Page 20 - Industrial Process Plant Construction Estimating and Man Hour Analysis

Introduction xxxv

The quantity takeoff is either above or below the known quantity and
satisfies the scope.
The lower or upper bound is the reference to increased or decreased quantities.
The known quantity is historical data from previous field installations.

The main advantages of comparison method
1. Estimate is based on comparison with actual unit man-hours and quantities.
2. Thescopeandquantitydifferencescanbeidentifiedandtheimpactsestimated.
3. Comparison method applies to any complexity of design, bid, and contract
for a project.
A simple example:
Estimator is using comparison to estimate duct work to be erected in a coal-
fired power plant.
Coal-Fired Power Plant; Ductwork
MH β <¼ MHc <¼ MH ə
where
MHc¼historical man-hour
MH ə ¼equipment quantity is increased
MH β ¼equipment quantities are decreased (Tables 5–7)

TABLE 5 MHc5historical man-hour estimate for over fire duct work
Estimate—duct
work Historical Estimate
Description MH Qty Unit Qty Unit BM
Over fire air duct 1930
Transition duct 32.00 20.0 Ton 20.0 Ton 640
section
Bolted connection- 0.26 200.0 EA 200.0 EA 52
duct transition to ID
fan
Duct sections 32.00 8.0 Ton 8.0 Ton 256
Duct elbow 32.00 8.0 Ton 8.0 Ton 256
Field joint-weld 0.35 8.0 LF 8.0 LF 3
flange
Bolted connection- 0.26 12.0 EA 12.0 EA 3
duct sections
Expansion joint 40.00 12.0 Ton 12.0 Ton 480
Duct support 40.00 6.0 Ton 6.0 Ton 240