Zhuojin Pipe Fitting Co., LtdApplication Study of Stainless Steel Strip Electrode Submerged Arc Surfacing Technology
Literature Overview
This study by Yu Hao, Ma Ming, and Li Wenyu, published in Welding (Issue 12, 2012, pages 53-57), investigates the application of strip electrode submerged arc welding (SAW) for stainless steel surfacing. The research systematically evaluates three strip electrode specifications (30mm×0.5mm, 60mm×0.5mm, and 90mm×0.5mm) through welding process trials, parameter optimization, and quality verification. The work is conducted at Harbin Boiler Works Co., Ltd., a major Chinese manufacturer of power generation and pressure vessel equipment, reflecting practical industrial application requirements. This research is directly relevant to engineers involved in large-area stainless steel overlay applications on boiler components, pressure vessels, and heat exchanger tubesheets.
Core Technical Findings
The study demonstrates that strip electrode submerged arc surfacing can produce high-quality stainless steel overlays with controlled thickness uniformity and surface finish. Through systematic parameter optimization, the authors achieved defect-free surfacing deposits with thicknesses controlled in the 6.0-6.5mm range. The research methodology involved progressive parameter adjustment to first identify defect conditions and then optimize toward quality, providing a comprehensive understanding of the process window.
Strip Electrode Specifications and Performance
| Parameter | 30mm×0.5mm Strip | 60mm×0.5mm Strip | 90mm×0.5mm Strip |
|---|---|---|---|
| Deposition width | Narrow | Medium | Wide |
| Deposition rate | Low | Medium | High |
| Heat input per pass | Low | Medium | High |
| Dilution rate | Higher | Medium | Lower |
| Surface finish | Good | Good | Excellent |
| Thickness uniformity | Difficult to control | Moderate | Excellent |
| Application suitability | Small areas | General use | Large areas |
The 90mm×0.5mm strip electrode was identified as optimal for large-area surfacing applications, offering the best combination of deposition efficiency, thickness uniformity, and surface quality. The wider electrode distributes heat more evenly across the deposition width, reducing thermal gradients that cause distortion and porosity.
Process Parameter Analysis
Optimal Parameter Window
The study establishes that successful strip electrode surfacing requires careful control of the following parameters:
| Parameter | Typical Range | Effect on Quality |
|---|---|---|
| Current (I) | 800-1500A | Controls penetration and dilution |
| Voltage (V) | 22-30V | Affects bead width and surface profile |
| Travel speed (v) | 200-400mm/min | Controls deposition thickness |
| Flux coverage | 15-25mm | Prevents oxidation and spatter |
| Electrode stick-out | 12-18mm | Affects arc stability |
| Preheat temperature | 100-200°C | Reduces cracking tendency |
Defect Analysis and Countermeasures
The study identifies several common defects and their root causes:
| Defect Type | Root Cause | Countermeasure |
|---|---|---|
| Surface porosity | Inadequate flux coverage | Increase flux depth to 20mm minimum |
| Undercut | Excessive travel speed | Reduce speed by 20-30% |
| Uneven thickness | Electrode alignment error | Implement mechanical positioning system |
| Cracking | Excessive heat input | Reduce current or increase travel speed |
| Inclusion | Contaminated flux or consumable | Dry flux at 250°C for 2 hours |
| Base metal exposure | Excessive dilution | Reduce current or use lower carbon consumable |
Verification Methods and Quality Criteria
The study employs multiple verification methods to confirm overlay quality:
- Mechanical property testing: Hardness (HV), tensile strength, and impact toughness measurements verify metallurgical bonding and material properties.
- Chemical composition analysis: Spectroscopic analysis confirms that the deposited alloy composition meets specification requirements, with particular attention to chromium and nickel content.
- Ferrite content measurement: Ferrite number (FN) determination ensures that the deposited stainless steel maintains appropriate microstructure for the intended application. For austenitic stainless steel overlays, FN values typically should remain below 10 to avoid excessive precipitation hardening and maintain corrosion resistance.
- Visual and dimensional inspection: Surface quality assessment and thickness measurement verify conformance to specification requirements.
Integration with Engineering Practice
Strip electrode submerged arc surfacing is particularly valuable for large-area overlay applications where conventional wire electrode SAW would require excessive number of passes. In boiler manufacturing, typical applications include:
- Steam generator tubesheet overlay for nuclear power applications
- Boiler drum internal surfaces requiring corrosion resistance
- Heat exchanger tubesheets for chemical processing
- Pressure vessel linings for aggressive service environments
The process offers significant productivity advantages:
| Method | Deposition Rate (kg/h) | Number of Passes for 6mm | Labor Hours |
|---|---|---|---|
| Wire electrode SAW | 20-40 | 8-12 | 4-6 |
| Strip electrode SAW (60mm) | 80-120 | 2-3 | 1.5-2 |
| Strip electrode SAW (90mm) | 120-180 | 1-2 | 1-1.5 |
Practical Implementation Considerations
Based on the study findings and industrial experience, the following implementation guidelines are recommended:
- Equipment requirements: The welding power source must provide stable current with low ripple (<5%) to maintain consistent arc characteristics. The strip electrode feed mechanism requires precise control to maintain constant stick-out length.
- Flux management: Flux must be stored in sealed containers and dried at 250°C for a minimum of 2 hours before use. Recycled flux should be screened to remove slag and contaminants, with a maximum of two recycling cycles.
- Substrate preparation: The base metal surface must be ground to remove oxide, paint, and contamination. A clean, oxide-free surface is essential for achieving metallurgical bonding and minimizing dilution-related defects.
- Parameter qualification: Each strip electrode specification requires individual qualification testing to establish the optimal parameter window. The process window is relatively narrow, and deviations can result in significant quality degradation.
Key Questions and Reflections
The study raises several important questions for engineering practice:
- How does the strip electrode surfacing process perform on curved surfaces (cylindrical tubesheets, spherical vessel heads)? The study focuses on flat substrates, but curved geometries present additional challenges related to flux coverage and electrode alignment.
- What is the fatigue performance of the deposited overlay under cyclic thermal loading, as experienced in boiler applications?
- How does the dilution rate vary with substrate geometry and thickness? Thicker substrates may require different parameter settings to achieve the same overlay quality.
- What are the long-term corrosion resistance characteristics of the deposited alloy in high-temperature chloride environments?
The study's systematic approach to parameter optimization, starting from defective conditions and progressively improving toward quality, is a methodology that should be adopted in all surfacing qualification programs. This approach provides a comprehensive understanding of the process boundaries and ensures that the final qualified parameters are robust against minor variations.
Study Insights and Implications
This research demonstrates that strip electrode submerged arc surfacing is a mature and reliable technology for large-area stainless steel overlay applications. The key insight is that the process window is well-defined and achievable with proper equipment and consumable management. The 90mm×0.5mm strip electrode specification offers the best balance of productivity and quality for most industrial applications.
The study's emphasis on systematic parameter optimization and multi-method quality verification provides a model for surfacing qualification programs. Engineers should adopt this approach to ensure that overlay applications meet both metallurgical and dimensional requirements. The demonstrated ability to control overlay thickness to within 0.5mm (6.0-6.5mm) is particularly significant for applications where overlay thickness directly affects equipment performance, such as tubesheet overlay in heat exchangers where the overlay serves as both a corrosion barrier and a mechanical seal.
The productivity advantages of strip electrode surfacing over conventional wire electrode methods are substantial, making this technology economically attractive for large-volume manufacturing operations. However, the investment in specialized equipment and consumable management must be weighed against the labor savings, particularly for smaller production volumes or highly varied geometries.