Pressure Testing Procedure and Precautions required to be taken at work site


Hydro Testing: Test of strength and leak-resistance of a vessel, pipe, or other
hollow equipment by internal pressurization with a test liquid.

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Pneumatic Testing: Pressure testing of vessel, line by the use of air pressure

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General Philosophy
Pressure testing of equipment, system, and pipelines is carried out to prove the strength of
equipment designed to contain pressure or a fluid head or both. It may also be employed
to check equipment / piping for leaks or conditioning favorable stresses.

• Pressure may be applied hydrostatically, pneumatically or in combination.
• The adequacy of testing procedure is generally outlined with the following
− Basing the test pressure on the weakest member.
− Observing allowable stress in relation to:
􀂾 Minimum Metal Design Temperature.
􀂾 Joint Efficiency.
􀂾 Area Classification (Design Factor).
􀂾 Minimum specified yield strength value.
− Selection & treatment of testing medium.
− Temperature of the test medium & the ambient temperature.
− Installation of adequate pressure / vacuum relieving devices.
− Proper support of the equipment / system under test.
− Accuracy of pressure gauges and its proper calibration.
− Installing pressure gauges at the lowest location to account for fluid head and
monitoring during the test period.
− Installing pressure gauge at the highest location to meet the proof test pressure.
− Proper sizing of blinds & spades.
− Proper venting.
Correct pressure increase during test schedule.
− Mechanical Clearance of all works.
− Competent supervision.
− Pressure testing of relevant segment rather than entire system.
− The following documents are to be submitted prior to commencing any pressure
test and shall be available at the site during the test time
− Material Test Certificate including material identification
− The inspection report witnessed by company representative during manufacturing
& assembly.
− All NDT (Non – destructive Test) reports


The following precautions are to be taken during pressure testing:
• The material shall be procured from Company’s approved manufacturer’s list.
• Full technical detail in conformation to material specification shall be made available.
• The company can send its representative to witness all or part of inspection & testing
activity during manufacturing or assembly phase, as deemed essential to ensure the
equipment integrity and functional reliability.
• The fabrication work shall commence only after quality assurance of material and
• The test area shall be clear from any obstructions and cordoned off to prevent any
unauthorized intrusion. The test area is to be barricaded by visual warning/caution
tape from all the sides and warning signboard should be displayed near the testing site
in local as well as English language stating, “Pipe Line Under Pressure Keep Away”.
Post warnings signs shall also be given before 24 hours prior to the test. Signal man
should also be assigned to prevent unauthorized intrusion
• The cooling affect due to temperature reduction while depressurizing the system shall
be taken into account addressing the risk of brittle fracture.
• It is absolutely imperative that tank/vessel vents are open and clear when emptying
after test to avoid creation of a vacuum.
• Competent personnel are in attendance whilst tank, Vessel vents are closed during a
test since these would need to be opened in the event of a loss of liquid for any

Do not change (exceed/decrease) the duration of hydro-test without the permission
from QC Engineer.

 Pneumatic Testing

Pneumatic testing shall be considered only under following circumstances:
• Where strength has been satisfactorily proven by a prior hydrostatic test and it is
necessary to pressure test the same by pneumatic pressure.
• Where the equipment cannot be safely filled with liquid.
• Where trace liquids cannot be tolerated & their complete removal is considered
• The pressurization procedure as listed here under shall be taken into consideration:
− The equipment shall be gradually pressurized up to 50% of test pressure and
allowed to stabilize.
− Thereafter the pressure shall be increased in stages @ 1/10th of test pressure each
time along with stabilizing period in between.
− The test pressure shall be constantly monitored and controlled safely.
• A pressure relieving device has to be provided always.
General Test Procedure
The following precautions shall be kept in view during general test procedure:
• The pressure testing shall not be carried out with valves closed for the system.
• A Dead Weight Tester to cross check the pressure gauge reading shall be utilized
• The test pressure shall be monitored with a minimum of one gauge at the pressurizing
source and one each at extreme end, the highest & lowest point of the equipment /
system under test.
• The pressure-relieving device (PRV) [installed on the equipment / system under test]
shall be set at 110% or 50psi more, whichever is less.
• All pumps / compressors to be utilized for pressure testing shall be of suitable pressure
& capacity ratings.
• The pressure gauges shall have rating & range more than 1.5 to 2.0 times the test
• The Halides content of the testing medium shall not be more than 25ppm for the
testing of Stainless Steel equipment / system.

The test procedure and the package shall be approved by the Client prior to
commencing any pressure test.
• Testing against closed valves shall only be carried out when unavoidable. In any case,
this technique shall only be utilized for piping and not for equipment items.
• The seat rating of the valve shall not be exceeded. The un-pressurized side of the
valve shall be vented.
• A suitably calibrated gauge shall be used and there shall be no intervening valves
between the gauge and the equipment under test. The gauge shall not be used if there
is any doubt about its accuracy or functional condition. The gauge must be clearly
visible to the operator controlling the pressure.
• Condition of equipment shall be assessed by referring to previous maintenance or
status record as well as through physical inspection at site.
• When applying high pressure pneumatic testing, a thorough inspection shall be
performed immediately prior to the test and supplementary non-destructive testing will
often be advisable. The need for temporary restrain of bellows or other expansion
joints and spring supports should be assessed.
• Whenever possible, Manufacturers’ recommendations shall be consulted,
• Once the test pressure is attained and stabilized, all pumping connection and
accessories shall be disconnected after safe depressurizing.
• Spades should be avoided in relief lines, as failure to remove them after test would
render relief valves inoperative in future service.

Test Fluid

• Consideration shall be given to the possibility that supports may not have been
designed for the weight of test liquid.
• Before filling equipment with liquid, the arrangement should be checked to ensure that
all air can be vented. In addition to aiding leak detection, this also serves to minimize
the energy stored and the potential hazard.
• To avoid undue stresses from temperature gradients, test fluid and equipment should
be allowed to reach the same temperature before pressurization.
• Flammable gas shall never be used for pressure or leak testing purposes.
• The use of flammable liquids shall be avoided if possible. The flash points shall exceed
by an ample margin of the maximum surface temperature of the equipment under test

and in any case must be not less than 50° C. The boiling point must be well in excess
of test temperature.
• Consideration shall be given to corrosive and other potentially detrimental effects on
materials of construction.
• When testing to high pressures pneumatically, an inert gas must be used if there is
any possibility of a flammable material being present. This is to avoid the possibility of
internal compression-ignition.

Competent Supervision

It is important that competent personnel supervise all stages of testing. In addition, it will
often be necessary for tests to be witnessed to satisfy contractual requirements or
• Pre-work tools must be done prior to the test.
• Supervisor should assign competent persons to check for the leaks.
• Leak inspection should be done only when the pressure is held.
• All workers responsible for the work must attend the training session on pressure
testing conducted by the site safety personnel.
• Good communication must be maintained during the pressure test.
• Do not leave the pressurized hose or pump unattended when the hydro-test is going

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