A notice for all considering buying an Aluminium SCUBA tank - please be aware that tanks manufactured prior to 1991 and made of a 6351 aluminium alloy may be 'at risk' of fracturing and/or exploding.
Many SCUBA stores around Australia now refuse to fill these tanks due to the associated risk of explosion and injury, regardless of whether the tanks are 'in test' or not. So please be aware that unless your tank was made after 1990/91 and/or is not one of those in question you may be buying an expensive door stop!
Details as follows:
Queensland Government Safety Warning:
‘SCUBA cylinders manufactured from aluminium alloy 6351 are presently the main basis for concern. WHSQ strongly advises that all SCUBA cylinders manufactured from this alloy, and other aluminium alloy cylinders 15 years or older, be non-destructively examined annually for cracks and flaws in the neck fold and thread areas by competent and suitably equipped persons.
This should be in association with annual internal visual and hydrostatic inspections by competent and suitably equipped persons covered by Australian Standard AS 2030.1:1999
The verification, filling, inspection, testing and maintenance of cylinders used for storage and transport of compressed gases. Part 1: Cylinders for compressed gases other than acetylene (known as the SAA Gas Cylinder Code).
At risk SCUBA cylinders manufactured from aluminium alloy 6351 include:
• Luxfer aluminium alloy cylinders manufactured between 1972 and 1988 (check oldest hydrostatic test date stamped into cylinder)
• Luxfer aluminium alloy cylinder specification DOT SP6498
• Luxfer aluminium alloy cylinder specification DOT E6498, E7042, E8107, E8364, E8422
• CIG (Australia) aluminium alloy manufactured in or before 1990 (check oldest hydrostatic test date stamped into cylinder)’
New South Wales Government Safety Warning:
'This safety alert is published following serious injuries to a person while filling an aluminium self-contained underwater breathing apparatus (SCUBA) cylinder in August 2009. The cylinder shattered into pieces (see photo).
This is the latest in a number of incidents involving the filling of aluminium SCUBA cylinders manufactured from 6351 alloy. The 6351 alloy was used in:
• aluminium alloy cylinders manufactured between 1972 and 1988 to specifications DOT SP6498, DOT E6498, DOT E7042, DOT E8107, DOT E8364, and DOT E8422
• Australian made aluminium alloy cylinders manufactured before 1991 to AS 1777.'
Luxfer (manufacturer of the Luxfer and CIG tanks affected) responded by issuing a safety notice advising that less that ~1.25% of their 1 million plus cylinders exhibited 'sustained load cracking'. And that only 40 instances of tank failure had been reported (12 of them scuba cylinders).
More information can be found on various Australian Work Cover and safety Bulletin web sites, and on the manufacturers (Luxfers) pages.
Safety testing exists to identify whether aluminium tanks have developed cracks (eddy current testing) and hydrostatic testing to identify deformation of the tanks, and they will cost around $70 from your local Scuba test centre.
However a pass rating of the tank (i.e the tank is 'in test') does not guaratee that your local scuba store will in fact fill your tank due to the potential risks associated with explosive decompression of the tanks if they should fail.
I have personally found the Scuba stores I have used will not fill them, and doing a quick google search will show other stores warning the same. As stated earlier - you MAY be buying an expensive doorstop.
It is very much a case of do your homework, assess the risks of buying second hand equipment (especially life support equipment) and buyer beware! :)