Estimating Process Instrumentation Projects

[Loopee]

I have worked most of my career for what is usually called A&E firms or Consultant Engineers. We make the construction drawings and develop instrument specifications for chemical process projects. Data sheets for instruments, schematics for connection to the PLC or DCS, instument location plans, wiring to cabinets and field junction boxes, and interface to equipment vendor packages are typically done in one of our projects.

The I&C (Instrumentation and Controls)discipline has lots of little things to worry about, i.e. transmitters, switches, control vavles, etc to specify. For example we might have project with an instrument list that contains 1500 instruments.

With the number of items we keep up with its natural that over time we have calculated the number of hours it takes us to do a project on a hours per instrument basis. We would count an instrument so that a valve is counted as one instrument and not count all the components associated with it- limit switches and solenoid valve, positioners, etc.

With increasing competition squeezing us for the hours we usually take, I'm wondering what other engineers in my position have found they need to do the work...10 hrs per instrument? 15 hrs per instrument?

I'd love to hear what others have found.
Thanks.

 

[ilan7]

I do a lot of specs and data sheets too, although it is not my only duty. As so, I do not consider calculating sizing and creating data sheet for a control valve to be the same as data sheet for a Pressure transmitter.
I do agree control valve calculation and data sheet needs 5 - 10 hrs, but Pressure & Temperature transmitters takes less then an hour, flow and level transmitters - one to two hrs according to the information needed to be collect for each one.

 

[Loopee]

Thanks Ilan,
I probably need to elaborate.
I was more interested in the manhour estimate for the entire construction package, which would include all the I&C parts of meetings, scheduling, estimating, drawings,specs and support tasks that make up a design effort. We like to reflect back and take the total I&C design manhours divided by the total instruments and get a hr/instrument estimate...to gauge future estimates.

I was just wondering if people in other Engineering firms' A&E I&C groups have done the same and if so what are their results. Ours range from 7-12 hours per instrument.

Thanks for you input.

 

[JLSeagull]

We typically use the same sort of format. Count bubbles on P&ID's. Prepare specification data sheets. Perform inline calculations. Prepare requisitions. Check drawings. Attend meetings. ...

Also several groups setup benchmarks. I&CS hours per piece of mechanical equipment, ... These may work to differing degrees depending upon the plant or project type. Hours per equipment don't work on a revamp. A complex machine like a GE LM2500 gas turbine driver could count as one item just like the electrical motor on a centrifugal pump. Also the pump and motor could be one piece of equipment.