An ultrasonic in-line inspection tool has successfully inspected a crude oil pipeline, which is 48-inches in diameter and 1287kms in length. This is one of the biggest crude oil pipeline systems in the world. The longest distance of a single inspection run is 1055 km. The survey runs have been carried out total eight times from 1989 to 1998. The ultrasonic
instruments were upgraded and the new ultrasonic tool was built in 1995. The new ultrasonic tool has 512 ultrasonic transducers and the firing interval of each transducer is 1.6 ms (625 Hz). The specified criterion for the grading of the data collected by the ultrasonic tool is single transducer grading. This criterion requires that corrosion will be reported when a single transducer detects a metal loss. The data observation software for personal computers is supplied to show inspection results and measured data collected by the ultrasonic tool. This paper describes the ultrasonic corrosion inspection technology of the ultrasonic tool applied for this project. Keywords: ultrasonic, ultrasonic inspection, ultrasonic inspection tool, pig, ultrasonic pig, wall thickness measurement, corrosion detection, metal loss