Basics of SMAW

7/28/2019 Basics of SMAW

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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

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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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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

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+

- 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

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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

Increased deposition ratesJuly 9, 2013 32


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+ -- +

50%

50%

Alternate Current -AC

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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

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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

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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

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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

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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

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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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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

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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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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


Effect of welding current

Effect of Travel speed


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Travel speed is too high:


Lack of root fusion

Incomplete root penetration

Insufficient volume of weld metal deposited

Travel speed is too low:

Excess penetration

Burn-through Undercut


Weld bead contour too high

p


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MMAW Techniques


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Arc Striking

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2 Methods


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Restarts

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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

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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

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GROUP 3 - SURFACE IRREGULARITIES


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Undercut

Overlap

Gas pore

Crater pipe

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GROUP 4 - SURFACE CRACKS


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GROUP 4 SURFACE CRACKS

Longitudinal/Centre-line

Parent metal/HAZ

Transverse

Crater

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GROUP 5 - MISCELLANEOUS


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Stray arc / arc strike

Spatter

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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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Overlap Excess weld metal


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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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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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Cracking tendency of deep

penetration weld:

a) Incorrect shape

b) Correct shape

Bridging large gap

gives concave weld

Cracking of deep

penetration fillet weld



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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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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

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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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Documents

Basics of SMAW