Vessel Pressure Testing

The Vessel Pressure Testing article provides you with information about pressure vessel hydro-static testing requirements and related item in pressure vessel inspection.

The requirements have been described based on ASME Code Section VIII. You need to do this test after completion of the construction process, but before the internal parts assembly and also before painting process.

This content covers all major requirements and provides you with guidelines for test performance.

Please note that performing the pneumatic test instead of the Hydro-Static Test is not allowed, and it can be replaced only when it is not possible due to the design and process.

Vessel pressure testing requirements have been addressed in UG-99 and UG-100 in ASME Code Section VIII Div. 1.

These are important points, which you need to take care of in vessel pressure testing:

Activities before pressure vessel hydro-static testing, which need to be checked by the manufacturer quality control team and a third party inspector:

1. Checking all welding already finished and fully accepted by the NDT examination per the project Inspection and test plan.

2. Making sure the inner part of the vessel is clean and free of remaining slag or other elements. making sure the external surface is dry for the correct execution of the visual inspection during the vessel pressure testing.

3. Checking the pressure gauges' calibration tag and certificate and the range of the lower limit and upper limit of the gauges. It needs to be between 1.5 and 4 of the pressure test value.

4. Controlling testing equipment such as the test pump and housing for soundness and tightness.

5. Making sure the test temperature will not violate the following values: 

Min. Test temperature= MDMT + 30°F

Max. Test temperature = 120°F

MDMT is the pressure vessel minimum design metal temperature, and it is stated in the pressure vessel design document.

This reduces the risk of a brittle fracture during the test.

6. Making sure which reinforcement pads are already soap tested.

7. Controlling the testing water quality and using corrosion inhibitor if it is necessary or when the vessel metal is sensitive material

8. Checking of vents. It is required to be placed at high points of the vessel in a position where it is possible to purge air pockets while the vessel is filling.

Activities during the pressure vessel hydro-static testing that need to be checked by the manufacturer quality control team and a third party inspector:

1. Making sure the filling and pressurizing are done from the lowest point and venting from the highest point.

2. Witnessing water overflow through the venting in order to assure that no air bubbles remain in the vessel.

3. Controlling and witnessing which pressurizing is done in three stages as follow:

First Stage: Raise the pressure to 40% of the final pressure, stop pressurizing, keep it for 5 minutes, and then make a fast visual inspection of the external surface.

Second Stage: Restart pressurizing up to 70% of final pressure, stop the operation, keep for 5 minutes and make a fast visual inspection on external surface.

Third Stage: Restart pressurizing up to 100% of the final pressure, stop the operation, and keep for 45 minutes.

4. When 45 minutes elapse, making sure the de-pressurizing is started and the pressure is dropped to the “Inspection Pressure.”

This inspection pressure can be calculated as following:

Inspection Pressure = Hydrostatic Test Pressure / 1.3

Making sure a detail and a comprehensive inspection is carried out over the whole body of the vessel and in the welding joints and attachments.

5. Making sure the pressure vessel hydro-static testing pressure calculated correctly as following:

Hydrostatic Test Pressure = 1.3 x MAWP X Stress ratio

Stress Ratio = (Allowable Stress at Test Temperature)/(Allowable Stress at Design Temperature)

6. Making sure the vessel is immediately and carefully drained after the test and dried by air.

Activities after the pressure vessel hydro-static testing that need to be checked by the manufacturer quality control team and a third party inspector:

1. The pressure vessel hydro-static testing report needs to be prepared by the manufacturer quality control team and signed by the third party or authorized inspector.

2. If the test failed by leaking from weld joints or any other kind of defect, it is necessary that the vessel is drained and dried and repaired based on approved repair procedure. pressure vessel hydro-static testing needs to be repeated.