Study On The Inspection Mechanism And Methods Of Pulsed Eddy Current Testing In Pipelines Corrosion Under Insulation

The insulated ferromagnetic pipes are widely used in oil and chemical industry.However, the pipes clad become thinner and thinner due to work condition andprocessing technique, and the nondestructive testing of ferromagnetic pipes’ corrosionunder insulation is always a difficult detection problem. The clad needs to be removedfirst to go on with traditional ultrasonic detection method, which is a time-consumedand expensive procedure. While radiography detection method needs safeguard becauseof potentially hazardous, and it costs too much. Guided wave, as an arisen techniquerecently, is applied because of long-distance detection and efficiency. The negative thingis that guided wave technique not only requires removing insulation partly, also theaccuracy is not high for the pipes’ average area of corrosion. This paper introduces thatpulsed eddy current testing, an emerging technology in recent years, solves the detectionproblem of ferromagnetic pipes corrosion under insulation, improving efficiency ofdetection and accuracy of ferromagnetic pipes corrosion under insulation.On the basis of summarizing the development of pulsed eddy current inspection inferromagnetic pipelines corrosion under insulation home and abroad, it studies thetheory and method of pulsed eddy current testing technology in testing insulatedferromagnetic pipes on area and local corrosion. Firstly, simulation model is establishedby finite element analysis software ANSYS. The vector distribution direction ofmagnetic field and eddy current field stimulated by probe is analyzed in insulated pipes.Two sensor probes are simulated according to area and local corrosion. The simulationresults of these two probes are analyzed in detecting pipe corrosion under insulation.Secondly, a series of experiments are designed making reference to simulation results.Area corrosion and local flute defects are processed simulatively in J55ferromagneticpipe and ordinary-carbon steel pipe. Single coil excitation and double coil currentreverse incentive sensors are made. In certain detection parameter, these two steel pipesin different sizes and with different corrosion defects are detected. Thirdly, the cutawaydrawing of induced voltage time on receiving coil sensor is got by data processing.Then the corrosion on insulated pipe can be observed from the cutaway drawing. Finally,through detecting the corrosion of ferromagnetic pipes insulated with different thickness,sensitivity changes are analyzed with the help of pulsed eddy current. And detection performance of those two sensor probes is also compared.The results of the thesis show that1mm area corrosion defect on insulated pipe that pipeline wall thickness8mm with maximum thickness300mm and local narrow flute corrosion defect (1mm in depth and5mm in width) with maximum thickness150mm and pipeline wall thickness8mm can be detected effectively with appropriate testing parameters.