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  • Vol. 54  期 6, 2024 2024年 54卷 第6期
    • Important Issuse

      SUN Jian,ZHU Yi,LIU Qing,LIU Fuguang,LIN He,LIU Hui,CHENG Xiaole

      DOI:10.7512/j.issn.1001-2303.2024.06.01
      摘要:Dissimilar steel welding is extensively applied in subcritical boilers, where the performance of the welded joint directly impacts the boiler's operational safety and service life. This study focuses on the T22/TP304H dissimilar steel welded joint in boilers that have been in service for over 200 000 hours, analyzing the changes in its microstructure morphology and mechanical properties. The residual life of the joint is evaluated based on high-temperature endurance test results. Findings indicate that precipitate aggregation occurs in the TP304H base material and weld, which can easily induce the initiation of cracks in the welding area. The tensile strength of long-term operational joint samples is consistently lower than the minimum value required by ASME standards, indicating a significant decline in mechanical performance. The remaining life of the joint is 29 745 hours, but its operational reliability has significantly decreased. Thus, it is recommended to inspect and repair the joint area and intensify subsequent inspection work. This paper provides a theoretical reference for the study of T22/TP304H dissimilar steel welded joint structure and properties, and the safe operation of the equipment in the future.  
      关键词:T22/TP304H dissimilar steel;long-term service;mechanical properties degradation;remaining life assessment;maintenance strateg   
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      更新时间:2024-06-27
    • ZHAO Yijia,JIU Yongtao,YING Huiming,ZHANG Lei

      DOI:10.7512/j.issn.1001-2303.2024.06.02
      摘要:To investigate the in-situ reaction process of AgCuSn-based active brazing materials, this experiment mechanically mixed elemental powders of Ag,Cu, Sn, and Ti in various mass fraction ratios, with an appropriate amount of binder and water to form a brazing paste, which was then heated to different temperatures and maintained. The microstructure of the brazing material was characterized using Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS), and the in-situ reaction process was explored based on thermodynamic theory and diffusion theory. The results indicate that the in-situ reaction mainly occurs in three stages. In the first stage, the melting of Sn leads to the formation of binary intermetallic compounds Cu6Sn5 and Cu3Sn within the brazing material. In the second stage, at approximately 650 ℃ to 750 ℃, the brazing material begins to alloy, forming a ring-layered diffusion layer around the Ti metal powder, composed of CuTi binary intermetallic compounds. In the third stage, at around 850 ℃, the brazing material fully alloys, making full contact with the graphite substrate and forming a metallurgical bond.  
      关键词:AgCuSnTi quaternary brazing material;in-situ reaction;microstructure;metallurgical bond   
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      更新时间:2024-06-27
    • LIU Benyou,GU Yu,PAN Jiajing

      DOI:10.7512/j.issn.1001-2303.2024.06.03
      摘要:Ultrasonic Lamb waves are one of the commonly used ultrasonic waves in the field of steel structure inspection and non-destructive testing, widely used because of their long propagation distance and the ability to carry overall structural information through point-to-point detection. Welded plate welds are prone to defects such as cracks due to changes in welding stress and other mechanical parameters, making them difficult to detect. Therefore, the propagation mechanism of Lamb waves in the structure of welded fillet welds and the interaction between damage and Lamb waves can be studied through finite element simulation. By setting up the excitation source in the piezoelectric ceramic model, the signal is emitted through the excitation source. Since the signal will be affected by some uncertain factors such as overlap and refraction during transmission, a method of setting up equidistant dual receiving points for signal reception is adopted. It is concluded that when the ultrasonic Lamb wave does not encounter damage in the welding angle, it propagates uniformly along the set route, following the Lamb wave spectrum, with stable amplitude strength and period. By setting an acceptable signal, the impact of different crack depths on detection can be compared, and a rule is derived that the amplitude is directly proportional to the crack depth. The wave packet of the ultrasonic Lamb wave is stable, and its flight time can be calculated through the amplitude. When the depth of damage changes, the amplitude of the ultrasonic Lamb wave will increase as the depth increases, and finally tend to a maximum value, which lays a solid foundation for the study of damage location methods.  
      关键词:ultrasonic lamb wave;defects;damage;simulation   
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      更新时间:2024-06-27
    • SHE Zongyu,WU Qingning,WU Qingfu,LIU Zongyuan,WU Guoyao

      DOI:10.7512/j.issn.1001-2303.2024.06.04
      摘要:This article is based on the elastic-plastic theory and introduces the stress state of ultra large welding drums under different loads. The strength verification formula of ultra large welding drums is obtained, providing theoretical guidance for the design of drum wall thickness. In addition, research was conducted on the welding process of the cylinder body and the outer flange plate assembly of the ultra large welding drum. The research showed that the cylinder welding joint obtained by alternating welding of the inner and outer grooves in a ratio of 1/4 has excellent comprehensive mechanical properties. The use of short weld seam segmented welding ensures the assembly welding strength and verticality requirements of the outer flange plate of the drum by correcting the alternating welding sequence on both sides.  
      关键词:welding drum;strength checking;welding deformation;welding process   
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      更新时间:2024-06-27
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