A large-scale equipment of a famous refining and chemical company of China had to be temporarily shut down for repairing, because one of its fractionation bottom reboiler tubes was suspected to leak. These tube bundles are densely distributed, and the outer casing of the reboiler is the fixed structure which can not be opened to check these tubes unless it is cut. The outer casing cutting for checking is very time-consuming (about 1–2 months) and costly. Possible pipe guided wave technology or endoscope method also can not be used because of acoustic attenuation from dense fins and severe corrosion of tubes or being inaccessible, so Acoustic Emission testing became the only choice for finding out the leaking tube in that time.
Also due to the significant acoustic attenuation, the traditional Acoustic Emission linear positioning method is difficult to find out leaked tubes, so the zonal localization method of acoustic sources was predominant in this test. The hydraulic test of pipelines was used to stimulate acoustic signals from leaking sources. However, the water from leaking holes will be splashed to the adjacent pipes and then drop onto pipes below, which will cause false leaking signals. For finding out the leaked tube, logic method is adopted to infer the real leaked tube complementarily. The spatial positions of all tubes and the sequences, frequencies, amplitudes and total hits of acoustic signals from all tubes monitored are considered in the analysis. Finally, the leaked tube was successfully found out in half a day by the combination of Acoustic Emission testing and logic analysis, the leaked tube was replaced and the production was resumed in the next three days.
Monitoring steel corrosion by using the combination of ultrasonic guided wave and acoustic emission
