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Velocity in piping system

In many occasions, I had to work on pipe routing or piping study using process diagram flow (PDF) only. Very often, this is the case when I work on brownfield projects or projects that are in early phase of development. I usually use 2D AutoCAD to sketch pipe routes, having different colours for the better visualization. Please see the figure below.
1-pipe-study
After having rough sketch of pipe routes in 2D drawing, I proceed with 3D modeling. Please see the figure below.
2-piping-model
Main difficulty that I was facing during piping study is a pipe size. Process flow diagram has information about mass flow, but it does not contain information about pipe size. In order to get pipe size, velocity in piping system must be known or it must be assumed. Most common velocity that process engineers used are:
Process piping
Carbon steel process pipe 3-5 ft/sec (long distance) and 7-8 ft/se (short distance).
Stainless steel process pipes 6-10 ft/sec. Please note that some standards will allow up 20 ft/sec for stainless steel piping, but experience shows that above 10 feet/sec piping energy cost will outweighs the saving in the pipe size.
Pump suction piping 0.5-3 ft/sec
Above values are for the clean liquid only. Any impurity requires lower velocity. Maximum velocity for two-phase lines is limited to erosional velocity as per API 14E .
Steam system
High pressure saturated steam (400# to 600#) 80-100 ft/sec
Medium pressure saturated stem (150# to 400#) 100-130 ft/sec
Low pressure saturated steam (50# to 150#) 140-175 ft/sec
Superheated steam 100-300 ft/sec
Steam and water mix 60-80 ft/sec
Gasses
Upper limit for the gas velocity is 60 ft/sec. Upper limit for gas is purely economic reason-higher velocity result in higher friction loss that has to be made up in compression.
Plastic piping
Velocity in plastic piping has limitation of 5 ft/sec due to high surge pressure.
Slurry piping system
In slurry transport system, it is important to keep velocity above certain level to avoid particle settling. On the other hand, max velocity should not be exceeded because of excessive pipe erosion. Velocity in slurry system largely depends of solid type.
Fine solid 3-5 ft/sec
Sand 5-7 ft/sec
Coarse 7-10 ft/sec
Note that pipe size and velocity in piping system is responsibility of process engineer. You can use above values for your pipe routing during study phase or when PID is not finalized yet. Of course, the pipe size in your final design must be taken from the process instrumentation diagram (PID).