Is there a chart somewhere that shows me the volume of water required (after a pipeline is full) to raise the pressure to 200#s??  I'm working a COE job and I'm required to reach test pressure by adding not more than 10 gallons of water once the line is full.  I have a 12" welded steel main, a 6" welded steel main, a 10" ductile iron main with flexible vic joints and an 8" ductile iron main with flexible vic joints.  It seems to me that each line may require a different volume of water to reach test pressure depending upon the pipe material, the type of joints, the lining of the pipe (cement lined DI) and etc.  This COE requirement seems very arbitrary.

The key is your starting point.  If you fill the line and let it breathe for a while, let the temperature equilibrate, then pressure it up to a few psi while venting it.  Call it "full" at that point and the volume that needs to be added to reach test pressure is very small.  If the water is saturated with air and at warmer temperature than the graound then the volume can be really large (compared to your 10 gallons).  

On a full system, every degree F will change pressure about 100 psi.  If you pump in cooler water than the ground temperature then you'll have to vent water to maintain pressure.  There really isn't a rule of thumb, but there are ways to make the system work as long as there isn't a major leak.

The COE (Controllable Operating Expense?) limit is pretty arbitrary, but most limits like that are quite arbitrary.

In some lines that require hydro testing there may be air pockets that do not have high point vents.  Two examples are externally pressured bellow expansion joints and open gate valves in the system.  Both the gate valve bonnets and the expansion joints have air pockets that might add up to substantial quantities of trapped air depending on how many are in the system.  So, the quantity of water to reach final pressure depends on the length and diameter of the pipe, the number of air pockets that cannot be vented, and the final test pressure.  So, the 10 gallon amount is completely arbitrary.  

Last summer, in Alaska, I heard from a second hand source about a Corp of Engineer rep at Ft. Wainwright stating that 10 gallon limit.  All you can do is try to limited or eliminate air pockets, and ensure that the system is vented at very low pressure.  As for the number of high point vents, if additional vents are required, request a change order to install them. 

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