Corrosion calc/time

[fasboater]

I am trying to apply an average life span of structural steel columns (A500 Grade B) with a reduced capacity due to corrosion. Where can I find some good information to put some kind of calculation to this?

Background information

We design structural steel gas station canopies all over the US with all of the structural steel exposed. I understand that typically this should not be an issue because of coatings. In doing some research I have found that many of these canopies were designed with an “internal splash drain” which pretty much dumped all of the drainage into the interior of the column. The columns base plates are also below grade with concrete laid about a .25 of an inch from the edge of the column walls in order to fully enclose anchor bolts etc. this leaves and area for water to set between the columns and the concrete.

I believe three conditions apply this.

Rain Water
Acid rain
Salt Water

Thanks in advance.

Jermey

 

[dbuzz]

I have seen some very badly corroded steel structures in smelters, refineries and gold plants and been heavily involved in remedial and replacement works.

You'll find that the column sections don't corrode uniformly. Flange tips will corrode at a significantly faster rate, right down to a feather edge, while at the root the flange may be close to its original thickness. This has huge implications for minor axis compressive buckling strength. I'm not sure whether this is an issue for your gas station canopies, as the governing design case may in fact be uplift.

As a design detail, perhaps you should build up the encasement around the column by 200 to 300 mm (8 to 12"), to minimise ingress of water and contaminants to the base plate. I have also seen these with conical or sloped tops.

All that aside, it may be incredibly risky for you try to predict a service life. After all, isn’t it the responsibility of the owner to adequately maintain his asset?

 

[SlideRuleEra]

"Corrosion of Steel Pilings In Soil", U. S. National Bureau of Standards, Monograph 58. You can download a .pdf copy from this page of my website

http://www.slideruleera.net/Steel-Piling.html

also, take a look at Section of 8 of "Bethlehem Steel H-Piles", downloadable from the same page. It refers to NBS Monograph 58.

http://www.SlideRuleEra.net