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n2 slug

n2 slug

we will start the calculation of N2 slug for pipeline purging purpose? the purging will be not be full but with just a slug of nitrogen, anyone have an idea obout the calculation of the exact volume of this slug, the pipeline is 28 in, 200 Km, i have no idea about the slug distance!

RE: n2 slug

There are many uses of the word "purge". What is the goal of running this "slug"?

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

RE: n2 slug

after satisfactory completion of vacuum drying operations of the pipeline,nitrogen purging and packing the pipeline are carried out.
A maximum of 2% by volume of oxygen shall be permitted in the pipeline following completion of the purge.
The purpose of these is to ensure that oxygen content of 0.015% inside the pipeline is confirmed to avoid any combustible mixture before the introduction of the hydrocarbon.
of course there are many methodologies, 1- full injection of N2 in pipeline which is costly, 2- just use a slug of N2 from the start to the end portion of the pipeline.

RE: n2 slug

There's no such thing as exact and it will depend clearly on how much back pressure you're going to keep when you're filling it.

I would go for a minimum of 1000m based on the operating pressure you expect to see in the line and two sealing pigs and would probably go for 2km.

Is this gas or liquid you're introducing?

You might be surprised at how little N2 you would require if the end pressure you get in the pipe is say 0.5 to 1 barg.

At low densities the velocity can be quite good and hence a good sweep of the pipe is achieved just as a nitrogen / air mix with gas being vented at the end.

Do you have any places where you could inject nitrogen along the line at e.g. valve stations or pig traps? then the pressure could be even lower if you monitor the gas until N2 is high, then shut off injection and start again at the valve station and gradually jump between injection points.

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