Double Your Burst Disk - Arguments For & Against, Please...

[wedivebc]

Burst discs that are raised on the back of the manifold can be dislodged and caused to flow if impacted by a force (you swimming or scootering full force into a rock ceiling). Saw it happen once, then did a test with a junk valve I had and a hammer. I've also asked other people and heard of it happening.

How would double disc prevent that? What you describe is damage to the disc carrier caused by impact.
I am referring to a disc bursting underwater or any other case double discing is suppose to prevent.

 

[Firefyter]

Lastly if Europe isn't worried about thier firemen dieing from exploding tanks then I don't think we should be.

Thanks, dude, nice to know you're looking out for us, and trying to keep us as safe as we're trying to keep you...

Now with that in mind, if you were to have a house fire, a fireman would really only be able to enter the house with temperatures reaching 150-200 degrees, at which point a rescue would be pointless.

Not quite. We regularly enter buildings where the temperatures far exceed that, just on the off chance that somebody may be in there and may have found someplace tenable. I've melted more than one helmet in my 20 years of firefighting.

Now the average house fire reaches around 500 degrees at floor level (where most tanks would be stored).At this level, a tank stored with 2640 would be holding 5781 PSI, which most tanks would be tested to between 4000 and 5000. It would be high, but the probability of failure at that point is still not great.

These figures are pretty accurate, especially as far as the temps go. Fire at ceiling level will get much, much higher, but at floor level 500-600° is about right. What you're not accounting for, though, is direct flame impingement. Direct flame impingement will drive those temps up considerably. I worked a fire at welding shop where the tanks were actually in the area of fire origin, and even though the burst discs did their job, the rate of expansion due to heat was so fast that it still blew the valves out of the tanks. There's nothing like hearing tank valves and caps whistling as they pass over your head to get the old adrenaline pumping. I realize that this is an extreme case, but it happens, and it's something we have to consider.

 

[Quarrior]

This link should quell any questions about fire and pressurized tanks. I live in St Louis.

http://www.msnbc.msn.com/id/8348387/

 

[Firefyter]

This link should quell any questions about fire and pressurized tanks. I live in St Louis.

http://www.msnbc.msn.com/id/8348387/

Thanks for that link, very interesting. The fire I was involved in was just a small welding shop, but it was enough to encourage respect from me. To see something like the St. Louis fire would be amazing. I'm just thankful no one was hurt there.

 

[Rick Inman]

This link should quell any questions about fire and pressurized tanks. I live in St Louis.

http://www.msnbc.msn.com/id/8348387/

There also was no word on the cause of the rapid-fire series of spectacular explosions at Praxair Distribution, which processes propane and other gases for industrial use...
Leland Darrow, assistant area director of the Occupational Health and Safety Administration office in St. Louis, said he was not aware of any safety violations at the plant.

There were no safety violations in this fire so there were no improper burst disks, so I don't see the connection.

Also, it sounded like propane tanks were the issue - which makes sense since we're talking highly flammable fuel. Anybody have one of those in their back yard right by the BBQ? Now that sounds dangerous. eyebrow

 

[Quarrior]

There were no safety violations in this fire so there were no improper burst disks, so I don't see the connection.

Also, it sounded like propane tanks were the issue - which makes sense since we're talking highly flammable fuel. Anybody have one of those in their back yard right by the BBQ? Now that sounds dangerous. eyebrow

Actually, it was a multitude of gases. Propane, acetyline, oxygen. Point I was getting at with the post is that all of them were in steel tanks. I"m not sure if they had burst disks, but several people had posted issues about fire related problems and I wanted to give some insight into that specific point.

Personally, I think your original post was excellent which is why I started the other thread after this one started running away from the original topic.

 

[miketsp]

..snip..
A set of PST LP104's at 2640 have 208cft. At 3600-3700, they have 285-290 cft. (or a built in 80cft stage bottle)
..snip..

Not quite true.
The figures you quote assume linear compressibility. One you get beyond 3000 incompressibility comes into play. By the time you get to 3600 this will be of the order of 7% for N2 and over 20% for He.
Use Van der Waals law to calculate.

 

[Dive-aholic]

So do you walk your tanks to the dive site? I agree, and have, double disked tanks, but ponder this...

...but DOT only governs cylinders "offered for transportation". I believe this refers to commercial operations conducting interstate transports. I don't think there is a legal issue for privately owned cylinders for personal use.

I'm not a commercial operation.

 

[Charlie99]

Do you have references for that warranty? I hear that all the time but have never seen it in official documentation.

I recall seeing the 10,000 cycles to 4,000psi in some old PSI literature, but it WASN'T a warranty. It was part of the initial qualification tests of the tank design. It is NOT a warranty. It is NOT something that says the rated working pressure is 4,000psi.

Because of tank to tank variations, because of possible unseen defects, and because of possible unnoticed variations in material strength from lot to lot, the rated working pressure of tanks is lower than the pressure at which they are expected to fail.

You can see this sort of conservatism in many areas. Normally, one will not go into central nervous system convulsions from oxygen toxicity until many minutes exposure at 2+ata, or even 3+ ata. But since ox tox is widely variable, we back off to 1.4ata or 1.6ata limits.

Ropes usually have an safe working load limit less than 1/10 of the expected breaking strength. You will see similar ratios between the test loads and rated working load on cranes, hooks, and other lifting gear.

Most of the time one can exceed the rated pressures, rated working loads, or accepted oxtox limits and not have a problem. Whether or not is a wise choice is something you have to decide for yourself.

 

[wedivebc]

...but DOT only governs cylinders "offered for transportation". I believe this refers to commercial operations conducting interstate transports. I don't think there is a legal issue for privately owned cylinders for personal use.

I'm not a commercial operation.

If you go on a charter boat that is commercial transport and is under DOT juristiction. At least in this country.