Procedure for Pressure Test or Hydrotest

SCOPE

This Procedure is applicable to Boiler External piping and Pressure vessels constructed to ASME Code B31.1 & sec VII Div 1. Respectively. It also applies to pressure retaining items repair or altered in accordance & the National Code (NBIC)

REFERENCES :

  1. ASME Sec . I Edition 2007 Addenda 2009.
  2. ASME B 3.1.1 Edition – 2004..         
  3. ASME Code Sec. VIII. Div 1 Edition 2007 Addenda 2009.

PROCEDURE.

Responsibilities.

The Concerned Procedure Engineer is responsible for preparation of the test item for Pressure Testing.

  1. The designated QA/QC Engineer / Inspector is responsible for witnessing the item being tested. He is responsible for arranging for notifying the TPI. Sufficiently in advance for witnessing pressure test.
  2. The designed Production Engineer is responsible for ensuring that during the test only essential personnel are present in the work area. The work area shall be suitable cordoned off otherwise isolated such hat unrelated personnel do not stray into it.
  3. The designated QA/QC Engineer / Inspector is responsible to verify that the NDE and all fabrication works are completed and accepted before releasing the item for pressure testing.

Equipment.

  • The test equipment shall be in accordance with the applicable client’s specification if any and shall be adequate to provide necessary test pressure at a safe rate of increases.
  • All components of the test system shall be rated to with stand test pressure.
  • Pressure and temperature recording devices may be used to record medium temperature and pressure on a continuous basis during the test duration.
  • A temperature measuring device shall be used to record the metal temperature during the test.

Preparation for Pressure test.

  1. Vent shall be provided at all high points of the vessel in the position in which it is to be tested to purge possible air pockets while vessel is filling.
  2. The QA/ QC Engineer / Inspector shall verify that coating is not applied prior to test at weld joints.
  3. Test pressure shall be according to table 1 of this procedure.
  4. All lines and appurtenances which do not form part of the test system shall be removed or otherwise isolated from the test system before the test.
  5. Blind flanges and gaskets shall be installed as necessary. All fitting shall be tightened expect the vent points.
  6. The test medium is portable water for carbon and low alloy steel items for high alloy steel such as stainless steel  de-mineralized water shall be used.
  7. The temperature of the test fluid shall be checked. It is recommended, that the metal temperature during test be maintained as per the table no. 2 of this procedure.
  8. It is also described that the steel temperature should not be too close atmospheric dew point so that the results may not be hampered by condensation of moisture from the atmosphere. Wherever possible; steps should be taken to ensure that the items are provided with an adequate cover such that the metal temperature does not rise significantly.
  9. The test pressure for Hydro-test shall be specified in the applicable fabrication drawing

Pressure Gauges.

  • At least once calibrated pressure gauge shall be directly connected to the code item being tested at the highest point, and shall be visible to the operated controlled the test.
  • The pressure gauge shall have a range of about double the test pressure, but shall not be less tan 1 ½ nor more than 4 times the test pressure. For boilers external piping dial pressure used in testing shall preferably have dials graduated over the range of about double the intended maximum test pressure. But no case the arrange shall be less than 1 ½ times the pressure.
  • An additional calibrated pressure gauge may be fitted at a suitable location visible to the operator controlling the pressure at all time. If not fitted at the highest point. Then the pressure shall be accordingly corrected for the static head difference.

Filling with test fluid

  • The test fluid is usually filled from the lower end of the item. Progressing towards the vents on completion. The rate of flow should be such that it does not cause excessive bubbles which may be entrapped in recesses.
  • The vent shall be closed after filling the vessel completely and ensuring that no air is left entrapped within the test system.

Testing

  1. After filling the test system with fluid, the pressure is gradually increased. He test pressure is determined from the drawing (approved fpr construction issue). In cases where this is not available the test pressure shall be obtained from desing engineer by the QA / QC engineer and communicated to the production engineer. He pressure is increased to around 25 50 % of the test pressure. The connections are then checked for leak tightness.
  2. If leaks are observed, the system is De – pressurized and the leaking points are attended suitably (by tightening or by replacing gaskets if necessary).
  3. After checking that, there is no leak, the pressure is gradually increased to the test pressure. The QA/QC Engineer / Inspector shall record the start time of the test after reaching the test pressure.
  4. The test pressure shall be held for specified minimum holding time. If holding period is not specified, the pressure shall be maintained for 60 minute minimum.
  5. After the holding time is elapsed, he pressure is reduced ( by bleeding the test system) to he inspection test pressure. At this point, the QA/QC Engineer / Inspector shall visually inspect the vessel to detect leaks. All weld joint and connections shall be checked visually.
  6. If leaks are detected at flange joints the pressure shall be reduced to zero, the concerned flanges tightened and retested.
  7. If leaks are detected at weld, the test item is considered to have failed in the test NCR shall be raise & disposition shall be undertaken.
  8. If the test is satisfactory, the QA/QC Engineer / Inspector shall approved it by endorsing the test report with attachments like chart, calibration certificates of pressure gauge etc.
  9. After completing the test, the test fluid shall be drained off from the test system and the system shall be cleaned and isolated. While draining, care shall be exercised to ensure that adequate venting is incorporated yo prevent damage item.

 

Table – 1: Test Pressure

Applicable Code Section Minimum test Pressure Visual Examination Pressure
ASME Code Sec VIII Div 1 MAWP multiplied by 1.3 Test pressure Divided by 1.3
ASME B 31.1 1.5 times of the design pressure Design pressure
ASME Code Sec I MAWP multiplied by 1.5 Test pressure Divided by 1.5

Table – 2: Recommended Maximum & Minimum Temperature During Hydro static Test.

Applicable Code Section Minimum Metal temperature Max Metal Temperature during close Eamination
ASME Code Sec VIII Div 1 30 Deg F (17 Dec C) above MDMT 120 Deg F ( 48 Deg C)
ASME B 31.1 & Sec I 20 Deg C (Water Temperature) 120 Deg F ( 48 Deg C)

 

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