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Re: Galvanized Steel Tube Column

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Jared,

We have been hot dip galvanizing tube sections for industrial projects for decades and have never seen this problem before.  You do need to be careful not to enclose both ends of the tube without relief holes otherwise the pressure can build up and split the tube (or even explode in very unpredictable ways!!).

Thomas Hunt, S.E.
Fluor



"Jared Keyser" <jkeyser(--nospam--at)LCMF.com>
05/01/2007 05:30 PM
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Galvanized Steel Tube Column





Dear list,

During a building inspection for a new project last week,  we came across an existing short galvanized steel tube column, HSS 4x4x3/16" x 10-1/2" tall with a 6" to 8" longitudinal crack running vertical adjacent to one corner of the tube.  This member is very lightly loaded with minimal chance for over loading.  

With a little research and help from AISC Steel tips, it appears to be a problem that can occur on galvanized steel tubing (strain-age embrittlement due to the forming process, accelerated by the galvanizing process).  The AGA recommends either not cold forming or heat treating the member prior to galvanizing.  I have not yet heard back from STI on their thoughts, but I believe this will be the classic case of one saying it is the other's problem and neither solving the problem.  I am not sure if this is an isolated issue - some mistake made in the fabrication/galvanizing process, or a systematic one that is more prevalent.  

My question to the list is, do designers regularly specify a requirement for heat treatment of the steel tubing for stress relief prior to galvanizing or should we?  It may be more cost effective to avoid galvanized steel tubing all together.  

Any thoughts or comments on this issue is appreciated.  

Jared F. Keyser, P.E.
Anchorage, AK



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