Abstract
Eddy current transducer with sensing coils placed orthogonally and connected in differential mode was introduced to evaluate fatigue cracks in clad pipeline circumferential welds. A dedicated embedded electronic hardware was developed to drive the transducer and measure the electrical complex impedance of the coils, and was specifically designed for operation under autonomous in-line inspection tool. In the laboratory experiments, an automated inspection was performed with the goal to evaluate transducer’s detectability, and different scanning speed was tested to reproduce in service situation. The results have confirmed that the introduced eddy current transducer is a potential solution for fatigue crack detection in clad circumferential weld root, while the hardware developed presented a reasonable SNR reaching the data rate required to be incorporated in an autonomous in-line inspection tool.
Highlights
The application of clad material to subsea pipelines is gaining ground in deep water oil exploration.Its bimetallic configuration presents an attractive combination of mechanical strength and corrosion resistance, ensuring the safety and integrity of pipelines that connect the reservoir to oil rig
The potential for fatigue cracks to occur in pipeline structures due to cycling loads inherent of offshore oil production makes it necessary to have an inspection tool to carry out periodic nondestructive inspection in the inner pipe surface
In case of clad material, it is crucial to detect fatigue crack on its initial stage, because if the crack propagates through the layer of the corrosion resistance alloy (CRA) and reaches the carbon steel, a strong galvanic couple is completed, accelerating, exponentially, the fatigue corrosion process [2]
Summary
The application of clad material to subsea pipelines is gaining ground in deep water oil exploration. The authors highlighted, in their conclusions, that the application of such a technique in in-line inspection tools is still a challenge Such a challenge gets even more complex in the case of clad material inspection, where the anti-corrosive layer results in an additional interface for the ultrasonic wave propagation, interfering directly in the incident and refracted wave. Once the ultrasound wave is sensitive to grain structures [10], Inconel welds significantly scatter the waves so that clear echoes due to defects cannot always be noticed Such challenges motivate the feasibility study of an in-line inspect tool development to detect fatigue cracks in the circumferential welds of clad pipelines based on eddy current concept. The goal of the present work is evaluating the capability of an EC transducer to successfully meet the previously described requirements: detect fatigue cracks in the circumferential weld root of clad pipelines when operating at different inspection speed. The results achieved demonstrated that the orthogonal EC configuration is a potential solution for fatigue crack detection on circumferential weld root of clad pipelines
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