Pipelines & Pipeline Safety - PIPELINE SPHERING PDF Print E-mail
Written by Norrie   
Thursday, 29 April 2010 19:53
Article Index
Pipelines & Pipeline Safety
TRANSMISSION OF FLUIDS
JOINING OF PIPELINES
PIPELINE SUPPORTS
PIPELINE ANCHOR POINTS
EXPANSION LOOPS (or BENDS)
PIPELINE SAFETY
'SHAFER' AUTOMATIC LINE-BREAK VALVE
LINE BREAK - SHAFER VALVE CLOSES
AUTOMATIC RESET
RE-OPEN THE SHAFER VALVE
PIPELINE SPHERING
All Pages

PIPELINE SPHERING

With long gas pipeline systems which also contain liquids such as gas condensate and are passing over (or under), uneven ground, the liquid will tend to collect in the low points of the pipeline. These pockets of liquid will cause 'Gas-Locks' in the pipeline, giving rise to fluctuations in pressure and flow.

In order to prevent these gas-locks, the line is periodically swept by launching a 'Sphere' or 'Pig' which is the same diameter as the ID of the pipe. As the device is launched into the pipeline, the flow and pressure of the following fluids, push the sphere or pig along the line sweeping the liquids ahead of it in the form of 'Slugs'. As the sphere arrives at the other end of the line, the liquid is diverted into a liquid separation vessel while the sphere passes into a receiver from which it can be removed from the pipeline and transported back to the launching station again.

In the case of a pipeline carrying liquid, a similar device is used but is generally referred to as a 'Scraper' or 'Pig'. In this case the purpose of the device is to scrape the inside of the pipeline to keep waxy deposits, scale .. etc from adhering to the pipe walls which, in time, would cause loss of efficiency and possible corrosion of the pipeline inner walls.

Figure: 12 -Shows a typical sphere launching arrangement as used in Operations in the Field. Because the sphere launcher is normally held at the same pressure as the pipeline, the system is fitted with various safety devices which will not allow the launcher to be opened until certain isolation and pressure conditions are satisfied.


Figure: 12

The following picture shows a sphere launching system as described on the previous pages. Loading of the barrel with up to 8 spheres can only be carried out when the isolation MOV is closed and the system pressure vented down to below 2" water gauge pressure. Pressure above this level will deactivate electrical circuits to prevent operation of the door mechanism.

When the spheres are loaded, the door is closed and the system re-pressured by using by-passes around the valves, until the launcher and the main pipeline are at equal pressure. The isolation MOV can then be opened.

The launch valve is designed with a cavity into which a sphere will just fit. When the launching of a sphere is required, the launch valve mechanism is activated, the valve rotates through 180° and the sphere drops into the main line where it is picked up by the fluid flow and pushed along the pipeline. The Launch valve is returned to its start position and the next sphere rolls into the cavity ready for the next launch.



Last Updated on Thursday, 29 April 2010 19:56