Help Validate Facts on Overfill to LDS

[stevetim]

Bitter, party of one, your table is ready.

ROFL! I work in a restaurant and that just made me laugh out loud.

 

[NutJob]

If, as an earlier poster indicates, they are stacking 2 or 3 burst discs on top of each other, they are talking about more than a few hundred pounds. Filling to service pressure is one thing, the impression I was getting was we were discussing significantly more. I have personally seen a pair of tanks not pass their first hydro, the tank bands had grooved the tanks, they had been overfilled that much.

 

[Charlie99]

they are constructed to take at least 10,000 fill cycles to around 5000 psi before failing and they must fail in a leak-before-burst failure mode.

I bet you use the lines on your boat and when mountain climbing right up to the breaking strength rather than the safe working load, right?

The only reference I've seen to 10,000 cycles to 5000psi was NOT in reference to rated pressure, but was instead a test of design strength.

I guess what you are really saying is that "hydro test pressure = working pressure". I've never seen any manufacturers say that.

Most people use a pretty healthy safety factor between design and working limits. For most scuba tanks there is a relatively low ratio of 5::3 between hydro and working pressures.

 

[Manta Matt]

If they aren't filled when full ask them to top them off for you since you paid for a full fill. I have a feeling that putting them back on the hook a couple of times will cure those short hot fills.

I agree. But on the Tank Structure issue... Tanks manufactured today have to be able to withstand a pressure of 2.5 times there service pressure. And tanks don't explode anymore, minus the pre 90's Luxfers, they rupture. Meaning they just buldge out somewhere on the tank. And my opinion on tanks, today's tanks are WAY over made. Just to protect the company's name. You know luxfer is sure making sure their tanks don't explode anymore....

So i think it is ok to over fill slightly

 

[PhinDiver]

Some people don't care for their LDS. A very few might even hate them. Most people do not hate their LDS.


No, we want to end up with a full fill, not a short fill.
Then be patient.

Most tanks are purchased from their LDS due to shipping costs. That's where I got mine.
Which are not a big money maker because of shipping costs.

No physical risk. There is this new invention called a burst disk. Again, no steel tank has ever exploded. There is much greater risk just driving to the shop.
Can you name ONE time a body part was blown off giving a fill that cools to full? Or even 200psi over. Heck, can you name a tank that caused a missing limb at 500psi over? (Remember, we already established that we're not talking about that one bad batch of ALs.)
It just doesn't happen.
YET.

 

[spectrum]

I know what you mean Rick.

My E7-80s say 3442 at 70F. So lets say I have that perfect fill and the cylinder sits in the back of my van and heats to 110F. (I think that's a resonable hot summer day number) Is anyone suggesting I run out to the parking lot and bleed off 200 PSI based on the 5PSI/1F rule of thumb? I don't think so.

So if my shop does a reasonably slow fill as he goes ito his banks, perhaps sets the cylinders in room temp water to help draw away excess heat and lets them settle on the whip at about 200 over (they are still warm, not hot) 3442 and they cool to within 50 PSI what is the difference between that and the cyliders in my hot van?

You would think that with the pressure being rated at a temperature that fill stations would have the latitude to apply Charles Law.

Pete

Augh! Sick of searching, and wading through old threads to try to find some posts I remember, hence this redundant thread.

Can anyone help me with some hard data on this subject?

I was saying to my LDS last night, about overfills, that it's OK to run my LP Steel Fabers over a couple hundred PSI, so they'll cool to the rated pressure. I said that I had read that there is no record of a Faber steel exploding (it's that old batch of AL). I said that I had read that the only detrimental thing to overfilling a couple hundred PSI is the stress on the steel shortens the life of the tank a bit, but that there was no risk to the LDS to put 2800PSI in my 95, so it will cool to 2640.

They said, can I document my postulations?

Can I? Can anyone show me to some data, or a document that validates what I'm suggesting?

Thanks!!

 

[Charlie99]

Can you name ONE time a body part was blown off giving a fill that cools to full? Or even 200psi over. Heck, can you name a tank that caused a missing limb at 500psi over? (Remember, we already established that we're not talking about that one bad batch of ALs.)
It just doesn't happen.

Not often at least. Not much comfort to the previous owner of the Dive Center of Sebastian, out in the Vero Beach, FL area, who died back in 2001 when a old steel tank blew up while he was filling it. Rusted old steel tank by Voit. Out of hydro.

http://www.hawaii.edu/ehso/diving/Steel Cylinder Explosion and Proper Filling Procedures.pdf

 

[TX101]

If I remember right the tensile strength is different in Europe then the US.

But I think Roak is right about focusing on the word "overfill"

Actually, I'm pretty sure it's the wall thickness that's different - ie. tanks over here have thicker walls and are heavier.

I'm so glad I don't have to worry about overfills, etc. Most compressors in dive shops here go to 300 bar and I haven't met anybody yet that won't fill a 232 bar tank to 250 (3675psi) if you are leaving immediately.

(one exception is inland dive sites such as Stoney.. they will fill to about 220 because they get soooo many cylinders to fill on a weekend. Stoney don't even do nitrox on weekends)

 

[Charlie99]

Actually, I'm pretty sure it's the wall thickness that's different - ie. tanks over here have thicker walls and are heavier.

The reason for that goes back to tensile strength. Generally there is a tradeoff between brittleness and tensile strength -- that's why there is a spec that, as strange as it sounds, sets a maximum limit on tensile strength, thereby requiring thicker walls.

 

[wettek]

Working on a floating oil production platform, we have a load of pressure vessels, and a scuba tank is classed as a pressure vessel. All pressure vessels must have a test pressure of at least 1.5 times working pressure. This is there as a safety factor in case of over-pressurisation, despite having relief valves, which in a scuba tank is your bursting disc. Don't know about the States, but here in OZ, it is illegal to fill a tank over it's working pressure, even if it's a hot fill. Basically, if the authorities caught your dive shop, overfilling a tank, the wrath of god would ensue. The only way around it, is to top your tank off when cool, rather than initially overfilling, and letting it cool down to full. Remember, it is actually ILLEGAL, so if you are in a hurry, technically the dive shop is doing the right thing, and you asking for an overpressure fill just because it's hot, is asking the shop to break the law. What you do with the tank afterwards (ie overpressurising it as it heats up in your car) is up to you.