Tying construction documents together can be a daunting task on larger projects. We have a lot of different document types and even more team members with their hands on all of these documents. I talked earlier about P&IDs and how they are often the starting point or foundation of a piping or ductwork system. In my experience these are typically developed and maintained in 2D CAD due to a lot of factors like software limitations. In our case, it’s typically due to the fact that we are doing retrofit work and large portions of the affected systems already live on existing 2D CAD P&IDs, so it makes sense to modify these in CAD for platform continuity across the campus. Whatever the reason is, or whether or not you agree with me, we’re going to assume that the P&ID and Model data are not intelligently connected through BIM and that we now have a continuity problem that we cannot get ourselves out of with software alone. We need a way to maintain references between documents. We need a way to “Connect the Dots”. Fortunately for us, we’re using Revit, and Revit is pretty good at helping us connect the dots.
Line Numbers
I also mentioned earlier that P&ID reviews with the trades is a good opportunity to establish line numbers. Line numbers, or line designators, are what piping and ductwork trades use to connect the dots, so we are going to use them to do just that. Before we jump into how to use line numbers to connect the dots though, let’s talk a little more about them. What are they, why are they used and who uses them? The primary purpose of line numbers is simple, it is a way to uniquely identify a specific line of piping or ductwork. They are a hyphenated alpha-numeric string of text that tell you everything you need to know about that line. Line numbers are used by many people throughout the project, from estimators, purchaser, engineers, and designers, all the way through the shop to pipe fitters. They should be established early on in the project, but not so early that rework is required because of large changes in the design of the system. So when is that? Ideally this would occur at the point between when the P&ID is essentially complete and modeling is about to begin. The designation process should involve both the design team and the trades involved in the installation. We have tried doing this as an independent effort where we would send the P&IDs to the trades and have them mark them up. However, we saw little success with this approach. That’s not because either party failed to live up to their end of the bargain, but because we side stepped the most important aspect of our project approach, Collaboration! So be sure to allocate time in your project to allow for this collaboration session. It can take anywhere from a couple of hours to a couple of days depending on the complexity and size of the system. Having the face to face time between designers and trades will promote discussions, questions and identifying potential challenges that may have otherwise been missed.
Without getting too technical, let’s break down the composition of a line number. According to James O. Pennock of pipingdesigners.com, there are two methodologies behind assigning line numbers, one is by the purpose of the line and the other by the size of the line. The use of these two methods will vary depending on contractor and client. Assigning line numbers based on the purpose or function of the line is where the line number would carry throughout a specific pipe routing based on the purpose of that line. For example, from the discharge of a pump to the inlet of a boiler. And similarly a new line number from the outlet of a boiler to the connection to the distribution system. Line numbers for this methodology would also change at branches if the branch served a different function, but not if the branch was a parallel function such as a parallel pump or boiler. Establishing line numbers by the line size method would result in the line number changing at each change in line size. For example, if you did have parallel pumps, your header would be one line number and each pump inlet would be a separate line number and maybe even multiple line numbers for each inlet if the line size and pump suction size were different as they often are. In either methodology, line number would also change whenever there was a change in piping material or pressure rating. An example line number might look something like:
CB2-10-HWR-ADA-002-(2HC)-(ET)
Where:
CB2 = Building or Work Location
10 = Pipe Size, 4”
HWR = System Service, Heating Water Return
ADA = Line Class or Piping Specification (Client Specific)
A = Pipe Material, Carbon Steel Shed. 40
D = Joint Method, Butt Weld
A = Pressure Class, 150 psig
002 = Line Number (Unique)
2HC = Insulation, 2” Heat Conservation (Optional)
ET = Heat Tracing, Electrical Tracing (Optional)
I have found that use of the line number by function method to be the most Revit friendly because it breaks them out logically and reduces the quantity of line numbers that require maintaining. It’s worth mentioning that the line numbers would first appear on the P&ID once they were identified.
In this example we have a primary pump taking off of the distribution and discharging into the inlet of a boiler. As you can see there are only 2 line numbers, one on the inlet side of the pump and one on the discharge to the boiler side. We can make easy use of a project parameter to populate the line number into the model elements. The line number can then be used to make the connection between the P&ID and the model to tie the two documents together. The line number parameter can be used to generate and filter schedules in Revit to be used for material takeoffs and BOMs. It can also be used to perform specific clash detection throughout the project and most importantly, prior to IFF as a sanity check and last line of defense against field conflicts.
Scope Parameters
So line numbers are all fine and great for pipers, but what about the rest of us? How do we manage data from one scope document to another? Keep in mind that the raw model and navisworks are both scope documents as well, not just drawings and specifications. Another very useful tool is to assign scope of work record numbers to a scope area or system. This is a very simple way to tie related scopes together across disciplines for estimating, clashing, reviewing and anything else you wanted to do that requires a way of filtering out everything else.
In the retrofit world it makes a lot of sense to assign a scope of work number even in addition to line numbers for piping. Retrofit scopes are typically nice and isolated micro-projects thought a building or across a campus and can be treated as such when estimating time, manpower, moneys, etc… So having these scope of work numbers in Revit as shared parameters allows for creating estimating schedules and performing clash detection, similar to piping line numbers, but across all disciplines. The scope of work number can be as simple as a three digit number or as complex as a line number and include construction package, building, and work area. I suggest keeping it simple because whatever format you decide to use, it needs to be consistent across all disciplines and all elements so that Revit filters and navisworks selection sets can be used effectively.
Line numbers and scope of work record numbers are just two of the possibilities for organizing and grouping model data. There are many other strategies that could be employed such as Revit Phases, Worksets, design options, or separate project models all together. The important thing is that you employ such a strategy. It is paramount when approaching a project at this level of detail that you enable the ability to review specific portions of the project as isolated opportunities for design improvement and cost savings opportunities. It will also promote granularity of schedule, deliverables, technical QA, and allow your team to bite off small pieces of a much larger project at a time.