Tank overfill = mini hydro?

[Scared Silly]

PV=nrT. Government regulations only concern pressure and temperature, but only the pressure is stamped on the tank, so fill stations only worry about the pressure.

If the fill station monkey is only worrying about what is on the cylinder then quite frankly they are diptubes. They should be worrying about what is on the cylinder right along with the CGAs, CFRs, OSHA, etc.

The above is what is wrong with much of the scuba industry. Failure to educate themselves.

 

[imwright1985]

I was wondering if this was a reference to annealing... Heat/cooling (properly) can really strengthen metal. The SR-71 Titanium skin annealed to the point that the skin material was about 15-20% stronger after the 30 years of flight ops than when it was built.

your thinking of heat treatments, not annealing, annealing is heating to a certain Fairly high temp for different time allotments to allow for the grains in the metal to restore to original style of layout making the metal elastic once again and causing it to loose strength. You wanna look up aging metals or heat treatments to learn what they did with the sr71, they do that on a ton of things though and the aging or heat treatment temps run from room temp up to whatever the spec is on the alloy, (the lower the temp though the more control they can use to drive the strength up cautiously

 

[WD8CDH]

Except that because of the mass of the tank and the time required for thermal transfer, you can't know what the temperature is inside during a fill, by measuring the outside.

Terry

Hi Terry,

I think that the CFR takes that into account with the 5/4 pressure limit. Besides, hot air inside of the tank doesn't weaken the tank walls, tank wall temperature does.

Measurements show that the air temperature in the tank can be substantially higher than the tank walls. That is one of the reasons that filling tanks in a water bath doesn't help much. The air inside is still hot.

So the pressure limit (5/4) is to limit stress and the tank temperature limit (131F) is to limit strength loss while under the higher pressure.

 

[SCUBA482]

Just a side note...OP here...I was wondering about yoke failure in addition to my question as to whether or not a 3900 hot fill is a mini-hydro? The numbers I initially posted weren't meant to start a class on algebraic equations, but simply wondering would you consider a 3900 PSI fill that cools to 3600 or so a mini-hydro and would this create a potential for yoke failure an ultimately weaken the integrity of the tank causing a potential failed hydro on a new tank???

 

[WD8CDH]

It's more than the code allows as a fill, but it is far less than a hydro. The amount of stress is infinitesimal toward causing a potential of a failed hydro later. Also, the pressure is well within the design safety factor of most modern and many vintage yokes. Your greatest risk is for o-ring extrusion and a slightly greater risk of yoke failure if it was under pressure and the yoke took a hard mechanical hit at the same time.

 

[SCUBA482]

It's more than the code allows as a fill, but it is far less than a hydro. The amount of stress is infinitesimal toward causing a potential of a failed hydro later. Also, the pressure is well within the design safety factor of most modern and many vintage yokes. Your greatest risk is for o-ring extrusion and a slightly greater risk of yoke failure if it was under pressure and the yoke took a hard mechanical hit at the same time.

Thanks Ron for the feedback...I do appreciate all the chatter about fills though and it seems there are several LDS doing the right thing and plenty of divers desirous of a "good" fill. I figured it was well within the safety parameters, but very curious about the "mini hydro" issue. I'll keep a good tab on my O rings and even with the good fills I get at my LDS, when the tank hits the water it's right at about 3400 to 3500 anyway...thanks all

 

[Wayward Son]

I have a bunch of 3442 tanks. While they are not rated for nor approved for any sort of over fill, I really don't think 3800 - 3900 hot, cooling to 3500 +- is a problem with them at all.

 

[Davidstealey3]

It's more than the code allows as a fill, but it is far less than a hydro. The amount of stress is infinitesimal toward causing a potential of a failed hydro later. Also, the pressure is well within the design safety factor of most modern and many vintage yokes. Your greatest risk is for o-ring extrusion and a slightly greater risk of yoke failure if it was under pressure and the yoke took a hard mechanical hit at the same time.

some old yokes are only rated to 2250. but if they were changed out durring servicing, they will be a ok

 

[imwright1985]

scuba482,
If your at all worried, performance specs/ warrenties, and all that stuff is given through factors of safety. Depending on how much "performance" a company wants they may just drop the factor of safety to a lower value and drop the warrenty to a lower interval. if they want the product reliable but cheaper they will also cut the warrenty back. They figure out from all the failures on a test batch how many failed peices are acceptable over certain time/use intervals that they are willing to cover the cost on at a rate their product is still desirable but their customers will be happy.

it is pretty much something many people dont think of and either go crazy over high performance or an impressive warrenty but dont realize they are trading off performance for warrenty, or paying more to have a warrenty that will cover the few fluke items that may break under the warrenty (your reason why non-warrentied ebay items that are new are often significantly cheaper).

to sum this all up MOST, not all people at the chain like stores are about as useful as someone at sears. i give them that over walmart because they atleast know what sells and what sells with the more serious divers rather than the noob or seasonal diver

wd8cdh,
thermodynamics comes into play with what your talking about, soaking tanks does help but the air inside is still hotter so your pressure when pulled from the fill whip will be higher than once everything does cool off, soaking tanks does however get your tank to start the cooling process while it is filling so instead of having to go to about 3250 for a 3000+ a few psi fill you might only have to go 3100

 

[WD8CDH]

If you actually measure a tank filled at room temperature in the air vs. in a room temperature soaking tank, you will find that pressure difference is closer to 50 psi rather than 150 psi. That's well worth eliminating the risk of the tank monkey dropping the fill whip in the water.

I have actually done it with thermocouples on the inside of the tank wall, the outside of the tank wall and in free space in the middle of the tank. You won't see industrial gas suppliers fill in water either.