Distribution of hydrogen occluded in bolts tightened beyond the yield strength and exposed at a seashore site

Abstract

The distribution of hydrogen occluded in high strength bolts tightened beyond the yield strength and exposed for 9 years has been investigated to establish an evaluation method for delayed fracture property. Hydrogen thermal desorption analysis was employed for determining hydrogen content in specimens cut out from the exposed bolts. Diffusive hydrogen causing delayed fracture is not uniform in concentration within the bolt and enriched in the threaded portion where diffusive hydrogen concentration was about three times that in the body portion. It is reasonable that diffusive hydrogen intrudes according to corrosion reaction, but no clear correlation between rusting and hydrogen concentration was recognized. From evaluation of the role of stress and plastic strain on hydrogen concentration, it is concluded that high concentration of diffusive hydrogen in the threaded portion was mainly caused by plastic straining.