7 replies to this topic

Hello to everyone,

Actually i want to know what are the rules to be followed to prepare a P&ID.

I have joined as a trainee and i have to prepare the P&IDs from the PFDs, i am very happy if i can get any kind of thumb rules, like which valves to place and where to place and why. So i want to know what is the normal procedure to prepare a new P&ID, like what kind of valves to use and abt. the control and all.

Thanks in advance

Regards

Anil

[Art Montemayor]

Anil:

What kind of “Trainee” are you? Are you a graduated chemical engineer? If you are so, what level of degree(s) do you have?

If you have no experience as a professional Chemical Engineer, you have no business even trying to convert a PFD into a P&ID. That is not only my opinion, that is a universal, industrial opinion shared by business, governments, safety agencies, and Insurance companies.

P&IDs are legally the instruments of record in the USA and in almost all developed countries. This is so because these documents are the official instructions and guidelines by which actual, real processing plants are designed, built, installed, and operated. In doing so, human lives are at risk should these documents be flawed or done with errors in them. To have a “trainee” do them goes against the very logic and reasoning I have just detailed out. Therefore, I protest and challenge the actions of any un-experienced person taking on the responsibility of generating P&IDs.

There are no so-called “thumb rules” employed in generating P&IDs. There is hard-won and proven experience – that must be confirmed and verified – in order to ensure that the process is capable of producing the expected results and do it SAFELY. There can be no other options or alternatives. This is NOT AN AREA FOR “FAST LEARNERS”.

Therefore, I think this thread is short-lived unless you can come back and explain just exactly what you mean by “i have to prepare the P&IDs from the PFDs”, because I frankly don’t believe what I interpret by that phase.

[smalawi]

Hi Anil,

I agree with what Art has said; please don't take this personally, but people lives are at stake here.

Nonetheless, one has to start somewhere, and it could be a very simple & basic PFD that you are working on. You should already have 100% review by a capable & experienced engineer. You need to answer Art's question and elaborate more on your specific case,

There are some "general" rules of thump for every industry. They are many, and mostly gained by experience. I've seen some on this very site and few others, they might not apply in your specific case, again experience in both design and operation are needed.

A general rules of thump for chemical engineers is the book by Carl Branan see link:

http://books.google....b...7&ct=result

Perry's Handbook is also a good source: http://www.amazon.co...t/dp/0070498415

hope this helps,

cheers,

sm

[Neelakantan]

dear mr anil,

I agree with both AM and sm; however, I can visualise the situation you are in and your bland statement that you have been asked to 'prepare' a P&ID.

I sincerely trust your seniors are not so sinister to ask a trainee engineer to prepare a p&ID; it goes against the concept of safety, time management, understanding of sow with the client etc.

Probably, you have been asked to 'produce' a p&id based on similar templates available in the company; even here, i am uncomfotable with the idea, though final signing /approving authority would be a qualified AND EXPERIENCED engineer. in fact by asking you to prepare one, he would be wasting time on checking the same.

If this is part of a mock training asking you to learn, there again it is a wrong way; best method would be to ask the trainee to study correct and completed p&IDs and explain the importance of the various parts thereon and why they are there. and also to compare two similar but different p&ids.

So i would like for you to come up exactly with what your company or senior wanted you to do.

best of luck
neelakantan

[papaya]

P&ID are normally not done by a single person right? I mean it involves so many disciplines, calculations & considerations... Designers & engineers from each discipline give inputs and draughman who draws the P&ID out. There may be ready made templates to suit the services but everybody still need to sit down and discuss about it in real detail.

I don't think it's something 1 person can manage can they? Normally new guys start with checking, preparing simpler things like equipment list etc etc, where there are already a design base to follow, I don't thing new comers are allowed to create the very basics like Design basis/philosophy, P&ID & specifications. For Specifications, there may be maybe guidelines, templates & standards so it's probably the 1st serious thing a new comer get to work on. Design Basis/philosophy & P&ID are too important as the basis if a design, they are like your text book and should be 99% correct, if it's written with errors the outcome can be dangerous. I don't think people with less than 8 years experience can handle these.

But then it might just be a simple pfd of a small equipment. Still I'll be ver impressed if you can pull it off yourself without making mistakes.

[astro]

anil

Your request covers a complex, intricate and safety critical aspect of the profession. I think it's a sensible question to ask and in the first instance I would direct you to the P&ID Legend Sheet(s) that sets your site's standard. This should always be your first port of call and every site or project typically works to a different standard.

In my opinion, a set of P&IDs without a legend sheet is incomplete and can be downright dangerous because the reader is left to assume the meaning of the drawing's symbology.

I am aware of a P&ID standard published by Process Industry Practices (PIP) being a consortium of process industry owners and engineering construction contractors:
PIC001 - Piping and Instrumentation Diagram Documentation Criteria
The standard is copyrighted which presents a financial barrier, however it is a very worthwhile reference. If I knew of a public domain equivalent, I'd let you know.

In any case, so long as you're receiving competent guidance from an experienced mentor / senior engineer who checks your work, you should keep yourself out of trouble.

It's a pity that a type of documentation that has such legal significance hung upon it, is not supported by guidelines for its production that are readily accessible to industry.

[appy11]

Hello Anil,

I am new too for the P&ID preparation and it is known that P&IDs are basic document for any project and if you know P&ID preparation and if you have mastered that subject, you will stay longer with your organization, bread butter for the process engineer.

Basic things are,
Follow project specific guideline, if it has been decided that all the lines coming from preceeding P&ID, then it should come from left and going to next P&ID, it should go to right side of P&ID. All utlity lines normally comes and goes from top, bottom. If you have dist column on your P&ID, there must be ESO (emergency shutoff valve) in the line coming out from bottom. If bottom goes to pump suction, then check for the instrumentation for the pumps. if auto start pump then LT is connected to the pump motor through MCC to start the pump at high level and stop at low level. There may be minimum pump circulation either by means of orifice or control valve. In case pump discharge CV closed , then pump should deliver minimum flow not to damage the pump. Line specifications are given as " unit no-line no-line size- type of insulation- steam or electrical tracing". All the line sizes to be checked by hydraulics.

There are many more things, this is just a heads up..

Hope it will be helpful

Regards

[dchem]

I think, Anil's question is if a trainee wants to learn P&ID preparation, how should he start?
Reply : P&IDs are the document which includes each and every line(including vents, drains, bypass etc) and instrument in the plant. First properly grasp the process and also operation requirement. Actually this is not so easy task, but this is the way to begin with. In a short-cut ay way, start learning unit operationwise. For example, take a centrifugal pump. Piping fittings and instruments in the suction/discharge line of the pump will be common in most of the plant. Further, you should know some common fundas like we use gate valve for isolation purpose and globe valve for regulating purpose. So, any bypass of the control valve will be globe valve. Cooling water outlet line from the exchanger will be having globe valve because operator sometimes control the temperature by throttling the cooling water outlet valve. These are some examples, you cam learn more and more as you get deeper into the subject. You should also have the knowledge of the process control, then only you can represent various intrelocks, types of instruments etc properly.

For actual preparation/drafting, prepare legends from any of reference projects from your organisation. You should learn from some existing P&IDs how to represent various parts of the plant piping like safety valves, pumps, orifices, control valves, interlocks etc.

Actually this is too broader subject. P&IDs are preppared with inputs from piping, inst., HSE, Mech depts. So coordinating will all these departments is essential part of the job.