Development of a Self-Propelled Surface Corrosion Inspection System for Medium Pressure Welded Steel Pipe

It is important to perform corrosion inspections on pipelines. The magnetic flux leakage (MFL) pig inspection system is applied to high pressure pipelines, but this system cannot be applied to medium pressure (under 1MPa) gas pipelines. To resolve the above problem, we have developed the Self-propelled Corrosion Inspection System for Unpiggable Gas Pipeline. The self-propelled inspection system can measure the pipe wall thickness with dry coupling ultrasonic sensors. The system consists of front/rear tractor, sensor unit, ultrasonic thickness measurement device, water supply unit, control unit, cable and monitor. In this system, the sensors (ultrasonic type) have particularly unique characteristics. (1) Adopting the ultrasonic pulse method achieves measurement precision superior to the MFL method. (2) The sensor unit is equipped with six tire type (dry coupling type) ultrasonic sensors that can perform wall thickness measurement at a rate of 3m/minute and at 5mm mesh. The following benefits are obtained by adopting the system. (1) Expanding the inspection range: The system can directly inspect corrosion of pipelines at locations where excavation is difficult or where a pipeline passes through a bridge, though the pipelines could not be inspected formerly. (2) Improving measurement performance: The self-propelled system with ultrasonic thickness sensors runs in the pipe and the wall thickness is measured automatically at all the positions of the pipe. This report describes the inspection system development process and the results of trial inspections.