Zhuojin Pipe Fitting Co., LtdAnalysis of Deoxidizer and Mandrel Lubrication Effects on Internal Scale Defects in Hot Continuous Rolling Seamless Steel Pipes
Literature Overview
This paper by Zhou Xiaofeng, Zhang Baohui, Zhang Chuanyou, and Shi Qingzhi from the Technical Center of Tianjin Pipe Group Co., Ltd., published in Steel Pipe in 2010 (Vol. 39, No. 3, pp. 41-44), addresses a critical quality issue in the production of hot continuous rolling (HCR) seamless steel pipes: internal scale defects caused by deoxidizer and mandrel lubrication processes. This is a topic of direct relevance to my expertise in steel pipe manufacturing and quality control, as internal scale defects are among the most challenging and economically significant quality problems in seamless pipe production.
Internal scale defects directly affect the first-pass quality rate and the overall yield of the production process. For a large-scale seamless pipe manufacturer such as Tianjin Pipe Group, even a small reduction in internal scale defect rate can translate into significant economic benefits through improved yield and reduced rework costs.
Core Technical Content and Methodology
The paper analyzes the causes of internal scale defects in HCR seamless steel pipes, with particular focus on the deoxidizer and its spraying process parameters, as well as the mandrel lubrication process. The authors identify that while the spraying of deoxidizer is an effective measure for removing oxide scale from the inner wall of the HCR pipe blank, it can simultaneously lead to the formation of internal scale defects if not properly controlled.
The technical challenge lies in the dual role of the deoxidizer. On one hand, it removes existing oxide scale from the hot pipe blank, which is essential for producing clean, defect-free pipe inner surfaces. On the other hand, the chemical reaction between the deoxidizer and the hot steel surface can produce new oxide formations or redeposit removed scale, creating internal scale defects that are difficult to detect and remove after the pipe has been rolled.
Root Cause Analysis and Prevention Measures
Using a systematic approach consistent with FMEA methodology, the authors identified the following key factors contributing to internal scale defects:
| Factor | Mechanism | Severity | Prevention Measure |
|---|---|---|---|
| Deoxidizer type | Chemical reaction with steel surface | High | Select appropriate deoxidizer chemistry |
| Deoxidizer concentration | Excessive reaction or insufficient cleaning | High | Optimize concentration within process window |
| Spraying pressure | Uneven coverage or surface damage | Medium | Control pressure within specified range |
| Spraying angle | Incomplete coverage of inner surface | Medium | Optimize nozzle geometry and angle |
| Mandrel lubrication | Lubricant decomposition and redeposition | High | Select high-temperature stable lubricant |
| Mandrel surface condition | Scale adhesion to worn mandrel | Medium | Regular mandrel inspection and maintenance |
| Blank temperature | Affects reaction kinetics and scale formation | High | Control blank temperature within optimal range |
The deoxidizer chemistry is critical because different chemical compounds react differently with the hot steel surface. Some deoxidizers may produce volatile reaction products that escape without causing defects, while others may produce solid reaction products that adhere to the pipe inner surface and become embedded during the rolling process.
Process Parameter Optimization
The authors propose specific measures for preventing internal scale defects from the perspective of deoxidizer and spraying process parameters. The key process parameters that require optimization include:
- Deoxidizer type and chemical composition
- Deoxidizer concentration in the spray solution
- Spraying pressure and flow rate
- Nozzle design and spray pattern
- Blank temperature at the time of deoxidizer application
- Mandrel lubricant type and application method
The optimization of these parameters requires a systematic approach that considers the interactions between parameters. For example, increasing the deoxidizer concentration may improve scale removal but simultaneously increase the risk of chemical reaction with the steel surface, leading to new defect formation. The optimal process window must balance these competing effects.
The mandrel lubrication process is also critical because the lubricant must withstand the high temperatures of the hot rolling process without decomposing or forming deposits. Inadequate lubrication leads to excessive friction between the mandrel and the pipe blank, which can cause surface damage and scale adhesion. Excessive lubrication, on the other hand, can lead to lubricant decomposition products that deposit on the pipe inner surface and become embedded during rolling.
Quality Control and Inspection
From a quality control perspective, internal scale defects are challenging to detect because they are located on the inner surface of the pipe and may be partially embedded in the pipe wall. Non-destructive testing methods such as ultrasonic testing (UT) and eddy current testing (ECT) can be used to detect internal scale defects, but the detection sensitivity depends on the size, depth, and orientation of the defect.
For HCR seamless steel pipes, the following inspection methods are commonly used:
| Inspection Method | Capability | Limitation |
|---|---|---|
| Ultrasonic testing (UT) | Detects internal defects | Requires coupling and surface preparation |
| Eddy current testing (ECT) | Detects near-surface defects | Limited penetration depth |
| Visual inspection (VI) | Detects surface defects | Cannot detect internal defects |
| Magnetic particle testing (MT) | Detects surface and near-surface defects | Requires ferromagnetic material |
| Radiographic testing (RT) | Detects volumetric defects | Limited by pipe wall thickness |
The selection of inspection method depends on the pipe diameter, wall thickness, and the expected defect size and location. For thin-walled pipes, ultrasonic testing is generally the most effective method for detecting internal scale defects. For thicker-walled pipes, radiographic testing may be more effective but is more expensive and slower.
Study Insights and Implications
The most important contribution of this research is the systematic analysis of the relationship between deoxidizer and mandrel lubrication processes and internal scale defect formation in HCR seamless steel pipes. The authors provide practical guidance for optimizing these processes to minimize defect formation while maintaining effective scale removal.
For steel pipe engineers, this research highlights the importance of process control in seamless pipe manufacturing. The deoxidizer and mandrel lubrication processes are critical process steps that require careful monitoring and control to ensure consistent product quality. Engineers should establish robust process control systems that include:
- Real-time monitoring of deoxidizer concentration and temperature
- Regular inspection and maintenance of spraying nozzles
- Periodic evaluation of mandrel surface condition and lubrication effectiveness
- Statistical process control of key quality parameters
- Root cause analysis of any internal scale defect occurrences
The economic impact of internal scale defects is significant because they reduce the usable length of each pipe, increase rework costs, and may lead to customer complaints and warranty claims. A systematic approach to process optimization, as advocated in this research, can significantly improve the first-pass quality rate and overall manufacturing efficiency.
This research provides a valuable technical foundation for the optimization of deoxidizer and mandrel lubrication processes in HCR seamless steel pipe production. The practical measures proposed by the authors should be implemented with careful attention to process parameter interactions and the establishment of robust quality control systems. Engineers should recognize that the prevention of internal scale defects requires a holistic approach that considers not only the deoxidizer and lubrication processes but also the blank preparation, rolling parameters, and post-rolling inspection procedures. By implementing the recommendations of this research and continuously improving the process control system, seamless pipe manufacturers can significantly improve their product quality and competitiveness in the global market.