Just as there can be a negative impact of sound on the human body, certain frequencies can wreak havoc on industrial equipment when played. When control valves are properly selected, there is an increased risk of cavitation, which will lead to high noise and vibration levels, resulting in very rapid damage to the valve's internal and downstream piping. In addition, high noise levels often cause vibrations that can damage equipment such as pipes, instruments, etc.
Over time, the valve deterioration of its components and cavitation caused by the valve causing serious damage to the piping system. Most of this damage is caused by vibration and noise energy, which accelerates the corrosion process. Large-amplitude vibrations with high noise levels reflected by cavitation result in the formation and collapse of bubbles near and downstream of the condensation. While this typically occurs in ball valves and rotary valves in the valve body, it can actually occur in the downstream side of a short, high-recovery similar wafer body V-ball valve, especially a butterfly valve. When the valve is stressed at a position, it is easy to produce cavitation, so it is easy to leak in the piping and welding repair of the valve, and the valve is not suitable for this section of the pipeline.
Regardless of whether cavitation occurs inside or downstream of the valve, equipment in the cavitation zone is subject to extensive damage. Ultra-thin film, spring and small cross-section cantilever structure, large amplitude vibration can excite oscillation faults. Frequent points of failure are found in instrumentation such as pressure gauges, transmitters, thermowells, flow meters, sampling systems. Actuators, positioners, and limit switches containing springs will suffer accelerated wear, and mounting brackets, fasteners, and connectors will loosen and fail due to vibration.
Fretting corrosion, which occurs between abrasion surfaces exposed to vibration, is common near cavitation valves. This creates a hard oxide that acts as an abrasive wears accelerated wear between surfaces. Affected equipment includes isolation and check valves, in addition to control valves, pumps, rotating screens, samplers, and any other turning or sliding mechanisms.
High-amplitude vibrations can also crack and corrode metal valve parts and pipe walls. Scattered metal particles or corrosive chemicals can contaminate the medium in the pipeline, which can have a significant impact on sanitary valves and high-purity pipes. This is also not allowed.
Predicting cavitation failure of a plug is more complex than simply calculating the choke pressure drop. Experience has shown that it is possible that the pressure in the main stream drops to the vapor pressure of the liquid as the area of local vaporization and vapor bubble collapse precedes. Some valve manufacturers predict initial eclipse failure by defining an initial damage pressure drop. A valve manufacturer's method of predicting cavitation damage is based on the fact that it is the vapor bubbles that collapse, resulting in cavitation and noise. Manufacturers have determined that significant cavitation damage can be avoided if the calculated noise level falls below the following limits.
Valve size up to 3 inches - 80 decibels
Valve size of 4-6 inches - 85 decibels
Valve size of 8-14 inches - 90 decibels
Valve size of 16 inches and larger - 95 dB
Ways to eliminate cavitation damage
Special valve designs to eliminate cavitation feature split and staged pressure drops:
"Valve shunt" is to divide a large flow into a number of small flows, and the flow path of the valve is designed so that the flow passes through a number of parallel small openings. Since the size of the cavitation bubble is partially calculated by the opening through which the flow flows. Smaller openings make for small bubbles, resulting in less noise and less damage when coming.
"Graded pressure drop" means that the valve is designed to have two or more adjustment points in series, so instead of the entire pressure drop in a single step, it takes several smaller steps. Less than the individual pressure drop prevents the shrinking pressure from dropping the vapor pressure of the liquid, thus eliminating the valve cavitation phenomenon.
The combination of shunt and pressure drop staging at the same valve allows for improved cavitation resistance by: During valve modifications, the pressure at the inlet of the valve is higher (e.g., farther upstream, or at a lower height) when the control valve is positioned, sometimes eliminating cavitation problems.
In addition, positioning the control valve at the location of the liquid temperature and therefore the vapor pressure, low (e.g. the heat exchanger on the low temperature side) can help eliminate cavitation problems.
summary
It has been shown that the cavitation phenomenon of valves is indeed more than just degrading performance and damaging valves. Downstream pipelines and equipment are also at risk. Predicting cavitation and taking steps to eliminate it is the only way to avoid the problem of expensive valve consumption expenses.