L51630 In-Line Detection and Sizing of Stress Corrosion Cracks Using EMAT Ultrasonics

The development of stress corrosion cracks (SCC) in buried gas pipelineshas posed a serious threat to pipeline integrity for many years. It can be reliably detected by magnetic particle techniques in the field or by laboratory studies using low frequency eddy currents. It is also possible to find and measure the depths of the cracks from the ID by careful scanning with an ultra-sonic angle beam probe but the transducer must be manipulated by a skilled operator. All of these approaches are not very satisfactory for in-line inspections because they are not suitable for covering the total area of a pipeline and they are too labor intensive to be automated. In order to address this problem with new technology, the PRCI requested proposals for any technique that seemed to be practical and the Electromagnetic Acoustic Transducer (EMAT) was suggested as very promising because it has already demonstrated operation in the environment of the inside of a gas pipeline. Magnasonics, Inc., of Albuquerque, New Mexico, was chosen from many respondents to conduct an in-vestigation of the use of EMATs for overcoming the problems expected to arise from in-line operation and to incorporate the latest developments in ultrasonic inspection with EMATs. The objective of the program described in this report was twofold. First, to apply the most recent developments in EMAT technology to the problem of detecting and sizing stress corrosion cracks (SCC) in operating gas pipelines and second to exploit the ability of EMATs to generate and detect a wide variety of ultrasonic waves in the walls of a pipeline under operating conditions.