Scuba Diving Cylinder Testing and Markings 0

Scuba Diving Cylinders, Markings, Testing and Useful Information
This is what the markings represent

Govt. Agency Supervision / Approval DOT or DOT/CTC = Dept. of Transport or Canadian Transport Comm.
Metal Type: 3AA = Steel / SP6498, E6498 or 3AL = Aluminum
Working Pressure: Maximum pressure lbs / inch2 (steel = 2250, al = 3000-4000 psi)
Serial Number: 12345 = Unique to tank Manufacturer
PST = Manufacturer of the Cylinder Hydrostatic Test Date / Hydrostatic Tester’s Mark
6 1996+ = Hydrostatic Test Date (Month, initials of tester, year)

+10% Overfill Allowed + = 10% overfill allowed on STEEL TANKS ONLY
These marking should always be checked before filling.
This is important even in different countries with different tank markings.
Cylinders manufactured, have specification stamped on the cylinder which include Working Pressure, Test Pressure, Data of Manufacture, Capacity and Weight.
Before filling a scuba tank with air, you should always check the tank markings, specifically looking for a current hydrostatic and pressure test date and maximum capacity / pressure. Don’t overfill scuba cylinders.

Diving Cylinders are required to be Hydro statically Tested (Pressure Test) every 5 years with an incremental visual inspection every alternate 5 years. Therefore your cylinder should be tested every 2.5 years alternating between the 2 tests. Cylinder tests now include a valve service as part of the test process.

Cylinders used for surface use ie Airguns and Paintball Cylinders need to be tested every 5 years. Our policy is that a cylinder with a diving valve in must be tested as a diving cylinder as it could always be used in Seawater for the purpose of SCUBA. If you wish to reduce your service costs then please fit a surface use valve.

Visual Inspection (every 2.5 years)
detailed visual inspection, both internal and external with the following checks being carried out
Any Bulge – all fail
Dent – fail if greater than 2mm
Wear – reduction of wall thickness greater than 25%
General Corrosion – reduction of wall thickness greater than 20% OR where original surface is not visible
Area Corrosion – (I.e. where corrosion is limited to less than 20% of surface) a reduction of wall thickness greater than 25%
Isolated Pitting – Reduction of wall thickness greater than 40%
Thread Damage – all physical damage or imperfections (re-cutting of threads can be achieved up to maximum tolerance)
Weight Check – Weight of cylinder (less valve & boot) less than 95% of the tare weight stamped on the cylinder
Any cylinder that has been subject to impact damage should be pressure tested before use.
If in the opinion of the inspector, any of the above criteria are borderline, then Hydrostatic testing may also be required.

Hydrostatic Test
The cylinder is filled with water and then placed inside a water filled, high pressure chamber. The water pressure inside the cylinder is the increased to five thirds of its maximum working pressure. This is sufficient to cause the cylinder to expand slightly. This expansion causes the water outside the cylinder to be displaced and this is channelled into marked collection tubes that allow it to be measured. If the cylinders expansion is within acceptable limits (<5%), it passes the test.

Test Procedures
Removal of the cylinder boot, bands and valve(s)
The exterior of the cylinder is then inspected for impact damage and corrosion
The interior of the cylinder is examined using a special endoscope
Examine the area around the inside of the tank neck
The valve is checked for smooth operation and its threads lubricated to help prevent galvanic action between the dissimilar metals of the tank and valve
Valves may also require periodic overhauls, just like scuba regulators
If no corrosion or damage is detected, the cylinder is reassembled and filled
A sticker is then placed on the tank which identifies the facility providing the inspection and the month and year in which the inspection was done
If damage or corrosion is detected, the technician will decide upon an appropriate course of action
Minor scale or the presence of contaminants on the inside of an aluminium cylinder can usually be removed by rinsing with distilled water and drying with warm air
Minor oxidation on the inside of a steel cylinder may be best left untreated due to the fact that the process of removing it might actually weaken the cylinder more than the oxidation itself
Extensive oxidation or deep pitting is treated by degrees of sand blasting

New Standards Testing
The new standards are more stringent and require that all but the very lightest of corrosion needs to be cleaned. This means that your maintenance costs will go up although they will be less frequent. In addition the criteria for failing cylinders are now much more strict. The new standard accepts less damage, set and corrosion on a cylinder before it is scrapped.

Enriched Oxygen Cylinders
These still require inspection and cleaning every 12 months.

At Waterfront Scuba we offer a full cylinder testing service to our club members and customers with a Thursday to Thursday turnaround time, cylinders can be repainted if required in a variety of colours at very competitive rates


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