Zhuojin Pipe Fitting Co., LtdOptimizing Doubled-Length Counts of Large-Diameter Seamless Steel Pipes to Improve Yield Rate
Problem Statement and Background
This paper by Lin Zhen and colleagues from Baotou Steel (Group) Co., Ltd. Steel Pipe Company, published in Steel Pipe in 2020, addresses a significant economic challenge in large-diameter seamless steel pipe production: the high cutting loss rate associated with the PQF (Piercing-Quadrilateral Rolling-Finishing) continuous pipe mill process. The study focuses on optimizing the doubled-length count of finished pipes, specifically proposing to increase the doubled length from two to three for thin-walled pipe specifications. The optimization targets a reduction in cutting loss rate of approximately 0.5% and a corresponding increase in yield rate, with annual cost savings exceeding 2 million yuan and production increases of 70,000 tons.
Technical Analysis of the Optimization
The core of the optimization lies in the relationship between the billet length, rolling process parameters, and the final pipe length. In the PQF process, the seamless pipe is produced by piercing and rolling a solid steel billet, and the final pipe length is determined by the initial billet length and the rolling reduction schedule. The cutting loss rate is defined as the ratio of the cut-off material (pipe ends) to the total produced pipe length.
| Parameter | Before Optimization | After Optimization | Improvement |
|---|---|---|---|
| Doubled Length Count | 2 | 3 | 50% increase in length |
| Cutting Loss Rate | Baseline | Reduced by ~0.5% | Direct cost saving |
| Yield Rate | Baseline | Increased by ~0.5% | Higher material efficiency |
| Annual Cost Saving | N/A | >2 million yuan | Significant economic benefit |
| Annual Production Increase | N/A | 70,000 tons | Capacity enhancement |
The key insight is that when the doubled length is increased from two to three, the total pipe length increases proportionally while the cutting loss at each end remains essentially constant. This means the cutting loss as a percentage of total production decreases, directly improving the yield rate. Furthermore, with longer billets per production cycle, the number of production cycles required to produce a given output decreases, improving overall mill throughput.
Implementation Considerations
The optimization of doubled length from two to three introduces several practical considerations that must be addressed:
- Billet length requirements: The initial steel billet must be proportionally longer, which may require adjustments to the upstream hot rolling or continuous casting processes to produce appropriately sized billets.
- Equipment capacity: The PQF mill equipment must be verified to handle the increased billet length without compromising rolling quality or equipment integrity.
- Process control: The rolling schedule, including temperature profiles and reduction ratios, must be adjusted to maintain consistent pipe quality across the longer production length.
- Quality assurance: Additional inspection points may be required along the longer pipe length to ensure uniform quality throughout the product.
Study Insights and Reflections
This study exemplifies the principle that significant economic improvements in manufacturing can often be achieved through process optimization rather than equipment upgrades or material changes. The 0.5% improvement in yield rate may appear modest in isolation, but when applied to the large production volumes of a major seamless pipe manufacturer, it translates into substantial annual cost savings. The approach also demonstrates the value of systematic process analysis in identifying optimization opportunities that may not be immediately apparent. For engineers in steel pipe manufacturing, this case study reinforces the importance of continuously evaluating process parameters and production configurations, as even small improvements in material efficiency can yield significant financial returns at scale.