Make sure your tank is visually inspected every year
In the United States, scuba cylinders are visually inspected by a trained professional every year. Regulations vary by country so again, check your local laws. There’s a few things we look for during a visual inspection:
- Any significant damage to the surface of the cylinder such as dents, cuts, or corrosion. This may require that any stickers are removed from the tank, especially if the technician suspects any rust or other damage is being hidden by the decal. It’s pretty easy for a little salt water to get trapped behind a sticker and to start causing problems, so I prefer to keep only two small decals on my tanks: a contents label near the valve, and a sticker showing the date of the most recent visual inspection.
- Signs of damage around and inside the neck of the cylinder. This includes taking a close look at the threads to make sure they haven’t been stripped or damaged.
Presence of any corrosion inside the tank. The technician is really interested in pitting that’s deep enough to compromise the strength of the cylinder. These pits tend to only get worse with continued use. Sometimes the corrosion can be removed by tumbling the tank with a ceramic beads or something similar.
- Damage to the valve, including the threads.
- In some circumstances, an eddy current test may be conducted to check for microscopic cracks in and around the tank threads. This is most commonly encountered with aluminum cylinders that are made from (or suspected to be made from ) the 6351-T6 aluminum alloy. Some cylinders made from this alloy have failed over the years, and it’s not uncommon for some dive shops to refuse to fill any tank that might be made from 6351-T6. For more information check out the DOT regulation. It’s important to note that no scuba cylinders have been made from this alloy since February 1989, so if your aluminum tank was made before 1990 it’s a good idea to look into this.
As it turned out, my friend’s tank had gotten mixed in with another group of cylinders and as a result it had not been visually inspected in a couple of years. If he had, there’s a good possibility that the technician would have condemned the tank due to the corrosion inside long before the cylinder blew up in his garage!