This will be done by pressurizing the system with a hydrotest medium such as water, glycol, or methanol to a specified strength pressure and leak pressures following client and pipeline standards such as CSA Z662. After cleaning and performing a gauge pig run the stages of a hydrotest are as follows:
1) Fill
Prior to fill, temporary hydrotest heads will be pre-loaded with bidirectional pigs and then installed on the pipeline. The lines will then be prepacked by FourQuest with oil free dry air or nitrogen to a required back pressure to accommodate the hydrostatic head pressure encountered during fill. This is essential to prevent gas and liquid from bypassing the fill pig which may cause vapour locking. Hydrostatic test instrumentation is to be installed using test tree manifolds and rated high pressure hoses. This includes but not limited to: chart recorders (pressure and temperature), test manifolds, pressure safety valves, gauges, and digital deadweights. Once the pre-pack is in place, fit for purpose pumps will be utilized to overcome high hydrostatic head pressures and maintain desired pig fill speed. Once fill is complete, the system pressure and temperature will be left to stabilize prior to pressurizing the pipeline.
2) Hydrotest
Pressurization – System will be pressurized using a positive displacement hydrotesting pump at a predetermined rate. It is recommended to build pressure in stages of approximately 25%, 50%, 75%, 100% of the strength test pressure. Yield plotting will be conducted by a professional engineer if required.
Strength Test – Once the strength test pressure is reached, stabilized, and the system has been visually checked for leaks, the positive displacement hydrotest pump can be disconnected and bull plug/flange is to be installed. The pressure is to be locked in and held between maximum and minimum strength test pressures at a specified percentage of the Maximum Operating Pressure (MOP).
Leak Test – Once the strength test is complete, the system will be depressurized at a controlled rate until the designated leak test pressure is attained.
Depressurize – System will be depressurized at a pressure controlled rate to the point where a desired back pressure is achieved for displacement.
3) Displacement
Similar to filling, the necessary back pressure will be applied to control pig speeds. Displacement of the hydrotest medium will typically be performed utilizing air or nitrogen.
