February 25, 1992
This report contains a
brief history of steel carabiners, as we know it, and SMC's recommendations for
their care and maintenance.
ALTHOUGH A STEEL 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 INSTRUCTOR 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.
Low-carbon steel is believed to have been the material of choice for early carabiners, due to its availability and its workability by hand-forging and other hand-tool shaping and finishing operations. Later on, carabiners were also made from high-carbon steel, which made it possible to increase their strength with a simple heat-treating process.
Some examples of these early carabiners still exist today in various collections. The ones we have seen are all bare steel with a certain amount of rust on their exposed surfaces, so they probably never received a protective surface treatment such as paint or electroplating.
During World War II, new aluminum alloys were developed that are stronger than low-carbon steel. This made possible the production of the first aluminum carabiners which, due to their light weight, opened up many mountain climbing opportunities, particularly on big walls. However, steel carabiners continued to be produced in Europe and most of them had a plated finish. The heat-treated steel models were stronger than aluminum carabiners, and all of the steel carabiners were more abrasion resistant than those made from aluminum.
SMC designed and produced its first steel carabiners in 1982, in response to requests from the developing rescue industry. These carabiners were made from alloy steel in both heat-treated and non-heat-treated versions. Two sizes were made, one somewhat larger than the European climbing carabiner models and the second one even larger. In 1991, we designed a new, light-weight alloy steel carabiner which is also heat-treated, and an all-stainless steel carabiner of the same size and weight. All SMC alloy steel carabiners have an electroplated finish.
Both corrosion and physical damage can reduce the strength of a steel carabiner. However, some types of damage are unavoidable in certain rescue situations and other abusive applications. Sooner or later, this damage will adversely affect the performance of the carabiner. A good care and maintenance program requires careful inspection of steel carabiners, after abusive use, in order to determine what damage may have occurred.
Plated finishes are now commonly used on carbon and alloy steel carabiners to protect them from surface oxidation (rusting). These finishes are expensive, particularly due to the environmental protection requirements which the plater must comply with in the United States. However, the plating is soft and easily damaged in use. Also, it can be worn through where different parts of the carabiner rub together, such as the gate pivot area or between the threaded locking knob and the gate.
Once the underlying steel is exposed, it may rust. This is most likely when exposed to corrosive environments which include such diverse things as chemicals in some industrial plants, acid rain, salt-water atmosphere, and even sweaty hands. Alloy steel containing chromium, as used in SMC carabiners, is less susceptible to rust than carbon steel but is not immune to it.
To protect carbon and alloy steel carabiners from rusting, clean and dry them after each use to remove dirt and moisture. Apply a generous amount of a good preservative, such as LPS1, to the entire gate surface including the cross-pins, gate pivoting area and under the locking knob. Inspect the body of the carabiner for damage to the plated finish and apply preservative there also, then wipe off the surplus from all of the carabincr's exposed surfaces. We suggest LPS1 because it will penetrate into tiny spaces and get between steel surfaces and the moisture that attacks them.
In normal use, stainless steel carabiners are usually free from the corrosion problems of those made from carbon and alloy steel. However, stainless steel is often chosen for use in harsh and corrosive environments. It is advisable to test any situation in which there is the possibility of unacceptable corrosive attack, in order to satisfy yourself that the carabiner may be safely used for that application. Stainless steel carabiners should also be cleaned and dried after use to remove dirt and moisture. Apply LPS1 to the gate pivot area and locking knob threads for lubrication, then wipe off the surplus.
There are types of corrosion other than surface oxidation that can affect steel carabiners, but they are much less common and usually do not occur in use if the parts have been properly made. They normally take place within the structure of the metal as a result of complex technical phenomena. One of the purposes of the inspection described below, for visible physical damage, is to detect cracks or other unacceptable conditions that may have been caused by such phenomena.
Steel is generally more resistant to physical damage than aluminum, but the various steels used in carabiners also vary in this respect, depending upon their type and quality. Carbon steel is the most easily damaged, alloy steel and stainless steel are more resistant to damage, and heat-treated alloy steel is the best. For these three types, there is also a corresponding increase in strength and load carrying capacity. It is important to choose carabiners made from steel that is capable of withstanding the level of abuse and loading to which they will be subjected in your application. This is a necessary prerequisite to a good care program.
The gate mechanism, including the tab on each end of the body, is the weakest part of any carabiner and this is where damage from physical abuse can usually be detected first. Check the gate carefully for signs of excessive side-loading, such as rough pivoting action, bent tabs, etc. If the gate has been side-loaded without the locking knob closed, it is often forced into the open position, leaving a mark on the inside surface of one of the tabs at the opening end. Also look for cracks in the gate tabs radiating out from the pin hole to the edge of the tab.
Both cross-pins in the gate should be checked for visible physical damage, looseness and proper positioning. If the pin at the opening end is damaged, the hook that it engages on the end of the body will often be damaged, also. The spring, and the small metal paddle that actuates it, often escape physical damage, but damage to the gate or body in this area can interfere with their smooth action when the gate is closing, so gate-closing action is another important check. This includes a visual examination of the spring and paddle for proper function and freedom from damage or foreign material that may interfere with their action.
The body, being the largest part of the carabiner, usually takes most of the general physical abuse (as opposed to overload abuse). Carefully inspect for plating damage and for cracks or gouges on the tabs at both ends of the body. If the body has been loaded with the gate open, its shape can be distorted so that the cross-pin at the opening end of the gate does not seat properly. Compare it with a new carabiner, if necessary, for proper gate closure.
All sharp edges found anywhere on the carabiner should be smoothed with a fine abrasive, particularly around scratches and gouges, so that they will not damage rope or webbing in subsequent use.
After inspection, consider your findings and also the usage history of your steel carabiners. Retire any carabiner if you are not fully satisfied that it will meet the needs of your intended use. Store steel carabiners in a dry place.
For further help on the care and maintenance of steel carabiners, consult with a well-qualified instructor in the use of rescue and climbing equipment. Through experience and personal training, that person will know how to best use steel carabiners without unnecessarily damaging them, and will be able to recognize equipment that has served its useful life and should be retired.
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