Re: SP Ogden Yard 50s


I have an answer on the different degrees of rusting on the galvanized running board / roofwalk.

These were fabricated in sections, made from stamped sheet metal, tack welded and fillet welded together, then hot-dip galvanized.  Actually, this issue could apply regardless of how the sections were fabricated.

Hot-dip galvanizing is usually a batch process, that is, a bunch of loosely supported metal pieces are dipped into the bath, pulled out and left first for the spangles to form and the remaining molten zinc to drip off, then to cool by being loosely stacked.  A problem that continues to this day is that, duh, the length of time the parts are left in the bath and the temperature of the bath affect the thickness of the galvanizing.

So some galvanized parts have an inadequate thickness of zinc if they aren't properly handled, and they rust first. 

Another place you may see that effect is the galvanized corrugated "iron" often used for roofs and sides of buildings.  Strongbarn was one of the early trademarks, which may still exist.  Some installers, to save the width of one corrugation and extend their material slightly, will flip every other sheet over so there is less of an overlap.  Ten years or more later, and for the life of the building, you can see that because every other panel is rusty.  This happens because galvanizing of these parts is more semi-automated and one face of each sheet gets more zinc than the other.  Without knowing for sure, I'd guess that the upper side of the sheet as it passes through the bath is the side that gets more zinc.

Off-topic note:  in my professional life I refuse to accept parts that are called "electro-galvanized", because they're not hot-dip galvanized at all but merely zinc-plated, which means the coating is thinner, cheaper and doesn't last as long.

Ron Merrick

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