prediction of sulphide-built-up in sewers
The dia. size of the pipe and its shape are accounted for within the calculations you reference. You should note that the calculation results have greater value in determining the potential for H2S generation and not as much on the accuracy/precision which specific H2S levels (mg/l) are measured. Velocity of the flow, total wetting area (M or Ft 2), and up stream conditions are key aspects to understanding the actual H2S generation.
Provided here is a simple excel spreadsheet which might help you further:
Hope that helps