Slug velocities in pipe

[Justice100]

Hi there,

I am am looking at 2-phase flow through a ~100m line of various sizes (3",4",6" and 8"), which is mainly horizontal pipe with a few short sections of vertical pipe. Based on Perry's 2-phase flow map I have slug flow.

I need to report slug velocities to check the piping support design but I am struggling to find a reference on how to calculate slug velocities. Perry's and GPSA do not mention this. Can anyone point me to a good reference for calculating this? Would the mixture superficial velocity be good enough?

 

[MortenA]

I dont think it would be accurate. The max velocity depends on where you are in the pipeline. Close to the outlet you may get a larger dP across a slug thus getting a higher velocity. You cant provide a number if you dont have the right tools the people in your organisation agrees gives right nos (e.g. a computer simulator or company guideline).

Best regards, Morten

 

[LittleInch]

You're dealing with transient flow here and "slug flow" is a very variable thing

The only real way is to put this into a transient piping analysis program like OLGA or similar.

Only then can you really find out what is going on and whether your slug flow is really slug like.

But with vertical riser elements, it could be quite severe or might be virtually nothing. My ROT has always been that if you can keep the gas phase running at around or above 3m/sec in actual velocity you don't really have an issue, but not sure if you're fixed in your conditions.
If you want a start point you could go for 10m/sec velocity for say a 5m long liquid slug and see how that pans out.



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[Justice100]

Thanks for your replies.

I have Hysys and have looked at the slug analysis tool on there, which gives slug velocities based on a paper by Bendiksen (1984) but I don't have this paper. The situation is difficult as this is for degassing a gassed up well therefore the gas to liquid ratio will go from 1 to near zero as the well is degassed. Most of the lines (3", 6" and 8") are existing.

I was hoping using something like Olga would be overkill for a piece of process piping but perhaps that is the only way.

 

[LittleInch]

Oooh, that's even harder. Changes in fluid properties, pressures and flows over time. Not sure anything will give you accurate results.

Your horizontal pipe should be Ok, Just make every third support a horizontal and vertical spaced guided support to stop the pipe jumping off the rack.

The end line stops and anchors though are rather more difficult.

Your only real hope is to set some maximum flows for the gas while de-gassing using an orifice or something to stop the operators just "opening 'er up" and then wondering why the pipe fails.

Then I would assume something like 10 to 15m/sec of say a 10m slug in this instance and see what sort of force that gives you.

Is this new or existing?



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Also: If you get a response it's polite to respond to it.

 

[Justice100]

Mainly existing just a short new section of 4" pipe to make an interconnection.