PSV Requirement

[patibar]

We are going to install a filter in tailgas compressor suction line of (18"). I would like to go with out any requirement of PSV. As it is a gas filled line, there is no possibility of pool fire scenario. If i keep open the both inlet and outlet valves in "Car Seal Open" position, I can omit the Blocked-In case also. I would like to protect the system with respect to System Design (UG-140) and not by the Pressure Safety Valve.

I would appreciate if somebody comeup and suggest the best way.

Thanks

 

[123engr]

@patibar,

I guess you do not consider the maintenance of the filters when you want to keep both the inlet and outlet valves in "Car Seal Open" position. You must put the filter maintenance into consideration.
I suggest you consider a sparing philosophy for the filter.
PSV installation is highly recommended to be considered in your system design.


I am what I am by His grace

 

[zdas04]

You're the Engineer. If you can justify using a code case, then you should. I generally have a problem signing off on a locked or car-sealed valve as making the blocked outlet scenario non-credible, but that is a personal preference and I see people with different preferences all the time (I've even overcome my reservations and done it a time or two myself in very specific cases).

As to needing a PSV during maintenance, I reject that idea every time it comes up. If an operator or maintenance man purposely violates a car-seal, then I feel very safe in assuming that they know what they are doing and will open the filter drain before the trapped liquid can expand to create a problem. I never call for a PSV based on a section of pipe being isolated for routine maintenance.

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.

 

[don1980]

As stated by zdas04, this is a risk management decision for you and the equipment owner to make. To define what is best, first define the criteria for that assessment. That takes insider knowledge. As outsiders, we don't have the necessary info & insight to distinguish acceptable and unacceptable risk for you.

I've used UG-140 many times. However, my default position is that a PRV is needed. That is, I start with that assumption and then evaluate whether there's a strong case for using UG-140. The point I'm trying to make is that one shouldn't automatically jump to a conclusion that UG-140 is OK whenever there are no credible causes for overpressure. Just because we can't think of any causes for overpressure, that doesn't automatically mean there are none. We just can't foresee exactly what someone might possibly do.

That said, this filter does indeed look like an acceptable case for considering UG140. It's small, vapor filled, and always open when the plant is running.

 

[patibar]

Thank you all.

I just like to know about the UG-140. When we should use this? I have clearly mentioned about the case. Its a gas service line (18") and we would like to install a single filter with bypass. Maintenance is not an issue by keeping the both isolation valves in "Car Seal open" position.I would like to know what ASME Code(latest) tells about the PSV installation. The operating pressure is >15 PSIG and Line size is 18". Should i go for a PSV with respect to the pressure vessel code or can i omit the PSV using system design (UG-140). As i mentioned earlier, Fire is not a credible scenario. Blocked-In case also not a credible scenario. Then on what basis should i go for a PSV?

Thanks

 

[TD2K]

Can you make the filter out of piping components rather than going with a registered pressure vessel?

I'm not clear what the CSO inlet and outlet block valves are giving you? What's the maximum source pressure relative to the filter design pressure?

 

[patibar]

@TD2K

The gas is coming from a knockout drum, which has a design pressure of 3.5 Kg/cm²g. The maximum operating pressure is 1.35 Kg/cm²g, and the filter design pressure is 3.5 Kg/cm²g.

 

[TD2K]

Does the knock-out drum have a PSV?

 

[patibar]

@TD2K

No There is no PSV on drum. Actually the tail gas is coming from PSA unit adsorption beds.

 

[TD2K]

You have vent gas coming from PSA units through piping, your filter to a compressor. What can the pressure go to if the compressor isn't running or if a valve on the compressor discharge is closed?

If there's no PSV on the upstream knockout vessel, which I'm assuming is also a pressure vessel, why is not providing a PSV on this vessel a question?

As said, if you don't have any overpressure causes (API 520 does have a method for calculating the relief load for a gas filled vessel engulfed in a fire, I don't think much of it but it is there) then it's up to you and your company not to provide a PSV. Your regulatory agency may insist if it's a pressure vessel it must have a PSV. I had a coworker who went through this for a cooler that was located above the fire zone, didn't have any other overpressure causes but the state inspector required a PSV on any pressure vessel.