The working lifetime of a scuba cylinder is entirely up to its owner and how well they care for it. The usual is years (there are several in service at headquarters that are older than some of our junior staff members) but abuse a cylinder and those years can be shortened to just months!
Because cylinders feel and look tough, which they are, some owners think of them as indestructible, which they are not! It’s not particularly difficult or time consuming to look after scuba cylinders… in fact they may be the simplest pieces of a diver’s kit to maintain… but they top the list of things that we take for granted and are right there with lead weights as the most likely items to suffer neglect.
Let’s look at some basics of cylinder care that if followed will mean longer life, a much better chance of passing annual visual inspections and periodic hydrostatic testing… and hugely diminished likelihood of kind of explosive rupture that can endanger lives and property.
Regular inspection by a qualified technician
First step is to make certain your cylinder is visually inspected (VIP) and hydrostatically tested on a regular basis.
An annual visual inspection is recommended as a minimum with average use. There are plenty of examples of use that’s outside the average. For example, when using a cylinder regularly in warm, humid climates, the recommended practice is to perform a VIP every three to six months.
Other instances where more frequent inspections are good practice include when knocks and dings damage the cylinder’s exterior; when there’s noise coming from inside the tank; if the tank feels heavier than usual; when there’s evidence of corrosion on the regulator filter; anytime the cylinder is completely emptied during use or when the valve is removed for shipping/travel or hydro testing; if a filter goes on the compressor while tank is online filling; and after long-term storage.
Hydrostatic testing is required every five years but once again, that’s a maximum time between tests.
The frontline defenses for dive cylinders are the dive professionals who inspect and service them. These inspections play a critical role and help to ensure cylinder owners will enjoy the maximum useful life from their equipment and that their equipment complies with the industry’s safety guidelines. Every year a few cylinders do explode, but visual inspectors and hydrostatic facilities catch hundreds of suspect cylinders and remove them from service before this happens.
Pre-dive and post-dive care
Treat your cylinders with respect when transporting them. Prevent them rolling around, bumping into each other or anything else hard. Keep them out of the sun, and extreme cold. DO NOT overfill them beyond their DOT or TC recommended working pressure. Fill them at the prescribed rate and do not allow them to be filled rapidly enough for the cylinder walls to become hot to the touch. Inspect the exterior for wear and tear, extruding ORings and deep digs and scrapes.
Post dive, disconnect regulator, rinse cylinder well with fresh water (unless you are diving in fresh-water lakes and springs in which case you can probably skip this step!). Dry them off, inspect valve and on off knob for wear or damage. Then store until the next use upright in a cool, dry location with about 20 bar or about 250 to 300 psi of gas in it.
Care during a dive
Simple: do not allow the internal pressure to drop below three times the ambient pressure. That means on a dive to 30 metres or 100 feet, do not let the pressure drop below 12 bar or about 175 psi.
Long-term storage (three months and more)
Clean and inspect the cylinder before storing it. Make sure there is no water in the cylinder, take off any boots or other accessories and dry the outside thoroughly. Store a scuba cylinder upright and secured with just a few bar or psi of air (not nitrox) in it. In a steel cylinder, this will help to reduce corrosion because of reduced oxygen partial pressure. While this is not so important with an aluminum cylinder it remains a sound practice.
Before putting the cylinder back into service, have it visually inspected and refilled.
One last point, always analyze your gas and always take a few trial breaths from your cylinder(s) before taking them into the water.