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304 corrosion


Original Post
M Hanna · · Seattle, WA · Joined Apr 2015 · Points: 5

Hey there fellow MPers

I wanted to share some observations about anchors of a different kind. These anchors are large commercial installations used throughout the US for the purpose of window cleaning and building maintenance.

My company inspects, tests, designs, and certifies this gear in Washington State predominantly, and in other areas around the country. A few manufacturers use 304 stainless for the eye connection welded to the top of galvanized A36 steel pipe piers.

In the course of my work, I'm starting to observe pitting and corrosion near the welds and even up the bent rod at the 15-20 year old mark in the Seattle/PNW vicinity. On a recent project in Houston, I found this anchor on a 7 year old project some 20 miles from the Gulf. Bear in mind this is a 5/8" bent rod.


Food for thought. In my view based on what I'm seeing in this industry (commercial roof anchors) around the country, the UIAA opinion that 304 is not suitable for exterior installations is a good idea. I won't use it in future climbing installations or commercial situations for this reason. Other than Fixe, Petzl, and Bolt Products, are there others that are making plate hangers in 316 or better?

M.Hanna
Jim Titt · · Germany · Joined Nov 2009 · Points: 490

The corrosion is nothing to do with the material grade, it´s poor workmanship. The right-hand spot on the rod is contamination from the bending jig or a steel shackle/karabiner was clipped in there and the corrosion around the weld is from inadequate cleaning and passivation on the edge of the HAZ. They´d look just as bad in 316 or any other grade.
AustriAlpin, Climbing Technology and Raumer make 316 hangers and probably some others as well.

M Hanna · · Seattle, WA · Joined Apr 2015 · Points: 5

Thanks Jim-

Do you think there is a field repair that could return the passivation? I could see the larger stain being scotch bright scrubbed but the HAZ one is into the surface it appeared.

MH

Jim Titt · · Germany · Joined Nov 2009 · Points: 490

The problem beside the weld is the black layer which is removed by pickling (acid paste) or mechanically and under this layer there is chromium depletion (this is called "sensitized") and you need to remove the base metal (iron) until enough chrome is exposed to make an oxide layer. Normally this is done chemically but welded onto a galvanised or steel object it´s going to be a disaster!
The thing to do is brush it with a rotary nylon abrasive brush to pull the iron out (it´s softer) and then machine polish which smears the chrome over the pits where the iron was. You can get these for a Dremel or just in a normal drill, normally the ones for stainless are grey. Polish wheels the same (make sure the polish is for stainless or aluminium otherwise the abrasive itself can give problems, the same for the brushes). A battery drill would do it but it´s a bit slow!

M Hanna · · Seattle, WA · Joined Apr 2015 · Points: 5

That's a wealth of knowledge and advice there Jim-

I have always been curious about the stainless to galvanized interface and how the chemical process used for passivation could work in the combination. They must hang the product from the U-bolt and do a partial hot dip. I'm seeing a lot of these conditions, generally from one or two manufacturers. For these types of anchors, we prefer to see all HD galvanized components. Our anchors have a forged carbon steel D ring. They just seem to fit the bill better in that application.

Thanks again-

MH
Guideline #1: Don't be a jerk.

Fixed Hardware: Bolts & Anchors
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