Page 277 - Industrial Process Plant Construction Estimating and Man Hour Analysis

256 Industrial process plant construction estimating and man-hour analysis

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Define the U model: Hn ¼ H1 (n b) where
Hn ¼ hours required for the nth unit of production
H1 ¼ hours required for the 1st unit
b ¼ natural slope of learning curve, illustrating if learning is rapid or slow
If H1 and b are known and the unit of production, the estimate of the hours for
unit n can be calculated.
Example: Historical data collected from first unit on project 1 is 23,351 h;
assume b ¼ 0.15, how many hours will the fourth unit require?

^ ^
ð
ð
H4 ¼ H1 n bð Þ ¼ 23;351Þ 4ðÞ 0:15Þ ¼ 18;967
System for measuring slope
The system for measuring slope, that is, rate of learning, measures rate of learn-
ing on a scale of 0—100, in percentage.
Slope of 100% ¼ no learning, and o% ¼ infinity rate of learning.
In practice, effective range of industrial learning is 70%–100%
Natural slope b is defined by the formula S ¼ 10 b log (2) +2 logarithm to
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base 10.
Example: If S ¼ 100% (no learning), b ¼ log (100/100)/log (2) ¼ 0 b ¼ 0
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substitute into Hn ¼ H1 n b results in Hn ¼ H1 for any value of n (no learning)
Example, if b ¼ 0.2, the value of S is?
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S ¼ 10 ( 0.2) log (2) +2 ¼ 87%
Prediction for the total hours for a "block" of production for waste heat
boiler erection
Define man-hours for a block of erection as the total man-hours required to erect
all units from unit M to another unit N, N > M.
TM, N is defined as

^ ^ ^ ^
ð
TM,N ¼ H1 M b + M +1ð Þ b + M +2Þ b + ⋯ + N b
Approximation formula:

^ ^
ð
½
TM,N ¼ H1= 1+ bފ N +0:5Þ 1+ bð Þ M 0:5Þ 1+ bÞ
ð
ð
ð
Example 12.8.1
Historical data for the erection of four waste heat boiler units at project 1
Unit Man-hour
1 18,967
2 16,813
3 15,513
4 15,357
Total project man-hours 66,650
Y bar = 16,662.5