3 replies to this topic

[Perumal M]

Hi,

 

Anyone clarify me about the blowdown valve. I think it should be used where the operating pressure of system should be 17 barg or the volume of the system should be 4 m³. But I could see BDV in a compression  system where,

 

Operating pressure is 1 barg,

design pressure is 7 barg

Operating temperature is 25 ^oC

Design temperature is 100 ^oC

 

(BDV installed in mist extractor. i.e after LP KOD) Is there BDV necessary? I need clarification about this. Please clarify this scenario.

 

Thanks in advance,

 

Regards,

Perumal M. 

Edited by Perumal M, 19 July 2018 - 12:41 AM.

[Amit J]

Perumal,

 

BDV is a safety arrangement to remove inventory out of system in case of emergency and minimise chances/impact of surface rupture of pipe/equipment.

emergency scenario for which BDV to be provided is system specific . typical example is Fire scenario.

 

As per API guideline, system pressure need to be reduced to 100 psig or 50% of design pressure, whichever is lower within 15 minutes of time.

 

also you may encounter low temperature issue while depressuring, hence an RO is installed downstream of BDV to limit flow such that low temperature will not cause metal embrittlement. or else you need to choose costly material which will withstand low temperature. Also it helps to limit noise and vibration problem.

 

For compression system, a BDV is generally provided if I) settleout pressure is exceeding design pressure ii) for Fire scenario

 

Since your operating parameters are quiet low in general terms, it seems that BDV is provided to remove inventory considering fire scenario.

 

I hope this helps to analyse you further 'System specific scenario'.

 

However please note that BDV Provision criteria suggested by you (i.e. 17 barg pressure or 4m3 of system volume ) is unheard of and seems came from some wrong information.

 

....

Amit

[Perumal M]

Thanks Amit, 

 

In API 521 6th edition, at page number 64, see the Application  Criteria. you can see the condition which i have mentioned above (i.e. Pressure of 17 bar or 1700 kPa). 

 

Thanks and regards,

Perumal M.

[fallah]

 

In API 521 6th edition, at page number 64, see the Application  Criteria. you can see the condition which i have mentioned above (i.e. Pressure of 17 bar or 1700 kPa). 

 

 

Hi Perumal,

 

As per API 521, emergency depressuring for the fire case should be considered just for large equipment operating at a gauge pressure of 1700 kpa or higher.

 

In the case you saw a BDV in a system with lower pressure than 1700 kpa, it might the relevant depressuring hasn't been considered as an emergency one and depressuring just being done in other cases such as maintenance case...