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RE: A490 bolts

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>Does anybody know why galvanizing A490 bolts is not allowed?
 
From ASTM A490-00 Section 5.4, "...[galvanizing is not allowed because] such bolts are subject to hydrogen embrittlement with subsequent stress corrosion cracking and delayed brittle fracture in service."
 
ASTM A490-00 Appendix X1 goes on to elaborate, "Steel sin the 200 ksi and higher tensile strength ranges are subject to embrittlement if hydrogen is permitted to remain in the steel and the steel is subjected to high tensile stress. The maximum strength for A490 bolts was set at 170 ksi to provide a 15% margin below 200 ksi. However, because manufacturers must target their production slightly higher than the required minimum, A490 bolts close to the critical range of tensile strength must be anticipated. For black bolts this is not a cause for concern. For hot-dip zinc-coated bolts, a hazard of delayed brittle fracture in service exists because the real possibility of inclusions of hydrogen into the steel during the pickling operation of the zinc coating process and the subsequent "sealing in" of the hydrogen by the zinc coating. Hot dip zinc coating of A490 bolts is therefore not recommended."
 
A reference is also given to a paper by Townsend in Metallurgical Transactions, Vol 6, April 1975, titled "Effects of Zinc Coatings on Stress Corrosion Cracking and Hydrogen Embrittlement of Low Alloy Steel".
 
Note that, although the Appendix discussion is specific to hot-dip galvanizing, ASTM A490-00 Section 5.4 also specifically prohibits mechanical galvanizing, electroplating with zinc and other metallic coatings on A490 bolts.
 
 
 
>Also, what measures are usually taken to protect these bolts against corrosion?
 
Corrosion protection is unnecessary in normal enclosed building usage, as indicated in AISC Specification Section M3.1 (see especially the Commentary discussion that alligns with this in Section M3). In other applications when corrosion protection is needed, painting is common. Type 3 atmospheric corrosion resistant bolts can also be specified for use with weathering steel.
 
Charlie