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I am facing a problem in vibration of control valve controlling atmospheric residue at 10 bar pressure,175 'C temperature and 620-630 m3/hr flow. Instrument team dropped the valve and found internals parts damaged and they explained that the reason of damaging the valve internals due to low opening of 15-16%.

The attended and fixed the valve but same vibrations still coming.

Can anyone explain the exact reason and solution for this?

Aug-2024

Answers

Charles Palmer, Charles Palmer Consulting, charles101143@gmail.com

Marcio has provided both an accurate assessment (cavitation) of the cause of the vibration as well as 2 good possible solutions. I have encountered similar problems, caused through a change in Process dynamics and found that simply fitting a 316 SS orifice plate on the outlet flange of the valve, solves the problem.

Sep-2024
VenkateshKumar Ramanujam, Retired, rvkumar61@yahoo.com

As recommended above, try to increase the downstream pressure by throttling a downstream valve.

Sep-2024
Marcio Wagner da Silva, Petrobras, marciows@petrobras.com.br

Considering the problem description and process data, this vibration in the valve seems to be related to cavitation phenomena. Cavitation phenomena in control valves occur when the pressure reaches values below or near to the vapor pressure of the process fluid, this condition allows the vaporization of the lighter fractions of the fluid creating bubbles which collapse as the pressure increases in the pipeline, leading to noise and vibration.Another effect of the cavitation is severe damages to the valve internals due to the erosion caused by the bubbles that collapse which remove material from the valve walls. A design strategy to improve the valve resistance to cavitation is to apply anti-cavitation internals with higher hardness aiming to avoid material losses in case of cavitation of the valve.

Regarding the process actions which can be taken to avoid the cavitation phenomena it's possible to quote:
- Increase the downstream pressure by throttling a downstream valve or installing an orifice;
- Reduce the differential pressure using two valves in series;
- Installing a bypass line in the control valve;
- Verify the valve design, if the valve is not adequately designed the operation conditions will facilitate the cavitation phenomena. The information from the instrumentation personnel regarding the low operating opening (15 - 16 %) can make sense;
- Place the control valve in a lower elevation or where the fluid temperature is lower can minimize the cavitation occurrence once raise the pressure in the valve and reduce the vapor pressure, respectively.

Sep-2024