Brian in SLC

Just swung the photo's by a metallurgist friend of mine. "Exfoliation corrosion". "Corrosion products building up along grain boundaries exert pressure between the grains and the end result is a lifting or leafing effect. Aluminum alloys that have been extruded or otherwise worked heavily, with a microstructure of elongated, flattened grains, are particularly prone to this damage. The damage often initiates at end grains encountered in machined edges, holes or grooves and can subsequently progress through an entire section. In this particular form of intergranular corrosion the expansive force of insoluble corrosion products tends to force the grains apart and leads to exfoliation corrosion, sometimes known as lamellar or layer corrosion. In extreme cases, the edges of the affected area are leaf like and resemble the separated pages of a wetted book that has become swollen and begun to open up." Sounds like. Surfin' around on the 'net, I wonder if the bolt material type, zinc plating, and certainly the environment (Index, pretty wet) all played a part. I'm thinkin' 20 year old aluminum hangers in a wet environment just aren't meant to last that long. When did folks start placin' a bunch of bolts/hangers with power drills? Late 80's. How long ago was that? Yeah, 20 years ago. Scary. -Brian in SLC

I'll have to check my stock, but, I think I have some in both stainless and aluminum. I seem to recall they made stainless, aluminum and plated. Crazy, but, it looked like aluminum to me. I've seen similar type corrosion on old, aluminum cave hangers (the old ones with the small, 1/4" inch hole and the eye oriented like a Petzl Coudee or a Lucky Alba). The one I saw was on a old (60's) route in Montana with rawl split shaft thread head bolts. Back side of the hanger had been "eatin'" out and was scaley, similar to the photo's of Kong hanger in question. Crazy, and, frightening. Cheers, -Brian in SLC