Author's note: Although this article
is based upon Canadian and US laws and standards, the general content may
provide useful information about cylinder safety.
Visual cylinder inspection (VCI) does not mean the same thing to all who
claim to conduct VCI nor to those who write laws or guidelines about VCI.
For example, the U.S. Occupational Safety and Health Administration (OSHA)
requires all respiratory equipment including SCUBA and SCBA (S/S) used by
employees to be visually inspected at least every month and after each
use.
Also, OSHA requires that all pressurized cylinders employees may be
exposed to shall be safe as determined by visual inspection. The
U.S. Department of Transportation (DOT) requires hydrostatic retesters to
conduct a visual inspection as part of the retest process. The
Compressed Gas Association (CGA) publishes cylinder related safety
guidelines that are, in some cases, incorporated into law by reference.
Even one cylinder manufacturer (Luxfer Gas Cylinders) and the scuba
instructor associations NAUI, PADI, NASDS and SSI have, at one time or
another, prepared information about VCI. Although each of those
associations stress the importance of a VCI, none tell the technician
clearly just what it is or how to accomplish it.
The PSI, Inc. visual cylinder inspector textbook, INSPECTING CYLINDERS is
the best single volume source for technical VCI information about steel
and aluminum S/S and composite SCBA cylinders. It was first published in
1987
and is now in its greatly expanded third (1997) edition. PSI, Inc.
publishes three additional cylinder inspector resource booklets, the
REPRINT FILE for scuba inspectors, HAZMAT TRAINING INSTRUCTOR GUIDE and
FILL STATION OPERATOR'S GUIDE.
Luxfer Gas Cylinders published an excellent guide in 1996 that clearly
describes how to conduct a technical VCI on Luxfer aluminum scuba
cylinders. Much of that information and procedures came from the program
developed by
PSI, Inc. over the past 17 years. A revised edition of the Luxfer
SCUBA Guide will be released late in 1999. Luxfer also published a
guide for inspecting SCBA cylinders. The technical SCBA inspecting
guide is printed in two volumes. Volume I deals with Luxfer aluminum
and composite cylinders made before 1988 and volume II covers newer solid
wall and several composite materials.
The INSPECTING CYLINDERS book and Luxfer's aluminum cylinder inspection
guide contain the details necessary for a thorough visual inspection.
A technical visual cylinder inspection is a complete assessment inside and
out against standards and damage limits. Cylinders that meet those
standards are returned to service. Many cylinders that do not meet the
standards can be serviced, usually cleaned or hydro retested, and returned
to service. Damage or other conditions that fail to meet the allowable
limits cause the cylinder to be condemned. Condemned S/S cylinders
should not be reconditioned.
INSPECTING PROCEDURES
Technical VCI begins with a careful review of the code marks stamped into
the cylinder shoulder or appearing on a composite SCBA side wall label.
In the U.S., the code must include DOT or ICC markings and in Canada, CTC
or
TC. The serial number MUST be legible. There must be an
original hydro tester's mark and a current mark, within 5 years for steel
or aluminum cylinders and 3 years for composite SCBA according to North
American regulations. Composite SCBA must be removed from service at
15 years. All other markings should be valid and compatible.
Specific information about correct and fraudulent marks is presented at
PSI, Inc. workshops. The
cylinder type must be correct for the intended service. For example,
composite SCBA cylinders MAY NOT be used for scuba or other underwater
purposes.
The cylinder exterior surface should be free of bands, boots, stickers or
other objects that might obscure damage. Cuts, dings, gouges, dents,
corrosion pitting, and bulges must be compared to specific damage limits
for each cylinder type. The inspector must be able to differentiate
between a banana (bowed) cylinder, which is acceptable, and a bulged
aluminum cylinder which is not.
The entire interior should be brightly illuminated to facilitate a
critical examination of any contents or damage. Corrosion indicates
moisture has been allowed into the cylinder, usually during fills in water
baths, or from
poorly maintained compressor moisture separators. The technical
inspector must estimate depth of any corrosion pitting and compare
findings to the allowable limit for the cylinder type. The PSI, Inc.
developed Master Pit
Reference Plate along with pit limit tables provided to PSI, Inc. workshop
participants simplifies this assessment.
Scuba and SCBA cylinder threads should be carefully checked for condition
and minimum number. The minimum number of threads allowed varies
with the type of cylinder and may range from 6 to 12 complete and
continuous threads measured from the top. Thread chasers should not
be routinely used to reshape cylinder threads. Certain 3AL and
composite cylinders with aluminum liners warrant a special examination
just below and within the threads. A
small magnifying mirror and bright, directed light will aid in detecting
occasional cracks that may propagate from crown folds. Training and
experience are essential to locate and differentiate cracks from tool
stops or other marks. The recently developed Visual Plus eddy
current apparatus is a valuable tool to augment the standard mirror and
light inspection by locating sometimes difficult to see cracks.
Valve Inspection
Although valve repair is not a part of the visual inspector's duty,
several items should be inspected. In North America, all valves used by
divers and fire fighters MUST have a pressure relief device, commonly
called a burst disc. Both the leaded plug type and single port
retainer nut type should be replaced with more effective designs.
Burst disc relief pressure must not exceed the hydrostatic test pressure.
Improper installation of the burst disc components may cause the device to
release at much higher than the rated pressures. Valves affixed with
high disc pressure ratings must not be placed in lower pressure cylinders.
Several valve manufacturers recommend this safety device be replaced at
specific intervals. Many valves used in Europe have no relief device
and have metric threads. Some metric threaded
scuba valves have appeared in U.S. made cylinders and are both dangerous
and illegal. One death and one serious injury have resulted from
such miss-matched components.
The cylinder to valve O-ring replacement policy varies among equipment
manufacturers but most technicians automatically replace the O-ring and
lightly coat the threads with a lubricant having dielectric qualities and
no
off-gassing solvents. Two dive equipment companies, U.S. Divers Co
and Scubapro and SCBA maker, Survivair at one time placed plastic dip
tubes on their valves. None proved satisfactory and those plastic
dip tubes have been recalled. Many plastic dip tubes remain on both
S/S valves even after more than 15 years since the first recall. Poorly
trained and careless visual inspectors have failed to replace these
recalled items.
Technical, high quality visual cylinder inspections are not difficult to
perform. However, without proper technical training, an inspector
has little chance of knowing or accessing the specific information
necessary to properly judge cylinder condition. The rules, industry
standards and other guidelines simply are too scattered for most
individuals to locate. PSI, Inc. has a single purpose and that is to
search out high pressure cylinder information important to visual
inspectors, fill station operators and cylinder handlers and make it
readily available in our one day, hands -on
workshops. Over 200 workshops are conducted annually in North
America and at some international locations.
For more information about PSI and cylinder
safety, visit our web site at www.psicylinders.com
e-mail at
psi@psicylinders.com or call us in the USA at 425.398.4300. We
train fire fighters, fill station operators, equipment repair technicians,
hydrostatic retesters, scuba instructors dive store staff and many more.