SAW

Introduction

SAW (Submerged Arc Welding) = Arc welding process where the arc is submerged beneath a blanket of granular fusible flux

Key Feature: Arc completely covered by flux - not visible during welding

Process Principle

1. Continuous wire electrode fed into weld joint
2. Granular flux deposited ahead of electrode
3. Arc burns beneath flux blanket
4. Flux melts, forming protective slag
5. Unfused flux recovered and reused
6. Automatic or semi-automatic operation

SAW Equipment

1. Power Source

• Constant voltage (CV) or constant current (CC)
• DC or AC
• High current capacity: 300-2000A
• Voltage: 25-40V

2. Wire Feeder

• Continuous wire feed
• Speed control
• Single or multiple wires

3. Flux Hopper

• Stores and dispenses flux
• Gravity feed or pressurized
• Positioned ahead of electrode

4. Flux Recovery System

• Vacuum system
• Collects unfused flux
• Recycles for reuse

5. Welding Head/Carriage

• Holds electrode and flux hopper
• Travels along joint
• Motorized or manual

6. Wire Electrode

• Solid wire (most common)
• Metal-cored wire
• Diameters: 2.0-6.0 mm (larger than GMAW)

Flux

Functions of Flux

1. Arc shielding: Protects from atmosphere
2. Slag formation: Covers and protects weld
3. Arc stabilization: Maintains stable arc
4. Deoxidation: Removes impurities
5. Alloying: Adds elements to weld metal
6. Thermal insulation: Slows cooling rate

Flux Types

1. Fused Flux

• Manufactured by melting and crushing
• Glassy appearance
• Low moisture absorption
• Good for high-speed welding

2. Bonded Flux

• Ingredients mixed with binder
• Granular appearance
• Can add alloying elements easily
• Requires drying before use

3. Agglomerated Flux

• Similar to bonded but different process
• Better flow characteristics
• Moderate moisture resistance

Flux Classification

By Basicity:

• Neutral flux: Minimal chemical reaction
• Basic flux: High basicity, good toughness
• Acidic flux: Good arc stability, higher speed

By Activity:

• Active flux: Affects weld metal composition
• Neutral flux: Minimal effect on composition

SAW Process Parameters

Current

• High current: 300-2000A (much higher than GMAW)
• Controlled by wire feed speed (CV mode)
• Higher current → deeper penetration

Voltage

• Range: 25-40V
• Controls bead width and shape
• Higher voltage → wider, flatter bead

Travel Speed

• Range: 10-100 cm/min
• Affects penetration and bead size
• Faster → less heat input

Wire Feed Speed

• Determines deposition rate
• Self-regulating with CV power source

Electrode Extension (Stick-out)

• Typical: 25-50 mm (longer than GMAW)
• Longer stick-out → preheating of wire → higher deposition

Flux Layer Thickness

• Typical: 25-50 mm
• Must completely cover arc
• Too thin → arc exposure, porosity
• Too thick → arc instability

SAW Variations

Single Wire SAW

• One electrode
• Standard configuration
• Most common

Twin Wire SAW

• Two electrodes in same flux pool
• Higher deposition rate
• Better productivity

Multiple Wire SAW

• Three or more electrodes
• Very high deposition rate
• For thick sections

Tandem Arc SAW

• Two electrodes in line
• Independent power sources
• High speed welding

Strip Electrode SAW

• Flat strip instead of wire
• Wide, shallow welds
• Surfacing applications

Advantages of SAW

1. Very high deposition rate: 5-10 times SMAW
2. Deep penetration: Single pass thick sections
3. High quality welds: Clean, sound, uniform
4. No arc flash: Arc submerged, safe for operators
5. No spatter: Flux contains spatter
6. Minimal fume: Flux absorbs fumes
7. High welding speed: Automated operation
8. Flux reusable: Unfused flux recovered
9. Consistent quality: Automated process
10. Minimal distortion: Concentrated heat
11. Good mechanical properties: Slow cooling under slag

Limitations of SAW

1. Position limitation: Flat and horizontal fillet only (flux would fall)
2. Joint accessibility: Requires open, accessible joints
3. Equipment cost: Expensive setup
4. Not portable: Large, heavy equipment
5. Joint preparation: Requires good fit-up
6. Flux handling: Storage, drying, recovery needed
7. Limited visibility: Cannot see arc or pool
8. Slag removal: Required after welding
9. Setup time: More complex than manual processes

Applications

Industries

Shipbuilding:

• Hull construction
• Deck panels
• Longitudinal seams

Pressure Vessels:

• Boilers
• Tanks
• Pipes

Structural Steel:

• Beams
• Girders
• Heavy fabrication

Pipe Manufacturing:

• Longitudinal seams
• Spiral seams
• Large diameter pipes

Rail Industry:

• Rail manufacturing
• Flash butt welding

Joint Types

Butt Joints: Most common Fillet Welds: Horizontal position Surfacing: Wear-resistant overlays

Materials Welded

Carbon Steel: Most common application Low Alloy Steel: Pressure vessels, structures Stainless Steel: With appropriate flux and wire Nickel Alloys: Special applications

SAW Joint Preparation

Square Butt Joint

• Thin sections (up to 12 mm)
• No edge preparation
• Single pass

Single-V Butt Joint

• Medium thickness (12-25 mm)
• 60° included angle
• May require backing

Double-V Butt Joint

• Thick sections (>25 mm)
• Welded from both sides
• Reduces distortion

Backing

• Copper backing bar (most common)
• Ceramic backing
• Flux backing
• Prevents burn-through

SAW Defects and Causes

Porosity:

• Moisture in flux
• Contaminated base metal
• Insufficient flux coverage
• Excessive travel speed

Slag Inclusions:

• Inadequate cleaning between passes
• Poor joint design
• Improper flux
• Low current

Lack of Fusion:

• Low current
• Fast travel speed
• Poor joint preparation
• Incorrect electrode position

Undercut:

• High voltage
• Fast travel speed
• Excessive current

Cracking:

• High restraint
• Improper flux
• Contamination
• Rapid cooling

Overlap:

• Low travel speed
• Excessive wire feed
• Low voltage

Flux Management

Flux Drying

• Remove moisture before use
• Typical: 250-400°C for 1-2 hours
• Store in heated containers

Flux Recovery

• Vacuum system collects unfused flux
• Screen to remove fines and slag
• Mix with fresh flux (typically 50:50)

Flux Storage

• Dry environment
• Sealed containers
• Avoid contamination

Comparison: SAW vs Other Processes

Process Variants

Electroslag Welding (ESW)

• Related process
• Vertical position
• Very thick sections (>50 mm)
• Arc starts, then slag conducts current
• Single pass thick plates

Electrogas Welding (EGW)

• Vertical position
• Gas shielding instead of flux
• Thick sections
• Single pass

Quality Control

Pre-weld:

• Flux drying verification
• Joint preparation inspection
• Equipment calibration

During Welding:

• Parameter monitoring
• Flux coverage check
• Visual inspection of slag

Post-weld:

• Visual inspection
• NDT (radiography, ultrasonic)
• Mechanical testing

Safety Considerations

1. No arc flash: Major advantage
2. Hot slag: Can cause burns
3. Fumes: Minimal but ventilation needed
4. Electrical safety: High current
5. Moving equipment: Automated carriage hazards
6. Flux dust: Respiratory protection during handling