The most common methods currently available for detecting cracks and linear features in pipelines are Ultrasonic Crack Detection (USCD) ILI and Electromagnetic Acoustical Transducer (EMAT) ILI. A third ILI technology using Spiral MFL with hard spot detection capability has also showed capability for detecting linear features within deformations that are not readily detectable by USCD or EMAT tools.
Any measurement technology, including ILI and field NDE tools, has a range of accuracy and detection capability. This paper analyzes and compares the performance of these ILI tools against the measurements obtained from field investigations. It will be shown that each technology has its own limitations, and features detected by one tool could be missed by the other tool.
Consequently, until one existing or new ILI technology has demonstrated its ability to catch all the features within its stated specification, employing multiple ILI technologies is an effective method to compensate for the weaknesses of any one particular ILI tool and ensure a higher level of safety for pipelines. An additional benefit of running multiple ILI tools is the opportunity for providing feedback of dig results to the different ILI vendors which could help them improve their own tool detection and sizing capabilities.