Zhuojin Pipe Fitting Co., LtdApplication of Intelligent Large-Diameter Steel Pipe Assembly and Welding Machine at Huang Jinping Hydropower Station
Literature Overview
The paper by Liu Xujun, published in Water and Power Construction Technology (2015, Vol. 46, No. 11, pp. 81-83), documents the practical application of the ZH120 intelligent assembly and welding machine for large-diameter steel pressure pipes at the Huang Jinping Left Bank Hydropower Station tunnel. This case study is particularly valuable because it addresses one of the most challenging construction scenarios in the water conservancy sector: the field assembly and welding of large-diameter carbon steel pipes within confined underground tunnel environments. The work was conducted by Sichuan Datang International Ganzi Hydropower Development Co., Ltd.
Project Background and Technical Challenge
The Huang Jinping Hydropower Station required the installation of large-diameter pressure steel pipes within a tunnel environment characterized by limited access, restricted overhead clearance, and challenging logistics. Traditional manual assembly and welding methods for such large-diameter pipes involve extensive temporary works, significant labor intensity, and often result in tunnel over-excavation to accommodate construction equipment. The ZH120 intelligent machine was introduced to transform this labor-intensive construction process into a technology-intensive mechanical operation.
| Parameter | Traditional Manual Method | ZH120 Intelligent Machine Method |
|---|---|---|
| Construction approach | Labor-intensive assembly | Mechanical precision assembly |
| Tunnel excavation requirement | Larger cross-section for access | Reduced cross-section possible |
| Transport cost | Higher due to bulky temporary works | Lower due to integrated equipment |
| Welding quality consistency | Operator-dependent | Process-controlled and repeatable |
| Construction schedule | Longer due to manual operations | Shorter due to mechanization |
| Safety profile | Higher risk in confined spaces | Improved with reduced manual work |
Assembly and Welding Process Analysis
The ZH120 machine integrates pipe alignment, gap adjustment, and welding into a unified mechanical system. The key to its successful application was the development of a field-specific assembly and welding process that accounted for the unique constraints of the underground powerhouse environment. The process development followed a systematic approach:
- Site assessment and constraint mapping: The tunnel dimensions, access routes, equipment transport limitations, and overhead clearances were thoroughly documented.
- Process design and parameter optimization: The assembly sequence, welding procedure specifications (WPS), and machine operating parameters were tailored to the site conditions.
- Trial runs and iterative refinement: Preliminary assembly and welding trials were conducted to validate the process before full-scale implementation.
- Full-scale execution and quality monitoring: The production assembly and welding proceeded with continuous quality inspection at each stage.
The welding process for large-diameter pressure pipes typically involves multi-pass welding with specific heat input control to manage residual stress and distortion. The intelligent machine provides consistent travel speed, torch height, and wire feed rate, which are critical for maintaining uniform weld bead geometry and metallurgical quality.
Quality Control Considerations
For large-diameter pressure steel pipes used in hydropower penstocks, the welding quality is paramount due to the internal hydrostatic pressure loads. The quality control framework should encompass:
| Inspection Stage | Method | Acceptance Criteria |
|---|---|---|
| Pre-weld | Visual inspection, fit-up check | Gap 2-3 mm, root face 0-0.5 mm, misalignment < 1 mm |
| During welding | Process parameter monitoring | Heat input within WPS range, no interruption |
| Post-weld | RT (radiographic testing) | No lack of fusion, no slag inclusion above threshold |
| Post-weld | UT (ultrasonic testing) | No cracks, no porosity clusters |
| Post-weld | Hydrostatic test | Pressure held for specified duration without leakage |
The transformation from manual to mechanized welding also affects the residual stress distribution. Mechanized processes typically produce more uniform heat input, resulting in more predictable residual stress patterns. However, the large diameter of the pipes means that circumferential and longitudinal welds intersect at complex geometries, requiring careful sequence planning to minimize angular distortion at multi-weld intersections.
Engineering Practice Insights
The most significant outcome highlighted by this paper is the concept of converting auxiliary engineering works into mechanical manufacturing operations. In traditional hydropower construction, the assembly of large-diameter pressure pipes in tunnels often requires extensive scaffolding, temporary support structures, and large numbers of skilled welders working in difficult positions. The ZH120 machine eliminates much of this burden by providing a self-contained assembly and welding platform.
From a project management perspective, the reduction in tunnel excavation size has direct cost implications. A smaller tunnel cross-section means less rock excavation, less support structure, and potentially faster excavation rates. The reduction in transport costs is also notable, as the integrated machine reduces the need to move bulky components and temporary materials through constrained tunnel access.
This case study exemplifies the principle that appropriate mechanization can fundamentally change the economics and risk profile of a construction project. For future projects involving large-diameter steel pressure pipes in confined spaces, the lessons learned from the Huang Jinping application should serve as a reference for process planning and equipment selection.
Summary
The application of the ZH120 intelligent assembly and welding machine at the Huang Jinping Hydropower Station demonstrates a successful paradigm shift from labor-intensive to technology-intensive construction for large-diameter steel pressure pipe installation. The method reduces tunnel excavation requirements, lowers transport costs, improves welding quality consistency, and enhances construction safety in confined underground environments. For engineers planning similar projects, the key takeaway is that early integration of mechanized assembly and welding equipment into the construction planning phase can yield substantial benefits in terms of cost, schedule, and quality, provided that the process is carefully adapted to the specific site constraints.