Abstract
In September 2011, the I-64 Sherman Minton Bridge over the Ohio River between New Albany, IN and Louisville, KY was closed due to the detection of cracks in fracture-critical tie chord members. The bridge remained closed for over five months while non destructive testing and repairs were performed. Metallurgical evaluations were conducted by Applied Technical Services, Inc. (ATS) on 21 cores extracted from fracture critical members of the bridge. The cores were reported to contain rejectable indications as identified by visual inspection (VT), magnetic particle inspection (MT), ultrasonic testing (UT) and/or radiographic testing (RT). The purpose of this investigation was to determine the nature and cause of the flaws and if there was any evidence of active propagating cracks. Of the 21 cores examined, 11 contained surface flaws within the vertical butt welds or heat-affected zones. One core contained a major subsurface planar discontinuity. Five cores contained minor subsurface indications. The base metal properties were consistent with high yield strength, quenched-and-tempered low alloy steel, i.e. “T1®”/ASTM A514. The weld metal properties were also consistent with low alloy steel. All flaws and other weld discontinuities observed both at and below the surface of the web members were associated with the original tie chord welds or subsequent early weld repairs. These flaws were formed during or shortly after welding while in the fabrication shop. Fracture mechanics calculations determined that at a critical flaw size, temperatures below 30° F (−1.1°C) could possibly result in failure of the bridge. Metallurgical analysis of the flaws revealed no evidence of active crack growth due to fatigue, corrosion fatigue or stress corrosion. The flaw surfaces exhibited intergranular separation along with mixed mode brittle and ductile features characteristic of hydrogen-induced cracking. The fracture critical members of the tie chords box girders were reinforced by bolted steel plates and the bridge placed back in service in February, 2012.