ABSTRACT

Susceptibility to hydrogen embrittlement (HE) is an ongoing concern for high-strength structural bolts. We evaluated the HE susceptibility of three high-strength alloys including a martensitic stainless steel, a high-strength carbon steel, and a duplex stainless steel. We conducted HE testing according to the Incremental Step Loading Technique of ASTM F1624. In order to charge the specimens with hydrogen, we used an electrochemical charging method and compared charging the specimens prior to testing to in situ charging during testing. We determined that in situ charging results in improved penetration of hydrogen into the test specimen compared to precharging, and thus provides a more accurate evaluation of the HE susceptibility of structural bolts.

INTRODUCTION

Cracking due to hydrogen embrittlement (HE) can be a concern for high-strength structural bolts. There have recently been several high-profile structural bolt failures that have been attributed to HE1. We evaluated the HE susceptibility of various high-strength corrosion resistant alloys for anchor bolts intended for a new bridge project, with a design life of 100 yrs.

Although the anchor bolts in this bridge are grouted to avoid corrosion, some of the anchor bolt heads are exposed to the atmosphere and could corrode over time, due to the presence of chloride aerosols from road salts applied to the roadway. The anchor bolt specification called for an alloy that is resistant to hydrogen cracking, as there is the possibility that long-term corrosion (and hence hydrogen evolution) could occur in the vicinity of the bolts, particularly if the grout degrades over time. Note that there is no cathodic protection system employed for the bolts in this bridge.

Specimens for HE testing can be charged in a hydrogen atmosphere at elevated temperature2. Due to Health and Safety factors, we opted to charge specimens using an electrochemical charging method. However, we determined that even after several days of charging, some materials were not saturated with hydrogen, so we decided to use in situ charging during testing. In situ charging allows improved penetration of hydrogen into a test specimen, due to the higher diffusion rate in the stressed region at the crack tip.

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