I know nothing about where you are, nothing about your company, your piping organization or the individual capabilities of the members of the direct piping staff or the related supporting groups. So it is hard to be very specific.

I question that you have only 20 lines and that all of them are the same maximum operating temperature.

But if you do indeed have only 20 lines and they are all at 450 degrees maximum operating then I you might have the following estimated labor hours for all piping activities.

Category Data Comments
A Number of lines 20
B Estimated number of Isometrics 80

1 Piping Design Hours 1335 (Includes all field trips to determine tie-in points and routing)
2 Piping Material Eng Hours 85 (Assume use existing specs, Review all)
3 Piping Material Control Hours 40 (Depends on how MTO is done)
4 Pipe Stress Hours 150
5 Piping Supervision Hours 90 (Assume working supervisor)

1 Piping Design Hour Percentage 78.5%
2 Piping Material Eng Percentage 5.0%
3 Piping Material Control Percentage 2.4%
4 Pipe Stress Percentage 8.8%
5 Piping Supervision Percentage 5.3%

1 Hours per Line Number 85
2 Hours per Isometric 21.3