Parameter KP0-122
KP122- 343
KP343- 481
KP481- 513
Underground pipeline temperature(° C) 20 20 20 20
* Saturation Vapour Pressure( mbar)( at underground pipeline temperature)
Density of water vapour at pipeline temperature( gr / m ³)
23.37 23.37 23.37 23.37
17.3 17.3 17.3 17.3
Evacuation time to 23.37 mbar( hr) 129.15 238.06 145.21 23.68 Evaporation time( hr) 24.6 45.35 27.67 4.51 Required dew point Temperature(° C)-10-10-10-10
* Saturation Vapour Pressure( mbar)( at required dew point temperature,-10 ° C)
2.6 2.6 2.6 2.6
Final drying time( hr) 23.63 41.71 25.44 4.15 Vacuum drying total duration( hr) 212 390 238 39 * Refers to Boiling Point of water at various vacuum levels
METHOD 2- Natural gas injection as propellant of a pig train confining a nitrogen batch
Pig assisted gas injection method is based on simultaneous displacement of dry air by natural gas injection assisted by an interface train of at least two pigs( mechanical separation), which includes a batch of nitrogen to prevent any possible formation of a gas and air mixture.
Due to the remarkably long pipeline and to dry inner pipe conditions, the recommended speed of the pig train was approximately 0.5 m / s.
If a pipeline is very long and the elevation changes, the control of the pig travel speed should be assured by a back pressure of 5 bar. This value, which is remarkably higher than the common practice of 2 bar adopted for shorter pipelines, is recommended in case of any possible pig stops, especially on sections with steepest slopes.
The method could be carried out using two or more pigs. The separation efficiency is increased, resulting in lower nitrogen consumption.
This is a common method chosen in pipeline commissioning if pigs are available. The recommissioning of SSGP pipeline Section 1 opted for this method after the pipeline drying was completed.
METHOD 3- Natural gas injection under pipelines pressure conditions without the use of pigs
Disposal of large volumes of combustible gas into the atmosphere should be minimised. When necessary, it is essential that the combustible gas is diffused into the air without any hazard to workers, the public or property. In general, this requires a vent long enough to carry the combustible gas far away. Consideration must also be given to public relations with regard to objectionable noise.
During purging operations, it is important that all possible sources of ignition be eliminated or controlled. In this respect static electricity is one of the most difficult ignition hazards to control.
Method 3.1- Inert purge by complete filling with an inert gas This is the most common pipeline purging method. An inert purge of a pipeline may be accomplished by filling the entire line with nitrogen.
A volume of 10 % to 50 % more inert gases than the total volume of the line, when added rapidly, will ensure complete filling. The vented gas is then analysed to make sure the line has
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