how and why do people carry out pipe friction tests??

Answer 1

Pipe friction are important to select the appropiate pump to be used in an instalation.
It is done by pumping a fluid (water) and mesuring the pressure loss across a section of pipe (pressure at beggining and end) for a certain flow.
With these readings friction factor can be calculated and amount of pressure drop calculated, allowing the selection of the pump capacity.

Answer 2

There are safety reasons to carry out this test, rather than simply relying on tables and theory.

These tests determine the venting capacity, given the length of pipe, in case of a process upset or runaway. If a reaction in a process runs away or goes awry and begins to produce massive volumes of gas (for example), you will build pressure if you cannot flow the process out of a piping system. The flow rate being dependent on the pipe friction value.

So, documenting the actual values and providing batch traceability is often an insurance / code requirement for process plant design and build.

Answer 3

How
At a given controlled pressure pump water for a controlled time and accurately measure the volume transmitted.
This is done in a clean new straight pipe of a given length with no other connections.
Work out the litres per minute and log that quantity as such.
Why
A pump has a quoted delivery volume at a stated head of pressure. From your tables (You can buy these) select the pipe size needed by that pump to pump the quantity you want.

This is only the basics, you have to take into account all the fittings (bends elbows valves etc)
So you don't want to pump water?
Use fluid viscosity tables to modify your answer to suit.

Answer 4

How:
By using liquids of different frictional viscosity

Why:
To prevent getting blisters on your shaft