Corroded bolt :O

[Bob Mehew]

I have been away for the past week without internet connection so apologies for lateness in responding.  I am not going to comment on chemistry apart from echoing the view that you should not use different materials in an anchor system.  But if there is any concern about corrosion, then there are two possible solutions either use a corrosion resistant anchor system or else use a removable system, i.e an expansion anchor.

For information, BCA's E&T are investigating both High Corrosion Resistant Steel and Titanium resin anchor systems for possible use in sea cliffs etc but the work is only just under way.  There has also been a very small amount of work done on expansion anchors.  Whist some gave good axial pull out strengths (35+kN from memory), others did not.  (The rock was not a problem in this work.)  I think the comment about using expansion anchors in potential corrosive locations and taking them out after use is probably the way forward here.  I have invited someone to come forward with a proposal to look at expansion anchors with BCA's anchor puller so we get some real data.  But I don't expect that work to take place until later in the year / next year.  (Volunteers always needed!) 

And at the risk of diverging from the original thread, I would add that probably big (12mm OD) and deep (>100mm) holes are better than small and shallow.  But beware, there is a mechanism with screwed down hanger that can dramatically reduce the strength of an anchor.  ALWAYS make sure the hanger is tight up against the rock.  If the hanger lifts off the rock surface, then the fulcrum shifts and magnifies (factor of two or so) the stress on the shaft of the anchor.

 

[mikem]

A useful reminder: https://www.climbing.com/gear/mixed-metals-and-galvanic-corrosion-ticking-time-bomb-or-tempest-in-a-teapot

 

[Fjell]

Raumer have done a fair amount of work on the use of stainless steels for hangers as you might expect. They had problems in a salt environment (sea cliffs) and have switched from 304 to 316L for all their kit. See attached.

I use 318LN duplex for anchor chain, and you still have to be careful about max temp and inspecting it.

 

[Bob Mehew]

From a skim read, Raumer are focusing on chloride stress corrosion cracking by switching from type 304 to type 316 stainless steel.  https://british-caving.org.uk/wiki3/lib/exe/fetch.php?media=equipment_techniques:chlscc_v2_130909.docx is relevant.  BCA E&T discussed this at its meeting see https://british-caving.org.uk/wiki3/lib/exe/fetch.php?media=equipment_techniques:131110_signed_minutes_of_meeting_131110.pdf and decided to stick to only using 316 except on sea cliffs where an even more resistant metal was required.  As I recall, E&T did not complete work to come up with a recommended material for use in sea cliffs.

But this is off topic from galvanic corrosion.

 

[Fjell]

Have seen standard alloy hangers turn completely to dust in warm caves after ten years. Crumbled when touched.
Unless you want to machine titanium, then high alloy stainless is it. We normally use duplex or GRP in seawater systems. Having paid millions for a lump of inconel, I doubt that type of material is a practical way forward.

 

[Tseralo]

Have seen standard alloy hangers turn completely to dust in warm caves after ten years. Crumbled when touched.
Unless you want to machine titanium, then high alloy stainless is it. We normally use duplex or GRP in seawater systems. Having paid millions for a lump of inconel, I doubt that type of material is a practical way forward.

Just an FYI if it's a real concern for you there are companies producing titanium bolts http://www.titanclimbing.com/

 

[Bob Mehew]

Just an FYI if it's a real concern for you there are companies producing titanium bolts http://www.titanclimbing.com/

PM me if you are thinking of going for these; I won't publish why.  There is also http://www.bolt-products.com/SeaWaterSeries_000.htm

 

[MarkS]

Just an FYI if it's a real concern for you there are companies producing titanium bolts http://www.titanclimbing.com/

PM me if you are thinking of going for these; I won't publish why.  There is also http://www.bolt-products.com/SeaWaterSeries_000.htm

For the sake of clarity, I would point you to this link to some previous E&T committee minutes, from which the following is copied:

"placed one titanium anchor purchased from Titan Climbing and 3 BP HCR anchors in Devonian limestone. The titanium anchor had broken in the metal head at 17.8kN."