Rule of Thumb for estimating number of engineering deliverables
Rule of Thumb for estimating number of engineering deliverables
(OP)
What are typical rule of thumb ratios that experienced engineers use when calculating number of deliverables for a process design? For example, if you know the approximate number of PFDs in a typical plant, how do you ratio to estimate of number of P&IDs, lines, major equipment, instruments etc? Recognizing that of course this will vary for each type of process. I'm looking for a starting point, say for a reasonably industrial process such as refinery, SAGD, LNG plant, Water Treatment, etc.
For example, how does the following look:
No of P&IDs = 6 x no of PFDs
No of LDT lines = 9 x no of P&IDs
No of plot plans = 0.5 x no of PFDs
No of major equipment items = 4 x no of PFDs
No of instruments = 7 x no of P&IDs
For example, how does the following look:
No of P&IDs = 6 x no of PFDs
No of LDT lines = 9 x no of P&IDs
No of plot plans = 0.5 x no of PFDs
No of major equipment items = 4 x no of PFDs
No of instruments = 7 x no of P&IDs





RE: Rule of Thumb for estimating number of engineering deliverables
You have the right idea here but you should make a spread sheet which allows for the different types of plants you noted in your post.
Example: A Crude Unit in a Refinery will need a higher multiplier (for the number of deliverables and hours per) than the Water Treatment Plant.
Request:
Please define "SAGD" & "LDT" for us.
prognosis: Lead or Lag
RE: Rule of Thumb for estimating number of engineering deliverables
You have not considered an important and expensive item in your estimation !.....the number of piping drawings !
The number of plot plans is usually pretty easy to estimate from job negotiations. How are the plot plans part of the process design ?
Where is the electrical estimate ? If the client decides to put his control room in the next county, the electrical costs can be stagering
I take HUGE EXCEPTION to your estimate of 7 instruments per PID.....I have worked on jobs where the number is closer to 100
I believe that each job is unique and you need a few geezers amongst the newbies to shepherd things along... :)
MJCronin
Sr. Process Engineer
RE: Rule of Thumb for estimating number of engineering deliverables
Instruments? Piping drawings? There's no meaningful way to estimate them from a PFD or equipment count. There's a huge variation based on project nature.
RE: Rule of Thumb for estimating number of engineering deliverables
Perhaps the best course of action is to ask for existing PIDs from the prospective client and make ratios and guesses.
I can't really see a client getting estimates from multiple parties (process engineering, piping, electrical etc) and then knitting it all together in the field.
Its best to have one consulting firm responsible for the WHOLE DOCUMENT PACKAGE and construction assistance.
Here is an excellent book on this subject:
http://www.amazon.com/Piping-Engineering-Leadershi...
MJCronin
Sr. Process Engineer
RE: Rule of Thumb for estimating number of engineering deliverables
Thanks for the book reference - I have now bought a copy.
In this instance, we were looking at conceptual & front end design only, hence why only plot plan but not piping deliverables were being considered.
RE: Rule of Thumb for estimating number of engineering deliverables
It will often be the factor controlling the final GO/NO-GO financial decision.
This is especially true regarding more exotic piping materials and valves.
MJCronin
Sr. Process Engineer
RE: Rule of Thumb for estimating number of engineering deliverables
RE: Rule of Thumb for estimating number of engineering deliverables
RE: Rule of Thumb for estimating number of engineering deliverables
RE: Rule of Thumb for estimating number of engineering deliverables
RE: Rule of Thumb for estimating number of engineering deliverables
RE: Rule of Thumb for estimating number of engineering deliverables
"How would I go about estimating the number of valves that would be required for a 1 MPTA Ethylene cracker? Would I use same P&ID method? What would be the coefficient?"
You do not need to factor the number of valves. If you have the P&IDs than it is a simple matter to count the actual valves (by size and type) on the flow sheets and qualify the count as a +/- 25% estimate.
prognosis: Lead or Lag
RE: Rule of Thumb for estimating number of engineering deliverables
MJCronin
Sr. Process Engineer