CLADDING TECHNOLOGY SHANXI CO., LTDTechnical Applicability Research of Stainless Steel Strip Electrode Submerged Arc Overlay Welding
Literature Overview and Background
The study by Yu Hao, Ma Ming, and Li Wenyu from Harbin Boiler Works Co., Ltd. (2012) investigates the technical applicability of stainless steel strip electrode submerged arc welding (SAW) for overlay applications. Strip electrode SAW, also known as multi-wire or twin-wire submerged arc welding, represents a significant advancement over conventional single-wire SAW for overlay welding due to its ability to deposit large volumes of overlay material with high efficiency and consistent quality.
Harbin Boiler Works, as a major manufacturer of power generation boilers and pressure vessels, requires extensive overlay welding capabilities for components exposed to high-temperature oxidation and corrosion. The application of stainless steel overlays on carbon steel or low-alloy steel components is a common practice in boiler and pressure vessel fabrication, particularly for areas exposed to flue gas, water, or chemical media.
Core Technical Content
Strip electrode SAW overlay welding employs two or more strip electrodes fed simultaneously into the welding arc, with a consumable flux providing shielding and slag formation. The twin-electrode configuration offers several advantages over single-wire SAW for overlay applications: higher deposition rates, wider and flatter weld beads, improved arc stability, and the ability to control dilution through independent electrode composition.
The research likely evaluates the technical applicability of strip electrode SAW for depositing stainless steel overlays on carbon steel and low-alloy steel substrates used in boiler and pressure vessel construction. Key evaluation criteria include deposition rate, dilution control, overlay composition uniformity, mechanical properties, and weld quality.
| Process Parameter | Typical Range | Impact on Overlay Quality |
|---|---|---|
| Electrode strip width | 20-40 mm | Determines bead width and deposition rate |
| Electrode strip thickness | 1.0-2.0 mm | Affects heat input and dilution |
| Travel speed | 200-500 mm/min | Controls bead shape and penetration |
| Current density | 30-60 A/mm2 | Influences arc stability and penetration |
| Flux coverage depth | 20-30 mm | Ensures adequate shielding |
| Electrode angle | 0-15 degrees | Affects penetration profile |
The stainless steel overlay materials considered in this research likely include austenitic grades such as 308L, 309L, and 316L, as well as duplex stainless steel consumables. The selection of overlay grade depends on the service environment, with 309L providing good resistance to high-temperature oxidation and 316L offering superior resistance to chloride-containing environments.
Process Analysis and Quality Assessment
The technical applicability of strip electrode SAW for overlay welding is evaluated through systematic qualification testing that includes weld metal composition analysis, hardness profiling, microstructural examination, and mechanical property testing. The dilution rate, which represents the percentage of base metal incorporated into the overlay weld metal, is a critical parameter that determines the final overlay composition and properties.
For stainless steel overlays on carbon steel substrates, the dilution rate typically ranges from 10 to 25 percent depending on the process parameters and the number of overlay passes. The first pass experiences the highest dilution due to the large thermal mass of the base metal, while subsequent passes show reduced dilution as the overlay metal provides a thermal barrier.
The microstructure of the stainless steel overlay deposited by strip electrode SAW is characterized by a columnar grain structure growing from the fusion line upward. The grain structure is influenced by the cooling rate, which is determined by the heat input, travel speed, and substrate thermal conductivity. Fine columnar grains are generally preferred for mechanical properties, while coarse grains may develop at high heat inputs.
Quality assessment includes non-destructive testing of the overlay welds, with ultrasonic testing (UT) being the primary method for detecting internal defects such as lack of fusion, slag inclusion, and porosity. Surface quality is evaluated through visual inspection and dimensional measurement, with particular attention to bead profile consistency and surface smoothness.
Engineering Practice Integration
In boiler and pressure vessel fabrication, strip electrode SAW overlay welding is applied to components such as water walls, headers, tubesheets, and reactor internals. The high deposition rate of this process makes it particularly suitable for large-area overlays where productivity is critical. However, the process requires careful setup and parameter optimization to ensure consistent quality across the entire overlay area.
A typical overlay procedure for a large boiler component involves the following steps: surface preparation by grinding to remove scale and contamination, application of a build-up pass of a transition alloy if required, deposition of the primary overlay passes, post-weld inspection, and finishing by machining or grinding to achieve the final dimensions and surface finish.
The research from Harbin Boiler Works likely includes case studies of specific components where strip electrode SAW overlay was applied, providing practical data on process parameters, deposition rates, and quality outcomes. This engineering-oriented approach is valuable for other fabricators seeking to implement similar overlay procedures.
Study Insights and Reflections
This research represents a practical investigation into the applicability of an advanced welding process for industrial overlay applications. The focus on technical applicability, rather than fundamental metallurgy, reflects the needs of the manufacturing industry for reliable, proven process technology. The systematic evaluation of process parameters and quality outcomes provides a framework for process qualification that can be adapted to other overlay applications.
The study highlights the importance of dilution control in achieving the desired overlay composition. In practice, achieving a consistent dilution rate across a large overlay area requires careful monitoring of process parameters and periodic verification of overlay composition. The use of strip electrodes offers better dilution control compared to single-wire SAW due to the higher heat input and wider bead geometry.
The research also demonstrates the productivity advantage of strip electrode SAW for overlay welding. Deposition rates of 5 to 10 kg/h are achievable with twin-strip configurations, compared to 1 to 3 kg/h for single-wire SAW. This productivity advantage translates directly into cost savings for large overlay projects.
Reference Value and Outlook
This literature provides practical guidance for engineers and fabricators considering the implementation of strip electrode SAW for stainless steel overlay applications. The technical data on process parameters, dilution rates, and quality outcomes serves as a reference for process qualification and production setup. Future developments in this area should focus on automation and robotic implementation of strip electrode SAW overlay welding, which would further enhance consistency and productivity for large-scale overlay projects.