East-west Gas Pipeline Project Construction Procedure for Cleaning, Gauging And Hydro testing of Pipelines Rev.: A1 China Petroleum Pipeline Bureau（CPP） Document No.: EWPL00-COS-PR-0014 .
Figure-10
After the installation and before the operation of water filling operators shall check that all equipment and devices are in good condition and well functional. 7.9.4 Pressurization
The pressurization shall be performed in the presence of Engineer-in-Charge at a moderate and constant rate not exceeding 2 bar/min. One pressure -recording gauge shall be installed in parallel with the dead weight tester. Volume required to reach the test pressure shall be recorded using a dead weight tester periodically throughout the pressurization as follows:
? Each 5 bar increments up to 80% of test pressure;
? Each 2 bar increments between 80% of 90% of test pressure;
? Each 0.2 bar increments between 90% of the test pressure to full test pressure; The pressurization shall be cycled according to the following sequence:
? Pressurize to 50% of test pressure, hold for 1 hour, ? Drop pressure to static head of test section at test head, ? Pressurize to 75% of test pressure, hold for 1 hour ? Drop pressure to static head of test section at the test head
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? Pressurize to test pressure. East-west Gas Pipeline Project Construction Procedure for Cleaning, Gauging And Hydro testing of Pipelines Rev.: A1 China Petroleum Pipeline Bureau（CPP） Document No.: EWPL00-COS-PR-0014
These periods of hydrostatic test shall be carried out as is shown in Figure-11:
50% P 100% 75%
During the pressurization to each test pressure, two tests shall be carried out for the calculation of air volume in the pipeline under test. Air volume shall be calculated as detailed subsequently. In case, during the hold periods, a decrease in pressure is observed, the above operations shall not be repeated more than twice, after which the line shall not be considered capable of test, until the Contractor has isolated and eliminated the cause for the lack of water tightness.
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1 1 24 Figure-11
Time (hour) 7.9 Air Volume Calculation East-west Gas Pipeline Project Construction Procedure for Cleaning, Gauging And Hydro testing of Pipelines Rev.: A1 China Petroleum Pipeline Bureau（CPP） Document No.: EWPL00-COS-PR-0014 In order to check the presence of air in the pipeline, two separate consecutive pressure lowering of 0.5 bar shall be carried out after pressurizing to test pressure.
For calculation of air in the pipeline, the second pressure lowering shall be used and the relevant drained water shall be accurately measured (V1). This amount measured shall be compared to the theoretical amount (VP) corresponding to the pressure lowering that has been carried out, by using the following formula:
r??Vp??0.884?i?A???10?6?Vt???P?Ks??Where:
Vp: Vt: ΔP: ri: t:
computed water quantity required to raise the pressure in the test section (m) geometrical volume of the line section, m. pressure rise, (bar)
nominal inner radius of the pipe, (mm) nominal pipe wall thickness, (mm)
3
3
A: isothermal compressibility value for water at the pressurization temperature in the P
range (bar×10
-1
-6)
K: a dimensionless coefficient equal to a value of 1.02 for longitudinally welded pipe
If there is more than one wall thickness in the pipeline section under test, Vp of each subsection shall be calculated separately. Different values of t, Vt and ri will be applied to its own section. Finally, the total Vp of the pipeline section
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East-west Gas Pipeline Project Construction Procedure for Cleaning, Gauging And Hydro testing of Pipelines Rev.: A1 China Petroleum Pipeline Bureau（CPP） Document No.: EWPL00-COS-PR-0014 is equal to the sum derived from that of each subsections. Figure-13 below shows how the water is discharged during double depressurization and the method to measure the water volume.
Figure-12
If no air is present in the length under test, then V1 / VP = 1
In order that the above ratio is acceptable, it shall not differ by more than 6% (i.e. 1.06). If the air found in the pipeline is within above established tolerance, then the pressurizing can continue. If the ratio of VI / VP exceeds 1.06, the hydrostatic testing cannot go on and additional pig passages shall be performed to remove the air pockets. The test shall be repeated as per the above procedure until above estimated tolerances are satisfied. The pressurizing can then continue to reach the test pressure. 7.10 Testing
After the section has been pressurized and the air volume test has given acceptable results the test pressure shall be held for a minimum of 24 hours after stabilization. After temperature and pressure has stabilized, the injection pump shall be disconnected and all connections at the test heads shall be checked for leakage. The pressure
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