Method and instrument for measuring inside diameter of conduit

摘要

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. The apparatus includes travel distance measuring means (65, 62D) for measuring a travel distance of the passage pig or the cleaning pig (60) within the pipeline; swing angle detector means (62E) for detecting a swing angle of a pig body during the travel distance measurement; displacement detector means (61) 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; computing means (62C) for computing an output from each of said means; and recording means (62B) for recording an output from the computing means. The computing means (62C) delivers a-detection result provided by the displacement detector means (61) corresponding to an output from the travel distance measuring means and a swing angle of the pig body at a travel position thereof.