WIS5 - Handout
WIS5 - Handout
WIS5 - Handout
1 Welding Inspector
WIS5
Introduction
1
Course Objectives
The Course
Course Contents
2
Course Assessment
3
CSWIP 3.1 Examination
Any standard/code
required for the
examinations will be
provided on the
examination day.
70% pass
mark
It is a mandatory
requirement to keep an
up to date log book as
documentary evidence
of your activities.
4
CSWIP 3.1 - 10 Year Renewals
10 years Renewal
examination.
30 General multiple
choice questions.
Assessment of a
welded sample.
5
TWI Certification Ltd
CSWIP Secretariat
TWI Certification Ltd
Granta Park
Great Abington
Cambridge CB21 6AL
United Kingdom
6
Typical Duties of Welding Inspectors
Section 1
Duties of a WI Objectives
Main Responsibilities
Code compliance.
Workmanship control.
Documentation control.
7
Personal Attributes
Welding Inspection
Illumination:
350 lux minimum required.
(recommends 500 lux - normal shop or office lighting).
Vision access:
Eye should be within 600mm of the surface.
Viewing angle (line from eye to surface) to be not less
than 30°.
600mm
30°
8
Welding Inspection
Other aids:
Welding gauges (for checking bevel angles, weld profile,
fillet sizing, undercut depth).
Dedicated weld-gap gauges and linear misalignment
(high-low) gauges.
Straight edges and measuring tapes.
Magnifying lens (if magnification lens used it should
have magnification between X2 to X5).
Measuring devices:
Flexible tape, steel rule.
Temperature indicating crayons.
Welding gauges.
Voltmeter.
Ammeter.
Magnifying glass
Torch/flash light.
Gas flowmeter.
5
6
HI-LO Single Purpose Welding Gauge
IN
0 1/4 1/2 3/4
9
Welding Inspectors Equipment
Multi-meter capable of
measuring amperage
and voltage.
Welding Inspection
Before welding:
(before assembly).
(after assembly).
During welding.
After welding.
10
Typical Duties of a Welding Inspector
Before welding
Preparation:
Familiarisation with relevant documents…
Application standard/code - for visual acceptance
requirements.
Drawings - item details and positions/tolerances etc.
Quality Control Procedures - for activities such as
material handling, documentation control, storage
and issue of welding consumables.
Quality Plan/Inspection and Test Plan/Inspection
Checklist - details of inspection requirements,
inspection procedures and records required.
Before welding
Welding procedures:
Are applicable to joints to be welded and
approved.
Are available to welders and inspectors.
Welder qualifications:
List of available qualified welders related to WPS’s.
Certificates are valid and in-date.
Before welding
Equipment:
All inspection equipment is in good condition and
calibrated as necessary.
All safety requirements are understood and
necessary equipment available.
Materials:
Can be identified and related to test certificates.
Are of correct dimensions.
Are in suitable condition (no damage/contamination).
11
Typical Duties of a Welding Inspector
Before welding
Consumables:
In accordance with WPS’s.
Are being controlled in accordance with procedure.
Weld preparations:
Comply with WPS/drawing.
Free from defects and contamination.
Welding equipment:
In good order and calibrated as required by
procedure.
Before welding
Fit-up
Complies with WPS.
Number/size of tack welds to code/good
workmanship.
Pre-heat
If specified.
Minimum temperature complies with WPS.
During welding
Weather conditions
Suitable if site/field welding.
Welding process(es)
In accordance with WPS.
Welder
Is approved to weld the joint.
Pre-heat (if required).
Minimum temperature as specified by WPS.
Maximum interpass temperature as WPS.
12
Typical Duties of a Welding Inspector
During welding
Welding consumables
In accordance with WPS.
In suitable condition.
Controlled issue and handling.
Welding parameters
Current, voltage and travel speed – as WPS.
Root runs.
If possible, visually inspect root before single-sided
welds are filled up.
During welding
Inter-run dressing
In accordance with an approved method (and back
gouging) to good workmanship standard.
Distortion control.
Welding is balanced and over-welding is avoided.
After welding
Weld identification
Identified/numbered as required.
Is marked with welder’s identity.
Visual inspection
Ensure weld is suitable for all NDT.
Visually inspect and sentence to code
requirements.
Dimensional survey
Ensure dimensions comply with code/drawing.
Other NDT
Ensure all NDT is completed and reports available.
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13
Typical Duties of a Welding Inspector
After welding
Repairs
Monitor repairs to ensure compliance with
procedure PWHT.
Monitor for compliance with procedure.
Check chart records confirm procedure compliance.
Pressure/load test
Ensure test equipment is suitably calibrated.
Monitor to ensure compliance with procedure.
Ensure all records are available.
After welding
Documentation
Ensure any modifications are on as-built drawings.
Ensure all required documents are available.
Collate/file documents for manufacturing records.
Sign all documentation and forward it to QC
department.
Resume:
Check all documentation.
Check all consumables.
Check materials, dimensions and condition.
Preheating, method and temperature.
Check fit and set-up.
Ensure no undue stress is applied to the joint.
Check welding equipment.
14
WI Duties During Welding
Resume:
Check amperage, voltage, polarity.
Ensure the correct technique, run sequence.
Check run out lengths, time lapses.
Cleaning between passes.
Interpass temperatures.
Consumable control.
Maintenance of records and reports.
Resume:
Post cleaning.
Visual inspection of completed welded joint.
Check weld contour and width.
PWHT.
Dimensional accuracy.
Weld reports.
Tie up with NDT.
Monitor any repairs.
Summary of Duties
15
Summary of Duties
Any Questions
?
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16
Welding Terminology and Definitions
Section 2
Terminology Objective
What is a Weld?
17
Welding Terminology and Definitions
What is a Joint?
Joint Terminology
T Edge Cruciform
Butt Preparations
18
Single Sided Butt Preparations
Double-J Double-U
Double-Bevel Double V
Angle of Angle
bevel of
bevel
Land
19
Joint Preparation Terminology
Root
Radius
Root Gap Root Gap Root Face
Root Face
Land
Weld Terminology
20
Welded T Joints
21
Weld Zone Terminology
Face
A B
Weld
metal
Heat
Affected Weld
Zone Boundary
Excess
Cap height
Excess Root
Penetration
Weld width
22
Heat Affected Zone (HAZ)
Toe Blend
Features to Consider
23
Fillet Weld Profiles
Mitre fillet
Concave fillet
A concave profile is preferred for
joints subjected to fatigue
loading.
Convex fillet
b
a = Vertical leg length
b = Horizontal leg length
Note: The leg length should be approximately
equal to the material thickness.
Horizontal
leg length
24
Deep Penetration Fillet Weld Features
a
b
25
Fillet Weld Sizes
Features to Consider
Throat Throat
thickness thickness
is larger is smaller
60° 120°
26
Features to Consider
Features to Consider
a b
4mm 8mm
4mm 2mm
Approximately the same weld volume in both Fillet Welds but the
effective throat thickness has been altered, reducing
considerably the strength of weld B.
4mm 6mm
a b
4mm 6mm
27
Fillet Weld Sizes
4mm a 6mm b
4mm 6mm
Features to Consider
a s
Bevel angle
28
Joint Design and Weld Preparation
Root face
Root face size set to:
Allow controlled root fusion.
Reduce the risk of burn-
through.
Root gap
Root gap set to:
Allow controlled root fusion.
Reduce the risk of burn-
through.
Weld Preparation
included angle
bevel angle
Typical dimensions
Bevel angle 30 to 35°
Root face ~1.5 to ~2.5mm
Root gap ~2 to ~4mm
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Weld Preparation
35°
Weld Preparation
Weld Preparation
MMA MAG
High heat input process allow a larger root face, less weld
metal required, less distortions, higher productivity.
30
Weld Preparation
Weld Preparations
Weld Preparations
31
Weld Preparations
Weld Preparations
offset
Weld Preparations
32
Weld Preparations
60º 70-90º
30º 35-45º
Steel Aluminium
Weld Preparations
Weld Preparations
33
Weld Preparations
Weld Preparations
Weld Preparations
t/3
t
34
Weld Preparation
60°
60°
30°
15°
Weld Preparation
Weld Preparation
60°
35
Weld Preparation
Weld Preparation
Cyclic load
Welding Terminology
Any Questions
?
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36
Welding Imperfections and
Materials Inspection
Section 3
Features to Consider
Root
penetration
Root bead width
37
Features to Consider
x
x x
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Welding Defects
Causes
Too small a root gap.
Arc too long.
Wrong polarity.
Electrode too large for joint preparation.
Incorrect electrode angle.
Too fast a speed of travel for current.
Welding Defects
c. Misplaced welds.
38
Welding Defects
Welding Defects
Smaller (correct)
diameter electrode.
Welding Defects
Causes
Too small a root gap.
Arc too long.
Wrong polarity.
Electrode too large for joint
preparation.
Incorrect electrode angle.
Too fast a speed of travel for current.
39
Welding Defects
Root concavity
Causes
Root gap too large.
Insufficient arc energy.
Excessive back purge TIG.
Welding Defects
Causes
Excessive amperage during
welding of root.
Excessive root gap.
Poor fit up.
Excessive root grinding.
Improper welding
technique.
Welding Defects
Root undercut
Causes
Root gap too large.
Excessive arc energy.
Small or no root face.
40
Welding Defects
Cap undercut
Causes
Excessive welding current.
Welding speed too high.
Incorrect electrode angle.
Excessive weave.
Electrode too large.
Welding Defects
Overlap
Excess weld
metal
Welding Defects
Lack of fusion
Causes
Contaminated weld
preparation.
Amperage too low.
Amperage too high (welder
increases speed of travel).
41
Welding Defects
Causes
Insufficient weld metal
deposited.
Improper welding technique.
Welding Defects
Causes
Insufficient weld metal deposited.
Improper welding technique.
Welding Defects
42
Welding Defects
Gas pores/porosity
Causes
Excessive moisture in flux or preparation.
Contaminated preparation.
Low welding current.
Arc length too long.
Damaged electrode flux.
Removal of gas shield.
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Welding Defects
Gas pores/porosity
Welding Defects
Inclusions - slag
Causes
Insufficient cleaning between passes.
Contaminated weld preparation.
Welding over irregular profile.
Incorrect welding speed.
Arc length too long.
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Welding Defects
Inclusions - slag
Causes
Insufficient cleaning between passes.
Contaminated weld preparation.
Welding over irregular profile.
Incorrect welding speed.
Arc length too long.
Welding Defects
Inclusions - tungsten
Causes
Contamination of weld caused by excessive current
through electrode, tungsten touching weld metal or
parent metal during welding using the TIG welding
process.
Welding Defects
Burn through
Causes
Excessive amperage during welding of root.
Excessive root grinding.
Improper welding technique.
44
Welding Defects
Spatter
Causes
Excessive arc energy.
Excessive arc length.
Damp electrodes.
Arc blow.
Welding Defects
Arc strikes
Causes
Electrode straying
onto parent metal.
Electrode holder with
poor insulation.
Poor contact of earth
clamp.
Welding Defects
Mechanical damage
Chisel
Chisel Marksmarks
Grinding marks
Chisel Marks
45
Welding Defects
2mm
Welding Defects
50mm
3mm
Angular distortion
Measure the distance to the edge of the plate (50mm).
Use a straight edge (rule) to find the amount of
distortion then measure the space (3mm).
This is reported as angular distortion 3mm in 50mm.
Welding Defects
Linear
Excess weld metal
height lowest plate to
highest point
3mm
3mm
46
Any Questions
?
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47
48
Destructive Testing
Section 4
49
Destructive Tests
Macro/micro
examination. 2 x Strength
(transverse
tensile)
Definitions
Malleability.
Ductility. Ability of a material to
withstand deformation
Toughness.
under static compressive
Hardness. loading without rupture.
Tensile Strength.
50
Mechanical Test Samples
Tensile specimens
CTOD specimen
Bend test
specimen
Charpy
specimen
Destructive Testing
Macro + hardness. 5
3
Transverse tensile. 2, 4
Bend tests. 2, 4
Charpy impact tests. 3
Additional tests. 3
4
5
Mechanical Testing
Hardness Testing
51
Hardness Testing
Definition
Measurement of resistance of a material against
penetration of an indenter under a constant
load.
There is a direct correlation between UTS and
hardness.
Hardness tests:
Brinell.
Vickers.
Rockwell.
Hardness Testing
Objectives:
Measuring hardness in different areas of a
welded joint.
Assessing resistance toward brittle fracture, cold
cracking and corrosion sensitivity.
Information to be supplied on the test
report:
Material type.
Location of indentation.
Type of hardness test and load applied on the
indenter.
Hardness value.
Hardness Testing
52
Vickers Hardness Test
53
Brinell Hardness Test
30KN
Ø=10mm
steel ball
Rockwell B Rockwell C
1KN
1.5KN
54
Mechanical Testing
Impact Testing
Objectives:
Measuring impact strength in different weld joint areas.
Assessing resistance toward brittle fracture.
Pendulum
Specimen (striker)
Anvil (support)
55
Charpy V-Notch Impact Test Specimen
Machined notch.
Fracture surface
8 mm
100% bright
crystalline
brittle fracture.
100% Ductile
Machined notch.
Large reduction
in area, shear
lips.
Randomly torn,
dull gray
fracture surface.
28 Joules
56
Comparison Charpy
Impact Test Results
Impact energy joules
Reporting results
Location and orientation of notch.
Testing temperature.
Energy absorbed in joules.
Description of fracture (brittle or ductile).
Location of any defects present.
Dimensions of specimen.
Mechanical Testing
Tensile Testing
57
Tensile Testing
Rm
ReH
ReL
Tensile Tests
58
Tensile Test
Tensile Tests
Tensile Test
TransverseTensile
Transverse tensile
specimen
Specimen
59
Transverse Joint Tensile Test
Objective:
Measuring the overall strength of the weld joint.
Information to be supplied on the test report:
Material type.
Specimen type
Specimen size (see QW-462.1).
UTS.
Location of final rupture.
Weld on plate
60
Transverse Tensile Test
Reporting results:
Type of specimen eg reduced section.
Whether weld reinforcement is removed.
Dimensions of test specimen.
The ultimate tensile strength in N/mm2, psi or
Mpa.
Location of fracture.
Location and type of any flaws present if any.
BS 709/BS EN 10002
All Weld Metal Tensile Testing
Elongation % = 14
X 100
50
Elongation = 28%
61
All-Weld Metal Tensile Test
Gauge length
Object of test:
Ultimate tensile
strength.
Yield strength.
Elongation
%(ductility).
Force Applied
62
All-Weld Metal Tensile Test
Reporting results:
Type of specimen eg reduced section.
Dimensions of test specimen.
The UTS, yield strength in N/mm2, psi or Mpa.
Elongation %.
Location and type of any flaws present if any.
STRA Test
Original CSA
Reduced CSA
63
UTS Calculation
STRA Test
Mechanical Testing
Macro/Micro Examination
64
Macro Preparation
Purpose
To examine the weld cross-section to give assurance
that:
The weld has been made in accordance with the
WPS.
The weld is free from defects.
Macro Preparation
Specimen preparation
Full thickness slice taken from the weld (typically ~10mm
thick).
Width of slice sufficient to show all the weld and HAZ on
both sides plus some unaffected base material.
One face ground to a progressively fine finish (grit sizes
120 to ~400).
Prepared face heavily etched to show all weld runs and all
HAZ.
Prepared face examined at up to x10 (and usually
photographed for records).
Prepared face may also be used for a hardness survey.
Macro Preparation
Purpose
To examine a particular region of the weld or HAZ
in order to:
To examine the microstructure.
Identify the nature of a crack or other
imperfection.
65
Macro Preparation
Specimen preparation
A small piece is cut from the region of interest (typically
up to ~20mm x 20mm).
The piece is mounted in plastic mould and the surface of
interest prepared by progressive grinding (to grit size
600 or 800).
Surface polished on diamond impregnated cloths to a
mirror finish.
Prepared face may be examined in as-polished condition
and then lightly etched.
Prepared face examined under the microscope at up to
~100 – 1000X.
Macro/Micro Examination
Object:
Macro/microscopic examinations are used to
give a visual evaluation of a cross-section of a
welded joint.
Carried out on full thickness specimens.
The width of the specimen should include HAZ,
weld and parent plate.
They maybe cut from a stop/start area on a
welders approval test.
Macro/Micro Examination
Will reveal:
Weld soundness.
Distribution of inclusions.
Number of weld passes.
Metallurgical structure of weld, fusion zone and
HAZ.
Location and depth of penetration of weld.
Fillet weld leg and throat dimensions.
66
Macro Macro/Micro Examination
Macro Micro
Visual examination for Visual examination for
defects. defects and grain
Cut transverse from the structure.
weld. Cut transverse from a
Ground and polished weld.
P400 grit paper. Ground and polished P1200
Acid etch using 5-10% grit paper, 1µm paste.
nitric acid solution. Acid etch using 1-5% nitric
Wash and dry. acid solution.
Visual evaluation under Wash and dry.
5x magnification. Visual evaluation under
Report on results. 100-1000x magnification.
Report on results.
Metallographic Examination
Metallographic Examination
Objectives:
Detecting weld defects (macro).
Measuring grain size (micro).
Detecting brittle structures, precipitates, etc.
Assessing resistance toward brittle fracture, cold
cracking and corrosion sensitivity.
67
Metallographic Examination
Mechanical Testing
Bend Testing
Bend Tests
Object of test:
To determine the soundness of the weld zone. Bend testing
can also be used to give an assessment of weld zone
ductility.
68
Bending Test
Root/face
t up to 12 mm
bend
Thickness of material - t
Bend Testing
69
Bend Tests
Reporting results:
Thickness and dimensions of specimen.
Direction of bend (root, face or side).
Angle of bend (90°, 120°, 180°).
Diameter of former (typical 4T).
Appearance of joint after bending eg type and
location of any flaws.
Bend Testing
Mechanical Testing
70
Fillet Weld Fracture Tests
Object of test:
To break open the joint through the weld to
permit examination of the fracture surfaces.
Specimens are cut to the required length.
A saw cut approximately 2mm in depth is
applied along the fillet welds length.
Fracture is usually made by striking the
specimen with a single hammer blow.
Visual inspection for defects.
Hammer
2mm
notch
Lack of penetration
71
Hammer
2mm
notch
Hammer
Reporting results:
Thickness of parent material.
Throat thickness and leg lengths.
Location of fracture.
Appearance of joint after fracture.
Depth of penetration.
Defects present on fracture surfaces.
72
Mechanical Testing
Nick-Break Testing
Nick-Break Test
Object of test:
To permit evaluation of any weld defects across
the fracture surface of a butt weld.
Specimens are cut transverse to the weld.
A saw cut approximately 2mm in depth is
applied along the welds root and cap.
Fracture is usually made by striking the
specimen with a single hammer blow.
Visual inspection for defects.
Nick-Break Test
3 mm
Approximately 230 mm
Weld reinforcement
may or may not be
removed
73
Nick-Break Test
Nick-Break Test
Reporting results:
Thickness of parent material.
Width of specimen.
Location of fracture.
Appearance of joint after fracture.
Depth of penetration.
Defects present on fracture surfaces.
74
Hydrostatic Test
Vessel configuration:
The test should be done after any stress relief.
Components that will not stand the pressure test
(eg flexible pipes, diaphragms) must be
removed.
The ambient temperature MUST be above 0°C
(preferably 15-20°C).
Hydrostatic Test
Test procedure:
Blank off all openings with solid flanges.
Use correct nuts and bolts, not G clamps.
Two pressure gauges on independent tapping
points should be used.
For safety purposes bleed all the air out.
Pumping should be done slowly (no dynamic
pressure stresses).
Test pressure - see relevant standards (PD 5500,
ASME VIII). Usually 150% design pressure.
Hold the pressure for minimum 30 minutes.
Hydrostatic Test
75
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76
Non-Destructive Testing
Section 5
Non-Destructive Testing
77
Non-Destructive Testing
Volumetric inspection
Ultrasonics (UT).
Radiography (RT).
Penetrant Testing
Main features:
Detection of surface breaking defects only.
This test method uses the forces of capillary
action.
Applicable on any material type, as long they are
non porous.
Penetrants are available in many different types:
Water washable contrast.
Solvent removable contrast.
Water washable fluorescent.
Solvent removable fluorescent.
Post-emulsifiable fluorescent.
78
Penetrant Testing
Step 1: Pre-cleaning
Ensure surface is very clean normally with the use of a
solvent.
Penetrant Testing
Penetrant Testing
79
Penetrant Testing
Penetrant Testing
Penetrant Testing
Fluorescent penetrant
Bleed out viewed under
a UV-A light source
80
Penetrant Testing
Advantages Disadvantages
Simple to use. Surface breaking defect
Inexpensive. only.
Quick results. Little indication of
Can be used on any non- depths.
porous material. Penetrant may
Portability. contaminate component.
Low operator skill Surface preparation
required. critical.
Post cleaning required.
Potentially hazardous
chemicals.
Can not test unlimited
times.
Temperature dependant.
Penetrant Testing
Advantages
Easy to interpret results.
No power requirements.
Relatively little training required.
Can use on all materials.
Disadvantages
Good surface finish needed.
Relatively slow.
Chemicals - health and safety issue.
Any Questions
?
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81
Magnetic Particle Testing (MT)
Main features:
Surface and slight sub-surface detection.
Relies on magnetization of component being tested.
Only ferro-magnetic materials can be tested.
A magnetic field is introduced into a specimen being
tested.
Methods of applying a magnetic field, yoke,
permanent magnet, prods and flexible cables.
Fine particles of iron powder are applied to the test
area.
Any defect which interrupts the magnetic field, will
create a leakage field, which attracts the particles.
Any defect will show up as either a dark indication or
in the case of fluorescent particles under UV-A light a
green/yellow indication.
Collection
of ink
particles
due to
leakage
field
Electro-magnet (yoke) DC or AC
Prods DC or AC
82
Magnetic Particle Testing
A crack like
indication
83
Magnetic Particle Testing
Advantages Disadvantages
Simple to use. Surface or slight
Inexpensive. sub-surface
Rapid results. detection only.
Little surface Magnetic materials
preparation required. only.
Possible to inspect No indication of
through thin defects depths.
coatings. Only suitable for
linear defects.
Detection is required
in two directions.
Advantages
Much quicker than PT.
Instant results.
Can detect near-surface imperfections (by current
flow technique).
Less surface preparation needed.
Disadvantages
Only suitable for ferromagnetic materials.
Electrical power for most techniques.
May need to de-magnetise (machine components).
Any Questions
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84
Ultrasonic Testing (UT)
Ultrasonic Testing
Main features:
Surface and sub-surface detection.
This detection method uses high frequency sound
waves, typically above 2MHz to pass through a material.
A probe is used which contains a piezo electric crystal to
transmit and receive ultrasonic pulses and display the
signals on a cathode ray tube or digital display.
The actual display relates to the time taken for the
ultrasonic pulses to travel the distance to the interface
and back.
An interface could be the back of a plate material or a
defect.
For ultrasound to enter a material a couplant must be
introduced between the probe and specimen.
Ultrasonic Testing
85
Ultrasonic Testing
Material Thk
defect
0 10 20 30 40 50
Ultrasonic Testing
UT set
A scan
display
Angle probe
Ultrasonic Testing
Initial pulse
Defect echo
defect 0 10 20 30 40 50
initial pulse
defect echo
defect 0 10 20 30 40 50
86
Ultrasonic Testing
Advantages Disadvantages
Rapid results. Trained and skilled
Both surface and sub- operator required.
surface detection. Requires high operator
Safe. skill.
Capable of measuring the Good surface finish
depth of defects. required.
May be battery powered. Defect identification.
Portable. Couplant may
contaminate.
No permanent record.
Calibration required.
Ferritic Material (mostly).
Ultrasonic Testing
Advantages
Good for planar defects.
Good for thick sections.
Instant results.
Can use on complex joints.
Can automate.
Very portable.
No safety problems (parallel working is
possible).
Low capital and running costs.
Ultrasonic Testing
Disadvantages
No permanent record (with standard
equipment).
Not suitable for very thin joints <8mm.
Reliant on operator interpretation.
Not good for sizing porosity.
Good/smooth surface profile needed.
Not suitable for coarse grain materials (eg,
castings).
Ferritic materials (with standard equipment).
87
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Radiographic Testing
88
Radiographic Testing
Radiographic Testing
Source
Test specimen
Radiographic film
Radiographic Testing
Source
Image quality indicator
Radiation beam
Test specimen
89
Radiographic Testing
Densitometer
Contrast - relates to the degree of difference.
Definition - relates to the degree of sharpness.
Sensitivity - relates to the overall quality of the radiograph.
Radiographic Sensitivity
7FE12
Radiographic Sensitivity
90
Radiographic Techniques
Film
Film
Film
91
Double Wall Single Image (DWSI)
Film
Identification
Unique identification.
IQI placing.
Pitch marks indicating EN W10
A B
ID MR11
Radiograph
Radiograph
92
Double Wall Double Image (DWDI)
Film
IQI’s are placed on the source or film side.
Source outside film outside (multiple exposure).
A minimum of two exposures.
This technique is intended for pipe diameters less than
100mm.
Identification
Unique identification. 4 3
IQI placing.
EN W10
Pitch marks indicating
readable film length.
1 2
ID MR12
Shot A Radiograph
4 3
1 2
Elliptical radiograph
93
Radiography
Penetrating power
Radiography
Gamma sources
Radiographic Testing
Advantages Disadvantages
Permanent record. Expensive consumables.
Little surface Bulky equipment.
preparation. Harmful radiation.
Defect identification. Defect require significant
No material type depth in relation to the
limitation. radiation beam (not good
Not so reliant upon for planar defects).
operator skill. Slow results.
Thin materials. Very little indication of
depths.
Access to both sides
required.
94
Radiographic Testing
Advantages
Good for non-planar defects.
Good for thin sections.
Gives permanent record.
Easier for 2nd party interpretation.
Can use on all material types.
High productivity.
Direct image of imperfections.
Radiographic Testing
Disadvantages
Health and safety hazard.
Not good for thick sections.
High capital and relatively high running costs.
Not good for planar defects.
X-ray sets not very portable.
Requires access to both sides of weld.
Frequent replacement of gamma source needed
(half life).
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95
96
Welding Procedures
Section 6
WPS Objective
97
Welding Procedure Qualification
98
Welding Procedure Qualification
According to EN Standards
Welding conditions are called welding variables.
99
Welding Procedure Qualification
According to EN Standards
Welding essential variables
According to EN Standards
Welding additional variables
According to EN Standards
Some typical essential variables
Welding process.
Post weld heat treatment (PWHT).
Material type.
Electrode type, filler wire type (classification).
Material thickness.
Polarity (AC, DC+ve/DC-ve).
Pre-heat temperature.
Some typical additional variables
Heat input.
Welding position.
100
Welding Procedures
Welding Procedures
Example codes:
AWS D.1.1: Structural Steel Welding Code.
BS 2633: Class 1 Welding of Steel Pipe Work.
API 1104: Welding of Pipelines.
BS 4515: Welding of Pipelines over 7 Bar.
Welding Procedures
101
Welding Procedures
Welding Procedures
Welding Procedures
102
Welding Procedures
Example:
Welding
procedure
specification
(WPS)
Welding Procedures
Purpose of a WPS
To achieve specific properties, mechanical
strength, corrosion resistance, composition.
To ensure freedom from defects.
To enforce QC procedures.
To standardise on methods and costs.
To control production schedules.
To form a record.
Application standard or contract requirement.
Welding Procedures
103
Welding Procedures
PA 1G/1F Flat/Downhand
PB 2F Horizontal-Vertical
PC 2G Horizontal
PD 4F Horizontal-Vertical (Overhead)
PE 4G Overhead
PF 3G/5G Vertical-Up
PG 3G/5G Vertical-Down
PG
PA
PF
PB
PC
PD
PE
Welding Procedures
104
Welding Procedures
Definitions
Processes to be designated in accordance with
ISO 4063.
Welding positions in accordance with ISO 6947.
Typical WPS form.
Welding Procedures
Welding Procedures
t<3 0.7t to 2t
0.7t to 1.3ta
3<t<12 3 to 2ta
0.5t (3 min) to 1.3ta
0.5t to 2t
12<t<100 0.5t to 1.1t
50 to 2t
t>100 Not applicable
105
Welding Procedures
t<3 0.75 a to No
0.7 to 2 t
1.5 a restriction
No
t>30 >5 a
restriction
Welding Procedures
Welding Procedures
BS EN ISO 15614-1:2012
(Replaced BS EN 288-3)
Range of approval
Other quirks
Approval valid only for process used.
Multi-process - valid for order used…during
approval test.
Processes… Processes may be approved
separately or in combination….
Cannot change multi-run to single run or vice
versa.
106
Welding Procedures
BS EN ISO 15614-1:2012
(Replaced BS EN 288-3)
Thickness definitions
Butt: Parent metal thickness at the joint.
Fillet: Parent metal thickness.
Set-on branch: Parent metal thickness.
Set-in/through branch: Parent metal thickness.
T-butt: Parent metal thickness.
For branch connections and fillet welds, the range of
qualification shall be applied to both parent
materials independently.
Welding Procedures
Note 1:
a is the throat as used for the test piece.
Note 2:
Where the fillet weld is qualified by means of a
butt test, the throat thickness range qualified shall
be based on the thickness of the deposited metal.
Welding Procedures
D<25 0.5 D to 2 D
107
Welding Procedures
108
Monitoring Heat Input
Arc energy
The amount of heat generated in the welding arc
per unit length of weld. Expressed in kilo Joules
per millimetre length of weld (kJ/mm).
Heat input
The energy supplied by the welding arc to the
work piece.
Expressed in terms of; arc energy x thermal
efficiency factor.
Thermal efficiency factor is the ratio of heat
energy introduced into the weld to the electrical
energy consumed by the arc.
136 Flux-cored wire metal-arc welding with active gas shield 0.8
137 Flux-cored wire metal-arc welding with inert gas shield 0.8
138 Metal-cored wire metal-arc welding with active gas shield 0.8
139 Metal-cored wire metal-arc welding with inert gas shield 0.8
109
Monitoring Heat Input
Example
A MAG weld is made and the following conditions
were recorded;
Arc volts = 24
Welding amperage = 240
Travel speed = 300mm/minute.
AE = 1.152 or 1.2kJ/mm.
HI = 1.2 x 0.8 = 0.96kJ/mm.
110
Monitoring Arc Energy
110 26 60 100 =
220 28 90 200 =
120 12 120 90 =
300 28 60 300 =
180 12 120 90 =
110 26 60 300 =
Welder Approval
Example BS EN ISO 9606
Welder Qualification
BS EN ISO 9606
Question: What is the main reason for qualifying
a welder?
111
Welder Qualification
BS EN ISO 9606
An approved WPS should be available covering the
range of qualification required for the welder
approval.
The welder qualifies in accordance with an approved
WPS.
A welding inspector monitors the welding to make
sure that the welder uses the conditions specified by
the WPS.
Welder Qualification
BS EN ISO 9606
The finished test weld is subjected to NDT by the
methods specified by the EN Standard - Visual, MT or
PT and RT or UT.
The test weld may need to be destructively tested - for
certain materials and/or welding processes specified by
the EN Standard or the Client Specification.
A Welder’s Qualification Certificate is prepared showing
the conditions used for the test weld and the range of
qualification allowed by the EN Standard for production
welding.
The Qualification Certificate is usually endorsed by a Third
Party Inspector as a true record of the test.
Welder Qualification
BS EN ISO 9606
The welder is allowed to make production welds within the
range of qualification shown on the Certificate.
The range of qualification allowed for production welding is
based on the limits that the EN Standard specifies for the
welder qualification essential variables.
A Welder’s Qualification Certificate automatically expires if
the welder has not used the welding process for 6 months
or longer.
A Certificate may be withdrawn by the Employer if there is
reason to doubt the ability of the welder, for example:
A high repair rate.
Not working in accordance with a qualified WPS.
112
Welder Qualification
BS EN ISO 9606
Essential variables
Welder Qualification
BS EN ISO 9606
Typical Welder Essential Variables
Welding Process.
Material type.
Electrode type – Filler Material Classification
Material thickness.
Pipe diameter
Welding position.
Weld Backing (an unbacked weld requires more
skill).
Welder Qualification
113
Welder Qualification
Welder Qualification
Welder Qualification
114
Welder Qualification
Example:
Welder
Approval
Qualification
Certification
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115
116
Material Inspection
Section 7
Material Inspection
117
Pipe Inspection
Welded seam
Specification
Plate Inspection
Specification
Rolling Imperfections
Direction of rolling
Cold Laps*
Lamination Segregation
118
Parent Material Imperfections
Lamination
Segregation line
Laminations are caused in the parent plate by the steel making
process, originating from ingot casting defects.
Segregation bands occur in the centre of the plate and are low
melting point impurities such as sulphur and phosphorous.
Laps are caused during rolling when overlapping metal does not
fuse to the base material.
Lapping
Lapping
119
Lapping
Lamination
Lamination
Plate lamination
120
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122
Quality in Welding Codes and Standards
Section 8
Quality in Welding
123
Quality in Welding
Standard/Codes/Specifications
Specifications Codes
Examples: Examples:
Plate, pipe. Pressure vessels.
Forgings, castings. Bridges.
Valves. Pipelines.
Electrodes. Tanks.
Standard/Codes/Specifications
Standard
A document that is established by consensus and
approved by a recognised body.
124
Standard/Codes/Specifications
Specification
A document stating requirements, needs or
expectations.
Standard/Codes/Specifications
Examples of specification
BS 4515
Specification for welding of steel pipelines on land
and offshore.
BS EN 26848
Specification for tungsten electrodes for inert gas
shielded arc welding and for plasma cutting and
welding.
Standard/Codes/Specifications
Examples of standards
BS EN ISO 17637
Non - destructive examination of fusion welds -
visual examination.
BS EN 440
Wire electrodes and deposits for gas shielded
metal arc of non - alloy and fine grain steels.
125
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126
Welding Symbols
Section 9
By symbolic representation.
127
Weld Symbols on Drawings
The above information does not tell us much about the wishes
of the designer. We obviously need some sort of code which
would be understood by everyone.
128
Arrow Line
Reference Line
(AWS A2.4)
Convention of the reference line:
Shall touch the arrow line.
Shall be parallel to the bottom of the drawing.
Reference Line
or
129
Elementary Welding Symbols
Square edge
butt weld
Single-v
butt weld
Single V butt
weld with broad
root face.
Single bevel
butt weld.
Backing run.
Single-J
butt weld.
Surfacing.
Fillet weld.
130
Double Side Weld Symbols
Double V Double U
Dimensions
Convention of dimensions
In most standards the cross sectional dimensions are given to
the left side of the symbol, and all linear dimensions are give
on the right side.
BS EN ISO 22553
a = Design throat thickness.
s = Depth of penetration, throat thickness.
z = Leg length (min material thickness).
AWS A2.4
In a fillet weld, the size of the weld is the leg length.
In a butt weld, the size of the weld is based on the
depth of the joint preparation.
Supplementary Symbols
Ground flush
111
MR M
131
Supplementary Symbols
Toes to be ground
Site Weld smoothly (BS EN only)
Concave or Convex
Welding Symbols
Reference lines
Arrow line
132
ISO 2553/BS EN 22553
Arrow side
Arrow side
Other side
Other side
Both sides
Both sides
133
ISO 2553/BS EN 22553
a b
c d
Mitre Convex
Toes
Concave shall be
blended
NDT WPS
134
ISO 2553/BS EN 22553
Peripheral welds
z10 z8
10 8
10 8
Fillet Welds
z8
or
z8
8
a 5 (z 8)
or
a 5 (z 8)
5
135
ISO 2553/BS EN 22553
n x l (e)
Welds to be
staggered
2 x 40 (50)
111
3 x 40 (50)
Process
All dimensions in mm
z8 3 x 80 (90)
z6 3 x 80 (90)
6
80 80 80
6
8 90 90
90
136
Intermittent Fillet Welds
z n×l(e) a n×l(e)
z n×l(e) a n×l(e)
or
All dimensions in mm
z5 3 x 80 (90)
z6 3 x 80 (90)
5
80 80 80
5
6 90 90 90
MR
M
137
ISO 2553/BS EN 22553
s10
10
15
138
ISO 2553/BS EN 22553
Butt Weld Example
7 10
35 20
30
15
139
ISO 2553/BS EN 22553
Compound Weld Example
Complete the symbol
drawing for the welded z10
cruciform joint provided 30
below. All welds are welded 135/111
with the MAG process and 20
fillet welds with the MMA 7 10 z10
process.
35 20
30
15
z10 a 7
35
135/111
15
z10 All fillet weld leg lengths 10mm
BS EN 22553 Rules
z 10 3 x 50 (50)
50
50
10
140
AWS A2.4 Welding Symbols
1(1-1/8)
1/8
60°
Groove angle
Effective throat
Welding process
GSFCAW
1(1-1/8)
1/8
60°
GMAW
GTAW
SAW
141
AWS Welding Symbols
GSFCAW
1(1-1/8)
Applicable to any
single groove weld
Single bevel
3 – 10
SMAW
3 – 10
Process
3 3
10
2nd operation
1st operation
FCAW
1(1-1/8)
1/8
60°
142
AWS Welding Symbols
Sequence of operations RT
MT
MT
FCAW
1(1-1/8)
1/8
60°
6 leg on member A
6/8
Member A 6
Member B
Fillet Welds
8
8
5 leg on
5x8
vertical
member
5
8
143
Intermittent Fillet Welds
z l-e
z l-e
z l-e
z l-e
Symbol to AWS A2.4
144
AWS A 2.4 Rules - Example
10 3 x 50 (70)
70
50
10
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146
Introduction to Welding Processes
Section 10
Welding Processes
147
Welding Processes
Welding Processes
Welding Processes
148
Welding Processes
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149
150
Welding Processes and Equipment –
Power Source
Sections 11-14
Power Sources
151
MMA - Principle of Operation
FILM MMA
Electrode angle 75-80°
to the horizontal
Consumable electrode
Filler metal core
Flux coating
Direction of
electrode travel
Solidified slag Arc Gaseous shield
Molten weld pool
Parent metal
Weld metal
MMA Welding
Main features:
Shielding provided by decomposition of flux.
Consumable electrode.
Manual process.
Welder controls:
Arc length.
Angle of electrode.
Speed of travel.
Current setting.
152
MMA Welding Variables
Voltage
Measure arc voltage close to arc.
Variable with change in arc length.
Too low, electrode stubs into weld pool.
Too high, spatter, porosity, excess penetration,
undercut, burn-through.
Current
Range set by electrode, diameter, material type
and thickness.
Approx 35A per mm diameter.
Too low – poor start, lack of fusion, slag
inclusions, humped bead shape.
Too high – spatter, excess penetration,
undercut, burn-through.
Polarity
Can be DCEP, DCEN, AC.
Determined by operation and electrode type.
Constant/Drooping
Current Characteristics
Amperage range
OCV
+/- 5 amps
50-90
- Voltage +
Operational
range 20-40V
- Amperage +
As arc length increases
voltage increases and
amperage decreases
153
The Effects of Polarity on Penetration
DC + DC - AC
Travel speed
Controlled by welder.
Often measured as run-out length as time to
burn single rod fairly standard at constant
current.
Too low – wide bead, excess penetration, burn-
through.
Too high – narrow bead, lack of penetration,
lack of fusion, difficult slag removal.
Left to right
Good conditions.
Current too low.
Current too high.
Arc length too short.
Arc length too long.
Travel too slow.
Travel too fast.
154
Operating Factor for MMA
Typical defects:
Slag inclusions.
Arc strikes.
Porosity.
Undercut.
Shape defects (overlap, excessive root
penetration, etc).
Advantages Disadvantages
Field or shop use. High welder skill.
Range of High levels of fume.
consumables. Hydrogen control
All positions. (flux).
Portable. Stop/start problems.
Simple equipment. Low productivity.
155
MMA Welding Consumables
Cellulosic Electrodes
Rutile Electrodes
156
Rutile High Recovery Electrodes
Basic Electrodes
E 50 3 2Ni B 7 2 H10
Covered electrode
Yield strength N/mm2
Toughness
Chemical composition
Flux covering
Weld metal recovery
and current type
Welding position
Hydrogen content
157
BS EN 2560 MMA Covered Electrodes
E 60 1 3
Covered electrode
Tensile strength (p.s.i)
Welding position
Flux covering
TYPES OF ELECTRODES
(for C, C-Mn Steels)
158
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TIG Welding
TIG Basics
Film TIG
Gas nozzle
Gas shield
Arc
Filler rod Weld pool
Weld metal
Parent metal
159
Equipment for TIG
Flow-meter
Arc Starting
Scratch start
Tungsten touched on workpiece.
Short-circuit starts current.
Arc established as torch lifted.
Can leave tungsten inclusions.
Lift Arc
Electronic control very low short-circuit current.
Builds to operational current as torch lifted.
HF
Superimposition of HF high voltage spark.
Polarity
DCEN
Most used.
Tungsten cooled by electron emission.
Workpiece receives more heat.
DCEP
Will clean oxide from Al and Mg.
Heat tends to melt tungsten.
Can be done with water cooled torch.
AC
Usual way to weld Al and Mg to get cleaning.
160
Constant/Drooping
Current Characteristics
Operational
range 20-40V
- Amperage +
As arc length increases
voltage increases and
amperage decreases
Cathodic Cleaning
Square Wave Maximum
AC
Cleaning cycle
70 70
30 30
AC
Penetrating Cycle
30 30
70 70
161
+
+
Negative cycle Positive cycle
0
Polarity
162
Manual TIG
DC Arc
163
AC Arc
GTAW Torch
Torch types:
GTAW Torch
Tungsten
electrode
Torch cap / tungsten Electrode
housing collet Collet
holder
Torch
body Ceramic
nozzle
On/off
switch
164
TIG Welding Sequence
2 4
1 5
1. Slope
2.
3.
4.
5. Postwelding
Pre
Main gas
welding
up
down
supply
current
gas
current
current
to
supply
protect
Timeline
molten pool
prevents burn
upon
craterthrough,
cooling
cracks
tungsten inclusions
4 5
1
2
165
Gas Lens
Stainless steel
wire sieve
Thread for
torch body
Commercially Available
Trailing Shields
166
Pipe Backing Gas Dams
Purging Methods
Tungsten Types
167
Electrode Tip for DCEN
Penetration
increase
electrode diameter
2-2.5 times
Increase
Vertex
angle
Decrease
Bead width
Electrode tip for low increase Electrode tip for high
current welding current welding
168
Orbital TIG
Orbital TIG
Orbital TIG
Click to play
169
Potential Defects
Tungsten inclusions
Thermal shock splinters W.
Touch start fuses spots to workpiece.
Spitting and melting can throw pieces into pool.
Very visible on radiograph but not critical defect.
Solidification cracking
Some compositions inherently crack sensitive.
Impurities often make eutectics.
Fillers designed with elements to react with
impurities, eg Mn used to give high MPt MnS.
Potential Defects
Oxide inclusions
Oxides contribute to lack of fusion.
No fluxing to absorb oxides.
Need to keep good gas cover to avoid oxidation
of reactive metals.
Advantages of TIG
170
Disadvantages of TIG
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MIG/MAG Welding
171
MIG/MAG Welding
Gas nozzle
Consumable
flux/metal cored wire
electrode
Gas shield Contact Tube
Process Characteristics
172
MIG/MAG Equipment
Internal wire
feed system Power cable &
hose
assembly
Power control
panel
Liner for wire
15kg wire spool
Welding gun
Power return assembly
cable
Wire Feeding
173
Types of Wire Drive System
Roll Grooves
174
Torch Components
Welding gun assembly Welding gun body
(less nozzle) On/Off switch
Spatter Hose
protection port
Voltage Dial on
weld machine
- Voltage +
Arc
Length
- Amperage +
Self-Adjusting Arc
Arc and wire feed Arc length increased Wire feed rate is
rate in equilibrium. momentarily, burn constant so original arc
off reduces. length is re established.
175
Self-Adjusting Arc
Arc and wire feed Arc length is decreased Arc length returns to
rate in equilibrium. momentarily, burn off original condition.
increases.
Wire feed at
constant speed
CTWD is increased
which momentarily
increases arc length
As wire feed is
constant, the original
arc length is re
established.
Welding Parameters
176
The Effect of Increasing Arc Voltage
Shielding Gas
Argon:
OK for all metals weldable by MIG.
Supports spray transfer, not good for dip.
Low penetration.
Carbon dioxide:
Use on ferritic steel.
Supports dip and globular, not spray.
Ar based mixtures:
Add He, O2, CO2 to increase penetration.
>20Ar + He, >80Ar + O2, CO2 can spray and
dip.
177
Metal Transfer Modes
178
Dip Transfer
Dip Transfer
No inductance
Time (sec)
179
Practical Effect of Inductance
Advantages
Low energy allows welding in all positions.
Good for root runs in single-sided welds.
Good for welding thin material.
Disadvantages
Prone to lack of fusion.
May not be allowed for high-integrity
applications.
Tends to give spatter.
Globular Transfer
180
Gas Metal Arc Welding
Spray transfer
When current and voltage are raised together higher energy
is available for fusion (typically > ~ 25 volts & ~ 250 amps).
This causes a fine droplets of weld metal to be sprayed from
the tip of the wire into the weld pool.
Transfer-mode advantages
High energy gives good fusion.
High rates of weld metal deposition are given.
These characteristics make it suitable for welding thicker
joints.
Transfer-mode disadvantages.
It cannot be used for positional welding.
Spray Transfer
Continuous transfer
of metal.
High voltage long
arc.
High heat input.
Fluid weld pool.
High deposition.
No spatter.
181
Spray Transfer
Pulsed Transfer
Amps
Time
Advantages
Good fusion.
Small weld pool allows all-position welding.
Disadvantages
More complex and expensive power source.
Difficult to set parameters.
But synergic easy to set, manufacturer
provides programmes to suit wire type, dia.
and type of gas.
182
Pulse Transfer
Although the arc length remains the same, the current will decrease
due to the increased resistance of lengthening the CTWD.
Although the arc length remains the same, the current will increase
due to the decreased resistance of shortening the CTWD.
183
Contact Tip to Nozzle Distance
Filler Wire
Potential Defects
184
MIG/MAG Attributes
Advantages Disadvantages
High productivity. Lack of fusion (dip).
Easily automated. Small range of
All positional (dip consumables.
and pulse). Protection on site.
Material thickness Complex equipment.
range. Not so portable.
Continuous
electrode.
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185
Gas Shielded Principle of Operation
Benefit of Flux
186
FCAW - Differences from MIG/MAG
Welding
Trigger
gun cable
Thread protector
Hand shield
Contact tip
Advantages Disadvantages
Preferred for flat or Produces higher weld
horizontal with profile.
FCAW. Difficult to follow
Slower travel. weld joint.
Deeper penetration. Can lead to burn-
Weld hot longer so through on thin
gasses removed. sheet.
187
Forehand (Push) Technique
Advantages Disadvantages
Preferred method for Produces low weld
vertical up or profile, with coarser
overhead with ripples.
FCAW. Fast travel gives low
Arc gives preheat penetration.
effect. Amount of spatter
Easy to follow weld can increase.
joint and control
penetration.
FCAW Advantages
188
FCAW Disadvantages
189
SAW FILM
SAW Film
Process Characteristics
Process Characteristics
190
SAW Basic Equipment
Transformer/
Power return Rectifier
cable
Power control Welding carriage
panel control unit
Welding carriage
Granulated
flux
Types of Equipment
Hand-held gun
Tractor
SAW Equipment
Wire reel
Slides
Flux
hopper
Wire feed
Feed roll motor
assembly
Torch
assembly
Tracking
Contact tip
system Courtesy of ESAB AB
191
Tractor Units
Courtesy of ESAB AB
Gantry
2D linear movement
only.
For large production.
May have more than
one head.
192
Power Sources
Preferred >1000A.
Can be mechanised or automatic welding.
Not self-regulating arc so must have voltage-
sensing WFS control.
More expensive.
Voltage from WFS control, power source
controls current.
Not for high-speed welding of thin steel.
193
Wire
Fused Fluxes
194
SAW Operating Variables
Welding current.
Current type and polarity.
Welding voltage.
Travel speed.
Electrode size.
Electrode extension why?
Width and depth of the layer of flux.
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195
196
Thermal Cutting Processes
Section 15
A jet of pure oxygen reacts with iron, that has been preheated to
its ignition point, to produce the oxide Fe3O4 by exothermic
reaction. This oxide is then blown through the material by the
velocity of the oxygen stream.
197
Oxyfuel Gas Cutting Process
Good cut - sharp top edge, fine and even drag lines, little oxide
and a sharp bottom edge.
Cut too slow - top edge is melted, Cut too fast - pronounced
deep groves in the lower portion, break in the drag line,
heavy scaling, rough bottom edge. irregular cut edge.
198
Oxyfuel Gas Cutting Quality
Good cut - sharp top edge, fine and even drag lines, little oxide
and a sharp bottom edge.
Preheat flame too low - Preheat flame too high - top edge
deep groves in the lower is melted, irregular cut, excess of
part of the cut face. adherent dross.
Good cut - sharp top edge, fine and even drag lines, little oxide
and a sharp bottom edge.
Nozzle is too high above the works Irregular travel speed - uneven
- excessive melting of the top space between drag lines, irregular
edge, much oxide. bottom with adherent oxide.
199
Mechanised Oxyfuel Cutting
Cutting and
bevelling head.
OFW/C Advantages/Disadvantages
Advantages: Disadvantages:
No need for power High skill factor.
supply portable. Wide HAZ.
Versatile: preheat, Safety issues.
brazing, surfacing, Slow process.
repair, straightening
Limited range of
Low equipment cost. consumables.
Can cut carbon and Not suitable for
low alloy steels. reactive and
Good on thin refractory metals.
materials.
200
Plasma Cutting
Plasma Cutting
No need to promote
oxidation and no preheat.
Works by melting and
blowing and/or vaporisation.
Gases: air, Ar, N2, O2, mix of
Ar + H2, N2 + H2.
Air plasma promotes
oxidation and increased
speed but special electrodes
need.
Shielding gas – optional.
Applications: stainless
steels, aluminium and thin
sheet carbon steel.
Plasma Cutting
201
Arc Air Gouging
202
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203
204
Welding Consumables
Section 16
Welding Consumables
205
Welding Consumables
SAW strips
MIG/MAG
solid wire
SAW Covered
solid wire Courtesy of ESAB AB
electrodes
Welding Gases
GMAW, FCAW, TIG, Oxy-Fuel.
Supplied in cylinders or storage
tanks for large quantities.
Colour coded cylinders to
minimise wrong use.
Subject to regulations concerned
handling, quantities and
positioning of storage areas.
Moisture content is limited to
avoid cold cracking.
Dew point (the temperature at
which the vapour begins to
condense) must be checked.
Welding Consumables
206
Quality Assurance
Welding Consumables:
Filler material must be stored in an area with
controlled temperature and humidity.
Poor handling and incorrect stacking may damage
coatings, rendering the electrodes unusable.
There should be an issue and return policy for
welding consumables (system procedure).
Control systems for electrode treatment must be
checked and calibrated; those operations must be
recorded.
Filler material suppliers must be approved before
purchasing any material.
Welding Consumables
207
MMA Welding Consumables
Tin can
Cellulosic electrodes.
Courtesy of Lincoln Electric
208
MMA Welding Consumables
Cellulosic electrodes:
Covering contains cellulose (organic material).
Produce a gas shield high in hydrogen raising the
arc voltage.
Deep penetration/fusion characteristics enables
welding at high speed without risk of lack of
fusion.
Generates high level of fumes and H2 cold
cracking.
Forms a thin slag layer with coarse weld profile.
Not require baking or drying (excessive heat will
damage electrode covering).
Mainly used for stove pipe welding.
Hydrogen content is 80-90 ml/100g of weld metal.
Cellulosic electrodes
Disadvantages:
Weld beads have high hydrogen.
Risk of cracking (need to keep joint hot during
welding to allow H to escape).
Not suitable for higher strength steels - cracking
risk too high (may not be allowed for Grades
stronger than X70).
Not suitable for very thick sections (may not be
used on thicknesses > ~ 35mm).
Not suitable when low temperature toughness is
required (impact toughness satisfactory down to ~
-20°C).
Cellulosic electrodes
Advantages: Disadvantages:
Deep High in hydrogen.
penetration/fusion. High crack tendency.
Suitable for welding in Rough weld
all positions. appearance.
Fast travel speeds. High spatter contents.
Large volumes of Low deposition rates.
shielding gas.
Low control.
209
MMA Welding Consumables
Rutile electrodes:
Covering contains TiO2 slag former and arc stabiliser.
Easy to strike arc, less spatter, excellent for positional
welding.
Stable, easy-to-use arc can operate in both DC and AC.
Slag easy to detach, smooth profile.
Reasonably good strength weld metal.
Used mainly on general purpose work.
Low pressure pipework, support brackets.
Electrodes can be dried to lower H2 content but cannot
be baked as it will destroy the coating.
Hydrogen content is 25-30 ml/100g of weld metal.
Rutile electrodes
Disadvantages:
They cannot be made with a low hydrogen
content.
Cannot be used on high strength steels or
thick joints - cracking risk too high.
They do not give good toughness at low
temperatures.
These limitations mean that they are only
suitable for general engineering - low
strength, thin steel.
Rutile electrodes
Advantages: Disadvantages:
Easy to use. High in hydrogen.
Low cost/control. High crack tendency.
Smooth weld profiles. Low strength.
Slag easily detachable. Low toughness values.
High deposition
possible with the
addition of iron
powder.
210
MMA Welding Consumables
Characteristics:
Coating is bulked out with iron powder.
Iron powder gives the electrode high recovery.
Extra weld metal from the iron powder can mean
that weld deposit from a single electrode can be as
high as 180% of the core wire weight.
Give good productivity.
Large weld beads with smooth profile can look
very similar to SAW welds.
Disadvantages:
Same as standard rutile electrodes with
respect to hydrogen control.
Large weld beads produced cannot be used for
all-positional welding.
The very high recovery types usually limited to
PA and PB positions.
More moderate recovery may allow PC use.
Basic covering:
Produce convex weld profile and difficult to detach slag.
Very suitable for for high pressure work, thick section
steel and for high strength steels.
Prior to use electrodes should be baked, typically 350°C
for 2 hour plus to reduce moisture to very low levels
and achieve low hydrogen potential status.
Contain calcium fluoride and calcium carbonate
compounds.
Cannot be rebaked indefinitely!
Low hydrogen potential gives weld metal very good
toughness and YS.
Have the lowest level of hydrogen (less than 5ml/100g
of weld metal).
211
MMA Welding Consumables
Basic electrodes
Disadvantages:
Careful control of baking and/or issuing of electrodes is
essential to maintain low hydrogen status and avoid risk
of cracking.
Typical baking temperature 350°C for 1 to 2hours.
Holding temperature 120-150°C.
Issue in heated quivers typically 70°C.
Welders need to take more care/require greater skill.
Weld profile usually more convex.
Deslagging requires more effort than for other types.
Basic Electrodes
Advantages: Disadvantages:
High toughness High cost.
values. High control.
Low hydrogen High welder skill
contents. required.
Low crack tendency. Convex weld
profiles.
Poor stop/start
properties.
Compulsory
Optional
212
BS EN 2560 MMA Covered Electrodes
E 50 3 2Ni B 7 2 H10
Covered electrode
Yield strength N/mm2
Toughness
Chemical composition
Flux covering
Weld metal recovery
and current type
Welding position
Hydrogen content
213
AWS A5.1 Alloyed Electrodes
E 60 1 3
Covered electrode
Tensile strength (p.s.i)
Welding position
Flux covering
E 70 1 8 M G
Covered Electrode
Tensile Strength (p.s.i)
Welding Position
Flux Covering
Moisture Control
Alloy Content
214
AWS A5.1 and A5.5 Alloyed Electrodes
Rutile: Flux-ends in 2 - 3 - 4
Examples: E5012, E6012, E6013, E6014
Basic: Flux-ends in 5 - 6 - 7 - 8
Examples: E6016, E7017, E8018, E9018
Moisture Pick-Up
Electrode Efficiency
215
Covered Electrode Treatment
Baking oven:
Need temperature control.
Requires calibration.
Heated quivers:
For maintaining moisture
out of electrodes when
removed from the holding
oven ie on site.
If necessary, dry up
Rutile electrodes to 120°C- No baking!
Baking in oven 2
Basic electrodes
hours at 350°C!
216
Covered Electrode Treatment
3. Electrode designation.
EN 2560-E 51 3 B
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Welding Consumables
TIG Consumables
217
TIG Welding Consumables
Welding rods:
Supplied in cardboard/plastic tubes.
Fusible Inserts
218
Fusible Inserts
Consumable inserts:
Used for root runs on pipes.
Used in conjunction with TIG welding.
Available for carbon steel, Cr-Mo steel, austenitic
stainless steel, nickel and copper-nickel alloys.
Different shapes to suit application.
Radius
Fusible Inserts
Argon
Low cost and greater availability.
Heavier than air - lower flow rates than Helium.
Low thermal conductivity - wide top bead profile.
Low ionisation potential - easier arc starting,
better arc stability with AC, cleaning effect.
For the same arc current produce less heat than
helium - reduced penetration, wider HAZ.
To obtain the same arc power, argon requires a
higher current - increased undercut.
219
Shielding Gases for TIG Welding
Helium
Costly and lower availability than Argon.
Lighter than air - requires a higher flow rate
compared with argon (2-3 times).
Higher ionisation potential - poor arc stability
with AC, less forgiving for manual welding.
For the same arc current produce more heat
than argon - increased penetration, welding of
metals with high melting point or thermal
conductivity.
To obtain the same arc power, helium requires a
lower current - no undercut.
Hydrogen
Not an inert gas - not used as a primary
shielding gas.
Increase the heat input - faster travel speed and
increased penetration.
Better wetting action - improved bead profile.
Produce a cleaner weld bead surface.
Added to argon (up to 5%) - only for austenitic
stainless steels and nickel alloys.
Flammable and explosive.
Nitrogen
Not an inert gas.
High availability – cheap.
Added to argon (up to 5%) - only for back purge
for duplex stainless, austenitic stainless steels
and copper alloys.
Not used for mild steels (age embrittlement).
Strictly prohibited in case of Ni and Ni alloys
(porosity).
220
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Welding Consumables
MIG/MAG Consumables
221
MIG/MAG Welding Consumables
Welding wires:
Supplied on wire/plastic spools or coils.
Random or line winding.
Welding wires:
Carbon and low alloy wires may be copper coated.
Stainless steel wires are not coated.
Wires must be kept clean and free from oil and dust.
Flux cored wires does not require baking or drying.
BS EN 14341 - G 46 3 M G3Si1
222
MIG/MAG Welding Consumables
Standard number
Cast diameter improves the contact force and defines the contact
point; usually 400-1200mm.
Gas shielded
metal arc welding
BS EN 14175
223
MIG/MAG Shielding Gases
Ar Ar-He He CO2
Argon (Ar):
Higher density than air; low thermal conductivity - the arc
has a high energy inner cone; good wetting at the toes;
low ionisation potential.
Helium (He):
Lower density than air; high thermal conductivity -
uniformly distributed arc energy; parabolic profile; high
ionisation potential.
Carbon Dioxide (CO2):
Cheap; deep penetration profile; cannot support spray
transfer; poor wetting; high spatter.
224
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Welding Consumables
225
Types of Cored Wire
Seamless cored wire Butt joint cored wire Overlapping cored wire
Strip reel
Flux input
Closing rollers
Thin sheet
metal
226
FCAW Wire Designation
BS EN 17632 - T 46 3 1Ni B M 4 H5
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227
Welding Consumables
SAW Consumables
BS EN 14171 S46 3 AB S2
Standard number
228
SAW Filler Material
Welding wires
Supplied on coils, reels or drums.
Random or line winding.
Welding wires:
Carbon and low alloy wires are copper coated.
Stainless steel wires are not coated.
Wires must be kept clean and free from oil and dust.
229
SAW Filler Material
SAW Consumables
Welding fluxes:
Are granular mineral compounds mixed
according to various formulations.
Shield the molten weld pool from the
atmosphere.
Clean the molten weld pool.
Can modify the chemical composition of the weld
metal.
Prevents rapid escape of heat from welding
zone.
Influence the shape of the weld bead (wetting
action).
Can be fused, agglomerated or mixed.
Must be kept warm and dry to avoid porosity.
SAW Consumables
Welding flux:
Supplied in bags/pails (approx. 25kg) or bulk
bags (approx. 1200kg).
Might be fused, agglomerated or mixed.
230
SAW Consumables
Welding flux:
Might be fused or agglomerated.
Supplied in bags.
Must be kept warm and dry.
Handling and stacking requires care.
Courtesy of Lincoln Electric
SAW Consumables
SA Welding flux:
Must be kept warm and dry.
Handling and stacking requires care.
Fused fluxes are normally not hygroscopic but
particles can hold surface moisture.
Only drying.
Agglomerated fluxes contain chemically bonded
water.
Similar treatment as basic electrodes.
For high quality, agglomerated fluxes can be
recycled with new flux added.
If flux is too fine it will pack and not feed properly.
Cannot be recycled indefinitely.
SAW Consumables
Fused flux
Flaky appearance.
Lower weld quality.
Low moisture intake.
Low dust tendency.
Good re-cycling.
Very smooth weld profile.
Fused flux:
Baked at high temperature, glossy, hard and black in
colour, cannot add ferro-manganese, non moisture
absorbent and tends to be of the acidic type.
231
SAW Consumables
Shooting the
melt through a
Product is stream of water.
crushed and
screened for
size. Pouring melt onto
large chill blocks.
SAW Consumables
SAW Consumables
Agglomerated flux
Granulated appearance.
High weld quality.
Addition of alloys.
Lower consumption.
Easy slag removal.
Smooth weld profile
Agglomerated flux:
Baked at a lower temperature, dull, irregularly
shaped, friable, (easily crushed) can easily add
alloying elements, moisture absorbent and tend to be
of the basic type.
232
SAW Consumables
SAW Consumables
SAW Consumables
Mixed fluxes
Two or more fused or bonded fluxes are mixed in any
ratio necessary to yield the desired results.
Mixed fluxes advantages:
Several commercial fluxes may be mixed for highly
critical or proprietary welding operations.
233
Ceramic Backing
Ceramic backing:
Used to support the
weld pool on root
runs.
Usually fitted on an
aluminium self
adhesive tape.
Allow increased welding current without danger
of burn-through increased productivity,
consistent quality.
Different profiles to suit different applications.
No backing/drying required.
Questions
Welding consumables:
QU 1: Why are basic electrodes used mainly on high
strength materials and what controls are
required when using basic electrodes?
QU 2: What standard is the following electrode
classification taken from and briefly discuss
each separate part of the coding? E 80 18 M
QU 3: Why are cellulose electrodes commonly used
for the welding of pressure pipe lines?
QU 4: Give a brief description of fusible insert and
state two alterative names given for the
insert?
QU 5: What standard is the following electrode
classification taken from, and briefly discuss
each separate part of the coding?
E 42 3 1Ni B 4 2 H10
234
Inspection of Consumables
How?
Non-specific inspection Specific inspection
Carried out by the Carried out before delivery
manufacturer in accordance in accordance to product
with its own procedures. specification.
Non-specific
inspection
documents
Specific
inspection
documents
Type 3.1 Type 3.2
Name: Inspection certificate Name: Inspection certificate
3.1. 3.2
Content: statement of Content: statement of
compliance with the order compliance with the order
(include specific test results!) (include specific test results!)
Who validate it - the Who validate it - the
manufacturer inspection manufacturer inspection
(independent of (independent of
manufacturing department!) manufacturing department!)
+ purchaser’s/official
designated authorised
inspector.
235
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236
Weldability of Steels
Section 17
Weldability Objective
Weldability of Steels
Definition
It relates to the ability of the metal (or alloy) to
be welded with mechanical soundness by most
of the common welding processes. The resulting
welded joint retain the properties for which it
has been designed is a function of many inter-
related factors but these may be summarised
as:
Composition of parent material.
Joint design and size.
Process and technique.
Access.
237
Weldability of Steels
Iron (Fe):
Main steel constituent. On its own, is relatively soft,
ductile, with low strength.
Carbon (C):
Major alloying element in steels, a strengthening element
with major influence on HAZ hardness. Decreases
weldability typically < ~ 0.25%.
Manganese (Mn):
Secondary only to carbon for strength, toughness and
ductility, secondary de-oxidiser and also reacts with
sulphur to form manganese sulphides typically < ~0.8% is
residual from steel de-oxidation. Up to ~1.6% (in C-Mn
steels) improves strength and toughness.
Silicon (Si):
Residual element from steel de-oxidation typically to
~0.35%.
238
Steel Alloying Elements
Phosphorus (P):
Residual element from steel-making minerals.
Difficult to reduce below < ~ 0.015% brittleness.
Sulphur (S):
Residual element from steel-making minerals.
Typically < ~ 0.015% in modern steels < ~ 0.003% in
very clean steels.
Aluminium (Al):
De-oxidant and grain size control.
Typically ~ 0.02 to ~ 0.05%.
Chromium (Cr):
For creep resistance and oxidation (scaling) resistance for
elevated temperature service. Widely used in stainless
steels for corrosion resistance, increases hardness and
strength but reduces ductility.
Typically ~ 1 to 9% in low alloy steels.
Nickel (Ni):
Used in stainless steels, high resistance to corrosion from acids,
increases strength and toughness.
Molybdenum (Mo):
Affects hardenability. Steels containing molybdenum are less
susceptible to temper brittleness than other alloy steels.
Increases the high temperature tensile and creep strengths of
steel. typically ~ 0.5 to 1.0%.
Niobium (Nb):
Vanadium (V): a grain refiner, typically ~ 0.05%
Titanium (Ti) :
Copper (Cu):
Present as a residual, (typically < ~ 0.30%) added to weathering
steels (~ 0.6%) to give better resistance to atmospheric
corrosion.
Materials
Iron Fe
Carbon C is for Strength
Manganese Mn is for Toughness
Silicon Si < 0.3% Deoxidiser
Aluminium Al Grain refiner, <0.008% Deoxidiser +
Toughness
Chromium Cr Corrosion resistance
Molybdenum Mo 1% is for Creep resistance
Vanadium V Strength
Nickel Ni Low temperature applications
Copper Cu Used for weathering steels (Corten)
Sulphur S Residual element (can cause hot
shortness)
Phosphorous P Residual element
Titanium Ti Grain refiner, Used a micro alloying
element (S&T)
Niobium Nb Grain refiner, Used a micro alloying
element (S&T)
239
Classification of Steels
It affects:
1. Strength.
2. Hardness.
3. Ductility.
Classification of Steels
240
Classification of Steels
Alloy steels:
Low Alloy Steels <7% alloying elements.
High Alloy Steels >7% alloying elements.
Classification of Steels
Carbon steels
Carbon contents up to about ~ 0.25%.
Manganese up to ~ 0.8%.
Low strength and moderate toughness.
Carbon-manganese steels
Manganese up to ~ 1.6%.
Carbon steels with improved toughness due to
additions of manganese.
Classification of Steels
241
Classification of Steels
9%Cr + 1%Mo.
Classification of Steels
Classification of Steels
242
Classification of Steels
Classification of Steels
243
Process Cracks
Cracking
Cracks
244
Hydrogen Induced Cold Cracking
Occurs in:
Carbon steels.
Carbon-manganese.
Low, medium and high alloy steels:
Mainly in ferritic or martensitic steels.
Crack type:
Hydrogen HAZ and weld metal cracking.
Location:
HAZ (longitudinal) weld metal (transverse).
Steel types:
All hardenable steels.
Including:
HSLA (high strength low alloy) steels. Quench and
tempered steels TMCP (thermal mechanically controlled
processed) steels.
245
Hydrogen Induced Cold Cracking
Susceptible
Tensile stress microstructure
Cracking
(at room
temperature)
High hydrogen
concentration
May occur:
Up to 72hrs after completion.
In weld metal, HAZ, parent metal.
At weld toes.
Under weld beads.
At stress raisers.
H2
Oxide or grease H2 H2
on the plate
246
Hydrogen Induced Cold Cracking
Atomic
hydrogen
(H)
Molecular
hydrogen
(H2)
Cellulosic electrodes
produce hydrogen as
a shielding gas Hydrogen absorbed in
a long or unstable arc
Hydrogen introduced in
weld from consumable,
oils or paint on plate Hydrogen crack
H22
H
247
Hydrogen Induced Cold Cracking
Susceptible microstructure:
Hard brittle structure – Martensite promoted by:
a High carbon content, carbon equivalent (CE)
CEV = %C + Mn + Cr+Mo+V + Ni+Cu
6 5 15
b High alloy content.
0.83 % Carbon
(Eutectoid)*
Tensile
Hardness
Strength
Ductility
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.2 1.4 1.6
%Carbon
248
Hydrogen Induced Cold Cracking
249
Hydrogen Induced Cold Cracking
Hydrogen Scales
250
Hydrogen Cold Cracking Avoidance
Prevention
Slow the cooling rate.
Reduce hydrogen level.
Reduce residual stress.
251
Residual Stress
Pre-Heat Application
Application of preheat
Heat either side of joint.
Measure temp 2mins after heat removal.
Always best to heat complete component rather
than local if possible to avoid distortion.
Preheat always higher for fillet than butt welds
due to different combined thicknesses and chill
effect factors.
252
Combined Thickness
t3
t1 t2 t1 t2
t = t1+t2 t = t1+t2+t3
Combined Thickness
Heat flow
Heat flow
Combined Thickness
253
The Chill Effect of the Material
Pre-Heat Application
Furnace:
Heating entire component - best.
Electrical elements:
Controllable; portable; site use; clean; component cannot be
moved.
Gas burners:
Direct flame impingement; possible local overheating; less
controllable, portable, manual operation possible, component
can be moved.
Radiant gas heaters:
Capable of automatic control, no flame impingement, no
contact with component, portable.
Induction heating:
Controllable, rapid heating (mins not hours), large power
supply, expensive equipment.
Pre-Heat Application
254
Heating Temperature Control
255
Heat Input
Cracks
Solidification Cracking
Solidification Cracking
256
Solidification Cracking
Crack type:
Solidification cracking.
Location:
Weld centreline (longitudinal).
Steel types:
High sulphur and phosphor concentration in
steels.
Susceptible microstructure:
Columnar grains In direction of solidification.
Solidification Cracking
Solidification Cracking
257
Solidification Cracking in Fe Steels
Solidification crack
Contractional strain
Solidification Cracking
Solidification Cracking
258
Solidification Cracking
Solidification Cracking
Contractional strain
Solidification Cracking
259
Cracks
Lamellar Tearing
Lamellar Tearing
Lamellar Tearing
Cross section
260
Lamellar Tearing
Lamellar Tearing
Critical area
Lamellar Tearing
261
Lamellar Tearing
Lamellar Tearing
Friction welded
Plate material extension stubs
Sample of 6.4mm
parent material DIA
262
Lamellar Tearing
Lamellar Tearing
Susceptible
Lamellar Tearing
Susceptible Non-Susceptible
263
Cracks
Weld Decay
Inter-Granular Corrosion
Occurs when:
An area in the HAZ has been sensitised by the formation of
chromium carbides. This area is in the form of a line
running parallel to and on both sides of the weld. This
depletion of chromium will leave the effected grains low in
chromium oxide which is what produces the corrosion
resisting effect of stainless steels. If left untreated
corrosion and failure will be rapid*
Inter-Granular Corrosion
264
Inter-Granular Corrosion
Inter-Granular Corrosion
Inter-Granular Corrosion
265
Inter-Granular Corrosion
Inter-Granular Corrosion
Inter-Granular Corrosion
Areas depleted of
Chromium below
12.5%.
266
Inter-Granular Corrosion
Weld Decay
Weld Decay
267
Basic Atomic Structure of Steels
The carbon atom is very much smaller than the iron atom and
does not replace it in the atomic structure but fits between it*.
Iron Carbon
atoms atoms*
α Alpha iron
This structure occurs below 723°C and is
body centred or BCC in structure
It can only dissolve up to 0.02% Carbon
Also known as Ferrite or BCC iron*
γ Gamma iron
This structure occurs above the UCT in
Plain Carbon Steels and is FCC in
structure.
It can dissolve up 2.06% Carbon
Also called Austenite or FCC iron*
*
Compressed representation could appear like this
268
Basic Atomic Structure of Steels
269
Summary of Steel Microstructures
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270
Weld Repairs
Section 18
Weld Repairs
271
Weld Repairs
Weld Repairs
272
Weld Repairs
Weld Repairs
Weld Repairs
273
Weld Repairs
Production repairs
Are usually identified during production
inspection.
Evaluation of the reports is usually carried out
by the Welding Inspector or NDT operator.
274
In Service Weld Repairs
Service repairs
Can be of a very complex nature, as the
component is very likely to be in a different
welding position and condition than it was during
production.
It may also have been in contact with toxic, or
combustible fluids hence a permit to work will
need to be sought prior to any work being
carried out.
The repair welding procedure may look very
different to the original production procedure
due to changes in these elements.
Weld Repairs
275
Weld Repairs
Weld Repairs
276
Weld Repairs
Welder time £
NDT ££
Penalty % NDT ££
277
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278
Residual Stress and Distortion
Section 19
Residual Stress
279
Residual Stress
At room temperature
On heating to 400°C
On cooling to room
200mm 1mm temperature
Residual Stress
Cool with
restraint
present
200mm
Cool with
restraint
removed
199mm 1
Residual Stress
Ambient temperature.
Heat to 400°C.
Cool with restraint present.
280
Residual Stress
Hot weld
Tension
Compression
Compression Tension
YS at room
temperature
The higher the heat input the wider the tensile zone!
281
Types of Residual Stress
Compression Tension
Residual stress
after PWHT
YS at PWHT YS at room
temperature temperature
After PWHT, peak residual stress is less than a quarter of its initial level!
Residual Stress
Types of Distortion
Transverse shrinkage
282
Distortion
400mm
5mm
Separate cooling.
398mm
Combined cooling.
400mm
Distortion
283
Residual Stress
Distortion Prevention
Distortion Prevention
Tack welding
a Tack weld straight through
to end of joint.
7
1 5
2 3
3 41 25 4
6 6
7
b Tack weld one end, then
use back-step technique
7 6 5 4 3 2 1
for tacking the rest of the
joint.
c Tack weld the centre, then
complete the tack welding
by the back-step
technique.
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Distortion
Joint design:
Weld metal volume.
Type of joint - butt vs. fillet, single vs double side.
Amount of restrain:
Thickness - as thickness increases, so do the
stresses.
High level of restrain lead to high stresses.
Preheat may increase the level of stresses.
Fit-up:
Root gap - increase in root gap increases
shrinkage.
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Factors Affecting Distortion
Welding sequence:
Number of passes - every pass adds to the
total contraction.
Travel speed - the faster the welding speed,
the less the stress.
Build-up sequence.
Types of Distortion
Angular distortion
Transverse shrinkage
producing angular
distortion.
Transverse
shrinkage
producing
distortion.
Distortion Prevention
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Distortion Prevention
Neutral
axis
Neutral
axis
Distortion Prevention
a. Assemblies tacked
together before
welding.
Distortion Prevention
as a function of
number of runs for
a 10mm leg length
10mm
weld).
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Distortion Prevention
Distortion Prevention
1 2 3 4 5 6 7 1 4 2 5 3 6
Distortion Prevention
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Heat Treatment of Welded Structures
Section 20
Heat Treatment
Why?
Improve mechanical properties.
Change microstructure.
Reduce residual stress level.
Change chemical composition.
How?
Flame oven.
Electric oven/electric heating blankets.
induction/HF heating elements.
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Heat Treatment Methods
Disadvantages:
Limited to size of
parts.
Disadvantages:
Elements may burn out
or arcing during heating.
Disadvantages:
High equipment
cost.
Large equipment,
less portable.
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Heat Treatments
Heating rate
Time
Heat Treatment
Recommendations
Provide adequate support (low YS at high
temperature).
Control heating rate to avoid uneven thermal
expansions.
Control soak time to equalise temperatures.
Control temperature gradients - No direct flame
impingement.
Control furnace atmosphere to reduce scaling.
Control cooling rate to avoid brittle structure
formation.
291
Heat Treatments
Heat Treatments
Pre-heat treatments
Are used to increase weldability, by reducing
sudden reduction of temperature, and control
expansion and contraction forces during welding.
Heat Treatments
Preheat:
We can preheat metals and alloys when welding for a
number of reasons. Primarily we use most pre-heats to
achieve one or more of the following:
To control the structure of the weld metal and HAZ on
cooling.
To improve the diffusion of gas molecules through an
atomic structure.
To control the effects of expansion and contraction.
Preheat controls the formation of un-desirable
microstructures that are produced from rapid cooling of
certain types of steels. Martensite is an undesirable grain
structure very hard and brittle it is produced by rapid
cooling form the austenite region.
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Heat Treatments
Heat Treatments
Pre-heat requirements
The welding heat input Increased – Reduced.
Carbon Equivalent Increased – Increased.
Hydrogen content Increased – Increased.
Combined material thickness Increased -
Increased.
Heat Treatments
293
Heat Treatments
Advantages of preheat:
Slows down the cooling rate, which reduces the
risk of hardening.
Allows absorbed hydrogen a better opportunity
of diffusing out, thereby reducing the risk of
cracking.
Removes moisture from the material being
welded.
Improves overall fusion characteristics.
Lowers stresses between the weld metal and
parent material by ensuring a more uniform
expansion and contraction.
180
Combined material
160
140
thickness
120
100
80
60
40
A B C D E
20 0.43 0.45 0.47 0.53 0.55
0
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
Heat input
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Post Weld Heat Treatment
Question:
What is the main reason for carrying out PWHT (to
steel joints)?
Answer:
To reduce residual stresses.
Supplementary question:
What is the benefit for reduce residual
stresses?
Supplementary answer:
To improve resistance to brittle fracture.
atomic structure.
100
295
Heat Treatments
Annealing (steels)
Temperature: 920°C hold for sufficient
time (full austenitization).
Cooling: Hold, slow cooling in furnace.
Result: Produces a very soft, low
hardness material suitable
for cold working or
machining operations.
Decreases toughness and l
owers yield stress
homogenising annealing.
Heat Treatments
Heat Treatments
296
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?
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298
Welding Safety
Section 21
299
Fire and Explosion
300
Checking Gas Cylinder for Leaks
Leak testing.
Welding Fume
Welding fume
sources:
Parent material.
(Cr6 thought to be
carcinogenic!)
Welding consumables.
(filler, flux, gas).
Action of heat/UV on air:
Nitrous oxide and ozone.
Surface treatments.
(paint, plating,
coatings).
Cleaning fluids.
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Welding Fume
Things to be addressed:
• Composition of the fume.
• Concentration of the fume.
• Duration of exposure.
Welding Fume
Welding Fume
a. In workshop.
b. In breathing zone.
c. Regular monitoring.
d. Regular auditing.
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Welding Fume
Welding Fume
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Electrical Shock
Points to be considered:
O.C.V. : for AC - 80V; for DC - 70V.
Modern equipment: 50V.
Plasma cutting: over 100V.
TIG uses HF: round 20,000V.
Electrical Shock
Points to be considered:
Check weld connections and cable insulation.
Bad! Good!
Electrical Shock
304
Electrical Shock
305
Skin Burns
Warning
notice
Summary
306
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?
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308
Calibration
Section 22
Calibration Objectives
Calibration/Validation
309
Calibration/Validation
Measuring in Welding
The purposes
of measuring
Demonstration of
conformance to specified Welding process
requirements control
Parameters to be measured:
310
The Tong Tester
311
Gas Flow Rate Measurement
Point of measurement -
see BS EN ISO 13916
If t 50mm - A = 4 x t
but max. 50mm.
The temperature shall
be measured on the
surface of the
workpiece facing the
welder.
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Welding Temperatures - Where?
Point of measurement -
see BS EN ISO 13916
If t > 50mm - A = min. 75mm.
Where practicable, the
temperature shall be measured
on the face opposite to that
being heated.
Allow 2 min per every 25 mm of
parent metal thickness for
temperature equalisation.
Interpass temperature shall be
measured on the weld metal or
immediately adjacent parent
metal.
Test equipment
Thermocouple
(TE)
Temperature
sensitive Thermistor
materials (CT)
(TS)
Optical/electrical
devices for
Contact contactless
thermometer measurement (TB)
(CT)
Temperature
sensitive materials:
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Temperature Test Equipment
Thermocouple
Based on measuring the thermoelectric potential
difference between a hot junction (on weld) and
a cold junction.
Accurate method.
Measures over a wide range of temperatures.
Gives the actual temperature.
Need calibration.
Thermistors
Are temperature-sensitive
resistors whose resistance
varies inversely with
temperature.
Used when high sensitivity is
required.
Gives the actual temperature.
Need calibration.
Can be used up to 320°C.
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PAMS (Portable Arc Monitor System)
PAMS UNIT
The purposes
of PAMS
Arc voltage
(connection
leads) Temperature (thermocouple)
Use of PAMS
Incorporated pair of
rolls connected to a
tachogenerator
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Use of PAMS
Heating element
sensor
Definitions:
Measurement = set of operations for determining a
value of a quantity.
Repeatability = closeness between successive
measuring results of the same instrument carried out
under the same conditions.
Accuracy class = class of measuring instruments that
are intended to keep the errors within specified limits.
Calibration = checking the errors in a meter or
measuring device.
Validation = checking the control knobs and switches
provide the same level of accuracy when returned to a
pre-determined point.
Monitoring = checking the welding parameters (and
other items) are in accordance with the procedure or
specification.
When is it required?
Measurement = set of operations for determining a value of
a quantity.
Repeatability = closeness between successive measuring
results of the same instrument carried out under the same
conditions.
Accuracy class = class of measuring instruments that are
intended to keep the errors within specified limits.
Calibration = checking the errors in a meter or measuring
device.
Validation = checking the control knobs and switches
provide the same level of accuracy when returned to a pre-
determined point.
Monitoring = checking the welding parameters (and other
items) are in accordance with the procedure or specification.
See BS EN ISO 17662 for details!
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Calibration and Validation
Welding Parameter
Calibration/Validation
Which parameters need calibration/validation?
Depends on the welding process.
See BS EN ISO 17662 and BS 7570 for details.
How accurate?
Depends on the application.
Welding current - ±2.5%.
Arc voltage - ±5%.
Wire feed speed - ±2.5%.
Gas flow rate - ±20% (±25% for backing gas
flow rate).
Temperature (thermocouple) - ±5%.
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Example 1 -
MMA Elementary Monitoring
In theory any MMA operation could require
monitoring of:
Welding current.
Arc voltage.
R.O.L.
Preheat/interpass temperature.
Electrode treatment and storage.
Example 2 -
High Integrity MMA Operation
In theory, this might require monitoring of all the
activities previously mentioned.
The equipment thus required:
Ammeter.
Voltmeter.
Stop watch. Or a PAMS
Tape measure.
Thermometer.
Calculator.
All of the above equipment would require calibration;
any meters fitted to the power source or electrode
ovens would also require calibration.
Example 3 -
MIG/MAG Welding With a Robot
In theory, the following would require monitoring:
Wire feed speed.
Amperage.
Voltage.
Travel speed.
Gas flow rate.
Repeatability of the controls.
In practice, a data logger would be preferred to
monitor all the parameters; also a PAMS would be
required to check the repeatability of the control
knobs.
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Summary
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?
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319