Determining Internal Local Corrosion of Screwed Pipes Through Ultrasonic Testing

In diagnosing air-conditioning pipe deterioration, it is especially important to inspect screwed parts because their original thickness is thinner than that of straight parts and it is comparatively easy for leakage to occur if there is local internal corrosion. Usually, a radiographic test is used, but this method requires a licensed person to carry out the inspection. We examined a method of applying an ultrasonic test for the inspection, and proposed a method for detecting internal local corrosions of screwed parts and estimating the size of corrosion with surface SH waves.

In this paper, we propose a method for detecting internal local corrosion of screwed parts of air-conditioning pipes with ultrasonic testing. The objective of the first step is to detect artificial corrosion and estimate its size and position. It is impossible to detect corrosion with a normal probe because a joint or valve overlapping the screwed pipe prevents ultrasonic waves from reaching the inside. Therefore, we used an angle probe, specifically a surface SH wave angle probe, because the thickness of the pipes requires a large angle of incidence, close to a right angle.

We describe the following in this paper:

• The results of experimental analysis on the echo from screwed parts of pipes.
• The method used to detect local corrosion and estimate the size and position by using the pipe-end echo.
• The results of tests on artificial corrosion pipes and the limitations of this method.