Storage of Full Steel 232 Bar (3364 PSI) Tanks

[Skating101]

I have recently purchased a 15L 232Bar (3364 PSI) steel dive tank and have been reading alot of information regarding their storage and care.

This is one article I have been reading

http://www.scubadiverinfo.com/2_cylinders.html

It says that tank should never be stored full and should only be stored at between 300 - 500 PSI to ensure no moisture in the tank.

If I was to go for a dive and then get the tank refilled and store it at 232 Bar and do another dive 2-3 days later then store it at 35 Bar for another 2-3 days before another dive, would it be bad for the tank?

When washing the tank in fresh water do you need to keep the valve dry or should it be washed as well?

 

[DuboisP]

my 15L is full at 240 bar since 3 months, located at 3 meters from this computer used for posting.
the valve can support any water, fresh or salt.

 

[DA Aquamaster]

Definitely rinse the valve as otherwise salt crystals will form there and corrosion can occur.

Before connecting a fill whip to a valve it's a good idea to crack the valve slightly to blow any water out of the threads to prevent any water from being blown into the tank.. The same applies to the fill whip - you need to ensure there is no water in it before connecting to the valve.

Never store a tank empty with the valve open - beyond tha don't worry about it.

 

[Doc Harry]

Your question has been asked and answered dozens of times on this board. Did you try the search function? You'll find answers to your questions, including the background information that led to the recommendations in the article that you quoted.

Generally, storing your cylinder full for a few days between dives is not harmful. The recommendation "Store cylinder upright with 300 to 500 psi of pressure in them" should include the preface, "If you are going to store your cylinder for greater than 3 months...then store cylinder upright with 300 to 500 psi of pressure."

 

[Skating101]

sorry you are right i did not use the search function thanks for the answers fellas

 

[GrumpyOldGuy]

The article was BS or you may have misread or misunderstood the time frame for long term storage. Steel tanks don't wear out from being stored under normal pressure. The great enemy of steel is rust. A tank stored with low pressure (100-200 PSI) is certainly safer to store than a full tank in the even it is knocked over or the valve broken off by force. Then again, choosing a good location to store the tank also reduces this. I shudder when I see tanks stored in the garage 2 feet from a cars bumper.

I would worry less about pressure in the tank (my are stored full year round) and more about the quality of the air in the tank. If you have been diving with questionable fills (some boats are dicey) that might have had moisture issues getting the tanks emptied and checked (VIP) before storage may prevent rust. The tendency of people of course is to leave the tanks set until start of the dive season and then discover the damage done from a wet fill last year.

 

[Doc Harry]

sorry you are right i did not use the search function thanks for the answers fellas

BTW... in case you haven't figured it out yet, the search function on Scubaboard doesn't work very well.

Try a Google (or other search engine) search like : scubaboard tank storage

You'll get better results.

GrumpyOldGuy is essentially correct. It ain't the pressure that's the problem it's the moisture that's the real killer. One study suggested that corrosion was accelerated under pressure (higher pO2), hence the recommendation to store almost empty (lower pO2 available for rust formation).

2Fe(s) + 2H2O(l) + O2(g) ==> 2Fe2+(aq) + 4OH-(aq)

 

[Skating101]

so i reviewed nearly this entire thread http://www.scubaboard.com/forums/ta...ylinder-long-term-storage-fact-fiction-7.html and it was full of interesting infomation however question still remains is continued short term storage at high pressure dangerous for a tank, if higher pressure lead to more rust formation then if you store a tank at full pressure for 4 days out of a week almost every week it would still damage the tank, correct?

 

[Doc Harry]

however question still remains is continued short term storage at high pressure dangerous for a tank, if higher pressure lead to more rust formation then if you store a tank at full pressure for 4 days out of a week almost every week it would still damage the tank, correct?

The pressure per se is not harmful. The tank is meant to withstand thousands of pressure cycles. At normal operating pressures the tank itself is within elastic limits of the alloy.

As far as moisture is concerned, yes, storing your tank with moisture will cause corrosion, regardless of the pressure. Yes, if your tank has moisture inside then it will continue to corrode during daily or weekly use. Yes, steel tanks are much more susceptible to damage from corrosion than aluminum tanks because of the thin walls (and because aluminum corrosion is generally self-limiting for small amounts of moisture). That is why it is so important to ensure that you don't moisture inside of the cylinder in the first place.

The concerns over higher pO2 were from a very small study conducted by the University of Rhode Island in the 1970s. If you read the details of the study, the concusion was drawn by comparing only one cylinder in the study to a matched cylinder in that study. Not very strong data.

The recommendations for storing the cylinder upright come from a few different studies, including Battelle and URI, as well as some real-world cases. Steel cylinder have very thin walls but thick bases, and the criteria for condemning steel cylinders based on corrosion depth is more liberal for the bases than the side walls. So theoretically it is better to concentrate corrosion on the bases by storing the cylinder upright than on its side.

The recommendation for annual visual inspections applies to cylinders that are used infrequently. If you are using your cylinder every 2 to 3 days, then your should have your tank inspected more frequently than once a year. This way you can be sure that your cylinder is not getting wet fills, and you can take care of any corrosion before it gets to bad that your expensive steel tank is condemned.

 

[Skating101]

ok thanks for the reply harry so basically its fine to have the tank at full pressure for short periods as there is no impact structurally on the tank however the higher amount of oxygen in the tank could have the effect of increasing the rust.