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.
History
Inspection, Care & Maintenance Corrosion Physical Damage Conclusion
HISTORY
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.
INSPECTION, CARE AND MAINTENANCE
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.
SEATTLE MANUFACTURING
CORPORATION
12880 Northnip Way
Bellevue, Washington 98005