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 CASE S11 - Bolt Failures, E. L. Mifflin & J. J. Cecilio
Problem: S11a - Failure of ASTM A-325 bolts. ASTM A-325 bolts hot dipped
galvanized can produce cracks or cracks can be produced at a later time when
they are exposed to a marine environment, if their hardness exceeds Rockwell
"C-32". Stress corrosion or other brittle type failure is likely.
Symptoms: Cracks can develop in the annular space around the bolts and in the
roots of the threads; consequently, heads of bolts may fall off.
Collection of Facts: Hot dipped galvanizing can release atomic hydrogen (H)
which permeates the ASTM A-325 bolts. This can result in hydrogen induced
cracking. This has been experienced in several situations including stitch
bolts for a 1500 foot guyed tower where the heads fell creating a hazard to
persons on the ground.
Solution: Do not dip galvanized ASTM A-325 bolts if their hardness exceeds
Rockwell "C-32". If galvanizing is necessary, hardness should not exceed C-32,
For stitch bolts, A-307 should be adequate and less costly than A-325.
CASE S11 - Continued
Problem: S11b - Failure of ASTM A-490 bolts.
ASTM A-490 bolts hot dipped
galvanized can produce cracks and fail.
Symptoms: Cracks can develop in the annular space around the bolts and in the
roots of the threads.
Collection of Facts: The problem of galvanized A-490 bolts is similar to that
experienced with A-325 bolts. Hot dipped galvanizing can release atomic
hydrogen (H) which permeates the ASTM A-490 bolts. This can result in
hydrogen induced cracking.
ASTM A-490 bolts should never be galvanized.
Solution:
Problem: S11c - Failure of non-galvanized ASTM A325 and ASTM A490 bolts. If
non-galvanized ASTM A325 and ASTM A490 bolts are attached to galvanized
plates, the non-galvanized bolts may develop cracks and fail, if their
hardness exceeds Rockwell "RC-32".
Cracks can develop in the annular space of the bolts.
Symptoms:
Collection of Facts: Bolts that are nut galvanized, if put into contact with
metal which is galvanized, may develop cracks. ASTM A325 or ASTM A490 bolts
with a hardness of RC-32 or greater are subject to this problem, and potential
failure.
Solution. Do not place ASTM A325 or ASTM A490 bolts, which have a hardness
equal or in excess of Rockwell C-32, in contact with a galvanized surface.
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