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As-Built Piping & Instrument Diagrams

As-Built Piping & Instrument Diagrams Not many young entrants in process engineering would be aware of this aspect of engineering and today's blog entry tries to put in perspective what "As-Builting" is all about.

Most of you are aware that during the engineering phase an important task by the process engineer is to prepare "Piping and Instrument Diagrams", in short known as P&IDs. P&IDs are the mirror of any chemical process plant and tend to be amongst the most important engineering document for any chemical process plant. Most of you are familiar with what P&IDs are, and their content.

P&IDs undergo several revisions during the engineering, procurement, construction and post-construction phase of a chemical process plant and a typical sequence of revisions could be as follows:

1. Issued for Comments or issued for Review
2. Issued for Approval
3. Issued for Design Review / HAZOP
4. Issued for Construction
5. As-Built

There may be further revisions in between where typically the terminology used is "Re-issued for ......"
In an existing old plant, modifications and / or re-vamps may be done over a period of the plant's life and these are generally covered by the title "Revised As Marked" where modifications done are provided a revision cloud and / or a revision triangle. I have seen P&IDs of existing plants which have undergone minor modifications with revisions up to 50 in number.

When a new plant is built in an engineering design office through P&IDs, there are so many aspects that cannot be visualized sitting in an office. The site construction / pre-commissioning / commissioning team typically uses the "Issued for Construction" drawings to construct the plant. During the construction phase so many surprises spring up which cannot be anticipated from an engineering office. Often, plant construction material specified such as valves, pipe, pipe fittings, instruments may not be exactly according to the purchase order specifications raised in an engineering office due to either human error or non-availability of a particular type of material considering the schedule for the plant commissioning. Compromise solutions have to be adopted to meet deadlines for plant commissioning. In short, everything is not as ideal as it should be and alternative solutions are required. Not to forget, there may be errors and ommisions during the engineering design itself, and these need to be rectified during the construction phase.

Based on what I have written in the aforementioned paragraph, the need of "As-Built"Drawing arises. As the name suggests the drawings reflect what has been actually built at the plant site. From the process engineering perspective it is the P&IDs that need to be as-built. Other documents such as Piping General Arrangement Drawings, Piping Isometrics, Instrument Loop Drawings may also require to be as-built but then the processs engineer is not directly involved in these.

Let us talk about the methodology of preparing an "As-Built" P&ID. Preparing an "As-Built" P&ID starts by "red-lining" the latest "Issued for Construction" drawing, wherein a process engineer having an experience of engineering, construction and commissioning walks-around the constructed plant with paper prints of the latest set of P&IDs and a red pen. He or she then marks the P&IDs with what has been constructed instead of what it should have been. Some typical mark-ups for an "As-Built" P&ID could be as follows:

1. Changed valve type, for example a ball valve used instead of a gate valve
2. Planometric change in piping which could mean that the sequence of pipe branches tapped from a main header has been altered during construction with the concurrence of the commissioning team.
3. Deleted lines based on the commissioning teams understanding that these are unnecessary from the procees point of view.
4. Provison of additional permanent drain and vent connections based ont the commissioning teams requirement and understanding of the process.
5. Provison of additional tappings on piping, considering future requirements
6. Addition or deletion of permanent instruments based on commissioning teams requirement.
7. Change in instrument type due to the commissioning expert's opinion on its functionality.
8. Addition or deletion of nozzles on equipment (tanks / vessels) due to the requirement put forward by the commissioning team. This is generally applicable to site fabricated tanks & vessels.
9. Possible relocation of equipment due to site constraints which were not envisaged during the engineering phase. This typically involves elevation changes of equipment from one floor level to another.

The above mentioned are just a few typical examples of what requires to be marked-up on an "As-Built" P&ID by the process engineer while walking around the plant. Ther could be many more.

After the P&IDs are "red-lined" for the entire plant or unit, these P&IDs are "CADDED" by a CAD Designer in an engineering office, back-checked against the red-line mark-up by the concerned process design engineer and then issued as "As-Built" P&IDs to the client.

"As-Built" P&IDs reflect what is actually there at the plant site, correctly representing the plant or unit as it is built. To conclude, the entire exercise of "As-Builting" of P&IDs needs to be considered as a very important task for completion of any process engineering.

Would like to hear comments from the readers of my blog.



Congratulation for this very important article.

The problem is that the majority of the owners don't seriously manage the changes in their plants and, as a results, even perfect "as-built" documents tend to quickly become obsolete as the plant undergoes modifications through its life...

The consequence is that the next engineering company in charge of a revamp in that plant (with "As-built" P&IDs but not "As-is" P&IDs) would better make a site survey to check everything....unfortunately this task is often not seriously considered and valued by most engineering companies and, worse of all, by the owners themselves.

Thanks for your appreciation. And I agree with your observation about the lackadaiscal approach to as-builting by plant owners and engineering companies. Improving this aspect of engineeering would definitely go a long way in the successful implementation of plant modifications and revamps.


Thanks for this wonderful article .I am fresh chemical engineer who has recently joined service industry which is doing asbuilting, this article will be very helpful for me in future.

Thanks alot,

Best Regards,

Atul Rai
Qalander (Chem)
Jul 07 2012 03:24 AM
Dear ankur!
A wonderful info shared for everyone's knowledge& awareness,but as said by sheiko;I add my little bit in my words.
  • Although I have seen many many problems during my past 34 years in Refinery business as regards item (5) of your article & 'the subject title'
  • Actually.it is nobody else except "we" the users/ proposer and modifying personnel to blame for not promptly updating/ Getting updated
  • Having a typical lethargic approach of ours& sort of totally non-professional and at times proving 'disastrous' attitude
  • That resulted in "recent" as well as "in early past" into small, Big, Mega scale events and even in catastrophe events involving Fires/ Explosions& sever damages to Process industry assets costing
  • We should be extremely careful ,strictly disciplined to ensure true "as-built P& ID's, P.F.D's in place without fail whenever any de-bottlenecking or process improvement is carried out.
  • Which changes piping geometry, physical location/ position of controls& any parameters or practices
Thanks very much
I agree with Sheiko, I worked for a company that provided simulation services and that was the main problem we found while studying plant optimization and revamps...the owners fail to maintain consistent and updated P&IDs, equipment datasheets, etc.

Going further, I definitely think this is a safety issue...although it is not the same case because it happened during maintenance, the Piper Alpha accident had its origin in a lack of documentation procedures. I consider that there are many potential risks related to this issue and I am surprised that there are no standards or law that require proper updating of process documentation. Or are there any?

Great article, thanks!

Thanks for throwing light on this very very important aspect of process design engineering. It is very important for new joinees who doesnt know about as-builting. This article gives a very good overall idea about the way of doing p&id as-builting and its usefullness.
May be the way of Rev. numering and Document maintenace, different in different companies as per their own instruction and guidelines. But the extract is the same what you have covered in your article.I recommend all my colleagues to go through it.

Best regards

Pravin Shukla
Thanks, Ankur, for your enlightening article.

Management of Change (MOC) processes are important throughout an entire project's life - from the earlist feasibility steps through to design, construction, commissioning, operations, end-of-life decommissioning and even perhaps site rehabilitation! Of course, this responsibility is shared across the various groups involved in those steps, from the designers/consultants, commissioning teams, and operations/owners. All these groups must operate within a robust and co-ordinated MOC standard, and your readers above are right - safety is indeed the key reason (notwithstanding the other problems that could invariably also occur, such as inefficiency, expense, and perhaps even project failure).

There are enough actual examples of major disasters that have occurred as a result of inadequate MOC (see http://engineeringfailures.org for some examples). Concerning for me is, reviewing your list of 'usual' construction/commissioning changes, they almost ALL have process safety implications. As a process engineer, I would be extremely worried that any of them would be implemented, even under construction/commissioning pressures, without proper and adequate investigations (such as re-HAZOP) being done under a formal MOC process.

Acknowledging that the point of your article is to highlight the importance of accurate documentation, I would like to add this broader context for consideration. Even a junior engineer asked to perform a 'process mapping' or 'as-building' task on a P&ID might uncover live examples of dangerous MOC failures ... and it would be best that they be aware of this possibility before they start, so that their 'radar is on' to identify and flag them to the appropriate people.

As stated in "Learning from the Piper Alpha Accident: A Postmortem Analysis of Technical and Organizational Factors" (Pate-Cornell, M., 1993, Risk Analysis, 13:2, 230):

"... tinkering with the [original] system [design], on the one hand, allows for imaginative innovations but, on the other hand, can prove fatal unless there is a clear understanding of the system’s characteristics in its final state. One of the benefits of developing a probabilistic risk analysis model for each system at the design stage and of using it as a “living document,” updated and modified as the system evolves and responds, is to be able to check the effects of successive modifications." (highlighting added)
Jan 28 2013 05:01 AM
I had been working in chemical industry for last 40 years.Most of the time as built drawings are never made as no body understands the importance of the same.People do not consider it as a important activity and need for the same.Real sad state of affair.
Sunil K.Deshpande
Apr 25 2017 02:31 AM







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