In relation to settling slurry systems, FluidFlow takes into account pipe inclination and applies a Durand correction factor which is dependent on the angle of inclination. The method implemented within the software applies to angles in the range of -20 to 80 degrees. For inclinations outside of this range, the software assumes a vertical pipe and applies a method by Worster & Denny which is a modified form of the solids effect.
When dealing with slurry piping systems, if you need to take account of pipe inclination, it is recommended that you use the WASC method as the Durand method and by association, the WASP methods don't take account pipe inclination. Further details on this topic are available in the following reference if you wish to review in further detail: Slurry Transport Using Centrifugal Pumps.