Acoustic Induced Vibration (AIV)
Acoustic Induced Vibration (AIV) occurs when very high sound levels are propagated in piping. If the sound levels are high enough, they will excite the circumferential vibration modes of the pipe. This allows the pipe to vibrate in and out as the sound wave moves through the piping. Most often this occurs downstream of pressure-reducing valves or safety-release valves but AIV can occur at any location where the pressure drop or mass flow rate is sufficiently large. The sound power level is first calculated for each valve and compared with the criteria shown in the following graph. The criterion is the thick black line. The axes are Sound Power Level and the Ratio of the outside diameter to the pipe wall thickness. The data points are the data used by Carucci in his 1982 ASME paper (V. A. Carucci and R. T. Mueller, ASME paper 82-WA/PVP-8). Although there are some non-failures above the criteria line, there are no failures below it.
Why You Should Care
When the sound power level of a valve is above the criterion curve the downstream piping will be excited with such intensity that non-symmetrical connections may be at risk of AIV damage. The sound power level is calculated downstream of the valve. At every pipe junction and every change of the diameter/wall thickness ratio, the sound power level is compared with the criterion. Non-symmetrical connections to the at-risk piping will be in danger of cracking at the welds. The animation shown below gives an exaggerated example of a small connection snapping off. As the pipe walls vibrate, the small connection can be seen wiggling back and forth. As shown, there is also a high risk of sparking which may ignite the flammable gas being released and create a catastrophe.
What We Do
The first task is to obtain all of the information for valves that could be at risk. This information includes not only the flow parameters but an accurate description of possible relief scenarios. At that point, we take the predicted sound power levels and propagate them in the downstream piping. This takes into account the attenuation due to distance through the piping, branch connections and expansions. Using this method we can determine how far downstream the piping is at risk. Once we have determined the problems, we can provide recommendations to solve the AIV problems.
Clients and Projects
Mustang Engineering, Hyundai East Area
Calculated AIV for the pressure release piping at a GX NGL Facility
Fluor Transworld Services, RasGas
Calculated AIV for pressure release piping and anti-surge valves for an LPG and LNG plant.
SBM Imodco, Chevron
Calculated AIV for pressure release piping for a LNG plant located on a ship.
Calculated AIV for pressure release piping for two offshore platforms