CORROSION AND STRESS CORROSION CRACKING FAILURE OF
CLIMBING ANCHORSUIAA 123 standard update, 2020
The UIAA Safety Commission is composed of national federation delegates, manufacturers andaccredited testing laboratories.
The subject of corrosion and stress corrosion cracking failure has been a work in progress forthe last ten years within SafeCom. December 2020, the Commission is able to release the results
and update its Standard UIAA 123 Rock Anchors V4_2020. This major update is based on
scientific research performed by Brest (France) and Prague (Czech Republic) laboratories,
coordinated and funded by the UIAA, for the safety of all climbers worldwide.
This Standard has been updated based on SafeCom’s best knowledge of atmosphericallyinduced stress corrosion cracking, i.e. with respect mainly to chloride resistance. Nevertheless,in some locations and environments this is not the appropriate procedure and where additional
tests need to be performed, e.g. under high sulphate content. Further research is ongoing togain a clearer understanding of this phenomena and how to determine which locations areconcerned.

Reminder of the quick facts
Recent incidents indicate unexpected failures of climbing anchors after being set-in place for afew months/years and under low loads. These failures occur mostly on stainless steel anchors
due to environmental degradation, i.e. corrosion and more specifically stress corrosion cracking(SCC).
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In worst cases, anchors can break under the weight of ten to twenty kilograms –obviously
less than the averageclimber’s weight.

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Usually in coastal locations, but even up to a few kilometres away from the coast.

●All material in warm coastal areas shall be considered as potentially affected●Corrosion is not always visible and can occur in cracks not seen by visual inspection.

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Stress corrosion cracking is the most virulent and can very rapidly initiate cracks shortly
after anchor installation. In some cases, within a few months and almost certainly within afew years.

●All metallic anchors, including parts made of stainless steel or aluminium alloys areimpacted, except those which are rated UIAA 123-SCC.

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The most critical factors are:○“Moderate” relative humidity locations. (The very dry and very humid locations areOK, it is the in-between the two extremes that is a problem)○

Areas NOT being washed clean by a rainfall (even being washed by the sea canbe OK!).

○Temperature: SCC can occur at 20°C, higher temperatures are worse.

What are the main changes?
•The list of acceptable materials for the most corrosion resistant class have beenremoved.

•The new Standard now tests the complete anchor to ensure as much as possible thestresses it may endure upon installation.

•The highest corrosion resistance class is Stress Corrosion Cracking (SCC)•The UIAA Safety Label certificate is given to anchors that have successfully passed thegeneral corrosion and Stress Corrosion Cracking (SCC) tests as per Table 1.

Why testing the complete anchor?
Influential factors: amount of internal Stress and resistance to SCC•

the manufacturing method: bending, welding, cutting, drilling, even laser engraving
adds a significant amount of internal stresses.

•the installation: expansion anchors are subject to additional stress when screwed inplace. Hammering with any metallic tool is also very detrimental and should be avoided.

This is why during testing the screw-in anchors are installed in a granite block as per
manufacturer's instructions for use and installation. For glue-in anchors (it is considered that theglue does not induce significant stress), they are fully immersed in the solution.

Why three classes?
The lastest research reveals that defining classes by only the material type is not pertinent sincesome anchors made of low SCC resistant alloys (e.g. 316L) could pass the test while otheranchors made of high-end SCC resistant material do not pass the same test. This is mainly
because the stress on the anchors from different manufactures could vary.

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For these reasons, it has been decided to have three classes, and only one of them withresistance to SCC.
Table 1: UIAA 123 Rock Anchor V4_2020 Classes and Environment Characteristics
UIAA
123Class

Signification

SCC
resistance

Generalcorrosion
resistance

Characteristics ofenvironment
SCC in evidence, forexample (but notonly):SCC

High SCCand General
Corrosion
Resistancehigh chloride
concentration,
HighHightemperature above
30°C,
humidity between 20%
to 70%,
sea salt and/or otherchloride salts, and/oracidic environment.

GCLCGeneral
Corrosion
Resistance

LowCorrosion
Resistance

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NO
(unspecified)

Importantconsiderations

Although SCC iscommonlyassociated withseaside cliffs, it canalso occur inlandand in otherlocations, e.g.
indoor swimming
pools.

No SCC in evidence
andHighnone suspected,
some corrosion agents.

NO(unspecified)

MediumNo SCC in evidence
andnone suspected.

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Rock anchors inindoor gyms and inproximity toindustrial areas,swimming pools, orthe sea may require
use of class SCC
anchor.

What is Stress Corrosion Cracking?
Stress Corrosion Cracking (SCC) is a very virulent type of corrosion that could provoke cracks
very rapidly. Contrary to general corrosion, which generates sufficient amounts of well visible
corrosion products such as rust, SCC can usually not be detected during on-site visualinspection. Many stainless steels, aluminium alloys and other metallic materials are affected.
SCC is influenced by many different factors, as presented in Table 2.
Table 2: Factors contributing to stress corrosion cracking of climbing anchors
FACTORSMOST CRITICAL ONE

remarks

ENVIRONMENTAL CHARACTERISTICS
concentration of chloride

magnesium chloride,
calcium chloride,
sea salt

temperature

NOT any cut-off/”safe”
level, but above 30°C
is worse

humidity

low relative humidity,
between 20% and 70%

location – coastal / windfrom the sea

next to the sea up to
typically 30 km fromthe coast

washed by rain or not

not washed by rainrock type

Unspecified, all rocktypes could beaffected

Chloride deposits containing salts with highsolubility can be formed.
SCC could start at 20°C, a higher temperature
increases the cracking speed; the temperatureof a bolt in the sun can be significantly higher
than the ambient air temperature.
RH close to the deliquescence point of thechloride solution poses a significant danger ofSCC. Localized RH of the anchor can besignificantly different from ambient RH, e.g.
when exposed to the sun.
There is no clear limit; winds from the sea withsignificant salt concentration can travel farinland.
The absence of washing allows the chloride toconcentrate locally on anchors.
Some rock types can make conditions worse
than others, depending on specificcircumstances.

ANCHOR CHARACTERISTICS

stresses

Page 4 of 7high tensile stress– from manufacturing, due to rolling, bending,cutting, drilling, and welding– from installation, due e.g. to tightening,hammering– from plastic deformation; e.g. multiple hard
falls

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Which locations are affected?
Potentially all coastal areas could be affected by atmospheric induced stress corrosion cracking,including up to several kilometres from the coast. To this day, it is still not possible to clearly
distinguish affected locations from safe ones. The variation of many parameters as presented inTable 2 can influence the corrosion conditions. For example, the wind can blow salt overhundreds of kms inland, and beyond the reach of sea breezes the rock itself can contain the ionsthat promote SCC.
The UIAA has created a Map of known corrosion locations. This map is intended only as areference to identify areas where examples of corrosion have been logged. It is designed only
as an informative guide based on data received and assessed. It is not intended as a complete
reference and is subject to changes beyond the UIAA’s control.
To support the UIAA Safety Commission with its analysis and to help add more areas to the map
thereby improving the information available to climbers about dangerous or potentially
dangerous areas to climb, a dedicated form is available to share information about corrosion or
failed anchors.

What you should know when installing bolts
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Use only UIAA123 – SCC class certified anchors. This class for locations where SCC
is common. In case of doubt and for areas with rare incidence of SCC or areas
where SCC is suspected but not documented always choose the highest class.
Do not combine bolts, nuts, washers or hangers of dissimilar metals, because
galvanic corrosion could be initiated due to the different electrochemical potentials.
Use a calibrated torque wrench to fasten the nut in order to avoid plastic deformationof the material and to keep the axial stress at moderate levels, as suggested by themanufacturers.
If possible, regularly inspect the material(s) in place.
If corroded anchors are found, contact the UIAA. Failed anchor parts can be sent toto the UIAA or one of its national federations for analysis:
https://theuiaa.typeform.com/to/rlBZyc

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How to check when climbing?
The UIAA123 V4_2020 Standard states that the anchors shall be marked with the letters UIAA
followed by the class SCC, GC or LC as per Table 1.
Evaluating the risk due to SCC is almost impossible for individual climbers because SCC
degradation is often not visible. Only destructive testing can confirm the presence/absence of
SCC on installed anchors. Even anchors that have been installed in recent months and/or lookbrand new could be compromised by SCC or some forms of corrosion.
SCC is very difficult to predict as it depends on a complicated set of factors, especially elevatedtemperature, low humidity, and formation of magnesium -or calcium- rich chloride deposits at
unwashed locations (Table 2). Small differences in microclimate can lead to SCC degradation
for some bolts, while other bolts on the same climb are unaffected. SCC is associated withseaside climbing but can also occur in inland areas where corrosive elements are present, either
naturally occurring in the rock itself or deposited inland by sea breezes.

Recommendations for climbers
When planning a trip
● Consider SCC when assessing the risk of climbing at a proposed climbing destination.
● Check with local climbers and/or climbing organizations regarding the prevalence of
SCC and the corrosion resistance of local bolts.
● Be prepared for the presence of SCC, especially at hot, seaside destinations.
When climbing● Consider SCC when assessing the risk of climbing a given route.
● Belay/lower from redundant, multi-bolt anchors.
● When in doubt, accept the need to back up bolts and belay/rappel stances with nuts,
camming devices, trees, and/or threaded hourglasses.
● Be prepared to abandon projects with suspect bolts.
In the event of bolt failure (once the climbers are safe and injuries have been attended to)● Collect the failed anchor parts; avoid disturbing the failure surface or trying to piece
together the failed anchor.
● Inform the local climbing community.
● Contact the UIAA. Faulty/failed anchor parts can be sent to the UIAA or one of its
national federations for analysis: https://theuiaa.typeform.com/to/rlBZyc

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What climbing organizations should know
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SCC and/or corrosion and the aging of existing bolts present challenges to the climbing
community that cannot be met by individual climbers.
The main obstacles to use of SCC and/or corrosion resistant anchors are cost andavailability. Individual bolters can be short of funds, and somewhat reluctant to spend
even more of their own money. When a bolting fund is available to provide funding, thebolters are always happy to use the more resistant anchors.
This means that the bulk of the climbing population needs to start paying more foranchors, whereas in the past most climbers had a “free ride”.
Bolting new climbs and re-bolting existing climbs to address the risks of both general
corrosion and SCC will require significant investment of both time and money for theinstallation of new bolts that are appropriately corrosion resistant. This initial cost is offset
by the increased lifespan of the resulting bolts and the decreased incidence of accidentand injury.
Quality control (QC) measures are necessary for responsible long-term management ofbolts, especially documentation of both anchor failures and anchor installation dates &types.
Monitoring of bolt integrity (pull testing of off-route bolts) is similarly important. Record
keeping for these QC measures must be in place for 50+ years.

The UIAA Safety Commission urges national federations and local climbing communities to plana future that includes responsible management of bolt corrosion and that asks for UIAA 123 v4
certified products.

ReferencesJiří Lieberzeit, Tomáš Prošek, Alan Jarvis, Lionel Kiener, Atmospheric Stress Corrosion Crackingof Stainless Steel Rock Climbing Anchors, Part 1, CORROSION. 2019;75(10):1255-1271.
Tomáš Prošek, Jiří Lieberzeit, Alan Jarvis, Lionel Kiener, Atmospheric Stress Corrosion Crackingof Stainless Steel Rock Climbing Anchors, Part 2: Laboratory Experiments, CORROSION.
2019;75(11):1371-1382.
https://www.theuiaa.org/safety-standards/

Click on this link to Donate to: Anchor Corrosion Project

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