Development of a non-destructive technique for the detection of hydrogen embrittlement in high-strength steels

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High-strength aircraft grade steel alloys need to be free from hydrogen, otherwise a sudden and complete failure, know as "hydrogen embrittlement", may occur. A recent and spectacular example of hydrogen embrittlement occurred when more than 30 3'' bolts at the new Bay Bridge in San Francisco broke, so that even before delivery, 25M$ worth of repairs were required. The hydrogen can be introduced during the service life of the component, due to corrosion, but it can also be a remnant of the processing, for example electroplating. During the plating, some hydrogen is unavoidably introduced into the steel and this must be removed by a thermal anneal (bake) within a short time span following the plating; this protocol avoids hydrogen embrittlement and constitutes "normal" processing practice. For off-normal practice, the bake is delayed or absent. How much delay can be tolerated ? Is it possible and safe to recover the piece ? Only if it can be established reliably that the piece contains neither hydrogen (at least, below a certain threshold) nor damage induced by hydrogen in the interim. This collaborative research project will be undertaken in response to actual questions from industry with regard to hydrogen embrittlement of high-strength steels. Its goal is to determine which physical property of steel is most affected by the presence of hydrogen and to select or develop a non-destructive testing method that allows one to ascertain that a manufactured part is free from hydrogen and its associated damage.