Research On Magnetic Flux Leakage And Electromagnetic Acoustic Hybrid Inspecting System Of Boiler Water-wall Tubes

The water-wall is known as the most important evaporating heating area inside the boiler.Due to the harsh service environment, the water-wall tubes are prone to serious accidents.Therefore, the in-service inspection on water-wall tubes is of great significance to ensure thesafe running of boilers. Based on the support of the National Natural Science Foundation ofChina (Grant No.51077059) and the National Key Technology Research and DevelopmentProgram of the Ministry of Science and Technology of China (Grant No.2011BAK06B04),the non-destructive testing (NDT) method and system for boiler water-wall tubes are studiedin this dissertation.Firstly, according to the inspection environment and defect features of boiler water-walltubes, a hybrid testing method which uses magnetic flux leakage (MFL) for local corrosionand electromagnetic acoustic transducer (EMAT) for wall thickness measurement, ispresented by analyzing these two testing methods comprehensively. Moreover, the keytechniques such as the magnetizer used in MFL and the EMAT coil type are studied, whichdemonstrate the feasibility of this hybrid method. This method is also proved a non-contacttesting way and easy to realize automation.Secondly, based on the hybrid testing method, the hardware of the inspecting system isdeveloped, which contains MFL sensor, the EMAT sensor, the crawler carrying sensorsupward and the EMAT thickness measurement set-up based on HS805virtual oscilloscope.The kinematic simulation of the clawer is also performed using a commercial softwarepackage named ADAMS.Finally, the software for EMAT thickness measurement is developed and the systemcomponents are integrated. Laboratory experiments are carried out to verify the performanceof the testing system. Results show that this system can climb up the erecting water-wall tubesand get over obstacles up to5mm height. The inspection component can detect the concavepit of3.2mm in diameter and1.5mm in depth on the inner surface of pipe wall and theaccuracy of wall thickness measurement is up to±0.1mm.