Fire Sprinkler acceptance testing: Pressure rise during 200 psi hydrostatic test 1

[jdelahunt]

All;

As an AHJ/Owner's Rep, we get called to accept new sprinkler installations. From time to time, we have installers that will fill the new system, then immediately pump the system up to 200+ psi, and allow the water to heat up in the South Texas sun. At the end of the two hour test, our pressure has risen (both due to the coefficient of expansion of the water and the dissolution of air due to increased temperature).

We can't tell from a pressure rise whether there are no leaks - the system might have a bleeder that lets 2 psi off, but the system temp creates a 7 psi gain, or it might be tight and the system temp has created a 5 psi gain. Since we can't tell, we reject the test. However, the result is "no pressure loss," which meets the letter of the code.

We prefer that they allow the water to temper for 24+ hours, but this doesn't always happen.

We can model temperature effect on pneumatic systems pretty well by applying PV=nRT, but hydrostaic testing is a little more finicky. How do you, my fellow AHJs, react to pressure gains on hydrostatic tests?

 

[stookeyfpe]

I've never worried about. Being located in South Texas, I've seen this numerous times and I anticipate it. The hydrostatic test utilizes an incompressible fluid so I expect pressure rise between the time the system is charged and the test is witnessed by the code official or the AHJ's agent. I've also seen the pressure drop if the system is filled and pressurized when it was 100+F outside and a cold front or other atmospheric change resulting in an outdoor temperature occurred.

 

[cdafd]

Agree

Especially if you can see most of the pipe and heads

 

[Duwe6]

At the end of the day, a sprinkler system is made of pipe. On a standard pipe hydro, you look at ALL of the joints, and then you are done [assuming no leaks are found]. 200# for 2-hours makes a lot of sense for underground piping, but seems silly to me for accessible pipes. Just sit in a chair and watch a gauge for 2 hours when, with a little walking, you could be done in 1/2-hour to 45 minutes.

 

[cdafd]

sorry duw disagree

would stick with two hour test even if you can see every inch of pipe

have not found an inspector that sets at a gage for two hours, some like to mark it and come back, now depends on the building, if it is going to take two hours to walk the entire buidling, than they can do that while the pressure sets.

It is better to have a problem during the test than in the future during a fire, or failure for some other reason.

 

[DavidCR]

NFPA 13 states a hydrotest without loss and 16.2.1.7 2004 defines loss. ("Loss shall be determined by a drop in gauge pressure OR visual leakage."

So from the rule point of view if you cannot see all the joints, this "OR" means if the gauge keeps above the test pressure it is OK.

I think that if it does not leak and the pressure is above the 200#, it does not matter what happens inside the pipe.

All the test may behave different and ideally it is better to specify to the contractor what sections shall be visually inspected for leaks and what sections may be witnessed just by the gauge reading.

 

[rconner]

[It probably should be mentioned that the magnitude of variation during any test duration due to temperature can be affected by how much volume of air has been trapped in the system, as in accordance with the gas laws air is much more pressure responsive to temperature variations than relatively incompressible water. While most standards have verbiage requiring such air to be evacuated, for various reasons this may not be effectively accomplished with a particular system design and/or installer knowledge/will involved. Just something to keep in mind.]

 

[Duwe6]

The air NEVER gets out, because the Design Engineer and/or the owner specify that the pipe runs are to be level. Just like a large, level concrete slab ponds up litle puddles of water EVERYWHERE, a large and complicated pipe system like a fully sprinklered building witt trap little pockets of air in hundreds of locations. The tiny variations in flatness of concrete and levelness of pipe guarantee it.

 

[abdelwaed]

jdelahunt

the attached link explain the relationship between Density of Fluids - Changing Pressure and Temperature
i hope it help.