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wopsushi
04-19-2008, 22:53
can anyone shed some light on proper storage for tanks for an extended time period, i have always been told 300-500 in tank and stored upright... now i have heard, just today as a matter of fact. my buddy called and said he spoke with someone who just completed the inspection course and they really pushed hard on the fact the bottles should be stored upright empty?????? what gives? i know things and tech is always changing, and that why i am asking.

navyhmc
04-20-2008, 00:11
I too was taught and follow the rule of 300-500 in the tank and store upright. IMO 300-500 is about as good as empty so as to have less constant strain on the tank. I'm not too worried about having a full tank at home during the dive season as I know I will empty it soon enough.

Upright stays in my mind as there was an incident back in '75 at a LDS in Kansas City where an instructor was killed when a steel 72 he was filling exploded. Seems that there was some water in it, and it had been stored on it's side. When he was filling it, it ruptured along the rust line. He was killed and another 4 people were injured-mostly barotrauma from the overpressure of an additional 72 cu ft rapidly entering the room.

Mind you, I had to really overstimulate some neurons to recall that incident, so if you will excuse me, I'm going to go drop a few tylenol and some more geritiol! :D :D :D

texdiveguy
04-20-2008, 00:16
As a general rule....500psi in a standing position (upright) is best for 'long' term storage.

wopsushi
04-20-2008, 09:42
Tanks being stored empty supposidly will elimate the sustained load cracking(room temperature grain creep)and even a tank with 300 can rupture catastrophically in a fire. but this goes against all that I and probably most you as well were taught. now this all came from my buddy yesterday, but i had to call back and get more deatails. this info is comming from a student who just completed his PSI tank inspection course and swears this is a very hot topic with instructors teaching the classes. I will get with my LDS, the tech there is very knowledgable and I trust his work maybe he can shed some light on this to see if anything had really changed recently. It very well could have!

terrillja
04-20-2008, 09:47
if they are empty, moisture can get in- bad
I keep all mine in one room at 500psi, and the door is marked saying that the room contains compressed gas cylinders.

Crimediver
04-20-2008, 10:38
Navyhmc stated why tanks should be stored upright. Any water trapped inside a tank can develop rust pits. Tanks stored on their side allow rust pits to appear in a linear arrangement which can considerably weaken the tank, just a perforations allow a check to be ripped out of a checkbook.
Cylinder bottoms are the thickest part of a tank and pitting in this area is less dangerous.
Water in a steel tank stored with a lot of air pressure has a rich supply of O2 in which to form rust. Steel tanks stored with only a couple of hundred psi will offer less O2 to promote rust than one with 3000 psi.
Hopefully in a fire situation most tank valves will have the burst dics go before reaching the pressure that will cause a tank to go boom.

cummings66
04-20-2008, 10:54
My psi cylinder inspection course discussed storing them, they say either full or around 20 psi. The reason for such a low pressure is that they claim cylinders have gone boom in a fire stored with 500 psi. They reason is that the cylinders (especially aluminum) will rupture if the temps exceed 350 degree's at around 1500 psi. Those pressures are able to be hit in a fire with a cylinder having 500 psi in it, so they claim.

Full the burst disk will go before the cylinder ruptures, at 20 psi it will never develop enough pressure to rupture.

That's what I was told at any rate. Looking through the books it only says to maintain some pressure. Assuming an AL80 6 psi per degree it only takes a rise of 166 degree's to hit 1500 psi which is claimed to be the pressure it takes to rupture an AL cylinder which has been exposed to heat. Talking to some firefighters in the class confirms that it's very easy to hit temperatures of that or way above in a fire. So, there is some basis for saying 20 psi is what you should use for storage, or full.

frogman159
04-20-2008, 11:06
I
4 people were injured-mostly barotrauma from the overpressure of an additional 72 cu ft rapidly entering the room.



would have never thought....

in_cavediver
04-20-2008, 12:38
My psi cylinder inspection course discussed storing them, they say either full or around 20 psi. The reason for such a low pressure is that they claim cylinders have gone boom in a fire stored with 500 psi. They reason is that the cylinders (especially aluminum) will rupture if the temps exceed 350 degree's at around 1500 psi. Those pressures are able to be hit in a fire with a cylinder having 500 psi in it, so they claim.

Full the burst disk will go before the cylinder ruptures, at 20 psi it will never develop enough pressure to rupture.

That's what I was told at any rate. Looking through the books it only says to maintain some pressure. Assuming an AL80 6 psi per degree it only takes a rise of 166 degree's to hit 1500 psi which is claimed to be the pressure it takes to rupture an AL cylinder which has been exposed to heat. Talking to some firefighters in the class confirms that it's very easy to hit temperatures of that or way above in a fire. So, there is some basis for saying 20 psi is what you should use for storage, or full.

I agree with this - either very low or full.

Fires can easily push the melting point of Al. I'd rather the burst disk let go that the tank itself.

I also do not buy the extra strain argument on a tank. Sure, in theory it will develop slight fatigue from the stress but its the fill cycle that really causes the stress issues. Think about all of the steel and Al in use today with static loads on it. Protect the metal from corrosion and its good to go for a very long time.

cummings66
04-20-2008, 13:35
Speaking of a 72 cf cylinder, the potential energy in a 71.2 cf cylinder at 2000 psig is approximately 800,000 ft pounds. That's enough to lift 4 100 ton locomotives about 1 foot off the tracks. Or a large Caddy hitting a brick wall at 500 mph.

An AL80 at 3000 psig would have 1,300,000 ft pounds of energy which is enough to put a fire truck on about the sixth floor of a building.

Barotrauma, sure. I can see it. Those figures courtesy of PSI.

texdiveguy
04-20-2008, 13:50
100 to 500 for LONG storage is fine. I never seem to let might sit long enough...lol...in the event of a fire you pray the cylinders will be removed//not go boom and the responding firefighters are advised of the tanks being present.

CompuDude
04-20-2008, 16:32
I generally keep my tanks full and ready to go. If there was some reason I literally would not use a tank for over a year (hasn't happened yet), bleed the air out to 100 psi or so. You do NOT want to empty the tanks completely, though.

Store in the upright position for rust reasons (both internal and external). If there's going to be some rust, you definitely want it at the bottom of the tank, not on the sidewalls.

aprilgoddess1987
04-20-2008, 19:43
I remember from ow to store them upright with at least 500 psi

cummings66
04-21-2008, 10:23
A steel cylinder according to a test done by a university in the 70's has an interesting problem during storage. Under the increased pressure rust occurs much faster, so if it's a steel cylinder being stored the lower the pressure the better, but you must keep enough pressure in it to be positive. So as low as you can get it and still have air in it is ideal. Especially if you dive in salt water and there is any chance it got inside it from a wet fill for example. A full steel cylinder can fail in much less time than you'd think if it got salt water in it and is full of air, more so if it's nitrox.

Personally, if my steel cylinders were being stored I'd get a visual done before storage to insure they're free of rust and water, then store it with almost no pressure in it. Just enough to be positive.

mike_s
04-21-2008, 10:40
someone who just completed the inspection course and they really pushed hard on the fact the bottles should be stored upright empty?????? .


boy, I hope he didn't pay for that class he took. Empty cylinders allow moisture in. moisture can run a tank. always store with some pressure in....




Tanks being stored empty supposidly will elimate the sustained load cracking

[snip].

this info is comming from a student who just completed his PSI tank inspection course and swears this is a very hot topic with instructors teaching the classes. I


The only tanks that are listed by DOT has having problems with Substained Load Cracking are the older AL6351T alloys. (older aluminum tanks).

sounds like to me this course was preaching paranoid or he didn't fully understand what tanks this applied to.

again, I hope he didn't pay for that course he took. sounds like mis-information.....





As a general rule....500psi in a standing position (upright) is best for 'long' term storage.


what he said....

but many people store them full also. I think anyone would agree that 500psi might be better for long term for many reasons, but you rarely see someone drain a $12 nitrox fill from each tank for storing over the winter.

CompuDude
04-21-2008, 12:29
Store upright. Full and ready to dive, OR drained to under 500 psi (but not empty... I personally wouldn't go under 100 psi).

Seriously. End of thread.

Sounder
04-21-2008, 16:20
An AL80 at 3000 psig would have 1,300,000 ft pounds of energy which is enough to put a fire truck on about the sixth floor of a building.

This is a PRICELESS quote!!

cummings66
04-21-2008, 16:44
You must have seen that in the PSI course to know it's a quote, although I took some liberties with it.

Nobody should ever store a cylinder empty, anybody who says that should retake whatever course that they think said to do so. That's just inviting trouble.

I don't have the issue, my cylinders are used year round so I never have to worry about it. I honestly would store an AL80 full. I would store a steel cylinder with very little pressure in it, but it would have pressure. But mine are in use every week so there's no storage here.

frogman159
04-22-2008, 21:46
Store upright. Full and ready to dive, OR drained to under 500 psi (but not empty... I personally wouldn't go under 100 psi).

Seriously. End of thread.

:smiley36:

cogrwy
04-23-2008, 07:31
When we talk storage, what kind of time frame are we talking about, 3 months, 6 months, a year?

CompuDude
04-23-2008, 13:24
When we talk storage, what kind of time frame are we talking about, 3 months, 6 months, a year?

Yes. ;)

(Although I wouldn't drain a tank unless I know it won't be used for a year. And that has NEVER happened. *knock on wood*)

Sounder
04-23-2008, 15:54
When we talk storage, what kind of time frame are we talking about, 3 months, 6 months, a year?

Yes. ;)

(Although I wouldn't drain a tank unless I know it won't be used for a year. And that has NEVER happened. *knock on wood*)

My tank boots don't even ever get totally dry... I love living here!!

cummings66
04-23-2008, 21:14
My gear is used most every week, sometimes it's every 2 weeks. I know that I hate tank boots so mine are dry right now because I don't have them on my cylinders I use most.

Currently I'm rehabbing my HP100's, not fun but I need to because I noticed a bit of rust starting where the boots used to be. Luckily I caught it before it got bad enough to make it fail a vis. So I might not dive this weekend, at least not the Hp100's. I've got to O2 clean them as well.

They have 100 psi in them right now.

wopsushi
04-24-2008, 12:36
I would imagine for a year or longer, like i said, i got this info from a very good friend who is also a diver and was on another dive forum when he got the info and called me about it.


When we talk storage, what kind of time frame are we talking about, 3 months, 6 months, a year?

cummings66
04-24-2008, 17:48
I got it, Internet expert. Well, I'm sure you've seen the collective wisdom says do not store it empty. Upright is the correct orientation.

I hope you told him he should be storing it with pressure, and if he has questions and took the PSI course he can even call them up and ask the question if he doesn't believe you.

ChrisA
04-24-2008, 18:48
An AL80 at 3000 psig would have 1,300,000 ft pounds of energy which is enough to put a fire truck on about the sixth floor of a building.

I don't know if the number is right but the units sure are wrong. "Pounds" is a unit of force, not energy. Likely maybe you ment "foot pounds".

Now lets see if the number is right. Converting to metric a ft/lbs is about 1.4J. So we have 929 kJ of energy. A kilowat hour is about 3600 kJ. So the tanks hold about 1/3rd of a KWH. This is just about as much energey as it takes to run a hair dryer for 20 minutes. or to run a one horsepower motor for half an hour. But lifting a truck sure sounds more impressive

That's likey because maybe a 1HP motor could lift a truck up six floors in 30 minutes. Seems reasonablebecause it takes something like a 1 HP motor 30 minutes to fill a tank.

USF_Diver
04-24-2008, 20:22
Great info, when get my tank I will know how to store :)

in_cavediver
04-25-2008, 05:37
For how 'powerful' a tank rupture is:

First, units are ft-pounds.
To get to Joules - 1 ft-lb = 1.3558 J
or 1.3 million ft-lb = 1.76 million Joules

Now, To go from energy to power, we have to define a time frame. The tank rupture is instantaneous (less than a second) so its hard to go that route. We can take common devices and determine time frame for their energy usage and see how long the energy released in the rupture would run said devices.

Hair Dryer (12A@120v) = 1440 Watts or 1440J/sec
TV (5A@120V) = 600Watts or 600J/sec
60 Watt Light Bulb = 60Watts or 60J/sec
8 Watt CFL bulb (it was just earth day) = 8J/sec

So, A tank rupture has enough energy to run a hair dryer for 20+ minutes or a standard light bulb for just under 8.5 hours. My TV can run for 48 minutes. A Compact Fluorescent - over 2.5 days.

1.3 million foot pounds can also be looked at in simple terms of moving weight. Quite literally, its enough energy to more 1.3 million pounds one foot. or 1lb 246 miles. The firetruck analogy - it comes from the fact its enough energy to move a 40,000lb vehicle (weight of our CAFS engine) 325 feet. (to move against gravity takes a different equation as you are converting the kinetic energy into stored potential energy)



An AL80 at 3000 psig would have 1,300,000 ft pounds of energy which is enough to put a fire truck on about the sixth floor of a building.

I don't know if the number is right but the units sure are wrong. "Pounds" is a unit of force, not energy. Likely maybe you ment "foot pounds".

Now lets see if the number is right. Converting to metric a ft/lbs is about 1.4J. So we have 929 kJ of energy. A kilowat hour is about 3600 kJ. So the tanks hold about 1/3rd of a KWH. This is just about as much energey as it takes to run a hair dryer for 20 minutes. or to run a one horsepower motor for half an hour. But lifting a truck sure sounds more impressive

That's likey because maybe a 1HP motor could lift a truck up six floors in 30 minutes. Seems reasonablebecause it takes something like a 1 HP motor 30 minutes to fill a tank.

No Misses
04-25-2008, 08:19
Sing along with me.

This is the thread that never ends
It goes on and on my friend
Some people started posting it, not knowing what it was
And they'll continue posting it forever just because...(repeat)

:smiley36:

cummings66
04-25-2008, 08:23
An AL80 at 3000 psig would have 1,300,000 ft pounds of energy which is enough to put a fire truck on about the sixth floor of a building.

I don't know if the number is right but the units sure are wrong. "Pounds" is a unit of force, not energy. Likely maybe you ment "foot pounds".


I abbreviated foot as ft, so I did say foot pounds, I know ft didn't stand out very well.

cogrwy
04-25-2008, 08:37
My gear is used most every week, sometimes it's every 2 weeks. I know that I hate tank boots so mine are dry right now because I don't have them on my cylinders I use most.

Currently I'm rehabbing my HP100's, not fun but I need to because I noticed a bit of rust starting where the boots used to be. Luckily I caught it before it got bad enough to make it fail a vis. So I might not dive this weekend, at least not the Hp100's. I've got to O2 clean them as well.

They have 100 psi in them right now.

Just out of curiosity, what do you mean by "rehabbing" your tahks?

cummings66
04-25-2008, 08:41
I removed the old paint and replaced it with ZRC by rolling it on. Done in accordance with how the cylinder maker wants it done.

If you choose to do it, run the process past your dive shops and anybody who's going to inspect them, show them the documentation of the process and what you're using and how you're using it.

A repainted cylinder can be failed on a visual, and if you do it wrong you can destroy the cylinder. No heat, and depending on the alloy even certain chemicals can damage them.

68raggtop
04-25-2008, 20:09
I truly believe the best way to store your tanks are at MY HOUSE! I will make sure they get a chance to go through multiple fill cycles so they don't feel unwanted.:smilie39:

burna
04-26-2008, 03:13
if they are empty, moisture can get in- bad
I keep all mine in one room at 500psi, and the door is marked saying that the room contains compressed gas cylinders.



boy, I hope he didn't pay for that class he took. Empty cylinders allow moisture in. moisture can run a tank. always store with some pressure in....


Hey everyone, first post here. :smiley20:

At the risk of sounding like a smart arrrrz, I don't understand how an empty tank with the valve shut can let in moisture.

I mean, the valve can hold in up to 3000 psi, surely it can hold out 14.5psi or 1 ATA.

The only time moisture can into an empty tank as I see it is if the valve is left open or it was in the compressed air.

Lone Frogman
04-26-2008, 04:01
I truly believe the best way to store your tanks are at MY HOUSE! I will make sure they get a chance to go through multiple fill cycles so they don't feel unwanted.:smilie39:

Close but no cigar, Best storage is full and on my back.

cummings66
04-26-2008, 07:17
The only time moisture can into an empty tank as I see it is if the valve is left open or it was in the compressed air.

I don't know for sure but I speculate that what happens is if it's truely empty that it will have let in normal air. Air that we breathe has humidity or water vapor mixed in with it so what can happen is rust or corrosion will form due to that.

If you could breathe it down to 20 psi it would never have an issue because it was not exposed. The other possibility is that the O rings under no pressure will not seal and let air by. You ever notice on a Yoke valve that the thing will leak a bit under the pressure comes up? That's the O ring letting it leak and then as the pressure pushes against it the seal finally happens. To be honest I don't know what amount of pressure it takes to insure the O ring seats and seals.

mike_s
04-26-2008, 07:51
if they are empty, moisture can get in- bad
I keep all mine in one room at 500psi, and the door is marked saying that the room contains compressed gas cylinders.



boy, I hope he didn't pay for that class he took. Empty cylinders allow moisture in. moisture can run a tank. always store with some pressure in....


Hey everyone, first post here. :smiley20:

At the risk of sounding like a smart arrrrz, I don't understand how an empty tank with the valve shut can let in moisture.

I mean, the valve can hold in up to 3000 psi, surely it can hold out 14.5psi or 1 ATA.

The only time moisture can into an empty tank as I see it is if the valve is left open or it was in the compressed air.


True... moisture can't get it when the valve is shut. but moisture/condensation will form as the tank is being emptied due to pressure changes. If you empty the tank there isn't as much gas left in the tank to absorb that much moisture and it stays in your tank. (like high humidity). You don't want that left inside the tank.

also, if you drain a tank, drain it as slow as you can... I mean let it take 15 minutes. or more...

RIght now a steel tank cost about $345 for a HP100. You typically buy them in sets. So you have about $700 invested before tax, o2 cleaning, etc...

It's just not something you want to risk getting moisture inside your tank and having rust spots (steel) or aluminum oxidatioin (alum tanks). Rememer you're breathing whatever air and particles are in there.

I know someone who left their steel doubles get drained out. They had huge rust problems that they couldn't tumble out. guess what.... he just spent $700 on new tanks. sucks huh?

so rule of thumb is to leave a little pressure in the tank. that way you know moisture isn't getting out.

cummings66
04-26-2008, 08:24
Really, all of this can be summed up by saying keep it as low as you can for storage and hope for the best. The reason for low is that if you have a higher pressure then the O2 will attack the rust faster causing it to pit quicker. That's what an experiement in the 70's showed. Of course it was extreme conditions but the results proved low pressure rusts slower.

burna
04-27-2008, 03:00
True... moisture can't get it when the valve is shut. but moisture/condensation will form as the tank is being emptied due to pressure changes. If you empty the tank there isn't as much gas left in the tank to absorb that much moisture and it stays in your tank. (like high humidity). You don't want that left inside the tank...


Thanks Mike, that makes sense, it certainly happens with industrial compressors, but isn't scuba air relatively dry??

cummings66
04-27-2008, 10:13
It's supposed to be, but I guarantee you this much, drain a cylinder fast and open it up, you'll see something you'd be surprised to find. That's probably why PSI wants them drained slowly when you inspect them.

Plus, not all shops maintain their equipment like they should, and you have no way of knowing for 100% that it's dry or filled with water.

JahJahwarrior
04-27-2008, 22:24
The storage issue brings up the problem of fire---what should you do if your house is on fire and a scuba tank is stored inside? If you are away and unaware, you would be unable to reach anyone to warn the firefighters. Should we be putting signs in our front lawn letting them know that we have scuba tanks? Should they be stored in the garage, where the firefighters probably expect things to blow up more than in other areas (because of cars, other chemicals, etc.)? Can one stop by the fire department and have them add some information in a file they keep on addresses or something to let them know where the tanks would be so they can be careful?

cummings66
04-28-2008, 21:40
Where I live I have to pay a dues to a rural fire department. In the dues application each year is a from and on that form I have to tell them where my guns, gun powder, compressed cylinders, and any other thing that might go bang are.

You may have a similar ability, or not.