Bursting disc queries 1

[chemks2012]

Hello all

I have few queries on bursting disc please and would appreciate your help.

Vessel design pressure: 1barg
MAWP: Unknown
Maximum vessel operating pressure: 25mbarg
Vessel design code: Unknown
Accumulation allowed: Unknown
Bursting disc data [data from bursting disc supplier] : 4”, set pressure of 1barg, manufacturing range 0%, tolerance +0% to -10%, maximum vessel operating pressure allowed is 95% of minimum burst pressure
Release phase type: two phase release

My queries:

1) Am I right saying that the minimum burst pressure is 0.9barg as manufacturing range is 0%, and tolerance is -10%?
2) Am I right saying that the maximum burst pressure is 1barg as manufacturing range is 0%, and tolerance is +0%?
3) Am I right saying that the maximum safe operating pressure for the vessel is 0.855barg as it should be 95% of minimum burst pressure which is 95% of 0.9barg?
4) Not sure, what design code this vessel is manufactured. Can I assume 10% accumulation i.e. accumulated pressure of 1.1barg?
5) I have calculated two phase release rate at maximum burst pressure which is 1barg. Is this correct?
6) If my understating in point#5 above correct, the busting disc line has two phase pressure drop of 0.1bar at calculated release rate. This means that the pressure drop of 0.1bar is acceptable because
1barg [burst pressure] + 0.1bar [built up back pressure during release] = 1.1barg [accumulation pressure]

Is that correct?

Your help/input would be much appreciated.
Regards,
KS

 

[don1980]

I'm guessing that this disk is fab'ed according to PED rules for installation at a European facility. Is that true? I say that because the information you listed doesn't align with ASME Sec VIII. What is the design code listed on the specification sheet, or on the vendor proposal? Does it say ASME Sec VIII or ISO 4126, or neither?

 

[chemks2012]

don1980
Yes, it's for EU country.
The rupture disc supplier stated ISO4126.
Thanks,
KS

 

[don1980]

My responses to your questions.....
1) Yes, 0.9 barg is the minimum burst pressure at the specified temperature. Temperature has a big effect on the burst pressure, and sensitivity will vary depending on the metallurgy.
2) Correct, and same comment about temperature.
3) In theory, that is the max safe operating pressure. Actual experience can vary.
4) No. You can't make any assumptions if you don't know the vessel's design code. In such cases, i would regard the vessel design pressure as a "do not exceed" value.
5) Refer to #4.
6) The allowable accumulation can't be known without knowing the vessel design code. If this vessel is new, or was built after 2003, then it's probably a pressure vessel (10% accumulation is acceptable) but that's an assumption. In Europe, pressure vessels start at 0.5 barg, whereas in ASME jurisdictions they start at 1 barg. Check the files, read the nameplate, or contact the vessel supplier to asertain the design code and the allowable accumulation. If you're still unsuccessful, then I would design for a relieving pressure of 1 barg rather than 1.1.

Note that there is no such thing as "manufacturing range" for a European disk (PED jurisdiction). ASME has "manufacturing range" and "burst tolerance". In PED jurisdiction, there is just a single range called "performance tolerance".

If precision is important, then you should specify that the manufacturer does the disk testing at the specified temperature. Otherwise the manufacturer is free to perform the testing at ambient temperature and make an adjustment based on a temperature correction chart. Disks are fickle devices, and premature failures are especially common at low burst pressures. So, it would be wise to maximize the manufacturing precision. In ASME jurisdiction, the testing is automatically done at the specified temperature as long as you specify the disk to be ASME Sec VIII certified.

 

[chemks2012]

Hi don1980

Thanks very much for your input, I am always learning from you.
Few things to ask on point 1, 2,4,5,6, I would say.

1) & 2) When you said minimum or maximum burst pressure are at specified temperature, I want to understand one thing please.

Situation # 1 if the bursting disc specified temperature is 200degC [at set pressure of 1barg] and relieving temperature is 150degC . What is the significance of temperature here?
Situation # 2 if the bursting disc specified temperature is 200degC [at set pressure of 1barg] and relieving temperature is 250degC . What is the significance of temperature here?

4) Assuming % pressure accumulation as 0% as it’s unknown. This means 0% overpressure and hence relieving pressure for bursting disc is 1barg. Is this correct?
5) I have calculated two phase flow at relieving pressure of 1barg based on point#4 above. Hope, this is correct?
6) For a given relief discharge line, the two phase flow pressure drop is 0.1barg which seems unacceptable as it exceeds vessel accumulation pressure [see below]. Am I missing anything here?

1barg [relieving pressure] + 0.1bar [built up back pressure during release] > 1barg [vessel design pressure or accumulation pressure]

Thanks for your help in advance.
Regards,
KS

 

[don1980]

Response..
Situation #1: This effectively raises the actual burst pressure.
Situation #2: This effectively lowers the actual burst pressure.
4) Zero accumulation means the relieving pressure (peak pressure) doesn't exceed the vessel design pressure.
5) Your relieving pressure, according to your previous comments, is 1.1 barg. Burst P = 1, Friction loss = 0.1.
6) You've designed for 10% accumulation (Relieving P = 1.1 barg). Whether that's acceptable from a compliance perspective depends on the vessel code. Of course, we're talking about a very small amount of pressure (0.1 bar). It's likely that the true safety risk associated with a relieving P of 1.1barg is very small, but that's a decision for you and the equipment owner.

 

[chemks2012]

Thanks don1980

Just want to clarify points 5 & 6 please.

5 & 6) As I understand, relieving pressure = set pressure + overpressure. Therefore, in above case as overpressure = 0%, set pressure = relieving pressure = 1barg. Is this not correct?

Now if we assume that the two phase pressure drop is 0.1barg [built up back pressure] at the bursting disc bursts at 1barg, as I understand, we need to limit the sum of this two pressure to maximum of design pressure in our case which is 1barg? Sorry if I am missing something here but what I learnt so far for bursting disc is as below:

Bursting disc relieving pressure + back pressure <= accumulation pressure of vessel

Regards,
KS

 

[don1980]

"Relieving pressure" is the pressure that the vessel experiences during the relief scenario. If the disk bursts at 1 barg, and the resistance through the relief system is 0.1 bar, then the vessel will see 1.1 barg. If you want to limit the relieving pressure to 1.0 barg, then make a slight reduction in the burst pressure.

 

[chemks2012]

Thanks don1980