CLADDING TECHNOLOGY SHANXI CO., LTDDevelopment of Local Dry Underwater High-Frequency Pulsed MIG Welding Power Supply
Literature Overview
The study by Wang Zhenmin, Jia Jianjun, Hu Jianliang, Liao Haipeng, Wu Jianwen, and Zhang Qin, published in Welding Journal (2024), addresses the development of a specialized power supply for local dry underwater high-frequency pulsed MIG welding. Conducted at South China University of Technology (School of Mechanical and Automotive Engineering and School of Computer Science and Engineering), this work was supported by the National Natural Science Foundation of China (U2141216), Guangdong Provincial Science and Technology Program (2021B1515420006, 2021B1515120026), Guangdong Provincial Marine Economy Development Special Fund (GDNRC[2021]46), and Shenzhen Technology Key Project (JSGG20201201100400001).
Technical Background and Challenges
Underwater welding presents unique challenges that distinguish it fundamentally from atmospheric welding operations. The presence of water introduces issues including arc instability, excessive cooling rates, hydrogen absorption, and contamination of the weld pool. Conventional underwater welding methods—including wet welding, submerged arc welding, and hyperbaric welding—each have significant limitations in terms of weld quality, productivity, or operational complexity.
The local dry underwater welding concept addresses these challenges by creating a localized dry environment around the weld zone using a protective gas envelope or mechanical barrier. This approach combines the advantages of atmospheric welding (superior arc stability, controlled atmosphere, predictable solidification) with the practicality of underwater operations (no need for hyperbaric chambers, reduced diver fatigue, lower operational costs).
| Challenge | Conventional Underwater Welding | Local Dry Underwater Welding |
|---|---|---|
| Arc stability | Poor, highly fluctuating | Stable, controllable |
| Heat input control | Excessive cooling, high HAZ hardness | Moderate, predictable |
| Hydrogen absorption | Significant, cracking risk | Minimal |
| Weld quality | Variable, often unacceptable | Comparable to atmospheric |
| Productivity | Low, frequent defects | High, consistent |
| Equipment complexity | Simple | Moderate (gas supply + barrier) |
Power Supply Design and High-Frequency Pulsing
The core innovation of this study is the development of a high-frequency pulsed MIG welding power supply specifically designed for the local dry underwater environment. The high-frequency pulsing (typically 200–500 Hz) serves multiple critical functions:
- Enhanced arc stability: High-frequency pulsing maintains consistent droplet transfer even in the presence of minor water intrusion or gas envelope instability.
- Precise heat input control: The pulsed waveform allows independent adjustment of peak current (for penetration) and background current (for arc maintenance), enabling fine-tuned thermal management.
- Reduced hydrogen absorption: The intermittent nature of the pulsed current reduces the total heat input per unit time, minimizing hydrogen dissolution into the weld metal.
- Improved gas envelope maintenance: The periodic current interruption allows the protective gas envelope to recover between pulses, maintaining a dry weld zone.
| Power Supply Parameter | Specification | Design Rationale |
|---|---|---|
| Pulse frequency | 200–500 Hz | Arc stability in water environment |
| Peak current range | 150–400 A | Sufficient penetration through water |
| Background current | 50–150 A | Arc maintenance between pulses |
| Pulse width ratio | 0.05–0.2 | Minimize total heat input |
| Output voltage range | 20–40 V | Adequate for underwater arc |
| Response time | < 5 ms | Rapid adaptation to process changes |
| Control mode | Closed-loop current/voltage | Stability under varying conditions |
Process Characteristics and Weld Performance
The study reports that the high-frequency pulsed MIG process in a local dry environment produces welds with mechanical properties comparable to atmospheric welding. Tensile strength values for carbon steel joints reach 400–550 MPa, with elongation exceeding 20%. Hardness profiles across the weld cross-section show minimal variation, indicating uniform solidification behavior despite the underwater environment.
The high-frequency pulsing creates a characteristic weld bead morphology with fine ripples and minimal spatter. The droplet transfer mode is predominantly short-circuiting with occasional globular transfer during peak current periods, producing a dense, well-bonded weld metal with minimal porosity.
Engineering Practice Considerations
From a practical implementation standpoint, the local dry underwater welding system requires careful integration of multiple subsystems:
- Gas supply system: Must deliver sufficient flow rate to maintain a dry envelope against hydrostatic pressure, typically requiring 50–150 L/min of shielding gas depending on depth.
- Mechanical barrier: A nozzle or shroud design that creates a physical separation between the weld zone and surrounding water, while allowing wire feeding and arc access.
- Diver/operator interface: Ergonomic considerations for underwater operation, including cable management, buoyancy control, and communication systems.
- Power supply deployment: The power supply itself must be positioned in a dry location (on the surface or in a dry chamber), with cable connections to the underwater torch.
Quality Assurance and Inspection
Underwater weld inspection presents additional challenges compared to atmospheric welding. The study recommends a multi-method approach:
| Inspection Method | Applicability | Limitations |
|---|---|---|
| Visual testing (VT) | Surface defects, geometry | Limited by water visibility |
| Magnetic particle testing (MT) | Surface/subsurface cracks | Requires ferromagnetic material |
| Ultrasonic testing (UT) | Internal defects, thickness | Water interference with transducer coupling |
| Dye penetrant testing (PT) | Surface-breaking defects | Limited to accessible surfaces |
| Radiographic testing (RT) | Internal voids, inclusions | Difficult underwater, requires specialized equipment |
Study Insights and Reflections
This research addresses a critical gap in underwater welding technology—the development of a power supply that can maintain stable, high-quality welding in the challenging underwater environment through the use of high-frequency pulsed current and a local dry atmosphere. The multi-disciplinary nature of this work, spanning power electronics, welding metallurgy, marine engineering, and control systems, reflects the complexity of modern underwater welding challenges.
The high-frequency pulsing approach is particularly noteworthy for its ability to maintain arc stability despite the inherently unstable underwater environment. The rapid current cycling effectively "averages out" transient disturbances, providing a consistent welding process even when the gas envelope is momentarily compromised. This robustness is essential for reliable underwater operations where conditions can change rapidly.
The study also highlights the importance of process parameter optimization for the specific underwater environment. Parameters that produce optimal results in atmospheric welding may not be suitable underwater, and systematic experimentation is required to establish the appropriate process window. The authors' emphasis on closed-loop control reflects the understanding that real-time adaptation is necessary to maintain quality under variable underwater conditions.
In conclusion, this study demonstrates that the combination of high-frequency pulsed MIG welding with a local dry environment provides a technically viable and practically significant solution for underwater welding applications, offering weld quality approaching atmospheric standards while maintaining the operational advantages of underwater work, and represents an important advancement in the field of underwater welding technology with broad implications for offshore construction, ship repair, and underwater infrastructure maintenance.