Heavily corroded maillons from the Filthy Five pitches in Giants

[Pete K]

Some months back, UKC user 'i think it goes' (Ollie) posted some pictures of some corroded maillons that had been removed from the fixed rigging on the Filthy Five pitches in Giants Hole. The details of that can be seen on the original thread here. Having recently put together a hydraulic rig capable of break testing and measuring the forces on metalwork at home, I reached out and Ollie was kind enough to post me over 5 of the maillons for testing. I've now had the time to break them and pull together some footage and photos and wanted to share the results here.

The lefthand maillon marked 'ref' in the image below is one from my bucket of dodgy kit, but the other 5 are the ones I was sent. All have been cleaned up by Ollie to show the damage, with the righthand one also looking like it was treated to remove the rust entirely.
All of the maillons were, as far as I can possibly determine, Maillon Rapide 7mm long pattern ovals. Their major axis breaking strength is 25kN when new.

Some closeup images of sample 5:

The break tester is a large steel girder with a 10 ton pullback ram and hand pump fitted. The load cell is a calibrated factory S-type unit, rated for up to 50kN. This outputs a data signal to my PC, which has some basic software to show the loads. When I want to show the results in a video, I just do a screen capture on on the live graph. The whole setup can be moved from site to site for demonstrations, and is compact enough to fit in my office when I want to test or film at home.

Testing​

Reference Sample​

I started with the reference sample. This one had a complete covering of surface corrosion, and one tiny area where the metal had started to flake and become pitted. I anticipated this would be a better reference than pulling and brand new one, and cheaper!
The reference sample broke at 30.5kN. It broke at the end bearing point after it had stretched a considerable amount.

Sample 1​

I started with what looked like the one with most metal remaining. The gate screwed open half way by hand and then needed a spanner. Unfortunately while applying force to get the gate unscrewed enough to fit it onto the chains, the maillon was bent out of shape. I could not bend it back or close it, so this one had to be tested open. So not a comparable result to the reference or other samples, but worth doing none the less.
The unscrewed sample reached only 2.9kN before it had bent open enough to detach from the chains.

Sample 2​

Another one with a seized gate, but this time I dug out some old 12mm maillons to use to attach it to the puller so there was no risk of me bending another sample. I figured the 2 larger maillons would easily be sufficient compared to the corroded small sample, but I was wrong! After the test I noticed that the triangular delta maillon was now more of a pear shape. The force required to break the sample was far higher than I had anticipated, and I was genuinely amazed considering the condition of the test maillon.
Sample 2 broke at 23.2kN. It stretched and broke at one of the thinner sections near to the bearing point.

Sample 3​

The gate worked fine on this one, so it was back to fitting it between the heavy duty 10mm chain links.
Sample 3 broke at 23.4kN. It stretched and broke in 2 places at one of the thinner sections near to the bearing point. It was only 0.2kN of a difference from the previous sample.

Sample 4​

The gate worked fine on this one, so again it was pulled between the chain links.
Sample 4 broke at 7.07kN. The lower threaded section of the screw (not the opening side) broke free of gate screw, which also split open.

Sample 5​

The shiny one worked fine, and was pulled between the chains. I had left this until last as it did appear to be the worst one of the lot for metal loss.
Sample 5 broke at 15.45kN. It broke at the bearing point where the metal was at its thinnest.

Conclusion​

Well, I was totally blown away by the strength of some of the samples. That does not however mean I would endorse or personally ever consider using something like this which I encountered underground or on a crag. The rust had been wire brushed off these samples, but underground the crusted layers would probably prevent you making a judgement about how badly corroded something was, and how much good metal was actually left. I spent quite a while pondering on whether I would even post the results for fear of giving people the impression that kit this corroded was still 'safe' to use. I hope the take-away is that some of these did return surprisingly high breaking loads, but no one underground could accurately determine the strength of these by sight when they are crusted with flaking rust layers. And of course, there were some low force failures. The sample which broke at the gate threads failed at just over 7kN, which is higher than the forces generated in SRT, but really not lot of safety factor at all. A bit more time in the cave and those threads would have corroded away completely leaving the maillon essentially undone and with a strength similar to the sample that was undone and failed at 2.9kN. That is certainly a level of force possible to generate during SRT in some cases.

If you can forgive me for being preachy for a moment, for goodness sake please use stainless steel hardware anytime you intend to leave something rigged for the long term. Especially 'up pitches' where there is no chance of inspecting the anchors before committing your life to them. I know stainless costs more, but all of these maillons were going to kill or seriously injure someone at some point in the future. They came out of the cave thanks to Ollie, but if they hadn't, they would have gotten worse until some poor soul in the future paid the price.

Thanks so much to Ollie for sending me these, and replacing them with stainless hardware out of his pocket. If you still want the samples back as souvenirs, PM me your address.
DCA has now agreed to rebolt these pitches with BP anchors and an installer has volunteered for the work. In future we hope the efforts to fix the St Valentines sump siphon are successful and the pitches no longer need to remain rigged. But if they do DCA, or even me if I need to, will be happy to contribute to the cost of stainless maillons that need to remain in situ so we don't see something similar to these rusty ones in future years.

If you want to see the video of the whole test and some immediate thoughts and observations by me, you can find it on YouTube here, or watch below.

 

[i think it goes]

Thanks for that, Pete! Scary stuff! I still have the textiles from the ff so when/if you want them just let me know. Also think the hangers would be interesting to pull test when they come out. The part of the filthy five that has had the maillons replaced is only the through route; a dig off to the right part-way up the series has some even more questionable hardware.

 

[Pete K]

Thanks for that, Pete! Scary stuff! I still have the textiles from the ff so when/if you want them just let me know. Also think the hangers would be interesting to pull test when they come out. The part of the filthy five that has had the maillons replaced is only the through route; a dig off to the right part-way up the series has some even more questionable hardware.

When it's all rebolted I'll ask Fabian to keep any stuff he pulls out for testing. I should have a rope breaker sorted in a few weeks so let me know if you're over this way and we can maybe bust some of the rope samples.

 

[pwhole]

Really good work Pete, thanks for putting so much time and effort into this - it's really valuable info

 

[badger]

Pete, I often look at cavers personal kit, especially cows tails and think are you that tight, how much is your like worth. Obviously not that much looking at your kit. The fact to cavers get away with it so often is pure luck. Good work on the caribiner/mallion tester.

 

[Ian Ball]

I read that as cavers with dodgy kit are actually safer than I thought! Those rusty old maillons holding 23kN is impressive, number 4 and 5 are thinned on the bar that I don't think anyone would trust them not backed up.

 

[Mark Wright]

It would be interesting to know when a typical rope or sling might break when attached to an old M/R with badly corroded sharp edges at the load points? I doubt they would perform so well if you applied a dynamic force.

 

[Brains]

Also reiterates that a good MR MUST be fully screwed up (not nipped tight) to be fully effective (My understanding is that nipping up will stress the threads as well as the barrels which may split).

 

[Mark Wright]

Peguet suggest M/R's are torque tightened to a certain setting for the different bar diameters.

https://www.peguet.mobi/recommendation-self-certified

 

[Chocolate fireguard]

... I doubt they would perform so well if you applied a dynamic force.

I don't understand why a force that's only present for a short time should be more damaging than the same force that's there for longer.

 

[Mark Wright]

I get involved with the substrate testing of EN795 anchor rails and padeyes as part of my job and we have come across a number of systems that have comfortably passed the 12kN static strength test but catastrophically failed the 9kN dynamic part of the test.

 

[Chocolate fireguard]

I' m not familiar with the test.
How is the dynamic test applied and measured?

 

[Mark Wright]

I' m not familiar with the test.
How is the dynamic test applied and measured?

A 100kg mass is dropped a set distance, usually onto a short dynamic rope lanyard with sewn terminations, e.g., Petzl Jane lanyard, with the forces measured with a suitable in-line load cell. It usually involves a few tries to get to the required 9kN force. Assuming it holds the 100kg test mass after the drop test, an additional 200kg is added to it and it has to hold the combined 300kg mass.

 

[Chocolate fireguard]

Do they use a load cell with a peak hold or do they record the output and then look at it on a screen?
Do you have a link that would show a typical load cell used?

 

[Mark Wright]

One of the companies we deal with do it like this;

Harken Access Rails | Refit International | Worldwide

Refit International are contracted to supply & fit Harken 27mm Access Rails. The Harken Industrial Access Rail system is designed to be used as an adjustable anchorage point for facility or vessel maintenance.

www.refit-international.com

 

[Chocolate fireguard]

One of the companies we deal with do it like this;

Harken Access Rails | Refit International | Worldwide

Refit International are contracted to supply & fit Harken 27mm Access Rails. The Harken Industrial Access Rail system is designed to be used as an adjustable anchorage point for facility or vessel maintenance.

www.refit-international.com

Thanks, it shows the drop well but what I wanted was details of the load cell readout.
The name of the manufacturer is clear but none of their online literature gives what I am after which is the time constant of the peak hold circuit.

 

[Mark Wright]

Thanks, it shows the drop well but what I wanted was details of the load cell readout.
The name of the manufacturer is clear but none of their online literature gives what I am after which is the time constant of the peak hold circuit.

Wardy might be able to help you with the technical details of the test equipment they use at Spanset for testing their energy absorbing lanyards?

My main involvement is in the post-installation static proof load testing once companies like Refit International have installed a Harken safety rail system.