CLADDING TECHNOLOGY SHANXI CO., LTDWear-Resistant Overlay Application on Large Diameter Shaft Kiln Material Seal Pipe
Literature Overview
Li Guanghui's 2005 study from Yuwang Cement Co., Ltd. documents the application of wear-resistant overlay welding on a Φ3m × 11m shaft kiln material seal pipe. Shaft kilns are large rotary or stationary kilns used in cement manufacturing, where material seal pipes serve as critical components controlling material flow and preventing gas leakage. These pipes are subjected to severe abrasive wear from cement raw materials, making overlay protection a cost-effective maintenance strategy. The study provides practical engineering data on overlay selection, application, and performance evaluation for this specific industrial application.
Core Technical Content
Service Environment Analysis
The material seal pipe in a shaft kiln operates under extreme conditions that create a demanding wear environment:
| Parameter | Value | Impact on Wear |
|---|---|---|
| Operating temperature | 800-1200°C | Thermal degradation, oxidation |
| Material flow rate | 50-100 t/h | High abrasive loading |
| Particle size | 0-50 mm | Abrasive impact |
| Material hardness | 6-7 Mohs (quartz, feldspar) | Severe abrasion |
| Service life requirement | 12-24 months | Cost-effective protection needed |
The combination of high temperature, abrasive materials, and continuous operation creates a challenging environment where conventional carbon steel pipe would fail within weeks. Wear-resistant overlay extends service life by providing a hard, wear-resistant surface layer while maintaining the structural integrity of the base pipe.
Overlay Material Selection
Several wear-resistant overlay materials were evaluated for this application:
| Material Type | Composition | Hardness | Temperature Limit | Cost |
|---|---|---|---|---|
| High carbon martensite | C 2-3%, Cr 5-10% | 50-60 HRC | 500°C | Low |
| Chromium carbide | Cr 25-30%, C 5-7% | 55-60 HRC | 800°C | Medium |
| Cobalt-based | Co 50-60%, Cr 25-30% | 40-45 HRC | 1000°C | High |
| Ceramic composite | WC-Co, Cr3C2-NiCr | 60-70 HRC | 600°C | Medium-High |
Based on the service conditions, a chromium carbide hardfacing alloy was selected as the optimal choice, providing adequate hardness and wear resistance at the operating temperatures while maintaining reasonable cost and weldability.
Overlay Application Methodology
The overlay was applied using submerged arc welding (SAW) with flux-cored wire and granulated flux. The process parameters were optimized for thick overlay deposition (3-5 mm) on the large diameter pipe:
- Wire diameter: 3.2 mm (1/8 inch)
- Current: 350-450 A
- Voltage: 28-35 V
- Travel speed: 200-300 mm/min
- Flux type: Low-hydrogen, high-silica
- Number of passes: 2-3 passes for full thickness
- Interpass temperature: 200-300°C
The large pipe diameter (3 m) presented unique challenges for overlay application, including:
- Maintaining consistent weld geometry over large circumference
- Managing heat input to prevent distortion of the large diameter pipe
- Ensuring uniform overlay thickness around the entire circumference
- Access for welding equipment and operator positioning
Performance Evaluation
The overlay performance was monitored over an extended service period:
| Time Period | Overlay Thickness Loss | Wear Rate | Condition |
|---|---|---|---|
| Initial | 4.0 mm | - | As applied |
| 3 months | 3.5 mm | 0.17 mm/month | Good |
| 6 months | 3.0 mm | 0.17 mm/month | Good |
| 12 months | 2.0 mm | 0.17 mm/month | Acceptable |
| 18 months | 1.0 mm | 0.17 mm/month | Replacement planned |
The wear rate of approximately 0.17 mm/month represents a significant improvement over unprotected carbon steel, which would wear at rates exceeding 5 mm/month under the same conditions. The linear wear rate indicates consistent abrasive wear without catastrophic failure mechanisms.
Engineering Practice Considerations
Pre-Weld Preparation
Proper substrate preparation is critical for achieving sound overlay welds:
- Removal of all mill scale, rust, and surface contaminants
- Machining of weld preparation groove (single-V or J-groove)
- Surface roughening to improve mechanical keying
- Preheating to 200-300°C to reduce thermal stress
Quality Control Procedures
The overlay application requires rigorous quality control:
- Visual inspection: Verification of weld appearance, penetration, and uniformity
- Hardness testing: Confirmation of overlay hardness (55-60 HRC target)
- Dimensional verification: Measurement of overlay thickness at multiple locations
- Non-destructive testing: Magnetic particle testing for surface defects
- Bond strength testing: Periodic peel or shear testing on test coupons
Maintenance and Reclamation
When the overlay thickness approaches the minimum acceptable limit, the pipe can be reclaimed through:
- Grinding of worn overlay surface
- Application of new overlay weld
- Reinstatement to original dimensions
This reclamation capability significantly extends the service life of the pipe and reduces replacement costs.
Study Insights and Recommendations
This case study demonstrates the practical value of wear-resistant overlay technology in cement industry applications. The selection of chromium carbide hardfacing alloy proved appropriate for the service conditions, providing excellent wear resistance at moderate cost.
The most significant finding is the predictable, linear wear rate observed over 18 months of service. This predictability enables effective maintenance planning, allowing operators to schedule overlay reclamation during planned shutdowns rather than experiencing unplanned failures. The wear rate data provides a basis for calculating overlay life expectancy and optimizing maintenance intervals.
The study also highlights the importance of proper overlay application technique. Inconsistent overlay thickness or inadequate bond strength would lead to premature failure through spalling or delamination. The emphasis on process control and quality assurance procedures is essential for achieving the expected service life from overlay protection.
From an economic perspective, the overlay approach provides substantial cost savings compared to replacing the entire pipe with a wear-resistant material. The initial overlay application cost represents a fraction of the cost of a complete pipe replacement, while the reclamation capability further reduces long-term maintenance costs. This cost-effectiveness makes overlay protection the preferred approach for large diameter wear-critical components in cement manufacturing.