Method and instrument for measuring inside diameter of conduit

An apparatus for measuring an inner diameter of a pipeline characterized by comprising:

• strain gauges disposed on a number of radii or concentric circles on an inner surface of a seal cup of an inner diameter caliper pig;
• a strain detector for detecting and recording a deformation of individual strain gauges;
• a travel distance recording device;
• a swing angle detector provided on a pig body;
• and
• a computing device for computing a variation in pipeline inner diameter from a measurement value provided by said measuring devices and a measurement value provided by said swing angle detector.

An apparatus for measuring an inner diameter of a pipeline, said apparatus being incorporated into a passage pig for checking for passableness through the pipeline or a cleaning pig for cleaning within the pipeline while running through said pipeline, said passage pig and said cleaning pig comprising at least one seal cup sealably sliding along an interior surface of said pipeline, said apparatus comprising:

• travel distance measuring means for measuring a travel distance of said passage pig or said cleaning pig within said pipeline;
• swing angle detector means for detecting a swing angle of a pig body during said travel distance measurement;
• displacement detector means for individually detecting a radial displacement of a peripheral portion of said seal cup at a number of points along an entire circumference during said travel distance measurement;
• computing means for computing an output from each of said means;
• and
• recording means for recording an output from said computing means, said apparatus characterized in that
• said computing means delivers a detected displacement from said displacement detector means corresponding to an output from said travel distance measuring means and an output from said swing angle detector means at a travel position thereof.