The original cost function (A1) for the pipe has as variable (dia) which is the diameter of the pipe in (mm). To convert it to variables in the system (Flow rate), the following relationship was used to express this area as a function of the flow rate
Where V is the flow velocity (normally 1,5 m/s); then, replacing:
Additional modifications to this function correspond to the correction of costs per year, with the CCI ENR index of 7446 of the year 2005, to obtain A3. Then the part B2 related to the elasticity index is added. This is done in the same way as explained in the Cost Functions Wiki — General.
Considering that the pipe has a length of 5 km, the function obtained is the following:
