Quick Note

A Certain Ring of Truth

This note was posted to the Titanium Bolting FB Group 7 March 2020

Everyone knows and loves those huge lower-off rings we find at the top of climbs at Railay/Tonsai.However, some of us began to love them a whole lot less when it became clear that they too were subject to the dreaded SCC.

If there was to be an exception to my theory of sulphate-reducing-bacteria (SRB) mediated corrosion this was it. The rings are normally clear of the rock by virtue of being threaded at three anchor points on lengths of old climbing rope, and all of my studies to date have pointed to the fact that the electrolytes soaked up by the fabric reflect the composition of sea water. It is only on the rock surface itself that we observe elevated sulphate levels, and a strikingly different electrolyte composition. Furthermore, SRB are strict anaerobes and it is not immediately clear how they could find a low-oxygen hidey-hole on the smooth metal surface, particularly one that is continuously being re-oriented by the action of climbers.

Some three years ago Qx sent me a Tonsai top anchor, complete with rings and ropes. Pretty quickly, I was able to establish that the ropes contained little more than sea water with a magnesium boost from climbing chalk. This finding really pointed away from an SRB-mediated mechanism of failure for the rings of this sort of anchor. Yes, there were some corrosion products visible, but nothing that would alarm me. I set the rings aside for the day when inspiration might suggest what better to do with them.

Lately I have been working toward getting evidence that SRB are actually active at the failure points of SS hardware. Very recently, I got a iodine-azide spot test for metal sulphides working. It’s very cool in that it will work with microscopic quantities of solid, insoluble, corrosion products. It easily distinguishes between the products of basic pitting corrosion and that induced by a sulphate reducer.

So what happens when I take a look at the rings Qx sent me some three years ago?

It turns out that the ‘rust’regions marked below are sulphide containing, and I’d suggest are evidence of what once were active SRB colonies. Only in Railay/Tonsai have I observed this form of “open-air” colony where the organism is capable of shielding its environment from atmospheric oxygen, but it is definitely a documented phenomenon for SRB organisms.

Having established that SRBs can colonize these rings, then I think it really comes down to sulphate availability as to how soon such a ring might fail in the field. I don’t think the conditions are anything like as favourable for a piece of SS embedded in the rock, but nevertheless we can see that these rings will fail, albeit with lower frequency than bolts.

Another piece of the jigsaw puzzle fits together.

Classic Tonsai top anchor – note the dark corrosion products
Following clean-up, these points of pitting corrosion were revealed
Electrolyte composition of samples taken from the ropes that make up the anchor – some contribution from climbing chalk, but sulphate not particularly elevated compared with sea water.
Scrapings of corrosion deposits within the pits in the ring surface test strongly positive in the iodine-azide test for metallic sulphide

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