Carbon Wedge Bolt Failure Due to Mild Rust

Example of clip seized on cone due to mild rust.  Power Trip at Maple Canyon.  See route page.

https://www.mountainproject.com/v/power-trip/109096490#a_112889465

Wedge bolts aren't meant to be dynamic anchors.  When they are tightened during installation the cone moves down the stud until it is properly wedged. Nothing should move after that. That's why it is so important to  torque them to the correct specifications when installing.  In the photo above, if the bolt had been properly installed, having the cone rust into place would not have reduced the strength of the bolt.

Bruce Hildenbrand wrote:

Wedge bolts aren't meant to be dynamic anchors.  When they are tightened during installation the cone moves down the stud until it is properly wedged. Nothing should move after that. That's why it is so important to  torque them to the correct specifications when installing.  In the photo above, if the bolt had been properly installed, having the cone rust into place would not have reduced the strength of the bolt.

Well...it's probably a 20 year old placement in soft rock and has no doubt seen many freeze/thaws and many hangs/falls...so things move overtime.  I think determining that it is a result of improper placement is a VERY  big stretch!

I haven't climbed at Maple Canyon so I don't know the type of rock.  If it is soft rock then a wedge type bolt is the wrong bolt type to use.  A sleeve type bolt such as the Powers '5-piece' or  a glue-in is the best type of bolt to use in soft rock.

Bruce Hildenbrand wrote:

I haven't climbed at Maple Canyon so I don't know the type of rock.  If it is soft rock then a wedge type bolt is the wrong bolt type to use.  A sleeve type bolt such as the Powers '5-piece' or  a glue-in is the best type of bolt to use in soft rock.

Maple is conglomerate comprised of quartzite cobbles in a softer matrix which I think is sandstone.  So, mixed bag at best.  Some of the matrix is quite hard, some is soft.  Tough bolting. 

Bruce Hildenbrand wrote:

 In the photo above, if the bolt had been properly installed, having the cone rust into place would not have reduced the strength of the bolt.

That's not necessarily true and wedge bolts do need to be able to move a small amount in order to work correctly (more so in softer rock). The basic principle behind how a wedge or sleeve bolt works is similar to how a cam works. An outward force results in the bolt's end cone being drawn into the expansion clip which results in the clip sliding up and along the cone and out and against the rock. As the load increases, the rock can compress and the expansion clip can compress to a small extent. This results in the need for further travel along the cone in order for the bolt to remain in place. If the expansion clip freezes to the cone, then outward force on the bolt may no longer result in sufficient outward force on the rock via the expansion clip which can result in the bolt pulling.

Fortunately, most bolts are loaded in shear which makes this issue less common as the outward force on the bolt is much less in that configuration, but if as many bolts were loaded in tension as were shear, we'd be seeing this problem a lot more commonly with rusted carbon steel wedge bolts.