Development of an Emat in-Line Inspection System for Detection, Discrimination, and Grading of Stress Corrosion Cracking in Pipelines

Abstract

Abstract:This report describes progress, experiments, and results for a project to develop a pipeline inline inspection tool that uses electromagnetic acoustic transducers (EMATs) to detect and grade stress corrosion cracking (SCC). There is a brief introduction that gives background material about EMATs and relevant previous Tuboscope work toward a tool. This work left various choices about the modes and transducers for this project.The experimental section then describes the lab systems, improvements to these systems, and setups and techniques to narrow the choices. Improvements, which involved transducer matching networks, better magnetic biasing, and lower noise electronics, led to improved signal to noise (SNR) levels. The setups permitted transducer characterizations and interaction measurements in plates with man-made cracks, pipeline sections with SCC, and a full pipe with SCC. The latter were done with a moveable and compact EMAT setup, called a lab mouse, which is detailed.Next, the results section justifies the mode and transducer choices. These were for magnetostrictive EMATs and the use of EMAT launched modes: SH0 (at 2.1 MHz-mm) and SV1 (at 3.9 MHz-mm). This section then gives details of measurements on these modes. The measurements consisted of signal to noise ratio, insertion loss, magnetic biasing sensitivities crack reflection and transmission coefficients, beam width, standoff and tilt sensitivities. For most of the measurements the section presents analysis curves, such as reflection coefficient versus crack depth. Some notable results for the chosen modes are: that acceptable SNRs were generated in a pipe with magnetostrictive EMATs, that optimum bias for magnetostrictive transmitters and receivers is magnetic saturation, that crack reflection and transmission coefficients from crack interactions agree with 2 D simulations and seem workable for crack grading, and that the mouse has good waveform quality and so is ready for exhaustive measurement EMAT scans of SCC interactions. This section also reviews further coil optimisation and implementation requirements. These involve transmitter and receiver power, acquisition parameters, and magnetic configuration. At this time all these seem reasonable for an ILI tool.