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AIV-FIV Analysis

Acoustical Induced Vibration (AIV) & Flow Induced Vibration (FIV) studies

Vibration fatigue induced by acoustic phenomena and fluid flows is one of the major problems encountered in process piping.

At the initial design stage of a new plant or when modifying an existing one, we offer a 2-step preventive approach to resolve such vibration issues.

This approach involves a qualitative assessment and prioritisation followed by a qualitative assessment which results in practical recommendations.

 

Step 1 – Qualitative assessment & prioritisation

Using a rigorous methodology, we carry out a qualitative assessment of all the main lines in a process system to identify the potential excitation mechanisms. We then produce a report prioritising and identifying the potential excitation mechanisms that need to be quantitatively analysed.

 

Step 2 – Quantitative assessment & Solutions

Main lines: For each excitation mechanism that has been identified as potentially at risk, a quantitative assessment is carried out to determine the likelihood of vibration-induced pipe failure.

The potential excitation mechanisms that can be addressed are:

  • Flow induced turbulence
  • Mechanical excitation
  • Pulsation:

– Reciprocating/Positive displacement pumps and compressors

– Rotating stall

– Flow induced excitation

  • High frequency acoustic excitation
  • Surge/Momentum change due to valve operation
  • Cavitation and Flashing

Small Bore Connection (SBC): For each piping line that has been identified as a potential excitation source for SBC, a quantitative assessment is carried out to determine the likelihood of vibration-induced pipe failure.

 

Intrusive elements: The risk of coincidence between thermowell (or, intrusive elements) vortex shedding excitation frequency and the structural natural frequency is assessed.

 

For each of the above investigated excitation mechanism, when a situation is identified as potentially critical, a corrective action is suggested or an appropriate vibration analysis recommended.

 

Note: The AIV & FIV assessment methodology is based on the “Guideline for the Avoidance of Vibration Induced Fatigue Failure in Process Pipework” published by Energy Institute.

 

Centrifugal compressors coincidence Analysis (AIV & FIV)

We offer a preventive approach to identify and mitigate the risk of Acoustical and Flow induced vibration in centrifugal compressors :

  • Support arrangement is assessed and design optimized against flow induced turbulence and when process condition cannot avoid pulsation generated by rotating stall.
  • A coincidence analysis is carried out for each no-flow side branch that can be subject to flow induced pulsation caused by periodic vortex shedding in T-joint.
  • The fatigue generated by high frequency acoustic phenomena is assessed by calculating the sound power level in each pressure reducing devices (e.g. Valve or high capacity & press. drop devices) and discontinuity.
  • Small bore connection (SBC) design is assessed against potential vibration excitation sources.
  • Coincidence analysis of intrusive elements (or thermowell) structural natural frequency with vortex shedding excitation frequency is carried out.