Hydrotest Pipes

So that the line can be filled up to this point and a pressure gauge screwed in prior to the test starting. This is done so that the minimum amount of air is present in the system that is being tested.

The need for further gauges will be determined either by the code applicable to the hydrotest, the end-user requirements or the requirements of the Engineer/Surveyor witnessing the test on behalf of the company that provides burst indemnity insurance for the equipment/installation.

In building construction, the pressure tests I have seen usually involve wet sprinkler system piping. I have seen gauges installed at the low or fill point and at the high or end point. In multi-story structures the high or end gauge is needed to show actual pressure because once the piping is filled (but not pressurized) the lower gauge will always show pressure based on the weight of the medium (water) within the pipe.

The lower gauge is also used as a reference point at the beginning of the test. Two readings are taken on the lower gauge, "filled" pressure and line filled under "pressure".

The gauges are connected in tandem (via a "T") with a ball valve at the tap points to purge air from the line.

The pipe system is filled and left pressurized for 24 hours. At the end of the test period the pressure is read at the top gauge and the bottom gauge is read for line under pressure and line filled pressure. Any pressure variation that cannot be explained away by temperature variations during the 24 hour period result in a "fail" of the test.

Thanks for the reply!

The high point tap is needed for a vent only.

Sounds like someone's made up rule.

ASME Section VIII, Division I gives specific instruction as to where the gauges are to be placed and what specific pressures they are capable of portraying. The same is true for ASME B31.1 and B31.3. The API 650 offers requirements for hydro testing tanks.

Hello Guest,

I'm assuming here that you're testing a buried pipeline (or water main) that is to convey water. If so, the proper name of the testing methodology is "Hydrostatic Pressure Test".

You should install 2 pressure gauges for this type of testing: one at the lowest point in the pipeline where the water main is filled and pressurized, and the other gauge shall be installed at the highest point in the line where there is also a valve and/or fire hydrant to bleed-off entrapped air.

The reason for the gauge located at the high point is because the water main must under go a minimum residual pressure in the main for the allotted testing period, hence it is logical to place the pressure gauge where the pressure in the main will be lowest.

Word of warning: If you're pressure testing a buried water main make absolutely sure that the water main is properly bedded and backfilled in compacted lifts otherwise you'll blow the main right out of the ground, especially if the initial hydrostatic pressure test starts at 150 psig and higher! I've personally witness improperly backfilled water mains lift right out of the ground during such a test.

If the pipeline is not buried, insure that you have flanged pipe joints where all bolts have been tightened and torqued to specification to prevent line movements laterally.....that is all joints must be restrained. Also, make sure that all fittings along the tested sections are mechanically restrained.

If you need additional information and/or clarification regarding Hydrostatic Pressure Testing of cast iron or ductile iron mains, please refer to the CIPRA handbook or do a Google Search.

I hope this posting answers your questions. Good luck with the testing!

In any pressure system like as piping or pressure vessel, during the hydrotest the pressure gauge shall be installed at the highest point to avoid the false reading of pressure gauge due to the excess weight of hydrotest liquid column above the point of measuring, to insure that there is a full exposure of all piping system to the hydrostatic test pressure. And that recommendation is considered as a rule of thumb in all codes and standards.

You can install more than one calibrated pressure gaug taking into onsiderederation to erect both gauges at the same height.

Doing a pressure test on a water system on a structure 100 meters high we always had a tap at the top to vent air and the gauge was at an accessible location - probably close to the ground. You have to keep the piping elevations in mind.

ASME and other codes were always used as a guide but not as a fixed point.

To rephrase Mr. Galala's GA, the pressure at the top of a pipe network is less than that at the bottom by 1 psi per 2.31 feet of vertical difference. If you measure the hydrostatic test at a lower point, the upper regions will not be subjected to full pressure. As others have noted, a top connection is necessary also to remove gases from the system to be tested.

In principle, you could increase the pressure at a low point, computing by height and fluid density to ensure that the top pressure is adequate. But I don't know if any code allows this (nor do I know if not, why not.)

Tornado, you're correct in that (as far as I know) there is no US Federal or state codes, laws or regulations governing the hydrostatic pressure testing of pipelines and water mains.

I have however encountered codes governing this type of testing adopted by individual municipalities where I have practiced in NY, VT, CT, and MA, with most being incorporated in Subdivision Regulations, as well as upholding minimum engineering standards for infrastructure construction within a municipality's borders.

Usually the Engineer of Record who has prepared Contract Documents for a construction project involving water mains will specify the required testing procedure, most often reciting the outlined procedure included in both the CIPRA Handbook (Cast Iron Producers Research Assoc., now DIPRA, the Ductile Iron Producers Research Assoc. located in Birmingham, AL) and AWWA Standards (American Water Works Assoc.), and USACE Standards.