Engineering Specification for Pressure Test of Piping System

This content provides you with a example specification for pressure test of piping system. This content is useful for field inspectors.

1.                 GENERAL - Pressure Test of Piping System

1.1.            SCOPE

This specification covers the minimum requirements for pressure testing, draining and reinstatement of the piping system (A/G & U/G) in the construction works for use in industrial plants. Pressure test shall be a hydrostatic leak test, only where a hydrostatic leak test is impractical, pneumatic leak test may be substitute but it shall be subject to Owner’s prior approval. Lines and systems which are open to the atmosphere, such as drains, vents and open safety valve discharges, do not require pressure testing. These lines shall be visually examined to determine that all joints are properly made up.

This specification covers non-metallic piping. This specification does not cover the testing of pressure vessels, exchangers, piping in fired heater and other equipment (including packages) which are tested in accordance with codes and standards under which they have been built.

All required equipment, devices, tools, materials and labors for any construction work, test and inspection shall be provided by Construction Contractor.

Sound engineering practices shall be followed in the absence of specified standards or specifications subject to Owner’s prior approval.

1.2.            CODES AND STANDARDS - Pressure Test of Piping System

ASME B31.3: Process Piping

ASME Sec. V: Non-Destructive Examination


The following related Engineering Specifications are applied as supplement of this specifications.

Cleaning for Pipe lines                                              

Inspection and test of piping construction                   

1.4.            RETEST - Pressure Test of Piping System

In the event repairs of additions are made following the pressure tests, the affected piping shall be re-tested, except that, in the case of minor repairs or additions the Owner may waive retest requirements when precautionary measure are taken to assure sound construction. 

1.5.            UNIT - Pressure Test of Piping System

SI units shall be applied except nominal size of pipe and nozzle shall be in inches and flange rating shall be in pounds. “BEDD shall also be considered”.

2.                 SAFETY

2.1.  Full care and precaution shall be given by the field management for the safety of the workmen to prevents accidents during the execution of the works.

2.2.  Especially the pneumatic testing involves the hazard due to possible release of energy stored in compressed gas.  Therefore, particular care must be taken to minimize the chance of brittle failure of metals and thermoplastics.

2.3.  Pressure testing shall be performed in presence of the Owner’s inspector.

2.4.  Pressure testing shall be performed when the weather condition is suitable for inspection.

3.                 TEST FLUID - Pressure Test of Piping System

3.1.            HYDROSTATIC TEST

3.1.1.    As a rule, test shall be hydrostatic, using fresh water or industrial water. The water shall have a suitable corrosion inhibitor which meets Owner approval. Where the use of sea water is unavoidable, agreement between Owner and Construction Contractor shall be made, before proceeding with the work. When sea water is used, quick draining and sufficient cleaning by fresh water shall be performed after completion of the testing.

3.1.2.   Where atmospheric temperature is 0 ºC or below water shall not be used unless water is heated by steam or other heat source, and maintained at temperature of 4ºC or above during the testing.

3.1.3.   If there is a possibility of damage due to freezing, or if the operating fluid or piping material would be adversely affected by the water, any other suitable liquid such as oil or kerosene may be used with agreement between Owner and Construction Contractor.

3.1.4. For testing of system containing stainless steel piping system, the chloride ion content of water refer to para. 8.5.7 of Spec. 0000-S1830-002


3.2.            PNEUMATIC TEST - Pressure Test of Piping System

As a rule, test shall be pneumatic, using air.  The use of other test fluid shall be subject to agreement between Owner. Pneumatic testing shall be made with oil free air.


4.                 TEST PREPARATION - Pressure Test of Piping System

4.1.            CLEANING

4.1.1.Testing shall be performed by qualified personnel of Construction Contractor who are thoroughly familiar with all equipment and test.

Prior to test, any piping system to be tested shall be cleaned.  And all joints, including welds, are to be left un-insulated and exposed for examination during the test, except that joints previously tested in accordance with this specification may be insulated or covered.

Construction Contractor shall consider temporary gaskets (free asbestos) for testing.

4.1.2.   Piping shall be inspected for completeness and conformity to piping drawings and specifications.

4.1.3.    All required non-destructive testing (NDT) and soap tests of reinforcing rings shall be completed with results satisfactory to Owner.

4.1.4.   Owner will release all piping system for flushing and testing after he has satisfied himself that the system is complete and ready for testing. Piping shall be divided into test system by using blinds caps or plugs suitably.

4.1.5.    All instruments in the test system shall be excluded from flushing / testing by isolation or removal.

4.1.6. Instrument piping shall be tested up to the first block valve.

4.1.7.  All other valves in the piping system shall be kept in open position.

4.1.8.   All tests executed with day temperature or fluid temperature of 5°C and lower or when frost is expected during night and system may stay filled over night shall have anti-freeze. (Glycol)

4.1.9.   Trash and construction debris shall be removed from the piping system by flushing with water or by blowing with air or nitrogen in line with the pressure test medium. All lines shall be completely free of weld slag and other foreign material and shall be reasonably clean.


Flushing through equipment or machinery is not allowed. Flushing shall be performed against open pipe ends.

4.1.11. All flushing operations shall be carried out in the presence of Owner’s inspector.

4.1.12.Flushing water shall be drained through hoses locations as indicated by Owner.

4.1.13.  Before commencing pressure test, the Contractor, shall prepare and submit for the Owner approval a detailed flushing test procedure.

4.1.14. The area shall be continuously monitored by test personnel while testing is being performed that-any change in test procedures or conditions will be noted immediately and corrective-action taken as required.

4.1.15.  Plugs shall be removed from tell-tale holes in compensating rings and reinforcement pads around branches (nozzle) and the holes left open hydrostatic testing to observed any leakage.

4.1.16. Pressure test flow diagram shall be prepared by Construction Contractor. These diagrams shall show the system to be tested, the valves to be opened, and the equipment to be blanked with blind flanges and necessary instrumentation.


4.2.            BLIND FLANGES AND BLANKS - Pressure Test of Piping System

4.2.1.   Where the piping system is required to be disconnected from equipment in the test, disconnected end of the piping shall be isolated by blind flange having the same rating with the piping system to be tested.

4.2.2.    Where the piping system to be tested is isolated at a pair of companion flanges, blank shall be inserted between the companion flanges.  Minimum thickness of blanks shall be as listed in Table 1.  And a record should be kept showing the location of all test blinds to assure their removal. These blanks shall be supplied by Construction Contractor.

4.2.3.   A grip shall be fixed to outside of the blank (blind flange) to be used for the test, and shall be painted in red to distinguish from other blanks. The blank shall be indicated on the pressure test flow diagram.

4.2.4.   No testing shall be down against closed valves, blind flange or blanks. Instrument block valves shall be exempted from this rule.

4.2.5.  For flanged control valves with block valves and a by-pass, if the test pressure upstream and down stream is the same, the block and by-pass valve shall be left open, with the control valve removed and blinds.

4.2.6.  In case the test pressure upstream and down stream of the control valve is different, the test on the upstream position shall be made with the by-pass valve open and blanked-off, upstream block valve open and blanked off and control valve removed. 

4.3.            PIPE SUPPORTING ELEMENT - Pressure Test of Piping System

4.3.1. Piping designed for vapor or gas shall be provided with additional temporary supported, if necessary, to support the weight of the test liquid.

4.3.2.  Prior to the liquid fill for test of the piping system, it shall be checked that springs with "down travel stop" have the "stop" inserted. The "stop" in the spring shall be removed after draining of test fluid from the piping system. 

4.4.            VENT - Pressure Test of Piping System

During water‑filling, the air is to be removed from the line by leaving the vent valves open until water spurts from them. 

4.5.            PRESSURE TEST GAUGES - Pressure Test of Piping System

4.5.1. Two calibrated dial indicating pressure gauges, at least, shall be provided at the pump discharge and other suitable locations.

4.5.2.  All gauges used shall be checked for accuracy. All test pressure gauges shall be calibrated at regular intervals at least every two weeks. Calibration certificate shall be available at the work site and all gauges shall be properly identified to enable tractability to the calibration certifications.

4.5.3.   The test pressure shall be checked by means of a gauge having a range from zero up to 1.5 to 2 times the intended maximum test pressure.

4.5.4. Pressure gauge shall be connected at point as near as possible in highest and lowest point of the piping system to be tested. Where practical, the static head of the water column shall be taken into account in the test pressure.

4.5.5. Calibration of gauges shall be repeated whenever requested by Owner.


4.6.            MISCELLANEOUS - Pressure Test of Piping System

4.6.1. Subject to permission lines which are to be tested with their service fluid (category D fluid) may be subjected to an initial service leak test in accordance with para. 345.7 of ASME B31.3 in lieu of the hydrostatic leak test. It shall be subject to Owner prior approval.

4.6.2.  Pressure‑relief valve which is calibrated shall be provided in order that excess test pressure can be escaped.

4.6.3.  Lines containing check valve shall have the source of pressure located in the piping upstream of check valve so that pressure is applied under the seat. If this is not possible, check valve disk shall be removed or located open.

4.6.4.  Expansion joints of the sliding sleeve or bellows type shall be provided with temporary restraint if required for additional load under-test, or shall be isolated from the test.

4.6.5. Prior to start test, the piping system shall be checked that all the valve discs are located suitable open and closed position, and the vents and drains are installed properly for the test.

4.6.6.The following items shall be isolated or block them out of the test. Field tests of these items, when required, are covered by their respective specifications; equipment, machinery, Relief valves, Rupture discs, Flame arrestor, Displacement meters, Rotameters, Pressure gauges, Gage glasses, Filter and strainer elements and Control valves with close tolerances. Steam traps, internals and any items not designed to with stand the pressure.

-          All instrument control piping down stream of first piping block valve

-    All orifice plates which interfere with filling, venting and draining shall be removed from the test.


5.                 TEST PRESSURE

5.1.            HYDROSTATIC TEST - Pressure Test of Piping System

The hydrostatic test pressure at any point in the system shall be as follows.

5.1.1.  Test pressure shall not be less than 1‑1/2 times the minimum design pressure, but shall not exceed the maximum allowable test pressure for flanges, according to ASME B16.5 OR ASME B16.47.

5.1.2.    The test pressure shall be corrected to take into account the line temperature as per clause 345.4.2 of ASME B31.3.

5.1.3. As a rule, the test pressure shall be as shown in "the line Designation Table".

5.1.4.   The following points shall be taken into account to determine the test pressure.

A. The weakest component in the piping system to be tested.

B. In case that the piping system is tested together with equipment having lower test pressure than the system.


5.2.            PNEUMATIC TEST - Pressure Test of Piping System

5.2.1. If the piping is tested pneumatically, the test pressure shall be 110% of the design pressure of the system. If the test pressure exceeds 6 bars written approval of the Owner shall be obtained. Welds of piping subject to pneumatic strength test above 6 bars shall be %100 radio graphed.

5.2.2.The test temperature is important in pneumatic test and must be considered when the choice of material is made in the original design.


6.                 TESTING PROCEDURES - Pressure Test of Piping System

6.1.            HYDROSTATIC TEST

6.1.1.   Hydrostatic test pressure shall be applied by means of a suitable test pump or other pressure source, which shall be positively isolated from the system until ready to test. Test equipment (hydrostatic, pneumatic, etc.) shall be approved by Owner.

The pump shall be attended constantly during the test by an authorized operator. Whenever the pump is left un attended, it shall be positively disconnected from the system, while the pressure gauge remains connected to the test system.

6.1.2.   Procedures for hydrostatic pressure test shall be as specified below:

A. After filling the water and purging the air in the piping system to be tested, the pressure shall be increased gradually in the steps as shown in Table 2, maintaining for at least 3 minutes in each step to allow the equalization of strain during test and to check for leaks.

B.  The test pressure shall be maintained for at least one hour prior to starting inspection and long enough to enable inspection of the complete test system by Owner.


            On water filling for the test in chilly district, or leaving the piping system liquid filling, the piping system shall be taken into account for variation of atmospheric temperature and due care shall be given for freezing or thermal expansion.

6.1.4.    The Construction Contractor shall be responsible for the supply of suitable pumps for the testing. As a minimum a high volume centrifugal pump for filling and a variable speed positive displacement, reciprocating pump, with sufficient discharge head and capacity for the pressurization shall be provided. The Construction Contractor shall provide chemical injection pump and means necessary for measuring of the inhibitor to be added to test water.

6.2.            PNEUMATIC TEST - Pressure Test of Piping System

6.2. Procedure for pneumatic test shall be as specified below:

The sequence of test pressurizing

A.   After evacuating all personnel from the test area The system shall be pressurized to 1.7 Bar G. and held for sufficient time to allow the piping to equalize strains (ten minutes minimum). All joints (threaded, socket welded, butt welded and flanged) shall be preliminary tested for leakage using the test solution.

B.    Pressurize the system gradually to 60% of the indicated test pressure, and hold at that pressure for a sufficient length of time to allow the piping to equalize strains (ten minutes minimum).

C. Reduce the pressure to 50% of the indicated test pressure and retest all joint for leakage.

D. Pressurize in steps of not more than 10%, until the indicated test pressure has been reached. The pressure shall be held at each step during pressurizing sequence (to allow the piping to equalize strains) for a period of not less than ten minutes. The indicated test pressure shall be held for a sufficient length of time to permit the testing of all joints, the pressure shall then be reduced to the design pressure before examining for leakage.

E. Each reinforcing pad (or each segment thereof) and similar attachments shall be tested at a designated test pressure with air, a soap solution shall be used to detect air leaks. Test and vent holes shall be left open upon completion of the test.

6.2.2.    A soap solution shall be applied to all screwed, weld and flanged joints undergoing pneumatic test.

6.2.3.    Where line list or line designation table indicate pneumatic testing, no hydro testing shall be performed.

6.2.4.       As pneumatic testing presents special risk due to possible release of energy stored in the compressed gas almost care shall be taken during pressurization and inspection of the system to prevent any danger to personnel or equipment and the chances of a brittle failure of piping. 

During testing precaution and procedure shall be as laid down on paragraph 345.5 of the ASME B31.3 

6.3.  The Construction Contractor shall make sure that prefabricated piping which are not included in the pressure test are certified by an authorized inspector.

6.4.  Welds or portion of welds that leak during hydrostatic test shall be repaired, cutout, rewelded, radiographed (if needed) and line shall be hydrostatically tested again.

6.5.   All costs incurred in repairing defective or rejected work and all consequential heat treatment and additional examination costs are to be borne by the Construction Contractor.

 7.                 PRESSURE RELEASING - Pressure Test of Piping System

After completion of the test, the pressure shall be released so as not to endanger personnel or damage equipment. As a rule, releasing rate shall be 300 Kg/Sq.cmhr, but lining pipe, tower filled with catalyst, etc., shall be less than 25 Kg/Sq.cmhr. 

8.                 DRAINING

8.1.  After completion of the test, the piping system including equipment to be tested shall be drained as completely as possible.

8.2.     All vents shall be opened before the piping system is drained and shall be remain open during draining to prevent pulling a vacuum on the piping system.

8.3.    After drainage, remove all temporary blinds and blanks, temporary supports, and temporary testing connections, as per drawings and specifications and reinstall all items such as control valves, relief valves, rupture discs, orifice plates etc., which were removed for test.  Ensure that line specification of gaskets and bolts are being used when reinstalling these items. All flange joints for the test shall be made up with new temporary gaskets provided by the Construction Contractor.

8.4.    All drained lines shall be dried after testing by blowing through with dry oil free air. Special care shall be taken that no freezing can occur in winter.

8.5.    Owner will confirm when a line is considered dried by Construction Contractor.

After approval by Owner and reinstallation, the system shall be released for activities like, tracing, painting, insulation, etc. 

9.                 EXTERNALLY PRESSURED PIPING - Pressure Test of Piping System

Piping subject to external pressure shall be tested an internal gage pressure 1.5 times the external differential pressure, but net less than 105kpa(15 PSi) 

10.            TEST RECORDS - Pressure Test of Piping System

Records shall be made for each piping system during the testing and these records shall include the following items.

A.    Extent of testing and specification

B.    Identification of piping tested

C.    Pressurizing apparatus

D.    Test pressure and test duration

E.    Test fluid

F.    Date of test

G.    Approval signature of witness (Owner's and Construction Contractor's representative)

H.       Signature of person in charge of testing

 I.     Applicable remarks concerning defects

J.     Water temperature and chloride content

K.    Design temperature and pressure

All tests satisfactory or not shall be record on the test form and complete set will be made part of the permanent job records. 

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