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Cylinder Testing
Sandwich Isle Divers is also a DOT authorized Propane Cylinder Requalifier.
Why should you have your cylinders tested?
Unless you own your own compressor you are required to have steel and
aluminum cylinders Hydrostatic tested every five years. Some SCBA are
required to be tested every three years.
In addition the scuba industry says that SCUBA cylinders should be visually
inspected at least once a year some times more often.
What is a Hydrostatic Test?
During a Hydrostatic Test a cylinder is filled with water (hence the
Hydro part of its name) and then pressurized to its appropriate test pressure.
For 3AA steel cylinders and 3AL aluminum cylinders this is 5/3 of its
working pressure, about 5000 psi for aluminum scuba cylinders and 3750
psi for most steel low pressure scuba cylinders. The pressure is held
for a minimum of 30 seconds (the Static part of the test) and the amount
the the cylinder expands is measured. Like balloons cylinders expand when
they are filled, a typical aluminum 80 scuba cylinder will expand about
55cc when it is filled to its working pressure, and like a balloon the
cylinder is a little bit bigger when the pressure is released. For most
cylinders they must return to within 10% of their total expansion. If
a cylinder passes the hydrostatic test and a visual inspection it gets
stamped with the date of the test. For most cylinders the Hydrostatic
test is good for five years.
If the cylinder fails either the Hydrostatic test or the visual inspection
the DOT markings are Xed out and the cylinder is condemned and should
not be used.
A cylinder that is less than two feet in length and less than two inches
in diameter and has a working pressure of less than 2000 psi does not
need a Hydrostatic Test.
A cylinder that does not have a current Hydrostatic test may not be filled.
What is a visual inspection and why should I have one?
During a visual inspection a scuba cylinder is inspected on the inside
and outside to standards set by the Compressed Gas Association (CGA) as
well as standards set by The Professional Cylinder Inspectors (PCI formally
PSI). The cylinders are inspected for bulges, dents, rust , other corrosion
and other forms of damage that can weaken the scuba cylinder and make
it unsafe to be used. The threads and neck of the cylinder are also inspected
for corrosion and cracks to insure that the cylinder is safe to fill.
In addition aluminum cylinders made by Luxfer and Walter Kidde prior to
1990 are required to have an additional test known as a Visual Eddy test,
these cylinders were made of a different grade of aluminum that the newer
cylinders and are susceptible to Sustained Load Cracks. A scuba cylinder
that has neck cracks may fail violently when being filled and kill the
fill station operator. A cylinder that has had a Visual Eddy test done
during it Hydrostatic test will have VE stamped next to the hydrostatic
test stamp.
Scuba cylinders are made out of either aluminum or steel, the valves are
made out of chrome plated brass. Whenever you have two dissimilar metals
in a saltwater environment electrolysis can occure and the two metals
will try and become chemically welded together. At that point the valve
will not come out when it needs to without damaging the cylinder. For
this reason it is a good idea to remove the valve at least one a year
and replace the o-rings and relubricate the threads. The burst disk should
be replaced at least every five years, generally at the time of the Hydrostatic
test.
Most dive operations will not fill a scuba cylinder that does not have a current visual inspection.
What is this "Visual Eddy" thing and why do I have to have it.
A Visual Eddy test is done on aluminum cylinders manufactured by either Walter Kidde or Luxfer prior to 1990. Luxfer also manufactured cylinders for USD (US Divers) and Dacor. These older aluminum cylinders were made with a different type of aluminum than the newer aluminum cylinders and they are susceptible to Sustained Load Cracks. The best way to describe Sustained Load Cracks is to imagine a brand new book self with no books on it, the self is nice and straight, put a dozen or so paper back books on it and after a while it will have a slight bow to it. Put a dozen or so hard back books on it and after a while it will have a pretty good bow to it. Put enough weight on the bookshelf and if the shelf was made from and inferior grade of wood it may eventually crack.
A full SCUBA tank is under a sustained load, it will expand and contract when it is filled and emptied. The older cylinders made from 6351 aluminum can develop cracks in the neck and threads of the cylinder. These cracks can weaken the cylinder and cause it to fail violently, generally killing the person filling them.
A Visual Eddy test sends a electromagnetic current through the neck and threads of a cylinder and helps find these cracks.
A cylinder that has neck cracks is generally condemned and removed from service.
Not all of these older cylinders will develop cracks. So as long as the cylinder is tested every year there is not normally a problem using them.
DOT requires that a Visual Eddy test be done at the time of the Hydrostatic
test if the cylinder is made of the 6351 aluminum (pre 1990 Luxfer or
Walter Kidde).
VE will be stamped next to the Hydrostatic test stamp to show that it
has been tested.
Some sort of indicator is generally marked on the Visual Inspection Sticker to show that a Visual Eddy Test has been done at the time of the visual.
Great, what else can go wrong with my cylinder?
SCUBA cylinders as well as other cylinders (Oxygen, Fire Extigushiers
and some SCBAs) generally will last a life time as long as they are taken
care of. With the exception of the older 6351 aluminum cylinders which
may have a birth defect most other cylinders do not die a natural death.....they
generally die from negligent homicide....they are murdered. As long as
a scuba cylinder is never emptied while diving water can not enter the
cylinder and cause corrosion, however many people do use up all of their
air, empty the cylinder and allow water into a cylinder. This can cause
steel cylinders to rust and die an early death. Water in an Aluminum cylinder
can cause pitting and other forms of corrosion that eat away the threads,
this also leads to an early death.
A cylinder that has rust or other corrosion in it may have to be "Tumbled"
or "Whipped". Tumbling a cylinder involves putting an abrasive
medium (such as ceramic chips) into the cylinder and having it rotate
for a number of hours to help remove the corrosion so that it can be inspected
properly. Whipping a cylinder while it sounds worse is a less sever cleaning
method and us used on cylinders that only minor corrosion. A special abrasive
nylon whip is attached to a drill and the inside of the cylinder is cleaned
of any minor corrosion.
Many people never or rarely rinse their scuba cylinders. This allows saltwater
to sit at the top of the cylinder between the valve and cylinder and cause
corrosion and cause the cylinder to die an early death.
Periodic valve maintaince is a must. The valve should be removed once
a year for scuba, the
o-rings should be replaced and it it should be relubricated and reinstalled,
burst disks should be replaced at the time of the Hydrostatic test. The
valve seat will have to be replaced occasionally to insure proper operation.
Proper cleaning and maintaince will help a cylinder last a long, long
time.
My oldest scuba cylinder is a steel cylinder manufactured in 1953, we
have an oxygen cylinder that has markings that indicate that it was manufactured
in 1922.
What about Propane tanks?
The small propane tanks that are used for home bar-b-ques and cookers must be requalified as well. Their initial test is good for the first 12 years of it life. At that point they can be inspected by an DOT authorized inspection facility, that inspection is good for five years. Since the home propane tanks are low pressure they do not need to have a Hydrostatic test done, all they need is an inspection done by a DOT authorized facility. The inspection is done to standards set by the DOT and the Compressed Gas Association. The propane cylinders are inspected for damage, corrosion and to insure that they have the proper "Over Pressure Device" installed.
Once a Propane tank has been properly inspected by a DOT authorized inspector they are marked with the date that it was inspected as well a the Visual Inspectors Identification Number (VIN) and is good for five more years.
