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

--""-- "-------

--""--""-"----- --

p8

(

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

(

----_._----._~-~_._-._-------------,

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

~--~-~--------------------

(

-_._--------~~

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

-----------------_.._. __ . __._-------

---------------- ._._. __ _---------

--------------- ._.---------_. ------

(

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