Zhuojin Pipe Fitting Co., LtdEffect of Rotation Speed on Cooling Uniformity of Seamless Steel Pipes
Literature Overview
This paper by Hu Shushan and Liu Rong'e, published in Hot Working Technology (Vol. 47, Issue 12, 2018, pp. 139–144), investigates the influence of steel pipe rotation speed on the cooling uniformity of seamless steel pipes during controlled cooling (quenching) operations using three-dimensional finite element numerical simulation. The research was supported by the Inner Mongolia Autonomous Region Higher Education Scientific Research Project (NJZY17404) and conducted at the School of Mechanical and Transportation Engineering, Ordos Institute of Applied Technology.
Core Technical Content
Controlled cooling is a critical post-rolling process for seamless steel pipes, determining the final microstructure and mechanical properties of the pipe. The cooling uniformity—axial, circumferential, and radial—is essential for achieving consistent product quality. The researchers developed a 3D finite element model of the controlled cooling equipment and simulated the cooling process under various rotation speeds to identify the optimal parameters.
The study systematically examines how rotation speed affects temperature distribution at different locations on the pipe: inner surface axial points, outer surface axial points, inner surface circumferential points, outer surface circumferential points, and radial cross-section points.
Technical Parameter Analysis
| Rotation Speed (rpm) | Inner Surface Axial Temperature Trend | Outer Surface Axial Temperature Trend | Circumferential Temperature Difference |
|---|---|---|---|
| Low (baseline) | Higher baseline temperature | Moderate variation | Larger fluctuation |
| Medium | Progressive temperature decrease | Minor change | Reduced fluctuation |
| High | Further temperature decrease | Negligible change | Minimal fluctuation |
The key findings from the simulation are:
- Inner surface axial cooling: As rotation speed increases, the temperatures at all axial points on the inner surface continuously decrease. This is because higher rotation speed increases the relative velocity between the cooling medium (typically water or air) and the pipe surface, enhancing convective heat transfer.
- Outer surface axial cooling: The rotation speed has minimal effect on the outer surface axial temperature distribution, indicating that the outer surface cooling is dominated by other factors such as ambient conditions and the cooling medium flow pattern.
- Circumferential uniformity: With increasing rotation speed, the temperature fluctuation at circumferential points on the inner surface decreases progressively, and the maximum temperature difference gradually reduces. This is the most significant benefit of increasing rotation speed—improved circumferential uniformity.
- Radial cooling: Radial temperatures show a slight decreasing trend with increasing rotation speed, but the effect is small. This suggests that the thermal gradient through the pipe wall thickness is primarily governed by the pipe diameter and wall thickness rather than rotation speed.
Process Engineering Insights
The cooling uniformity directly impacts the following quality characteristics:
- Microstructural homogeneity: Non-uniform cooling leads to mixed microstructures (e.g., martensite in some regions and bainite in others), causing property variation.
- Residual stress distribution: Thermal gradients generate residual stresses that can cause distortion or cracking.
- Mechanical property consistency: Hardness, tensile strength, and impact toughness vary with local cooling rate.
For seamless steel pipe production, the rotation speed should be optimized based on:
| Pipe Parameter | Recommended Rotation Speed Range | Rationale |
|---|---|---|
| Small diameter (<100 mm) | 5–15 rpm | High surface-to-volume ratio, fast cooling inherently |
| Medium diameter (100–300 mm) | 10–25 rpm | Balance between uniformity and equipment capability |
| Large diameter (>300 mm) | 15–30 rpm | Higher speed needed for circumferential uniformity |
| Thick wall (t/D > 0.1) | 15–35 rpm | Enhanced internal cooling requires higher speed |
Practical Considerations
In actual production, several factors constrain the selection of rotation speed:
- Equipment limitations: The cooling equipment (typically a cooling tower or quenching tank) has mechanical limits on the rotation speed it can impart to the pipe. Excessive speed may cause pipe vibration, surface damage, or equipment failure.
- Cooling medium flow: The effectiveness of rotation depends on the cooling medium flow pattern. If the water or air jets are not properly aligned with the rotating pipe, increasing rotation speed may not improve cooling uniformity proportionally.
- Pipe material: Different steel grades have different thermal properties. Higher carbon steels with faster transformation kinetics may require different rotation speeds than low-carbon steels to achieve the desired microstructure.
- Production efficiency: Higher rotation speeds may reduce cooling time, improving throughput, but may also increase energy consumption and equipment wear.
Quality Control Implications
From a quality control perspective, this research supports the following recommendations:
- Monitor rotation speed as a critical process parameter during controlled cooling.
- Implement temperature monitoring at multiple circumferential positions to verify uniformity.
- Adjust rotation speed based on pipe diameter, wall thickness, and target microstructure.
- Conduct periodic metallographic examinations to verify microstructural homogeneity at different pipe locations.
Summary
This study provides quantitative evidence that increasing rotation speed during controlled cooling of seamless steel pipes improves circumferential cooling uniformity, particularly at the inner surface. The effect on axial and radial temperature distributions is less pronounced. Engineers should optimize rotation speed as a function of pipe geometry and material requirements, balancing uniformity improvement against equipment constraints and production efficiency. The finite element methodology employed offers a valuable tool for process optimization without the cost and time of full-scale physical trials.