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Scuba Cylinder and Valves Support Pages
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SCUBA Cylinder Manufacturing
Specifications & test standards are |
photo courtesy of the Asia Industrial Gas Association http://www.asiaiga.org/
The full AIGA report is
AIGA cylinder
incidents.pdf 3.4Mb
Click here to book your IDEST High Pressure Cylinder Visual & Hydrostatic Inspection Training Course |
The skills and information necessary to safely inspect and test high pressure scuba tanks are learnt by attending the following ASSET approved courses.
The best free handbook available for the guidance of personnel involved in the visual inspection of DOT 3AL3000 scuba cylinders is the Visual Inspection Guide produced and made available free of charge by the Luxfer company. You may download it here (see below). Please check the Luxfer site from time-to-time for a more recent download. There is plenty of other hard to find useful info listed here
Download Luxfer DOT3AL Visual Inspection Guide(English) - new version with extra photos.pdf (1.42Mb)
United Kingdom HSE Guide to 'Safe Use of Scuba Tanks' (192Kb)
how_to_make_a_steel_scuba_tank_video.flv 5.7Mb
Download German language tank testing information "flaschen_und_Ventile" (12.2Mb)
Catalina Tank Valve Insertion Instructions .PDF (30Kb)
Thermo Valve Maintenance Instructions.pdf (1.08Mb)
Offshore compressed air cylinder explosion report .pdfion (143Kb)
high pressure hose connectors from foster_couplers_2004.pdf (1.9Mb)
NASTY THREAD CORROSION - Click here for a short thread disaster movie
Inspectors comments
Isn't it strange how the CGA Grade 'E' divers breathing air standard doesn't
specify the amount of moisture permissible in a divers breathing air. Guess they
must be in the tank selling business, since with that sort of breathing air
spec, this sort of corrosion is guaranteed.
try Visual Plus NDT by Advanced Inspection Technology
visualplus_manual.pdf 1.8Mb
Visual PLus 3 Computer controlled NDT Training Video 11.4Mb
Presenting - A scuba tank that even a Yemeni Beduin compressor operator straight off the camel won't fill...
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.
Identifying the need to carry out Thread Form testing of DOT 3AL3000 cylinders using a Thread Gage· The US CFR law calls for the DOT 3AL3000 cylinders to be inspected to CGA-C6.1 · The latest CGA-C6.1-2006 calls for the thread form to be inspected and verified 'to have the specified number full threads of proper form as required in the applicable thread standards every time the valve is removed' · The applicable thread standard for the 3/4 x 14tpi NPSM thread used in the DOT3AL3000 cylinders is ANSI/ASME B1.20.1 - 1983. This calls for the thread form to be verified with a thread gauge · The gauging methods standard describing how to use a thread gauge is ANSI/ASME B1.2-1983, and calls for a maximum of 3 turns to be allowed on the thread gauge used for internal threads. Extract from the latest CGA C-6.1 (Copyright & Courtesy of http://www.cganet.com/ ) To download your own original licensed copy of the full CGA C6.1 follow this link http://www.cganet.com/customer/publication_detail.aspx?id=C-6.1
CFR49 part 171 - General Information, Regulations and definitions - DOT NPSM thread gauging
Thread_standard_npsm_tolerance.pdf
Identifying the need gauge DOT 3AL3000 threads
dynamics-of-gaging-complete.pdf
H28_thread_standard.zip |
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
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Thread Form testing
The "by the book" answer is that there should be
no turns allowed on a Not Go gauge (if you
think about it, that's why it's called a Not Go gauge!).
However, in many industries, particularly where maintenance
activities are concerned, it is common to allow something
for reasonable wear and tear.
In the past, the general advice given (and widely accepted)
in the UK concerned only the G3/4" thread and that advice
was that up to 4 turns on the Not Go gauge could be allowed
on the valve, providing that the cylinder thread was good.
However, over the past 20 years or so, European M25, G5/8"
and the American 3/4" NPSM used on DOT-3AL3000 cylinders
threads have become widely used. Additionally ASSET's
membership has become Worldwide, therefore, it has been
necessary to revise and rationalize this advice.
To keep matters simple, we believe a reasonable
rule of thumb to be as follows: Providing the
technician is satisfied that all threads are physically
sound and the cylinder neck threads have been gauged and the
Not Go gauge does not go then 1 (one) turn on the Not Go
gauge might be allowed on the valve stem thread for every
four good turns engaged. In effect this means approx 1
Turn on a 200 bar Din outlet, 2 Turns an M25, and 3Turns on
a G3/4 and so on.
This guidance should be applied with
caution and is at the discretion of the individual
technician who must take into account the circumstances as
they present themselves.
Best regards
C Stewart Meinert
ASSET Chief Instructor an Technical Coordinator
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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.
Relevant Standards effecting compressor operators and high pressure cylinder users are listed online here:- http://www.tisi.go.th/standard/cat_eng.html
TIS 358-2551 (2008)
Use and maintenance of compressed gas cylinders
TIS 88-2517 (1974)
Identification colours and marking for industrial gas cylinders
TIS 359-2530 (1987)
Pressure gas cylinders, seamless type
TIS 1095-2535 (1992)
Medical gas cylinder valve connections
TIS 642-2529 (1986)
Rubber hoses for compressed air
Sadly, lack of effective legislation and enforcement of not only the cylinder inspection standards but also divers breathing air standards by PADI in Thailand leads to most dive centers pumping scuba air that does not meet international divers breathing air standards.
ASSET/IDEST technicians working in this region are reporting near 100% of all scuba cylinders supplied for re-testing from recreational dive centers are suffering from extensive internal corrosion, plus nearly all compressors supplied for service/repair from Dive centers have non functioning or incorretly set Pressure Maintaining Valves (PMV) - The single most important component of the compressor responsible for removing moisture from the breathing air, and the starting point of creating EN12021/CGA Grade-E divers breathing air.
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 below to download).
download Thai Industrial Standard 358-2531 (ISBN 974-8112-29-2) 1.6Mbyte
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 within the recreational scuba industry is practically non-existent.
Uneducated fools, usually from a sales back-ground hawking dodgy cylinders have been heard to state, "Their is no requirement to test scuba cylinders or inspect high pressure air hoses in Thailand..." & "there is no requirement to check the thread form of the valve and cylinder neck when refitting valves". Resulting in the following typical calamities:-
A comprehensive examination of the different International techniques outlined above is covered during the ASSET Cylinder Inspector Pt1 & Pt2 course training.
Fibre Wrapped High pressure cylinders
paintball_usa_carbon_composite_cylinders.pdf 361Kb
dot_cffc_5th.pdf 69Kb
dot_e_10915.pdf 187Kb
luxcompinspectmanual.pdf 4.3Mb
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
INSPECTORS NOTE - The problem above (left hand photo) is absolutely not
visible from the small thumbnail above in any way
Click on the image to download a high resolution 400Kb Photo to view the problem
running along every thread. The right hand photo is presented from the
manufacturers inspection guide. This is a really difficult inspection call and
often requires a manufacturers decision.
Manufacturers Comments
The (high resolution left hand photo) appears to me to be corrosion that has
propagated along the grain boundary. I have seen many times in scuba where
corrosion will begin between the 8th and 12th thread of the cylinder, at the
exact location where the valve ends in the cylinder. This is most likely due to
the moisture that sits at the junction between two dissimilar metals. The
corrosion is greatest in the grain boundary, inter-granular corrosion, and
propagate along the grain. The grains predominately run perpendicular to the
axis of the threads and when attacked by corrosion can appear as linear
indications similar to folds or cracks – but are not. It appears in the second
picture that some metal is missing in the 11th thread - a condition typically
associated with corrosion, never a crack.
In checking a cylinder with an eddy current device usually a 2 thread indication
is reason for reject. This cylinder may be rejected for a linear condition,
corrosion, that extends more than 2 threads but it is not rejected for a
manufacturing defect.
Manufacturer Decision:-
In a case like this we would offer our replacement program to the owner of this
cylinder.
Click each image for Hi-Res 135Kb image
Inspectors comments
"Even my Yemeni goat herdsman employed as a tank filling boy refused to fill
this one"
This has kindly been answered with a very clear series of pictures by the nice folks at SeacSub
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