Do you show flanges on a plant P & ID? 18

[LittleInch]

Ok, we're having a debate internally here about what is "normally" done on a P & ID.

Do you
A) Show deliberately a little vertical line next to each flanged valve to indicate it's a flanged valve or
B) Assume all the valves in a plant are flanged valves.

If B how do you show when it is deliberately a welded end valve you want (e.g. last valve going into a long gas pipeline)

I've seen both ways and A really annoys me as you get little lines all over the place and then you can't see it or it gets lost in all the other data.
We're talking fairly basic P & IDs here, not the all singing all dancing "intelligent" P & IDs.

Spool pieces, blind flanges on e.g. drain valves are shown but "normal valves"?

Answers on a postcard please....

Thanks, LI

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

 

[georgeverghese]

My opinion - yes, they should all be shown - there can be some serious installation errors otherwise. This is the job of the process and piping engineers on the design project.

 

[moltenmetal]

The interesting, and frustrating, thing about working for many clients from many different companies is that you see how different people tackle the same problem. Sometimes there are good reasons, and sometimes (very often) the reasons behind what is done (what is on the legend sheet) is long forgotten or only known partially and by a few.

Some companies' P&IDs show every valve that gives a person access to the process fluid. Personally I agree with that approach. Others find that showing instrument blocks, bleeds, vents, drains, equalizing valves etc. adds unnecessary complexity and makes the drawings too difficult to read, and they imply all these valves by means of a separate document such as a set of instrument installation details. Personally I hate that, both from a construction and operation point of view. I take it to the extent of even showing (as a symbol, without tags), the suction and discharge check valves in PD pumps etc. If you want to analyze how something will flow, you need to know what is and isn't in the way.

Some companies give each item on the P&IDs (including most valves) a unique tag number, i.e. HV-1234. Others only give valves what amounts to a model number or spec call-out ID and fail to give them a unique identifier. Just try to write an operating or maintenance procedure using drawings like those...Others try to include both, and to differentiate valve types to an extreme degree using different symbols. Sometimes they run out of space or end up with twice as many P&IDs to fit everything. I prefer to give every valve and instrument a unique tag number and then give the details in a separate bill of materials or the like, though the "model numbers" right on the drawing can be very handy. As to hand valves, at an early stage in a project, valves are of only three types: they are either block valves, throttling valves or check valves. The detailed symbols, if they're necessary, to differentiate a ball from a gate etc., go in after selection is complete.

The same goes for controls: some try to duplicate the entire cause and effect, including linkages, on the P&IDs. That's typically a failure. Some kind of numbering system referring back to the cause and effect just works better.

And then there's the OP's original ask: piping details such as flanges and other split/breakpoints in lines and equipment. The best approach is what Pennpiper suggested- to show them when they're need to understand function. We usually show flanged nozzles and body flanges on vessels., flanges for removable spoolpieces, where components such as spectacle blinds, static mixers etc. are to be inserted into a line, where a line joins a flex joint or hose etc. Attempting to show every pair of flanges, coupling or union or Victaulic coupling etc. on a line can result in a set of drawings which are needlessly garbled. P&IDs aren't isometrics or pipe routing drawings.

Weld dots and other shortforms from isometrics or routing diagrams do not belong on P&IDs in my opinion.

Smart P&IDs are centralizing the information and making errors between documents less frequent. That gets rid of the need for a lot of checking, but that checking sometimes catches other things that people miss. On balance it's a good thing, if not taken to an extreme.

 

[BigInch]

Exactly why standards are not useful all the time.
The best practice is to show something whenever you think you need to show it.

 

[IFRs]

Sometimes there is a distinction between P&ID and PFD drawings, the valve type is certainly shown on the PFD ( process flow diagram ). Sometimes the drawings are combined, but called P&ID.

 

[Gator]

Isn't there always (not just "sometimes") a distinction between P&IDs and PFDs though? PFDs typically won't show valves that are assumed to be present (blocks and checks at pumps, for example) unless they are critical to the overall process.

Valve types are always shown on P&IDs, and the concept of "installation errors" due to wrong symbology on P&IDs I don't really understand unless it relates to bi-directional flow or some other unusual cases. I would hope that such "unusual cases" are monitored separately as happens with critical lines for stress analysis.

Vents and drains on P&IDs are only to be shown if they are critical to normal (or expected upset) operations. Locations of HP and LP vents and hydrotesting vents and drains are often better left to the field* to determine since the P&ID designer cannot be expected to know the final physical piping routing.

moltenmetal's comment, "P&IDs aren't isometrics or pipe routing drawings" is a very good one.

Paul


* Fab shops will have input on this if testing is not performed on site.

 

[LittleInch]

Thanks for all the comments, I didn't expect quite so many comments but it's clearly something that varies a lot with different sets of usage.

Moltenmetal I agree completely with your points about tagging. I much prefer lots of individual tag nos even for manual valves.

If were taking this a bit further, in my opinion and I've found it in a few company specifications, is the number of valves and equipment you show on a PFD. I always argue that the only things you show on a PFD are things which affect the fluid, so pumps, heaters, HXs, control valves, but no other items which don't change pressure temperature or composition such as isolation valves, esd valves, pig traps.

I come across a range of opinions on this and would like to know if I'm in the majority or not??

Thanks, LI

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

 

[moltenmetal]

We put piping vent and drain valves on the as-built P&IDs.

Instrument block/bleed/bypass always go on our drawings, but as I noted we have some clients who don't want them on there.

A PFD and a P&ID are as different as a P&ID and an isometric drawing. A PFD only shows equipment and main control loops, and stream and equipment tag numbers.

 

[BigInch]

I always argue that the only things you show on a PFD are things which affect the fluid, so pumps, heaters, HXs, control valves, but no other items which don't change pressure temperature or composition such as isolation valves, esd valves, pig traps./

IMO, as you already know, valves that control flow are not limited to "control valves". On/Off valves also control flow and can be especially important in pipeline PFDs. In fact in some systems (esp. pipelines) they just might be the only kind of valves installed at all.

 

[LittleInch]

I can appreciate the point but where do you stop. The whole point to me of a PFD is to show what is supposed to happen during operation. It after all a Process FLOW diagram, not a process no flow diagram...

I usually like to include a control schematic diagram to illustrate how the on/off and other parts function, but keep the PFD as simple as you can and assume the system is working as it should be.

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

 

[KernOily]

"I still haven't got any feedback on how people show welded valves if the convention is to not show flanges. - Anyone?"

Bueller here. Ha We don't show welded valves on P&IDs. The P&ID line number shows the line class/spec and that spec tells you the valves are welded.

Now. If you have a one-off, for example if you need a buttwelded valve in a line that is of a spec that normally uses only flanged valves, then we would show a spec break OR put a note on the drawing where that BW valve goes.

For flanged pipe, you don't show flanges on the P&ID. However, we will show flanges where they are important for the process, e.g. break-out spools, future tie points, future spool pieces where a meter will be added, etc. As was said above, one of the main uses of the P&ID is the formal communication tool between the engineer and the designer. If you want a flange pair in the line you need to make it on the P&ID so the designer knows to put it in for you.

A great question; one that always engenders a ton of debate, although it shouldn't, in theory.

 

[BigInch]

Well I think it can be very important process-wise to know that you're not going to be continuously blending gasoline with jet fuel, for example.

 

[Gator]

Often valves are annotated NC or NO (normally open or closed) if there could be some confusion about what's supposed to be going where.

 

[MickMc]

KernOily,

With respect to adding a valve or other piping component which is not included in the piping class it would be treated as a special piping item and assigned a tag number e.g. SP-XXXX.

 

[LittleInch]

BI - In that instance then yes, showing a valve on a PFD would be required because without it the composition would change. Otherwise no (IMHO).

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

 

[KernOily]

MickMc - Thanks. I've not seen this myself. Typically in my experience, SP numbers are assigned to things like: expansion joints, ball joints, startup strainers, etc. I've always seen a spec break or a note on the P&ID when using out-of-spec components, just the way God and Mother Fluor intended. Ha Probably depends on the owner's preference and the P&ID lead sheet for the particular project. I could see using an SP number for an out-of-spec valve and I wouldn't get heartburn about it if the team wanted to do it that way.

 

[11echo]

You show no special symbol for welded end valves or any valve (other then type i.e ball, gate, globe, & etc.) the piping spec for any line "should" dictate what type of valve it is (flanged/weld end/screwed/SW). I agree with Kern oily on use of a SP number for any "odd-ball" items that may be generated.

 

[SNORGY]

Sorry guys ("guys" in the all-inclusive, gender-neutral sense)...

If *I* draw, or have drawn for me, a P&ID, then it is my complete expectation that to the extent practical, every flange is shown, no exceptions. With CADD today, and construction isometrics and bills of material automatically generated from the 3-D model, there is absolutely no excuse (in my mind) why this cannot or should not be so. When I do as-building and walk-downs in the field, I use the P&ID. It is my expectation that, as I walk down a line from point A to point B, every branch, valve, bleed ring, vent, drain and flange can be seen and "yellowed out". When this is not the case, I mark the P&ID such that this is indeed the case. I've been doing things this way for 34 years, and I am going to continue to do it this way through to my retirement. I don't subscribe to, nor do I agree with, any rationalization that P&IDs get too busy to show these details; if that's the case, split the P&IDs across enough sheets in order that these details *can* and *will* be shown. I also strongly push for every valve to be denoted by its corresponding valve tag number on the P&ID; I believe that final selection of manual valves is an *engineering* function, not a *drafting / design* function. I want to be able to do a 100% accurate valve count in support of BOMs and RFQs and RFPs directly from the P&ID.

I do not subscribe to, nor do I agree with, the assertion that the P&ID is not a fabrication drawing. WRONG! - It *IS*.

I don't always get things the way that I want, but I've been in the EPCM business for more than three decades and I have never willingly settled for less than what is described above, and I strive for as close to 100% accuracy on the P&IDs as I can get. For what it's worth, everyone I've ever worked with in Canada - employers, clients, producers and EPCMs alike - appear to share my expectations.

In short, if you know the thingy exists, and it is possible to show the thingy on the drawing, then show the thingy on the drawing. Anything less is a measure of laziness, complacency, and lack of due diligence.

 

[Gator]

When I do as-building and walk-downs in the field, I use the P&ID

 

[cjabhijit]

Dear SNORGY this stands true for you at field however, this isn't stands true when Engineering is being done. P&ID is considered as a mother document for Piping guys to do their design for Piping.

Process designers/engineers are not in the position to understand the piping material specification like different ratings, end connections requirements etc.

As you have mentioned above, if you are using P&IDs for tracing lines from point A to B in the plant, you should also take piping as built isometrics with you to get 100% details for all the items in each & every line you are tracing.


What we also can do in the engineering phase is that update P&IDs to the as-built state based on the as built isos. Does that makes sense?

Dear all, let's discuss this topic further to fine tune the understanding we have about this important topic.



Thanks & Regards,
Abhijit

 

[SNORGY]

cjabhijit,

Sorry, I disagree. Process Engineers or Systems Engineers or Project Engineers or P&ID Engineers - whichever engineers draw the P&IDs - in my mind are responsible to make sure that they are in complete alignment (to the maximum extent possible) with the piping drawings or isometrics before they get to the field. If the guys doing the 3D model want to add flanges, delete flanges, change valves etc. then the appropriate thing for them to do is to communicate those changes via a master P&ID stick file prior to IFC.

"Process designers/engineers are not in the position to understand the piping material specification like different ratings, end connections requirements etc."

I believe, personally, that anyone fitting that description is not adequately competent to draw a P&ID.