Feedforward Adaptive Control of Wall Thickness in Seamless Pipe Tension Reduction

Literature Overview

The paper by Liu Shan from Zhejiang University and Xue Jianguo and Zheng Jianmin from Baosteel Company, published in Baosteel Technology in 2006, describes the implementation of feedforward adaptive control technology for wall thickness control in the tension reduction process of seamless steel pipes at Baosteel's steel pipe plant. The tension reduction process is a critical rolling operation that reduces the wall thickness of the pipe while simultaneously reducing its diameter, and achieving precise wall thickness control is essential for meeting product specifications and ensuring downstream processing quality.

Tension Reduction Process and Wall Thickness Control Challenges

The tension reduction process involves rolling the pipe through a series of rolling mills while applying axial tension to the pipe. The wall thickness reduction is achieved through the compression of the pipe wall by the rolling mills, while the axial tension prevents the pipe from buckling and helps maintain dimensional stability. The key challenges in wall thickness control include:

Variability in incoming pipe wall thickness: The wall thickness of the incoming pipe blank varies due to variations in the preceding hot rolling and piercing processes.
Complex wall thickness distribution: The wall thickness distribution along the pipe length is not uniform, and the relationship between incoming wall thickness and final wall thickness is complex.
Real-time control requirements: The wall thickness must be controlled in real-time during the rolling process, with adjustments made to each rolling mill stand as the pipe passes through.
Multi-stand coordination: The wall thickness control must be coordinated across multiple rolling mill stands, each of which contributes to the overall wall thickness reduction.

Feedforward Adaptive Control Technology

The feedforward adaptive control technology described in the paper uses accurate material flow tracking to obtain the weight of the incoming pipe blank and the length measurement data after the continuous rolling mill. These data are used to calculate the incoming pipe wall thickness, which is then used to adjust the rolling speed distribution of each mill stand in real-time. The key components of the control system include:

Material flow tracking: Accurate tracking of the pipe blank from the start of the process to the tension reduction mill, using weight measurement and length measurement systems.
Wall thickness calculation: Calculation of the incoming pipe wall thickness based on the weight and length data, using the known geometry of the pipe blank.
Wall thickness distribution model: A model that relates the incoming wall thickness to the desired final wall thickness distribution along the pipe length.
Rolling speed adjustment: Real-time adjustment of the rolling speed of each mill stand to achieve the desired wall thickness reduction.

Control Parameter	Measurement Method	Control Action	Response Time
Incoming pipe weight	Weighing system	Wall thickness calculation	Real-time
Incoming pipe length	Length measurement system	Wall thickness calculation	Real-time
Incoming pipe wall thickness	Calculated from weight and length	Rolling speed adjustment	Real-time
Final pipe wall thickness	Wall thickness gauge	Feedback correction	Real-time
Rolling speed of each stand	Speed control system	Wall thickness reduction	Real-time

Technical Implementation and Performance

The paper describes the implementation of the feedforward adaptive control technology at Baosteel's steel pipe plant, demonstrating the effectiveness of the control system in reducing wall thickness deviations. The key performance improvements include:

Reduced wall thickness deviation: The wall thickness deviation of the finished pipe was significantly reduced compared to the conventional control method.
Improved product quality: The improved wall thickness control led to better dimensional accuracy and consistency of the finished pipe.
Reduced scrap rate: The reduction in wall thickness deviation reduced the number of pipes that had to be scrapped due to dimensional non-conformance.
Improved production efficiency: The improved control system allowed for faster production rates while maintaining product quality.

Engineering Practice and Standards Compliance

The feedforward adaptive control technology has important implications for standards compliance in seamless pipe production. Key standards that specify wall thickness tolerances include:

GB/T 8162: Specifies dimensional tolerances for seamless steel pipes, including wall thickness tolerance.
ASTM A53: Specifies wall thickness tolerances for welded and seamless steel pipes.
ISO 3183: Specifies dimensional tolerances for seamless steel tubes for pipeline transport.
API 5L: Specifies wall thickness tolerances for line pipe, including both seamless and welded pipes.

The feedforward adaptive control technology enables pipe manufacturers to meet the stringent wall thickness tolerance requirements of these standards, particularly for high-grade and specialty applications where dimensional accuracy is critical.

Key Questions and Reflections

This paper raises several important questions for engineers involved in seamless pipe production:

How sensitive is the feedforward adaptive control system to measurement errors in the weighing and length measurement systems? The accuracy of the wall thickness calculation depends directly on the accuracy of these measurements, and any systematic errors will propagate through the control system.
How does the control system perform for different pipe grades and compositions? The wall thickness distribution model may need to be adjusted for different steel grades, and the paper does not extensively discuss this aspect.
What is the role of feedback control in complementing the feedforward control? The paper focuses on feedforward control, but in practice, a combination of feedforward and feedback control is often used to achieve the best performance.

Study Insights and Implications

After studying this paper, I find it to be a valuable example of advanced process control technology applied to seamless pipe production. The feedforward adaptive control approach is particularly effective for addressing the variability in incoming pipe wall thickness, which is a major source of dimensional variation in the finished product.

For welding engineers involved in seamless pipe production, the paper highlights the importance of dimensional accuracy in the tension reduction process. The wall thickness of the pipe directly affects the weld quality in subsequent welding operations, such as the welding of pipe fittings or the welding of pipe segments in pipeline construction. Inconsistent wall thickness can lead to uneven weld penetration, increased residual stress, and reduced weld quality.

The paper also has implications for the design of seamless pipe production lines. The accuracy of the feedforward control system depends on the accuracy of the measurement systems and the precision of the rolling speed control systems. Investment in high-quality measurement and control systems is therefore essential for achieving the best wall thickness control performance.

Summary

This paper presents a successful implementation of feedforward adaptive control technology for wall thickness control in the tension reduction process of seamless steel pipes. The technology uses accurate material flow tracking to calculate incoming pipe wall thickness and adjusts rolling speeds in real-time to achieve the desired wall thickness distribution. The results demonstrate significant improvements in wall thickness accuracy and product quality, with direct implications for standards compliance and downstream processing. Engineers involved in seamless pipe production should consider the adoption of similar advanced control technologies to improve product quality and reduce scrap rates.