High Pressure Letdown Stations - Vibration

[StressGuy]

Does anyone have some pointers to good references on the high energy vibrations induced in piping system due to large pressure drops. I've specficially got a min flow bypass that is dropping pressure from about 1700psig to around 20psig and that is going to be a lot of energy.

I've seen some general references and details on restraining this kind of piping (big chunk o'concrete and beefy hold down straps). But I was hoping to find something more quantitative as far as predicting the dynamic forces, frequency, etc. I'm not as strong on dymanics as I'd like to be, but I'm not aware that programs like Caesar are setup for this kind of issue, since I expect it's going to depend a lot on specifics about the valve operation.

So, any books, articles, or bits of wisdom that the forum can offer are appreciated. Edward L. Klein
Pipe Stress Engineer
Houston, Texas

All opinions expressed here are my own and not my company's.

 

[MJCronin]

Stressguy,

Is this sytem making a lot of noise too ?

The only reference I have read, about this kind of problem, is contained in a book authored by Fischer Control Valves.

In a book, that they did publish at one time, there was a discussion about the installation of spargers inside of piping systems... just downstream of control valves that would have a large pressure drop. I have never seen it done, however the sparger would mitigate (somewhat) the vibration and noise effects of a large pressure drop.

At one time, an ancient and venerable firm called "Stone & Webster" of Boston Mass had a requirement for design of pressure reducing stations on steam systems. Because of a history of vibration and damage encountered on HP steam systems in coal plants, the large delta p was to be taken across two (or more) pressure reducing stations. This helped reduce wear and maintenance costs as well as solve a vibration problem. The steam systems were from 1900 psig to 260 psig.

CAESAR-II would not help you much. CAESAR-II is set up to calculate piping stresses and support loads based on a forcing function defined by the user.

Good Luck

MJC

 

[butelja]

Typically something like this would be let down in multiple (2-3) stages. You didn't state if it is liquid or gas. Liquid would almost certainly have severe cavitation, noise, vibration, and erosion damage. Gas would still have noise and vibration damage potential.

There are special valve trims for letting down high pressure in 1 stage. They typically have a "tortuous path" through the trim, which is made up from stacked disks that have a maze-like pattern etched into them. An ASME published paper discussing their performance is at:

http://www.ccivalve.com/pdf/277.pdf

.