March 15, 1991
This report contains a brief history of the development of modem climbing carabiners and SMC's recommendations for their care and maintenance.
ALTHOUGH A CARABINER IS
NOT, IN ITSELF, INHERENTLY DANGEROUS, AS SOON AS IT IS PUT INTO USE BY APPLYING
A LOAD OR FORCE OF ANY KIND, SERIOUS INJURY OR DEATH CAN RESULT FROM ITS MISUSE
OR MISUSE OF ANY OTHER EQUIPMENT TO WHICH THE CARABINER IS CONNECTED. FOR
YOUR OWN HEALTH AND SAFETY, ALL USERS OF CARABINERS SHOULD OBTAIN PERSONAL
INSTRUCTION FROM A QUALIFIED INSTRUC-ROR IN ALL PHASES OF THEIR USE. WHAT
FOLLOWS IS PROVIDED FOR INFORMATIONAL, CARE AND MAINTENANCE PURPOSES ONLY, AND
IS NOT A SUBSTITUTE FOR PROPER INSTRUCTION.
Virtually all climbing carabiners available in the U.S., before 1967, were made in Europe, except for a small quantity of aluminum ovals that were being made in Berkeley, California. There was a variety of different shapes and sizes available, made from either steel or aluminum, with a wide variation in apparent quality of manufacture. The breaking strength of these carabiners ranged from about 1900 pounds to 5400 pounds. In 1967, the symmetrical aluminum oval was the carabiner most commonly used for climbing in the United States. Typically, it weighed two ounces and had an average breaking strength of 2900 pounds.
During the 1970's and 1980's, several significant improvements were made in aluminum carabiners. These resulted in either an increase of approximately 80% in breaking strength for a given size, or a reduction in size (and weight) without a corresponding reduction in strength, or some combination of these two features. Today, the locking "D" shape aluminum carabiner and its smaller cousin, the lighter weight, non-locking modified "D" are the carabiners most commonly used for climbing in the U.S. Typically, the former weighs 2.2 ounces and has an average breaking strength of over 6000 pounds, while the latter weighs 1.7 ounces and has an average breaking strength of over 5000 pounds.
Today's aluminum climbing carabiners are miracles of performance. What other device is available that will, when new, support more than a ton of load per ounce of its own weight and is quick and easy to connect to? The modem aluminum carabiner has the confidence of thousands of climbers, worldwide, who depend daily on its load-supporting capability. The PRICE for this performance is not just an aluminum carabiner's cost when you buy it, but the CARE that it must be given if it is to provide a reasonable level of performance over a period of time. It is important to know, and avoid, those things that are destructive to aluminum carabiners, and to also know the few simple steps that will help prolong their life.
Corrosion, gate side-loads, and surface abrasion are all harmful to aluminum carabiners. Loss of strength is immediate when physical damage occurs, whereas corrosion damage, and its resultant loss of strength, takes time to develop.
Corrosion starts when moisture penetrates between the cross-pins and the gate material, or between the cross-pins and body of the carabiner at the pivoting end of the gate. Also, moisture left between the inner surfaces of the gate tabs and the adjoining surfaces of the body will start the corrosion process. The result, over time, can be extensive damage to the aluminum in these areas. This is particularly true if salt is present, as from sweat on the hands. Corrosion damage is virtually invisible when it occurs in the holes occupied by the carabiner cross-pins.
In addition to oxidation-type corrosion, there are some unusual types that can affect high-strength alloys of aluminum. These complex processes are not yet fully understood and are therefore considered to be phenomena. In one such process, moisture, combined with stress in the aluminum, causes penetration of the aluminum micro-structure by corrosion by products. Eventually the aluminum cracks. This process is appropriately known as "stress corrosion cracking," and can occur in aluminum carabiners.
A carabiner with a stress corrosion crack in its gate could have experienced the stress-inducing load when the gate was excessively side-loaded. This is the most common form of abuse that we have seen on damaged carabiners retured to us for inspection over a period of more than 20 years. The results are bent, cracked or broken gate tabs. Often, there are dramatic markings on these carabiners at both ends of the gate, indicating the presence of excessive side-load on the gate when it reached the position where it cleared the end of the body, while moving in the opening direction. Other factors such as the small shock load that is transmitted to the gate tabs by the cross-pin each time a carabiner gate snaps shut may contribute to the stress requirement, particularly over time.
Aluminum is relatively soft on its surface and abrades easily, especially when it comes into contact with a rough, hard surface, such as granite. Very little of the two ounces of aluminum in a carabiner is utilized in the gate tabs that connect the ends of the gate to the body. A deep scratch here can significantly reduce critical cross-sectional area, and can provide yet another place for invisible corrosion to develop.
Although undesirable, all of the conditions described above can be experienced while climbing. This is particularly true for equipment that is used frequently, or on difficult routes where there are times when equipment is unavoidably abused in the service of protecting the leader. The secret is to know that aluminum carabiners decline in strength and integrity with use, just as climbing ropes do, but in a more subtle and less visible manner.
Dry your aluminum carabiners in a warm place after using them. If there is dirt in the gate mechanism, clean it out. Use a chemical-based preservative/lubricant, such as LPS or WD 40, on the cross-pins and gate pivoting area. Wipe off the surplus from the carabiner's outer surfaces. These products were developed to get between moisture and the metallic surfaces that it attacks, and will penetrate into tiny spaces to do so. The use of anodized carabiners will reduce (but not eliminate) the corrosion problem. Anodizing is an excellent corrosion barrier in addition to its appearance benefits.
Inspect your carabiners before use, especially around the cross-pins and gate tabs. Make sure that what looks like a scratch is not actually a crack. Consider the usage history of your carabiners and the possibility of their having taken some damaging abuse on hard climbs. Retire any carabiner if you are not fully satisfied that it will meet the needs of your intended use.
Ask a well qualified climbing instructor to show you the techniques he or she uses to protect critical items of climbing equipment when in use. Also ask about back-up systems which avoid having it all hanging out on one piece of gear.
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