Welding Processes
Submerged Arc Welding(SAW)
-~-------~~-----~~-----_.
Lecture 3 P 1
SAW: Process Fundamentals
• In SAW the welding heat source is an arc maintained between a consumable electrodeand the workpiece
• The arc and molten metal are "submerged" in ablanket of granular fusible flux
• The electrode is continuously fed into the arcand additional flux is distributed in front as theweld head moves along the joint
--------- --------
--- ------
------------
p2
(
-----------.----------
Submerged Arc Welding
NELD3ACKING'lATE
TO wELDERPOWER
TO AUTOMATICWIRE FEED
TO FLUXHOPPER
-----------------------
Lecture 3 p:
SAW Weld Pool (
l_
Electrode
> ,¥Grariular" , Flux
Arc Cavity
Solidified Weld Metal Weld Pool
....._._-----
re 3 p4
SAW Electrodes
• Functions of the electrode:- Conducts electrical current to the arc- Supplies joint filler material
• Electrodes may consist of- solid rod or wire- composite electrode (a metallic sheath encasing metal
powders)
----------------------- ._------ ._------------~
Lecture 3 p~
e3
SAW Fluxes
• Functions of the flux- Establish the electrical characteristics of the electrode
and arc stability- Control the composition and metallurgy of the weld
deposit- Supply additional filler material- Control weld bead shape
• Flux constituents- The flux consists of granular minerals and metals in the
form of fused and crushed or bonded agglomeratedparticles
p6
(
Lecture 3
SAW Flux Types for Steels
• Various formulations in use• Calcium silicate• Manganese silicate• Aluminate rutile or basic• Basic fluorides
• Fluxes termed "neutral" or "active" according totheir potency in modifying weld composition
• Also categorized as "basic" or "acid" based onvarious indices e.g.:
1CaO +CaF2 +MgO + K2 0+Na 2 0 +4MnO + FeO)
B 0 2
Si0 2 + ..!..-(A/20 3 + TiO 2 +Zr0 2)2
p7
e3
SAW Fluxes
• "Acid" silicate fluxes are active types
• Active fluxes and/or electrodes deoxidizedwith silicon and manganese are useful whenmaking single pass welds on scaled or rustysteel plate.- However, Si and Mn build up may give poor toughness
and soundness in multi-pass welds
• Basic fluxes give optimum strength andtoughness in steel welds
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--""--""-"----- --
p8
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Lecture 3
Classification of SAW Electrodesand Fluxes for Carbon Steel
• AWS/ASME A5.17 specification
• Solid electrodes are classified on the basis oftheir chemical composition
• Composite electrodes and fluxes areclassified according to the composition of theweld metal deposited with a particularelectrode
• FXXX-EXXX designates a flux/wirecombination- e.g., F7A6-EM12K
pS
e3
SAW Welding Procedures
• Operating Variables (in approximate orderof importance for weld quality)- welding current- flux type and particle size distribution- welding voltage- welding speed- electrode size- electrode stick-out- type of electrode- width and depth of flux layer
-~ ------.----------
p10
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----_._----._~-~_._-._-------------,
SAW Welding Procedures
Single-electrode single pass welding of steelplate with backing strip
aJ:P: \Steel backins strip
P 11
SAW Welding Procedures
Flux backing technique for single sided welding,e.g. ship panel manufacturing lines
(
FLUXBACKING
FLEXIBLESHEETMATERIAL
e3
INFLATEDHOSE
mOUGH
..~_._---~ ---
p12
Lecture 3
SAW Welding Procedures
Single-electrode two-pass welding of steelplate
T
Root Pass
p13
SAW Welding Procedures (
Correct
~c=t..--------,}=EC:-le-cC:-tr-od--:-e-~· I
Iignment ino-pass
elds
Lack of fusion
II
Incorrect
e3
Exception-unequal thicknesses
_.~ __J
P 14
I,------------- --------
SAW Welding Procedures
Electrode position effects in circumferential welding
JJ~ WJlhdffJA wJmtlJTJI1,Too much
<:, CorrectY--:1 Displacement
Slag spills _
'-----~-~~--
Lecture 3 P 1~
--~ ~-- ~----~-~-----------------~
SAW Variants
Twin-wire dclac system:1-dc power source, 2-ac power source, 3-lrail are, 4-lead arc
~--~-~--------------------
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-_._--------~~
e3
--- ~~ .. --~---------
p16
~~ ----~--------------------------------,
SAW Variants
Strip CladdingstripElectrode
WeldingDirection
Power Supply
Lecture 3
E.g. cladding the internal surfaces of pressure vessels
pH
e3
SAW Equipment
• Power Supply- Constant current or constant voltage type 100% duty cycle
1000 A output
• Wire Feeder- Constant speed (for constant voltage power supplies) or
voltage sensing (for constant current power supplies)
• Travel & Positioning Device- e.g. weld head crawler or rotary positioner
• Flux delivery/recovery system
• Process Controls- welding current, travel/workpiece positioning, wire feed
sequencing
p16
(
Lecture 3
-- - ---- ---------------------
SAW Applications
p1E
SAW Applications
• Joining heavy sections in steel, stainlesssteels- pressure vessel & piping circumferential & longitudinal
seams- plate girder fabrication- ship panel subassembly
• Surfacing- multi-wire & strip cladding variants
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---------------- ._._. __ _---------
--------------- ._.---------_. ------
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I,
e3 P 20
- ~ .._----~--- -~~~~- -~~~~~--~~~
SAW Capabilities & Limitations
Lecture 3
+ High deposition ratesand productivity
+ Tolerant to variationsin joint edgepreparation and fit up
+ Good weldmechanicalproperties (withappropriate choice ofwelding procedure)
- Flat or horizontalposition only -
- Mostly limited tosteels, stainless steeland nickel alloys
- Flux and slagresidues
P 21
3
Welding Processes
Electro-Slag Welding(ESW)
----,-
~---'-- -
P 22
(
Lecture 3
ESW Process Fundamentals
• In ESW, electrical current passes from acontinuous electrode to the workpiece through a conductive molten slag
• Resistance heating of the slag supplies thewelding heat source. The slag also shieldsthe weld pool from contamination
• The weld is formed by melting andresolidification of the joint edges and filler
ESW: Process Fundamentals (
ce 3
MOLTEN WELDPOOL
WELD DIRECTION ./
WORKPIECE
ELECTRODE GUIDETUBE
ELECTRODE
J..-~- WATER-COOLEDSHOE
COMPLETED WELD
p24
r--ESW Consumable Guide Method
Lecture 3
POWER SOURCE CONTROLPANEL
ELECTRODEWIRE FEEDER
WORKPIECE/
P 2~
e3
ESW Welding Procedures
• Process Variables- Joint Preparation & Fit-up- Welding Current- Welding Voltage- Electrode Extension- "Form Factor"- Electrode Oscillation- No of Electrodes & Spacing
p26
(
ESW: Joint Types
Bull Joint
"-- Flam. cut typically
--- ..
T-Jolnt
-
Comer Joint
Transilion Joint
--- ...
'-
Fillet Weld
T-Joint
Lecture 3
I l
-Cross Joint Overlay Buildup
P 27.
03
ESW: Joint Fit Up and Alignment
Run-off TabS~:r;~rJ::;'
Temporary StrongbacksWelded to Plate
- Outboard shoe side
40 mm min.
Starting Sump
I Root Opening
~=Width of Moving Shoe + 50mm
P 28
(
Lecture 3
ESW Welding Procedures
Typical ESW Welding ConditionsSingle electrode, non-oscillating, carbon steel
p29
ESW: Weld Metal Grain Structure
A
L
Transverse Section
Plate Thickness
(
e3
SolidificationFront
lonoitudinal Section at A-A
WeldingDirection
P 30
Lecture 3
ESW: Weld Grain Structure
SolidificationFront
P 31
ESW: Weld Faults (
(cl Centre-Line
[lJcrackl~g
~=:::-(f) Incomplete
Fusion
{]D'?,-)~k
(e) Incomplete Fusion
(a) Porosity
(d) Incomplete Fusion
{]I] {]I] [IJ(b) Centre-Line Cracking
(glOvertap (hI Undel1ll1 (I) Copper pickUp& Intemalcracks
m Overtap caused by metal spillage
e3 P 32
ESW: Production Rates
o 100mm200 300 400
500
1000 ...~E
1500
3 Electrodes
2 Electrodes
2
IRoot O~!!!9 29 mm IlL-J.......J.-.L-I-~~~~~~O
4 6 8 10 12 14 16
PlATE THICKN~SS (in)
...=E 60c-CwWQ. 40(I)
C)z:-920~ 1 Electro e
Lecture 3 P 33
e3
ESW Applications
• Most types of carbon steels, low alloy andstainless steels
• Pressure vessel longitudinal seams
• Heavy structural fabrications, machinery
P 34
(
(
ESW Capabilities and Limitations
Lecture 3
+ Very high depositionrates
+ Ability to weld verythick materials
+ Minimum jointpreparationrequirements
+ Minimum materialshandling
- Limited to carbon,low alloy and somestainless steels
- Joints must bevertically positioned
- Risk of stop/startdefects
P 3~
33
Welding Processes
Electro Gas Welding(EGW)
-~._-- --
P 36
(
Lecture 3
EGW Process Fundamentals
• In EGW the welding heat source is an arcmaintained between a continuous electrodeand the weld pool
• The weld is formed by melting andresolidification of the joint edges and filler inthe vertical position
• The weld zone is shielded from contaminationby shielding gas and/or flux supplied fromflux-cored wire
p37
EGW Process Fundamentals(
___-~~.DriveRolls
~~;;~;; Primety= .- Shielding Gas_ Supplementary
Shielding Gas
SOLIDIFIEDWELD METAL
ElectrodeConduit
Water
FIXed Shoe
WELDING •DIRECTION ~~ t
Gas <;'¥"h,!i:~~~fJl:"_ ......._;
ELECTRODE
03 P 38
Lecture 3
EGW Welding Procedures
• Operating Variables- Materials and consumables- Joint fit-up and alignment- Welding Voltage- Welding Current/Electrode Feed Speed- Electrode Extension- Electrode Oscillation
P 3'
e3
EGW Consurnables
• Both flux cored and solid wires are used inEGW
• EGW flux cored wires contain lessslag-forming compounds than FCAWelectrodes
• Flux-cored and solid wires are available invarious chemical compositions to achievedesired weld metal strength and notchtoughness.
L ~
------ - -----
P 40
(
Classification of EGW Consumables• AWS A5.26 Specification for Consumables Used for
Electrogas Welding of Carbon and High Strength Low AlloySteels,--------- • Denotes an EGWelectrode
i
-------- . Indicates the min. weld metal strength in10 ksi
1
,------- . Indicates the minimum impac1 strength
• Designates a flux-cored electrode (TheEG X X T X X X letter S designates a solid elec1rode
t= . Indicates the chemicalcomposition of the depositedweld metal
Example: EG 6 2 8-1: Solid carbon-manganese EGW elec1rode with 60 ksi minstrength and 20ft-lb impact energy at -40F
Lecture 3 P 41
-~~--~-----------------------,
EGW Welding ProceduresMoving or Stationary Shoes
{ J L----'< f"Ca~~22mm
(A) Butt Joint With Square Groove Weld
(
r---=i I- 4mm
<--I \ ?---I22mml--
s~;..;»Moving ShOD
e3
(B) Butt joint with Single V Groove Weld
p42
EGW Welding Procedures
Typical Conditions for Electrogas Welds Using a 3mm Diameter AWS Class EG72T1 Electrode withMoving Shoes
Lecture 3 p43
ra 3
EGW Equipment
• Power supply
• Electrode feeder
• Electrode guide
• Electrode guide travel and oscillator
• Retaining shoes
• Controls
P44
c
EGW: Applications~~~~~~~-
Lecture 3
The principalapplications of EGWinclude storage tanks,pressure vessels,structural membersand ship hulls.
p45
EGW Capabilities and Limitations (
e3
+ High DepositionRates
+ Simple JointPreparation
+ Applicable to thinnermaterials than ESW
- Limited to carbon,low alloy and-somestainless steels
- Joints must bevertically positioned
- Risk of stop/startdefects
P 46