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Safety aspects of welding
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Electric shock
Fume, dust and ozone
Ultraviolet radiation
Hot workpiece and welding equipment
Fire and explosion hazards
Handling compressed gas cylinders
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The welder is insulated from the floor, workpiece, electrode holderand electrode by wearing rubber-soled footwear suitable gloves and
overalls.
The welder stand on a dry, insulated mat or platform.
The work area is dry, clean and tidy.
The welding power source is correctly installed and in
good working condition.
All cables are suitable & in good condition (e.g. no bare
wires) and they are dry.
All cable connections are clean and tight (no loose contacts)
The current return cable (earth cable) is firmly attached to the job or
firmly attached to the metal workbench
The electrode holder properly insulated and is in good condition.July 9, 2013 4
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Wrong
positioningduring
welding
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Correctpositioning
duringwelding
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Choice of Filter glass
July 9, 2013 10
Current range Filter mumber
15-40 A 7-9
40-60 A 8-10
60-150 A 10-11
150-250 A 11-12
250-500 A 12-14
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Protective Cloathing leather aprons
July 9, 2013 11Recommended
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Unsafe
working
Conditions
Poor
Housekeeping
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Safe
Working
Conditions
Good
House
keeping
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Unsafeworking
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Safe
working
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July 9, 2013 17
MMAW Process - Basics
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The name implies
Welding with Electric arc
and Shielding from
Coated electrode
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AdvantagesMost versatile process.
Can be used for all positions and for wide thickness range.
Can be used in Shop and site. Highly portable
Almost all metals can be welded by this processes.
External shielding etc is not required. So less numberof equipment and gadgets.
The investment for equipment is relatively less,
Process is simple.
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July 9, 2013 20
Arc is discharge of current between two
contacts through air gap
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Electric discharge between
two electrodes through
ionised gas
10 to 2000 amps at 10 to 50 V
arc voltage
Column of ionised gas at high
temperature and Magnetic
Forces enable
Transfer of molten metal from
electrode to workpiece
Can have a cleaning action,
breaking up oxides on
workpiece
21July 9, 2013
+
- Cathodedrop zone
Anode drop
zone
4,000 K
Peak
temperatures
18,000 K
Electric Welding arc
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MMAW welding process.
Intense heat of welding arc causes flux coating to form aslag and a gaseous shield which protect the weld from
atmospheric contamination.July 9, 2013 22
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1)electrode holder
2) flux coatedconsumable
electrode
3) welding arc
4) component being
welded
5) fume extractor
6) current return cable
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Electrical Circuit for arc welding
July 9, 2013 24
Welding
power source
Earthing
cable
Earth clamp
Work piece for
welding
Electrode
Welding cable
Electrode holder
Electric Arc
Voltage
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Voltage
Current
Arc voltage
Is directly
In proportion
with
Arc length
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+_
1/3
2/3
Straight polarity
DCEN Electrode Negative
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Direct Current DCEN - Straight Polarity
+
+
+
+
-
-
-
-
+
-
DCENJuly 9, 2013 29
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+_
2/3 (66,6%)
1/3
(33,3%)
Reverse Polarity
DCEP - Electrode Positive
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Direct Current DCEP - Reverse Polarity
+
+
+
+
-
-
-
-
+
-
DCEPJuly 9, 2013 31
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Comparison of PolarityDCEP Used for low hydrogen type electrodes
Used for non-ferrous welding
Better for root pass, vertical and overhead welding Maximum penetration
DCEN
All steels except low hydrogen type
Not suited for non-ferrous welding
Shallow, narrow penetration
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+ -- +
50%
50%
Alternate Current -AC
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July 9, 2013 34
MMAW Equipments and Accessories
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Power Sources
Types of Power Sources used for SMAW
Alternating Current (AC)
Transformer Motor-alternator
Direct Current (DC).
Transformer-rectifier Motor-generator
Inverter
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Comparison of Power SourcesAC Type
Voltage drop is lower
Arc Blow problem not encountered
DC Type
Easy arc striking (especially small diameter)
Better for all positions Welding with short arc lengths is easier
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Duty CycleDefinition
It is the portion of the total working time that the powersource must deliver its rated output without exceeding
a predetermined temperature limit.
Normally defined in a total time span of 10 minutes.
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Inverter Rectifier Generater
6800 kwh/year 8500 kwh/year 12500 kwh/year
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0
2000
4000
6000
8000
10000
12000
14000
0 50 100 150 200 250 300
Welding Current - A
EnergyCon
sumption
(KWH/
year)
Generator
Transformer
Inverter
Energy consumption by SMAW Power sources
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Comparison of Invertor & Rectifier
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July 9, 2013 41
MG Set Diode Based
machines
Thyristor
based
machines
Inverterised
Machines
Assumption Input supply 400 V, 3 PH
Investment
Electrical cost
Input current consumption for 4 mm
electrode welding at 160 amps.
2 to 3 X
24 A
1.25 X
18 A
1.25 X
16 A
X
7 A
Electrical units consumed for 1 stick
electrode per minute( Considering
welding time of 1 minute per
electrode)
0.249 KWH
( 3x400x24x0.9)
1000 x 60
0.187 KWH
( 3x400x18x0.9)
1000 x 60
0.166 KWH
( 3x400x16x0.9)
1000 x 60
0.0727 KWH
( 3x400x7x 0.9)1000 x 60
Cost @Rs. 6 per electrical unit per
electrode of 4 mm Rs. 1.50 Rs. 1.122 Rs. 0.996 Rs. 0.436
Cost of average no. of 180 electrodes
consumed per shift per machine Rs. 270 Rs 202 Rs. 180 Rs. 78
Saving per shift over other machines
Rs.( -)192 Rs. (-)124 Rs. (-)102 ---------
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Electrode holders
This model has a fixed jawand a spring loadedflexible jaw to applypressure to grip theelectrode
42July 9, 2013
This model has a
swival handle to grip
the electrode
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Slag removal Chipping Hammers
Manual arc welding
leaves slag on top of
weld bead
This slag must be
removed completely
after each pass.
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Wire Brush
Used for removing
loose slag particles on
the weld bead.
Also for cleaning base
metal before welding
44July 9, 2013
Note - Always use the wire brush suitable for the
basic metal - to avoid any traces of contamination
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Earth clamps
The return cable for
current is fixed by
earth clamps with
spring or by screw.
They are usually made
in brass or copper.
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Welding Shield
Necessary to
protect againstradiation
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Choice of Filter glass
July 9, 2013 47
Current range Filter mumber
15-40 A 7-9
40-60 A 8-10
60-150 A 10-11
150-250 A 11-12
250-500 A 12-14
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MMAW Electrodes
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In the begining arc welding was attempted with bare wire
and then various coated electrodes were developed
1885 Russia, Great Britain Benardos & Olszewki (carbon arc)
1889 Russia + USA Slavianof + Coffin (bare electrode)
1907 Sweden Kjellberg (covering for stabilise arc)1912 USA Strohmerger (asbestos covering)
1914 UK (cellulose covering)
1927 Extrusion
1930 Iron oxide
1932 Rutile1948 Iron powder
1960 Calcium, Zirconium, Iron powder coating.
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Functions of Flux Coating
Primary Functions
Provide shielding for the arc
Provide deoxidizers & fluxing agents
Provide slag blanket to the molten weld pool
Improve arc stability
Providing alloying elements to the weld metal
Improve deposition efficiency
July 9, 2013 50
Componants of flux
tiFunctions
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coatingPrincipal Secondary
Cellulose Shielding Gas former Improve arc force
Calcium bi carbonate Shielding Gas former Improve fluidity
Flurospar Slag former Improve fluidity
Dolomite Shielding Gas former Improve fluidity
Rutile (TiO2) Slag former Arc Stabiliser
Potassium titanate Arc Stabiliser Slag Former
Feldspar Slag former Arc Stabiliser
Mica Assist in extrusion Arc StabiliserArgile Assist in extrusion Slag Former
Silica Slag former ---
Asbestos Slag former Assist in extrusion
Manganese di oxide Slag former Metal addition
Iron oxides Slag former ---
Iron powder Improve deposition rate Adherence of coating to core wire
Ferro silican De-oxidiser Metal addition
Ferro manganese Alloy addition (Mn) De-oxidiser
Sodium Silicate Binder Improve fluidity
Pottassium Silicate Arc stabilser BinderJuly 9, 2013 51
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AWS A5.1 classification
July 9, 2013 52
E XXXX - H
Useable positions
1=all positions2=flat + horizontal
4=vertical down
Tensile Strength
in KPSI
Flux type (yz)20 = acid (iron oxide)
10, 11 = cellulosic
12, 13 = rutile
24 = rutile iron powder
27 = acid iron powder
16 = basic
18, 28 = basic iron powder
Hydrogen level (HmR)
H = 5 ml / 100g of WMR = low moisture pick-up
IS 814
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July 9, 2013 53
IS 814
E B X X X X H J
Metal recovery 120%
Hydrogen control < 15ml / 100gm
Welding current
Welding Position
%E and Impact at specified temp
UTS and YS
Coating type basic
Covered electrode
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Selection of electrodes Material is to be welded - its chemical composition
Its susceptibility to weld-metal cracking
Strength - mechanical properties required Thickness of the material
Type of joints
Welding positions to be used
Type of welding power source used, AC or DC
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Electrode Identification
Colour coding
Tip and/or grip end Name Printing Brand Name and/or Spec
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Packing of Electrodes
Cardboard carton Plastic cartons
Vacuum sealed in Al foil
Hermetically sealed cans
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Recommended Storage for Electrodes
Below 50% relative humidity Between 20 to 40 degree C
Conditioning of Electrodes before use
Drying at 100 to 300 deg C depending
on type of electrode
Holding above 100 deg C till use
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Storage and conditioning of
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Storage and conditioning of
electrodes
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Ovens for welding electrodes
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MMAW Process Variables
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Electrode polarity (DC welding)
Welding current Electrode angle
Electrode travel speed
Arc length
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Influence of Polarity on Penetration in SMAW
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Penetration produced with the alternating current is midway
between that achieved with negative polarity and positivepolarity.
Influence of Polarity on Penetration in SMAW
DCENDCEPAC
July 9, 2013 63
Welding with DCEP produce deeper penetration
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Welding with DCEP produce deeper penetration
Welding with DCEN gives more filling and finishing
DCEN DCEPAC
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Arc Length
Longer arc lengths = increased puddle heat, flatter
and wider weld bead, less penetration
Shorter arc lengths = less puddle heat, flatter andnarrow weld bead, deep penetration
Use arc length to control puddle size, penetration,
and burn through.
Normal arc length is 1.5- 3.0 mm
Use a slightly longer arc length during a start or
restart.
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July 9, 2013 66
Low welding current cause
Poor starting
Slag inclusions
Irregular weld profile
Weld bead contour too high
Lack of root fusion
Incomplete root penetration
High welding current cause
Excessive spatter
Excess penetration
Burn-through
Undercut
Irregular weld profile
Effect of welding current
Effect of Travel speed
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July 9, 2013 67
Travel speed is too high:
Irregular weld profile
Lack of root fusion
Incomplete root penetration
Insufficient volume of weld metal deposited
Travel speed is too low:
Excess penetration
Burn-through Undercut
Irregular weld profile
Weld bead contour too high
p
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July 9, 2013 68
MMAW Techniques
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Arc Striking
69July 9, 2013
2 Methods
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Restarts
July 9, 2013 70
Stagger all starts and stops or use run-on, run-offtabs
Feather all restarts & start on top, or start in front
and remelt
Dont restart in a coupon area.
Also stagger all beads on a single pass.
Use a longer arc length when starting a weld.
C
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Craters
Fill craters by reversing direction at the weldend
Use a short arc length to control heat.
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Weld Bead A weld resulting from a pass
July 9, 2013 72
Stringer BeadWeave Bead
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Techniques Stringer (drag) (whip)Weave
Circles
crescent
zig zag
box weave
double J
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Positions of welding
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Positions of welding
Down hand 1G Horizontal 2G Vertical 3G Overhead 4G
Downhand 1F Horizontal 2FJuly 9, 2013 74
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Progression (vertical)
Up deeper penetration
Higher deposit rate (Kg/hr)
Use near 90 degree travel angle or slightly up
Down
faster (point to point)
less penetration for thin metal
less dilution
Use steep grag angle
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Electrode angles for Horizontal butt welding
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Electrode angles for Horizontal butt welding
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600 included angle
Root faces
Tacking
Feather Tacks
Butt Joint Preperation
1 3 mm
(Joints without backing)
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O R t T h i
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Open Root Technique Use root opening to allow increase in amperage for smoother
welding
Whip backwards for penetration
Whip forwards to reduce penetration
Do Not Weave a root pass.
Maintain a short arc gap
Stay slightly in front of the puddle at all times. Use thekeyholing technique.
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Root faces - 0
450 included angle
Remove all mill scales and rust
Tacking - not in groove
Tack away from coupon area.
Flush on backing
Butt Joint Preperation(With Backing)
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Welding grooves with Backing Keep the root opening wide
Make the root pass in one bead
Avoid tight areas at the weld toes
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Root pass welding
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1
2
3
4
5
Weld bead position forMulti-pass with weaving
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1
2
3 4
5 6 7
8
9 10
Weld bead position for
Multi-pass with Stringer beads
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Weld Defects
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Group 2 contour defects
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Group 2 contour defects
Incompletely filled groove
Bulbous contour
Unequal legs
89
GROUP 3 - SURFACE IRREGULARITIES
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Undercut
Overlap
Gas pore
Crater pipe
90
GROUP 4 - SURFACE CRACKS
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GROUP 4 SURFACE CRACKS
Longitudinal/Centre-line
Parent metal/HAZ
Transverse
Crater
91
GROUP 5 - MISCELLANEOUS
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Stray arc / arc strike
Spatter
92
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Weld Spatter
Bubbles of gas becoming entrapped in the molten globule ofmetal, expanding with great violence and projecting small
drops of metal outside the arc steam
The spatter may be due to
1. Excessive arc current.
2. Longer arcs.
3. Damp electrodes.
4. Electrodes with improper wire or flux ingredients.
5. Arc blow making the arc uncontrollable.
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GROUP 5 - MISCELLANEOUS
94
Overlap Excess weld metal
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GROUP 5 - MISCELLANEOUS
95
Excess penetration Root concavity
Weld defects: Their effect
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Indications with major dimensions greater than 1.6 mm aretermed as relevant indications (ASME Sec VIII)
Cracks Pose the danger ofgrowing under stress duringservice
Lack of penetration-reducesthe load carrying cross-section, corresponds
geometrically to a crack
Lack of fusion correspondsgeometrically to a crack
Having a length > than 3times the width
All relevant linearindications areunacceptable
No tungsten inclusions areacceptable
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Weld defects: Their effect
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Weld defects: Their effect Porosities/Slag inclusion
reduce the load carryingcross-section
Undercut create notch
effect at weld toe/trap slag- up to 0.8 mm
acceptable if it lies parallelto the applied force
- up to 0.25 mmacceptable if it liestransverse to the appliedforce.
Rounded indication (circularor elliptical with length =< 3
times width
Up to 4.8 mm are acceptable
4 or more rounded
indications in a line
separated by 1.6 mm or lessedge to edge distance are
unacceptable
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Weld Defects
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Hydrogen Induced Crack
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Cracks in welds How to avoid Cold cracks
Ferritic steels
Proper preheat/ postheat- Use of thoroughly bakedelectrodes /fluxes
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Cracks in welds How to avoid
Hot cracks
Ensure low S&P in Materials
High S to Mn ratio in weld
Use of Welding consumableswith adequate ferrite content(Austenitic SS)
Use of low heat input
Ensuring high degree of
cleanliness during welding
Proper W/D ratio
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Cracks in welds How to avoid
July 9, 2013 102
Effect of weld shape on cracking tendency:a) W:D = 1, sound weld
b) W:D = 1.4, sound weld
c) W:D = 0.7, weld tends to crack
d) W:D = 2.0, weld tends to crack
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C k i ld H t id
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Cracks in welds How to avoid
July 9, 2013 105
Cracking tendency of deep
penetration weld:
a) Incorrect shape
b) Correct shape
Bridging large gap
gives concave weld
Cracking of deep
penetration fillet weld
Cracks in welds How to avoid
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Cracks in welds How to avoid
Control joint fit-up to reduce gaps.
Clean off all contaminants from the material
Welding sequence will not lead to a build-up ofthermally induced stresses.
Select parameters/technique to produce a weldbead with an adequate D to W ratio, or withsufficient throat thickness (fillet weld) (recommenda depth to width ratio of at least 0.5:1).
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Cracks in welds How to avoid
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Cracks in welds How to avoid
Too large a D to W ratio which will encouragesegregation and excessive transverse strains inrestrained joints. As a general rule, weld beadswhose D to W ratio exceeds 2:1 will be prone to
solidification cracking.
Avoid high welding speeds (at high current levels)which increase the amount of segregation andthe stress level across the weld bead.
At the run stop, ensure adequate filling of thecrater to avoid an unfavourable concave shape.
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Lamellar tearing
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Lamellar tearing Transverse strain - the
shrinkage strains on weldingmust act in the short
direction of the plate ie
through the plate thickness
Weld orientation - the fusionboundary will be roughly
parallel to the plane of the
inclusions
Material susceptibility - the
plate must have poor
ductility in the through-
thickness direction108
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Porosity in welds How to avoid
Types of porosity
distributed
surface breaking
pores wormhole
crater pipes
110
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Porosity in welds How to avoid Nitrogen, oxygen and hydrogen absorption due to
poor gas shielding
As little as 1% air entrainment in the shielding gaswill cause distributed porosity and greater than 1.5%results in gross surface breaking pores.
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Porosity in welds How to avoid
Air entrainment- Seal any air leak
- Avoid weld pool turbulence
- Use filler with adequate level of deoxidants
- Reduce excessively high gas flow
- Avoid draughts
Hydrogen- Dry the electrode and flux- Clean and degrease the workpiece surface
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Porosity in welds How to avoid Crater pipe
- Sudden drop of welding current &/or stopping wire
addition during termination of welding cause craterpipe formation
- Can be avoided by using down slope in Power Source
and with adequate wire addition
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Welding Quality Control
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Welding quality controlAvailability of approved Welding Procedurescomplying with Codes/ Specifications
Verification of Welder Performance Qualification
Records
Familiarity with workmanship standards and all
phases of good shop practice
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Welding quality control Review materials/welding consumables to be used
Review storage and issue procedures of welding
consumables
Check condition of Power Sources and Calibration
Records
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Welding quality control Check fit-up and alignment of weld joints as per the
Drawing Requirement
Check adequacy of preheating/ postheating
arrangements
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Welding quality control
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g q y
Proper included angle sufficient for reaching root of joint
to ensure fusion to side walls
Proper root opening/root face To ensure proper penetration
Too large a root face no penetration
Too small a root face burn through
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Weld traceability process
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Weld traceability process
At planning stage, each weld is allocated a weld number
Procedures are selected for each weld number & recorded
After fit-up, inspector signs off fit-up inspection box
Welder marks his name, WPS number, consumable batch
number against weld with paint marker.
Inspector performs visual & notes this information on
traceability database
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Distortion in Welding
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Distortion Types
Transverse
shrinkage
Longitudinal
Shrinkage
Angular distortion
Bow
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Angular distortion
Vs
Weld size
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DistortionControl
Locate the
welds on or
close to the
Neutral Axis
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Distortion Control
Use pre-setting tocounteract the
direction of distortion
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Distortion Control
Use back-to-back
Setup with orwithout offset to
increase rigidity
of assembly
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Distortion Control
Use rigid clamps to
prevent distortion
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Rigid clamps may
promote crackingtendency.
Use clamping with
imagination to allowmovement in some
direction while
preventing distortion in
required directions
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Ensure that
clamps do not
restrict access
for welding
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Distortion Correction
By application ofmechanical force
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Distortion Correction
By flame straightening
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Distortion
Correction
Wedge shapedheating rapidly at
high points is key
to flame
straightening
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Productivity in Manual ArcWelding
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Productivity in Welding
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Eliminate any extra welds from the design
Optimize joint preparation
Enhance current welding processes and procedures
Control shop tendency to overweldAnalyze whether material handling is effective
Deliver consumables and accessories close to the
welding points
Conduct energy audit of existing power sources
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Productivity in Welding
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Operator Factor ( Arcing Time)
Manual Process 20
40 %
Semi-automatic 30 50 %
Mechanised 40 60 %
Automatic 50
90 %
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MG Set Diode Based
machines
Thyristor
based
machines
Inverterised
Machines
Assumption Input supply 400 V 3 PH
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Assumption Input supply 400 V, 3 PH
Investment
Electrical costInput current consumption for 4 mm
electrode welding at 160 amps.
2 to 3 X
24 A
1.25 X
18 A
1.25 X
16 A
X
7 A
Electrical units consumed for 1 stick
electrode per minute( Considering
welding time of 1 minute per
electrode)
0.249 KWH
( 3x400x24x
0.9)
1000 x 60
0.187 KWH
( 3x400x18
x0.9)
1000 x 60
0.166 KWH
( 3x
400x16x0.9)
1000 x 60
0.0727 KWH
( 3x400x7x 0.9)
1000 x 60
Cost @Rs. 6 per electrical unit per
electrode of 4 mm Rs. 1.50 Rs. 1.122 Rs. 0.996 Rs. 0.436
Cost of average no. of 180electrodes consumed per shift per
machine
Rs. 270 Rs 202 Rs. 180 Rs. 78
Saving per shift over other machinesRs.( -)192 Rs. (-)124 Rs. (-)102 ---------
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WEAVING/ RUN OUT LENGTH
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WEAVING/ RUN-OUT LENGTH
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Quality & Productivity in Welding
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Where will you focus your
Improvement Initiatives ?
Towards Saving Money ?Or
Towards Saving Time ?
R f t bilit
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Reasons for traceabilityAdditional and auditable evidence that the correct
material was used
Enables re-design for unforseen conditions using the
actual properties Evidence for use at an inquest
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