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Velocity limit for Flow Induced Vibration 5

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leostar81457

leostar81457

Mechanical
Mar 22, 2024
4
Hello All,

Can anyone share any experience or reference on what is the maximum velocity that is allowed in a piping, mostly in terms of Flow induced Vibration? I am expecting static analysis will not be affected by the increased velocity, only the dynamic needs to be considered (FIV). This is for both gas and multi-phase fluid (no slug flow as confirmed).

On one of our facility, they increased the production by increasing the velocity. Since it is already in operation with the increased velocity, we just had an assessment by visual inspection, and we measured the vibration frequency and amplitude using accelerometer and plotted the obtained frequency and RMS reading in T7-1 of EIG guidelines and it was found acceptable.

Now the problem is that they want to increase the velocity much further, and they want to know until how much further it can be increased.

I am not doing much of this FIV calculations and I am only aware of the EIG guidelines' LOF factor to assess this. If I use the LOF factor criteria to back calculate the velocity, I believe it will be very conservative.

So I was wondering if anyone has done the same calculation/assessment before; and hoping to hear some of your insight or possible references that you could share.

Thank you all.
 
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OP,
It's a critical subject you have touched. You should be dealing with both AIV and FIV as your process contains gas. I am not sure of your vibration reading locations in your piping system. Usually, AIV vibrations are generated in radial and FIV longitudinal directions, with longer time to fatigue failure. Both mode of vibration will result in fatigue failures in location of stress discontinuities (pipe fittings, bends, reducers, pipe supports etc).

I haven't seen a document that tells about maximum velocity. Crane's TP-410 gives velocity guidance on what typical velocities should be in different piping system.

Unfortunately, almost all piping systems when these are built don't consider a dynamic analysis.

GDD
Canada
 
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There isn't a set fluid velocity range that will initiate vibration, as the fluid is only half the story. Besides the various fluid densities, velocity and flow regime, the other half are the pipe characteristics. Pipe diameters, wall thicknesses, span length and length of adjacent spans and support regidity can all affect the natural frequency of the pipe itself, not to mention the types of centrifugal or recip pumps and compressors and even control valves can also influence the forcing functions.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."
 
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For multiphase process lines, slug flow is usually the cause for high piping stresses that can knock out pipe supports. So tell us how you conclude that slug flow is not a risk here. Large low point piping pockets will almost surely cause slug flow. Fast ramp up from low flow to high flow also cause high velocity liquid slug induced damage on piping. Several hydraulic simulations with different operating scenarios should be carried out and assessed.

The velocity at which AIV becomes a concern on gas lines is much higher and is dependent on gas density, line velocity, pipe wall thickness and maybe some other parameters also. On gas lines, detailed AIV checks typically need only be done when rho-v2 > 200e3, where rho is in kg/m3, v = m/sec. If you dont have company standards with methods for assessing single phase gas line AIV, then an external engineering contractor who has these methods would be required.
 
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AIV may be occurred at the systems or locations as follows:
- Compressor spill back systems,
- Depressurization systems, blowdown/ plant relief systems
- High pressure gas service piping

The AIV issue of the potential piping can be evaluated per Energy Institute Tech module 2.7 and API-521 per piping noise level 155dB limit. Here is a calculation sample of the pipe D/t vs mass flow rate W for reference
IMG_0736_th6iqu.jpg
 
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If they don't destroy the system by erosion first ...

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed
 
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Dear All,

Thank you all for your reply.

It is really critical considering the business management want an immediate response.

Thank you all for the references that you shared, I will look in to it. For the slug flow, the confirmation was taken from the process team to rule out the slug flow as they are not expecting it to happen.

Regarding the AIV assessment from EIG guidelines, will it still be applicable for straight pipes with no pressure reducing device? Like for a header with only normal valves; and no restriction orifice, psv's, control valves, etc; and which the pressure upstream and downstream is the same?

With regards to the vibration reading, it is just a frequency and amplitude reading, not sure if the device (AMS 2140 Machinery Health Analyzer) can tell if it is radial or longitudinal. (attached pic for the readings obtained)

measured_vibration_kic8rs.png
 
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Quote:


"It is really critical considering the business management want an immediate response" .... Ohh .. Oh well then !!

I will notify my FELLOW UNPAID ENG-TIP'S Comerades that they better get Cracking !!!

Damnit, We will GET THOSE LAZY GERIATRICS OUT OF THOSE Wheelchairs and walkers .... An UNKNOWN STRANGER demands Action !

--------------------------------------------------------------------------------------
Payment ? ... Respect ?.. How about even a correctly spelled "PLEASE and THANK YOU" ?

Not from the third world ... if experience is your guide

and for you Retired GEEZER SLUGS !!! .... Put down that applesauce and answer the question !!! --- CHOP CHOP !!

MJCronin
Sr. Process Engineer
 
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[love]

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
 
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Your response on this key subject is rather telling:

"For the slug flow, the confirmation was taken from the process team to rule out the slug flow as they are not expecting it to happen."

Sounds like this is a presumption rather than a quantified conclusion. Its better to challenge this now, before things get set into stone.
 
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MJ, thanks again for fighting the good fight. This time, the OP did actually say "thank you". But I'll put down my applesauce when I'm damn good and ready. I can only add that the OP has data indicating a fairly high frequency pipe rattle (well, at 250 Hz, maybe more of a moan?), and that can only spell hardship if the flow velocity increases - add energy to a system, and you get to find even more vibration modes to dissipate it. That adage, given to me by an old, grey-haired rocket engine designer some 30 years ago, applies as well to this situation.
 
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Apologies for the misunderstanding.

"It is really critical considering the business management want an immediate response" - I wrote this not to force anything out of anyone. Just wanted to share what most workers have to deal with every time regarding the business side, and which most of us all experienced.

Apologies for the wrong spelling or wrong grammar that I might have committed. I thank you all for all the resources and experience you shared.
 
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I do not think there is one single recommended velocity for all possible fluids and pipe configurations. Above a mach number of about 0.2M there is a concern related to noise and vibration, but the pipe geometery , pipe supports, and pipe thickness each plays a role. This is espescially true for the pipe branches that feed the pressure relief valves, but other special piping components, such as check valves or fast acting valves can also initiate vibrations, including "waterhammer " events.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick
 
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@shvet - Energy Institute Guidelines for the avoidance of vibration induced fatigue

The assessment process is split into modules. T.7.1 is one of those modules

There’s a version specific to subsea as well

Steve Jones
Corrosion Management Consultant


All answers are personal opinions only and are in no way connected with any employer.
 
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Leo,

I think you're looking for something that doesn't exist. There is no magic Max V, only an increasing risk. "Guidelines" are exactly that, a GUIDE.

Each system will be very different in terms of supports, stiffness, branches, elbows, valves, flanges etc etc.

Normally the biggest risk is small bore connections or instruments which get fatigued out at the stress concentration p points attached to the pipe which is vibrating.

I don't know enough to say whether your vibration measurements are an issue or not. Modelling of your actual system can provide data, but is takes a long time and then what do you do? Increased production waits for no man.

I would see where your risk is increasing and monitor the pipe, getting some expert advice on this to know where do you need to add supports, reinforce connections, provide more dampening, etc

Erosion is a key issue, especially in multi phase. Examine your system very carefully looking at areas of high wear, tees, elbows, control valves.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
 
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How have you increased velocity (flowrate) added pumps, increased pump speed, reduced static head, Have you monitored pump vibration levels?

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
 
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Hi,
Ask third party, contractor working in the field to perform vibration analysis and provide a report.
My 2 cents
Pierre
 
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