This is a very interesting article for those interested in good bolting practice: RI_201403_BoltCorrosionArticle.pdf.  

The key take-outs, that aren't very widely recognised among climbers are:

1) Stainless steel is still at risk of pitting corrosion in highly aggressive environments (especially, but not only, marine). This kind of corrosion isn't obvious to the naked eye and can lead to sudden failure.  

2) Sun can cause high temps in the steel and this greatly accelerates this pitting corrosion.  

3) Expansion bolts are far more susceptible to this problem than glue-ins (principally because there are less "crevices").  

As a result of this I have made one change to the way I make U-bolts and that is to grind the notches only where they will be embedded at least 10 mm below the surface.  The notches are a weak-point for corrosion so having them well-covered is important.  

My opinion on stainless expansion bolts in Tas is that for most non-coastal cliffs they appear to have a good track record.  On coastal cliffs (within a few km of the sea) we can't be so sure and hence it is probably better to use a replaceable style (e.g. "dynabolt") rather than non-replaceable (e.g. "trubolt").  Be especially careful with sunny sea-cliffs.  

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4 Comments

  1. Ben Thorp

    Good article Roger!  Thanks for uploading.  It brings home the importance of rebolting for the long term so we don't end up with multiple replacements and ugly remnants of bolts everywhere.  I agree about trubolts - better to have the option to remove and replace which with trubolts you don't.  At Ceuse in France some of the bolts have been replaced twice already, next to the one you clip there will be a a couple of ugly stubs and it's a shame to see this on some of the most beautiful rock.  We need to think long-term and use the best bolts possible.  

  2. garry phillips

    Hey Ben
    Just to let you know its possible to hide the stubs of the tru bolts.
    If you have a 90mm long tru bolt , drill the hole say 100mm deep.
    Place the hanger on the bolt and knock it in with a hammer (this way you won't loose the bolt in the hole).
    Tighten the bolt (nyloc nuts are best)
    In years when they need replacing undo the hanger and pound the bolt into the back of the 100mm hole.  Cover the hole with glue.
    What you have seen in europe (or other places around the world) is they have drilled the hole to shallow, say 80mm deep.  Its impossible to pound the bolt in. 

     

    As for dyna bolts that have the expanding sleeves, they really are not suitable for the long term.  That expand in the sun, they loosen when there is a significant side ways load on them etc etc.  
    Also what roger said about placing the first notches on the u bolts at least 10mm under the surface is a good idea.
     

  3. Ben Thorp

    Thanks Garry, good info.  I imagine a lot of people using trubolts don't realise this.  

    Good point about the expansions that come loose too.  I've seen this a lot on popular routes at the bolt that people always hang on or fall at.  The horizontal hanger is the tell-tale sign even from the ground.  It would make sense to selectively replace some of these bolts with U's on the really high use routes.  

  4. Jon Nermut

    A recently issued UIAA paper saying SCC corrosion isn't limited to tropical environments (it can occur at 20deg)

    http://www.theuiaa.org/upload_area/Safety/Anchors/UIAA-WARNING-ABOUT-CLIMBING-ANCHORS-FAILURES.pdf