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Scuba Cylinder and Valves Support Pages

Aluminium, Steel and zinc dipped steel scuba tanks spare parts and support
Good tanks, bad tanks and tanks that go 'bump' in the night!
LATEST NEWS...DOT3AL3000 CGA C-6.1-2006 Thread Gauging requirement clarification...

SCUBA Cylinder Manufacturing Specifications & test standards are
Located in the technicians password protected area
<click here to Enter>

exploded scuba tank bombexploded scuba tank bombexploded scuba tank bombexploded scuba tank bombexploded scuba tank bombexploded scuba tank bomb

big steel J-bottle goes bang - thankfully nobody killed. Click to open incident report 150kb pdf

condemned scuba cylinder bursted to convince African natives that they are no longer safe to use

Corosion in cylinders

photo courtesy of the Asia Industrial Gas Association http://www.asiaiga.org/

Asia Industrial Gas Association
The full AIGA report is  AIGA cylinder incidents.pdf 3.4Mb

'TRAINING TO SERVICE SCUBA TANKS

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.

Cylinder Testing Course - Level 1 (Practices and Procedures - VISUAL INSPECTION)

Cylinder Testing Course - Level 2 (Metallurgy, Inspection and Determination - HYDROSTATIC INSPECTION)

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.


Need NDT Crack Detection for T6351 copper-aluminum alloy?

try Visual Plus NDT by Advanced Inspection Technology

Visual Plus 3 computer controlled NDT testing for crack detection in aluminum cylinders

visualplus_manual.pdf  1.8Mb

Visual PLus 3 Computer controlled NDT Training Video  11.4Mb


How Bad can corrosion pits get ?

Presenting - A scuba tank that even a Yemeni Beduin compressor operator straight off the camel won't fill...

Isolated corrosion pits of biblical proportions 1 - CLICK FOR HIRES 0.5MBIsolated corrosion pits of biblical proportions 2 - CLICK FOR HIRES 0.5MbIsolated corrosion pits of biblical proportions 3 - CLICK FOR HIRES 0.5MbIsolated corrosion pits of biblical proportions 4 - CLICK FOR HIRES 0.5MB


Introduction to high pressure cylinder SCUBA tank testing regulations

1.    American DOT-3AL3000 Cylinders

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$

  • C-1      Methods for Hydrostatic Testing of Compressed Gas Cylinders
  • C-6      Carbon Dioxide
  • C-6.1   Standards for Visual Inspection of High Pressure Aluminum Compressed Gas Cylinders
  • G-4      Oxygen
  • G-4.1   Cleaning Equipment for Oxygen Service
  • G-4.3   Commodity Specification for Oxygen
  • G-6.2   Commodity Specification for Carbon Dioxide
  • G-6.3   Carbon Dioxide Cylinder Filling and Handling Procedures
  • G-7      Compressed Air for Human Respiration
  • G-7.1   American National Standard Commodity Specification for Air
  • G-8.2   Commodity Specification for Nitrous Oxide
  • P-1      Safe Handling of Compressed Gases in Cylinders
  • P-2      Characteristics and Safe Handling of Medical Gases
  • P-5      Suggestions for the Care of High Pressure Air Cylinders for Underwater Breathing
  • P-14    Accident Prevention in Oxygen Rich and Oxygen Deficient Atmospheres
  • P-2.5   Tran filling of High Pressure Gaseous Oxygen to be Used for Respiration
  • PS-7    CGA Position Statement of the Safe Transportation of Cylinders in Vehicles
  • SB-7    Rupture of Oxygen Cylinders in the Diving Industry

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

  • CFR   Title 49 Parts 100 to 185
  • CFR   Title 21 Parts 200 to 299
The current approved USA DOT testers listing is given here http://hazmat.dot.gov/sp_app/approvals/hydro/hydro_retesters.htm

Special Notes for Fill Station operators DOT-3AL3000 Cylinders

  • No cylinder can be filled with altered markings. Condemned DOT Cylinders have the 'DOT' and the pressure ratings 'X'd out
  • Only cylinders with approved burst disks may be filled
  • Only aluminum cylinders marked '3AL' may be filled.
  • All the cylinders below must be removed from service

        SP890    ,    SP6688    ,    E6688    ,    SP6576    ,    SP7039    ,    E7235-4500psi

  • All cylinders marked below cannot be filled until they have been tested by a hydro facility, NDT tested, and over stamped with '3AL'. Also note:-
    • That these older cylinders are made of the troublesome T6351 aluminum alloy.
    • The alloyed used in these cylinders has well known susceptibility to Static Load Cracks (SLC)
    • They have caused several catastrophic explosions and the deaths of many cylinder fillers.
    • They are subject to 4 monthly visual inspection periods if in heavy use such as at a dive school

    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.

Thread Form Testing

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

Special Publication Note Dec 2007 - Gauging NPSM 3/4 threads. Clarification statement for ASSET members

CFR49 part 171 - General Information, Regulations and definitions - DOT NPSM thread gauging

CGA C6.1 thread standards comments #1CGA C6.1 thread standards comments #2
Extract from CGA C6.1 standard 'threads must be of proper form according to the thread standards'

Thread_standard_npsm_tolerance.pdf
[Code of Federal Regulations 171.2]
[Code of Federal Regulations 178]
[Code of Federal Regulations 180]

Identifying the need gauge DOT 3AL3000 threads
CFR Thread Testing References
thread_standard_npsm.pdf
thread_standard_npsm_tolerance.pdf
threadcheck_catalogue.pdf

dynamics-of-gaging-complete.pdf
iso_metric_plug_gauges.pdf
plain_gauges_limits_and_fits.pdf
Straight Pipe Thread Plug Gages
thread_pitch_diameter_standards_reference.doc

H28_thread_standard.zip
Luxfer Valves Thread gauging Instructions

2.    European Cylinders

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

  • BS5045 pt3 for Seamless Aluminium Cylinder
  • BS5045 pt 1 for Seamless Steel Cylinders.

T6351 Aluminium Alloy Scuba Cylinders (requiring NDT) identification guide

  • All HOAL
  • EC type prior to 1992
  • BS 5045 Part 3 prior to 1994
Are made from 6351 alloy. The date is stamped on the cylinder
Alloys in later production are   • Identified by a letter code adjacent to the standard number
    A = 6082, B = 6351 and C = 6061
    e.g. BS 5045/3/C/S = 6061 alloy
The current approved UK IDEST stations listing is given here http://www.sita.org.uk/

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

 

SCUBA Cylinder Manufacturing Specifications for testing to BS/EN/CGA limits
Located in the technicians password protected area - <click here to download>

 

3.    Thailand

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).

Thai Industrial Standard 358-2531 Standard for use and maintenance of compressed gas cylinders.

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:-

  • Valve ejected (mismatched thread)    Mae Haad, Koh Tao, Thailand 2006. Dive shop compressor room damaged, Roof holed. cylinder valve presumably still orbitting the earth...
  • Dive Instructor leg nearly amputed by ejected valve. Mae Haad, Koh Tao, Thailand 2005. Cylinder went through 2 concrete walls and landed on a tourist beach bungalo...
  • Valve ejected during filling, thread failure, Chalong, Phuket, Thailand 2002. Dive boat sunk
  • Filling hose failure, Pattaya, Thailand 2006. Dive Instructor severly injured when hose hit his face. wound exposed jaw bone.14 stiches to close the wound.

A comprehensive examination of the different International techniques outlined above is covered during the ASSET Cylinder Inspector Pt1 & Pt2 course training.

Luxfer cylinders web site linkCatalina cylinders web site link

Both the manufacturers above have excellent web sites contain the latest up-to-date information and news on scuba tanks. 

PAINTBALL Cylinder Inspection Information

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


Special Notes on Fibre-wrapped Composite Cylinder Types

fibre hoop wrapped composite scba cylinder

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
 


DIY Hydro test Rig manufacturing Information

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


Unusual DOT3AL3000 Threads 'Condemn'
Thread corrosion that has propagated along the grain boundary.

grain boundary thread corrosion - CONDEMNthreads inspection - you really need to have your good eyes inspecting threads against wishy-washy standards
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.


Worst Corrosion every seen on DOT3AL3000...
(unless you have seen worse - gulp!)


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"


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