cfelliot
Contributor
Would it make sense to refurbish an old steel tank? This would mean a hydro and new valve? Does the cylinder itself have a lifetime if not abused?
Refurbish Old Steel Tank
- Thread starter cfelliot
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captain
Contributor
A 3AA steel cylinder that has not been abused meaning no rust, dents, overpressured or exposed to fire has an indefinate life. There are steel welding gas cylinders in use that are over 80 years old. I have a few steel 72's that are 50 years old.
Our local hydrotest facility still hydros and passes welding tanks from the WW-I era and I have seen steel welding tanks from the 1920's still qualify for a plus rating, so they do virtually last forever.
Steel tanks are not prone to the sustained load cracking that can plauge an aluminum tank. However the thing that will kill a steel tank is standing water droplets in the tank as they will eventually cause pits to form in the tank and these pits becomes stress risers that will cause the tank to fail a VIP. Similarly, not removing accumulated flash rust periodically (maybe every 10 years or so) creates a substrate that will attract and hold moisture and eventually lead to pitting.
If there is no visible pitting in the bottom of the tank and there is not too much flash rust, it is worth having hydro tested. If there is an excessive amount of flash rust it will need to be tumbled before a thorough VIP can be completed. If it looks good, then it is worth sending in for a hydro test.
So... the cost can be pretty minor if the tank is clean or, in the case of accummulated flash rust, it can cost you a bit to determine if it is worth hydro testing. The hydro test itself is most likely a non event as it is exceedingly rare for a steel tank to ever fail a hydro test as what kills them is rust pits, not metal fatigue.
The nay sayers will say that by the time you pay for the hydro, VIP and new valve you have spent a fair amount toward the cost of a new AL 80. But steel tank fans will point out that if you buy an AL80 all you have is an AL 80 that will probably last only 20 years. They will point out that you refurbish the steel 72, you will have tank with better bpouancy traits that will still be going strong in another 20 years and will probably outlast your diving career.
As a practical matter, if it is a galvanized steel tank, it is worth the effort while if it is a non galvanized painted tank, you need to carefully consider the exterior condition of the tank as well as it is more maintenence intensive to keep it painted.
Steel tanks are not prone to the sustained load cracking that can plauge an aluminum tank. However the thing that will kill a steel tank is standing water droplets in the tank as they will eventually cause pits to form in the tank and these pits becomes stress risers that will cause the tank to fail a VIP. Similarly, not removing accumulated flash rust periodically (maybe every 10 years or so) creates a substrate that will attract and hold moisture and eventually lead to pitting.
If there is no visible pitting in the bottom of the tank and there is not too much flash rust, it is worth having hydro tested. If there is an excessive amount of flash rust it will need to be tumbled before a thorough VIP can be completed. If it looks good, then it is worth sending in for a hydro test.
So... the cost can be pretty minor if the tank is clean or, in the case of accummulated flash rust, it can cost you a bit to determine if it is worth hydro testing. The hydro test itself is most likely a non event as it is exceedingly rare for a steel tank to ever fail a hydro test as what kills them is rust pits, not metal fatigue.
The nay sayers will say that by the time you pay for the hydro, VIP and new valve you have spent a fair amount toward the cost of a new AL 80. But steel tank fans will point out that if you buy an AL80 all you have is an AL 80 that will probably last only 20 years. They will point out that you refurbish the steel 72, you will have tank with better bpouancy traits that will still be going strong in another 20 years and will probably outlast your diving career.
As a practical matter, if it is a galvanized steel tank, it is worth the effort while if it is a non galvanized painted tank, you need to carefully consider the exterior condition of the tank as well as it is more maintenence intensive to keep it painted.
skyking
Contributor
Lemme throw in another twist - If it's a J-valve by all means replace it, but if it's a K-valve it may only need refurbished, which can often be done for the cost of a couple of o-rings and a burst disk (generally less than 5 bucks), and if not then a $20 rebuild kit isn't out of order, or a good new/almost new/gently used pull-off valve from someone putting together a doubles set or from an AL 80 that just failed hydro can usually be had for $20-30. Not a bad investment at all for a tank that with a little simple care your grandchildren will still be using.cfelliot:
Scuba is like many other things - half the fun's gettin' there!
Tom
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