Quality Assurance Testing of a High Performance Steel Bridge in Virginia
Duke, John C. Jr.
Reynolds, William T.
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One of the original objectives of this study was to recommend appropriate procedures for welding bridge members of high performance steel HPS70W to assure quality welds. The final objective was to determine whether hydrogen-induced microcracking might occur and go undetected using the standard welding and weld inspection processes. Laboratory testing of steel specimens A588 and HPS70W with and without hydrogen charging were conducted. A588 was selected in part due to material availability and because its mechanical properties were reasonably close to under matched weld metals used with HPS70W. Acoustic emission (AE) monitoring was used as the means of detecting plastic zone formation, crack extension, and possible microcracking due hydrogen embrittlement. Although there is strong evidence to suggest that hydrogen-induced microcracking can occur in weld metal of bridge steels, including HPS70W, AE monitoring did not detect the formation of such damage in this study. The following recommendations are offered: (1) If the costs associated with detecting and repairing delayed, or cold, cracking due to hydrogen embrittlement are considered too high despite infrequent occurrence, every precaution possible should be taken. This would include preheating the steel, either baking the consumables or using specially packaged consumables, and post heating to drive off excess hydrogen absorbed during welding. (2) To reduce the added cost associated with the welding procedure precautions for every bridge project, an effort should be undertaken to develop a nondestructive weld inspection procedure that can reliably detect the presence of hydrogen-induced microcracking. The one-time cost of the enhanced AE system developed in this study is approximately $25,000. This system could be incorporated with VDOT's current procedures to ensure the quality of welded structural steel bridge elements. Quality assurance of welded steel elements prior to erection is critical. Crack detection and repair in service may cost on the order of hundreds of thousands of dollars, depending upon the severity of the crack and the criticality of the element to the bridge structure.