will they rust?

[pheel]

Hello all,

Let say I empty my 2 HP120, remove the valves, install new K-valves to set-up a manifold for double. As soon it's finish I go the to LDS to fill them up.
Is there any good chances of rusting inside? Is there something specific to be done to prevent any rust when the valve is removed?

thanks

 

[ajduplessis]

Nope. I would however empty the tanks slowly as expanding air cools down and forms moist (on the outside of the tank/valve). I would also have the cylinder lay on its side with the opening of the valve pointing downwards. Once you have the valve off, take a look inside to satisfy your own curiosity.

 

[oly5050user]

LDS may want to perform a vip, being that the tanks are completey empty. Perhaps set them up in the bands with original valves on with air inside them ,take to lds and explain what you want to do ..if the vip is not current or about to expire let lds perform vip .Want to save $,then ask lds to perform vip and that you will disassemble/assemble ..they may agreee toit.

 

[oxyhacker]

Hardly any. For moisture to accumate the tank has to be cooler than the ambient temperature (so it condenses water from the air) and enough air has to circulate through the tank to bring in a troublesome amount of moisture. But the hole in the tank is small, so air exchange happens slowly and only minimal amounts of moisture will get in if you are reasonably expeditious in inspecting the tank and revalving it.

It is good practice, though, to empty the tank all the way, then let it sit with the valve still on until it warms back up to ambient - overnight or a few hours at least - so the tank will not be cool enough to condense moisture. If you are in a humid climate it might be worth doing the valve swap in the evening when it is cool and the air drier, or in an air conditioned room since this will reduce the amount of moisture in the air the tank is exposed to. But this is probably overkill in most situations.

What you don't want is for a tank which is enough cooler than the ambient air to be exposed to circulating damp air long enough to condense significant amounts of water, as could happen in a tropical climate if you drained a tank quickly enough to leave it frosty, then left it opened for a few days.

 

[Akimbo]

If you live in a really humid climate and are that concerned, have the LDS pressurize the tank to ~500 PSI/30+ atmospheres, bleed it down to ~10 PSI and then fill it. This precaution “might” be worth the effort if you plan on storing the cylinder for a long time — probably not if you plan on diving the cylinder soon and refilling.

If you have access to the gas and want to store a cylinder long term, purging and filling with pure nitrogen to 50-100 PSI eliminates any chance of oxidation.

 

[pheel]

makes sense, thanks !

 

[oxyhacker]

Or just flush the tank out with scuba air, which is very, very dry, immediately before valving. Easy to do by undoing the first stage of a regulator from its hose and sticking the hose end in the tank.

 

[Doc Harry]

When you drain the cylinder, it will get cold during the process. If you remove the valve while the tank is still cold, condensation will form inside of the cylinder and rust will form. The more humid the environment, the higher the risk of condensation.

It doesn't matter that the cylinder opening is small, air penetrates everywhere and air contains mositure. A cold cylinder wall will form condensation inside and out if you remove the valve while the cylinder is still cold from the draining process.

So once you've got the cylinder drained, let it sit for a few hours to return to ambient temperature before you remove the valve.

You should also do this process indoors in an air-conditioned environment where the ambient humidity is lower than outdoors.