Environmental Hydrogen Embrittlement of G41400 and G43400 Steel Bolting in Atmospheric Versus Immersion Services

Abstract

This article is based on a review of data in the literature and those released by the California Department of Transportation and reported by the Bureau of Safety and Environmental Enforcement (BSEE). In 2013, hot dip galvanized (HDG) threaded rods failed due to environmental hydrogen embrittlement (EHE) cracking on the San Francisco–Oakland Bay Bridge. These rods were made of G41400 steel, conforming to ASTM A354 Grade BD (39 HRC max). All 32 EHE failures occurred in the bottom threads that had been immersed in pools of water, inadvertently, under no stress, for over four years before they were pretensioned. Several failure analysis reports stated that they failed due to EHE cracking because they were pretensioned while being immersed in water. This is erroneous, however, because one or more of the failed rods were not immersed in water during pretensioning and afterward. Conversely, hydrogen from metal corrosion of the HDG BD rods can diffuse into them under no stress while corroding in standing water for several years. The EHE cracking occurred when subsequently pretensioned. None of about 4000 threaded ends of HDG BD rods that have been exposed only to marine atmosphere (but not immersed in water) has failed in three to four years in service under a pretension load. These data are compared with recent EHE cracking of G43400 bolting in subsea oil production facilities in the Gulf of Mexico, reported by the BSEE.