Justin Lawson’s recent posting about him breaking a bolt on Quasimodo at The Steeple in Montagu raised a few eyebrows and flurry of activity to replace the entire route’s anchors. (I considered maybe finding out what training / diet Justin was doing out in Montagu in order to emulate his superhero power). I have done a bit of research with my engineering colleagues here at work and can share the following with you:
When Quasimodo and Gospel Express were rebolted, the bolts on Quasimodo broke much easier than its next door neighbour (Gospel Express). They are both similar routes (ie slabs). Visual inspection of the removed bolts shows that the Quasimodo bolts have suffered from normal wastage corrosion in the hole and they failed at the sleeve taper (ie thinnest part of the shaft). These bolts have not suffered any Stress Corrosion Cracking (carbon steel is not susceptible to SCC, unlike stainless steel). From what we can see the normal sleeve taper is 6.5mm in diameter. The picture below shows a bolt that has corroded to a sleeve diameter of 4mm (GULP!).
Montagu is a pretty dry area which is why carbon steel bolts do not exhibit much corrosion externally. So what happened with Quasimodo? This route is a slab so the bolts have been drilled at an incline into the rock. Accordingly water was able to collect in the holes and corrosion was able to continue unabated.
But why was Quasimodo affected more than Gospel Express? I strongly suspect the bolts in Quasimodo were of a poor quality material and may even had some inclusions. The failure surfaces of the Quasimodo bolts exhibit some corrosion (immediate corrosion post failure or possibly corrosion of inclusions) while the Gospel Express failure surfaces look pretty healthy.
See the failure surfaces of the bolts in the picture to the right :
Everyone wants to jump on the glue-in band wagon and although glue-ins would prevent any water ingress, I really don’t think they are necessary for a dry area like Montagu. Glue-ins are a mission and have different failure modes (e.g. glue not mixing or people not cleaning the hole)
I was also very intrigued how Justin managed to break a bolt “easily” with a spanner. As a rule ARF has struggled to break bolts off, but like I said maybe Justin has a secret training program. So below is a rough calculation on what the expected failure torques would be for bolts in various states of corrosion for a low grade steel (4.6):
The importance of material selection can be seen by comparing the ultimate tensile strengths of some other steels below:
• Mild Steel (grade 4.6) – 400MPa
• Stainless Steel – 600MPa
• High Strength steel (grade 8.8) – 800MPa
I also did a little test with a 19 spanner to determine what kind of torque a burly young lad like myself could produce.
• Normal pull 20Nm
• Hard pull 35Nm
• Full body push 70Nm
So even a weak old man can break those bolts.
To conclude, these failures are simply caused by wastage corrosion that has been exacerbated by moist conditions in the hole and a poor quality material.
Lessons learnt from this little escapade are:
• If you’re going to equip a route, do it for life and buy good quality equipment. (I know for a fact that some high profile climbers in Cape Town are still using the cheap UPAT bolts that break).
And for my up country friends, I remember a similar issue with corrosion on Fabergé so please think carefully about not using good quality stainless steel anchors. (If you’re gonna by a rope, are you going to buy an expensive one with a good reputation and quality assurance or some cheapie from the boat shop?)
ARF recommends the following 90mm long, 10mm diameter 316 stainless steel anchors :
- Hilti HSA-R M10x90/20/25
- Fischer FBN 10/15+23 A4
• If possible try and drill bolt holes with a slight downward incline so that water can drain out the hole.
Andy Davies (BSc Mech Eng UCT)
MCSA – Anchor Replacement Fund
Montagu Bolting Fund:
Anyone who wants to support the Montagu Bolting Fund can deposit donations into the account below – I’ve opened this savings account specifically for bolting in and around Montagu. I will keep a spreadsheet record of what was received by whom as well as outgoing expenditures.
Please email me the deposit slip & you are also welcome to include suggestions of whether you would like the funds to go to re-bolting or new routes.
Climb ZA’s emphasis right now is to bolt “lower grade” routes at easily accessible crags as this grows the sport.
Bank: Standard Bank
Account Name: Lawson
Account Number: 07 616 676 7
Account Type: Pure Save
Branch Code: 051001
Bolt Corrosion Investigation