ULTRASONIC TESTING OF RAILS REQUIRED FOR FABRICATION OF POINTS AND CROSSINGS
New rails without bolt holes and suitable for laying in track are used for the fabrication of points and crossings. These rails, therefore, do not have any chance of fish bolt hole cracking or any progressive type of defects. The defects like pipe, seam, lap, inclusions, segregation can only be expected in these rails. Therefore, in the procedure for ultrasonic testing of these rails only normal probe (Zero degree) is required. Probing shall be carried out from top of the rail head, side of the rail head and side of the web. The use of angle probe has not been included as transverse progressive crack of fish bolt hole cracks are not expected. This testing will be undertaken besides visual examination of rails for freedom from any surface defects.
Scope: This chapter stipulates the ultrasonic testing technique of new rails required for fabrication of points and crossings by hand probing using ultrasonic flaw defector and lays down the acceptance standard.
Probes: One single crystal normal probe 20/25 mm dia, 2/2.5 MHz frequency for checking the efficiency of the ultrasonic flaw detector. One double crystal normal probe of 4 MHz frequency, 18mm dia (overall), stainless steel casing and with perspex insert having a path length equal to 50mm of steel required for testing of rails.
Both the probes shall meet the requirement of the tests stipulated in equipment specification.
Battery: The battery shall be a rechargeable, plug-in type (preferably Ni-Cd type) 6V/12V suitable for working about eight hours continuous operation per charge.
Battery charger: The battery charger shall be suitable for charging the battery provided with the flaw detector.
Co-axial cable: Two meter co-axial cable fitted with BNC connector for connection with single crystal probe.
60x50x50mm block of steel to grade 45C8 of IS:1875 – 1992.
Standard test rail:
The rail piece shall be 250/300 mm in length preferably of the same
section used for the manufacture of crossings, having 1.5mm dia and 2.0mm dia flat bottom holes drilled along the central axis of the head, web and foot locations as indicated in Fig.
Checking the sensitivity of the probe: The double crystal normal probe shall be able to detect 1.5mm, 2.0mm and 2.00mm dia flat bottom holes in the rail head, web and foot respectively of the standard test rail. The amplitude of the peaks shall be set at 60%
Surface preparation: The probing faces of the rail shall be cleaned with hard wire brush to make it free from dirt, etc. for achieving acoustic coupling.
Checking the equipment: Check the correct functioning of the flaw detector or probe and adjust the sensitivity of the unit with standard test rail.
Calibrate the unit for 300mm range for testing the rail while probing from top of the rail and for 100mm range while testing from the side head and web.
After calibration of the unit the rails shall be tested manually using double crystal normal probe 4.0 MHz frequency with water/oil as couplant. The rails shall be tested by probing from the rail head top, rail head side and web. Typical oscillogram pattern for various probe positions are given for guidance as indicated below:
(i) Probing from the rail table: Oscillogram pattern for sound rail will be as given at Fig.
The pattern obtained on the defective rails will be as in Fig. for segregation, Fig. for vertical longitudinal split in web.
(ii) Side probing from rail head: Oscillogram pattern for sound rail shall be as given at Fig.
The pattern obtained on defective rails will be as given in Fig. for vertical split in head.
(iii) Side probing from web: Oscillogram pattern for sound rail shall be as given in Fig.
The pattern obtained on defective rails will be as given in Fig. for vertical split in web.
Acceptance standards: Any flaw peak appearing on the cathode ray tube of amplitude higher than 60% of the full screen height shall indicate a defective rail and such rails shall not be used for fabrication of points and crossings.