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Scuba Cylinder and Valves Support Pages
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SCUBA Cylinder Manufacturing
Specifications |
In America, the standards for testing high pressure cylinders are developed by the CGA (Compressed Gas Association) in conjunction with DOT (Department of Transport). The relevant CGA copyrighted specifications are listed below and are available for download here (from the CGA web site).
Test stations applying for DOT approval must have their own individually licensed copies of the CGA documents needed to carry out the cylinder inspections the test station offers.
Note:- That the CGA charges fees for each downloaded document. A handful of documents may well cost you a few hundred US$
The necessity for compressed gas cylinders to be tested and approved when transported by road (in accordance with the CGA regulations) is enshrined with US law within the Code of Federal Regulations
Special Notes for Fill Station operators DOT-3AL3000 Cylinders
SP890 , SP6688 , E6688 , SP6576 , SP7039 , E7235-4500psi
SP6498 , E6498 , E7042 , E8364 , E8422
An example of a 'dodgy' cylinder thus marked is DOT-E6498-3000. This marking should make you instinctively reach for your NDT tester if it ever graces your test bench.
Read this US DOT report for further information http://hazmat.dot.gov/regs/notices/sa/not94_7.htm
EC legislation has given rise to the Carriage of Dangerous Goods acts CDGCPL-2 requiring all transportable pressure vessels be subject to periodic inspection by an approved person. Though in many of the countries that make up the E.C., testing to older legislation (such as the old British Standard system in the United Kingdom) still continue to be applied until replaced by unified European wide standards which includes all the member states wishes for the different types of pressure vessel in use.
New European Standards
Older British Standards
T6351 Aluminium Alloy Scuba Cylinders (requiring NDT) identification guide
SCUBA Cylinder Manufacturing
Specifications for testing to BS/EN/CGA limits
Located in the technicians password
protected area - <click here to download>
Thailand represents one of the largest and fastest growing scuba destinations world wide, and has good legislation in place for the testing high pressure cylinders.
TIS (Thai Industrial Standards) booklet TIS 358-2531 (1988) "Standards for use and maintenance of compressed gas cylinders" ISBN-974-8112-29-2 uses hydrostatic methods similar to that used in USA, European and UK standards.
This booklet is currently only available in Thai language (click image to download).
Key points from this standard voice a '3 year' periodicity for hydrostatic testing, and that condemned cylinders must be 'cut in half' to prevent them from being used again.
Sadly, given the size of the Thai recreational Scuba Market consisting of more than 600 Dive Centers, this test standard is almost unknown, and government enforcement of it's procedures is practically non-existent.
download Thai Industrial Standard 358-2531 (ISBN 974-8112-29-2) 1.6Mbyte
A comprehensive examination of the different International techniques outlined above is covered during the ASSET Cylinder Inspector Pt1 & Pt2 course training.
Unlike most steel or aluminium cylinders, fibre wrapped composite types have quite a short pre-defined life span of usually only 15 years.
Hydrostatic re-test periods are similar to metal cylinders of between 3-5 years, but the number of times you may subject the cylinder to hydrostatic test may also be limited. some types permit only 3 hydro test attempts following manufacture, and then the cylinder must be condemned.
Contact the manufacturer directly if in any doubt about the latest test methodology for these very special cylinders. The following represents typical test/re-test data for this cylinder type.
Lifespan:-
15years only
Hydrostatic re-test period:-
3 years
Hydrostatic Test Pressure:-
5/3 of Working Pressure
Permanent Set allowed:-
5% of volumetric expansion
Hold duration at Test Pressure:- 30secs minimum
(most testers hold the hydrostatic test pressure for 60 secs )
Cylinder Marking:-
No metal stamping on the cylinder body is allowed
at all
The re-test station verifies the hydrostatic test pass by affixing a custom
label with the test station mark,month and year, sealed onto the cylinder
body with epoxy resin
Training in Visual inspection plus the required test equipment and tools is relatively inexpensive to obtain. However, hydrostatic test rigs costs are very expensive and cost around US$15,000 minimum.
If you have the formal engineering skills and fancy building your own hydro rig for a fraction of the cost.
Download the engineering drawings for a scuba
tank hydrostatic test system
here
This has kindly been answered with a very clear series of pictures by the nice folks at SeacSub
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