PSV Sizing Criteria 1

[10815L]

Hi,
I would like to size psv for, Description: dear sir, we required psv for air receiver of 2.0 m height and 1.5 m ID , 6 mm shell thickness and 600 mm grade height. how to design psv for this criteria? air is instrumental air,set pressure:-7.00kg/cm2g
could you pleadvise me what criteria must be used for this vessel.
Thanks

 

[zdas04]

For about the last 30 years, the size of the vessel has not been part of the PSV sizing criteria. If you go by API 520 you need to develop a "credible scenario" analysis that evaluates the flow rate of any overpressure scenario that is credible and then size your overpressure protection to prevent any of these scenarios from resulting in a vessel pressure that is higher than the MAWP plus allowable overpressure (10% for most scenarios, 22% for a credible fire case).

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

 

[GHartmann]

For the example in question I believe the case to evaluate is the maximum capacity of the compressor or system suppling the instrument air.

If the maximum rate of the compressor is 100 Nm3/h then the required relief valve capacity is 100 Nm3/h.

This would be a blocked flow case.

 

[Drexl]

Hi,
I agree that in order to size a safety valve you have to think through the possible scenarios, in this case is shouldn't be too difficult.
If it is possible to close the outlet and this way exceed the design pressure, which I assume is 7 bar(g), then you have to consider what the possible incoming flow is in this scenario. If the whole compressor stream can be supplied to this tank then this is the flow you need to size for. If the valve is unreasonably large this has to be compared to other ways to solve the issue.

Drex

 

[don1980]

For an air reciever it's very likely that there are no credible scenarios that can cause overpressure. That's ofetn the case for air receivers. If there are no credible overpressure scenarios, then there's no basis for sizing calculations. You have to install a PSV, but the size is arbitrary. Pick a PSV size and calculate the piping losses. Pipe losses are based on rated capacity. You don't need a sizing basis to calculate the rated capacity.

 

[asade]

The possible scenario you can consider is blocked gas outlet from the receiver. Therefore size the PSV for maximum flowrate from the air compressor as stated by GHartmann.

I am what I am by His grace

 

[10815L]

Hi,
Thanks for your valuable inputs.
10815L