Recently, I gave the presentation at the Kansas City Regional Steel Fabricators Association biannual meeting. 110 steel fabricators, engineers, architects, detailers, and others attended the breakfast.
I talked about the benefits of involving a specialty subcontractor like Chicago Metal Rolled Products in the design process when curved steel elements are included like rolled HSS and W beams.
During the question-and-answer session, a fabricator asked me if there was any special preparation of curved steel sections that should be done prior to galvanizing to avoid unwanted distortion and warpage.
In other words, when we are bending pipes, bending beams, or doing any other steel bending, is there anything prior to the bending process, during the bending process or subsequent to the bending process that would minimize or eliminate the chances of any problems with galvanized curved steel. One member of the audience suggested that the distortion was unpredictable
- I answered that rolled angle rings made out of, say, 2 x 2 x 3/16 angle are galvanized after rolling with no resulting distortion. We also regularly curve, press-brake-formed 6 x 4 x 3/8 angle segments which are galvanized after rolling with no detrimental effects whatsoever.
- Also, ring segments (more common in construction) are sometimes galvanized prior to the rolling process. Depending on the radius, section size, and bending orientation (e.g. x-x or y-y axis), the galvanizing may rub off in the rolling process and need further attention.
- But generally, from our experience of bending pipes, bending beams, or doing any steel section bending, galvanizing subsequent to rolling does not cause warpage or other distortion. It may be the case that, despite the fact that we produce a significant amount of curved steel that is galvanized without a problem, we may not have encountered curved steel sections that actually do distort when galvanized.
- On the other hand, we regularly bend galvanized sheet and plate into cylinders and cylinder segments with no deterioration of the pre-galvanized material.
Has anyone had experience in galvanizing curved steel sections—either positive or negative?
I welcome comments on these matters since the ability to galvanize steel often provides an attractive solution for the built environment.
George Wendt, President
Chicago Metal Rolled Products
One comment on “Galvanizing Curved Steel”
Heath
January 4, 2011 at 9:35 pmThis is an interesting and complex issue. Here’s the information that we’ve been able to come up with so far:
• One suggestion that was made was to galvanize it before you bend it (which is what you said your experience has been). That most likely means you have to do more fabrication on it after galvanizing which brings up other problems.
• It was proposed that some pre galvanize stress relief might reduce further distortion in the kettle, but this may simply make the distortion occur before the zinc bath instead of in the zinc bath.
• Usual stress relief is at higher temperatures than the galvanizing bath which might lead to the idea that the total distortion might be greater than if you just galvanized it.
• Trying to fix the shape (e.g. tie an arch shape across the ends) before it goes in the bath was proposed, but the general reaction was that these sorts of solutions often result in unanticipated and worse responses.
• The idea of stress relief leads to the thought of ovens big enough to heat the whole piece. This means that for many fabricators, stress relieving these parts one would require finding an oven big enough and shipping the parts to the company operating it.
So far, I think that this shows that there are many issues related to stress relief and, at this time, it doesn’t seem like an effective solution to the issue. So, if galvanizing is to be done after the member is rolled, there should be provision made to straighten the curved member after galvanizing. If we get any more thoughts or information on this, I will forward it to you.
Heath Mitchell, P.E.
Director of Technical Assistance
American Institute of Steel Construction
This has been prepared in accordance with information made available to the American Institute of Steel Construction at the time of its preparation. While it is believed to be accurate, it has not been prepared for conventional use as an engineering or construction document and should not be used or relied upon for any specific application without competent professional examination and verification of its accuracy, suitability, and applicability by a licensed engineer, architect or other professional. AISC