Fe-05 Wear-Resistant Alloy Powder Block Overlay on Blower Blades

Literature Overview

This 1991 paper by Zhang Jiakun from the ash-water division of Longkou Power Plant documents a practical industrial application of overlay welding technology for extending the service life of forced draft fan (blower) blades. The case study involves two 100 MW units equipped with dry cyclone dust collectors, where poor dust collection efficiency (only 70-80%) due to equipment aging and inadequate flushing water led to accelerated blade erosion. The use of Fe-05 wear-resistant alloy powder blocks (a consumable welding material) represents a straightforward, cost-effective solution to a significant operational problem in thermal power generation.

Core Technical Content

The document describes a straightforward but industrially significant application of overlay welding in the power generation sector. The blower blades, which handle hot flue gas containing abrasive particulates, experienced accelerated wear that threatened equipment availability and forced draft performance. The Fe-05 powder block overlay was applied to restore blade thickness and provide enhanced wear resistance.

Service Conditions and Failure Analysis

The root cause analysis identifies that the primary degradation mechanism is erosive wear from high-velocity gas streams carrying abrasive ash particles. The poor dust collection efficiency, attributed to equipment aging and insufficient flushing water, resulted in excessive particulate carryover into the forced draft system, dramatically accelerating blade erosion.

Fe-05 Powder Block Characteristics

Fe-05 is a commercially available iron-based wear-resistant welding consumable in the form of a consumable block (powder block or flux-cored block). Its typical composition includes:

• Base: Iron (Fe)
• Alloying elements: Cr, Mo, V, B, and/or Si (specific composition proprietary)
• Hardness: Typically 40-50 HRC after welding (higher with post-weld heat treatment)
• Microstructure: Martensitic or martensitic + carbide structure
• Application: Abrasive wear protection on carbon steel components

The powder block form factor offers advantages over stick electrodes for industrial repair applications:

• Higher deposition rate
• Better wetting and coverage on irregular surfaces
• Reduced operator fatigue
• Consistent composition delivery

Engineering Practice Integration

This case study exemplifies the practical application of overlay welding in industrial maintenance scenarios. The key engineering considerations include:

1. Economic justification: The cost of overlay repair versus blade replacement or complete fan replacement. For 100 MW units, blade replacement can require significant downtime, making overlay repair economically attractive even if the overlay provides only moderate life extension.
2. Process selection: Powder block welding is chosen for its balance of deposition rate, operator skill requirements, and coating quality. For critical applications, plasma arc overlay or GMAW with wire electrodes may provide better results but at higher equipment cost.
3. Geometric considerations: Blower blades have complex curved geometries that require careful welding technique to ensure uniform overlay thickness. The overlay must follow the aerodynamic profile of the blade to avoid performance degradation.
4. Inspection and quality control: Post-weld inspection should include thickness measurement, visual examination for defects (porosity, cracks, incomplete coverage), and hardness verification.

Recommended Procedure for Blower Blade Overlay

Based on the principles illustrated in this case study, a systematic overlay procedure for blower blades should include:

1. Surface preparation: Remove existing wear, rust, and coatings by grinding or shot blasting to expose clean base metal
2. Preheating: 150-200°C to reduce cracking risk in carbon steel substrate
3. Overlay application: Multi-pass welding with controlled bead overlap (50% minimum) to ensure complete coverage
4. Post-weld treatment: Optional tempering at 400-500°C to relieve residual stress
5. Inspection: Visual and dimensional inspection; hardness testing on representative areas
6. Balancing: Re-balance the fan wheel after overlay to prevent vibration issues

Key Questions and Reflections

While this paper is relatively brief and focused on practical application, it raises several important questions for modern practice:

1. Long-term performance: The paper documents the initial application but does not provide follow-up data on the actual service life achieved. The wear life of Fe-05 overlays under high-temperature erosive conditions may be limited by thermal softening of the martensitic structure.
2. Root cause vs. symptom treatment: The overlay addresses the blade wear symptom, but the root cause (poor dust collection) remains. A comprehensive solution should address both the immediate repair and the underlying system deficiency.
3. Material alternatives: Modern overlay materials (e.g., Cr-C-Mo-B systems, cobalt-based alloys, ceramic-reinforced composites) may offer superior performance for this specific application. The choice of Fe-05 in 1991 reflects the materials available at that time.
4. Thermal effects: The overlay process introduces heat to the blade, which may cause distortion of the aerodynamic profile. For precision fans, this must be accounted for in the welding procedure.

Study Insights and Implications

This case study, while technically straightforward, embodies a critical principle in industrial maintenance engineering: the most effective solution is often the simplest one that addresses the immediate problem while providing acceptable long-term performance. The Fe-05 powder block overlay represents a pragmatic approach to extending equipment life in the face of operational deficiencies that cannot be immediately resolved. For modern practitioners, this work serves as a reminder that overlay welding remains a valuable tool in the maintenance engineer's arsenal, particularly for applications where component replacement is impractical or excessively costly. The work also highlights the importance of understanding the complete operating environment—temperature, particulate loading, gas velocity, and chemical composition—all of which influence overlay selection and performance. The enduring value of this case study lies in its demonstration that practical, well-executed overlay welding can provide significant economic and operational benefits in industrial settings.