September 2017

Tackling acoustically induced vibration

Paul Emmerson

Paul Emmerson

Multiple excitation sources exist within modern process plants that can cause damage due to vibration related degradation mechanisms. Without identification and control, these can lead to component failure and the associated safety, environmental, business and reputational losses.

Vibration Pe 1

One such issue is acoustically induced vibration (AIV) choked gas flow through pressure reduction devices which can generate high levels of acoustic energy. This can excite the higher frequency pipe shell modes of the downstream piping and potentially lead to excessive cyclic stress at discontinuities such as small bore connections and pipe supports.

Vibration Pe 2
Vibration Pe 3

The vibration team has developed a robust assessment methodology to reduce the risk of AIV failures which encompasses screening assessments through to detailed modelling and analysis to fully quantify the integrity risk. Our expertise and experience can identify and solve AIV issues on new and existing plants.

Choked gas flow is present at multiple areas of modern process plants, including: pressure relief devices; blowdowns; pressure control; restriction orifices and recycle / anti-surge.

Shock noise and turbulent mixing develops high levels of acoustic energy. This is broadband and high frequency and can cause high external sound pressure levels and excitation of the downstream piping higher (shell) modes. This leads to both a health and safety issue because of the excessive noise levels and an integrity issue due to the potential fatigue damage to the piping system.

Vibration Pe 4

Vibration of the wall of the parent piping can also lead to excessive cyclic stress at discontinuities such as small bore connections and welded pipe supports. The increased use of alloy materials such as duplex has led to the use of thinner walled piping with the unfortunate consequence of being more vulnerable to shell mode excitation due to its greater flexibility. Because of the high response frequency (typically 500 – 200 Hz), time to failure can be very short – potentially a one-off event such as activation of a pressure relief valve.

Our solution
AIV is a well-studied phenomenon and basic screening methodologies have been available since the 1980s. However, our engineering team has been involved in the development of more advanced screening assessment techniques that are now published as part of the Energy Institute’s ‘Avoidance of Vibration Induced Fatigue Failure in Process Pipework (AVIFF)’ guidelines. 

Vibration Pe 5

As well as deploying cutting edge data gathering and analysis hardware and software, we have invested in proprietary technology to ensure a class-leading service. Our HAWXEYE tablet based analyser and asset integrity management (AIM) software allows customer personnel to manage the vibration integrity threat on their own assets, accessing remote assistance from Xodus engineers only when required. The Hazardous Area Long Term Monitoring System (HALTMS) allows vibration threat to be quantified over extended periods without the requirement for Xodus personnel to remain on-site.

Vibration Pe 6

We can deploy the optimum engineering techniques to increase understanding and accuracy of analysis while reducing the time and associated cost. As well as proprietary software, such as HAWXEYE, for anomaly management and rapid screening of piping to the Energy Institute AVIFF guidelines, we have experts in the use of:

ANSYS finite element modelling

Siemens STAR-CCM+ computational fluid dynamics

Caesar II static and dynamic pipe stress analysis

PULS acoustic modelling and simulation

OLGA multiphase flow modelling

Solidworks mechanical modelling

Pipenet transient surge analysis

Our vibration engineering division has over 250 years’ combined experience managing vibration related concerns across the spectrum of process industries. We have engineers permanently based in the UK and Middle East providing us with a global reach. Our integrated multi-disciplinary approach allows us to call upon the technical competencies of experts in process and facilities, subsea engineering and technical safety meaning we are leading the way in vibration engineering.