Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Re: Galvanized Bolts

[Subject Prev][Subject Next][Thread Prev][Thread Next]
I guess this depends upon which standard or which types of bolts you need galvanized.  And, also whether or not they need to be tensioned into yield like a structural bolt.  Admittedly, some fastener standards more clearly address the needs of galvanizing than others.
For structural bolting, things are pretty good:  ASTM A325 includes within the body of the standard a direct reference to ASTM A153 for hot dip galvanizing, and the matching nut standard (ASTM A 563 Type DH) includes 'overtapping' allowances and limits to accommodate the coatings.
Further, ASTM A325 requires 'Rotational Capacity Testing' which, among other things, is one way to detect 'fit' problems.  My field experience has suggested to me that many 'fit-related' problems are really 'lubrication' problems.  (lack thereof.)  This is due to the fact that ASTM A563 DH nuts are not always lubricated ---- unless the purchaser invokes Supplementary requirement 'S1' which requires that a lubricant 'clean and dry to the touch' be added, or 'S2' (my favorite) which requires that this lubricant also have a color that makes the presence of the lubricant obvious.  Remember, hot-dip galvanized nuts are tapped AFTER plating, so if there isn't any lubricant put on them it won't take them long to get some rust.
Once they get rust, they tend to feel like they have a 'fit' problem, and even if they manage to go together, there's little chance of tightening them to slip-critical values if that is required.  This usually leads the contractor to call me to find out why they can't crush my DTIs --- so can we take them off the job.  I show up with a tube of 'stick-wax' and miraculously make the air-impact guns seem to have 10X the power they had the day before.
 AASHTO members and some engineering firms routinely require that all galvanized nuts be lubricated with a product that has color and is clean and dry to the touch.  On the other hand, I've been on quite a few building structures that did not require this.
With respect to the broader question of 'hot dip galvanizing on other bolts' ---- you may wish to borrow from the language in A325 and A563.  For example, consider language like this from Section 3.2.2 of A325:  "When Specification A194/A A194M 2H zinc coated nuts are supplied, the zinc coating, overtapping, lubrication, and rotational capacity testing shall be in accordance with Specification A563." 
Lastly, I think Mark Anderson's advice is good.  When possible, source the fasteners from the same supplier or even the same manufacturer if you can.   This can minimize many of the problems.  For what it's worth, the trend seems to be towards mechanical galvanizing ---- which is much less problematic when it comes to fasteners.
David Sharp
TurnaSure LLC
----- Original Message -----
Sent: Thursday, December 26, 2002 8:43 PM
Subject: Galvanized Bolts

Is there a standard for hot-dip galvanizing bolts and nuts that assures that the nuts will fit the bolts after galvanizing?
Nels Roselund
Structural Engineer
South San Gabriel, CA