METHOD AND MEASURING DEVICE FOR IDENTIFYING THE WELD SEAM OF LONGITUDINALLY SEAM-WELDED TUBES

摘要

The invention relates to a method for identifying the weld seam of individual longitudinally seam-welded tubes made of a ferritic or austenitic material during which the individual tube (1) is placed in a direct current magnetic field and is rotated around the longitudinal axis thereof. The differences in structure and/or permeability resulting between the parent material and the seam weld are established as a differentiation criterion by a probe (8) placed in proximity to the tube. According to the invention, the probe (8) introduces eddy current of an appropriate frequency into the tube (1) and the received signal is converted into a display which produces either a low signal (parent material) or a high signal (weld seam). The invention also relates to a measuring device for identifying, according to said method, the weld seam of individual longitudinally seam-welded tubes (1) made of a ferritic or austenitic material. The measuring device comprises an eddy current unit (10) and a probe (8) connected thereto, and comprises a measuring circuit which is provided in the eddy current unit (10) and which is provided for evaluating eddy current signals in that a signal is produced which can be distinguished as having been emitted from the parent material or from the weld seam. The probe is dimensioned so that it can be placed on the smallest nominal dimension to be tested without affecting the measured result.