Patent ID: 7164276

Claim:
Method for determining the wall thickness of a metal tube in a process for the continuous production of longitudinally welded metal tubes, said method comprising the steps of: welding a longitudinal seam in said metal tube, in which both the outside diameter and the wall thickness are reduced in the same operation; preparing a reference tube whose outside diameter is the same as said metal tube but whose wall thickness corresponds to the wall thickness of said metal tube before the reduction; determining the resistance of said reference tube by: (a) arranging two clamp contacts on said reference tube with an exactly defined distance of separation; (b) connecting the ends of said reference tube with a power source; (c) measuring the voltage drop in said reference tube between said two clamp contacts; and (d) calculating said resistance of said reference tube using said voltage drop; determining the resistance of said metal tube by: (a) arranging two clamp contacts on said metal tube with an exactly defined distance of separation; (b) connecting the ends of said metal tube with a power source; (c) measuring the voltage drop in the metal tube between said two clamp contacts; and (d) calculating said resistance of said reference tube using said voltage drop; and calculating the wall thickness of said metal tube using a comparison of the measured resistances of said metal tube and said reference tube.