Leave pressure in my compressor tank, or drain it every time I shut it off?

[RaisedByWolves]

In pressurized boilers the pressure keeps the oxygen away from the iron so it won't rust. I would have to think
the same would apply to a pressure tank. Thanks for reminding me I need to drain the water from my air tank
today.

True, but the oxygen is displaced by steam.

Here, you’re multiplying the amount of oxygen available.

 

[RaisedByWolves]

My quick disconnects bleed down anyway. However, what about safety. If a line breaks or a child is fooling around? On the other hand a couple of hundred PSI in a steel shop tank probably does not harm the tank.shop much as he had mobility issues, so the tank seldom got drained. It developed a rust hole!

By the way, I Scuba dive .. a little. In this case, the filled pressure is ~3000psi and the air is suppose to be dry as water is not suppose to get into the regulator and gauges. I have a couple of Al 80 cubic foot (80 at STP when filled to 3000psi) tanks. They have to be inspected via pressure tested every 5 years to ensure there are safe to use. I am not for sure, but I think the test takes them up to 5000psi or so. I think constant fill pressure in the tanks can increase the likely hood of cracks forming. One can also remove the valve and inspect the tanks visually or inductively for cracks, but the 5 year pressure testing is required before it can be refilled. On the other hand one never wants to completely empty a Scuba diving tank as this would either indicate it was emptied under water during a dive and could indicate that there was no back pressure on the value .... to prevent water from getting inside. Dive shops should not fill a tank that has been completely emptied without first inspecting the insides. Getting water, especially salt water, into the regulators means that the regulator has to be rebuilt! There is a rule, return from the dive while there is still a few hundred pounds of pressure left in the tank .... 500psi, but even 100psi will do.


Dave L.

There are cyclic forces that work the tank and can cause failure.

Different manufacturers have different requirements but I read something like 500-1000 cycles is considered the “Lifetime” of an average tank.

Aircraft have this type of rating also.


I just watched this the other day. This guy had a cyclic failure precipitated by rust. His thoughts are a bit out there in some spots, but he literally just got blown up and is speaking unscripted so factor that in.

 

[verbotenwhisky]

I’ve only read this far in the thread, but food for thought.

It takes oxygen to allow oxidation to form and eat away at the walls of your tank.

A non pressurized tank will only have so much oxygen in it available to allow oxidation, while a pressurized tank will have ~10 times as much air, hence oxygen in it.

With this in mind you can see how much more potential for oxidation on a pressurized tank long term vs one that is blown down.

Will it ever matter? I don’t know, but that is the long/short of it, and you usually don’t find good tanks that need a new pump, it’s usually the other way round.

I see wear and tear on the pump as being negligible and I don’t worry bout the lectric as I get it delivered fresh daily.

On mine the compressor head bleeds down so the compressor doesn't have to start in a loaded state. My tank doesn't not bleed down by design.

 

[pontiac428]

I follow your logic, but I would think the law of partial pressures applies. You're not increasing the concentration of oxygen. It's kind of like having a balloon with a gallon of seawater vs. 10 gallons of seawater. You're adding more mass of salt, but the chemical concentration is the same. The change in pressure doesn't put a dent in the intermolecular bonds either, that's like apples to skyscrapers.

 

[RaisedByWolves]

I follow your logic, but I would think the law of partial pressures applies. You're not increasing the concentration of oxygen. It's kind of like having a balloon with a gallon of seawater vs. 10 gallons of seawater. You're adding more mass of salt, but the chemical concentration is the same.The change in pressure doesn't put a dent in the intermolecular bonds either, that's like apples to skyscrapers.

Doesn’t work for me, air is compressible, water is not.

So in effect you don’t wind up with a larger volume(water) you wind up with a higher concentration of everything the compressor is pulling in and several atmospheres worth in a smaller space.

Gas exchange property’s in this situation are unknown, but the extra oxygen is in there if it can be used.

This is talking strictly 1 atmosphere vs 10-15 .

 

[toprecyler]

My thinking after reading thru this thread is as follows.

If steel rusts due to oxygen and a catalic (water usually) will steel rust if there is just oxygen and no water?

So, if the air in the tank is dry, there should be little concern about leaving the tank pressurized. But, if there is water in the tank, it could then accelerate the rusting process.

Now, as to wether it is good to leave pressure in tanks, it probably is from the standpoint of not allowing atmosphere air, with humidity into the tanks. This is more app to high pressure tanks like Oxygen and other welding gas tanks. If the valves are left open to the atmosphere when emptied, then other contaminants can get into the tank, and effect the usage of said gases when refilled, if the tank is not properly cleaned/ purged when refilled.

I knew guys that would be so cheap, they would bleed all the gas out, just so the gas supply shop would not get any bonus gas back. Little did he know that it really cost him more in the long run, especially when he had a contaminated tank come back to him that might not have shown any problems til only a couple PSI left in tank.

And I have experienced bad gas in argon tanks before when running low. Welds turned crappy, even though couple hundred PSI left. Change tank out, and problems go away.


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[verbotenwhisky]

Doesn’t work for me, air is compressible, water is not.

So in effect you don’t wind up with a larger volume(water) you wind up with a higher concentration of everything the compressor is pulling in and several atmospheres worth in a smaller space.

Gas exchange property’s in this situation are unknown, but the extra oxygen is in there if it can be used.

This is talking strictly 1 atmosphere vs 10-15 .

Yes but by volume the % do not change thus reactivity remains constant. FYI for any process argument water is not compressible; but.....

 

[verbotenwhisky]

My thinking after reading thru this thread is as follows.

If steel rusts due to oxygen and a catalic (water usually) will steel rust if there is just oxygen and no water?

So, if the air in the tank is dry, there should be little concern about leaving the tank pressurized. But, if there is water in the tank, it could then accelerate the rusting process.

Now, as to wether it is good to leave pressure in tanks, it probably is from the standpoint of not allowing atmosphere air, with humidity into the tanks. This is more app to high pressure tanks like Oxygen and other welding gas tanks. If the valves are left open to the atmosphere when emptied, then other contaminants can get into the tank, and effect the usage of said gases when refilled, if the tank is not properly cleaned/ purged when refilled.

I knew guys that would be so cheap, they would bleed all the gas out, just so the gas supply shop would not get any bonus gas back. Little did he know that it really cost him more in the long run, especially when he had a contaminated tank come back to him that might not have shown any problems til only a couple PSI left in tank.

And I have experienced bad gas in argon tanks before when running low. Welds turned crappy, even though couple hundred PSI left. Change tank out, and problems go away.


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Corrosion is a product of electrolysis which is why you can protect against the corrosion of marine structures through galvanic means (give it something else to eat). In steel marine structures (ships, Docks, platforms, etc.... the worst corrosion occurs in the splash zone, i.e. where the surface gets wet then dry then wet then dry......

 

[RaisedByWolves]

Yes but by volume the % do not change thus reactivity remains constant. FYI for any process argument water is not compressible; but.....

Yes, reactivity remains constant but availability goes up.

The water, surface interaction (calm vs turbulated)and gas exchange are what keeps things constant as far as rate of corrosion is concerned.

Nothing speeds up, just over time one scenario has more compounds available to do work than the other.

 

[RaisedByWolves]

And I have experienced bad gas in argon tanks before when running low. Welds turned crappy, even though couple hundred PSI left. Change tank out, and problems go away.


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That could be a different animal altogether.


Argon tanks contain a volume of acetone and if you go above a certain amount of use per hour per liter of some formula, you begin to pull off and burn the acetone.

This is bad juju and you want to be aware and prevent this from happening.


Looked it up, 1/7 rule.

What is the 1/7 acetylene rule

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