Characteristics of Corrosion Damage under the Deposition in a Boiler Water-cooled Wall Tubes and its Ultrasonic Testing Technique
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摘要: 通过金相、扫描电镜、超声波检测等试验，对某锅炉20 G钢水冷壁管内壁介质沉积物下腐蚀损伤特征及其超声技术进行分析。结果表明：水冷壁管内壁沉积物下腐蚀产物氢元素与钢中渗碳体反应，造成内部组织脱碳、空隙，沿晶产生裂纹并扩展，材料力学性能降低。横波超声检测对水冷壁氢腐蚀裂纹比较敏感，5 MHz、K1及小晶片尺寸的横波探头能对材质损伤裂纹进行可靠检测，根据超声检测波形特征及缺陷回波波幅当量值，能很好地反映其氢腐蚀及裂纹扩展程度。Abstract: The steam-side corrosion damage characterization and ultrasonic testing technique of the internal surface of water-cooled wall tube made of 20G steel removed from boiler of some power plant had been investigated by metallurgic inspection, scanning electron microscope-energy dispersive and other tests. The examination results showed that the reaction process of hydrogen and cementite in grain boundary caused decarburization of water-cooled wall tube, void fraction and grain boundary cracks initiation and propagation, and mechanical performance degradation. Due to the fact that the ultrasonic transverse wave is sensitive to the hydrogen corrosion cracks, small chip size of transverse wave probe of K1, 5MHz frequency is used to test the corrosion grain boundary cracks, showing high reliability. The wave form characteristics of the echo by hydrogen corrosion cracks in the samples and its equivalent amplitude can be used to assess the degree of hydrogen corrosion cracks.
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