Will Rec & Tek SCUBA Inc. fill my aluminum 6351-T6 alloy SCUBA cylinder?
Rec & Tek SCUBA Inc. will fill an aluminum 6351-T6 alloy SCUBA cylinder if Rec &
Tek SCUBA Inc. has performed the annual visual inspection on the cylinder
including an eddy current exam. Rec & Tek SCUBA Inc. does not recommend renewing
the visual inspection or hydro-static test for aluminum 6351-T6 alloy SCUBA
cylinders because of issues associated with sustained load cracking (SLC) in
those cylinders. We recommend that aluminum 6351-T6 SCUBA cylinders be removed
from service. At the end of your Hydrostatic Test date on your 6351-T6 Aluminum
Cylinder, Rec & Tek SCUBA will fill the
cylinder providing it passes the visual inspection including the eddy current
exam.
How do I know if my aluminum cylinder is made from the 6351-T6 alloy?
Different manufacturers ceased using the alloy for production of SCUBA cylinders
at different times. Luxfer phased 6351-T6 out over two years and had completely
ceased using it by mid-1988, Cliff Impact ceased using 6351-T6 by mid-1990,
Walter-Kidde ceased SCUBA cylinder production using 6351-T6 in 1989, and
Catalina never used 6351-T6. The US Department of Transportation (DOT) issued an
Advisory at
http://hazmat.dot.gov/pubs/reports/cylinder/3al_advisory.pdf
which
identified in detail most 6351-T6 alloy cylinders (including many non-SCUBA
cylinders) manufactured in the US. You should consult the advisory to precisely
determine which cylinders are made of from the 6351-T6 alloy.
What is an eddy current exam?
This examination uses a tiny current of electricity and is performed on some
types of aluminum cylinders to assist in the detection of cracks in the threaded
neck area. It alerts the inspector to specific locations on the neck threads
that need further evaluation. The devices using eddy current technology are sold
under the brand names Visual Plus, Visual Eddy, and Simple Eddy. The exam is
notorious for false results as a result of poor operator technique and is
intended only to supplement, not replace, the visual inspection. Eddy current
exams are not meaningful on any type of steel. Go to
www.visualplus.net for more
information on our Visual Plus machine.
Why do aluminum cylinders made from the 6351-T6 alloy require an eddy current
test to help detect cracks?
This particular alloy, used during the early days of aluminum cylinder
production, has a history of a phenomenon known as sustained load cracking (SLC)
that can cause a cylinder to fail. Go to
http://www.psicylinders.com/library/Current/6351_review.htm
read an article by Bill High, President of Professional Scuba Inspectors, Inc. (PSI),
for more information about sustained load cracking in aluminum cylinders.
Why will you only fill 6351-T6 cylinders that Rec & Tek SCUBA Inc. has
inspected?
According to Luxfer, your 6351-T6 cylinders are safe for us to fill only "as
long as your 6351-alloy scuba tank is properly inspected". The problem is some
aluminum 6351-T6 SCUBA cylinders are NOT properly inspected, and therefore may
be unsafe to fill because of SLC. According to Bill High, President of
Professional Scuba Inspectors, Inc. (PSI) only about 10% of the people
performing SCUBA cylinder inspections in North America are trained inspectors.
Proper inspection of 6351-T6 alloy cylinders requires special tools and
additional specialized training. Because we have no way of being certain the
cylinder has been properly inspected, and the increased risk to our fill station
operators if it hasn't, we choose to require all 6351-T6 alloy cylinders be
inspected by our trained staff before we will fill them.
Aren't 6351-T6 cylinders properly inspected when they are hydrostatically
tested?
Effective January 1st 2007, the DOT now requires 6351-T6 cylinders receive a
combined visual and eddy current examination when they are hydrostatically
tested. However, it appears all DOT test operators are not yet qualified or
equipped to perform eddy current examinations. Further, the DOT has not clearly
established a training and inspection standard for combined visual and eddy
current examination; they leave it to each facility to determine their own
specific procedures. If you have a 6351-T6 cylinder that has been
hydrostatically tested after January 1st 2007, AND you can provide documentation
that the DOT testing facility also performed a combined visual and eddy current
examination to visual standards, our Fill Station Operators at their personal
discretion may elect to fill the cylinder. As always, Rec & Tek SCUBA Inc.
reserves the right to refuse to fill any cylinder for any reason.
Why do you recommend 6351-T6 SCUBA cylinders be removed from service?
Because our customers tell us it's becoming increasingly difficult to find
facilities that are willing to fill the 6351-T6 SCUBA cylinders. Some dive shops
will not fill 6351-T6 alloy cylinders unless they have performed the visual
inspection and some shops will not fill them under any circumstances. We feel
it's a disservice to our customers to charge to perform an inspection or hydro
when they may have difficulty getting the cylinder filled elsewhere.
Update on the Scuba Tank Explosions:
http://www.napsd.com/cscuba.htm
http://www.connected.bc.ca/~baquatics/explode.html
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