Study On On-line Ultrasonic Detecting System Of Ductile Iron Pipe's Thickness And Spheroidization Rate

Since the coming out in 1974, it has been widely used as materials of mechanical engineering because the extensive adaptability and excellent technical performance. Because it's superior corrosion resistance, strength and toughness ductile iron pipe can withstand high water pressure, soil pressure and ground load which make the use of safe and reliable. Ductile iron pipe can make the transmission distance extended and can laid underground pipelines in adverse conditions, so widely used in water, oil and gas pipelines. Ductile iron pipes used in transportation and underground installation, often to withstand impact and soil pressure, in addition, the pipe used to eliminate sewage also often be corroded by acid wastewater. So quality testing of ductile iron pipes is very necessary, and the testing of thickness and spheroidization rate is particularly important. Thickness uneven or local thin easily cause drop of the local bearing capacity, which make the pipe burst accident easily happen. Spheroidization rate directly influence the mechanical properties of the ductile iron, it is to the main index to measure the quality of ductile iron.Thickness of the tube's two terminals can be measured with measuring tools, but intermediate part is difficult to measure. Evaluation of spheroidization rate now are mostly random sampling pieces of samples at the pipe ends, judge their spheroidization rate by metallographic experiment, and sampling test results represent the of the whole batch pipes. The testing results can not reflect the whole pipe's real thickness and spheroidization, so can not guarantee the use reliability of the whole pipe. Test methods can not guarantee the reliability of the whole pipes, and need to use manual operation, which waste of time and materials.The ultrasonic on-line detection device we developed, can online measure each point's thickness and spheroidization rate of the ductile iron pipes. Measuring the thickness by reflection method. Measuring the ultrasonic velocity by transmission method, and then based on the linear relationship of velocity and spheroidization rate, calculated this point's spheroidization rate. Measuring results can be intuitive and real-time display on the screen.From the experimental results of laboratory and preliminary actual testing, the ultrasonic on-line detection device can full-length, automatic, fast measure the ductile thickness and spheroidization rate of the iron. Stability and accuracy is good. Because of the surface coarse of ductile iron pipe's external surface is larger and the internal surface may exist defect of dreg. Rough surface influence the thickness accuracy. In this paper, the law of the surface coarse influences on the pulse-width, the peak location and the thickness measured with ultrasonic method are summarized. This not only have very important meaning for the on-line detection of ductile iron but also has guiding significance for ultrasonic thickness of all kind of rough surface materials.