Research On Several Techniques Of Pulsed Eddy Current Testing Of Ferromagnetic Metal Pipeline Under Insulation

The insulated ferromagnetic industrial pipes are widely used in the oil,nuclear industry,chemical industry and electric power industries.Pipeline operation in harsh conditions for a long time,easy to cause pipeline wall thickness thinning,leading to failure.Therefore,it is of great significance to carry out periodic inspection and testing of the insulated industrial pipes.In the past for industrial insulation pipeline safety testing,Ultrasonic testing requires removal insulation,Guided wave testing requires partial removal the insulation and the Radiation testing needs special radiation safety protection range.All the above testing methods need to stop the machine for inspection.So the testing costs are high and low efficiency.In recent years,the new Pulse Eddy Current Testing technology has a series of advantages such as non-disassembly,rapid testing operation without stopping,and low cost,etc.,which can effectively detect the reduction of the wall thickness of the insulation Industrial pipeline.This dissertation focuses on several technical problems existing in pulsed eddy current testing with insulation ferromagnetic pipes.Firstly,using the method of testing to study the effects of an adjacent pipeline in the around the insulation pipe.Based on this,this paper use a self designed metal electromagnetic shield.to apply it on the probe to suppress the electromagnetic interference from the adjacent metal pipes,and studied the effect of electromagnetic interference suppression.The results show that the application of metal electromagnetic shielding cover to the testing probe can effectively reduce the distance affected by adjacent pipes.Although the sensitivity of pulsed eddy current testing with insulation pipe is decreased,but the decrease range is acceptable.Secondly,by using experimental means,the pulse eddy current testing technology for the testing thinning of the thickness quantitative of the insulation pipe was studied.Processing related specimen and tested by pulsed eddy current testing technology.The corresponding relationship between the measured voltage amplitude and the thickness of the metal wall thickness(such as thickness,the length of the defect and the width)was analyzed.Using the polynomial function and single exponential decay curve fitting method to calculate,and compared those two kinds of calculation methods.By using the fitting curve,the quantitative testing of thin defects in the wall thickness of the insulated pipes is realized.Thirdly,a set of self-built pulsed eddy current testing system platform withpartial thickness thinning for insulation ferromagnetic pipe is constructed by this paper.Combined with the laboratory and the actual industrial field,a test method based on the left and right symmetry of the detection voltage amplitude is proposed to identify whether there is any corrosion defect in the elbow of the pipeline.The fourth,this paper carried out the actual online non-stop testing of insulation pipes in a chemical area in ningbo city,zhejiang province.The testing results of the elbow under insulation in the field show that by observing whether the detected voltage amplitude has left-right symmetry,it can be effectively judged whether there is a local wall thickness thinning defect at the insulation pipe elbow.At the same time,the test results of the straight pipeline under insulation show that due to the existence of double overlap of the galvanized iron sheet at the joints of the protective layer,a distorted signal was generated,which caused a certain impact on the on-site inspection results.Finally,the paper discusses further work that needs improvement.