Inspection Of Delamination And Liner Wall Thickness Of Bimetallic Tubing Using Pulsed Eddy Current Technique

Mechanical bimetallic tubing has been widely used in the onshore and offshore oil and gas transportation due to its excellent corrosion resistance and mechanical properties.However,it is prone to the interlayer debonding and the liner wall unevenness during the manufacturing process,which would seriously degrade its mechanical properties and service life.Therefore,to ensure its reliable quality and service life,it is necessary to use Non-Destructive Testing(NDT)methods to test the integrity of the bimetallic tubing before its sale.Traditional Ultrasonic Testing(UT)and Magnetic Flux Leakage Testing(MFLT)techniques are usually used to inspect the defects or measure the wall thickness in common single-layer pipelines,but turn out to be barely applied for evaluating the bonding quality of bimetal tubing.Limited by skin effect,Eddy Current Testing(ECT)technology is mainly used for inspecting surface defects in metal workpieces.Pulsed Eddy Current Testing(PECT)technology has been widely used in the inspection of deep defects due to its deep penetration depth and high instantaneous power.It shows the potential to provide a novel solution for the integrity testing of bimetallic tubing.This thesis serves as an exploratory research on the inspection of delamination and liner wall thickness of bimetal tubing.The main contents are as follows:(1)The bimetal tubing was equivalent to a four-layer plate structure.Based on the DoddDeeds ECT model,the time-domain analytical model of the layered gap and liner wall thickness of the bimetal tubing was constructed by using the Fast Fourier Transform-Inverse Fast Fourier Transform(FFT-IFFT)method and Truncated Region Eigenfunction Expansion(TREE)method.By using this model,the induced voltage signal of the PECT probe can be obtained rapidly,which provides an efficient algorithm for solving the positive problem of the PECT of bimetal tubing.(2)The waveform characteristics of PECT signal of bimetal tubing were analyzed,and the signal difference approach based on the testing signal of non-failed bimetal tubing was determined.On this basis,the influence of excitation parameters and probe structural parameters on the induced voltage signal were studied,and the parameters were optimized with the bimetal tubing of 10 mm thick carbon steel outer pipe and 4 mm thick liner as the detection object.(3)The change rules of PECT signal features including peak value,time to peak and timeto-zero crossing(TZC)against the liner wall thickness and the interlayer gap were respectively studied.From the perspectives of enhancing the probe's sensitivity and reducing the lift-off effect,the time to negative peak(TNP)was selected as the signal feature for the quantitative evaluation of liner wall thickness and interlayer gap.Results showed that the TNP appeared later as the liner wall thickness and the interlayer gap increased and was slightly affected by the probe lift-off variation,thus qualifying as the signal feature for evaluating the liner wall thickness and the interlayer gap.(4)A PECT probe was made and a PECT platform was set up for experiment verification.The experimental results shows that the characteristic changes of the detection signal has the same rule with the calculation result of the analytical model,which verified the correctness of the analytical model of the bimetallic tubing PECT,and also proved the feasibility of using PECT technology to test the layered gap and liner wall thickness of bimetallic tubing.This thesis extends the application of PECT technology and provides a novel NDT method for the before-sale quality check of the mechanically bonded bimetallic tubing.