5 replies to this topic

[omid64]

dear all

I have a question regarding isolation philosophy in following scenario: a compression stage have a common scrubber and 2 compressor and cooler in duty standby configuration.outlet of each compressor equipped with shut down valve which with a manual isolation valve provide double block isolation scheme.inlet line of scrubber will be depressurized and isolated by single valve which provided enough isolation. there are an spill back stream equipped with control and by pass valve. the stream is branched off from compressor discharge line after shutdown valve described before.for human entry to scrubber need a positive isolation against live plant.the problem in this regard is spill back stream. by pass stream of control valve has only a globe valve. which combination will provide proved isolation to insert spectacle blind on inlet stream of scrubber against leakage through spill back line and control valve bypas.

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[VeryProfessionalEngineer]

Given what you showed, I don't see a solution if that line has to stay live. I'm used to seeing the spillback taken prior to the SDV (and often a manual block valve and/or check valve as well). 

[omid64]

Given what you showed, I don't see a solution if that line has to stay live. I'm used to seeing the spillback taken prior to the SDV (and often a manual block valve and/or check valve as well). 

Dear Sir

Thanks for your corporation.

wiith the configuration you proposed there will be a better isolation  but not a proved isolation since double isolation criteria shall be respected again by using a block valve in addition of ESDV to achive double block scheme.also piping class upstream of ESDV shall be upgraded to higher class exist to compressor discharge since there are no protection (PSV) upstream of ESDV in this regard.connection of Spill back down stream of ESDV is more secure since the PSV on drum could protect piping against pressure built up initiated with spill back valve.

I have a design practice which explain that a double bock isolation is required for control valve by pass in class 800 # and greater.I'm in doubt whether it is a normal choice and how it will be implemented.

Regards

Edited by omid64, 05 September 2017 - 11:47 PM.

[VeryProfessionalEngineer]

 

Given what you showed, I don't see a solution if that line has to stay live. I'm used to seeing the spillback taken prior to the SDV (and often a manual block valve and/or check valve as well). 

Dear Sir

Thanks for your corporation.

wiith the configuration you proposed there will be a better isolation  but not a proved isolation since double isolation criteria shall be respected again by using a block valve in addition of ESDV to achive double block scheme.also piping class upstream of ESDV shall be upgraded to higher class exist to compressor discharge since there are no protection (PSV) upstream of ESDV in this regard.connection of Spill back down stream of ESDV is more secure since the PSV on drum could protect piping against pressure built up initiated with spill back valve.

I have a design practice which explain that a double bock isolation is required for control valve by pass in class 800 # and greater.I'm in doubt whether it is a normal choice and how it will be implemented.

Regards

 

In the cases I'm referencing, we have a PSV just upstream the SDV, a block downstream of the SDV and a drain between. If you haven't done so already, I would suggest walking down your plant to confirm the representation on the P&ID and your understanding that the line downstream must be live is correct.

[omid64]

 

 

Given what you showed, I don't see a solution if that line has to stay live. I'm used to seeing the spillback taken prior to the SDV (and often a manual block valve and/or check valve as well). 

Dear Sir

Thanks for your corporation.

wiith the configuration you proposed there will be a better isolation  but not a proved isolation since double isolation criteria shall be respected again by using a block valve in addition of ESDV to achive double block scheme.also piping class upstream of ESDV shall be upgraded to higher class exist to compressor discharge since there are no protection (PSV) upstream of ESDV in this regard.connection of Spill back down stream of ESDV is more secure since the PSV on drum could protect piping against pressure built up initiated with spill back valve.

I have a design practice which explain that a double bock isolation is required for control valve by pass in class 800 # and greater.I'm in doubt whether it is a normal choice and how it will be implemented.

Regards

 

In the cases I'm referencing, we have a PSV just upstream the SDV, a block downstream of the SDV and a drain between. If you haven't done so already, I would suggest walking down your plant to confirm the representation on the P&ID and your understanding that the line downstream must be live is correct.

 

As I know, since succeeding stage will fed from two sources (this compressor and a feed from production unit), it could be in operation and its suction which is discharge of the compressor under the  maintenance is under pressure.

[VeryProfessionalEngineer]

 

 

 

Given what you showed, I don't see a solution if that line has to stay live. I'm used to seeing the spillback taken prior to the SDV (and often a manual block valve and/or check valve as well). 

Dear Sir

Thanks for your corporation.

wiith the configuration you proposed there will be a better isolation  but not a proved isolation since double isolation criteria shall be respected again by using a block valve in addition of ESDV to achive double block scheme.also piping class upstream of ESDV shall be upgraded to higher class exist to compressor discharge since there are no protection (PSV) upstream of ESDV in this regard.connection of Spill back down stream of ESDV is more secure since the PSV on drum could protect piping against pressure built up initiated with spill back valve.

I have a design practice which explain that a double bock isolation is required for control valve by pass in class 800 # and greater.I'm in doubt whether it is a normal choice and how it will be implemented.

Regards

 

In the cases I'm referencing, we have a PSV just upstream the SDV, a block downstream of the SDV and a drain between. If you haven't done so already, I would suggest walking down your plant to confirm the representation on the P&ID and your understanding that the line downstream must be live is correct.

 

As I know, since succeeding stage will fed from two sources (this compressor and a feed from production unit), it could be in operation and its suction which is discharge of the compressor under the  maintenance is under pressure.

 

 

I'm guessing that's what the drawings show you (you only posted the drawing for the scrubber you mention so I am taking your word on that). What I'm saying is to go outside, walk down the lines and visually verify that what you have installed in the plant matches your drawings 100%. Highlight each line as you walk it out to confirm there isn't anything that deviates from your drawing that would allow you to perform an isolation to swing the blind. If the drawing is right, you'll probably have to shut down the other part of the plant to make an isolation to do the work, but you don't want to shut down the plant just to have an operator come up to you afterward and say "why didn't you just shut valve X, or line this up somewhere else" and then you have to say "oh, I shut down the plant because that option wasn't on my drawing."