9 replies to this topic

[anandmach08]

Dear All,

I am involved in checking the existing flare line piping systems in offshore platform for possible AIV (Acoustic Induced Vibration) failures.
Am following EI Guidelines for avoidance of vibration fatigue failures.

I have listed down the process and design data’s across a PSV considered for AIV study.
The 10” PSV whose rated flow rate is 263345 kg/hr (73.15 kg/s).
The Pressure drop is 97.9 bar.
Upstream temperature is 321.26 Kelvin.
Molecular weight of flow fluid 18.6 g/mol.

The sound power level am getting was 175 db.
The safe limit prescribed by guidelines is 155 db.

Since it is existing piping system how I can address the issue?
Is the acoustic silencers are the only way?

Please help me in this issue.

[fallah]

anandmach08,

Seems you are facing with a high frequency vibration in downstream of the PSV vent line due to sonic flow that will lead to Acoustic Induced Vibration, and you might need to apply an absorptive type silencer in order to decrease sound power level down to safe limit.

Fallah

Edited by fallah, 24 March 2012 - 06:01 AM.

[aju_1807]

Having higher SPL does not mean we will have pipe failure. We need to ensure that d/t is sufficient enough and it also depends on the type of joint we have (whether weldolet or sweepolet connection).

Regards,

Ajay S

[Lowflo]

Having higher SPL does not mean we will have pipe failure. We need to ensure that d/t is sufficient enough and it also depends on the type of joint we have (whether weldolet or sweepolet connection).

Regards,

Ajay S

Ajay's comments are right on target. The key point is that the connection to the flare header must be strong enough to resist mechanical failure due to AIV. There are particular fitting and pipe design details that should be used, and there are others that should be avoided. The d/t that Ajay mentions is diameter / thickness ratio which is a key indicator of risk. Any line can be at risk of AIV failure, but those mainly at risk are the small bore pipe connections to a large flare header.

You can find lots of good reference info and guidance related to AIV on the internet.

[anandmach08]

anandmach08,

Seems you are facing with a high frequency vibration in downstream of the PSV vent line due to sonic flow that will lead to Acoustic Induced Vibration, and you might need to apply an absorptive type silencer in order to decrease sound power level down to safe limit.

Fallah

Thanks a lot fallah for ur idea.

[anandmach08]

Having higher SPL does not mean we will have pipe failure. We need to ensure that d/t is sufficient enough and it also depends on the type of joint we have (whether weldolet or sweepolet connection).

Regards,

Ajay S

Thanks Ajay for your suggestion,


Actually my client wants AIV study for all PSV's and impact on pipeworks in its downstream.

They are asking me to follow EI (Energy Institute Guideline) for Avoidance for vibration induced fatigue failure.

The guideline calculates LOF (likelihood of failure) by considering Sound poer level and piping parameters.

It recommends 155 db as safe limit. But for PWL higher than 155 db, the LOF always reaches the value 1, which demands me a corrective actions.

Even if i alter the D/t ratio(higher thickness), it doesn't brings down the LOF from 1. Because the LOF formulations of guidelines are in such a way, that they are heavily influenced by Sound power level (PWL).

Could any one help me with some refernce which quantifies the damage based on D/t.

Thanks in advance for help.

[aju_1807]

Anand,

The pipe failure due AIV is mainly dependent on pipe thickness and type of branch connection we are using. If we use sweepolet connection then we are minimizing the impact of AIV failure to great extent. However, if PWL is >165 than it shall be assessed more critically and FE analysis shall be done.

If its existing set up to minimize the impact (i.e. pipe schedule change, pipe joint), finite element analysis shall be performed and there are several consultant available who performs this kind of study.

rgds,
Aj

[anandmach08]

anandmach08,

Seems you are facing with a high frequency vibration in downstream of the PSV vent line due to sonic flow that will lead to Acoustic Induced Vibration, and you might need to apply an absorptive type silencer in order to decrease sound power level down to safe limit.

Fallah

dear fallah,

The pipeworks am designing are nuder the higher PWL (178 db), as you said i may have to use absorbent silencer.

could you refer any experienced vendors in this regard.

Thanks and Regards,
Anand

If you need any assisstance in performing AIV of FIV studies please contact me (peter.sharpe@petrofac.com). I manage an engineering integrity group of 35 engineers globally and we have over 20 years of experience of undertaking these types of studies for all major oil companies.

Attached Files

•  Acoustic Induced Vibration - Flare Systems.pdf   240.19KB   743 downloads
•  Acoustic Induced Vibration - Flare Systems.pdf   240.19KB   411 downloads
•  Piping Integrity for Oil and Gas Plants.pdf   419.88KB   499 downloads

[anandmach08]

Thanks a lot solentskier,

I have completed my AIV study successfully.
Will contact for any future difficulties.

Regards,
Anand S