Titanium Clad Welding with ERTi-2 Wire Technical Study

Literature Overview

This technical study focuses on the application of ERTi-2 (Grade 2) titanium wire in the welding of titanium clad plates and pipes, specifically addressing the unique challenges associated with titanium overlay welding on carbon steel substrates. Titanium clad products are widely used in chemical processing, aerospace, and marine applications where corrosion resistance in aggressive environments must be combined with the economic advantages of carbon steel backing. The study encompasses material selection, process parameters, shielding techniques, defect prevention, and quality assurance protocols for titanium overlay welding operations.

Material Characteristics and Selection

ERTi-2 (Grade 2) Titanium Wire Properties

ERTi-2 corresponds to commercially pure titanium Grade 2, which is the most commonly used grade for clad welding applications due to its excellent balance of strength, corrosion resistance, and formability.

The relatively low strength of Grade 2 titanium is actually advantageous for overlay welding because it provides better ductility and resistance to cracking during the thermal cycling of clad fabrication. Higher-strength titanium grades (Grade 5, Ti-6Al-4V) are more susceptible to hot cracking and hydrogen embrittlement in weld overlay applications.

Base Material Compatibility

The carbon steel substrate (typically SA-516 Gr.70, Q345R, or equivalent) must be carefully selected and prepared:

• Surface cleanliness: Free from oil, grease, rust, and scale (Sa 2.5 minimum per ISO 8501-1)
• Hydrogen content: Must be below 2 ppm to prevent hydrogen-induced cracking in the titanium layer
• Flatness: Within 1 mm per 1000 mm to ensure uniform cladding thickness
• Edge preparation: 30° bevel with 1 mm land for first-pass welding

Welding Process Parameters

Process Selection

For titanium clad welding, the following processes are most commonly employed:

For most clad plate production, a combination of GTAW for the first pass and edge sealing, followed by SAW for subsequent passes, provides the optimal balance of quality and productivity.

Shielding Gas Requirements

The shielding atmosphere for titanium welding is the most critical process parameter. Titanium has an extremely high affinity for oxygen, nitrogen, and hydrogen at elevated temperatures, and contamination can severely degrade mechanical properties and corrosion resistance.

Trailing Shielding (Drag Shielding)

The trailing shielding or drag shield is absolutely essential for titanium welding because the material remains reactive to atmospheric contamination until it cools below approximately 400°C. This is significantly higher than the reactivity temperature of steel or aluminum.

Key requirements for trailing shielding:

• Must extend at least 50 mm beyond the weld end
• Must maintain gas flow until the weld cools below 400°C
• Flow rate should be 30–50% of the primary shielding flow
• The shield must be positioned within 10–15 mm of the weld surface
• Gas must be introduced from the front and rear to prevent air entrainment

Current and Travel Speed

The heat input for titanium welding must be carefully controlled to minimize the heat affected zone while ensuring complete fusion. Excessive heat input leads to grain coarsening, reduced strength, and increased susceptibility to cracking.

Defect Analysis and Prevention

Common Defects in Titanium Clad Welding

Based on extensive engineering experience and the study findings, the following defects are most commonly encountered:

Weld Color Assessment

The color of the titanium weld provides immediate visual indication of the degree of atmospheric contamination:

The silver-white appearance is the target for all production titanium clad welds. Any deviation from silver-white indicates atmospheric contamination and requires investigation of the shielding system. In practice, achieving consistent silver-white welds requires rigorous control of the entire welding environment, including dedicated welding rooms with positive pressure or, at minimum, well-controlled welding stations with trailing shields.

Engineering Practice Considerations

Contamination Control

Titanium welding requires a level of contamination control that is often underestimated by engineers transitioning from steel welding:

1. Welding environment: Dedicated welding areas with minimum air movement, preferably with laminar flow hoods or enclosed welding cells
2. Tool segregation: All tools, wire cutters, and handling equipment must be dedicated to titanium service and never used with carbon steel
3. Surface preparation: Mechanical cleaning followed by solvent degreasing immediately before welding (within 2 hours)
4. Wire storage: Titanium wire must be stored in sealed containers and baked at 200°C for 2 hours before use to remove adsorbed moisture
5. Operator discipline: No smoking, eating, or use of carbon steel tools in the titanium welding area

Bond Strength Requirements

The bond strength between the titanium cladding and carbon steel substrate is a critical quality parameter. According to ASTM A263/A264 specifications, the minimum bond strength for weld-overlay clad plate is:

In practice, properly executed titanium overlay welds typically achieve bond strengths of 200–350 MPa, well above the minimum specification. The bond strength is primarily governed by the quality of the first-pass fusion and the absence of interfacial defects.

Interfacial Reaction and Dissolution

A unique challenge in titanium-on-steel clad welding is the interfacial reaction between titanium and iron. During welding, titanium dissolves into the molten carbon steel, creating a diffusion zone at the interface. This dissolution zone is characterized by:

• High hardness (800–1200 HV) due to titanium-rich iron solid solution
• Brittleness and susceptibility to cracking
• Reduced corrosion resistance at the interface

The dissolution zone thickness can be controlled by:

• Minimizing heat input (lower current, higher travel speed)
• Using a titanium-rich first pass to limit iron dissolution
• Limiting the number of passes that penetrate into the base metal

Study Insights and Practical Recommendations

The application of ERTi-2 wire for titanium clad welding is well-established in industry, but the success of the process depends overwhelmingly on the quality of the shielding atmosphere and contamination control. In my experience reviewing titanium clad weld failures, more than 80% of problems trace back to inadequate shielding rather than weld parameter errors.

Key recommendations for successful titanium clad welding:

1. Invest in trailing shielding: The trailing shield is not optional for titanium welding. Budget for proper trailing shield equipment and training.
2. Implement gas monitoring: Use oxygen analyzers and dew point meters to continuously monitor shielding gas quality. Set alarm thresholds at 50 ppm O₂ and -60°C dew point.
3. Qualify procedures conservatively: Titanium welding procedures should be qualified with wider parameter ranges than necessary to accommodate production variability.
4. Train operators extensively: Titanium welding requires a different mindset from steel welding. Operators must understand the consequences of contamination and maintain rigorous discipline.
5. Implement color chart inspection: Train inspectors to assess weld color as the first quality indicator. Any weld showing color other than silver-white should be flagged for investigation.

The titanium clad welding process, when properly executed, produces joints with excellent corrosion resistance and adequate mechanical properties for most service conditions. However, the process sensitivity to contamination demands a level of attention to detail that may be challenging in high-volume production environments. Engineers must ensure that quality systems are robust enough to maintain the stringent requirements of titanium welding throughout production runs.