An obstacle detecting pig for preliminary inspection of a section of a pipeline travels through the section and determines if there are any restrictions that exceed industry guidelines or that might damage other pigs that require the full bore of the
pipe. In a first embodiment, a disk-shaped segmented resilient member (14) is mounted in the body of the pig. Its outside
diameter is smaller by a spacing (21) than the inside
diameter of the pipeline (15). The spacing is set at the maximum tolerable size of the obstacle encountered. The deformation of the member (14) is transmitted by a linkage (22) to a slider (16) activating a switch
system signaling that an obstacle has been encountered. A non-resiliently deformable checkup disk (19) may be provided at the rear end of the pig, to
double check that a no-
signal passage through the
pipe is not due to failure of the switching
system. In a particularly preferred embodiment, the resilient member is a disc-shaped
detector (46) made from an
elastomer and provided at its leading surface with a scratch
recording layer (51), for instance a layer of lead which is thin enough to follow resilient deformations of the elastomeric ring (50) as it encounters an obstacle, and return of the ring back to its regular, shape. The scratches caused on the
recording layer are evaluated after the passage of the pig through the examined pipeline section. The
detector is mounted directly on a slider (44) or the like operating device designed to produce
electric signal when an anomaly is encountered. Preferably, the
detector (46) is a replaceable element of the pig.The device is structurally simple thus providing low manufacturing and operation costs and simple operation.