Distance for Pressure Relief in Long Steam Duct

[code1]

Dear all,

Currently I have the question on the need for pressure relief downstream of turbine bypass station/ steam conditioning station.

The bypass station (2nos) reduce pressure of 40 bar/400 deg. C to 0.6bar(a)/105 deg. C. The steam outlet (1.5m diameter) is connected to the steam manifold leading (2.4m diameter) to the Air Cooled Condenser.

The steam manifold is protected against overpressure by relief valves that are located some distance (20m) downstream of the turbine bypass station.

There are no isolating valves from these stations to the relief valves.

Question: Are relief valves necessary immediately after the bypass stations,or can the downstream pressure relief valves do the job.

Thanks and regards.

 

[gerhardl]

A pipeline diagram would help understanding the actual layout in detail. Also mass flow figures, but it would be too complicated to give you a detailed answer through this forum.

The question you should ask yourself is if there is any chance that some of the equipment could be fed with a higher pressure,temperature (and volume) than design values. Secondly what this would cost in risk of human life or injury and materiel damage.

I am a bit suspicious here, valves in general have a tendency to be left out or tried to be rationalized away when large and costly, in stead of being installed as safety would normally demand when smaller or cheaper.

Check the layout with a steam consultant, it seems that possibly isolating valves, checkvalves and extra relief valves or bursting discs should be considered by an outside expert here before final answer.

 

[code1]

Reason I posted this query is because the score right now is 2 vs 1. For NOT installing: 2 who are my suppliers.

1st supplier: the ACC contractor, who is already supplying the SRV in his ducts. He told me I can rely on his SRV because there is no isolation between the steam conditioning station to his PRV.

2nd supplier: who is supplying the steam conditioning station because he told me there are pressure transmitters that can be interlocked to a motorized valve upstream==> exceed pressure, shut off the supply of HP steam. I agree with him. He can potentially do more business by providing the additional SRV's or bursting discs but he tell me there is no need.

For Installing: my engineer.. because it should be done, but no technical justifications.

My own thought experiment: because the SRV (which is adequately sized) is some distance downstream, if there any too high pressure into the steam duct, is it possible that the steam outlet bulges and burst, instead of the pressure being seen at the 20m away SRV? Most unpleasant.

How long does it take for this over-pressure to be seen 20m downstream where the SRV's are located? Anyway to quantify this so that I can make my own decision. either 3-1 or 2-2 score. thanks.

 

[CJKruger]

code1, assuming I understand your system correctly, you can locate the PSVs 20 m downstream provided the MAWP is not exceeded anywhere in your system. One way to achieve this, is to reduce the PSV set pressure (maybe stagger them).

Regarding your 2nd question, a pressure pulse is propagated at the speed of sound.

 

[JoeWong88]

Opinion from 1st supplier :
It is acceptable to provide a PSV 20 m downstream. Nevertheless the PSV set point shall be set such that the maximum accumulated pressure plus the pressure drop for the 20 m shall be lower than MAWP of the system. Your engineer can assist you on this calculation.

Opinion from 2st supplier :
I am not sure your application and industry has adopted the most stringent requirement as seen in oil and gas. Generally relying on trip is not sufficient unless it can be demonstrated that the SIL level of overpressure protection system (sensor + trip + loop + shutting device +...) is higher than the required SIL (at least the PSV).





JoeWong
Chemical & Process Technology

 

[code1]

Dear all,

Thank you for the explainations.

Best regards,
code1