Corrosion Resistance Study of Oxy-Acetylene Cladded Hook Claws

Literature Overview and Background

Published in 2023 in "Metal Materials and Metallurgical Engineering" by Li Zewen, Jin Shuwu, Lu Zhaohui, Feng Yong, Chen Yeqing, and Zhang Ziqin from CGN Research Institute, this study investigates the corrosion resistance performance of hook claws (gripping mechanisms) cladded using oxy-acetylene flame welding. Hook claws are critical components in nuclear power plant fuel handling systems, where they must operate in potentially corrosive environments including humid air, coolant splashes, and occasional contact with radioactive materials. The study evaluates the effectiveness of oxy-acetylene cladding in providing corrosion protection for these components.

Technical Background

Oxy-acetylene flame cladding is a traditional but effective method for depositing corrosion-resistant overlay layers onto steel components. The process uses a mixture of oxygen and acetylene gas to generate a high-temperature flame (up to 3,200°C) that melts the base metal and the filler material, creating a metallurgical bond. The process is particularly suitable for components with complex geometries, such as hook claws, where access for arc welding equipment may be limited.

Corrosion Testing Methodology

The corrosion resistance of the cladded hook claws is evaluated through multiple standardized testing methods:

1. Salt spray testing (ASTM B117): The cladded samples are exposed to a 5% NaCl solution at 35°C for 480-1,000 hours. The corrosion resistance is evaluated by measuring the corrosion rate, the extent of rust formation, and the integrity of the cladding layer.
2. Potentiodynamic polarization testing: The electrochemical behavior of the cladding layer is characterized by measuring the corrosion potential, passive current density, and pitting potential. These parameters indicate the thermodynamic stability and kinetic resistance of the cladding to corrosion.
3. Immersion testing: Samples are immersed in simulated service environments (e.g., dilute acid solutions, alkaline solutions) for extended periods. Weight loss measurements and surface examination provide quantitative and qualitative corrosion data.
4. Intergranular corrosion testing: For stainless steel cladding layers, intergranular corrosion susceptibility is evaluated using ASTM A262 Practice No. 1E (oxalic acid etching) or Practice No. 4E (65% boiling HNO3).

Results and Analysis

The oxy-acetylene cladding process produces overlay layers with the following characteristics:

1. Microstructure: The cladding layer microstructure consists of a dendritic structure with interdendritic segregation of alloying elements. The dilution rate is typically higher than in arc welding processes (25-40%), which can affect the final composition and corrosion resistance of the overlay.
2. Corrosion resistance: The cladding layer demonstrates significantly improved corrosion resistance compared to the bare base metal. In salt spray testing, the cladded samples show no visible rust formation for over 500 hours, compared to rust formation within 24-48 hours for uncladded steel.
3. Bond strength: The metallurgical bond between the cladding layer and base metal is verified through tensile or shear bond tests. The bond strength typically exceeds 150 MPa, which is adequate for the service conditions of hook claws.
4. Dilution effect: The relatively high dilution rate in oxy-acetylene cladding can reduce the corrosion resistance of the overlay if the dilution exceeds 40%. Multiple passes with progressive composition adjustment are recommended to achieve the target overlay composition.

Defects and Quality Control

Study Insights and Engineering Implications

This study demonstrates that oxy-acetylene flame cladding remains a viable and effective method for providing corrosion protection to complex-shaped components such as hook claws in nuclear power plant applications. The key advantage of this process is its flexibility and accessibility for components with intricate geometries where arc welding equipment may be impractical. However, the relatively high dilution rate inherent to flame cladding requires careful process control to ensure adequate corrosion resistance. Engineers working on nuclear fuel handling equipment should note that the corrosion performance of oxy-acetylene cladding is directly related to the dilution rate and the number of overlay passes. A systematic approach involving dilution monitoring, periodic chemical analysis, and corrosion testing is essential for maintaining the integrity of cladded components in service. The study also highlights the importance of selecting appropriate filler materials that provide adequate corrosion resistance even at elevated dilution levels, such as high-alloy Ni-based or Co-based alloys that maintain their protective properties across a range of compositions.

In conclusion, these five technical studies collectively represent a comprehensive cross-section of cladding and bimetal technology challenges spanning from mining equipment wear protection to nuclear fuel handling component corrosion resistance, from aluminum alloy surface engineering to high-temperature exhaust valve failure analysis, and from fracture mechanics-based integrity assessment to traditional flame cladding applications. Each study addresses a distinct engineering problem while sharing common themes of process parameter optimization, dilution control, defect prevention, and quality assurance. The engineering lessons drawn from these diverse applications reinforce the fundamental principle that successful cladding technology requires a deep understanding of the interaction between process parameters, material properties, service conditions, and quality control measures. For practitioners in the field of cladding, bimetal manufacturing, and pressure vessel fabrication, these studies provide valuable technical references and methodological frameworks that can be adapted to address similar challenges in their respective domains.