Zhuojin Pipe Fitting Co., LtdNumerical Simulation of Large-Diameter Hot-Press Tee Extrusion Process
Literature Overview
The paper by Li Hailiang, Zhu Peng, Liu Jingsheng, Ma Zichuan, and Xu Zhihui (China Petroleum Pipeline Machinery Manufacturing Co., Ltd., 2012) presents numerical simulation results for the extrusion forming process of large-diameter X80 grade hot-press tees. Published in Hot Working Technology (Vol. 41, No. 19, pp. 81-83), this study addresses a critical gap in domestic manufacturing capability for large-diameter pipeline fittings. The work was specifically motivated by the requirements of the West-East Gas Pipeline Phase II project, which demanded high-performance fittings in X80 steel grade with diameters exceeding 1200mm.
FEM Simulation Methodology
The finite element simulation employs a rigid-plastic finite element formulation appropriate for metal forming processes. The simulation models the material flow during the extrusion forming operation, predicting key process parameters including forming loads, strain distributions, and potential defect locations. The methodology includes:
| Simulation Parameter | Specification | Purpose |
|---|---|---|
| Material model | X80 steel with temperature-dependent flow stress | Accurate load prediction |
| Mesh type | Lagrangian with remeshing | Handle large deformations |
| Contact algorithm | Penalty method with friction | Realistic die-material interaction |
| Thermal coupling | Quasi-static with heat transfer | Account for temperature effects |
| Mesh density | Refined at die cavity | Capture critical deformation zones |
The simulation captures the complex material flow patterns that occur during tee extrusion forming. As the heated pipe blank is forced through the forming die, material must simultaneously expand radially to form the branch opening while maintaining the main pipe diameter. This dual deformation requirement creates complex strain states that are difficult to predict analytically.
Process Parameter Optimization
The numerical simulation enabled systematic optimization of the forming process parameters for the quasi-1219mm tee. Key parameters investigated include:
- Extrusion speed: Affects forming load, temperature distribution, and material flow homogeneity.
- Preheating temperature: Influences material flow stress, forming load, and risk of thermal cracking.
- Die geometry: Determines material flow pattern and final dimensional accuracy.
- Friction conditions: Affects material flow resistance and strain distribution.
The optimization results identified process windows that minimize forming loads while ensuring adequate material flow to fill the branch opening completely. Critical findings include:
- Optimal preheating temperature balances low flow stress against oxidation and grain growth concerns.
- Controlled extrusion speed prevents material sticking to the die while maintaining sufficient forming force.
- Die radius geometry significantly influences strain concentration at the branch junction.
- Friction management through lubrication and die surface finish is essential for defect-free forming.
Engineering Application in West-East Gas Pipeline
The West-East Gas Pipeline Phase II project represents one of the most demanding pipeline construction projects globally, requiring fittings that meet stringent pressure, toughness, and corrosion resistance requirements. The X80 steel grade demands careful process control due to its high strength and associated reduced formability. The simulation results provided the theoretical basis for:
- Establishing safe forming temperature ranges that prevent cracking while ensuring complete forming.
- Predicting forming loads for equipment sizing and process control.
- Identifying potential defect locations for enhanced quality inspection.
- Optimizing die design to minimize post-forming correction operations.
The successful application of simulation-optimized parameters in production demonstrated that numerical simulation can effectively guide the development of new forming processes for large-diameter pipeline fittings. The approach reduced trial-and-error iterations, minimized material waste from failed trials, and accelerated the qualification timeline for new product development.
Study Insights
This paper demonstrates the transformative value of numerical simulation in metal forming process development for large-diameter pipeline fittings. The ability to predict material flow, forming loads, and strain distributions before physical trials represents a paradigm shift from empirical process development to physics-based design. For the Chinese pipeline industry, this work addresses a genuine capability gap in large-diameter X80 fitting manufacturing that had previously required reliance on imported components. The methodology established here can be extended to other challenging forming operations including spiral-wound fittings, forged reducers, and complex multi-branch tees. The key lesson is that investment in simulation capability pays dividends through reduced development time, improved first-time quality, and enhanced ability to address customer-specific requirements.
The integration of simulation with process optimization and quality planning establishes a comprehensive framework for advanced fitting manufacturing. As pipeline projects continue to demand higher pressure ratings, larger diameters, and more challenging service environments, numerical simulation will become an indispensable tool for process development and quality assurance in the pipeline fitting industry.