P&ID Header / Branch configuration Schematically represented vs actual in the field? 1

[PipeStretcher]

Hopefully i can fully communicate the question i have. ***The question is "should a P&ID be schematically accurate in configuration to whats in the field"? or, does it not matter?*** I have been a Piping Designer for the last 20 years. Ive spent quite a bit of time in the field walking down P&ID's and helping contractors with construction management on process plants/facilities. It has been my experience that P&ID's should always be Schematically correct. What i mean is that Headers (main runs) and branches should be graphically correct in how they are configured in the field. in my eyes this would should not fly. if the process flow/configuration is different between the P&ID and the model how would one describe a proper shut-down, operation, purging or start up procedure with this type of discrepancy? If a plant operator out in the field had a P&ID with a configuration discrepancy it could inject a level of confusion that might trigger questions to the plant manager, or even worse, the operator might shut the wrong valve, especially if its not tagged?

 

[LittleInch]

Yes you are correct, but what's the question or point?

One or the other is incorrect - so which should be followed - P&ID or piping drawing. Has this been built? If so amend the P&ID, if not amend the piping drawing.

TBH, I think the piping designer has made an error as you wouldn't normally want your metering system to have all those bends and elbows if it doesn't have to.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[PipeStretcher]

The question is "should a P&ID be schematically accurate in configuration to whats in the field"? or, does it not matter?

The P&ID should have been followed, the piper is at fault or should have went to the engineer to confirm it was ok to change, then push the change to the P&ID.

 

[LittleInch]

IMHO, yes, the P&ID should be schematically accurate.

something similar happens if you've got a manifold and say 5 offtakes. They should all be physically correct in which offtake is which in the correct order as you left to right or axially along the pipe.

I'm surprised the process engineer or even the instrumentation/metering engineer allowed this if he was involved in the checking as it alters quite markedly the flow pattern through the meter and could compromise the accuracy of the meter, even if there is a flow straightener there. Bad show all round from that company. If I was the client I would not be happy.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Gator]

There are LOTS of things that are done differently now that CAD has taken over, the old timers are retired or gone and software often dictates how things get done.

 

[LittleInch]

Gator, Yes, but an "intelligent" P&ID should have recognised that the tee is there for a reason and drawn the piping the correct way as shown on the P&ID.

This is a just a FU by the piping designer IMHO. But the two drawings should match. Having one saying one thing and the other something different is not good practice or design.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

They should be exactly the same, except dimensions, flow directions and other information that does not appear (never shown) on piping drawings.

In fact I'd say the length dimensions on the PID above should be on the piping drawing, not the PID.

 

[SwinnyGG]

There are LOTS of things that are done differently now that CAD has taken over, the old timers are retired or gone and software often dictates how things get done.

This is true, but it doesn't mean (imo) that the P&ID can just be disregarded. As far as I'm concerned, the P&ID is the bible. When it comes time to QC, test, and commission, I care much more about what the P&ID says than what piping drawings might say. P&ID always wins that conflict.

 

[Agnul93]

Hi.I agree that P&ID shall be accurate.
Of course the P&ID is done before the 3D model, hence some different configuration can occur.
IMHO is good practice to align the P&IDs in accordance with 3D model (for some customer this is a mandatory step), in order to give to the erection company the actual situation of what has been designed.
Important as well is also to revise the P&ID according to what done in site at the end of the project, hence "as built" P&ID, especially for the futures LOTO operations.

 

[danschwind]

If I drew that P&ID and later a piping guy showed me that he did THAT, I'd probably implode.

Daniel
Rio de Janeiro - Brazil

 

[davefitz]

The field engineer should have redlined the "for construction" p+ID as to what the actual built configuration was and then send it to the design engineer to confirm that no saftey issues or operating issues will be expected . Then the design engineer would re-isue the P+ID as an "as built " p+ID.

It is a potential safety hazard to have an incorrect P+ID used by the operators - the operators must have a correct P+ID to ensure they can safely operate the plant. There are also potential safety issues with incorrectly routed pipes as the assumptions used by the design engineer when he/she calculated the max overpressure of the piping and pressure vessels when a control valve fail-open scenario occurs.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick