AIV Fundamentals
At what pipe diameter and wall thickness should one be concerned about AIV? What is the relevant D/T ratio?
This depends on the Sound Power Level (PWL) produced by the valve. Using the NORSOK L-002 standard, the equation PWL = 173.6 − 0.125 D/t can be used to determine at which D/t ratio AIV becomes a concern for a given PWL.
What is the acceptable frequency range for AIV assessment?
A higher frequency will lead to earlier failure. Note, however, that the noise generally consists of multiple frequencies within a certain range.
Should one be concerned about AIV in multiphase lines?
Yes. As long as sound can propagate through those lines, failure due to AIV can occur.
Does the Joule-Thomson (JT) effect influence the AIV calculation approach?
All flow-related effects are implicitly included in the derivation of the empirical relation for sound power, so the JT effect does not need to be accounted for separately.
PWL Calculations
From which standard does the 6 dB sound reduction originate?
It comes from the paper by Carucci and Mueller, although they describe it as 3 dB for every 50 pipe diameters.
Is this primarily applicable to PSV discharge piping?
Yes. PSVs tend to have large pressure drops or flow rates, but AIV can occur at any valve or pressure-reducing device.
Is the Cw term in the PWL calculation associated with the source itself, or does it only apply when sonic flow occurs downstream of the source?
Some guidelines specify that 6 dB should be added to the calculated power level when sonic conditions are present.
In most cases, design pressure and temperature are available. Should the calculation be performed for the most probable operating conditions? Is using design conditions conservative?
Yes. Using design pressures and flow rates will generally yield conservative results.
Is there an update to the Carucci and Mueller equation?
No update is currently in widespread use, though one would be beneficial.
EI Guideline & LOF Assessment
The EI guideline accounts for vibration dissipation through friction in straight pipes, but does not address dissipation caused by fittings. What approach can be used for fittings in a way that remains compliant with the EI guideline?
The EI guidelines only specify losses in straight pipes. The original source did include sound power losses at sudden expansions — for example, using the equation Latt=2(D2/D1−1) — but this is not included in the guidelines. The conservative and compliant approach is to ignore these effects, which is what the EI guidelines prescribe.
Are results from various AIV/LOF calculation methods different? Which is more conservative and which is more accurate?
The Sound Power Level calculation is identical across all AIV methods. The LOF calculation in the EI Guidelines is generally considered the most accurate.
If the LOF is between 0.5 and 1, should the main line be redesigned?
Yes. If the main line LOF falls between 0.5 and 1, the main line should be redesigned.
Where can definitions of "discontinuities" be found?
Discontinuities refer to all locations where something is welded onto the pipeline, such as tees. In BOSfluids, these must be specified manually.
Can LOF calculations be shown at each discontinuity?
Yes. You must specify the discontinuities for which you would like the LOF to be calculated.
The NORSOK standard is more liberal than EI. In which countries is it used, and can it be proposed to a client instead of EI if the system fails per the EI guideline?
NORSOK is primarily used in the Norwegian petroleum industry. Whether it can be proposed as an alternative to EI depends on the client’s requirements and applicable project standards.
Mitigation Measures
Are clamped supports typically recommended instead of welded supports?
Yes. Clamped supports are a recognised mitigation option and are unlikely to fail due to AIV.
Is there a way to estimate how much PWL can be reduced by adding stiffeners?
Stiffeners do not reduce the PWL; they mitigate the consequences. A detailed analysis is required to verify whether the stiffeners prevent fatigue failure at the same PWL.
If pressure reduction and low-noise trim valves are not feasible, the remaining options are increasing pipe wall thickness or adding supports to small-bore connections. Can BOSfluids recommend whether a local wall thickness increase is needed?
Increasing wall thickness is indeed one of the applicable mitigations. The most suitable option depends on the specific situation.
Could orifice plates be added in BOSfluids to reduce SPL?
Orifice plates introduce an additional source of Sound Power. They can be included in BOSfluids, but doing so will increase the SPL rather than reduce it.
How about changing the fitting type for small-bore connections?
Yes, that could be a valid mitigation option.
How about using encirclement pads?
Yes. Encirclement pads convert the discontinuity into a circumferential discontinuity and can be an effective mitigation option.
Can inline silencers be used in any situation, or are there specific conditions that apply?
Per Carucci and Mueller: when inline silencers are used, a detailed review of their design should be performed, covering weld details, thermal expansion, and pressure. Since the silencer must itself withstand acoustic fatigue, the design and fabrication of internal components — especially on the inlet side — should reflect a high standard of mechanical integrity.
Can acoustic insulation reduce LOF?
No. Acoustic insulation only prevents noise from propagating to the surroundings; it does not reduce the Sound Power Level inside the piping. It may even increase internal SPL, as less energy is dissipated to the environment.
BOSfluids Software Capabilities
Does BOSfluids consider local PWL attenuation due to pipe reductions and bends?
Diameter changes are accounted for by calculating the 6 dB per 100 pipe diameter attenuation separately for each section with the same diameter. Bends are treated the same as straight pipe sections, which yields conservative SPL results.
Can this analysis be performed using the BOS B31 program within the PRG suite, or is BOSfluids required?
The AIV calculation feature is not available in BOS B31. However, a steady-state version of BOSfluids is available with a reduced feature set that does include AIV calculations.
Does the software also calculate branch tuning?
If branch tuning refers to periodic flow-induced excitation, then BOSpulse — a separate Dynaflow software package — should be used for that purpose
Does the software locally identify sections that require qualification for acoustic fatigue assessment?
Yes. The Sound Power data set can be used to identify sections where the Sound Power Level exceeds 150 dB.
Can the software consider angled branch connections to reduce noise?
No. BOSfluids follows the calculation rules specified in the EI guidelines, which do not address angled branch connections.
Can BOSfluids perform calculations in accordance with API 618?
No, but BOSpulse can perform API 618 calculations.
How can BOSfluids model a strainer (perforated-sheet filter) and the noise induced by fluid passing through it?
Strainers can be modelled using an orifice element. The source Sound Power Level is then calculated automatically.
Does BOSfluids provide interfaces with other software such as CAESAR II or FEA tools? How is piping imported from CAESAR II?
Yes. BOSfluids supports import and export interfaces with CAESAR II via a CAESAR II neutral file, among other tools.
Can simulation reports be exported in formats such as CSV, XLSX, or TXT?
Yes. Results can be exported to CSV or TXT, and report contents can be copied and pasted directly into Excel.
How does BOSfluids determine the SFF value when calculating PWL?
BOSfluids adds 6 dB when the flow through the orifice or valve is sonic.
Can a CAESAR II model be imported into BOSfluids to calculate PWL? Does BOSfluids apply the 3 dB reduction per 50 pipe diameters at each discontinuity?
Yes on both counts. CAESAR II neutral files can be imported, and the 3 dB reduction per 50 pipe diameters is applied in the calculations.