It says right on my tanks - DO NOT OVERPRESSURIZE

[Ted Judah]

A year ago, I bought tanks for my wife and I. In that year we have used them on 16 dives and had them filled at 5 different dive shops. The pressures after each fill seem to vary wildly and is often overfilled.

Here are the markings on the tanks:

FABER MADE IN ITALY M8303 21/0154/ 073 02•21+
TC - 3AAM - 184/DOT - 3AA2400 DO NOT OVERPRESSURIZE REE67 BS85S


Below are the start fill pressures for each dive:

2400 lbs.
3400 lbs.
2600 lbs.
2500 lbs.
2500 lbs.
2500 lbs.
2200 lbs.
2800 lbs.
2800 lbs.
2800 lbs.
2950 lbs.
2400 lbs.
3000 lbs.
2750 lbs.
3250 lbs.
3525 lbs.

Am I missing something? should I be concerned? Should I request a certain pressure from dive shops?

 

[grantctobin]

I understand the math isn't 100% accurate, but when I plan I use a SAC a good bit higher than average... in the grand scheme of things in the real world I'm not sure it matters.

So with the z factor what would an LP 85 filled to 3442 actually have?

Z Factors for SCUBA | Dive Gear Express®

Z Factors for SCUBA Cylinder volume is defined by the internal dimensions of the tank, and normally measured in cubic inches or liters of water. Free capacity is ...

www.divegearexpress.com

 

[Angelo Farina]

I was saying the heat from filling... pressurizing a tank I don't think is what I would consider "hot".... that's all. Agreed on all the other points.

Sure, heating to 50 °C is not dangerous. Heating to 500 °C, instead, weakens significantly the steel resistance.
Tanks heated under the sun can explode because the internal pressure grows significantly, not because the steel weakens.

 

[LeeIom]

Yes, but the issue is worrisome only for many 1000's or 10's of thousands of cycles, not the few our cylinders undergo, and even then it is for stressing to near maximum, towards the elastic limit, not the lower levels we use in scuba.

That’s why they have hydro testing, I go to different places and end up with a different amount each time even at my local dive shop my 300bar 12s come out anywhere from 250bar to 320bar also depends if it’s a hot / cold day and how quick they where filled ie left on a slow cook fill for hours or just blasted in if it’s the later it’s going to show more to you jump in the water and it cools !

 

[rob.mwpropane]

Sure, heating to 50 °C is not dangerous. Heating to 500 °C, instead, weakens significantly the steel resistance.
Tanks heated under the sun can explode because the internal pressure grows significantly, not because the steel weakens.

Again, I (and I assume others) were only talking about the heat generated from filling or the added minute stress from heat from overfilling.. that's it.

Tanks heated under the sun (here in the states) are prone to having the OPV blow off but nothing more (as far as I know....which isn't much).

Do you have any links to scenarios where tanks left in the sun did rupture? Say in a hot car? I would be interested to read them. Curious as I know that they don't use OPV's in other countries, so I'm wondering how often that happens.

 

[Superlyte27]

Sure, heating to 50 °C is not dangerous. Heating to 500 °C, instead, weakens significantly the steel resistance.
Tanks heated under the sun can explode because the internal pressure grows significantly, not because the steel weakens.

Lol. Lol lol. No. Do the math. 3600 at 70 degrees heated to 140 degrees in a car. I have personally seen what it takes to blow a properly maintained (cave filled) tank. Its almost triple its rated limit.

 

[rob.mwpropane]

Lol. Lol lol. No. Do the math. 3600 at 70 degrees heated to 140 degrees in a car. I have personally seen what it takes to blow a properly maintained (cave filled) tank. Its almost triple its rated limit.

I have never heard of that happening either, but I know we have the OPV in the states where others do not.

What psi does a "hot" as in in the car in the sun tank even reach? I just couldn't imagine it being that much...

 

[inquis]

What psi does a "hot" as in in the car in the sun tank even reach?

70->140 deg F is only a 13% increase in Kelvin (what the gas cares about). Not even up to LP hydro pressure.

 

[Angelo Farina]

Again, I (and I assume others) were only talking about the heat generated from filling or the added minute stress from heat from overfilling.. that's it.

Tanks heated under the sun (here in the states) are prone to having the OPV blow off but nothing more (as far as I know....which isn't much).

Do you have any links to scenarios where tanks left in the sun did rupture? Say in a hot car? I would be interested to read them. Curious as I know that they don't use OPV's in other countries, so I'm wondering how often that happens.

We had a case of a bus with tanks overfilled with natural gas on the roof which exploded after leaving it in the sun, in July in North Italy. Here a report on the event (in Italian): Esplosione di un autobus di linea urbana alimentato a...
Regarding the lack of burst disks here: they are terribly dangerous with flammable gas. Better the risk of a tank explosion 1 time over 100, than 100 times of disc rupture and subsequent flames. Here a case where there was no burst disk, but the valve did rupture releasing the gas:

 

[Ted Judah]

Tanks heated under the sun can explode because the internal pressure grows significantly, not because the steel weakens.

 

[Angelo Farina]

As I already posted, here in Italy we had a couple of cases of natural gas tanks on top of a bus exploding due to overfilling and overheating.
This was proofed by the technical investigation following the accidents.
The technical consultant on one of these accidents was prof Groppetti, a fellow colleague in my department, who discussed with me the details of his report before releasing it. So I have first hand knowledge of one of these two accidents.
Of course you need to BOTH overfill and overheat for this to happen...
One hint: at very high pressure, the compressibility factor Z plays a role. For a fixed volume, the increase of Z makes the increase of pressure to become more than proportional to the Kelvin temperature of the gas, as the perfect gas law would suggest.