Locating joint sleeve in buried ferromagnetic pipeline - magnetising pipeline and externally measuring field anomalies caused by non-magnetic sealing material

摘要

A magnetic field is generated in the pipe by an excitation coil (3) introduced, e.g. down a manhole. A stepped change in the magnetic flux (2) arises in the region of the joint sleeve (6). THe resultant field anomalies arise from high magnetic dispersion loss (7). The latter are measrued and evaluated so that the position of the joint can be accurately located. A higher magnetic reluctance occurs at the joint sleeve on account of the sealing material used, usually packed hemp and lead with a circular contact region between the pipes remaining. A voltage quatient measurer can be used to measure the quatient of the horizontal components of the magnetic induction from two measuring coils at two positions directly. ADVANTAGE - Rapid results at low equipment expenditure.