9. Phased array ultrasonic testing method for easy detection of flaws in bogie frame welds

Since the bogie frames of railway vehicles are fabricated with numerous welds, any flaws within welds can pose risks of serious damage. Conventional inspection methods require a high level of skill to detect flaws, however. In light of this, we formulated a method and procedure for detecting flaws in bogie frames based on the phased array ultrasonic testing (PAUT) method. The method is capable of easily detecting any flaws inside welds.

Unlike conventional ultrasonic testing methods, which transmit and receive ultrasonic waves at a fixed angle (conventional UT method), the PAUT method transmits and receives waves at various angles to obtain cross-sectional images that enable visualization of flaw detection results (Fig. 1). Since images are used to discern flaws, distinguishing flaw signals from noise due to the shape of welds is easy, greatly reducing the chances of missing flaws. And since ultrasonic waves can be directed at flaws from various angles, this method is also effective in detecting inclined flaws with an inclination of 30°or more, which are typically difficult to detect using the conventional UT method (Fig. 2). Although detecting flaws in bogie frames is usually performed after removing the coating, our analysis has shown that even when this inspection method is applied without removing the coating, detection sensitivity is reduced by no more than 20% for coating thicknesses up to 1 mm.

With the conventional UT method, the flaw detection procedure is based on the Japanese Industrial Standard (JIS) “Method for ultrasonic testing for welds of ferritic steel.” In the newly developed PAUT method procedure, a sensitivity adjustment procedure based on the same standard flaw as used in the JIS method, enables a flaw detection sensitivity equal to or better than the conventional UT method. Since flaw detection results with the new PAUT method are comparable to those of the conventional UT method, transition to the new method is easy.

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