Consider the following true story:
It’s the mid-2000s and two friends are on a long, multi-pitch sport climb. They’re excited—it is the climbing vacation to paradise they’ve dreamt about. They’ve been on clean, hard limestone all week. They’re prepared and plenty experienced for this climb.
The leader has reached a belay stance and is getting ready to bring up their partner. They are building an anchor on two shiny new bolts. As the leader flakes the rope, they see the first bolt on the next pitch is close, and they decide to clip the rope into it—giving their partner a little more of a top-rope in the last moves and setting them up for swinging into the next pitch. The follower gets to the anchor and clips in. What a climb! They both lean back to laugh.
Both anchor bolts break. They fall.
Only that extra bolt on the next pitch holds, keeping them from dying, but all three bolts were shiny and brand new.
Corrosion isn’t always visible, and there are a few different kinds of severe corrosion that result in scary failures like the one described above. These have been known for a long time in industries like construction and nuclear power, but it has only been in the last 20 years or so that we’ve recognized them in climbing anchors. These failures don’t require a lot of corrosion, just a very small amount. The two main types are Stress Corrosion Cracking (SCC) and Sulfur Stress Cracking (SSC), but there are others as well. For a number of reasons, these are really terrifying problems in climbing safety: they can happen very quickly without any easy-to- spot outward signs; they are difficult to predict; and they happen on stainless steels that climbers and route developers commonly think of as bomber. Like in any other part of climbing, assumptions can kill.
Starting in the late 1990s, climbers started talking about this issue. The problem seemed particularly obvious in coastal climbing areas, but it began to crop up elsewhere as well. Companies were quietly adjusting the alloying content of their wedge bolts, scientific papers were being written, and developers were beginning to use glue-ins and titanium. And ultimately, the Union Internationale des Associations d’Alpinisme (UIAA) Safety Commission (SafeComm) started looking into the issue in a rigorous way.
The UIAA is where the buck stops with global climbing safety. It is a union of climbing federations from 73 countries that works on things like mountain medicine, protecting climbing areas globally, organizing Ice Climbing World Cups, and standardizing training curricula and safe practices. It is where gear failure from all countries gets analyzed. It is where climbers, manufacturers, and labs come together to make climbing safer. As the national organization for climbers in America, the American Alpine Club is the U.S. representative to the UIAA.
To address the SCC issue, the SafeComm worked for almost 15 years to develop a new Rock Anchor Standard that tests the complete anchor—UIAA123. In the summer of 2025, we updated it at our 50th anniversary meeting with guidance on welding.
SCC starts with a pit on the surface of the material. This could be a small defect in the steel, damage caused by placing the bolt, or something left over from manufacturing. Pitting corrosion can also start the process. Pitting corrosion causes deepening pits to form in the surface and is typically fueled by the presence of chlorine. In all these types of corrosion, chlorine isn’t consumed, it is just something that facilitates the corrosion’s progress. That means it doesn’t take very much to make this happen—a high concentration, but not a large amount.
Once there is a deep enough pit, the process changes—in some cases it will stop here, but in others, the corrosion will develop into SCC and a crack will begin to extend from the bottom of the pit. This crack drives forward through the shaft of the bolt via a complex mechanism that doesn’t cause the outside of the bolt to corrode. In a short time, the bolt could break with body weight but show little sign of this danger.
Sulfur Stress Cracking (SSC) is similar in effect, but not in process. For now, we’ll focus on SCC.
Stress Corrosion Cracking requires three things: a susceptible material, a suitable environment, and sufficient stress in the material. None of these things are quite as straight-forward as they seem and the rate of cracking can ...
https://americanalpineclub.org/news/2025/8/14/guidebook-xvpolicy-spotlight
