Review of the state of the art in EMAT technology as applied to the petrochemical industry

The petrochemical and chemical process industry utilizes a large number of high-temperature processes (up to 1200 degrees F). This means that their giants must have piping and pressure vessel systems that can operate safely at these high temperatures. Since safety is a key issue in the industry, it is imperative to periodically inspect the piping and pressure vessel systems to verify that safe operational standards have been met. One inspection method often used is ultrasonics. However, conventional ultrasonics cannot be applied at these high temperatures, so the systems are usually shut down for inspection. The industry would like to be able to conduct inspections at high temperatures. A sensor technology called Electro-Magnetic Acoustic Transducers (EMATs) has the potential to insert ultrasonic waves into metal through electromagnetic coupling. This technology has had no proven track record even though a number of so called "fieldable" EMAT systems exist. The Materials Technology Institute (MTI) believed that EMAT technology has sufficient potential to justify an unbiased review of the state of the art to detect corrosion-type defects and wall thinning. Southwest Research Institute was funded by MTI to (1) contact a large number of EMAT vendors (total of 13), (2) develop a testing protocol, (3) develop test specimens for both ambient and high-temperature testing, (4) assist the various EMAT vendors in conducting the tests at SwRI, and (5) report the results. The purpose of this paper is to discuss the testing that was conducted, the results obtained, and summarize the present state of the art in EMAT technology in terms of ultrasonic thickness resolution, corrosion defect detection, and fieldability at high temperatures.