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Shielded Metal Arc Welding
By L D Poyyara
POYYARA CONSULTANTS 2
What Is Welding ?
Process of joining metals / alloys
The process performed by Heat with or without Pressure
Filler metal may or may not be used
The joint will be homogeneous
POYYARA CONSULTANTS 3
Classification Of Welding
1 Pressure Welding – With Heat & Pressure
2 Fusion Welding – With Heat & mostly with Filler
POYYARA CONSULTANTS 4
Pressure Welding Process
Metal parts heated to forging temperatureHeating by Oven, Oxy fuel flame or Electric ResistancePressure applied on heated parts – by Hammer, Hydraulic Press or Mechanical leverThe Parts remain permanent homogeneousjoint
POYYARA CONSULTANTS 5
Types Of Pressure Welding
Forge WeldingResistance Butt / Flash Butt / Stud WeldingResistance Spot WeldingResistance Seam welding
POYYARA CONSULTANTS 6
Fusion Welding Process
Metal parts locally heated to melt along the joint.
Heating by oxy fuel flame or electric Arc.
Invariably filler metal added to molten pool.
On cooling, molten puddle solidifies to permanent homogeneous joint.
POYYARA CONSULTANTS 7
Types Of Fusion Welding
Shielded Metal Arc Welding- SMAW Gas Tungsten Arc Welding - GTAWGas Metal Arc Welding – GMAW (MIG / MAG / FCAW)Submerged Arc Welding – SAWGas welding – Oxy Fuel GasElectron Beam Welding - EBWThermit Welding
POYYARA CONSULTANTS 8
An electric Arc struck between electrode and base metal jointBase metal melts under arcElectrode tip melts in drops and transfers to molten pool of BMElectrode with Arc moves along the joint keeping constant arc lengthOn cooling pool solidifies
Arc
Base Metal
Flux Coating
Core Wire
Pool
SMAW Process+
_
POYYARA CONSULTANTS 9
Equipment, Accessories & tools
Power Source
Welding Cables, Holder & EarthingClamp
Head Screen, Hand gloves, Chipping Hammer & Wire Brush
POYYARA CONSULTANTS 10
Types Of Power Source
Inverter- DC
Thyristor – DC
Diesel Generator Set -DC
Rectifier – DC
Transformer - AC
POYYARA CONSULTANTS 11
Characteristic Of Power Source
VVLinear – Cons. V Drooping – Cons. A
Machine weldingManual welding
A A
Vertical Curve
Horizontal Curve
V1
V2
A1 A2
V1V2
A1 A2
POYYARA CONSULTANTS 12
Electrode
Consumable
Metallic Wire Coated with Flux
Conducts Current and generates Arc
Wire melts & deposited as filler in joint
POYYARA CONSULTANTS 13
Flux Coating On Electrode
Sodium ChloridePotassium ChlorideTitanium DioxideSodium SilicateFerrosilicon Iron Powder Alloying ElementsBinding Material
POYYARA CONSULTANTS 14
Function Of Flux In welding
Stabilizes ArcPrevents contamination of weld metalCleans the weld from unwanted impuritiesIncreases fluidity of molten metalGenerates inert gas shielding while metal transfers
POYYARA CONSULTANTS 15
Function Of Flux In welding
Forms slag after melting & covers weldAllows deposited metal to cool slowlyIntroduces alloying elements in the weldIncreases deposition efficiencyMinimizes the spatter generationHelps in even & uniform bead finish
POYYARA CONSULTANTS 16
CS & LAS Electrode Sizes & Recommended Currents
60 -70
80 - 90
110 - 120
120 - 140
---
---
Average electrodes
consumed in 8 Hrs shift
240 – 250 A
150 – 210 A
130 – 180 A
100 – 130 A
60 – 85 A
40 – 60 A
CurrentLengthDia
95-10044506.36
90-95645055
85-90845044
80 -85104503.153
60-65123502.52
50-551430021
Time required for burning in seconds
Gage
Core Wire (in mm)
No
POYYARA CONSULTANTS 17
Appx. Cost Of CS & SS Electrodes
E309
E308L
E7018
E6013
AWS Classification LengthDia
31.603503.15
22.303503.15SS
6.304503.15
3.004503.15CS
Cost Per Piece( in Rupees)
Core Wire ( in mm )Electrode Quality
POYYARA CONSULTANTS 18
ASME Classification Of Electrodes
SFA 5.1E 7018
E = Electrode70 = UTS in 1000 psi ( 60/70/80/90/100/ 110)
1 = Position (1= all, 2= 1G, 1F & 2F, 3= 1G & 1F)
8 = Type of coating (0,1,2,3,5,6,8)
POYYARA CONSULTANTS 19
Baking Of Basic Coated Electrodes
Bake the loose electrodes in a baking OvenBaking Temperature 250° C to 300° CBaking Time 2Hrs to 3 HrsReduce the temperature to 100° C Hold the electrodes at this temperature till useUnused / left over electrodes to be re-baked
POYYARA CONSULTANTS 20
Why Baking?
To remove the moisture (H2O) from coating to avoid possible cracking of weld
POYYARA CONSULTANTS 21
How Does Moist Electrode Generate Crack Within Weld?
Moist electrodes introduce atomic hydrogen at high temperature in weldOn cooling, atomic hydrogen try to form moleculesThe reaction results in stresses and fine cracksCracks occur within hardened metal - HAZ Known as “Hydrogen Embrittlement” , “Under Bead Crack”, HIC, Delayed Crack, Cold Crack.
POYYARA CONSULTANTS 22
Important Terminologies used in Critical Welding Operation
PreheatingPost Heating or DehydrogenationIntermediate Stress leavingInter pass TemperaturePost Weld Heat Treatment
POYYARA CONSULTANTS 23
What Is Preheating?
Heating the base metal along the weld joint to a predetermined minimum temperature immediately before starting the weld.Heating by Oxy fuel flame or electric resistant coilHeating from opposite side of welding wherever possibleTemperature to be verified by thermo chalks prior to starting the weld
POYYARA CONSULTANTS 24
Why Preheating? Preheating eliminates possible cracking of weld and HAZ
Applicable toHardenable low alloy steels of all thicknessCarbon steels of thickness above 25 mm.Restrained welds of CS & LAS of all thickness
Preheating temperature vary from 75°C to 300°C depending on hardenability of material, thickness & joint restraint
POYYARA CONSULTANTS 25
How does Preheating Eliminate Crack?
Preheating promotes slow cooling of weld and HAZ Slow cooling softens or prevents hardening of weld and HAZSoft material not prone to crack even in restrained condition
POYYARA CONSULTANTS 26
What Is Post Heating/Dehydrogenation?
Raising the pre heating temperature of the weld joint to a predetermined temperature range (250°C to 350° C) for a minimum period of time (3 Hrs) before the weld cools down to room temperature.Post heating performed when welding is completed or terminated any time in between.Heating by Oxy fuel flame or electric resistant coilHeating from opposite side of welding wherever possibleTemperature verified by thermo chalks during the period
POYYARA CONSULTANTS 27
Why Post Heating?Post heating eliminates possible delayed cracking of weld and HAZApplicable to
Thicker hardenable low alloy steelsRestrained hardenable welds of all thickness
Post heating temperature and duration depends on hardenability of material, thickness & joint restrain
POYYARA CONSULTANTS 28
How does Post Heating Eliminate Crack?
SMAW introduces hydrogen in weld metal
Entrapped hydrogen in weld metal induces delayed cracks unless removed before cooling to room temperature
Retaining the weld at a higher temperature for a longer duration allows the hydrogen to come out of weld
POYYARA CONSULTANTS 29
What Is Intermediate Stress Relieving?
Heat treating a subassembly in a furnace to a predetermined cycle immediately on completion of critical restrained weld joint / joints without allowing the welds to go down the pre heat temperature. Rate of heating, Soaking temperature, Soaking time and rate of cooling depends on material quality and thicknessApplicable to
Highly restrained air hardenable material
POYYARA CONSULTANTS 30
Why Intermediate Stress Relieving?
Restrained welds in air hardenable steel highly prone to crack on cooling to room temperature.
Cracks due to entrapped hydrogen, hardened HAZ and built in stress
“Intermediate stress relieving” makes the joint free from crack prone by
- Relieving built in stresses- Relieving entrapped hydrogen.- Softening HAZ.
POYYARA CONSULTANTS 31
What Is Inter- Pass Temperature?
The temperature of a previously layed weld bead immediately before depositing the next bead over itTemperature to be verified by thermo chalk prior to starting next beadApplicable to
Stainless SteelCarbon Steel & LAS with minimum impact
POYYARA CONSULTANTS 32
Why Inter Pass Temperature?
Control on inter pass temperature avoids over heating, there by
Refines the weld metal with fine grainsImproves the notch toughness propertiesMinimize the loss of alloying elements in weldsReduces the distortion
POYYARA CONSULTANTS 33
What Is Post Weld Heat Treatment?
Heat treating an assembly on completion of all applicable welding, in an enclosed furnace with controlled heating/cooling rate and soaking at a specific temperature for a specific time. Rate of heating, Soaking temperature,
Soaking time and rate of cooling depends on material quality and thicknessApplicable to
All type of CS & LAS
POYYARA CONSULTANTS 34
Why Post Weld Heat Treatment?
Welded joints retain internal stresses within the structure HAZ of welds remains invariably hardened“Post Weld Heat Treatment” relieves internal stresses and softens HAZ. This reduces the cracking tendency of the equipment in service
POYYARA CONSULTANTS 35
Welding Terminologies used in Qualifications
Heat In PutHeat Affected Zone – HAZDilutionOverlap In Weld Overlay Tempering Bead
POYYARA CONSULTANTS 36
What Is Heat In Put In Welding?
The extent of heat energy generated in Joules per unit length while making each weld bead. “Heat In Put” is the Function of Welding Current, Arc Voltage, And the Welding SpeedIt is measured in Joules -
Heat In Put In Joules / mm= (A x V x 60) ÷ Travel Speed in mm / min
POYYARA CONSULTANTS 37
Why Control On Heat in Put?
Heat In put” controls the grain size of weld metal.
Lower the Heat in put finer the grain size. Finer the Grain size Better the impact properties
“Heat In Put” Also controls Dilution, HAZ & Geometry of Bead size
POYYARA CONSULTANTS 38
What Is Heat Affected Zone (HAZ)
A small volume of BM adjacent to weld fusion line, which is totally changed in its structure due to intense heat of each weld bead is known HAZ
Weld Zone
HAZDiluted BM
Diluted BM
Weld Zone
Fusion Line
POYYARA CONSULTANTS 39
What Is Significant Of HAZ
It is a part and parcel of weld jointIt is inevitableIt has properties different from BM & Weld Metal
Weld Zone
HAZDiluted BM
Diluted BM
Weld Zone
Fusion Line
POYYARA CONSULTANTS 40
What Is Dilution In Weld
In all Fusion welding, a small portion of BM very close to the welding heat gets melted and added to weld zone / fusion zone. Dilution is the ratio of molten base metal volume (Area) to the volume ( Area) of total fusion zone
HAZ
Diluted BM
Weld / Fusion Zone
Fusion Line
% Dilution = (Area of Diluted BM ÷Total Fused Area) × 100
POYYARA CONSULTANTS 41
What Is Significant Of Dilution Weld metal chemistry changes depending on the extent of dilutionChemical elements influence Physical properties of the joint. Weld chemistry influences corrosion resistance of weld overlays
Weld Zone
HAZDiluted BM
Diluted BM
Weld Zone
Fusion Line
POYYARA CONSULTANTS 42
What Is Overlap In Weld Overlay?
The extent of covering or over lapping of previous weld bead by the adjacent bead.
40 to 50 % Over Lap
Less Dilution More Dilution
10 to 15 % Over Lap
More ThicknessLess Thickness
POYYARA CONSULTANTS 43
What Is Significant Of Overlap In Weld Overlay?
Overlap of 40 to 50% results in Less Dilution & more weld overlay Thickness per layerLess dilution results weld metal chemistry more towards filler metal chemistry
40 to 50 % Over Lap 10 to 15 % Over Lap
Less Dilution More DilutionMore Thickness
Less Thickness
POYYARA CONSULTANTS 44
What Is Temper Bead Technique?
In a multi pass groove & Fillet Welds, each bead & its HAZ are getting tempered (heat treated) by the welding heat of the next bead. Thus all beads & their HAZ, except those in last layer, are tempered. Temper beads are the specially & carefully welded temporary beads on the top of final weld reinforcement with out allowing to generate any HAZ within the BM. Temper beads are to be ground flush with the required reinforcement.
POYYARA CONSULTANTS 45
Temper Bead
Temper Bead T1 & T2 Not To Generate HAZ In BMTemper Beads To Be Ground Flush
T2T1
21
3 34 4
55
T1 & T2 To be ground Flush
HAZ
Rqd. Reinforcement
POYYARA CONSULTANTS 46
Common Defects In SMAW
1. Cracks 2. Lack Of Fusion3. Slag 4. Porosity5. Pinhole 6. Piping 7. Undercut 8. Overlap9. Lack Of Penetration 10. Excess Penetration11. Spatters 12. Suck Back 13. Under Flush 14. Burn Through 15. Uneven Bead 16.Stray Arcing
POYYARA CONSULTANTS 47
Crack
1) Use Right Electrode2) Qualify Procedure3) Preheat Uniformly4) Post heating or ISR
1) Wrong Consumable2) Wrong Procedure3) Improper Preheat4) Excessive Restrain
RemedyCause
crack
POYYARA CONSULTANTS 48
Lack Of Fusion
1) Use Right Current2) Train /Qualify welder3) Train/Qualify Welder
1) Inadequate Current2) Wrong Electrode angle3) Improper bead placement
RemedyCause
Lack Of Fusion
POYYARA CONSULTANTS 49
Slag
1) Clean each bead2) Use Right Current3) Train / Qualify welder4) Train / Qualify Welder
1) Inadequate Cleaning2) Inadequate Current3) Wrong Electrode angle4) Improper bead placement
RemedyCause
Slag
POYYARA CONSULTANTS 50
Porosity
1) Bake the electrodes2) Replace the electrodes3) Clean & warm the BM4) Replace the electrodes
1) Damp Electrode2) Damaged coating3) Wet surface of BM4) Rusted core wire
RemedyCause
Porosity . .
POYYARA CONSULTANTS 51
Pinhole
1) Bake the electrodes2) Replace the electrodes3) Clean & warm the BM4) Replace the electrodes
1) Damp Electrode2) Damaged coating3) Wet surface of BM/WM4) Rusted core wire
RemedyCause
Pinhole•
POYYARA CONSULTANTS 52
Piping
1) Bake the electrodes2) Replace the electrodes3) Clean & warm the weld4) Replace the electrodes
1) Damp Electrode2) Damaged coating3) Previous beads wet4) Rusted core wire
RemedyCause
Piping•
POYYARA CONSULTANTS 53
Undercut
1) Reduce the Current2) Reduce Arc length3) Train & Qualify the
Welder1) Replace the electrode
1) Excess Current2) Excess Voltage3) Improper Electrode
angle1) Eccentric Coating
RemedyCause
Under cut
POYYARA CONSULTANTS 54
Overlap
1) Train & Qualify welder
2) Increase the current
1) Wrong Electrode Angle
2) Inadequate current
RemedyCause
Overlap
POYYARA CONSULTANTS 55
Lack Of Penetration*
1) Reduce Root Face2) Increase Root Opening3) Reduce electrode size4) Train / Qualify Welder5) Train / Qualify Welder6) Train & Qualify Welder
1) Excess Root Face2) Inadequate Root opening3) Over size electrode 4) Wrong Electrode angle5) Improper bead placement6) Improper weaving
technique
RemedyCause
LOP
* Applicable to SSFPW
POYYARA CONSULTANTS 56
Excess Penetration*
1) Reduce root gap2) Reduce Current3) Increase Root face4) Train / Qualify Welder
1) Excess root opening2) Excess Current3) Inadequate root face 4) Wrong Electrode angle
RemedyCause
Excess Penetration
* Applicable to SSFPW
POYYARA CONSULTANTS 57
Spatters
1) Reduce to Right Current2) Reduce Arc length3) Correct the polarity4) Use Baked electrodes5) Clean BM surface6) Replace the electrodes7) Replace the electrodes
1) Excess Current2) Excess Voltage3) Wrong Polarity4) Wet Electrodes5) Rusted BM surface6) Rusted Core wire7) Eccentrics coating
RemedyCause
Spatters• • •
POYYARA CONSULTANTS 58
Suck Back*
1)Reduce weaving2) Reduce Current3) Increase Root face4) Train / Qualify Welder
1) Excess weaving in root2) Excess Current3) Inadequate root face 4) Wrong Electrode angle
RemedyCause
Suck Back
* Applicable to SSFPW in 4G, 3G & 2G
POYYARA CONSULTANTS 59
Under Flush
1) Weld some more beads in final layer
2) Train / Qualify welder
3) Train / Qualify Welder
1) Inadequate weld beads in final layer
2) Inadequate understanding on weld reinforcement requirement
3) Wrong selection of Electrode size for final layer
RemedyCause
Under flush
POYYARA CONSULTANTS 60
Burn through*
1) Reduce the Current2) Reduce root opening3) Increase root face4) Train / Qualify Welder
1) Excess Current2) Excess Root opening3) Inadequate Root face4) Improper weaving
RemedyCause
Burn trough *Applicable to root pass
POYYARA CONSULTANTS 61
Uneven Bead Finish
1) Train & Qualify the Welder
2) Reduce Arc length3) Train & Qualify the
Welder
1) Improper bead placement
2) Excess Voltage3) Excess / inadequate
current
RemedyCause
Uneven bead finish
POYYARA CONSULTANTS 62
Stray Arcing
1) Train the Welder2) Train the Welder
1) Wrong Arc Striking Practice2) Inadequate Skill of Welder
RemedyCause
Arc Strikes
63
Good Engineering Practices in
Shielded Metal Arc Welding
POYYARA CONSULTANTS 64
Good Engineering Practices In SMAW
Do Welding with properly baked electrodes Basic coated CS electrodes to be baked to 250°C to 300°C for two hours Baked electrodes to be directly used on job or to be retained in a hold over oven at 100°C to 150°C until useUnused balance electrodes shall be returned to baking oven
POYYARA CONSULTANTS 65
Do not weld with damp ElectrodesDo not try to heat electrodes by touching the job (Short circuiting)Do not use electrodes with damaged coating Do not use electrodes with cracked coatingDo not bend the electrodes after holding it in the holder
Good Engineering Practices In SMAW
POYYARA CONSULTANTS 66
Do not weld on groove / surface with mill scale or rustingPrior to welding, clean the weld groove with power wire wheelDo not weld with unidentified electrodesDo not leave balance electrodes unattended on shop
Good Engineering Practices In SMAW
POYYARA CONSULTANTS 67
All connections with earthing and welding cables shall be tight fittedEarthing clamp shall always be tightly connected to the jobBurn the full length of electrode till 37 mm stub length
Good Engineering Practices In SMAW
POYYARA CONSULTANTS 68
Earthing cable shall directly connect to the job with an earthing clamp.Tacks for set up shall be minimum 5 times the electrode diameterWeaving shall be limited to three times the electrode diameter.Only trained & qualified welders shall be employed for welding
Good Engineering Practices In SMAW
POYYARA CONSULTANTS 69
Do not direct fan or blower to welding arcRemove paint if any from the area near weldingWhile welding in open, area shall be covered to protect from rain water & breezeWeld edge preparation shall be free from serrations
Good Engineering Practices In SMAW
POYYARA CONSULTANTS 70
Use poison plates between the job material & structural supports.Do not damage parent metal while removing temporary supports.Locations where from temporary supports are removed shall be touched up by welding / grinding and PT checked.
Good Engineering Practices In SMAW
POYYARA CONSULTANTS 71
Remove visible defects from welds before placing the subsequent beadsDo not weld over a visible crackElectrodes kept out side more than 2 Hrs shall be returned to baking ovenMaximum 15 electrodes at a time shall be taken from oven for welding
Good Engineering Practices In SMAW
POYYARA CONSULTANTS 72
When preheat is required, heat from opposite side of welding.Use temperature indicating crayons for checking temperatureDo not Weld more than specified weld size- Fillet / Reinforcement.
Good Engineering Practices In SMAW
73
Safety Precautions in Shielded Metal Arc Welding
POYYARA CONSULTANTS 74
Safety Precautions In SMAW
Welders shall use safety devises – Hand gloves, Head screen with right glass & Safety shoesWelders shall use full sleeve boiler suit Use welding glass-DIN 11/12 up to 250 Amps and 13 above 250 AmpsDo not look at the arc with naked eyes
POYYARA CONSULTANTS 75
Do not throw Stubs on ground. They shall be placed in stub collector.Do not keep electrode in the holder when work is not in progressDo not touch the electrode held on holder and the the job when the power source is onKeep welding cables duly wound near power source when no welding is done
Safety Precautions In SMAW
POYYARA CONSULTANTS 76
Do not breath welding fumesWhen working in confined area, ensure adequate ventilation / exhaustGas cutting torch / preheating burner shall not be taken inside confined area unless the flame is lit When not in use, switch off the the power source from electric supply
Safety Precautions In SMAW
POYYARA CONSULTANTS 77
Acetone / inflammable liquids (Chemical for dye penetrant test) shall not be brought near weldingGas cutting unit / fuel gas cylinders shall be away from welding area Wet safety Shoes or wet hand gloves shall not be worn while welding
Safety Precautions In SMAW
Thank You