Patent ID: 8941376
Filing Date: 2015-01-27
Classification: G01N,G01R

Abstract:
1. A method for measurement of a residual field strength of an elongated magnetized ferromagnetic workpiece having at least one end, comprising the steps of: providing an elongated ferromagnetic test piece having a residual magnetic field strength, said test piece defined by a pipe diameter and a material characteristic, placing a magnetic measuring sensor in direct contact with an end face of the test piece and measuring in a first measurement the residual magnetic field strength directly on the end face, and further separately measuring in a second measurement an axial component, a radial component and a circumferential component of the residual magnetic field strength with the magnetic measuring sensor or with another magnetic measuring sensor at a plurality of defined positions located radially outwardly from an exterior surface of the test piece distal from the end face, correlating the residual magnetic field strength of the first measurement to the axial, radial and circumferential components of the residual magnetic field strength of the second measurement at the plurality of defined positions to determine a correlation curve between the first and second measurements, repeating the first and second measurements for test pieces having different pipe diameters and material characteristics and storing the correlation curves determined therefor in a database, measuring with the magnetic measuring sensor or with the other magnetic measuring sensor at least one of the axial and the radial magnetic field component at a plurality of defined positions located radially outwardly from an exterior surface of a workpiece at least in a region of at least one end of the workpiece, retrieving from the database a correlation curve of the test piece having the pipe diameter and the material characteristic that correspond to the pipe diameter and the material characteristic of the workpiece, and determining from the measured at least one axial and radial magnetic field component of the workpiece and the retrieved correlation curve the residual magnetic field strength present at the end face of the workpiece.