Warning: bolt failure on North Wales limestone

Posted by Elfyn Jones on 29/05/2013
A "Thunderbolt" climbing anchor in place on a route.
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Following the catastrophic failure of a bolt on a North Wales limestone route, the BMC is advising climbers to treat all ‘Thunderbolt’ anchors with caution. Read on for more details and advice on how to detect these bolts.

The bolt that failed was the first bolt on the route "One Ard 1-Der" a 6b sports route at the newly developed Craig Heulog on the West Shore of the Great Orme. The bolt that snapped was the first bolt in a four bolt route and snapped cleanly when the leader fell off while above the third bolt - therefore there was no direct fall onto the failed bolt, only the slight sideways tug of the quick draw as the rope went tight. This implies that the bolt failed at a low load.

Until a more thorough investigation is undertaken its not known what the cause of the failure might be. Until then, its advised that climbers treat all bolt placements with "Thunderbolt" placements with great caution. Enquiries and investigations are underway with first ascentionists and other route developers in North Wales to establish the extent of the problem. It's known that both this route and another adjacent route "Simpl-City" 6a both use these type of bolts, but these bolts will have been removed by BMC volunteers by this time.

The manufacturers of "Thunderbolt" have categorically stated to the BMC that this product is not tested or recomended for the purposes of fixing climbing anchors.

It's possible that other recently developed routes at Castle Inn, Penmaenbach Quarry and other North Wales limestone venues may have been equipped with similar bolts. The routes known to have been equipped with these bolts were developed in late 2011 and its likely that only routes developed at that time or since that date are affected.

How to identify "Thunderbolt" bolts

  • "Thunderbolt" bolts are self-tapping threaded bolts with a fixed hexagonal gold coloured head. The one that snapped was an M8 x 100mm that had been placed in a drilled hole and resined in place with a Petzl hanger placed on the bolt. The hanger did not fail - the failure appears to be a clean break of the bolt itself, some 14mm in from the hexagonal bolt-head, inside the drilled hole.
  • The bolt head is embossed with the letters "APT" and "8 x100".
  • Conventional expansion bolts used on North Wales sports routes  tend to use 12mm "through bolts", where the nut that hold the hanger in place is separate from the bolt itself (see photos)
  • With the "Thunderbolts" the bolt head is flush with the hanger (see photos).

This issue will be discussed at the next BMC Cymru North Wales area meeting on Tuesday 4 June.

 

 



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13
29/05/2013
Thanks for this article which I've posted on UKBouldering.

The use of "catastrophic failure" is inappropriate given that from the description of the incident no injury was caused.

Rgds, Simon
2) Elfyn Jones (author comment)
29/05/2013
Thanks for this Simon-but the term "catastrophic failure" is accurate in this instance as there was a complete & total failure of the anchor. It's a term frequently used in engineering when such an incident occurs. Thankfully in this instance there was not a human catastrophe as well.
3) Binder
29/05/2013
I suspect the bolt was over torqued when placed. It looks like, at first 'glance', like it was already weakened to this. Possibly over torquing incurred a fracture line in the bolt? Thus, the right angle and load causing failure? Thoughts?
29/05/2013
Maybe but my first thought was "the poor sod". But I'm not an engineer. Nor are the majority of readers. No biggie.
5) Tony
30/05/2013
I was going to agree with Binder's comment on over-tightening. But looking at photo No.2 and the ash grey fracturing running with the thread (is the bolt slightly bent or is that the camera lens used?) I think it more likely it was done after the bolt was installed, by someone attempting to remove the bolt with a spanner and fracturing it but not managing to remove it. I feel this is more likely than a batch defect in the metal itself, just waiting to fail on other routes with a similar fixing.
30/05/2013
Having used thunder bolts in the building industry I know that every now and then one will fail in normal use. The second picture is typical of most of the failures I have seen. I would never use thunder bolts for fixing hangers. I like my life too much.
30/05/2013
Until a full report is published it is unhelpful to speculate. However, the above comments referring to possible over-torquing of the bolt are misunderstanding what a Thunderbolt is and how is works. As pointed out, the Thunderbolt design has a self tapping thread that is designed to work in brick and masonry, but it is of crude type and not equivalent to a self tapping thread used for metal or plastic. The article mentions the use of "resin": Thunderbolts are not intended for use with chemical anchors. One thing that is certain is that it is the wrong fixture and wrong application. The level of ignorance of whomever placed the bolts in this case is quite shocking.
30/05/2013
Until a full report is published it is unhelpful to speculate. However, the above comments referring to possible over-torquing of the bolt are misunderstanding what a Thunderbolt is and how is works. As pointed out, the Thunderbolt design has a self tapping thread that is designed to work in brick and masonry, but it is of crude type and not equivalent to a self tapping thread used for metal or plastic. The article mentions the use of "resin": Thunderbolts are not intended for use with chemical anchors. One thing that is certain is that it is the wrong fixture and wrong application. The level of ignorance of whomever placed the bolts in this case is quite shocking.
30/05/2013
Some years ago there were similar failures on bolts in Victoria Australia where the threaded machine bolts used were screwed into the drilled holes using a lot of torque - seems the metal was weakened near the heads of the bolts as the lower end of the bolt became tight in the drill hole so the upper end of the bolt was taking too much pressure from the wrench used. Happened at Mount Buffalo when bolting granite with the same type of failure - without a hard fall - occurring on a number of different sites - Freezing conditions in Winter and very hot in summer was suspected as having contributed to the failures - carrots were then used with removable hangers and purpose made glue in bolts at belays with no hard screw in required etc to replace the suspect method.
31/05/2013
Yeh, I don't climb them or know about sport routes, but I do know about bolts. The one that failed is not rated for high tension and has clearly been over torqued, failure was inevitable. One point I must make one your article: you say the normal type of bolting used is an expansion bolt (good) and you show a picture of the through bolt type with the nut on the end. there is another type of expansion bolt that may be commonly used called a "rawl bolt" similar system except with a bolt not a threaded bar and nut, IN ALL INSTANCES the bolts used with these fixings should be high tensile. The tensile strength WILL be stamped on the bolt head as 8.8 or 10.8 or 12.8, if lower ratings are stamped or worse as in the picture there are no such markings, then they are not high tensile and are liable to failure. The bolt that has been used and failed is only supposed to fix wooden structures such as fencing.
31/05/2013
The 2nd image of the fractured fastener is consistent with a brittle failure. It is not consistent (from what can be seen) with a torsional failure. If the fracture surface could be visually examined more closely and checked under an SEM, a final determination could be made.

It is noteworthy that the fastener appears to have been electroplated and coated with a supplementary yellow conversion coating. If so, it is also relevent was to whether or not the fastener was case-hardended to provide a hardened surface for this application. If so, I would investigate whether or not the failure was the result of a hydrogen-related failure ---- either hydrogen embrittlement during manufacturing processes or hydrogen-related stress-corrosion cracking due to the service environment.

From an engineering perspective, there are two avenues to consider: 1) To keep the present design which has no redundancy in attachment and seek manufacturing perfection in the production of parts, or 2) consider a 2-fastener clip design that has redundancy for the situation were a single defective part is inadvertently produced and installed.

If, however, this is a processing problem related to introduction of hydrogen as discussed above --- then the redundancy solution would not work, as embrittled fasteners frequently fail as a group.
12) Anonymous User
28/11/2013
My guess is it was epoxy'd into place, but the hanger spun, and someone came along and tried to tighten it after it set, but broke the bolt in doing so as the epoxy would not let the bolt turn.
13) Anonymous User
07/12/2013
What were they thinking using a bolt not designed or at very least proven for the purpose in hand and M8! Regardless of the spec those hangers are not designed to be used with any M8's there's a clue in there. Makes you wonder how much more risky is trad if at all when people are bolting with this level of naivety . (I'm trying to be polite). I hate the idea of over legislating but who are the people placing these bolts and what is there experience in doing so?

And yes I am an engineer!

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