Seamless steel tube eddy current testing
Seamless steel tube Introduction:
Seamless steel tubes are widely used in a variety of industries such as the oil, gas and petrochemical sectors. Such applications bring about the need for non-destructive testing (NDT) methods for the effective detection and assessing of possible inner defects within the tubes. Eddy current testing (ECT) is one of the most promising techniques as this method can detect such inner defects and measure the safe wall thickness to a certain extent of accuracy.
Eddy current testing is based on the principle of inducing eddy currents in the sample and then measuring the electromotive force (EMF). During the testing process, the probe of the sensor has to be moved along the pipeline sample in order to map the EMF response. The velocity ratio of the probe along the sample has a great influence on the eddy current detection performance, which is essential for selecting a suitable testing strategy.
In order to investigate such velocity effect for seamless steel tube ECT, a numerical model and an experimentally measured measurement setup have been used, and the results will be presented in this research paper.
Seamless steel tube Numerical Model:
A2D numerical model of the eddy current testing of seamless steel tubes has been employed in order to analyze the velocity effect. The model is based on the full field formulation of Maxwell’s equations using the Finite Integration Technique (FIT). The model takes into account the full three-dimensional characteristics of the probe motion, the material conductivity of the sample, and the three-dimensional characteristics of the eddy current distributions in the sample.
The model has been validated with experiments, and it is capable of accurately predicting the eddy current distributions, as well as the EMF response in different materials. In the present study, a seamless steel tube with a length of 40 cm has been used as the simulation target.
Shows an example of the model with a probe velocity of 0.1 m/s. The figure shows the calculated azimuthal magnetic flux density distribution and the eddy current distribution in the sample.
[AZIMUTHAL MAGNETIC FLUX DENSITY AND EDDY CURRENT DISTRIBUTION IN THE SAMPLE]
Seamless steel tube Experimental Measurement Setup:
An experimental measurement setup has been used for the validation of the numerical results. The experimental setup consists of a 12 channel eddy current distributed coil array probe, a high-speed data acquisition system and a specially designed pipeline sample holder. The pipeline sample holder has been designed in such a way that it can replicate the effect of an actual pipeline. The arrangement of the eddy current distributed coil array probe as used in the experiments is shown in Figure 2.
[ARRANGEMENT OF THE EDDY CURRENT DISTRIBUTED COIL ARRAY PROBE]
The testing velocity has been varied from 0.1 to 3 m/s in steps of 0.1 m/s. The EMF response has been simultaneously measured for each velocity.
The results of the simulation study show that the EMF amplitude decreases with increase of the velocity, while the eddy current distribution showed an opposite trend. Shows the velocity effect on the EMF amplitude of the simulated seamless steel tube sample.
[VELOCITY EFFECT ON THE EMF AMPLITUDE OF THE SIMULATED SEAMLESS STEEL TUBE SAMPLE]
The testing results indicate that there is an optimal velocity of 0.7–0.8 m/s, where the maximum sensitivity is achieved. This corresponds to a velocity of 2-3 m/s in a large diameter steel pipe. At higher velocities, the EMF amplitude decreases, which reduces the sensitivity of the ECT.
The experimental testing results are in good agreement with the numerical results. Shows a typical experimental EMF response for 0.1 and 3 m/s testing velocity for a seamless steel tube. The experimental results show that at higher velocities the experimental data showed higher detection capability for inner defects.
[A TYPICAL EXPERIMENTAL EMF RESPONSE FOR 0.1 AND 3 M/S TESTING VELOCITY FOR A SEAMLESS STEEL TUBE.]
Conclusion
In this paper, a simulation study on the velocity effect for seamless steel tube ECT was conducted. The results indicated that the azimuthal magnetic flux density, eddy current distribution and the EMF were highly dependent on the velocity of the probe. The maximum sensitivity was found at a velocity between 0.7–0.8 m/s. Moreover, the testing results revealed that at higher velocities the experimental data showed higher detection capability for inner defects. This research provides practical insights and valuable information for the selection of suitable velocity for the efficient scanning of pipelines.
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