I am writing a software that involves calculation of pressure drops in a electric heater pressure vessel as in related to pipes and flanges as described in ASME B16.10, B16.47, B36.10. I am not a mechanical engineer, but in order to create an intuitive data input sequence (and for my interests), I hope to understand why pressure drop limtation is a design specification, what causes the pressure drops and how to calculate it. And whether this pressure drop is a consideration for determination of pipe schedules. Can anyone explain the theory or point me to the relevant links that shows in an easy to understand manner about the concepts behind the pressure considerations? Thanks!