Infrared and Laser Engineering, Volume. 54, Issue 6, 20250053(2025)

Research onstructural damage detection technology of small-diameter nozzles of pressure vessels based on induction thermography

Wenpei ZHENG1,2,3, Xiaoru SUN1,2,3、*, and Zikai WANG1,2,3
Author Affiliations
  • 1College of Safety and Ocean Engineering, China University of Petroleum (Beijing), Beijing 102249, China
  • 2Key Laboratory of Oil and Gas Safety and Emergency Technology, Ministry of Emergency Management, Beijing 102249, China
  • 3Key Laboratory of Oil and Gas Production Equipment Quality Inspection and Health Diagnosis, State Administration for Market Regulation, Beijing 102249, China
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    ObjectiveThe welding joints of small-diameter nozzles of pressure vessels usually have complex structures and groove types. During the production and manufacturing process, defects such as porosity, lack of penetration, and lack of fusion are prone to occur, which can easily cause stress concentration, resulting in fatigue cracks, leakage, and even explosion accidents. Structural damage detection of small-diameter nozzles is of great significance for the safe service of pressure vessels. However, the current technology applied to the welding seam detection of small-diameter nozzles of pressure vessels is limited by the special structure of small-diameter nozzles and the high requirements for surface quality. Therefore, the detection effect is limited. Research on detection technology suitable for the complex structure, poor surface quality, and narrow space of small-diameter nozzles is of great significance for effectively evaluating the safety status of small-diameter nozzles. Eddy current thermography detection can detect objects within a large field of view from a distance, especially suitable for complex structures such as small-diameter nozzles of pressure vessels.MethodsBased on the principle of eddy current thermography (Fig.1), a small-diameter nozzle of a pressure vessel model and an excitation coil model were constructed using SolidWorks (Fig.4-Fig.5). Using COMSOL finite element software for electromagnetic thermal coupling simulation analysis, the temperature distribution around the weld defect of the small-diameter nozzle under the excitation of the arc-shaped double coil and the adaptability of the coil are studied. Exploring the thermography method for small-diameter nozzle defects in pressure vessels using the intersecting line scanning mode in simulation, achieving intelligent detection of defect signals in the intersecting line dimension, and laying the foundation for the industrial application of this technology. Meanwhile, an eddy current thermography experimental simulation system was set up in the laboratory to simulate the welding defects of small-diameter nozzles of pressure vessels (Fig.13), and the results were compared with the simulation for verification. Finally, using MATLAB to extract grayscale and pixel positions from the thermal imaging results, thus completing the quantitative evaluation and detection of defect length.Results and DiscussionsThrough COMSOL simulation, it can be concluded that under static inspection, the temperature difference between the defective area and the non-defective area of the small-diameter nozzle weld seam in the pressure vessel can reach a maximum of 10 ℃ or more (Fig.8), therefore the effect is good. In the dynamic detection of intersecting line scanning mode, defects of different sizes showed significant temperature changes, and the highest heating temperature could reach 283 ℃ (Fig.12). The laboratory has set up an eddy current thermal imaging detection system, and through actual simulation under non ideal conditions, the temperature in the defect area has increased by about 5 ℃ (Fig.18). The above research results indicate that eddy current thermography technology can meet the demand for defect detection of small-diameter nozzle welds in pressure vessels. The quantitative evaluation of defect length was achieved through MATLAB and related formulas. The calculated values of defect length were 7.74 mm and 3.91 mm, respectively, with errors of 3.25% and 2.25% compared to the actual length.ConclusionsBased on eddy current thermography technology, a new type of excitation coil suitable for defect detection of small-diameter nozzle welds in pressure vessels was designed. Through COMSOL simulation, it was found that when the excitation coil heats the defect, the temperature change in the defect area is significant, and the defect causes disturbance in the induced eddy current, mainly concentrated at the two ends of the defect, forming the high-temperature zones. And completed the intersection line scanning mode of thermography along the spatial curve for detecting small diameter nozzle defects in pressure vessels. Preliminary verification has been conducted on the effectiveness of eddy current thermography technology in detecting small diameter nozzle welds in pressure vessels. In the experimental simulation, the heating effect of the excitation coil on small-diameter nozzle welds defects is significant, and the existence of defects can be effectively detected. This indicates that the arc-shaped double coil has good applicability to the welding seam of small-diameter nozzle, and verifies the effectiveness of eddy current thermography technology in the detection of welding seams of small-diameter nozzle in pressure vessels. By using MATLAB to extract grayscale and pixel positions from thermal imaging images, quantitative evaluation and detection of the length of small-diameter weld defects in pressure vessels have been achieved.

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    Wenpei ZHENG, Xiaoru SUN, Zikai WANG. Research onstructural damage detection technology of small-diameter nozzles of pressure vessels based on induction thermography[J]. Infrared and Laser Engineering, 2025, 54(6): 20250053

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    Paper Information

    Category: Infrared

    Received: Jan. 16, 2025

    Accepted: --

    Published Online: Jul. 1, 2025

    The Author Email: Xiaoru SUN (2023215847@student.cup.edu.cn)

    DOI:10.3788/IRLA20250053

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