THICKNESS EVALUATION OF INSULATED PIPELINES AND PRESSURE VESSELS USING PULSED EDDY CURRENT TECHNOLOGY

Information about integrity of pipelines and pressure vessels is vital to the oil and gas industry. This emphasizes the need for fast and cost effective non-destructive testing solutions for monitoring and inspection of these components. However, due to reasons such as corrosion protection and temperature maintenance, pipelines and pressure vessels are usually coated throughout the oil and gas industry. These coatings also present a barrier to inspections and typically need to be removed prior to inspection with nondestructive evaluation (NDE) methods. This article presents a pulsed eddy current (PEC) system suitable for nondestructive evaluation of steel pipelines and pressure vessels without the need for removing the coating layers. A PEC probe was fabricated and a custom computer code with built in signal processing and data analysis functions was developed to collect the measurement signals and calculate thickness variations in the test objects. From a lift-off distance of 12mm, experiments were performed on eight SS304 stainless steel samples with thicknesses ranging from 1mm to 8mm. The SS304 steel was chosen as the test material to represent the steel type commonly used in the pipeline industry. A calibration curve based on the zero crossing time of initial measurements was obtained and implemented into the measurement software. Using the calibrated system, 25 measurements where performed on each sample. Statistical analysis of results showed that the proposed system can accurately detect thickness variations in the test samples with maximum measurement error of 3.3 percent.