Aimed for all.
1️⃣ The decision criterion
The decision criterion is based on the observation of a constant link between a specific environmental circumstance, a specific alloy composition and the pitting "phenomenon".
2️⃣ The experiments
Specifically, the UIAA team examined bolts from the widest possible range of rock walls, and for each anchor examined
- The alloy composition
- The minerals deposited on the anchors (from the rock in which the anchors were fixed)
- the composition of he rock in which the anchors were fixed
- The morphology of the surrounding environment.
Calcium Sulphate
from web
from web
3️⃣ The results
The results of the experiments show two common circumstances in all the anchors affected by the pitting phenomenon:
- The steel alloy was for all classifiable as A2 (different from A4).
- The presence of sulphate traces (Sulphates are salts in which a sulfur atom is bounded to four oxygen atoms) on all the A2 steel anchors affected by the pitting phenomenon
4️⃣ The difference between stainless steel A2 and A4
To put it as simple as possible: the stainless steel l’A4 is an A2 “spiked” with a 2.5-3% of molybdenum, to achieve a better corrosion resistance.
A2 vs A4: note the inscription A4-80
on the nut.
On the A2 nuts, instead,
there is A2-70
from web
on the nut.
On the A2 nuts, instead,
there is A2-70
from web
5️⃣ Distinguishing at a glance between stainless steel A2 and A4
We put this question to Emanuele Pellizzari: “The only way to distinguish at a glance between the two consists in reading the markings, that (as regards the expansion bolts) is written on the nut. Specifically: on the A2 bolts there is A2/70, whereas on the A4 there is A4/80 [cfr see the third pic n.d.e.]. ”
6️⃣ UIAA Conclusions
Thus the UIAA commission
- Absolutely banned the use of stainless steel A2 in marine environment and anywhere outdoors.
- Recommended for all the marine rock walls a test to detect the presence of sulphates into the rock.
7️⃣ How to choose the anchors according to the presence of sulphate in the rock
- If the results of the test indicate a percentage of sulphate greater than a pre-set threshold, even if only in some points, titan anchors should be used. The usi of stainless steel is forbidden (whether it's A4, or A2, or HCR).
- If the results of the test indicate a percentage of sulphate lower than a pre-set threshold, instead, stainless steel A4 or Her can be used, but you need to carefully monitor the behavior of the anchors.
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