Abstract

In this study, the quality of simulated welded pearlitic railhead steel has been assessed using regular and phase array ultrasonic techniques. Three 136 RE premium, head hardened rail sections, 18 inch in length, were used. The rail sections were acquired from the Transportation Technology Center (TTCI), Pueblo Colorado. Slots of 1 inch (25.4 mm) in length and 0.75 inch (19 mm) in depth were machined into the center of the railheads. The welding process was optimized via preheating to promote weld flow, consequently yielding better fusion between the parent and the weld material. The rails were preheated using two electrical heating strips (6-inch length and 2.5-inch width) attached to the rail web below the slot. The rail section to be welded was held in a box filled with ceramic fiber to insulate the rail section from the surroundings. The maximum pre-heated temperature was 500 °C. The slots were then filled using POSTALLOY® 2892-SPL hard facing filler wire.

Nondestructive inspection for weld discontinuities and porosity was performed using the OLYMPUS EPOCH 1000i ultrasonic flaw detector. The transducer/probe detects a variety of defects, forms, and sizes caused by welding flaws and/or slag inclusions. The same probe was used in the calibration of the equipment so that multiple variables such as specimen thickness, intensity of the reflected beam off the rear wall, and frequency could be preset. The device was calibrated, and a grid was constructed to guide the probe’s movement during the phased array and ultrasonic tests, ensuring that a high level of accuracy was achieved. A coupling agent was applied to the surface (cross-section) of the railhead at the end of the rail section. The phase array probe was placed on that surface, pressed gently, and moved across the rail cross-section. The parameters utilized for conventional ultrasound techniques were a 5 MHz frequency, a velocity of 0.2320 in/μs and a gain of 30 dB. In phase angle mode, an angle of 45 was utilized. These parameters were optimized and chosen for the calibration of the device with a section of the parent rail having the same length as a welded rail. All three samples were evaluated; sample A had no defects, while samples B and C had defects with a diameter of 1/20 inch (1.25 mm) and 1/10 inch (2.5 mm), respectively.

According to the American Railway Engineering and Maintenance-of-Way Association (AREMA), standard, defects that are below a diameter of 1/16 inch (1.56 mm) within the sound path located on the railhead are acceptable. Thus, based on the AREMA standard, two of the rails passed the ultrasound inspection and one did not pass. Destructive testing is being performed to slice the welded rail sections to locate the defects in order to confirm the resolution of the ultrasound techniques used.

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