Stress Corrosion Cracking in Stainless Steel Anchors

Hello All, What is happening here is called Stress Corrosion Cracking. There are many different forms and it can effect any type of metal metal if the conditions are correct. These conditions include, but aren't limited to: high temperatures, a preload (static load) on the anchor, and the presence of a corrosive element. In tropical marine environments we encounter all of these. The large seasonal swings in humidity play a role to accelerate the process as well as the hummic acid rich waters that permeate the limestone itself. Marine environments also can have high levels of magnesium salts which contribute to this problem with stainless steels. one of the main difficulties, as pointed out above, is that it is impossible to adequately inspect the anchors. there may be little to no rust visible, but where the anchor enters the rock small cracks can penetrate through the entire bolt (perpendicular to the stress vector). Another issue is that the porosity and salt content inside the rock can vary greatly from place to place and so some anchors on a route may be affected whereas others are not. The bottom line is that stainless steel is dangerous in tropical marine environments. How do we climb safely? The guys at Petzl make great points above. Additionally, glue-in anchors are safer by definition as there is no axial static stress. Unfortunately, this problem is inherently a material problem and some stainless steel resin anchors have still failed in the field. Without doubt, the Petzl Bat'inox and Collinox have shown them selves to be the safest stainless steel resin anchors used in Southern Thailand, but they have still failed in laboratory testing with the the same environment. The solution that we have found to address this problem on the Pra Nang Pennisula in Southern Thailand (Tonsai) is using titanium resin anchors with a marine (impermeable) resin. Titanium is not subject to stress corrosion cracking under the same circumstances as 304 and 316 stainless steels. The anchors have proven safe in the field and in labs. Currently this is the best practice and is being done in several locations throughout the world. For more information check out Josh Lyons has made a great video on this dangerous issue and it is full of information. We are currently working hard to replace all of the anchors in Southern Thailand. Be educated, be safe, and I hope to see you in Thailand! -Stephen Gladieux Metallurgist and member of the Thaitanium Project


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