Quick Note

Corrosion Observations for Heuco Wall

This note was posted to the Titanium Bolting FB Group 29 January 2020

The hero of this piece is Martin Roberts who burnt countless hours of quality time, when he could have been climbing, installing a large range of anchor types in a whole pile of locations across Railay/Tonsai.

My motto is to “measure more and speculate less”, but I confess to fail in this regard. Martin has done the very opposite, and the climbing community owe him a debt of gratitude.

See previous post for details of this site.

There are 5 test clusters we are considering. Inside the cave we have #2, #3 and #4, and outside, set some 20m into the jungle from the beach, we have clusters #5, #6 and #7.

I took some very quick photos of clusters 2-7 on my phone. Poor photography, for sure, but nevertheless they confirm earlier speculation.

Over the six year period we see no sign of corrosion of titanium bolts or any bolt comprised of a material with a molybdenum content greater than 3%. We see some minor corrosion on 316. All significant corrosion is confined to 304 anchors and Fixe PLX chain sets.

I’ve presented just the 304 results and have done a fairly “mickey mouse” estimate of degree of corrosion according to a set of rules I’ll attempt to justify in a later post.

The high sulphate, high chloride conditions within the cave, clusters 2-4, give rise to higher corrosion rates for 304 compared with what is happening back in the jungle.

As far as the “sulphate theory” goes, note that it is easy to point to the fact that chloride levels are also greatly attenuated by the jungle, and what we are seeing may be no more than chloride enhanced corrosion. I’ll get to this in a later post.

The wall-wash samples illustrate the extreme attenuation of the marine aerosol by the vegetation. Recall that none of these sites are exposed to rainfall in any way.

For Heuco Wall a wall-wash sample taken at cluster #2 is labelled cave left. That for cluster #4 is labelled cave right, and that for cluster #5 is back left, while cluster #7 is back right.

Just for fun I’ve added the wall wash results for Klong Ying Seua (another UIAA test site just north of Tonsai) to the wall-wash data for Heuco Wall in the plot below.

Electrolyte ratios – note the elevation of sulphate compared with sea water for the samples from within the cave
Actual areal concentrations of electrolytes – note the attenuation by the jungle at the back wall

S5 is taken directly from cluster #38 while S6 is from the same wall a few metres away. Notice the same sort of electrolyte levels as we see at Heuco Wall but with sodium and chloride displacing calcium and magnesium because the sea is really close. So close that marine snails are crawling around among the bolts! And yeah, it eats 304SS.

sea snails clip bolts at Klong Ying Seua

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