Originally posted by Green_Manelishi
actually, a tank boot serves no useful purpose other than to
stand a tank up (and we KNOW the hazards of that practice)
inquiry: what is the point of a boot on an ALUMINUM tank?
First of all, tanks should be stored upright. (this business of storing tanks on their sides is another one of those "everybody knows" things that's crept into the Scuba literature and common knowledge that falls apart on examination)
As for the boot on an aluminum tank, it's dual purpose is to protect the fancy paint job, and to keep the tank from rolling when laid down on a not-quite-level surface. (That doesn't make it a good idea to have a boot on an aluminum tank, but the question was "what is the point?" and those are they)
Here are some cites on the vertical storage:
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http://www.scubadiving.com/gear/tanks/
HANDLE WITH CARE
Scuba cylinders are tough, but they're not Sherman tanks and should not be needlessly banged about. With cylinder walls averaging one-half inch for aluminum and one-fifth inch for steel, it's not possible for divers to puncture a cylinder. However, all metals are susceptible to metal fatigue, cracks, and corrosion or rust. When weak spots are subjected to the pressure of compressed gas they can give way.
Even if the cylinder isn't damaged by rough handling, the chrome-plated brass valves might be. Valves should be kept clean and serviced on a regular basis. To prevent leaks, replace damaged O-rings and keep them free of tape and salt residue.
Secret number three: Regardless of the material it's made of, keeping moisture out of your cylinder is the most important act of preventive maintenance.
The best way to do this is to keep some pressure in it - 100 to 300 psi will do the job. After use, wash and dry the cylinder and valve. Every once in a while it's a good idea to remove boots, bands and other protective coverings so salt deposits can be cleaned away and the exterior can be inspected for corrosion or damage. When stored, the cylinder should be secured vertically in a cool, dry place.
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http://www.scubadiving.com/gear/27tanktips/
Steel oxidation-rust-is more serious because the process can continue deep into the metal. Salt water inside the tank, and storage of the tank under pressure in one position, which concentrates the water and rust in one spot, can even turn a tank into a missile (see: "We Have Liftoff"). Lying on its side will be worse than standing on end, because the walls of the tank are thinner than the bottom. A tank charged with nitrox will also be at greater risk because of the greater concentration of oxygen in the mixture.
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On the other hand, Bill High swears this is a true story: A tank stored in a house, standing upright, fully charged and rusting from the inside out, burst a two-inch hole through its bottom. The tank shot up through the roof of the house and came down through the roof of a factory a mile away.
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The following is from the Compressed Gas Association guidelines... (note the fourth "Shall")
http://www.ehs.iastate.edu/publications/gascylinder.htm#compressed
All gas cylinders:
Shall not be stored in exits or egress routes.
Shall be stored within a well-ventilated area.
Shall not be stored in damp areas, near salt or corrosive chemicals, fumes, heat or where exposed to the weather.
Shall be stored in an upright position.
Shall be secured with a chain or appropriate belt above the midpoint, but below the shoulder. Laboratory cylinders less than 18" tall may be secured by approved stands or wall brackets.
Shall be capped when not in use or attached to a system (if the cylinder will accept a cap).
Shall be kept at least 20 ft. away from all flammable, combustible or incompatible substances. Storage areas that have a noncombustible wall at least 5 ft. in height and with a fire resistance rating of at least 30 minutes may be used to segregate gases of different hazard classes in close proximity to each other.
Shall be stored so that cylinders are used in the order in which they are received.
Shall be stored so that gases with the same hazard class are stored in the same area. Inert gases are compatible with all other gases and may be stored together.
Shall not be stored longer than one year without use.
Shall be stored so that full cylinders remain separate from empty cylinders.
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And now, for a shiny new dime, who can tell me why aluminum cylinders should be stored at either working pressure or with less than 300 psi in them, but never in between?
Rick
