Skipping Hydro

[captain]

As far as the DOT goes, if a tank doesn't fall under DOT jurisdiction, then it really doesn't matter whether it is a spec, or a exemption, homemade, or a commie rebreather flask - it just isn't their concern.

Which I would assume is the case with my Navy aluminum twin 90 cu/ft non magnetic tanks.
The hydro shop hydroed and eddy current tested them but did not stamp them. I know they are good and I fill them.

 

[imwright1985]

If you have the wrong tail lights on your car you can get a ticket because they arnt in DOT regulation. I have worked in the auto industry for a little and know that for a fact. If someone pulls you over and sees a tank filled in your car and it is outa hydro they can cite you for it. Chances are they wont because most of them dont know any better but if you get a cop that does, he isnt in a good mood or just wants to write as many tickets as he can your outa luck.

Asfar as needing the hydro every 5 years, structurally you dont, Its just a standardized practice based on the elasticity of the alloy the tanks are made and depending on overfilling, pressurised time, heat exposure and trauma, that outside of a 5 year period your more likely to have a failure if tank doesnt fit within certain specs on a hydro test. Kinda the same principal warrenties are generated on based on failure rates for whatever "standardized" number they set for companies cost of repair or replacement but since scuba tanks could kill you the number is very high so failures are almost nonexistant based on the number used

 

[dannobee]

...If someone pulls you over and sees a tank filled in your car and it is outa hydro they can cite you for it.

Noooo, they can't.

The coppers can give you a ticket in your previous example because your state's vehicle code says the lights must be DOT approved (or unaltered), not because the DOT says that they're illegal. The ticket you receive will cite the pertinent section of the vehicle code, NOT a DOT reg.

How the heck would you transport a tank to the hydro shop if it's out of hydro? If that were the case the lazy cops would hang out in front of hydro shops, giving tickets to everyone bringing in a tank.

 

[captain]

If you have the wrong tail lights on your car you can get a ticket because they arnt in DOT regulation. I have worked in the auto industry for a little and know that for a fact. If someone pulls you over and sees a tank filled in your car and it is outa hydro they can cite you for it. Chances are they wont because most of them dont know any better but if you get a cop that does, he isnt in a good mood or just wants to write as many tickets as he can your outa luck.

How does he determine when the tank was filled. DOT regulations say a tank with an expired hydro date can be used indefinately until empty, so just because it's full doesn't mean squat if it was filled while in hydro.
I have welding tanks in my shop that have expired hydro dates but the still contain gas and are perfectly legal but will have to be hydroed before they can be refilled.

 

[duckbill]

If you have the wrong tail lights on your car you can get a ticket because they arnt in DOT regulation.

So, does DOT say you must have one, two, or three tail lights? Because I'm pretty sure that the rule is that a car must at least be equipped with what was originally on the car when it was manufactured. I had a 1942 slat grill Willy's jeep that only had a left tail light and no seat belt. Perfectly legal. Same for my 1964 Kaiser M151 MUTT. I believe Model Ts had the same thing. Now cars are made with three tail lights, but you cannot go to two, or even one tail light without being cited. I don't think anyone is cited under USC for a tail light infraction. I'm 99% sure it is under CVC. So much for DOT regulation. LOL!

Its just a standardized practice based on the elasticity of the alloy the tanks are made and depending on overfilling, pressurised time, heat exposure and trauma, that outside of a 5 year period your more likely to have a failure if tank doesnt fit within certain specs on a hydro test.

"Pressurized time" has nothing to do with it. The rest of your list is good though. The main element outside of environmental factors is cycling, and the degrees to which the steel has been stretched in that cycling. Time itself is not a factor. You could fill it once for one hour in a five year period, and the result would be the same as if you had filled it once and left it filled for the entire five years.

 

[DepthCharge]

I have had some conversation with DOT and they just will not give a clear answer.
They say a privately owned, filled and transported tank does not fall under DOT regulation in one breath and in the next breath say that a DOT spec cylinder that is not in hydro can not be filled or transported. So which is it, it appears they are hedging their bets.

Imagine that, a gov't agency that doesn't give the same answer twice:rofl2:

 

[DaleC]

How does he determine when the tank was filled. DOT regulations say a tank with an expired hydro date can be used indefinately until empty, so just because it's full doesn't mean squat if it was filled while in hydro.
I have welding tanks in my shop that have expired hydro dates but the still contain gas and are perfectly legal but will have to be hydroed before they can be refilled.

I've got a 1/2" ST72 last hydroed in 1958 still with air in it. I haven't drained it yet because no one will fill it even with a hydro and I don't want it to rust. I guess I could get one more dive out of it...

 

[DepthCharge]

So.............what I'm hearing is that if a tank is hydro'd, then it won't blow up for another 5 yrs when filled. Is that correct? (I sure hope people don't believe that)

 

[WD8CDH]

<snip>

"Pressurized time" has nothing to do with it. The rest of your list is good though. The main element outside of environmental factors is cycling, and the degrees to which the steel has been stretched in that cycling. Time itself is not a factor. You could fill it once for one hour in a five year period, and the result would be the same as if you had filled it once and left it filled for the entire five years.

Not totally true. While fairly insignificant for most tanks, time that the tank is pressurized does have a very tiny effect. For real world purposes, it is only significant (and still not hugely significant) for 6351 alloy tanks.

 

[captain]

So.............what I'm hearing is that if a tank is hydro'd, then it won't blow up for another 5 yrs when filled. Is that correct? (I sure hope people don't believe that)

If you believe that one can than you should hydro it before every fill.

If it is filled to the proper pressure with dry gas and is not subject to fire or corrosion then it shouldn't blow up for the next 500 years or more.
How does the hydro prevent it from blowing up. The hydro merely says that nothing in the last 5 years has altered the strength of the tank.
I have tanks that have been under pressure for 50 years that at one time had been out of hydro for ten years or more when I was not using them and are now back in hydro.