Comparing the Welding Techniques Used in CRA Weld Overlay Pipes

Welding Techniques Used for CRA Weld Overlay

1. GTAW (Gas Tungsten Arc Welding)

Also known as: TIG (Tungsten Inert Gas) Welding

Key Features:

· Heat Source: Non-consumable tungsten electrode

· Shielding Gas: Argon or argon-helium

· Filler Metal: Can be added separately (manual or wire-fed)

· Typical CRA Usage: Nickel alloys, stainless steels, precise internal weld overlay

- Advantages:

· Excellent control over weld quality and dilution (low dilution ideal for CRA)

· Produces high-purity welds with minimal spatter

· Suitable for thin layers and small-bore cladding (nozzles, valves, pipes <DN150)

Limitations:

· Slow deposition rate → higher cost per meter²

· Requires high operator skill

· Less economical for thick or large-area overlays

Best Used For:

· High-alloy precision cladding (Inconel 625, Alloy 825, 316L)

· Internal bore welds in small diameter pipe spools, elbows, nozzles

2. GMAW (Gas Metal Arc Welding)

Also known as: MIG (Metal Inert Gas) or MAG (Metal Active Gas) Welding
(in CRA overlay, it usually means wire-fed welding)

Key Features:

· Heat Source: Consumable wire electrode fed through gun

· Shielding Gas: Argon-CO₂ or Ar-He blends

· Deposition Mode: Pulsed spray transfer common for overlay

- Advantages:

· Higher deposition rate than GTAW

· Suitable for mechanized or robotic cladding

· Moderate dilution control

· Efficient for medium-large diameter pipes and flanges

Limitations:

· Higher dilution risk than GTAW (needs good parameter control)

· Risk of lack of fusion if improperly set

· Requires flat or slightly curved surfaces

Best Used For:

· Pipe ID and OD overlays

· Medium-diameter components (flanges, fittings, reducers)

· Automated or semi-automated overlay systems

3. SAW (Submerged Arc Welding)

Used in: Large-area overlay, particularly longitudinal or circumferential seams

Key Features:

· Heat Source: Consumable wire beneath granular flux blanket

· Shielding: Flux provides full protection from air

· Deposition Rate: Very high — ideal for heavy-wall components

- Advantages:

· Extremely high deposition (5–10× GTAW)

· Deep penetration and fusion

· Ideal for plate, vessel shells, pipe longitudinal welds

Limitations:

· High dilution → not ideal for single-layer CRA overlays (often requires 2 layers)

· Not suitable for small diameters or complex geometries

· Requires rotary or flat welding positions

Best Used For:

· Pressure vessels, columns, shell & tube heat exchangers

· Outside diameters of large CRA-clad pipes

· Cladding large surface area of clad plates

Dilution Comparison (Typical for CRA Cladding)

Application in CRA Weld Overlay Pipes