Quality Influencing Factors of Strip Cladding

Literature Overview

This 2006 study by Han Yue, Tang Chuanjian, and Bi Xiaomin from Lanzhou Lanshi Petrochemical Equipment Company examines the quality factors affecting strip cladding (also known as strip submerged arc welding or strip overlay) processes used in petrochemical equipment manufacturing. Strip cladding is a highly productive method for applying corrosion-resistant overlay layers to large surface areas, and it is widely used for producing clad plates, pressure vessel linings, and heat exchanger components. The study systematically identifies and analyzes the key factors that influence cladding quality, including process parameters, material selection, equipment condition, and operator skill.

Core Technical Findings

The researchers identify multiple categories of factors that affect strip cladding quality. These include process parameters (current, voltage, travel speed, strip width), material factors (strip composition, substrate preparation), equipment factors (welding machine condition, wire feed mechanism), and environmental factors (ambient temperature, humidity, contamination). The study emphasizes that strip cladding quality is the result of the interaction of all these factors, and that systematic control of each factor is essential for producing high-quality cladding layers.

Process Analysis and Quality Control

Strip cladding typically uses submerged arc welding (SAW) or electroslag welding (ESW) processes with a continuous strip of cladding material fed into the molten pool. The strip is usually 10-30 mm wide and 1-3 mm thick, and it is fed at a constant speed synchronized with the welding head travel speed. The quality of the cladding layer depends on maintaining consistent contact between the strip and the molten pool, ensuring complete fusion at the interface, and preventing defects such as lack of fusion, porosity, and cracking.

The study highlights that substrate preparation is critical for achieving good bond strength. The substrate surface must be thoroughly cleaned to remove rust, scale, oil, and other contaminants that can interfere with fusion. The fit-up between the strip and the substrate must be tight, with gaps no greater than 0.5 mm. Any gaps or irregularities can lead to lack of fusion and reduced bond strength at the interface. The study recommends using magnetic particle testing or ultrasonic testing to verify bond quality after cladding.

Defect Analysis and Countermeasures

Common defects in strip cladding include lack of fusion at the interface, porosity in the overlay layer, cracking in the overlay or at the interface, and excessive dilution leading to reduced corrosion resistance. The study provides a systematic analysis of the causes and countermeasures for each defect type. Lack of fusion is typically caused by inadequate heat input, poor substrate preparation, or excessive travel speed. Porosity is often related to flux contamination, inadequate shielding, or hydrogen absorption from moisture. Cracking can result from excessive residual stress, improper material selection, or inadequate preheating and post-heating.

The study emphasizes the importance of process qualification and welder certification. Strip cladding is a specialized process that requires skilled operators and well-maintained equipment. The qualification procedure should include testing of bond strength, hardness, and corrosion resistance of the overlay layer, as well as non-destructive testing for defects. The study recommends regular monitoring of process parameters and periodic verification of cladding quality through destructive testing of sample coupons.

Engineering Practice and Standards Compliance

For petrochemical equipment applications, strip cladding must comply with relevant standards such as GB/T 150, NB/T 47002, ASME VIII Div.1, and ASTM A263/A264/A265. These standards specify requirements for materials, welding procedures, inspection, and acceptance criteria. The study provides guidance on how to ensure compliance with these standards through proper process control and quality assurance. The study also addresses the economic aspects of strip cladding, noting that while the initial equipment investment is significant, the high productivity and low labor cost make it economically attractive for large-scale production of clad plates and pressure vessel components.

Study Insights and Reflections

This research provides a comprehensive framework for understanding and controlling the quality factors in strip cladding processes. The systematic approach to identifying and managing quality factors is particularly valuable for establishing quality assurance systems in manufacturing environments. The study emphasizes that strip cladding quality is not determined by any single factor but by the interaction of multiple factors, and that a holistic approach to process control is essential. The findings have direct applicability to petrochemical equipment manufacturing, where reliable corrosion-resistant cladding is essential for equipment integrity and safety. The study also highlights the importance of operator training and equipment maintenance in achieving consistent cladding quality. Future improvements in strip cladding technology should focus on automation, real-time monitoring, and advanced quality control techniques to further enhance productivity and quality.