Sizing Stress Corrosion Cracking in Natural Gas Pipelines Using Phased Array Ultrasound

Gas transmission pipelines are inspected periodically by robotic systems that pass through the pipe. These inspection systems typically use electromagnetic nondestructive evaluation (NDE) techniques to detect flaws such as stress corrosion cracking (SCC). The electromagnetic techniques can detect and measure the length of the cracks, but cannot measure through wall depths. In some cases it would be desirable to excavate down to a cracked area of the pipe, inspect it “in the ditch” to determine the depth of the cracking, and use the depth information to support repair/replacement decisions. The objective of the research was to develop a nondestructive inspection technique capable of measuring the depth of stress corrosion cracks from the outside surface of a gas transmission pipe in the field. EPRI participated in the round robin study by using a linear phased array technique. Field removed specimens were provided by the Gas Technology Institute (GTI) containing SCC for depth sizing. In most cases sizing was difficult to accomplish because of the colony of cracks that existed. This presentation discusses the results obtained and comparing them to destructive analysis results.