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August 28 - September 3, 2016

Structural engineers often prefer mechanically galvanized bolts for accurate tightening while corrosion experts often prefer hot-dip galvanized bolts for superior corrosion protection. How do you resolve this inherent conflict?

Selected Answers

From Alan Denney of AKD Materials Consulting Ltd on December 7, 2017:
I have not come across the term "mechanically galvanized." What is this? To me there are "galvanized,"  i.e., hot dip galvanized, electroplated coatings and paint coatings.

From michael beitzel of Modjeski and Masters on August 29, 2016:
I am not sure there exists a conflict when ASTM A325 bolts are to be used. To my knowledge there is no structural reason for preference for mechanically galvanized high strength bolts over hot dip galvanized provided proper tightening protocals are followed. There is a restriction on the use of hot dip galvanized bolts on ASTM A490 bolts due to concerns with hydrogen embrittlement as a result of the galvanizing process and these bolts can only be mechanically galvanized or treated with other zinc coatings. A good practice would be to paint mechanically galvanized bolts. This should include a zinc prime coat and all other coats of the structure paint system to enhance fastener coating life as well as for aesthetic considerations. The zinc primer is needed to address the loss of galvanizing that results from bolt tightening impacts.

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Tagged categories: Asia Pacific; Corrosion; Corrosion protection; EMEA (Europe, Middle East and Africa); Galvanized steel; Galvanized/thermal spray coatings; Latin America; North America

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