Failure analysis of connecting bolts used for anchoring streetlights of a mountain highway

• Fractured bolts used for holding streetlights in a mountain highway were analysed.
• The fracture occurred in correspondence to crevices formed in bolted joints.
• The bolt material showed a bad corrosion resistance in chloride media.
• Bolt material should be changed to prevent failures.
• In chloride environments crevices should be avoided in design.

This paper presents a failure analysis of connecting bolts used for holding streetlights inside the tunnels of a mountain highway. The fracture occurred in correspondence to crevices formed in bolted joints. Fractographic and metallurgical studies indicate that the bolt failure is due to a deep crevice corrosion process that is further aggravated by the presence of chlorides coming from the spray formed inside tunnels during the winter when sodium chloride is spread for de-icing roads.Metallographic studies highlighted also that corrosion affects only bolts, while all the other joints’ components are intact. EDS analyses revealed that the bolt material was a Cu-bearing stainless steel that, in chloride media, has a bad corrosion resistance because Cu destabilises the alloy passive film. Therefore, it is recommended that the bolt material should be changed to prevent similar failures and that in such environment crevices should be avoided in design.