Abstract: An apparatus for measuring an inner diameter of a pipeline is incorporated into a passage pig for checking passableness through the pipeline or a cleaning pig for cleaning within the pipeline, the passage pig and the cleaning pig including at least one seal cup sealably sliding along an interior surface of the pipeline. The apparatus includes a travel distance measuring unit for measuring a travel distance of the passage pig or the cleaning pig within the pipeline, a swing angle detector for detecting a swing angle of a pig body during the travel distance measurement, a displacement detector for individually detecting a radial displacement of the peripheral portion of the seal cup at a number of points along an entire circumference during the travel distance measurement, a computing unit for computing an output from each of said means, and a recording means for recording an output from the computing unit.

Abstract: An apparatus for measuring an inner diameter of a pipeline according to the present invention is incorporated into a passage pig for checking passableness through the pipeline or a cleaning pig (60) for cleaning within the pipeline while running through the pipeline, the passage pig and the cleaning pig including at least one seal cup (60B to 60D) sealably sliding along an interior surface of the pipeline.