Figure 5. Solutions for valve buffeting might include a grid seat ring( left) to straighten the flow profile, or a spoked plug, stronger valve stem, or larger actuator to arrest vibration. Courtesy of Emerson. π www. valve-world. net Valve World February 2026 27
Control valves
Figure 2. Red and lighter colors in these images highlight very high fluid velocity and pressure fluctuations. This turbulence can set up resonance in piping systems. Courtesy of Emerson.
tees, elbows, and dead legs. It can also occur when there are long, unsupported piping runs, which tend to set up consistent, high amplitude vibrations, concentrating stress at the endpoints. The resulting vibration may quickly result in catastrophic pipe fatigue failures( Figure 3). Fortunately, some FIV can be anticipated using piping modeling software and analytical techniques, which can predict problems with piping arrangements prior to construction. FIV damage can be mitigated by using larger diameter piping, which reduces velocity. It can also be mitigated by spacing out piping transitions, especially downstream of a control valve taking a large pressure drop— to minimise flow turbulence, and by adding additional piping support to minimise movement and metal fatigue.
Acoustic induced vibration
AIV is typically higher frequency(> 500 hertz), and it occurs in the downstream of a control valve or in nearby piping. AIV is often the result of very high pressure drops across a valve, which creates supersonic flow, resulting in high turbulent shear regions that generate high frequency sound. Very high sound levels can damage hearing,
Figure 3. High fluid velocities passing through this piping manifold set up resonant frequencies in the small diameter piping that ultimately cracked welds in several of the piping connections. Courtesy of Emerson.
and they can create metal fatigue in the control valve and surrounding piping. AIV and FIV can occur simultaneously in close coupled piping configurations( Figure 4). When an installation lacks adequate upstream and downstream straight pipe runs before and after a control valve, the FIV induced by a valve can be amplified by the increased turbulence from the close coupled piping, which can also generate noise and potentially AIV. Sound not only emanates from the valve, but it also radiates from downstream piping. Sound radiating from piping systems loses energy slower with distance than noise from a point source, so it can be bothersome to even far-flung site personnel, and to neighbouring communities. AIV risks can be mitigated in several ways, for example with special, low-noise control valve trim, which dramatically reduces sound levels. AIV can also be reduced by using thicker walled pipe, or by downstream sound diffusers, which extend the pressure drop across multiple devices. Lower intensity AIV can be addressed with acoustic insulation or sound absorbing blankets. Often a combination of several of these solutions may be employed to address very high AIV applications.
Buffeting
FIV inside a valve can create a condition called buffeting. In this case, flow turbulence within the valve body creates localised lowpressure zones and pressure fluctuations.
Normally, buffeting is a low frequency phenomenon(< 20 hertz), so it cannot be heard, but the impact on the process can be significant. Figure 2 shows how incoming flow can set up a recirculation region, with high pressure fluctuations at the control valve cage inlet. The resulting recirculation obstructs flow and reduces valve flow capacity. These pressure fluctuations also create low frequency shudders in the valve trim, creating erratic forces on the actuator, which impacts valve positioning and control. Buffeting can be eliminated in a number of ways. Adequate upstream and downstream straight pipe runs can settle the flow profile and reduce FIV enough to mitigate the condition. If piping modifications are not possible, the condition may be addressed by installing a grid seat ring on the inlet to smoothen the flow profile, or by stiffening the valve trim, stem and / or the actuator to dampen vibration and minimise valve damage( Figure 5). A particularly troublesome example of buffeting occurred in the inlet pressure letdown valve feeding a very large liquefied natural gas( LNG) facility. The upstream and downstream piping was less than ideal and contributed to the condition, but it could not be easily altered. The high pressure drop across the valve was generating very high noise and vibration, which was limiting the throughput of the entire LNG train. It was also damaging the valve internals,
Figure 4. Close coupled piping transitions can amplify FIV from the valve and create additional high amplitude AIV that resonates in the downstream piping. Courtesy of Emerson.
Figure 5. Solutions for valve buffeting might include a grid seat ring( left) to straighten the flow profile, or a spoked plug, stronger valve stem, or larger actuator to arrest vibration. Courtesy of Emerson. π www. valve-world. net Valve World February 2026 27