2. Poyyara Consultants
SAW
• Fusion Welding Process
• Automatic / Semi Automatic
• Arc Between Consumable Electrode And Work
• Arc Covered Under granular Flux
• Wire / Electrode Continuously Fed To Weld Pool
• Wire / Arc Under Flux Moves Along The Groove
• Wire, BM & Flux Close to Arc Melt Under Flux
• On Cooling Weld Metal Solidifies
• Molten Flux Forms Thick Slag Coating On Weld
6. Poyyara Consultants
Types Of Flux
• Neutral Flux
- Very little deoxidizers
- Wire compatible to base metal with deoxidizers
- Best suitable for multi pass welding
- No significant change in weld chemistry due to change in
arc length
- Consistent weld chemistry trough out the weld volume
- Single flux suitable for several material
7. Poyyara Consultants
Types Of Flux
• Active Flux
- Contains Mn & Si as deoxidizers
- Suitable for single pass welding on rusted
surfaces
- Mn & Si in weld metal vary with change in
arc length
- To be welded within the recommended
parameters
- Not suitable for better impact properties of
weld metal
8. Poyyara Consultants
Types Of Flux
• Alloy Flux
- To be used with CS wire to produce alloy steel
weld metal
- Required quantity and quality of alloys added to
flux
- Single flux for specific application
- Wire will be different from base metal
- To be welded within the recommended parameters
- Inconsistent weld chemistry
9. Poyyara Consultants
Function Of Flux In SAW
• Stabilizes Arc
• Prevents contamination of weld metal
• Cleans the weld from unwanted impurities
• Increases Fluidity of molten metal
• Generates inert gas shielding while metal transfers
• Forms slag after melting & covers weld
• Allows deposited metal to cool slowly
• Compensates alloying elements Within the weld
• Eliminates spatter generation
• Helps in even & uniform bead finish
10. Poyyara Consultants
Baking Requirements For Flux
• Spread the loose Flux in a Tray Of baking Oven
• Identify The Tray With The Quality/Grade Of Flux
• Bake Tray in an Oven Between 300° C to 350° C
• Baking Time 2 Hrs to 3 Hrs
• Reduce the temperature to Min 100 ° C
• Hold the Flux at this temperature till use
12. Poyyara Consultants
How Does Moist Flux Generate
Crack Within Weld?
• Moist Flux introduce atomic hydrogen at high
temperature in weld
• On cooling, atomic hydrogen try to form
molecules
• The reaction results in stresses and fine cracks
• Cracks occur within hardened metal - HAZ
• Known as “Hydrogen Embrittlement” or “Under
Bead Crack” or “Delayed Crack”
13. Poyyara Consultants
Reuse Of Flux
• Flux May Be Reused Provided
- Weld Not Highly Critical In Impact / Chemistry
- Reuse Limited To Maximum Twice
- All Slag Particles Are sieved & Removed
- Rebaked If not Remained In Hot
- Minimum 50% Fresh Flux Well Mixed
- Customer Spec. Doesn't Prohibit The Same
14. Poyyara Consultants
Types Of Power Source
• Thyrister – DC
• Rectifier – DC
• Motor Generator – DC
• Transformer - AC
16. Poyyara Consultants
SAW Wire - Electrode
• Consumable Electrode / Wire
• Layer Wound On Spool / Coil
• CS & LAS Wires Coated with Cu
• Conducts Current and generates Arc
• Chemistry Compatible To Base Metal
• Grade Of Flux Can Be Same For CS & LAS
• Wire melts & deposited as filler in joint
19. Poyyara Consultants
Tandem SAW
1 Displacement between two wires – 25 - 50 mm
2 While starting first Arc is struck with DC wire
3
Immediately after DC wire starts moving with arc in the groove, AC wire
is made to strike the second Arc
4 While DC Arc leads, AC arc lag behind by 35 mm
5 While stopping, first DC arc is cut off followed by AC
••••••••••••••••
DC Wire
Flux
Slag
Weld
Base Metal
Arcs
AC Wire
35 mm gap
Welding Direction
20. Poyyara Consultants
Tandem SAW
Advantages Disadvantages
1
Double the weld deposit
(15kg / arc hr)
Requires uniform - jerk free -
movement of welding nozzle / job
2 Higher productivity
Requires precise placement of wires
in the groove
3 Less consumption of flux Higher skill of operator
••••••••••••••••
DC Wire
Flux
Slag
Weld
Base Metal
Arcs
AC Wire
35 mm gap
Welding Direction
21. Poyyara Consultants
Multi Wire SAW
••••••••••••••••
Wire1
Flux
Slag
Weld
Base Metal
Arcs
Wire 2
Advantages Disadvantages
1 Higher weld deposit
Requires higher capacity power
source
2 Higher productivity
Requires precise placement of
nozzle in the groove
3 Less consumption of flux Higher skill of operator
3 mm gap
Welding Direction
Nozzle
+ –
DC
22. Poyyara Consultants
Important Terminology used in
Critical SAW
• Preheating
• Post Heating or Dehydrogenation
• Intermediate Stress leaving
• Inter pass Temperature
• Post Weld Heat Treatment
23. Poyyara Consultants
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 coil
• Heating from opposite side of welding
wherever possible
• Temperature to be verified by thermo chalks
prior to starting the weld
24. Poyyara Consultants
Why Preheating?
• Preheating eliminates possible cracking of weld
and HAZ
• Applicable to
-Hardenable low alloy steels of all thickness
-Carbon steels of thickness above 25 mm.
-Restrained welds of all thickness
• Preheating temperature vary from 75°C to 200°C
depending on hardenability of material, thickness
& joint restrain
25. Poyyara Consultants
How does Preheating Eliminate
Crack?
• Preheating promotes slow cooling of weld
and HAZ
• Slow cooling softens or prevents hardening
of weld and HAZ
• Soft material not prone to crack even in
restrained condition
26. Poyyara Consultants
What Is Post Heating?
• 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 coil
• Heating from opposite side of welding wherever
possible
• Temperature verified by thermo chalks during the
period
27. Poyyara Consultants
Why Post Heating?
• Post heating eliminates possible delayed
cracking of weld and HAZ
• Applicable to
-Thicker hardenable low alloy steels
-Restrained hardenable welds of all
thickness
• Post heating temperature and duration
depends on hardenability of material,
thickness & joint restrain
28. Poyyara Consultants
How does Post Heating Eliminate
Crack?
• SAW 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
29. Poyyara Consultants
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
thickness
• Applicable to
Highly restrained air hardenable material
30. Poyyara Consultants
Why Intermediate Stress
Relieving?
• Restrained welds in air hardenable steel
highly prone to crack on cooling to room
temperature.
• Cracks due to entrapped hydrogen and built
in stress
• Intermediate stress relieving relieves built in
stresses and entrapped hydrogen making
the joint free from crack prone
31. Poyyara Consultants
What Is Inter- Pass Temperature?
• The temperature of a previously layed weld
bead immediately before depositing the next
bead over it
• Temperature to be verified by thermo chalk
prior to starting next bead
• Applicable to
Stainless Steel
Carbon Steel & LAS with minimum
impact
32. Poyyara Consultants
Why Inter Pass Temperature?
• Control on inter pass temperature avoids
over heating, there by
-Refines the weld metal with fine grains
-Improves the notch toughness
properties
-Minimize the loss of alloying elements in
welds
-Reduces the distortion
33. Poyyara Consultants
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 thickness
• Applicable to
-All type of CS & LAS
34. Poyyara Consultants
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
