workforce willreact
accordingly.
Is he seen to be leading from the front in a fair and consistent
manner?
Favouritism in the treatment of staff, on disciplinary matters,
the
allocation of work, allotment of overtime, weekend working
andholidays are common causes of problems
Keep them informed in all aspects of the job and their
situation.Rumours of impending redundancies or cuts in allowances
etc will notmake for good morale.
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12 Discipline
Any workforce must be working in a disciplined manner, normally
to rulesand standards laid down in the Companys conditions of
employment orrelevant company handbook. The SWI must have a good
understanding of
these requirements and be able to apply them in a fair and
equitablemanner.
He must have a clear understanding as to the limits of his
authority knowing how far he can go in disciplinary
proceedings.
The usual stages of disciplinary procedure are:
The quiet word
Formal verbal warning
Written warning
Possible demotion, transfer, suspension Dismissal with
notice
Instant dismissal.
Usually after the written warning stage the matter will be
handled by theCompanys Personnel or Human Resources Department.
It is of vital importance that the company rules are rigorously
followed asany deviation could result in claims for unfair or
constructive dismissal.
In dealing with disciplinary matters the SWI must:
Act promptly
Mean what he says
Treat everyone fairly and as an adult.
Avoid constant complaining on petty issues
Where there are serious breaches of company rules by one or two
peoplethe rest of the workforce should be informed of the matter so
that rumourand counter-rumours can be quashed.
Some matters of discipline may well arise because of incorrect
workingpractices, passing off below quality work, signing for work
which has notbeen done, etc.
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In all such cases the SWI will need to carry out an
investigation and applydisciplinary sanctions to the personnel
involved. To do this:
First establish the facts by interviewing staff, from the
relevantrecords, by having rechecks on part of the job.
If any suspicions are confirmed, transfer/remove suspect
personnelfrom the job pending disciplinary proceedings. If the
personnel areemployed by a sub-contractor then a meeting with the
sub-contractorwill be needed to achieve the same end.
Find out the extent of the problem, is it localised or
widespread?
Is there need to inform the customer and third party
inspector?
Formulate a plan of action, with other company departments
wherenecessary, to retrieve the situation.
Carry out the necessary disciplinary measures on the
personnelinvolved.
Convene a meeting with the rest of the workforce to inform them
of thesituation and ensure that any similar lapses will be dealt
with severely.
Follow up the meeting with a written memo.
13 Summary
The Senior Welding Inspectors role can be varied and complex, a
numberof skills need to be developed in order for the individual to
be effective in therole. Every Senior Welding Inspector will have
personal skills and attributeswhich can be brought to the job, some
of the skills identified above mayalready have been mastered or
understood. The important thing for the
individual to recognise is not only do they have unique
abilities which theycan bring to the role, but they also need to
strive to be the best they can bystrengthening identifiable weak
areas in their knowledge and understanding.Some ways in which these
goals may be achieved is through:
Embracing facts and realities.
Being creative.
Being interested in solving problems.
Being pro-active not reactive
Having empathy with other people.
Having personal values.
Being objective.
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Section 2
Terms and Definitions
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Note:The following definitions are taken from BS 499-1:1991
Welding terms andsymbols Glossary for welding, brazing and thermal
cutting
Welding:
An operation in which two or more parts are united by means of
heat orpressure or both, in such a way that there is continuity in
the nature of themetal between these parts.
Brazing:A process of joining generally applied to metals in
which, during or afterheating, molten filler metal is drawn into or
retained in the space betweenclosely adjacent surfaces of the parts
to be joined by capillary attraction. In
general, the melting point of the filler metal is above 450C but
always belowthe melting temperature of the parent material.
Braze welding:The joining of metals using a technique similar to
fusion welding and a fillermetal with a lower melting point than
the parent metal, but neither usingcapillary action as in brazing
nor intentionally melting the parent metal.
Weld:A union of pieces of metal made by welding.
Joint:A connection where the individual components, suitably
prepared andassembled, are joined by welding or brazing.
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Type of joint Sketch Definition
Butt joint A connection between the endsor edges of two parts
making an
angle to one another of 135 to
180inclusive in the region of thejoint
T joint A connection between the end oredge of one part and the
face ofthe other part, the parts makingan angle to one another of
more
than 5up to and including 90inthe region of the joint
Corner joint A connection between the endsor edges of two parts
making anangle to one another of more
than 30but less than 135in theregion of the joint
Edge joint A connection between the edgesof two parts making an
angle to
one another of 0to 30inclusive
in the region of the joint
Cruciform joint A connection in which two flatplates or two bars
are welded toanother flat plate at right anglesand on the same
axis
Lap joint A connection between twooverlapping parts making
an
angle to one another of 0 to 5inclusive in the region of the
weldor welds
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1 Types of Welds
1.1 From configuration point of view
Butt weld Fillet weld
Autogenous weld:A fusion weld made without filler metal. Can be
achieved by TIG, plasmaelectron beam, laser or oxy-fuel gas
welding.
Slot weld:A joint between two overlapping components made by
depositing a filletweld round the periphery of a hole in one
component so as to join it to thesurface of the other component
exposed through the hole.
In a butt oint
In a T oint
In a corner oint
Butt weld
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Plug weld:A weld made by filling a hole in one component of a
workpiece with fillermetal so as to join it to the surface of an
overlapping component exposedthrough the hole (the hole can be
circular or oval).
1.2 From the penetration point of view
Full penetration weld:A welded joint where the weld metal fully
penetrates the joint with completeroot fusion. In US the preferred
term is complete joint penetration weld or
CJP for short (see AWS D1.1.)
Partial penetration weld:A welded joint without full
penetration. In US the preferred term is partialjoint penetration
weld or PJP for short.
2 Types of Joint (see BS EN ISO 15607)
Homogeneous jo int:Welded joint in which the weld metal and
parent material have no significantdifferences in mechanical
properties and/or chemical composition. Example:two carbon steel
plates welded with a matching carbon steel electrode.
Heterogeneous joint:Welded joint in which the weld metal and
parent material have significantdifferences in mechanical
properties and/or chemical composition. Example:a repair weld of a
cast iron item performed with a nickel base electrode.
Dissimilar joint:Welded joint in which the parent materials have
significant differences inmechanical properties and/or chemical
composition. Example: a carbonsteel lifting lug welded onto an
austenitic stainless steel pressure vessel.
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3 Features of the Completed Weld
Parent metal:Metal to be joined or surfaced by welding, braze
welding or brazing.
Filler metal:Metal added during welding, braze welding, brazing
or surfacing.
Weld metal:All metal melted during the making of a weld and
retained in the weld.
Heat-affected zone (HAZ):The part of the parent metal that is
metallurgically affected by the heat ofwelding or thermal cutting,
but not melted.
Fusion line:
The boundary between the weld metal and the HAZ in a fusion
weld. This isa non-standard term for weld junction.
Weld zone:The zone containing the weld metal and the HAZ.
Weld face:The surface of a fusion weld exposed on the side from
which the weld hasbeen made.
Root:
The zone on the side of the first run farthest from the
welder.
Toe:The boundary between a weld face and the parent metal or
between runs.This is a very important feature of a weld since toes
are points of high stressconcentration and often they are
initiation points for different types of cracks(eg fatigue cracks,
cold cracks). In order to reduce the stress concentration,toes must
blend smoothly into the parent metal surface.
Excess weld metal:Weld metal lying outside the plane joining the
toes. Other non-standardterms for this feature: reinforcement,
overfill.
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Root
Parentmetal
Weldmetal
HAZ
Weldzone
Fusionline
Weldface Toe
Parent
metal
Excessweld metal
Excessweld metal
Butt weld
Fusionline
Weldmetal
Root
Parentmetal
HAZ
Weldzone
Weldface
Toe
Parentmetal
Excessweld metal
Fillet weld
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4 Weld Preparation
A preparation for making a connection where the individual
components,suitably prepared and assembled, are joined by welding
or brazing.
4.1 Features of the weld preparationAngle of bevel:The angle at
which the edge of a component is prepared for making a weld.In case
of a V preparation for a MMA weld on carbon steel plates, this
angle
is between 25-30. In case of a U preparation for a MMA weld on
carbon
steel plates, this angle is between 8-12. In case of a single
bevelpreparation for a MMA weld on carbon steel plates, this angle
is between
40-50.In case of a single J preparation for a MMA weld on carbon
steel
plates, this angle is between 10-20.
Included angle:The angle between the planes of the fusion faces
of parts to be welded. Inthe case of single V, single U, double V
and double U this angle is twice thebevel angle. In case of single
bevel, single J, double bevel and double J, theincluded angle is
equal to the bevel angle.
Root face:The portion of a fusion face at the root that is not
bevelled or grooved. Itsvalue depends on the welding process used,
parent material to be weldedand application; for a full penetration
weld on carbon steel plates, it has avalue between 1-2mm (for the
common welding processes).
Gap:The minimum distance at any cross section between edges,
ends orsurfaces to be joined. Its value depends on the welding
process used andapplication; for a full penetration weld on carbon
steel plates, it has a valuebetween 1-4mm.
Root radius:The radius of the curved portion of the fusion face
in a component preparedfor a single J, single U, double J or double
U weld. In case of MMA,MIG/MAG and oxyfuel gas welding on carbon
steel plates, the root radiushas a value of 6mm in case of single
and double U preparations and 8mm incase of single and double J
preparations.
Land:The straight portion of a fusion face between the root face
and the curvedpart of a J or U preparation. Can be 0. Usually
present in case of weldpreparations for MIG welding of aluminium
alloys.
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4.2 Types of preparation
Open square butt preparation
This preparation is used for welding thin components, either
from one sideor both sides. If the root gap is zero (ie if
components are in contact), thispreparation becomes a closed square
butt preparation (unrecommendeddue to the lack of penetration
problems!).
Single V preparation
The V preparation is one of the most common preparations used in
welding;it can be produced using flame or plasma cutting (cheap and
fast). Forthicker plates a double V preparation is preferred since
it requires less fillermaterial to complete the joint and the
residual stresses can be balanced onboth sides of the joint
resulting in lower angular distortion.
Angle ofbevel
Included angle
Gap Root face
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Double V preparation
The depth of preparation can be the same on both sides
(symmetric doubleV preparation) or the depth of preparation can be
deeper on one sidecompared with the opposite side (asymmetric
double V preparation).Usually, in this situation the depth of
preparation is distributed as 2/3 of thethickness of the plate on
the first side with the remaining 1/3 on thebackside. This
asymmetric preparation allows for a balanced welding
sequence with root back gouging, giving lower angular
distortions. Whilstsingle V preparation allows welding from one
side, double V preparationrequires both sides access (the same
applies for all double sidepreparations).
Single U preparation
U preparation can be produced only by machining (slow and
expensive).However, tighter tolerances obtained in this case
provide for a better fit-upthan in the case of V preparations.
Usually it is applied for thicker platescompared with single V
preparation (requires less filler material to completethe joint and
this lead to lower residual stresses and distortions). Similar
withthe V preparation, in case of very thick sections a double U
preparation canbe used.
Included angle
Angle ofbevel
Root
radius
Root faceGap
Land
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Double U preparation
Usually this type of preparation does not require a land
(exception:aluminium alloys).
Single V preparation with backing strip
Backing strips allow the production of full penetration welds
with increasedcurrent and hence increased deposition
rates/productivity without thedanger of burn-through. Backing
strips can be permanent or temporary.Permanent types are of the
same material being joined and are tack weldedin place. The main
problems related with this type of weld are poor fatigueresistance
and the probability of crevice corrosion between the parent
metaland the backing strip. It is also difficult to examine by NDT
due to the built-increvice at the root of the joint. Temporary
types include copper strips,ceramic tiles and fluxes.
Single bevel preparation
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Double bevel preparation
Single J preparation
Double J preparation
All these preparations (single/double bevel and single/double J)
can be usedon T joints as well. Double preparations are recommended
in case of thicksections. The main advantage of these preparations
is that only onecomponent is prepared (cheap, can allow for small
misalignments).
For further details regarding weld preparations, please refer to
BS EN ISO
9692 standard.
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5 Size of But t Welds
Full penetration but t weld
Partial penetration butt weld
Actual throatthickness
Design throatthickness
As a general rule:
Actual throat thickness = design throat thickness + excess weld
metal.
Full penetration butt weld ground flush
Butt weld between two plates of d ifferent thickness
Actual throat thickness=design throatthickness
Design throatthickness
Actual throatthickness
Actual throat thickness =maximumthicknessthrough the joint
Design throat thickness= thickness ofthethinner plate
Run (pass):
The metal melted or deposited during one passage of an
electrode, torch orblowpipe.
Single run weld Multi run weldLayer:
A stratum of weld metal consisting of one or more runs.
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Types of butt weld (from accessibil ity poin t of view):
Single side weld Double side weld
6 Fillet Weld
A fusion weld, other than a butt, edge or fusion spot weld,
which isapproximately triangular in transverse cross section.
6.1 Size of fil let welds
Unlike butt welds, fillet welds can be defined using several
dimensions.
Actual throat th ickness:The perpendicular distance between two
lines, each parallel to a line joiningthe outer toes, one being a
tangent at the weld face and the other beingthrough the furthermost
point of fusion penetration
Design throat thickness:The minimum dimension of throat
thickness used for purposes of design.Also known as effective
throat thickness. Symbolised on the drawing with
a.
Leg length:The distance from the actual or projected
intersection of the fusion facesand the toe of a fillet weld,
measured across the fusion face. Symbolised onthe drawing with
z'.
Leg length
Actual throatthickness
Design throatthickness
Leg length
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6.2 Shape of fil let welds
Mitre fillet weld:A flat face fillet weld in which the leg
lengths are equal within the agreedtolerance. The cross section
area of this type of weld is considered to be a
right angle isosceles triangle with a design throat thickness a
and a leglength z. The relation between design throat thickness and
leg length is:
a = 0,707 z. or z = 1,41 a.
Convex fi llet weld:A fillet weld in which the weld face is
convex. The above relation betweenthe leg length and the design
throat thickness written in case of mitre filletwelds is also valid
for this type of weld. Since there is an excess weld metalpresent
in this case, the actual throat thickness is bigger than the
designthroat thickness.
Concave fillet weld:A fillet weld in which the weld face is
concave. The above relation betweenthe leg length and the design
throat thickness written in case of mitre fillet
welds is not valid for this type of weld. Also, the design
throat thickness isequal to the actual throat thickness. Due to the
smooth blending betweenthe weld face and surrounding parent
material, the stress concentrationeffect at the toes of the weld is
reduced compared with the previous type.This is why this weld is
highly desired in case of applications subjected tocyclic loads
where fatigue phenomena might be a major cause for failure.
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Asymmetrical fi llet weld :A fillet weld in which the vertical
leg length is not equal with the horizontalleg length. The relation
between the leg length and the design throatthickness written in
case of mitre fillet welds is not valid for this type of
weldbecause the cross section is not an isosceles triangle.
Throatsize
Verticalleg size
Horizontal
leg size
Deep penetration fillet weld:A fillet weld with a deeper than
normal penetration. It is produced using highheat input welding
processes (ie SAW or MAG with spray transfer). Thistype of weld
uses the benefits of greater arc penetration to obtain therequired
throat thickness whilst reducing the amount of deposited
metalneeded, thus leading to a reduction in residual stress level.
In order toproduce a consistent and constant penetration, the
travel speed must bekept constant, at a high value. As a
consequence, this type of weld isusually produced using mechanised
or automatic welding processes. Also,the high depth-to-width ratio
increases the probability of solidificationcentreline cracking. In
order to differentiate this type of welds from theprevious types,
the throat thickness is symbolised with s instead of a.
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6.3 Compound of but t and fil let welds
A combination of butt and fillet welds used in case of T joints
with full orpartial penetration or butt joints between two plates
with different thickness.Fillet welds added on top of the groove
welds improve the blending of weld
face towards parent metal surface and reduce the stress
concentration atthe toes of the weld.
Double bevel compound weld
Filletweld
Bevelweld
7 Welding Posit ion, Weld Slope and WeldRotation
Weld posi tion:The orientation of a weld expressed in terms of
working position, weld slopeand weld rotation (for further details,
please see ISO 6947).
Weld slope:The angle between root line and the positive X axis
of the horizontalreference plane, measured in mathematically
positive direction (ie counter-
clockwise).
Weld rotationThe angle between the centreline of the weld and
the positive Z axis or aline parallel to the Y axis, measured in
the mathematically positive direction
(ie counter-clockwise) in the plane of the transverse cross
section of theweld in question.
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Welding position Sketch Definition
Flat A welding position in whichthe welding is horizontal,with
the centreline of
the weld vertical. Symbolaccording ISO 6947 PA.
Horizontal-vertical A welding position in whichthe welding is
horizontal(applicable in case of filletwelds). Symbol accordingISO
6947 PB
Horizontal A welding position in whichthe welding is
horizontal,with the centreline of theweld horizontal.
Symbolaccording ISO 6947 PC
Vertical up A welding position in which
the welding is upwards.Symbol according ISO 6947 PF.
Vertical down A welding position in whichthe welding is
downwards.Symbol according ISO 6947 PG
Overhead A welding position in which
the welding is horizontal andoverhead, with the centre-line of
the weld vertical.Symbol according ISO 6947 PE.
Horizontal-overhead
A welding position in whichthe welding is horizontal andoverhead
(applicable incase of fillet welds). Symbolaccording ISO 6947
PD.
PG
PF
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Tolerances for the welding positions
8 Weaving
Transverse oscillation of an electrode or a blowpipe nozzle
during thedeposition of weld metal. This technique is generally
used in case of vertical
up welds.
Stringer bead:
A run of weld metal made with little or no weaving motion.
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Section 3
Planning
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1 General
The Senior Welding Inspector would almost certainly be involved
in planningfor inspection at one or more of the following stages of
a project;
Pre-contract Identification of the job requirements, recruiting
andallocating suitably trained and qualified staff, gathering
together
relevant normative documents, technical data and drawings,
producingwork/inspection schedules and quality plans as well as
generaladministration.
In-contract Application of inspection methodologies to
therequirements of the contract specification, production and
collection ofinspection and test reports/documentation.
Post-contract Compilation of inspection reports, certification
and testdata.
There are a number of methods of planning for inspection
activities, themethod selected being dependant on a number of
factors, primarily therequirements of the client and the specific
project.
The various methods are as follows;
In-situ inspection; an inspector(s) placed permanently at the
work place. Theinspector would be expected to work independently,
responsible for usingthe allocated inspection time in a useful and
expedient manner. Periodicvisits to the work place would be made by
the Senior Inspector.
2 Gantt ChartsGantt charts define stages of production and
estimated work time for eachstage.
A Gantt chart is a popular type of bar chart/graph that
illustrates a projectscheduleie list of a project's terminal
elements. Terminal elements comprisethe work breakdown structure
(WBS) of the project and are the lowestactivity or deliverable,
with intended start and finish dates. Terminalelements are not
further subdivided,
Terminal elements are the items that are estimated in terms of
resourcerequirements, budget and duration linked by dependencies
and schedules.
An example of a typical Gantt chart that could be used to plan
inspectionactivities for either manufacturing or construction is
shown below.
The WBS/task elements are listed on the left hand side and the
start andcompletion of each activity is represented by a bar to the
right of the activity.
The time period in this example is represented in months, both
planned andactual. Some Gantt charts may show time in weeks, which
can also bebroken down into days.
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http://../wiki/Bar_charthttp://../wiki/Schedule_%28project_management%29http://../wiki/Schedule_%28project_management%29http://../wiki/Projecthttp://../wiki/Terminal_elementhttp://../wiki/Work_breakdown_structurehttp://../wiki/Work_breakdown_structurehttp://../wiki/Terminal_elementhttp://../wiki/Projecthttp://../wiki/Schedule_%28project_management%29http://../wiki/Schedule_%28project_management%29http://../wiki/Bar_chart
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3 Critical Path Analysis (CPA)
Critical path analysis (CPA) is a powerful project management
tool thathelps to schedule and manage complex projects. Developed
in the 1950s tocontrol large defence projects, CPA has been used
routinely since then. As
with Gantt charts, CPA helps plan all tasks that must be
completed as partof a project. They act as the basis both for
preparation of a schedule, and ofresource planning. During
management of a project, they allow monitoringof achievement of
project goals.
CPA can also show where remedial action needs to be taken in
order to geta project back on course.
The benefit of using CPA over Gantt charts is that CPA formally
identifiestasks which must be completed on time in order for the
whole project to becompleted on time, and also identifies which
tasks can be delayed for a
while if resources needto be reallocated to catch up on missed
tasks.
A further benefit of CPA is that it helps to identify the
minimum length of timeneeded to complete a project. Where there is
a need to run an acceleratedproject, fast track, it helps to
identify which project steps should beaccelerated in order to
complete the project within the available time. Thishelps to
minimise cost while still achieving objectives.
The disadvantage of CPA is that the relation of tasks to time is
not asimmediately obvious as with Gantt charts. This can make them
more difficultto understand for someone who is not familiar with
the technique.
CPA are presented using circle and arrow diagrams. These circles
showevents within the project, such as the start and finish of
tasks. Circles arenormally numbered to allow identification of
them. An arrow runningbetween two event circles shows the activity
needed to complete that task.A description of the task is written
underneath the arrow. The length of thetask is shown above it. By
convention, all arrows run left to right.
An example of a very simple diagram is shown below:
This shows the start event (circle 1), and the completion of the
Recruit &allocate inspection staff task (circle 2). The arrow
between the two circlesshows the activity of carrying out Recruit
& allocate inspection staff. Thetime allocated for this
activity is 4 weeks.
1 24 Wks
Recruit & allocate
inspection
staffSimple Circle and Arrow
0 4A
START
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Rev 1 July 2008Planning.
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In the example above, the numbers above the circles show the
earliestpossible time that this stage of the project will be
reached.
Where one activity cannot start until another has been completed
and whenother activities need to be scheduled it is useful to
tabulate the terminal
elements and allocate time against each activity. For example
the inspectionactivities for a project could be shown as:
The above tabulated terminal elements can now be shown as an
algorithm,see the following example
IDENTIFICATIO
NTERMINAL ELEMENT /
ACTIVITY
SCHEDULED
COMPLETION
TIME
ALLOCATED
A Recruit & allocateins ection staff To be completed first 4
weeks
B
Review fabrication
drawings, material &
consumable certificates
Start when A is
completed 2 weeks
CReview WPSs, WPQRs
& WATCs Start when A is
completed 2 weeks
D
Witness & test WPSs &
WPQRs
Start when B is
completed
3 weeks
E
Witness welder qualificationtests
Start when C is
completed 2 weeks
F
Prepare quality plans &
identify inspection
requirements
Start when C, D & Eare completed
2 weeks
GVisual inspection andtesting of production
welds
Start when F is
completed 9 weeks
TOTAL TIME ALLOCATED 24 weeks
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Critical path analysis for inspection project.
1 2 3 5 6
4
AB D
CE
F
4 Wks 2 Wks 3 Wks 2 Wks
2
Wks
2
Wks0 4 6
6
11 13
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R
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In the example, the activities of B & C' cannot be started
until 'A' has beencompleted.
This diagram also brings out a number of other important
points:
Within CPA, reference to activities is made by the numbers in
thecircles at each end. For example, task A would be called
'activity 1 to2'.
Task 'B' would be 'activity 2 to 3'.
Activities are not drawn to scale. In the diagram above,
activities are 8,4, 3 and 2 weeks long.
In the example the numbers above the circles indicate the
earliestpossible time that this stage in the project will be
reached.
CPA is an effective and powerful method of assessing:
What tasks must be carried out
Where parallel activity can be performed
The shortest time in which you can complete a project
Resources needed to execute a project
The sequence of activities, scheduling and timings involved
Task priorities
The most efficient way of shortening time on urgent
projects.
An effective Critical Path Analysis can make the difference
between
success and failure on complex projects. It can be very useful
forassessing the importance of problems faced during the
implementation ofthe plan.
4 Programme Evaluation and Review Technique (PERT)
PERT is a variation on CPA but takes a slightly more sceptical
view of timeestimates made for each project stage. To use it,
estimate the shortestpossible time each activity will take, the
most likely length of time, and thelongest time that might be taken
if the activity takes longer than expected.
The formula below is used to calculate the time for each project
stage:
Shortest time + 4 x likely time + longest time6
This helps to bias time estimates away from the unrealistically
short time-scales normally assumed.
A variation of both CPA and PERT is a technique known as
reversescheduling, which the completion date for the last terminal
element for theproject is determined and then all other operations
are worked back from
this date, each operation having its own target date.
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Rev 1 Jul 08Planning.
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5 Summary
The Senior Welding Inspector doe not need to have an in-depth
knowledgeof planning and would not be responsible for the planning
of inspectionactivities on a large project or contract, this would
be the responsibility of
the planning team or planning department.IHowever the SWI does
need to have a basic understanding of projectplanning as inspection
tasks must link in with other terminal activities toensure that
inspection tasks are carried out on a timely and cost
effectivebasis, in accordance with the planning system being used
on a particularproject or contract.
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Section 4
Codes and Standards
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GeneralThe control of quality in a fabrication and welding
situation is achieved byworking to company procedures and codes of
construction or standards.The latter may be international,
national, companys own or specific to theparticular client or
contract.
Company procedures are usually covered in Quality Manuals the
scope ofwhich may vary widely depending upon the size of company,
its range ofwork, its working practices and many other factors.
1 Company Manuals
1.1 Quality assurance manual
Quality assurance is defined in IS0 9000 as; part of quality
managementfocused on providing confidence that quality requirements
will be fulfilled.
Essentially what the QA manual sets out is how the company is
organised,to lay down the responsibilities and authority of the
various departments,how these departments interlink. The manual
usually covers all aspects ofthe company structure, not just those
aspects of manufacture.
1.2 Quality control manual
Quality control is defined in ISO 9000 as; part of quality
managementfocused on fulfilling quality requirements.
The QC manual will be the manual most often referred to by the
SWI as itwill spell out in detail how different departments and
operations areorganised and controlled.
Typical examples would be: production and control of drawings,
howmaterials and consumables are purchased, how welding procedures
areproduced, etc.
Essentially all operations to be carried out within the
organisation will havecontrol procedures laid down.
In particular it will lay down how the Inspection function,
whether visual,dimensional or NDT, will be performed. Inspection
being defined as theactivity of measuring, examining and testing
characteristics of a product orservice and comparing these to a
specified requirement. Such requirementsare laid down in codes of
practice and standards.
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2 Auditing
Auditing is a term originating from accountancy practice which
involves anindependent accountant checking the accounts of a
company to see if theaccounts are fair and accurate. A similar
checking process is now widely
practised in manufacturing and construction industries and
inspectionpersonnel will be involved in the carrying out of this
operation.
Different types of audits may be performed:
Full audit of a company, usually carried out by a third party
such as aCertifying Authority, checking the company for the award
of a QAaccreditation system such as ISO 9000 or ASME Stamp.
Major audit by a potential customer prior to placement of a
largecontract. This is usually carried out to demonstrate the
company has allthe necessary facilities, plant, machinery,
personnel and quality systems
in place to enable them to successfully complete the contract.
Part audits carried out as ongoing demonstration that the quality
system
is working properly.
An example of the latter case would be where a Senior Inspector
isresponsible for signing-off the data book or release certificate
for a product.After checking that all the necessary documents are
in the package and thatthey have been correctly completed and
approved where necessary, theSWI would look at a part of the job a
beam, a piece of pipework etc andcrosscheck against the drawings,
mill certificates, inspection reports etc thatall comply with the
job requirements.
3 Codes and Standards
It is not necessary for the Inspector to carry a wide range of
codes andstandards in the performance of his/her duties. Normally
the specification ormore precisely the contract specification is
the only document required.However the contract specification may
reference supporting codes andstandards and the inspector should
know where to access these normativedocuments.
The following is a list of definitions relating to codes and
standards whichthe Inspector may come across whilst carrying
inspection duties
3.1 Definitions
Normative document:A document that provides rules, guidelines or
characteristics for activities ortheir results.
The term normative document is a generic term, which covers
documentssuch as standards, technical specifications, codes of
practice andregulations.*
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Standard:A document that is established by consensus and
approved by a recognisedbody.
A standard provides, for common and repeated use, guidelines,
rules, andcharacteristics for activities or their results, aimed at
the achievement of theoptimum degree of order in a given context.
*
Harmonised standards:Standards on the same subject approved by
different standardising bodies,that establish interchangeability of
products, processes and services, ormutual understanding of test
results or information provided according tothese standards*
Code of practice:
A document that recommends practices or procedures for the
design,manufacture, installation, maintenance, utilisation of
equipment, structuresor products.
A code of practice may be a standard, a part of a standard or
independentof a standard*
Regulation: A document providing binding legislative rules that
is adopted by anauthority.*
Author ity: A body (responsible for standards and regulations
legal or administrativeentity that has specific tasks and
composition) that has legal powers andrights.*
Regulatory authority: Authority that is responsible for
preparing or adopting regulations*
Enforcement authority:Authority that is responsible for
enforcing regulations*
Specification:Document stating requirements. Meaning full data
and its supportingmedium stating needs or expectations that is
stated, generally implied orobligatory.**
Procedure:Specified way to carry out an activity or a process*.
Usually it is a writtendescription of all essential parameters and
precautions to be observed whenapplying a technique to a specific
application following an establishedstandard, code or
specification
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Instruction: A written description of the precise steps to be
followed based on anestablished procedure, standard, code or
specification.
Quality plan:A document specifying which procedures and
associated resources shall beapplied by whom and when to a specific
project, product, process orcontract*
* ISO IEC Guide 2 Standardisation and related activities General
vocabulary** EN ISO 9000 2000 Quality management systems
Fundamentals andvocabulary
4 Summary
Application of the requirements of the quality manuals, the
standards andcodes of practice ensure that a structure or component
will have anacceptable level of quality and be fit for the intended
purpose.
Applying the requirements of a standard, code of practice or
specificationcan be a problem for the inexperienced Inspector.
Confidence in applyingthe requirements of one or all of these
documents to a specific applicationonly comes with use over a
period of time.
If in doubt the Inspector must always refer to a higher
authority in order to
avoid confusion and potential problems.
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BS NUMBER TITLE
BS499: Part 1 Glossary of Welding Terms.
BS 709 Methods of destructive testing fusion welded joints and
weld metal in steel.
BS 1113 Specification for design and manufacture of water-tube
steam generatingplant.
BS 1453 Specification for filler materials for gas welding.
BS 1821 Specification for class I oxy -acetylene welding of
ferritic steel pipe work forcarrying fluids.
BS 2493 Low alloy steel electrodes for MMA welding
BS 2633 Specification for class I arc welding of Ferritic steel
pipe work for carryingfluids.
BS 2640 Specification for class II oxy - acetylene welding of
carbon steel pipe workfor carrying fluids.
BS 2654 Specification for manufacture of vertical steel welded
non-refrigeratedstorage tanks with butt-welded shells for the
petroleum industry.
BS 2901 Part 3: Filler rods and wires for copper and copper
alloys.
BS 2926 Specification for chromium & chromium-nickel steel
electrodes for MMA
BS 2926 Specification for chromium & chromium-nickel steel
electrodes for MMA
BS 3019 TIG welding.
BS 3604 Steel pipes and tubes for pressure purposes; Ferritic
alloy steel withspecified elevated temperature properties for
pressure purposes.
BS 3605 Specification for seamless tubes.
BS 4515 Specification for welding of steel pipelines on land and
offshore.
BS 4570 Specification for fusion welding of steel castings.
BS 4677 Specification for arc welding of austenitic stainless
steel pipe work forcarrying fluids.
BS 4872 Part 1: Approval testing of welders when procedure
approval is not required. Fusionwelding of steel.
BS 4872 Part 2: TIG or MIG welding of aluminium and its
alloys.
BS 6323 Specification for seamless and welded steel tubes for
automobile,mechanical and general engineering purposes.
BS 6693 Method for determination of diffusible hydrogen in weld
metal.
BS 6990 Code of practice for welding on steel pipes containing
process fluids or theirresidues.
BS 7191 Specification for weldable structural steels for fixed
offshore structures.
BS 7570 Code of practice for validation of arc welding
equipment.
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BS EN NUMBER TITLE
BS EN 287 Part 1: Qualification test of welders - Fusion welding
- Steels.
BS EN 440 Wire electrodes and deposits for gas shielded metal
arc of non-alloyand fine grain s teels.
BS EN 499 Covered electrodes for manual metal arc welding of
nonalloy and finegrain steels.
BS EN 3834-Parts 1 to 5
Quality requirements for fusion welding of metallic
materials
BS EN 756 Wire electrodes and flux wire combinations for
submerged arc welding ofnon-alloy and fine grain steels.
BS EN 760 Fluxes for submerged arc welding.
BS EN 970 Non-destructive examination of fusion welds - visual
examination.
BS EN 910 Destructive tests on welds in metallic materials -
Bend tests.
BS EN 12072 Filler rods and wires for stainless steels.
BS EN ISO 18274 Aluminium and aluminium alloys & magnesium
alloys. Nickel & nickelalloys.
Note:The Inspector should have an awareness of s tandards that
are printed in bold.
BS EN NUMBER TITLE
BS EN 1011Part 1:Part 2:Part 3
Part 4.
Welding recommendations for welding of metallic
materials.General guidance for arc welding.Arc welding of ferr it
ic steels.Arc welding of stainless steels
Arc welding of aluminium and aluminium alloys.EN 1320
Destructive tests on welds in metallic materials.
EN 1435 Non-destructive examination of welds - Radiographic
examination of weldedjoints.
BS EN 10002 Tensile testing of metallic materials.
BS EN 10020 Definition and classification of grades of
steel.
BS EN 10027 Designation systems for steels.
BS EN 10045 Charpy impact tests on metallic materials.
BS EN 10204 Metallic products - types of inspection
documents.
BS EN 22553 Welded, brazed and soldered joints - symbol ic
representation on
drawings.BS EN 24063 Welding, brazing, soldering and braze
welding of metal. Nomenclature
of processes and reference numbers for symbolic representation
ondrawings.
BS EN 25817 Arc welded joints in steel. Guidance on quality
levels forimperfections.
BS EN 26520 Classifi cation of imperfections in metallic fusion
welds, withexplanations.
BS EN 26848 Specification for tungsten electrodes for inert gas
shielded arc welding andfor plasma cutting and welding.
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ISO NUMBER: TITLE:
ISO 857 - 1 Welding and allied processes - Vocabulary - Part 1 -
Metal weldingprocesses.
ISO 6947 Welds - Working posit ions - definitions of angles of
slope and rotation.
ISO 9606 2 Qualification test of welders fusion welding.Part 2
Aluminium & aluminium alloys.
ISO 15607 Specification and qualification of welding procedures
for metallicmaterials - General rules.
ISO 15608 Welding - Guidelines for a metallic material grouping
system.
ISO 15609 - 1 Specification and qualification of welding
procedures for metallicmaterials - Welding procedure specification
- Part 1: Arc welding.
ISO 15610 Specification and qualification of welding procedures
for metallic materials-Qualification based on tested welding
consumables.
ISO 15611 Specification and qualification of welding procedures
for metallic materials-Qualification based on previous welding
experience.
ISO 15613 Specification and qualification of welding procedures
for metallic materials -Qualification based on pre -
production-welding test.
ISO 15614 Specification and qualification of welding procedures
for metallicmaterials - Welding procedure test.
Part 1:Part 2:Part 3:Part 4:Part 5:Part 6:Part 7:
Part 8:Part 9:Part 10Part 11Part 12Part 13
Arc and gas welding of steels and arc welding of nickel and
nickel alloys.Arc welding of aluminium and its alloys*Welding
procedure tests for the arc welding of cast irons*Finishing welding
of aluminium castings*Arc welding of titanium, zirconium and their
alloys.Copper and copper alloys*Not used
Welding of tubes to tube-plate joints.Underwater hyperbaric wet
welding*Hyperbaric dry welding*Electron and laser beam weldingSpot,
seam and projection welding*Resistance butt and flash welding*
Note:The Inspector should have an awareness of s tandards that
are printed in bold.*Proposed
.
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Section 5
Calibration of Welding Equipment
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Rev 1 July 2008Calibration of Welding Equipment
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1 Introduction
BS 7570 - Code of practice for validation of arc welding
equipment is astandard that gives guidance to:
Manufacturers about the accuracy required from output meters
fitted towelding equipment to show welding current, voltage etc
End users who need to ensure that the output meters provide
accuratereadings
The Standard refers to two grades of equipment - standard grade
andprecision grade.
Standard grade equipment is suitable for manual and
semi-automaticwelding processes.
Precision grade equipment is intended for mechanised or
automatic weldingbecause there is usually a need for greater
precision for all weldingvariables as well as the prospect of the
equipment being used for higherduty cycle welding.
2 Terminology
BS 7570 defines the terms it uses - such as:
Calibration:Operations for the purpose of determining the
magnitude of errors of a
measuring instrument etc
Validation:Operations for the purpose of demonstrating that an
item of weldingequipment, or a welding system, conforms to the
operating specification forthat equipment or system
Accuracy:Closeness of an observed quantity to the defined, or
true, value
Thus, when considering welding equipment, those that have output
meters
for welding parameters (current, voltage, travel speed etc.) can
be calibratedby checking the meter reading with a more accurate
measuring device and adjusting the readings appropriately.
Equipment that does not have output meters (some power sources
forMMA, MIG/MAG) cannot be calibrated but they can be validated,
that is tomake checks to see that the controls are functioning
properly.
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3 Calibration Frequency
BS 7570 recommends re-calibration/validation:
At yearly intervals (following an initial consistency test at 3
monthly
intervals) for standard grade equipment At 6 monthly intervals
for precision grade equipment.
However, the Standard also recommends that
re-calibration/validation maybe necessary more frequently. Factors
that need to be considered are:
The equipment manufacturers recommendations
The users requirements
If the equipment has been repaired re-calibration should always
becarried out
There is reason to believe the performance of the equipment
has
deteriorated
4 Instruments for Calibration
Instruments used for calibration should:
Be calibrated by a recognised calibrator - using standards that
aretraceable to a national standard
Be at least twice, and preferably five times, more accurate than
theaccuracy required for the grade of equipment
For precision grade equipment it will be necessary to use
instrumentswith much greater precision for checking output
meters
5 Calibration Methods
The Standard gives details about the characteristics of power
source types,how many readings should be taken for each parameter
and guidance onprecautions that may be necessary.
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Rev 1 July 2008Calibration of Welding Equipment
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The Standard gives guidance about minimising any drop in line
voltage byensuring that:
The current return cable is as short as practical and is heavy,
lowresistance, cable
The current-return connector is suitably rated and is firmly
attached andso does not overheat due to high resistance
The standard gives data for line voltage drops (DC voltage)
according tocurrent, cable cross section and cable length (for both
copper andaluminium cables).
Wire feed speedFor constant voltage (self-adjusting arc)
processes such as MIG/MAG thestandard recognises that calibration
of the wire feeder is generally notneeded because it is linked to
current.
If calibration is required, it is recommended that the time be
measured (inseconds) for ~1m of wire to be delivered (using a
stopwatch or an electronictimer).
The length of wire should then be measured (with a steel rule)
to anaccuracy of 1mm and the feed speed calculated.
Travel speedWelding manipulators, such as rotators and robotic
manipulators, as well as
the more conventional linear travel carriages, influence heat
input and otherproperties of a weld and should be checked at
intervals.
Most of the standard devices can be checked using a stopwatch
andmeasuring rule, but more sophisticated equipment, such as a
tacho-generator, may be appropriate.
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Power
Source
Wire Feeder
17
{arc voltage
4
5
32
6
An example of a welding circuit (for MIG/MAG)
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Section 6
Destructive Testing
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1 Introduction
European Welding Standards require test coupons that are made
forwelding procedure qualification testing to be subjected to
non-destructivetesting and then destructive testing.
The tests are called destructive tests because the welded joint
is destroyedwhen various types of test piece are taken from it.
Destructive tests can be divided into 2 groups, those used
to:
Measure a mechanical property quantitative tests
Assess the joint quality qualitative tests
Mechanical tests are quantitative because a quantity is measured
amechanical property such as tensile strength, hardness and
impact
toughness.
Qualitative tests are used to verify that the joint is free from
defects theyare of sound quality - and examples of these are bend
tests, macroscopicexamination and fracture tests (fillet fracture
and nick-break).
2 Test Types, Test Pieces and Test Object ives
Various types of mechanical test are used by material
manufacturers/suppliers to verify that plates, pipes, forgings etc
have the minimum propertyvalues specified for particular
grades.
Design engineers use the minimum property values listed for
particulargrades of material as the basis for design and the most
cost-effectivedesigns are based on an assumption that welded joints
have properties thatare no worse than those of the base metal.
The quantitative (mechanical) tests that are carried out for
weldingprocedure qualification are intended to demonstrate that the
joint propertiessatisfy design requirements.
The emphasis in the following sub-sections is on the destructive
tests and
test methods that are widely used for welded joints.
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2.1 Transverse tensile tests
Test objectiveWelding procedure qualification tests always
require transverse tensile teststo show that the strength of the
joint satisfies the design criterion.
Test specimensA transverse tensile test piece typical of the
type specified by EuropeanWelding Standards is shown below.
Parallellength
Standards, such as EN 895, that specify dimensions for
transverse tensiletest pieces require all excess weld metal to be
removed and the surface tobe free from scratches.
Test pieces may be machined to represent the full thickness of
the joint butfor very thick joints it may be necessary to take
several transverse tensiletest specimens to be able to test the
full thickness.
Test methodTest specimens are accurately measured before
testing. Specimens arethen fitted into the jaws of a tensile
testing machine and subjected to acontinually increasing tensile
force until the specimen fractures.
The tensile strength (Rm) is calculated by dividing the maximum
load by thecross-sectional area of the test specimen - measured
before testing.
The test is intended to measure the tensile strength of the
joint and therebyshow that the basis for design, the base metal
properties, remains the validcriterion.
Acceptance cri ter iaIf the test piece breaks in the weld metal,
it is acceptable provided thecalculated strength is not less than
the minimum tensile strength specified,which is usually the minimum
specified for the base metal material grade.
In the ASME IX code, if the test specimen breaks outside the
weld or fusionzone at a stress above 95% of the minimum base metal
strength the test
result is acceptable.
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2.2 All-weld tensile tests
Test objectiveThere may be occasions when it is necessary to
measure the weld metalstrength as part of welding procedure
qualification particularly for elevated
temperature designs.
The test is carried out in order to measure not only tensile
strength but alsoyield (or proof strength) and tensile
ductility.
All weld tensile tests are also regularly carried out by welding
consumablemanufacturers to verify that electrodes and filler wires
satisfy the tensileproperties specified by the standard to which
the consumables are certified.
Test specimensAs the name indicates, test specimens are machined
from welds parallel
with their longitudinal axis and the specimen gauge length must
be 100%weld metal.
Round tensile specimen from awelding procedure qualification
testpiece
Round tensile specimen from anelectrode classification test
piece
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Test methodSpecimens are subjected to a continually increasing
force in the same waythat transverse tensile specimens are
tested.
Yield (Re) or proof stress (Rp) are measured by means of an
extensometer
that is attached to the parallel length of the specimen and is
able toaccurately measure the extension of the gauge length as the
load isincreased.
Typical load extension curves and their principal
characteristics are shownbelow.
Load-extension curve for a steelthat shows a distinct yield
point atthe elastic limit
Load-extension curve for a steel (orother metal) that does not
show adistinct yield point; proof stress is ameasure of the elastic
limit
Tensile ductility is measured in two ways:
% elongation of the gauge length (A%)
% reduction of area at the point of fracture (Z%)
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The schematics below illustrate these two ductility
measurements.
2.3 Impact toughness tests
Test objectiveCharpy V notch test pieces have become the
internationally acceptedmethod for assessing resistance to brittle
fracture by measuring the energyto initiate, and propagate, a crack
from a sharp notch in a standard sizedspecimen subjected to an
impact load.
Design engineers need to ensure that the toughness of the steel
that is usedfor a particular item will be high enough to avoid
brittle fracture in serviceand so impact specimens are tested at a
temperature that is related to the
design temperature for the fabricated component.
C-Mn and low alloy steels undergo a sharp change in their
resistance tobrittle fracture as their temperature is lowered so
that a steel that may havevery good toughness at ambient
temperature may show extreme brittlenessat sub-zero temperatures as
illustrated in following figure.
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-50 -40 -30 -20 -10 0 10 20 30 40
Ductile fracture(0% crystallinity)
Britt le fracture(100% crystall inity)
Upper shelf
Lower shelf
Transition Range
Test temperature, C
Impactenergy
The transition temperature is defined as the temperature that is
mid-waybetween the upper shelf (maximum toughness) and lower shelf
(completelybrittle). In the above the transition temperature is
20C.
Test specimensThe dimensions for test specimens have been
standardised internationallyand are shown below for full sized
specimens. There are also standarddimensions for smaller sized
specimens, for example 10mm x 7.5mm and
10mm x 5mm.
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Charpy V notch test piece dimensions for fu ll sized
specimens
Specimens are machined from welded test plates with the notch
positionlocated in different locations according to the testing
requirements buttypically in the centre of the weld metal and at
positions across the HAZ asshown below.
Typical notch positions for Charpy V notch test specimens from
double Vbutt welds
Test methodTest specimens are cooled to the specified test
temperature by immersion inan insulated bath containing a liquid
that is held at the test temperature.
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After allowing the specimen temperature to stabilise for a few
minutes it isquickly transferred to the anvil of the test machine
and a pendulum hammerquickly released so that the specimen
experiences an impact load behindthe notch.
The main features of an impact test machine are shown below.
Impact testing machine
Impact specimen on the anvil showingthe hammer position at point
of impact
Charpy V notch test pieces before and after test ing
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The energy absorbed by the hammer when it strikes each test
specimen isshown by the position of the hammer pointer on the scale
of the machine.Energy values are given in Joules (or ft-lbs in US
specifications).
Impact test specimens are taken in triplicate (3 specimens for
each notch
position) as there is always some degree of scatter in the
results particularly for weldments.
Acceptance cri ter iaEach test result is recorded and an average
value calculated for each set ofthree tests. These values are
compared with the values specified by theapplication standard or
client to establish whether specified requirementshave been
met.
After impact testing, examination of the test specimens provides
additionalinformation about their toughness characteristics and may
be added to the
test report:
% crystallinity the % of the fracture face that has
crystallineappearance which indicates brittle fracture; 100%
indicates completelybrittle fracture
Lateral expansion the increase in width of the back of the
specimenbehind the notch as indicated below; the larger the value
the tougherthe specimen
A specimen that exhibits extreme brittleness will show a clean
break. Bothhalves of the specimen having a completely flat fracture
face with little or nolateral expansion.
A specimen that exhibits very good toughness will show only a
small degreeof crack extension, without fracture and a high value
of lateral expansion.
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2.4 Hardness testing
Test objectivesThe hardness of a metal is its resistance to
plastic deformation. This isdetermined by measuring the resistance
to indentation by a particular type
of indenter.
A steel weldment with hardness above a certain maximum may
besusceptible to cracking, either during fabrication or in service,
and weldingprocedure qualification testing for certain steels and
applications that requirethe test weld to be hardness surveyed to
ensure that are no regions of theweldment that exceed the maximum
specified hardness.
Specimens prepared for macroscopic examination can also be used
fortaking hardness measurements at various positions of the
weldment referred to as a hardness survey.
Test methodsThere are 3 widely used methods for hardness
testing:
Vickers hardness test uses a square-base diamond pyramid
indenter
Rockwell hardness test uses a diamond cone indenter or steel
ball
Brinell hardness test uses a ball indenter
The hardness value being given by the size of the indentation
producedunder a standard load. The smaller the indentation, the
harder the metal.
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The Vickers method of testing is illustrated below.
2
ddd 21
+=
Both Vickers and Brinell methods are suitable for carrying out
hardnesssurveys on specimens prepared for macroscopic examination
of weldments.
A typical hardness survey requires the indenter to measure the
hardness inthe base metal (on both sides of the weld), in the weld
metal and across theHAZ (on both sides of the weld).
The Brinell method gives an indentation that is too large to
accuratelymeasure the hardness in specific regions of the HAZ and
is mainly used tomeasure hardness of base metals.
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A typical hardness survey (using Vickers hardness indenter) is
shownbelow:
Hardness values are shown on test reports as a number followed
by lettersindicating the test method, for example:
240HV10 = hardness 240, Vickers method, 10kg indenter load
22HRC = hardness 22, Rockwell method, diamond cone indenter
(scale C)
238HBW = 238 hardness, Brinell method, tungsten ball
indenter
2.5 Crack tip opening displacement (CTOD) testing
Test objectiveCharpy V notch testing enables engineers to make
judgements about risksof brittle fracture occurring in steels, but
a CTOD test measures a materialproperty - fracture toughness.
Fracture toughness data enables engineers to carry out fracture
mechanicsanalyses such as:
Calculating the size of a crack that would initiate a brittle
fracture undercertain stress conditions at a particular
temperature
The stress that would cause a certain sized crack to give a
brittle fractureat a particular temperature
This data is essential for making an appropriate decision when a
crack isdiscovered during inspection of equipment that is
in-service.
Test specimensA CTOD specimen is prepared as a rectangular (or
square) shaped bar cuttransverse to the axis of the butt weld. A V
notch is machined at the centreof the bar, which will be coincident
with the test position - weld metal orHAZ.
A shallow saw cut is then put into the bottom of the notch and
the specimenis then put into a machine that induces a cyclic
bending load until a shallowfatigue crack initiates from the saw
cut.
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The specimens are relatively large typically having a cross
section B x 2Band length ~10B (B = full thickness of the weld). The
test piece details areshown below.
Test methodCTOD specimens are usually tested at a temperature
below ambient andthe temperature of the specimen is controlled by
immersion in a bath of
liquid that has been cooled to the required test
temperature.
A load is applied to the specimen to cause bending and induce
aconcentrated stress at the tip of the crack and a clip gauge,
attached to thespecimen across the mouth of the machined notch,
gives a reading of theincrease in width of the mouth of the crack
as the load is graduallyincreased.
For each test condition (position of notch and test temperature)
it is usualpractice to carry out three tests.
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The schematics below illustrate the main features of the CTOD
test.
Fracture toughness is expressed as the distance that the crack
tip openswithout initiation of a brittle crack.
The clip gauge enables a chart to be generated showing the
increase inwidth of the crack mouth against applied load from which
a CTOD value iscalculated.
Acceptance cri ter iaAn application standard or client may
specify a minimum CTOD value thatindicates ductile tearing.
Alternatively, the test may be for information so thata value can
be used for an engineering critical assessment.
A very tough steel weldment will allow the mouth of the crack to
open widelyby ductile tearing at the tip of the crack whereas a
very brittle weldment willtend to fracture when the applied load is
quite low and without any extensionat the tip of the crack.
CTOD values are expressed in millimetres - typical values might
be
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2.6 Bend testing
Test objectiveBend tests are routinely taken from welding
procedure qualification testpieces and sometimes have to be taken
from welder qualification test
pieces.
Subjecting specimens to bending is a simple method of verifying
that thereare no significant flaws in the joint. Some degree of
ductility is alsodemonstrated.
Ductility is not actually measured but it is demonstrated to be
satisfactory iftest specimens can withstand being bent without
fracture or fissures abovea certain length.
Test specimens
There are 4 types of bend specimen:
Face bendSpecimen taken with axis transverse to butt welds up to
~12mm thicknessand bent so that the face of the weld is on the
outside of the bend (face intension).
Root bendTest specimen taken with axis transverse to butt welds
up to ~12mmthickness and bent so that the root of the weld is on
the outside of the bend(root in tension).
Side bendTest specimen taken as a transverse slice (~10mm) from
the full thicknessof butt welds >~12mm and bent so that the full
joint thickness is tested (sidein tension).
Longitud inal bendTest specimen taken with axis parallel to the
longitudinal axis of a butt weld;specimen thickness is ~12mm and
the face or root of weld may be tested intension.
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Test method
Bend tests for welding procedure qualification (and welder
qualification) areusually guided bend tests.
Guided means that the strain imposed on the specimen is
uniformlycontrolled by being bent around a former with a certain
diameter.
The diameter of the former used for a particular test is
specified in the code,having been determined by the type of
material that is being tested and theductility that can be expected
from it after welding and any PWHT.
The diameter of the former is usually expressed as a multiple of
thespecimen thickness and for C-Mn steel it is typically 4t (t is
the specimenthickness) but for materials that have lower tensile
ductility the radius of theformer may be greater than 10t.
The standard that specifies the test method will specify the
minimum bendangle that the specimen must experience and this is
typically 120-180.
Acceptance cri ter iaBend test pieces should exhibit
satisfactory soundness by not showingcracks or any signs of
significant fissures or cavities on the outside of the
bend.
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Small indications less than about 3mm in length may be allowed
by somestandards.
2.7 Fracture tests
2.7.1 Fillet weld fractures
Test objectiveThe quality/soundness of a fillet weld can be
assessed by fracturing testpieces and examining the fracture
surfaces.
This method for assessing the quality of fillet welds may be
specified byapplication standards as an alternative to macroscopic
examination.
It is a test method that can be used for welder qualification
testing accordingto European Standards but is not used for welding
procedure qualification toEuropean Standards.
Test specimens
A test weld is cut into short lengths (typically 50mm) and a
longitudinalnotch is machined into the specimen as shown below. The
notch profile maybe square, V shaped or U shaped.
Test methodSpecimens are made to fracture through their throat
by dynamic strokes(hammering) or by pressing, as shown below. The
welding standard orapplication standard will specify the number of
tests (typically 4).
Moving pressHammer stroke
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Acceptance cri ter iaThe standard for welder qualification, or
application standard, will specify theacceptance criteria for
imperfections such as lack of penetration into the rootof the joint
and solid inclusions and porosity that are visible on the
fracture
surfaces.
Test reports should also give a description of the appearance of
the fractureand location of any imperfection
2.7.2 Butt weld fractures (nick-break tests)
Test objectiveThe objective of these fracture tests is the same
as for fillet fracture tests.
These tests are specified for welder qualification testing to
EuropeanStandards as an alternative to radiography. They are not
used for weldingprocedure qualification testing to European
Standards.
Test specimensTest specimens are taken from a butt weld and
notched so that the fracturepath will be in the central region of
the weld. Typical test piece types areshown below.
Test methodTest pieces are made to fracture by hammering or
three-point bending.
Acceptance cri ter iaThe standard for welder qualification, or
application standard, will specify theacceptance criteria for
imperfections such as lack of fusion, solid inclusionsand porosity
that are visible on the fracture surfaces.
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Test reports should also give a description of the appearance of
the fractureand location of any imperfection.
3 Macroscopic Examination
Transverse sections from butt and fillet welds are required by
the EuropeanStandards for welding procedure qualification testing
and may be requiredfor some welder qualification testing for
assessing the quality of the welds.
This is considered in detail in a separate section of these
course notes.
Macro examination Micro examination
Objectives Detecting weld defects. (macro)
Measuring grain size. (micro)
Detecting brittle structures, precipitates.
Assessing resistance toward brittle fracture, cold cracking and
corrosionsensitivity
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European Standards for Destructive Test Methods
The following Standards are specified by the European Welding
Standardsfor destructive testing of welding procedure qualification
test welds and forsome welder qualification test welds.
EN 875 Destructive tests on welds in metallic materials
Impacttests Test specimen location, notch orientation
andexamination
EN 895 Destructive tests on welds in metallic materials
Transverse tensile test
EN 910 Destructive tests on welds in metallic materials Bend
tests
EN 1321 Destructive tests on welds in metallic materials
Macroscopic and microscopic examination of weld
BS EN 10002 Metallic materials - Tensile testing. Part 1: Method
of test atambient temperature
BS EN 10002 Tensile testing of metallic materials. Part 5:
Method of testat elevated temperatures
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Section 7
Heat Treatment
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1 Introduction
The heat treatment given to a particular grade of steel by the
steelmaker/supplier should be shown on the material test
certificate and may bereferred to as the supply condition.
Welding inspectors may need to refer to material test
certificates and it isappropriate that they be familiar with the
terminology that is used and havesome understanding of the
principles of some of the most commonly appliedheat treatments.
Welded joints may need to be subjected to heat treatment after
welding(post-weld heat treatment) and the tasks of monitoring the
thermal cycle andchecking the heat treatment records are often
delegated to weldinginspectors.
2 Heat Treatment of SteelThe main supply conditions for weldable
steels are:
As rol led, hot ro lled, hot finishedPlate is hot rolled to
finished size and allowed to air cool; the temperature atwhich
rolling finishes may vary from plate to plate and so strength
andtoughness properties vary and are not optimised;
Appl ied to Relatively thin, lower strength C-steel
TMCP*, control-rolled, thermo-mechanically rolledSteel plate
given precisely controlled thickness reductions during hot
rollingwithin carefully controlled temperature ranges; final
rolling temperature isalso carefully controlled;
Appl ied toRelatively thin, high strength low alloy steels
(HSLA) and for some steelswith good toughness at low temperatures,
eg, cryogenic steels* TMCP =thermo-mechanical controlled
processing
NormalisedAfter working the steel (rolling or forging) to size,
it is heated to ~900C andthen allowed to cool in air to ambient
temperature; this optimises strengthand toughness and gives uniform
properties from item to item for aparticular grade of steel;
Appl ied to C-Mn steels and some low alloy steels
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Because the main reason for (and benefit of) PWHT is to reduce
residualstresses, PWHT is often called stress relief.
Note 1: There are circumstan