Research On The Corroded Pipeline Based On Metal Magnetic Memory Testing

The pipeline is an important means of transporting energy. With the extensionof the pipeline in service time, there are a lot of holes and cracks by corrosion in thepipeline. The traditional non-destructive testing has some limitations, such asultrasonic testing and magnetic flux leakage testing, the former requires the pipesurface is smooth, the latter requires the magnetization device, they can’t directlydetect buried pipeline. Although it is possible to use the pipeline detection robot inthe pipe, domestic pipeline robot can only detect large-diameter pipe, and pipelinesneed to be destroyed, then implanted in the robot, the oil level of the pipeline alsohave certain requirements. Therefore, the traditional non-destructive testingtechnology is not suitable for detection of buried pipeline. The metal magneticmemory testing is a novel non-destructive testing technique, which made up for thedeficiencies of the traditional non-destructive testing methods. The metal magneticmemory method is based on use of the own magnetic leakage field, arising inferromagnetic and paramagnetic products on defect location. Under geomagneticfield, the nodes of magnetic domain appear and abnormal magnetic signals generatein the defect location. The metal magnetic memory is effective for detecting buriedpipelines. Currently, there is not the equipment which is used for detecting buriedpipelines in our country. However, the foreign equipment of metal magneticmemory is only to provide services and charge exorbitant fees, the technology isstrict blockaded and secrecy.The paper analyzed the method of metal magnetic memory, developeddetecting equipment. The sensor is the Honeywell magnetic sensor with highsensitivity which is used for collecting the weak magnetic signals. And designset/reset circuit and electromagnetic shielding to achieve anti-interference. Bylow-noise amplifier circuit amplifies the weak signals. PIC controls the data afterAD conversion in order to achieve the display, preservation, communication andother functions.The paper conduct research on the ground pipelines by the developedequipment. The sensor is to get a certain height to collect the magnetic signals ofthe ground pipelines. By analyzing the characteristics of the metal magneticmemory signals, the paper put forward the signal processing methods of wavelettransform to use for non-stationary random weak magnetic signal. By comparing avariety of wavelet de-noising method, the paper put forward with wavelet threshold de-noising to process the experimental datum. Practice shows that the verticaldirection of the signal after wavelet de-noising processing can display the defectlocations. In addition, the wavelet detail component and wavelet transformationenergy can be used to assist in judgment.Owing to the sensor is placed a high position, therefore there are manyinfluencing factors. The experiment studied the influence factors of the pipelinecoating, defect location, detecting height and speed. The paper points out pipelinecoating don’t impact on test results. And the paper determined the appropriate speedof detection, points out the defect location and detecting height greater impact ontest results. And the paper quantitatively analysis of the relationship with thegradient feature, provide help for the future detection of buried pipeline.