Sizing Stress Corrosion Cracking Using Laser Ultrasonics

Managing Stress Corrosion Cracking (SCC) damaged pipe has been a formidable challenge to the pipeline industry. Development of a practical solution for measurement and evaluation of SCC has been marred by the complexity of crack shapes, their distribution within a crack colony, and the lack of non-destructive technology capable of reliably measuring the crack depths. Laser Ultrasonics is an inspection technology wherein lasers are used for generation and detection of ultrasonic waves in the pipeline steel to be inspected. Unlike conventional ultrasonic testing, Laser Ultrasonics has a large frequency bandwidth and a tiny (∼0.5mm) footprint. These characteristics make it ideally suited for application as a depth sizing tool for closely-spaced cracks in a colony. It has been conclusively proved that laser ultrasonic inspection using the time of flight diffraction (TOFD) technique can reliably and accurately measure the depth of naturally occurring SCC and potentially other cracks and seam weld anomalies. This presentation describes the results of this co-sponsored project, including recent full scale demonstrations where a laser ultrasonic measurement subsystem has been built onto a prototype scanner.