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.

Regards,
Ankur.