Alloy Cladding Technology Application on Coke Quenching Fan Impellers

Literature Overview

This paper by Li Xuanliang and Han Fujian from the Coke Plant of Jinan Iron and Steel Group, published in Shandong Metallurgy (2005, Vol. 27, Issue Z1, pp. 241-242), presents a practical case study on extending the service life of dry quenching coke (DQC) dust collection fan impellers through alloy cladding technology. The work is classified under TG455 and addresses a significant operational challenge in the coking industry: the severe abrasive and corrosive wear experienced by fan components in the coke quenching gas handling system.

Operational Environment and Wear Mechanisms

The dry quenching coke process is an environmentally superior alternative to wet quenching, but it creates an extremely harsh operating environment for dust collection fans. The gas stream contains fine coke particles, sulfur compounds, hydrogen sulfide, and other corrosive species at elevated temperatures. The fan impellers are subjected to a combination of:

Abrasive wear from solid particle impact and erosion
Corrosive attack from sulfur-containing gases and moisture
Thermal cycling from hot gas handling and ambient cooling
Mechanical vibration and fatigue from continuous operation

The combined wear mechanisms make conventional material upgrades or surface treatments insufficient. Alloy cladding provides a robust solution by depositing a wear- and corrosion-resistant surface layer while retaining the structural integrity of the base material.

Cladding Process and Material Selection

Based on the paper's description and industry practice for similar applications, the cladding process likely involved one or more of the following approaches:

Process	Advantages	Limitations
Submerged arc welding (SAW)	High deposition rate, low dilution, suitable for thick overlays	Requires open geometry, post-machining needed
Metal arc gas welding (GMAW)	Good flexibility, moderate deposition rate	Higher dilution than SAW, more sensitive to gas protection
Flame spraying	Suitable for complex geometries, low dilution	Lower bonding strength, requires post-treatment
Electric slag welding	Very high deposition rate	Requires specific geometry, limited flexibility

For fan impellers, the geometry presents challenges due to the curved blade surfaces, hub regions, and potential access limitations. The cladding material selection would typically target:

Hardness in the range of 40-55 HRC for adequate abrasive resistance
Sufficient toughness to resist cracking under impact loading
Corrosion resistance in sulfur-containing environments
Compatibility with the base steel (typically Q235 or Q345 carbon steel)

Common cladding materials for this application include:

Stellite 6 (Co-Cr-W alloy) for superior corrosion and wear resistance
High-carbon martensitic stainless steels (e.g., 410, 420) for cost-effective wear resistance
Chromium carbide-containing alloys for high hardness and abrasion resistance
Nickel-based alloys for high-temperature corrosion resistance

Process Parameters and Quality Control

The cladding process for fan impellers requires careful attention to several quality factors:

Pre-Welding Preparation

Thorough cleaning of the base surface to remove rust, scale, and contaminants
Preheating to 150-250°C to reduce residual stress and prevent cracking
Edge preparation to ensure adequate fusion between cladding and base metal

Welding Execution

Multi-pass welding to achieve the required overlay thickness (typically 3-8 mm)
Controlled travel speed to maintain consistent bead geometry
Adequate gas shielding to prevent porosity and oxidation
Interpass temperature control to limit thermal distortion

Post-Welding Treatment

Stress relief annealing to reduce residual stresses
Surface grinding or machining to achieve dimensional accuracy and surface finish
Hardness testing to verify overlay properties
Penetrant testing (PT) or magnetic particle testing (MT) for surface defects

Engineering Practice and Life Extension Results

The paper reports that the alloy cladding technology significantly extended the service life of the fan impellers in the DQC dust collection system. While specific life extension factors are not provided in the abstract, industry experience suggests that properly applied alloy cladding can extend impeller life by 3-5 times compared to unclad carbon steel components.

The economic benefits of this approach are substantial:

Reduced frequency of impeller replacement, minimizing downtime
Lower cost compared to replacing the entire fan with a more corrosion-resistant material
Ability to maintain the original fan design and aerodynamic performance
Reduced environmental impact from fewer component replacements

Key Technical Considerations

Thermal Distortion Control

Fan impellers are thin-walled components susceptible to thermal distortion during welding. The following measures are essential:

Symmetrical welding sequence to balance thermal input
Backing plate or chill to limit heat penetration through thin sections
Fixturing to restrain movement during welding
Lower heat input per pass with multiple passes

Interface Integrity

The bond strength between the cladding and base metal is critical for the overlay's ability to resist wear. Inadequate fusion can lead to spalling or delamination during service. Quality control measures include:

Visual inspection of each pass for adequate fusion
UT or RT for internal defects if required
Bend testing or peel testing on coupon specimens during process qualification

Dimensional Accuracy

After cladding, the impeller must be returned to its original aerodynamic profile. This requires:

Sufficient cladding thickness to allow for machining allowance
Careful monitoring of dimensional changes during welding
Precision machining after stress relief

Study Insights and Implications

This paper represents a practical application of alloy cladding technology in the steel and coking industry. Its value lies in demonstrating that established welding processes can be effectively applied to extend the life of critical components in harsh operating environments. The approach is particularly relevant for:

Power plant dust collection systems
Cement plant fan systems
Mining industry ventilation equipment
Chemical process fan applications

For engineers evaluating similar applications, the following lessons can be drawn:

Material selection should be based on the dominant wear mechanism (abrasive, corrosive, or combined)
Process selection should consider component geometry, access, and production volume
Quality control should focus on interface integrity and dimensional accuracy
Economic analysis should compare cladding cost against replacement cost and downtime cost

In summary, this study demonstrates the practical effectiveness of alloy cladding technology for extending the service life of coke quenching fan impellers. The approach offers a cost-effective alternative to material upgrade or component replacement, with significant benefits in terms of reduced downtime and maintenance costs. Engineers should carefully evaluate the specific wear conditions, component geometry, and production requirements when applying this technology to similar applications.