Pressure Test and Leak Test STUDY MATERIAL

STUDY MATERIALS FOR PRESSURE VESSELS

1. Pressure Test and Leak Test

2. Pressure: Force applied perpendicular to the surface of an object per unit area. P= Force Area S.I unit is Pa( Pascals ) , generally expressed with N/m 2 or Kgf /cm 2  

3. Pressure Testing Pressure tests are performed to ensure the safety, reliability, and leak tightness of pressure systems . Pressure test are performed in pipelines , pressure vessels, cylinders , tanks Pressure test is performed 1.In case of new installation. 2.In case of Existing System ( After repair or alteration) 3.Upon mandatory requirements

4. Mandatory Requirements

5. Types of Pressure Testing standard hydraulic acceptance test ; - A ‘ standard’ test for acceptance is carried out on a pressure vessel where the required thickness of all pressure parts can be calculated . i.e. (Calculated design pressure = Safe Working Pressure) pneumatic acceptance test; hydraulic proof test ; - Proof test carried out when strength of vessel cannot be calculated , proof test of acceptance is carried out to establish design pressure i.e. (expected design pressure = Safe Working Pressure) combined hydraulic/pneumatic test.

6. Hydrostatic testing - Test medium water Pneumatic Testing - Test medium air , nitrogen , non flammable and non toxic gas pressure tests must be hydrostatic unless pneumatic tests can be justified

7. Justification for performing Hydrostatic with other fluids and Pneumatic Test Other fluids are used when there is : Poor mechanical integrity i.e. the vessel or structure cannot withstand the water weight. Difficulty in removing water completely Chances of water freezing due to cold weather. Pneumatic Test: It is carried out only when Pressure system are designed so that they can not be filled with water/liquids. Intolerant to traces of liquid. T he removal of liquid is impracticable.

8. Manual Hydrostatic Test Kit

9. Pneumatic Test-Schematic Diagram

10. Hydrostatic Test-Schematic Diagram

11. Factors to be considered in the choice of test method Test Fluid Size of Vessel Location of the vessel A detailed procedure defining area of risk and controls should be developed

12. Standard Test Pressure

13. Proof hydraulic test Vessel are equipped with strain gauges or strain indicating coating Pressure is increased gradually Stopped when significant yielding occurs at a point

14. Procedure for testing Pressure tests must always be performed under controlled conditions Important procedure for testing Formulating a test plan and get approved. Performing the test safely Documenting the test records

15. Basic Test Method 1.Thorough visual inspection 2.Desirable to carry out leak test 3.Gradually raise to 50% of test pressure, increase 10% in stages until test pressure reached. 4.Maintain for 30mins 5.Close inspection is restricted 6.Check signs of plastic yielding never allow vessel to exhibit such sign 7.Ensure the vessel test is carried out in ambient temperature

16. Precautions Against Hazards of vessel failure Blast protection. Safety area clearance. Degree of confidence in stress analysis of vessel. The adequacy of NDT carried out the test. Resistance of the vessel material to fast fracture. Local chilling during filling & emptying. Extent of remote monitoring

17. Pressure testing: safety precautions Test to be carried out by competent person Permit to work system to be adopted Isolation of the test area Testing personnel shall maintain suitable distance and facilitated with remote viewing Hazards of explosion , ejection of plugs , fluid jets to be considered Pressure vessel to be monitored by acoustic emission

18. Hydraulic testing: safety precautions Effect of static head should be checked Ability of the structure to withstand the weight Water should not be used in temperature less than 7⁰C Prevention against over pressure should be taken Accurate and reliable means of pressure measuring devices to be installed. i.e. Freshly calibrated pressure gauges The possibility of overpressure due to water temperature rise and expansion should be considered Disconnect all lines that are not intended to testing Secure devices so that it doesn’t eject during testing The vessel under test should not be subject to any form of shock loading such as hammer testing.

19. Pneumatic testing: safety precautions Avoid pneumatic test in material liable to brittle fracture Always minimize volume of testing , test components separately Consideration should be given to the possibility of condensation in the vessel, which can defeat the purpose of using pneumatic testing Protection against overpressure by the use of suitable reducing valves, pressure gauges and pressure relief valves . Flexible connections used in pneumatic testing should be firmly secured . On completion of the test the vessel should be emptied in such a way as not to cause under pressure and collapse .

20. Leak Testing and Detection Pressurizing the equipment (pressure used may be below the design pressure ) All safely precautions to be followed as described in pressure testing. LEAK DETECTION: Liquid leak is hydraulic. Soap bubble method is pneumatic. Evaluation of air bubbles when it is immersed in water is the equipment is small. Gas detection (gas is introduced into the air ) L= -V d P d t   L = leak rate ( pa. m 3 /s ) P= pressure V= volume T= time.

21. Leak rate methods The main methods for leak rate determination are: ( 1) pressure decay method; ( 2) flow method; ( 3) search gas flow method. The pressure decay method is to pressurize the system, isolate it and measure the rate of pressure decrease . The flow method involves measuring the inlet flow required to maintain the pressure constant . In the search gas flow method, air is passed over the surface of the equipment and through some form of hood or containment and the flow of air and concentration of search gas in the air are measured.

22. Search gas Detector Halogen gas Halide torch Halogen diode detector Hydrogen Thermal conductivity detector Helium Nitrous oxide Infrared absorption detector