Apparatus for observing the passage of a pig in a pipeline

摘要

A device to give an indication of the passage of a pig through a pipeline and methods of performing various pipeline operations using the device are described. The device has a magnetic sensor based on a dip needle and the output of the sensor controls a flag actuating mechanism. Passage of a pig beneath a pig indicating device causes a flag to be raised giving a visual indication that the pig has passed that location. Methods are described in which one or more devices are used to find a lost pig, for accurately locating a defect in a pipeline, for determining if a pig has been correctly launched or received, and for determining and controlling the speed of a pig in a pipeline.