Only titanium bolts and anchors should be installed in Tonga – this is why:
In tropical marine environments stainless or galvanised steel are no longer considered safe materials to be used for rock climbing anchors or fixed protection. There are many stainless alloys available, each comprising different ratios of iron, carbon, chromium, molybdenum, nickel and other metals. Examples you may have heard of include 304, 316 and HCR. While some of these alloys are suitable for many climbing areas, most are not suitable for tropical marine environments. Climbing magazine has an excellent article on alloys and corrosion of climbing anchors here.
Steel fixed protection in coastal limestone has proved to be particularly unreliable, with anchors failing within just months of installation in extreme cases.
Thailand is a great example where all original steel bolts have needed to be replaced. You can read the story of the Thaitanium project, which conducted most of this re-bolting here.
To test corrosive conditions on Eua we installed 4 different commercially available stainless bolts alongside a titanium ring bolt in August 2016. After just eleven months the stainless bolts were showing substantial surface corrosion, while the titanium bolt looked new.
While a visual inspection can identify surface rust on the parts of anchors and bolts that remain outside host rock, serious corrosion may also be hidden by the host rock, particularly when it is porous, as is limestone.
Further complicating things is the phenomenon of Stress Corrosion Cracking (SCC), which has recently been identified as a common bolt failure mode. SCC is particularly alarming because it occurs at a microscopic level, inside steel equipment and is not able to be detected by visual inspection. You can read more about SCC here.
Titanium is pricey, but not obscenely so, and has a higher strength-to-weight ratio than steel, as well as excellent corrosion-, fatigue-, and crack-resistance. A complication with titanium is that when bent it must be annealed (heat treated) properly to prevent cracking, which again can occur at a microscopic level which can be difficult to detect visually. The manufacturing process and post-production testing are thus important considerations when sourcing titanium anchors and bolts.
It is possible to procure expansion bolts, ring bolts and staples manufactured from titanium. While the limestone rock in Eua is typically solid enough for expansion bolts, they are more expensive, allow the contact with water within bolt holes and the metallurgy of various components comprising an expansion bolt are often of slightly different, which can lead to greater galvanic corrosion, something that may be a problem when using a low grade titanium alloy.
Staples can be placed under tension in overhung or roof anchor placements, where ring bolts tend to slide out when being glued in place. An 8mm diameter staple is considered sufficient, but they are more difficult to install, with holes needing to be drilled at the perfect distance apart. Another consideration is that drilling two 10mm holes takes longer and consumes more glue and battery power.
Ring bolts, on the other hand, are secured in place with adhesive which prevents moisture and oxygen within the host rock coming in contact with the bolt and promoting corrosion. They have a consistent metallurgy, discouraging galvanic corrosion and have the added advantage of being able to be used as anchors.
Procurement. You can buy professionally manufactured and rigorously tested titanium bolts and anchors from Titan Climbing (http://www.titanclimbing.com/).
These were deemed too expensive for our initial exploratory purposes on Eua however, so the Kaka Maka Group had some simple P style titanium ring bolts manufactured in China. Some of these were tested to 12kN without deformation, so have been used since. These were initially designed to have an installed depth of 110mm, but the next batch will be reduced to 80mm as the rock in Eua has proved to be very hard and compact.
TA2 grade titanium is used for these bolts which are anodized with a Borax solution.
For steep or roof placements, a bolt with a ring centred on the shaft is considered best practice, as this reduces torsional forces in the event of falls, which may otherwise twist a bolt, breaking the seal of glue to rock and thus leading to bolt failure. In the future we will likely use staples for such placements on Eua however, as the adhesive we use is slow drying and staples can be bent to hold themselves in place, while glue sets.
Cost. To date, in small batches, bolts have cost USD$5.85 each to manufacture, but freight, customs and tax can add another few dollars. The Kaka Maka Group periodically orders batches of these bolts. If you want to buy through us get in contact via firstname.lastname@example.org to see if we have spare stock available.
Otherwise, you can procure these same bolts yourself from:
BAOJI ZHONG YU DE TITANIUM INDUSTRY CO LTD
Contact: Ms Sophia（Sales Manager)
Our last shipment is pictured here:
Please don’t hestitate to contact me directly with any questions.