VENT AND DRAIN FOR HYDROSTATIC TEST (GUIDELINES)

This post provides guidance for designing test vents and drains for piping systems subject to hydrostatic testing. Pneumatically tested systems do not require venting and draining for testing.
Test vents and drains are required only when the high and low points in the section of the line to be tested are not free venting and draining. The number of test vents and drains shall be minimized. They are to be provided only if there is no other means of venting and draining the line, such as process vents and drains or appropriate instrument connections.

Test vents are not required for lines 1 ½” and smaller. Test drains are required on all lines. Valves are normally not required.

Test vents and drains shall be installed at the piping high and low points respectively. The branch shall be as short as possible. The branch shall be braced if bracing is called in standard support drawing. Vents and drains shall be closed with a blind flange or a threaded cap/plug as provided in the relevant piping class.

Normally size of test vents and drains shall be:

- ½” for line size up to 14”
- 1 ½” for line size 16” and larger.

But it will be vary depends on the fluid, project and client.

Drain point location shall allow sufficient space underneath for temporary installation of draining facility to discharge testing liquid.

This guide states the minimum requirements to be met when developing piping design.

Preparation for Piping Testing

All joints in a test section shall be accessible during tests and shall not be painted, insulated, backfilled or otherwise covered until satisfactory completion of testing in accordance with this specification.

All vents and other connections which can serve as vents shall be open during filling so that all air is vented prior to applying test pressure to the system.Test vents shall be installed at high points.

Equipment which is not to be subjected to pressure test shall be either disconnected from the piping or blocked off during the test.Safety valve sand control valves shall not be included in site pressure testing.

Temporary spades and blanks installed for testing purposes shall be designed to withstand the test pressure without distortion.Presence of spades shall be clearly visible during testing.

All control valves shall be removed or replaced with temporary spools or
blinded off during pressure testing.

Check valves shall have the flap or piston removed for testing, where pressure can not be located on the upstream side of the valve.The locking device of the flap pivot pin shall be reinstated together with the flap and anew cover gasket shall be installed after completion of the test.

Spring supports shall be restrained or removed and expansion bellows
removed during hydrostatic testing.

Drain points for fluid disposal after testing, shall be provided.
Care shall be taken to avoid overloading any parts of the supporting
structures during hydrostatic testing.

Piping which is spring or counterweight supported shall be blocked up temporarily to a degree sufficient to sustain the weight of the test medium.Holding pins shall not be removed from spring supports until testing is completed and the system is drained.

Pressure in the system shall be introduced gradually until the pressure is the lesser of one-half of the test pressure or 170 kPa gauge.Maintain pressure for 10 minutes and then gradually increase pressure in steps of one tenth of the test pressure until the test pressure is attained.

Posted by: ANTONY in Design guidelines, Learn Piping, Piping Design system, Piping Questions, Piping Tips