What Is the Allowable Loss in Pressure in a Hydrostatic Test of DICL Pipe?

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Hydrostatic testing ensures pipes will not rupture under expected pressure loads.

Ductile iron pipe (DICL) pipe is used in water and waste water networks. Hydrostatic tests build up the pressure inside of pipes and check for leaks. The minimum pressure standards of DICL pipe depend upon the application.


Minimum Pressure in Hydrostatic Test

Residential water main pipes must hold a pressure of 150 pounds per square inch. In fire protection systems like piping, the test pressure must be at least 200 psi. For fire protection piping kept above 200 psi, the test pressure must be 50 psi over the maintained pressure. The American Water Works Association requires pressure be maintained within 5 psi (34.5 kPa) of the test pressure during hydrostatic testing. Makeup water can be added to the pipe for tiny amounts of water loss as vapor.


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Allowable Loss

Allowable pressure loss during hydrostatic testing depends on the pipe diameter and test pressure.

The testing allowance or allowed make up water is found by multiplying the length of pipe in feet by the nominal diameter of the pipe in inches. This value is divided by 148,000. The result is multiplied by the square root of the average hydrostatic test pressure. For a 10 foot pipe length with a 10 inch nominal diameter tested at 150 psi, the allowable loss of water in the pressure test is 10 x 10 or 100, which is then divided by 148,000, resulting in 0.0006757. The square root of the test pressure 150 psi is 12.247. The result of 0.0006757 is multiplied by 12.247 gives the 0.0008275 inch-pounds of allowable pressure loss.


Allowable pressure loss is based on American Water Works Association (AWWA) standard C600-82. AWWA standard C600 is shared with the American National Standards Institute (ANSI). American Society for Testing and Materials (ASTM) international standards require hydrostatic testing of DICL pipe be performed before water or sewer pipe is installed.


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