Bolt failure at Kalk Bay

Let everyone know about any suspect/dodgy/misplaced bolts to be renewed or avoided.
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Justin
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Bolt failure at Kalk Bay

Post by Justin » Thu Jul 30, 2009 4:15 pm

Whilst trying to remove a bolt hanger on a project at Kalkbay the attached bolt fell off. This is the 6th bolt to have failed from Stress Corrosion Cracking in the Western Cape so please be careful out there.

Andy Davies
For The Anchor Replacement Fund


Thanks to all those who have donated time and money to (ARF) Anchor Replacement Fund

In the image below you can see the exterior of the bolt and the side facing towards the rock where the failure happened!
Notice how the exterior of the bolt looks in good condition - remember whenever possible never trust a single bolt.
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failed_bolts_arf_06.jpg
Failed bolt at Kalk Bay
failed_bolts_arf_06.jpg (30.7 KiB) Viewed 2870 times
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XMod
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Re: Bolt failure at Kalk Bay

Post by XMod » Fri Jul 31, 2009 12:00 am

Woah! Scary-ass!
Was that off your project Andy? Im keen to replace all the old anchors at KBay. (Still need to finish up some stuff at Lowers too, give us a shout if youre heading to KBay.)

Michaelt
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Re: Bolt failure at Kalk Bay

Post by Michaelt » Fri Jul 31, 2009 7:39 am

Is it just me, or have like all bolt failures happened in the cape? :afro:
is it the salty air? Bad bolting? Incorrect bolts?
Dont think KZN has had a failed bolt? ( touch woood )

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ScottS
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Re: Bolt failure at Kalk Bay

Post by ScottS » Fri Jul 31, 2009 8:45 am

Michael - You can find more detailed information if you follow the links in Justin's post.

Basically, over-torqued stainless steel in a salty environment is susceptible to Stress Corrosion Cracking. The corrosion is not evident as surface rust and perfectly safe looking bolts can fail because the corrosion has happened inside tiny cracks that you can't easily see from the outside.

The older bolts in KZN are mainly mild steel, which is not susceptible to SCC - but they do deteriorate much faster than stainless steel and should *never* be used to bolt new routes. Our crags are also typically further from the sea and therefore in a less corrosive environment.

I think we will see some bolt failures here in the next few years, but the failure mechanism will be due to corrosion (rusting) of mild steel bolts, not SCC.
At the chaaaaains boet!!

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Justin
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Re: Bolt failure at Kalk Bay

Post by Justin » Fri Jul 31, 2009 9:10 am

Regarding over-torqued bolts...
Is it better to use a Torque wrench to tighten bolts?
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jellybelly
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Re: Bolt failure at Kalk Bay

Post by jellybelly » Fri Jul 31, 2009 10:34 am

Justin

In a former life I was an aircraft mechanic. It is advisable to use a torque wrench. Bolts are subject to a number of effects which set them on the path to eventual (guarenteed) failure. When a bolt is inserted and typically rotated in the hole on tightening it is scratched. Even fine hairline scratches offer opportunities for corrosion to start. Bolts also stretch when you tighten them. In aircraft measuring bolt stretch with a micrometer was a technique used to load bolts correctly as opposed to measuring torque. So overtightening puts the bolt permanently under excessive tension which hastens it's (guaranteed) failure.

Humans, in particular the grungy, overmuscled, pumped, bi-polar species homo-rockusjockus typically over tighten bolts by a substantial amount with ordinary spanners. You will be surpised at how little effort it takes with a torque wrench to achieve the specified loading.

The best torque wrenches (also the most expensive) allow you to set the torque you need on a gauge and will then click and release when the torque is reached.

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Justin
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Re: Bolt failure at Kalk Bay

Post by Justin » Fri Jul 31, 2009 11:04 am

Wow! Thanks for the insight jellybelly.

Perhaps each section of the MCSA should look at purchasing a torque wrench for bolters to use (those that are climbing/bolting actively)?
:idea: Anyone from the MCSA be able to comment on this?

It seems pointless buying more expensive bolts (316 steel) and taking all the other precautions (cleaning/brushing) while bolting to possibly ruin the process by over-tightening at the end of it!! :?:
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jellybelly
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Re: Bolt failure at Kalk Bay

Post by jellybelly » Fri Jul 31, 2009 4:09 pm

Stick to the expensive bolts Justin (safety of life issues and so on...) - they are less likely to have internal impurities and flaws ("inclusions" in the jargon) in the metal which are also sources of failure, and are consequently better able to withstand abuses such as over tightening.

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Re: Bolt failure at Kalk Bay

Post by Andy Davies » Mon Aug 03, 2009 9:27 am

Hi - here are some answers and more info:

1] If you use a normal spanner and tighten the anchor until the stud stops pulling out it should be OK. Big rugby thugs who hang on the spanner in order to prevent spinning, should ease off. If you want to prevent spinning use a spring washer.

2] Once again the bolt is a UPAT bolt - no mark on the head and machine cutting visible. These are bad bolts and we banned them a long time ago - but I see one of my friends still insisted on using them at the Fortress the other day. Please only use Fischer or Hilti 90mm bolts.
AndyDavies

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