PRESSURE TESTING

PRESSURE TESTING

Bayu Nurwinanto

Hydrostatic Leak Test

Test Fluid 
The fluid shall be water unless there is the possibility of damage due to freezing or to adverse effects of water on the piping or the process. In that case another suitable nontoxic liquid may be used. If the liquid is flammable, its flash point shall be at least 49°C (120°F), and consideration shall be given to the test environment.

Test Pressure
The hydrostatic test pressure at every point in a metallic piping system shall be as follows:

• Not less than 1.5 times the design pressure.
• When the design temperature is greater than the test temperature, the minimum test pressure, at the point under consideration, shall be calculated by eq. When the piping system contains more than one material or more than one design temperature, eq. Shall be used for every combination, excluding pipe supporting elements and bolting, and the maximum calculated value of P_T is the minimum test gage pressure.

P_T = 1.5 PR_r

where :

P	internal design gage pressure
PT	minimum test gage pressure
Rr	ratio of ST/S for pipe or components without established ratings, but shall not exceed 6.5
	ratio of the component pressure rating at the test temperature to the component pressure rating at the component design temperature for components with established ratings, but shall not exceed 6.5
S	allowable stress value at component design temperature
ST	allowable stress value at test temperature

Alternatively, for carbon steel piping with a minimum specified yield strength not greater than 290 MPa (42 ksi), the test pressure for the assembly of components, excluding pipe supporting. 

elements and bolting (e.g., pipe, fittings, valves, flanges), may be based on R for any of the components in the assembly.

if the test pressure as defined above would produce a nominal pressure stress or longitudinal stress in excess of the yield strength at test temperature or a pressure more than 1.5 times the component rating at test temperature, the test pressure may be reduced to the maximum pressure that will not exceed the lesser of the yield strength or 1.5 times the component ratings at test temperature. For metallic bellows expansion joints.

Hydrostatic Test of Piping With Vessels as a System

• Where the test pressure of piping attached to a vessel is the same as or less than the test pressure for the vessel, the piping may be tested with the vessel at the piping test pressure.
• Where the test pressure of the piping exceeds the vessel test pressure, and it is not considered practicable to isolate the piping from the vessel, the piping and the vessel may be tested together at the vessel test pressure, provided the owner approves and the vessel test pressure is not less than 77% of the piping test pressure.

Pressure Relief Device 

A pressure relief device shall be provided, having a set pressure not higher than the test pressure plus the lesser of 345 kPa (50 psi) or 10% of the test pressure.

Test Fluid 

The gas used as test fluid, if not air, shall be nonflammable and nontoxic.

Test Pressure 

The test pressure shall be not less than 1.1 times the design pressure and shall not exceed the lesser of :

• 1.33 times the design pressure. 
• the pressure that would produce a nominal pressure stress or longitudinal stress in excess of 90% of the yield strength of any component at the test temperature.

Procedure

The pressure shall be gradually increased until a gage pressure which is the lesser of one-half the test pressure or 170 kPa (25 psi) is attained, at which time a preliminary check shall be made, including examination of joints. Thereafter, the pressure shall be gradually increased in steps until the test pressure is reached, holding the pressure at each step long enough to equalize piping strains. The pressure shall then be reduced to the design pressure before examining for leakage. 

CALCULATE A HYDROSTATIC OR PNEUMATIC LEAK TEST PRESSURE

Hydrostatic-Pneumatic Leak Test

If a combination hydrostatic-pneumatic leak test is used, shall be met, and the pressure in the liquid filled part of the piping shall not exceed the limits.