CLADDING TECHNOLOGY SHANXI CO., LTDDouble-Sided Simultaneous TIG Welding Process for Aluminum-Magnesium Alloy Silos
Literature Overview
This paper by Sun Wantian from Sinopec Fifth Construction Engineering Company, published in the journal Welding Machine in 2014, describes the development and application of a double-sided simultaneous TIG welding process for aluminum-magnesium alloy silos. Aluminum-magnesium alloys (such as 5083 and 5086) are widely used in chemical storage silos due to their excellent corrosion resistance, good formability, and moderate strength. The challenge of welding thin-walled aluminum structures lies in maintaining dimensional accuracy while achieving full penetration and sound welds on both sides.
Core Technical Content
Process Rationale
Double-sided simultaneous TIG welding involves two welding torches operating on opposite sides of the same joint simultaneously. This approach offers several advantages for aluminum-magnesium silo fabrication:
- Thermal balance: Equal heat input from both sides minimizes warping and distortion, which is critical for large-diameter cylindrical silos where dimensional tolerances are tight.
- Reduced heat input per side: Each torch delivers approximately half the total heat, reducing the risk of burn-through on thin sheets (typically 3–6 mm for silo walls).
- Improved productivity: Both sides of the weld are completed in a single pass, eliminating the need for flipping the workpiece or repositioning the welder.
- Consistent bead profile: Simultaneous welding produces symmetrical weld beads with uniform reinforcement on both sides.
Process Parameters
| Parameter | Typical Value | Notes |
|---|---|---|
| Base material | 5083-H112 or 5086-H321 | Aluminum-magnesium alloy |
| Sheet thickness | 3–6 mm | Silo wall thickness |
| Welding current | 120–200 A per torch | DCEN polarity |
| Arc voltage | 10–14 V | Typical for aluminum TIG |
| Travel speed | 400–800 mm/min | Depends on thickness |
| Shielding gas | 100% Argon | Flow rate 10–15 L/min per torch |
| Tungsten electrode | 2.4–3.2 mm, pure tungsten | DCEN for aluminum |
| Filler wire | ER5356 or ER5183 | Matched to base alloy |
| Joint preparation | V-groove or square butt | Depends on thickness |
Process Challenges and Solutions
The primary challenge of double-sided simultaneous TIG welding is maintaining precise synchronization between the two torches. If one torch leads or lags, the heat input becomes asymmetric, causing distortion and uneven penetration.
Synchronization methods:
- Manual synchronization: Two experienced welders work simultaneously, coordinating their travel speed through visual communication. This method is labor-intensive but flexible.
- Mechanical synchronization: Both torches are mounted on a common carriage that moves at a fixed speed. This method ensures perfect synchronization but requires specialized equipment.
- Semi-automatic synchronization: One torch is operated manually while the other follows on a guide track or fixture. This is a compromise between flexibility and precision.
Shielding gas considerations:
When welding from both sides simultaneously, the shielding gas from one torch can interfere with the arc stability of the other. The authors discuss the use of:
- Backing gas (argon) on the root side to prevent oxidation of the root bead.
- Gas lenses to increase shielding coverage and reduce gas consumption.
- Wind shields and draft curtains to protect the weld area from air currents.
Engineering Practice Integration
In my experience with aluminum silo fabrication, the double-sided simultaneous TIG process is particularly effective for circumferential welds on silos with diameters exceeding 3 meters. The thermal balance achieved through simultaneous welding reduces post-weld straightening operations, which is a significant cost and schedule advantage.
Quality Control Considerations
| Inspection Method | Purpose | Acceptance Criteria |
|---|---|---|
| Visual inspection (VT) | Surface defects, bead profile | No cracks, porosity, undercut > 0.5 mm |
| Dye penetrant testing (PT) | Surface-breaking defects | No indications |
| X-ray radiography (RT) | Internal defects | No porosity > 3 mm, no cracks |
| Ultrasonic testing (UT) | Lack of fusion, cracks | No indications above threshold |
| Hardness testing | Heat-affected zone softening | HV ≥ 80% of base metal |
Common Defects and Countermeasures
- Porosity: Aluminum-magnesium alloys are highly susceptible to hydrogen porosity. Countermeasures include thorough cleaning of the joint (acetone or alkaline cleaning), preheating to 100–150°C to remove surface moisture, and maintaining high shielding gas purity (>99.99% argon).
- Warping and distortion: Even with double-sided welding, some distortion is inevitable. Countermeasures include fixture design with back-up bars, intermittent welding sequences, and post-weld stress relief at 160–180°C for 2 hours.
- Lack of fusion: Incomplete penetration at the root or cap. Countermeasures include adjusting travel speed, increasing current, and ensuring proper joint fit-up (gap 0.5–1.5 mm).
Study Insights
This paper demonstrates a practical engineering solution to a common fabrication challenge. The double-sided simultaneous TIG approach is not merely a productivity improvement but a quality enhancement strategy, as the thermal balance reduces residual stresses and distortion. For aluminum-magnesium silos in the chemical industry, where the internal surface must be free of defects to prevent corrosion, the ability to produce sound welds on both sides in a single operation is a significant advantage.
The paper also highlights the importance of process development and qualification in aluminum welding. Unlike carbon steel, aluminum alloys require careful control of heat input to avoid excessive grain growth in the heat-affected zone, which can reduce mechanical properties and corrosion resistance. The process parameters presented in this paper should be validated through welding procedure qualification (WPQ) in accordance with applicable standards such as ASME IX or GB/T 150 before production application.