In our country, we meet different consultants specifying different external underground water pipeline hydrostatic testing time frame even from 2 hours to 24 hours. Sometime due to the weather, consistent pressure could not be maintained with long testing hours. Can I know what is the international standard testing hours for pipeline hydrostatic test ? Please share your experience with me. Thanks

cckla,
There is no such thing as a "International Standard" for conducting a Hydrotest.
However is some common agreement on certain steps that should be taken:
- walk down the system to insure that all the flange bolts are tight
- Check all the valve packing bolts or gland nuts
- open all the high point vents
- close all the drains
- add the test water
- as you are filling, close the vent valves starting with lower ones first and working up to the highest
- Bring the pressure up in steps to hold points
- at each hold point (pressure) walk the system to check for leaks (Flanges or Valves)
- When the final "Test Pressure" is reached hold for a minimum of 10 minutes (for short close configurations)
- For longer systems or configurations hold the pressure until the whole system has been checked
- Continue to hold until the Client representative or designated inspector signs off on the test
- After the approval open all the vent valves
- Connect temporary drain pipes or hoses to designated drain valves to control water recovery if required
- Drain the system

for the oil and gas pipelines that we lay...the NZ government inspectorate requires a 24 hour hydrotest (with chart recorder and deadweight tester) on sections of the pipeline that are buried and do not have the welds exposed for visual inspection during the test. for sections of the pipeline which can be visually inspected and tested independently then the test duration drops back to 4 hours. however it becomes a moot point when you have a mix of AG and UG pipeline within the same test i.e. you are compelled to test for 24 hours