Testing Steel Rails

Abstract

A DESCRIPTION is given in the Electrical Review of November 22 of the method developed by Sperry Products, Inc., Hoboken, New Jersey, U.S.A., for examining steel running rails of railways in situ for internal defects. A recording car is used, and operation is based on the fact that any internal discontinuity in a metal bar creates an area of high resistance to the flow of direct current; consequently a difference of potential will occur at the site of the internal flaw. Indicating currents are conveyed to the track rails by brush holders attached behind the front bogie and underneath the frame of the rear bogie of the coach. A current of about 1,500 amp. up to 8 volts is injected for pre-energizing the rails to ensure uniformity of molecular arrangement prior to the introduction of the detecting current just in front of the two pairs of searching coils. This precaution is necessary because running rails are generally magnetized by the normal effect of the earth's field, augmented by vibration due to the pounding of passing train wheels.