vibration in pipelines

[ruballs]

Is there an equation/method for determiining the maximum velocity/flow rate of fluid in pipeline before vibration begins?

 

[samuelliu]

No. The pipeline vibration also depends upon pipe support, etc.

 

[DavidCR]

Above 3 m/s flow speed is a general value were Reynolds number is going bad. But not only the flow speed can produce bad effects. Is more common to find vibration problems by other causes, and most deal with non steady conditions.

In most cases what you have to do is to design a pipe line which has a natural frecuency higher than any spected excitation frecuency. (In other words, a system with vibration sources that would not be close to those that may produce a bad "vibrational" response).

As a rule of thumb, for a well supported steel pipe (following ASME B31 code design criteria for example, with tipical geometries on a plane), excitation frecuencies higher than 30 Hz would not be dangerous (i.e. a fatigue problem would be hardly met).

 

[ruballs]

Thanks for that, I have, however, seen rules where for a given density x velocity squared value a maxium flow rate is given. Is this an in house rule of thumb or a more established corelation?

Daniel

 

[EEG]

Several thing will cause vibration of a piping system:
1) bad support system
2) improper support of piping connected to recipricating equipment
3) Slug flow, also known as two phase flow
4) water hammer

Velocity by inself is not going to be a problem. If you have a system that is vibrating it can usally be traced back to one of these four.

EEG

 

[1969grad]

I think that the formula you are looking for is in API 14E which gives a formula for erosion velocity which is a constant divided by the square root of the density.

 

[caccp]

The liquid speed in a pipeline doesn’t produce pipe vibration by itself, it would be rather the rate of change of such speed that will possibly cause it. 3 meter per second maximum, also DavidCR suggests, is the limit for a good design in that, as much is your speed as much your system instability will increase such rate of change. Change of speed, anyway, affects the most the water hammer phenomena, with an over pressure that could burst your pipe. Two phase flow in some case causes cavitation and consequent vibration, but in this case the problem is it could seriously damage and disrupt your pipe.