CLADDING TECHNOLOGY SHANXI CO., LTDSecondary Overlay Welding Technology for TCS-TI Wear-Resistant Strips
Literature Overview
This 2014 study from China National Petroleum Bohai Petroleum Equipment Manufacturing Co., Ltd. First Machinery Factory addresses a highly practical industrial problem: the secondary overlay welding of TCS-TI type wear-resistant strips. The TCS-TI designation refers to a composite wear-resistant strip system where the base strip provides structural support and the overlay layer delivers wear resistance through a specific metallurgical design. The authors—Wang Qian, Xiang Guilin, Li Wentong, Wang Kehui, and Hu Jianxiu—present findings from production-scale application rather than purely academic research, which gives the work considerable engineering credibility.
Core Technical Content
The fundamental challenge in secondary overlay welding of wear-resistant strips lies in maintaining metallurgical compatibility between the existing overlay layer and the newly deposited material while ensuring adequate bond strength at the interface. In the context of Bohai Petroleum's operations, these strips are typically used in high-wear environments such as drilling equipment components, subsea production systems, and heavy-duty mechanical assemblies where abrasive and erosive conditions prevail.
Material System and Process Parameters
| Parameter | Typical Range | Rationale |
|---|---|---|
| Base strip material | Low-carbon or low-alloy steel | Provides structural toughness and weldability |
| Overlay alloy | Hardfacing alloy (Cr-Co-Ni or Cr-CrC type) | Delivers abrasion resistance |
| Shielding gas | Ar + CO₂ mixture (80:20 or 90:10) | Balances penetration and arc stability |
| Wire feed speed | 4–8 m/min | Depends on wire diameter (1.0–1.4 mm) |
| Travel speed | 150–350 mm/min | Controls dilution and bead profile |
| Interpass temperature | ≤150°C | Prevents thermal cracking in hardfacing layers |
| Preheat temperature | 80–120°C | Reduces hydrogen-induced cracking risk |
Key Technical Challenges Identified
The study highlights several critical issues encountered during secondary overlay welding:
- Thermal cycling effects: The previously deposited overlay layer experiences repeated thermal cycles during secondary welding, which can cause microstructural coarsening, grain boundary segregation, and loss of hardness in the existing layer.
- Dilution control: Achieving the correct dilution ratio between the base metal and the overlay alloy is essential for maintaining the designed hardness profile. Excessive dilution reduces wear resistance; insufficient dilution leads to cracking susceptibility.
- Interface bonding: The bond between the secondary overlay and the existing layer must meet minimum shear strength requirements, typically ≥200 MPa for industrial applications.
- Cracking prevention: Hardfacing alloys with high carbon and chromium content are inherently susceptible to solidification cracking and reheat cracking, especially during multi-pass deposition.
Engineering Practice Integration
In my own experience with overlay welding operations, the secondary overlay scenario is particularly demanding because it introduces an additional variable—the condition of the existing overlay layer. Before applying a secondary overlay, a thorough assessment of the existing layer is essential:
- Visual and dimensional inspection: Check for porosity, cracks, undercut, and profile irregularities on the existing overlay surface.
- Hardness mapping: Perform a Vickers hardness survey across the existing overlay to identify zones of microstructural degradation.
- Surface preparation: Grinding or machining the existing overlay surface to remove defects and create a sound substrate for new deposition.
- Welding procedure qualification: A WPS/PQR specific to secondary overlay conditions should be developed and qualified, accounting for the modified thermal history.
The Bohai Petroleum application demonstrates that with proper procedural control, secondary overlay welding can extend the service life of wear-resistant components significantly, offering an economical alternative to complete component replacement. The study's production-oriented approach—emphasizing repeatability and field applicability over laboratory optimization—makes it particularly valuable for engineers working in maintenance and repair operations.
Study Insights and Reflections
This work underscores a principle I have observed repeatedly in industrial welding: the quality of the final component is often determined not by the initial fabrication but by the ability to maintain performance through repair cycles. Secondary overlay welding represents a mature strategy for life extension, but it demands rigorous procedural discipline. The 2014 timeframe of this study predates many recent advances in welding monitoring and process control, yet its fundamental approach remains sound. Engineers today should complement such classical approaches with modern non-destructive testing capabilities (PAUT, TOFD) and real-time process monitoring to further enhance the reliability of secondary overlay operations.