Help Validate Facts on Overfill to LDS

[DepthCharge]

......... 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.

I'd beleive corosion causing the grooves, not overpressureization. When I was diving OC, I'd routinely fill LP tanks to 3500-4000 psi. All of them passed hydro X 2. One set of PST dbls did start to groove, but it was due to salt water sitting behind the bands, not the overpressure.(discolored galvanize) Top band were effected, bottom bands were not (on both tanks).

 

[Rick Inman]

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.

So, basically in OZ, it's legal to have an over pressurized tank in your car, or house, or other hot place, but if you have one in a dive shop hooked up to a compressor, it's illegal.

Got it...

 

[wettek]

So, basically in OZ, it's legal to have an over pressurized tank in your car, or house, or other hot place, but if you have one in a dive shop hooked up to a compressor, it's illegal.

Got it...

No, I didn't say it was legal. All I implied was as long as the dive shop hadn't overfilled it, their liability ended there. Don't go reading things that aren't there.

 

[NutJob]

I'd beleive corosion causing the grooves, not overpressureization. When I was diving OC, I'd routinely fill LP tanks to 3500-4000 psi. All of them passed hydro X 2. One set of PST dbls did start to groove, but it was due to salt water sitting behind the bands, not the overpressure.(discolored galvanize) Top band were effected, bottom bands were not (on both tanks).

Grooved wasn't the right word, what I should have said was the tank had bulged over the bands. It wasn't much, about 1/16, but it was visible. The hydro company told us not to bother sending it, it was automaticlly condemed. I have no idea how much they had been getting fills to.

 

[Rick Inman]

No, I didn't say it was legal. All I implied was as long as the dive shop hadn't overfilled it, their liability ended there. Don't go reading things that aren't there.

OK, please clear it up for me.

1) Is it legal to have a tank that is hot and therefore overfilled by a couple hundred PSI in your vehicle?

2) Is it legal to have a tank getting a hot fill at the dive shop 200psi overfilled?

Thanks

 

[nauidiver2004]

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.

They are cycled to their rated service pressure

 

[nauidiver2004]

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.

I agree. But then their are those people who don't understand why a trooper is writing them a speeding ticket when they were only driving 80mph in a 65mph zone.

 

[nauidiver2004]

So, basically in OZ, it's legal to have an over pressurized tank in your car, or house, or other hot place, but if you have one in a dive shop hooked up to a compressor, it's illegal.

Got it...

Rick,
Not trying to be *explative omitted* here but as it applies to the US, in a word, yes. The dive shop is regulated by various orginizations, OSHA, DOT, State and local Building and Fire Codes, ect. You, as an individual usually are not. I'm getting really annoyed because I have been looking for about an hour and a half to the answer to your original question and I haven't been able to find the specific federal code section to cite. I'm kinda tired so I'm going to bed but I will keep trying to find it over the weekend.
Basicaly you are asking for a code section that will allow a compressed gas cylinder to be filled, albiet temporarily, over it's rated working pressure. Confidence is high that there isn't one. There is, somewhere a reg that will state that a cylinder 'shall not be filled above it's marked pressure limit'. I am looking thru DOT regulations (49CFR) which unfortunatly incorporates many CGA (compressed gas assn.) publications thru reference. I don't have access to most of the CGA pubs here at home but I will keep looking.

Ken

 

[mech]

I love my local shop...well almost local 25 minutes from home and just pass 3 unworthy shops (crummy fills being just part of it).
Unless they are with a customer they will stop whatever they are doing and give my any fill I ask for and I'm out of there shortly there after.
Near half the time it's free or near free.
Gonna have to do something nice for then around the holidays.
It works for me.
YMMV

Now about them tanks being over filled...
The next paragraph or so is my personal experiance with some tests.
Yours might be different.
I will not gaurentee **** (other than my poor spelling)but might answer a PM.

As an Engineering contractor that used to specialize in industrial process piping,pumps and tank installations, I worked a gig about 10 years ago as a consultant to give a report on 2" stainless steel tubing for a large cereal company in Woodland Ca.
This was destructive testing for a safety report.
Readers digest version...
2" .065 ss tube orbit computer welded (fused).
100 samples 2 welds each (spools)
Id of tube polished out 100% by die grinder and flapper wheel.
Cereal excrude at 160 degree pumped via a screw pump pressurized samples untill failure.
All failures (explosions) were between 2350-2625lbs and 5/16 -3/8 of an inch away from weld edge (heat effected zone).
Because the ID of the weld was removed by a hand operated flapper wheel the wall thickness was reduced to near 1/16 in some locations.

My fills don't scare me.

 

[nauidiver2004]

49 CFR (chapter I) 173.301
(e) Container pressure. The pressure in the container at 70 °F. must not exceed the service pressure for which the container is marked or designated, except as provided in § 173.302(c).

Section 173.302 (c) is the section that allows the + designation on certain cylinders and allows an excess fill of 10%

The only thing I could find that allowed any excess pressure was:
(2) When a cylinder is charged in accordance with § 173.302(c), the pressure in the cylinder at 130 °F. must not exceed 5/4 times the filling pressure authorized therein.


Ken