Near pressure-reducing devices, such as valves, installed in gas or multiphase systems, acoustic-induced vibrations can occur. When this happens, the phenomenon may cause fatigue failure in a matter of minutes or hours. This phenomenon exists in the high-frequency domain, typically between 300 and 2500 Hz. For thin-walled piping components, this can become a major challenge when the shell wall frequencies align with this phenomenon.

To avoid AIV, we can apply the Energy Institute’s Guidelines (EI), at least as a screening method. EI provides formulas to calculate the sound power level (SPL), which is important for the initial screening. If the SPL meets the established criteria, no further action is required, and everyone is happy.

If a component shows a too-high SPL, then the 3D piping model will be reviewed to determine if there are any critical piping components (such as weld-o-lets, instrumentation, welded supports, etc.) in the area. The SPL will be adjusted based on the distance from the SPL source to the component.

If the component still doesn’t meet the acceptance criteria, which is where the Energy Institute’s guidance stops, what do you do? There’s no clear guidance. There’s one option, albeit a complicated one: create an acoustic model and couple it with a mechanical finite element model. The acoustic model is based on the SPL calculated manually, and the goal is to ensure that the dynamic stress range is less than the endurance limit of the material, including all safety and stress concentration factors (well, not all welds exhibit endurance limit plateau, but this is a topic for another day).