Piping Hydrostatic Test / Hydrotesting

1. Purpose of Hydro test.
2. Types of Pressure Test.
3. Procedure of Hydro test.
4. Limitations of Pneumatic Test.
5. Hydro testing test Pressure.
6. Test pressure subjected to external pressure.
7. Hydro test Pressure according to different process.
8. Volume required for the Hydro testing.
9. Pipeline De watering, Cleaning & Drying.

1. Hydro testing Abhijeet Nagale. January 22,2018

2. Purpose: Pressure tests are performed to ensure the safety, reliability, and leak tightness of pressure systems . Newly constructed pipelines are typically Pressure tested , upon completion of construction. OR Older lines already in service may be re-tested either to confirm an earlier test or to qualify the line for a higher operating pressure . (During Plant Modification)

3. Types of Pressure Tests: Hydrostatic Test: Is performed by using water as the test medium. Pneumatic Test: Is performed by using air , nitrogen, or any non-flammable and non-toxic gas .

4. Procedure Hydro testing is generally Performed by hydrostatic testing contractor hired by the pipeline owner, or hydrostatic testing may be included as a part of the main construction contract . Water is filled inside the pipe for the pressure test. For the Hydro testing the water must be filtered by the means of Strainer or online filters. (The used water must be non corrosive or treated) Deadweight pressure and temperature readings are recorded after the prescribed test pressure has been reached and the pressures and temperatures have stabilized . Pressure vs. time plot is made the reading are usually made at 15 minutes interval for the first hour and at 30 minutes intervals thereafter.( Procedure may vary from company to company) If the there is no Pressure drop for the 3 hours, then the leakage test is accepted. Recorded data will become a permanent record which must be retained for as long as the facility tested remains in operation.

5. Pressure tests must be performed under controlled condition. Pneumatic tests are potentially more dangerous than hydrostatic because of the higher level of potential energy. Performed only when at least one of the following conditions exists: When pressure systems are so designed that they cannot be filled with water. When pressure systems are to be used in services where traces of the testing medium cannot be tolerated.

6. Hydro testing Test Pressure. Hydrostatic Test Pressure = 1.5 × Design Pressure × Stress Ratio Where, Minimum calculated hydrostatic test pressure ( Pt) (kg/ ) Design pressure ( P) is internal design pressure (kg/ )  

7. Test pressure for piping subjected to external pressure For the Jacketed lines, the internal line shall be pressure tested on the basis of the internal or external design pressure, whichever is critical. This test shall be preformed prior to completion of the jacket . The jacket shall be pressure tested of the basis to the jacket design conditions. Where systems require hydrostatic testing through static equipment, the test pressure shall be selected so as not to exceed vessel test pressure.

8. Test pressure according to different systems Test pressure for various process system must be calculated by: System Code Hydrostatic Pneumatic Boiler Power ASME Section I 1.5×MAWP Not Permitted Power Piping ASME Section B31.1 1.5×Design Pressure 1.2×Design Pressure Process Piping ASME Section B31.3 1.5×Design Pressure 1.1×Design Pressure Building Services ASME Section B31.9 1.5×Design Pressure 1.25×Design Pressure Sprinkler System NFPA 13 200 Psi 40 Psi MAWP: Maximum Allowable Working Pressure.( Defined by Mechanical) NFPA : National Fire Protection Association

9. Volume required for the hydro testing L= length of the test section, feet d= diameter of pipe, inches V= gallons required to fill @ 0 psig  

10. Volume required at test pressure = Gallons contained in test section at test pressure P, and temperature T , V = Volume required for hydro test. =Factor to correct the compressibility of water due to pressure 0 psig to test pressure P psig = Factor to correct the volume change due to pressure increase = = Correction factor for temperature change, = Factor to correct for the thermal change in water which can be determined from book Pipeline Rules of Thumb. (Table No.1)  

11. Pipeline Dewatering, Cleaning & Drying Pipelines used to transport natural gas will need some drying, depending on the operating pressure and the location of the line, to prevent the formation of hydrates. Pipelines may require drying to protect the pipe from internal corrosion caused by the formation of corrosive acids , such as carbonic acid in the case of carbon dioxide pipelines. If the pipeline is to be cleaned and/or dried, the pig will be pushed by either compressed air or gas . T he pig will form a perfect seal with the inner periphery of the pipe and will not allow any of the material behind the pig to leak past. Brush pig is used in order to remove the debris from the pipe line by the help of air or gas. Internal sand blasting is used to dry some section of pipe line. ( Sand is blasted in pipe by using Nitrogen or air to propel the sand)

12. References Pipeline Rules of thumb Fifth Edition ISBN 0-7506-7471-7 Hydrostatic Pressure testing for piping by KLM Technology Group. SLAC National Accelerator Laboratory Environment , Safety & Health Division Chapter 14 | Pressure Test Procedures 9

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