The invisible weakening of stainless steel bolts

Published in Climbing June 2001

Sport routes allow today’s climber to focus on doing moves without worrying about the consequences of a fall. His protection — modern stainless steel bolts — is so strong that he can casually take multiple leader falls. However, few climbers realize that these bolts are also susceptible to corrosion and sudden failure.

A hanger with large Stress Corrosion Cracks that couldn’t be seen until it was removed. (S. Harper)

Tropical, seaside climbing areas such as Thailand’s Railae Beach and the Caribbean’s Cayman Brac were among the first to experience serious accidents due to bolt failure. What’s worse, many of these injured climbers didn’t even fall. The bolts and/or hangers broke when the climber said, “Take,” and hung, and in one case in Thailand the result was a two-bolt zipper! Everyone is familiar with oxidation corrosion, or rust, and galvanic corrosion, that mold-like growth on their car battery. But now climbers need to know about stress corrosion cracking (SCC) as well. SCC is like roots growing in a crack in concrete; as they grow, they expand the crack.

Notice the cracks in the nut, hanger and ring.  You can see this bolt on “Shooting the Curl” at the Wave Wall. Please don’t yank on it, it will break off. (Larry Hamilton)

All three types of corrosion (which can occur simultaneously) on climbing bolts can be caused by similar conditions. Water must be present for oxidation, and salty water for galvanic corrosion and SCC. The longer the metal is wet, the faster corrosion proceeds; warm temperatures accelerate all three mechanisms.

Salt can come from the sea but it may be in the rock itself. Granite, basalt and other types of rock don’t appear to be a problem. Porous limestone, however, may have salt embedded within it. One theory is that rain falling atop a limestone cliff percolates through the rock, picking up salt or other contaminants before finding its way to the bolts. Some climbs have only a single bad bolt where the rock seeps water.

A stainless steel “clad” nut that disintegrated when we removed it with a wrench. The cladding can be easily seen. (Harper)

On tropical Cayman Brac, with its warm temperatures and sea-battered limestone, stainless steel bolts and hangers have failed in as little as 18 months. In cooler, drier, less salty Rifle, Colorado, bolts placed in seeping crags like the Skull Cave showed obvious corrosion after about 7 years.

Although oxidation and galvanic corrosion can easily be seen on a bolt, SCC is generally invisible. Not only are the cracks microscopic, SCC often occurs behind the hanger where it can’t be seen. More than one perfect-looking bolt has snapped off under body weight. A climber on Cayman Brac hit the deck when he weighted the second bolt of Throwin’ the Hula Girl. (I had done the route a few weeks earlier, luckily without falling, and except for a light patina of rust on them, the bolts looked perfect.)
SCC also attacks aluminum. A carabiner that was exposed to salt water for about a year was tested and failed due to SCC. If you climb by the sea, wash all your gear in fresh water once a month or when you return home.

An old corroded stainless bolt and the Titanium bolt that replaced it. Note the purple discoloration on the stud. (S. Harper)

Needless to say, if you’re bolting limestone, keep corrosion in mind. Does the rock seep for months? Do existing bolts show any signs of corrosion? In dry areas where there are no signs of corrosion, the least expensive option is to use solid stainless steel bolts and hangers. Do not use stainless-clad bolts, which have a mild steel core encased in a thin layer of stainless steel. If the cladding cracks, the bolt will fail in short order. Stainless steel glue-in bolts are a better choice, but not in seaside rock or seeping limestone.

Note 2104: at this time the titanium Eterna bolt can be purchased at Titan Climbing.