Vessel Ovepressure Protection

[alex2010]

I would like to know if the the pressure safety valve installed on the vessel (shown in the attached sketch) is required by the code to relieve the steam capacity in the event of steam ovepressurization, even though the steam input has its own safety device set at the same pressure of the vessel?

Thank you,
Alex

 

[athomas236]

alex2010,

Where are the isolating valves.

athomas236

 

[alex2010]

The valves are installed upstream of the safety valve, as shown in the sketch.

 

[GenB]

valve 2 looks redundant but again the designer may have taken consideration of the supply steam.
the pv sv may be only enough to relief the PV capacity in pph, the SV2 then should be for the supply pipe relief in addition.

 

[yamoffathoo]

An ASME VIII vessel requires PSV-001 to be capacity certified for the steam overpressure threat.

VIII Appendix M could be cited to keep the air valve locked closed during normal operation and provide continuous operator presence when opened during maintenance.

PSV-002 might have been added when it was discovered that the vessel supplied PSV-001 capacity wasn't sufficient.

Adequate capacity can be provided by one or more ASME VIII capacity certified safety relief valves.

 

[unclesyd]

Just remember that for all cases you have to account for the air supply and it's relief vale (psv-003) setting of 100 psig). This another energy source so you have insure that the tank can't be blocked in with only the air supply.

 

[Duwe6]

And size for 'Fire Case'. This could evolve more steam that PSV-001 & 002 can handle. The PSV-003 can be eliminated, as both 001 & 002 protect up to the air block valve. 003 cannot be used for calc's, as it is 100% overpressured for the vessel.

 

[davefitz]

SEction VIII requires all pressure vessels be provided with a relief valve. It is possible the relief provided on the vessel was a minor "whistle" provided by the vessel mfr to meet the letter of the code, separate and independent of any knowlwedge of the required relieveing capacity.

The true releiving capacity should be calculated by the system designer, who has knowledge of the casualty flow thru all process connections based on knowing the control valve and piping flow limitations. It looks like each of the systems supplying fluid to the vessel have their independent releif valves, likely sized according to the max casualty flow thru the supply control valves.

So, the basic lessons to be learned are:
a) the "whistle" provided by the vessel mfr is nearly never sufficient for overpressrue protection, except perhaps thermal expansion of the fluid.
b) the engineer of record who is responsible for the process desing needs to document the casualty flow thru all systems contributing to the vessels' fluid, and size the releif valves accordingly
c) any future change to the control valves that supply fluid to the vessel imply you revisit the releif valve capacity requirements.

 

[alex2010]

Thank you for the great advice.
Alex

 

[alex2010]

Thanks to all for the great advice.
Alex