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RE: Galvanizing Bolts

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Not really.  The hot dip process heats the bolt to about 850 degrees F
which is below the range to appresably change the mechanical properties.
However, steels in the 200 ksi and higher tensile strength range are
subject to hydrogen embrittlement.  This topic is covered well in the
"Specification for Structural Joints Using ASTM A325 or A490 Bolts".  The
new 2000 version of this specification can be downloaded from the following
web site:

Thomas Hunt, S.E.
Duke/Fluor Daniel

----- Forwarded by Tom Hunt/DFD on 10/18/01 09:10 AM -----
                    William N."          To:     "'seaint(--nospam--at)'" <seaint(--nospam--at)>                         
                    <William.Scott       cc:                                                                       
          >           Subject:     RE: Galvanizing Bolts                                        
                    10/18/01 08:54                                                                                 
                    Please respond                                                                                 
                    to seaint                                                                                      

Does the hot dipping process effect the strength and ductility of bolts?
Specifically, ASTM A325 and A320.

-----Original Message-----
From: Tom.Hunt(--nospam--at) [mailto:Tom.Hunt(--nospam--at)]
Sent: Thursday, October 18, 2001 6:45 AM
To: seaint(--nospam--at)
Subject: Galvanizing Bolts


Among other issues there are two main items you need to know.  First is
that hot dip galvanizing is thicker than mechanical galvanizing and second,
mechanical galvanizing is considerably more expensive.  For most outside
applications specify hot dip galvanized A325 bolts.  They are pretty much
"off the shelf" items.  Mechanically galvanized bolts are most likely a
special order which will cost more and delivery schedule could be an issue.
One exception is twist off bolts which are required to be mechanically
galvanized in order to meet their stringent torque requirements.

Thomas Hunt, S.E.
Duke/Fluor Daniel

----- Forwarded by Tom Hunt/DFD on 10/18/01 07:25 AM -----


Galvanizing A 325 bolts, . . . hot-dip galvanizing
or mechanical galvanizing. When prefering the use
of which ? Advantages and/or drawbacks of the
two procedures ? Are there any cases or situations,
where hot-dip galvanizing is a must ?
I'll appreciate any hint on this issue.

Thanks all

Raul Labbé

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