Vanity burst discs

[rjack321]

Burst disk are intended to protect a tank from bursting during a fire.

At one time I think they were supposed to let go at about 50% overpressure (I can't remember exactly), or just below the normal testing pressure>

They are supposed to be the same as hydro test pressure. And release between 90% and 100% of hydro pressure.

 

[Luis H]

Originally Posted by Luis H
"Burst disk are intended to protect a tank from bursting during a fire.

At one time I think they were supposed to let go at about 50% overpressure (I can't remember exactly), or just below the normal testing pressure>"

They are supposed to be the same as hydro test pressure. And release between 90% and 100% of hydro pressure.

If you do the math you will see that is exactly what I said: 150% / 166% = 90.3%
Since:
150% is the same a "50% overpressure"
166% is the same a 5/3 testing pressure


But, the important question is could you point me to the document were this is specified? Is it in CFR49 or is it in a CGA document?

Thanks

 

[captain]

I believe part of the process of a manufacture getting DOT approval on a tank design is that they be tested to determine the actual burst pressure. I seem to recall seeing about 8,000 to 10,000 psi as the burst pressure on a LP steel tank. Luis do you have any info on this.

 

[royalediver]

According to my reading of the bulk of responses on this board, engineers that design high pressure cylinders know nothing of their craft and create arbitrary safety standards just to annoy us, we actually are much better educated and understand the issues much better than they do.

 

[Gil57usa]

Yes, but why do some people insist that they may explode if they the are overfilled to a pressure much lower the the threashold of the burst disc?

Perhaps they don't know what they are talking about?

 

[J.R.]

According to my reading of the bulk of responses on this board, engineers that design high pressure cylinders know nothing of their craft and create arbitrary safety standards just to annoy us, we actually are much better educated and understand the issues much better than they do.

Yea... what he said!!! Darned engineers... just because they actually make a living at this stuff they act like they know more than we do... harumph!!!

 

[HarleyDiver]

If you had ever seen a burst disk from a tank that had been overfilled on a regular basis, you would understand why we upgrade, double-disk, or plug them. They do get severly warped over time.

Let's not do a repeat of the old 'should you or shouldn't you overfill', that horse is bleeding on a dozen other threads.

The question was Why? The answer is the disks do warp with repeated fills, and become a weak point in the system. PC or not, thats why it's done.

 

[rjack321]

If you do the math you will see that is exactly what I said: 150% / 166% = 90.3%
Since:
150% is the same a "50% overpressure"
166% is the same a 5/3 testing pressure


But, the important question is could you point me to the document were this is specified? Is it in CFR49 or is it in a CGA document?

Thanks

Both. See 49CFR180.205

(4) For a specification 3, 3A, 3AA, 3AL, 3AX, 3AXX, 3B, 3BN, or 3T
cylinder filled with gases in other than Division 2.2, from the first
requalification due on or after December 31, 2003, the burst pressure of
a CG-1, CG-4, or CG-5 pressure relief device must be at test pressure
with a tolerance of plus zero to minus 10%. An additional 5% tolerance
is allowed when a combined rupture disc is placed inside a holder. This
requirement does not apply if a CG-2, CG-3 or CG-9 thermally activated
relief device or a CG-7 reclosing pressure valve is used on the
cylinder.

 

[Luis H]

Both. See 49CFR180.205

Thanks

The copy of CFR49 section180.205 I have reads a bit different, basically the same information. I think you have a newer revision.

 

[Luis H]

I believe part of the process of a manufacture getting DOT approval on a tank design is that they be tested to determine the actual burst pressure. I seem to recall seeing about 8,000 to 10,000 psi as the burst pressure on a LP steel tank. Luis do you have any info on this.

No, I can't recall seen anything about destructive testing during engineering development. That doesn't mean there isn't.
Calculating ultimate burst pressure is very easy, since a cylinder is a very simple pressure vessel. But, the allowable range in material properties will provide a range of results, not an exact value.