Hi all,

Good Day!

To our experienced senior's, i would like to ask this following questions...
This questions will be partly process but our concern...
Excluding steam generator, Does anyone incounter 2 phase fluid condition pipe line?
My opinion, in evalluating this line is that I will have to consider two condition(water filled and no content).... but is there realy 2 phase condition in pipeline? And how will it be posible to compute vibration from turbulence flow for the dynamic analysis?

Please give me an advice...
Thank you very much!!!

Regards!

It depends what kind of 2 phase you are referring to, liquid/liquid 2 phase or liquid/gas.

Liquid/gas 2 phase fluid flow is something most designers want to avoid as not only is it very difficult to calculate hydraulically but it also damages the pipeline and equipment through abrasion of the liquid particles (think waterjet knife) and requires constant calibration of the instrumention due to fluctuating flow conditions.

You would need to hydraulically calculate the system first, in a single pipe there are a couple of methods such as the Beggs and Brill Correlation. For a pipe network, gravitational effects have a major effect on the 2 phase split at pipe junctions so you would need to know the exact physical layout of the system and then treat each pipe as a single system using something like beggs and brill with the output of one calculation feeding the input of the next (not very accurate). This will only give you a steady state hydraulic solution for a steady state Caesar Run.

For dynamics almost all process software assumes single phase for calculation purposes, so getting slug flow and vibration input parameters for Caesar would be difficult. I believe there are some high end simulators that are capable of these calculation but I have never seen it done.

Anyone have any ideas?

What we're talking about here is flow-induced vibration. Outside of some type of Computational Fluid Dynamics software it would be impossible to predict. This is done in Caesar II not predictively, but rather after a system in operation is experiencing a vibration problem. In such a case you need measurements of displacements throughout your piping system (or at least in several locations around the problem area). Then using Caesar II's harmonic analysis routines you use trial and error (changing the harmonic force location and magnitude) until you match Caesar II's dynamic output displacements to that measured. At that point you know you have a good Caesar II model and can make corrective changes from there.

Hi Sir Andrew and Sir Loren,

Good Day!

I speak to one of the process incharge.
He said ("The worst case of the flow is a slug flow").. In this statement my understanding in my concern is when two phase occurs in any line I shall consider the worst case that is availlable and that is the slug flow.. But is it overdesign?...... Is it rigth to consider 2phase liquid/gas with a small ratio in volume(ex. 1:10) for a slug???

Regards!

Bom,
When process says that line is two phase that means that line will see two phase in its operating conditions.
As a stress engineer one should consider all possibe conditions that may exist in a line.
It is evident that you have to put extra supports, guides and axial stops which may result in higher cost (which is very less as compare to cost of rework) but it is better to spend money on supports rather spending afterwords.

Two phase flow by itself is a meaningless term as far as flow induced vibration or dynamic loading is concerned. A plumbing drain is two-phase flow liquid and air and maybe an occasional solid yet one does not strap down plumbing drains as though they were about to be ripped asunder.

Flow induced vibration is a science unto itself and its practitioners are experts in it. This forum offers no expertise in this subject and frankly you inquiring here demonstrates your understanding of the problem. Read some papers on flow induced vibration and talk to a fluids expert. Two phase flow maybe bad or may simply be a drain!