CLADDING TECHNOLOGY SHANXI CO., LTDAlloy Overlay Welding Technology Applied to Blast Fans in Coke Quenching Systems
Literature Overview and Industrial Context
This 2005 paper by Li Xuanliang and Han Fujian from the Coke Plant of Jinan Iron and Steel Group (Jigang) documents the application of alloy overlay welding technology to extend the service life of blast fan components in a dry coke quenching system. The dry quenching process, which uses circulating red hot coke gas instead of water to cool red hot coke, operates at significantly higher temperatures and under more abrasive conditions than conventional wet quenching. The blast fans in this system are subjected to continuous exposure to hot, abrasive coke dust and corrosive gases, making them critical components whose failure can result in costly production shutdowns.
Technical Analysis of the Application
Operating Environment and Failure Modes
The blast fans in dry coke quenching systems face a combination of degradation mechanisms:
- Abrasive wear: Hard coke particles (containing quartz, pyrite, and other minerals) impinge on fan blades and housings at high velocities
- Corrosion: Sulfur compounds, hydrogen sulfide, and other corrosive gases present in the coke gas stream attack the metal surface
- Thermal fatigue: Temperature cycling between operating conditions (typically 800–1000°C in the quenching system) and ambient conditions during shutdowns
- Erosion-corrosion: The synergistic effect of mechanical erosion and chemical corrosion, which is often more severe than either mechanism alone
The conventional carbon steel construction of these fans results in relatively short service intervals, with frequent blade replacement or complete fan overhaul required, leading to significant production downtime and maintenance costs.
Overlay Alloy Selection
The selection of overlay alloy for this application requires careful consideration of the operating environment:
| Overlay Alloy | Key Properties | Suitability for Coke Gas Environment |
|---|---|---|
| Stellite 6 (Co-Cr-W) | Excellent abrasion resistance, good corrosion resistance | Excellent — handles abrasive and corrosive conditions |
| Hardfacing (Cr-C) | High hardness, moderate corrosion resistance | Good for pure abrasion, limited for corrosive conditions |
| Ni-Cr alloy (Incoloy 800) | Good high-temperature strength and corrosion resistance | Good for high-temperature applications |
| Austenitic stainless steel (309) | Good general corrosion resistance | Moderate — limited abrasion resistance |
Based on the operating conditions described in the literature, a cobalt-based Stellite-type alloy or a chromium-cobalt hardfacing alloy would be the most appropriate selection for the fan blade leading edges and critical wear surfaces, while an austenitic stainless steel or nickel-based alloy might be more suitable for the fan housing and less severely worn areas.
Welding Process Selection
The literature discusses the application of overlay welding to restore or enhance the surface properties of fan components. The process selection depends on several factors:
- Component geometry: Fan blades with complex aerodynamic profiles may require processes capable of precise deposition, such as GTAW or laser cladding
- Production rate: For large numbers of components requiring regular maintenance, high-deposition-rate processes such as SAW or FCAW may be preferred
- Dilution control: Critical for maintaining the corrosion and wear resistance of the overlay layer
- Distortion sensitivity: Fan blades are thin-walled components susceptible to distortion, requiring low-heat-input processes
Engineering Implementation and Results
Process Development Approach
The development of the overlay welding process for this application would typically follow a systematic approach:
- Failure analysis: Examination of failed components to identify primary wear/corrosion mechanisms
- Material selection: Selection of overlay alloy based on service requirements
- Process parameter optimization: Systematic variation of welding parameters to achieve optimal overlay quality
- Qualification testing: Mechanical, metallurgical, and corrosion testing of the overlay
- Field trial: Application to a limited number of components with performance monitoring
- Full-scale implementation: Standardization of the process for routine maintenance
Performance Evaluation
The effectiveness of the overlay welding treatment is typically evaluated through:
| Evaluation Parameter | Method | Acceptance Criteria |
|---|---|---|
| Overlay hardness | Vickers hardness test | ≥ 400 HV for hardfacing, ≥ 250 HV for Stellite |
| Bond strength | Transverse tensile test or bend test | ≥ 350 MPa or no cracking in 5T bend test |
| Dilution rate | Metallographic examination with optical emission spectroscopy | < 30% for first pass, < 15% for top layer |
| Service life | Operational tracking | ≥ 3× improvement over untreated components |
| Surface integrity | MT/PT inspection | No cracks, porosity, or lack of fusion |
Key Reflections and Practical Implications
This literature represents a practical application of overlay welding technology in the metallurgical industry, demonstrating how welding-based surface engineering can significantly extend the service life of critical components in severe operating environments. The dry coke quenching system presents a particularly challenging combination of wear, corrosion, and thermal cycling that is representative of many industrial applications.
The economic benefits of overlay welding in this context are substantial. Rather than replacing entire fan assemblies or using expensive exotic materials for the entire component, overlay welding allows the use of a cost-effective carbon steel base with a thin, high-performance overlay layer. This approach can reduce material costs by 50–80% while achieving comparable or superior service performance.
From a metallurgical perspective, the dilution rate remains the most critical parameter in determining overlay performance. In applications where the overlay must withstand both abrasive and corrosive attack, the top layer dilution should ideally be below 15% to ensure that the surface composition closely matches the intended alloy. This may require 4–6 overlay passes, which must be balanced against productivity considerations.
The work also highlights an important principle in industrial maintenance: the integration of welding technology into planned maintenance programs can transform reactive, costly repairs into proactive, cost-effective life extension strategies. For engineers managing maintenance operations in metallurgical, mining, or chemical processing industries, this literature provides a clear demonstration of the value of overlay welding as a surface engineering solution.
The findings are directly transferable to similar applications involving fan components, pump impellers, valve trim, and other rotating or sliding components subjected to combined wear and corrosion in high-temperature industrial environments.