Zhuojin Pipe Fitting Co., LtdAnalysis of Jet Impact Heat Transfer Characteristics in Hot-Rolled Seamless Steel Pipes
Literature Overview
This paper by Zhang Yansheng, Zhang Rui, Li Zhenlei, and Yuan Guo from the State Key Laboratory of Rolling and Automation at Northeastern University addresses a critical bottleneck in seamless steel pipe production: achieving uniform and high-intensity cooling during the controlled cooling process. The work was published in Mechanical Design and Manufacturing (2025, Vol. 4, pp. 121-125) and was supported by the National Natural Science Foundation of China (Key Joint Fund Project U1860201 and Youth Fund Project 51804074). The authors established a finite element model of annular jet impact cooling on steel pipes and systematically investigated the influence of nozzle diameter, jet flow rate, inclination angle, and number of jets on cooling performance using orthogonal experimental design.
Core Technical Content
The fundamental challenge identified in this work is that the annular cross-section of seamless pipes makes uniform cooling significantly more difficult than the planar cooling achieved on flat sheet products. Controlled cooling technology has become indispensable in plate and strip production, yet its application to seamless pipes remains limited. The authors argue that high cooling intensity and cooling uniformity directly determine the success or failure of online cooling applications in the seamless pipe industry.
The research methodology employed a combination of numerical simulation and experimental validation. A finite element model was constructed to simulate the jet impact cooling process on a cylindrical pipe surface. The four key process parameters studied were:
| Parameter | Optimized Range | Unit |
|---|---|---|
| Nozzle diameter | 3-4 | mm |
| Jet flow rate | 6-8 | L/min |
| Inclination angle | 0-10 | degrees |
| Number of jets | 8-12 | beams |
Key Technical Findings
The most significant finding is the concept of "regional average heat transfer coefficient" characterization. Rather than treating the pipe surface as a single uniform zone, the authors divided the surface into distinct regions and evaluated the average heat transfer coefficient in each region separately. This approach revealed that by properly matching jet flow rate with nozzle diameter, the range (extremum difference) of average heat transfer coefficients across all regions can be controlled within 1000 W/(m²·K). This represents a meaningful quantitative criterion for evaluating cooling uniformity on curved surfaces.
The orthogonal experimental design approach allowed the authors to decouple the effects of multiple parameters and identify their relative contributions. The results indicate that jet flow rate and nozzle diameter have the most significant influence on heat transfer performance, while inclination angle and number of jets play secondary but still important roles. The inclination angle range of 0-10 degrees suggests that near-perpendicular impingement is preferred, with only slight angular deviation being acceptable to maintain uniform coverage without excessive spray pattern distortion.
The authors also established a nonlinear mathematical model relating the average cooling rate of the pipe to each of the four factors. This model provides a theoretical foundation for nozzle system design and uniform cooling optimization in practical applications.
Process Analysis and Engineering Implications
From a metallurgical perspective, the cooling rate directly governs the microstructure evolution in the heat-affected and cooled zones of hot-rolled steel pipes. For seamless pipes, non-uniform cooling can lead to:
- Differential microstructure development between the outer surface and inner surface
- Residual stress gradients through the wall thickness
- Potential cracking in high-strength grades during rapid cooling
- Variability in mechanical properties along the circumference
The annular jet impact configuration is particularly suitable for seamless pipe cooling because it can provide circumferential coverage. However, the gap between the nozzle array and the pipe surface creates complex flow interactions, including jet-jet interference, wake effects, and boundary layer development on the curved surface. The turbulent intensity plays a crucial role in enhancing heat transfer, and the authors specifically investigated this aspect.
The optimized parameter window identified (3-4 mm nozzle diameter, 6-8 L/min flow rate) suggests moderate cooling intensities rather than aggressive quenching. This is consistent with the metallurgical requirements of most seamless pipe grades, where controlled cooling rates in the range of 10-100 °C/s are typically needed to achieve desired microstructures without introducing excessive thermal stresses.
Integration with Engineering Practice
In practical seamless pipe production lines, the controlled cooling system is typically installed between the coiler and the downstream processing stations. The nozzle arrangement must account for:
- Pipe diameter variation within a production batch
- Axial movement of the pipe during coiling
- Heat dissipation from the pipe ends versus the mid-section
- Water consumption and environmental constraints
The finding that 8-12 jets are optimal suggests a practical nozzle array size that balances uniformity with equipment complexity and water usage. For large-diameter pipes (e.g., 300-600 mm OD), the number of jets may need to be increased to maintain adequate coverage density.
Key Questions and Reflections
Several questions arise from this work that merit further investigation:
- How does the model account for the variation in heat transfer coefficients between the top, sides, and bottom of the pipe as it moves through the cooling zone?
- What is the sensitivity of the optimal parameters to pipe diameter and wall thickness?
- How do the results translate to different steel grades with varying thermal properties?
- What is the effect of scale formation on the pipe surface during cooling on the heat transfer characteristics?
The nonlinear mathematical model developed in this work provides a valuable starting point for process optimization, but its predictive accuracy under varying production conditions should be validated through additional experimental work. The approach of using regional average heat transfer coefficients as a uniformity metric is innovative and could potentially be extended to other curved-surface cooling applications.
Study Insights and Implications
This research demonstrates the value of combining numerical simulation with systematic experimental design in solving complex engineering problems. The orthogonal experimental approach efficiently identified the optimal parameter window without requiring an exhaustive full-factorial study. The emphasis on cooling uniformity rather than merely maximizing cooling intensity reflects a mature understanding of the metallurgical requirements for seamless pipe production.
For engineers involved in seamless pipe mill design and operation, this work provides actionable guidance for controlled cooling system design. The key takeaway is that achieving uniform cooling on a cylindrical surface requires careful matching of nozzle parameters rather than simply increasing water flow or jet pressure. The 1000 W/(m²·K) criterion for regional heat transfer coefficient variation offers a practical target for process optimization.
Future work should extend these findings to include the effects of pipe movement speed, multi-stage cooling configurations, and the integration of controlled cooling with downstream heat treatment processes to achieve comprehensive microstructure control in seamless pipe production.