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AD 355: Hydrogen embrittlement of bolts

The Advisory Desk has been asked to draw attention to the need to ensure avoidance of hydrogen embrittlement of higher grade bolts (above property class 8.8) that are galvanized or metal coated. This is unrelated to the requirement that bolts have sufficient toughness to meet the requirements for avoidance of brittle fracture at low temperatures, which was discussed in Advisory Desk Note AD 332.

Guidance on avoidance of hydrogen embrittlement in higher grade bolts is given in Guidance Note 8.02 in Steel Bridge Group: Guidance notes on best practice in steel bridge construction (SCI publication P185, available on Steelbiz). Generally, the risk of hydrogen embrittlement is avoided by appropriate treatment during manufacture but it is essential that proper and reliable certification is provided for the bolts and their coating in accordance with the recognised European and international standards.

Contact: David Iles
Tel: 01344 636525

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