PIPING NOISE PROBLEMS 2

[ryuchangmyong]

Dear All

Currently, we are now in a pre-commissioning test for Demi-water piping at Power Plant alongwith 8 bar operation pressure of Demi-water pump (Transfering water from Demi-Tank), this piping include restruction orifice at the middle of recirculation pipe from discharging to Demi-Tank, Globe valve and Cone type filter also installed at Dicharge line, However, especially too much noise and vibration occurs at Discharge. Currently I guess that the problems is due to thin pipe line even though required thickness in accordance with ASME B31.1 satisfied.
1) Suction line : A312-TP304, 10" SCH. 10S (Thk 4.19mm)
2) Discharge line : A312-TP304, 8" SCH. 10S (Thk 3.76mm)
3) Recirculation line : A312-TP304, 6" SCH. 10S (Thk 3.4mm)

At first, we guessed that Restruction size and Location occurs noise, so, we have tried and changed orifice hole size and installed Dual orifice, finally we tried to install with Multiple hole type in order to reduce Dynamic flow force through Orifice, However, nothing could we shooting this problems.
So, I strongly believe that thin pipe thickness occurs this noise because in suction line, cosidering NPSHa of 0.5 Bar, there is no expected Pump cavitation or surging, hammering. (See Attached Piping Photo)
Could you have any similar experience such as this kind of trouble.

 

[ryuchangmyong]

Dear Saplanti

This Demi-Pump have a inlet head from Demi Tank (App.18m), so we don't need to consider cavitation due to NPSHa.

 

[saplanti]

Inlet side orifice might be causing large pressure drop, this may be reducing the pressure at the inlet. In case you know the pressure drop at the orifice I can't say more.

 

[BigInch]

Don't get confused. It's not NPSH - pump cavitation. It is liquid flashing across the orifice and recirculation valve due to the large pressure drop. This type of fluid vaporization is sometimes called cavitation. I believe the best term for it here is flashing, specifically to distinguish it from pump cavitation.

 

[casflo]

The cavitation is local flashing that disappears downstream the orifice because the fluid pressure is partially recovered when its velocity decreases from the hole orifice value to the internal pipe value and the pressure is again above the vapor pressure.
The flashing is when you have always the fluid pressure below the vapor pressure. For example if the fluid that passes through the restriction orifice were saturated water, the flashing would be permanent in the orifice and in the downstream pipe.

 

[ryuchangmyong]

Dear ALL

I guess that piping noise is nothing regard to cavitation at downstream of Orifice becasue water temperature is below 30oC and may not be flushing under this condition, Even if not condensated water. When I calculate this fluid Dynamic force, it could be noise through thin wall pipe through orifice.
However, in this kind of condition, we need to consider Throttling fluid passing orifice nozzle. Generally, let me say in this regards of how to occurs flushing downstream of orifice when fluid is passing orifice nozzle, downdtream volumn will be increased(ie, decreased density) so this could be flushing alongwith decreased partial pressure. Enthalpy is constant between front and rear side, therefore, decreased density where downstream fluid will absorb heat passing orifice nozzle, finally this cause of flushing. However, I don't expect this flushing in a condition of low temperature and low pressure drop.

 

[bimr]

Have you considered using a multistage orifice?

http://www.rototherm.co.uk/pdfs/15.pdf

Refer to the linked paper, it has a methodology to predict cavitation.

https://neutrium.net/fluid_flow/cavitation-in-restriction-orifices/

 

[georgeverghese]

Though water temp in the demin tank may be 30degC, since the recycle line is back to pump suction, and there is no consumer, the pumping temp may be much higher. This may also increase the risk of flashing across this globe valve / multi stage orifice at the vena contracta, since vena contracta pressure may be closer to vapor pressure at elevated recycle temp? Is there a temp guage on pump discharge?

 

[ryuchangmyong]

Dear Bimr,

As I mentioned previous, we tried to install multi-stage orifice as well as Double stage also.

 

[gerhardl]

Most of the posts seems to agree that there might be cavitation at the orifice. to me, this seems logical, cavitation is not depending on inlet pressure, but on throttling degree and the then given pressure drop.

If the noise is caused by turbulence and/or pressure drop and cavitation, the originating component (orifice) has to be improved, and if this seems not to help, alterations given in my previous post (support, straight stretches, altering of pipeline layout and changing to other types of flow limiting devices (regulating valves instead of orifices) have to be considered.

When noise in a system occurs by cavitation (and/or turbulence) the whole system (bends/support/resonance) will contribute and may give as much as 50% or more of the noise level.

 

[ryuchangmyong]

Dear ALL

I have one solution to reduce this noise due to thin thickness of S.S. pipe. The way is to install Bending Stiffener ring on piping in a 3 times Diameter(3*D) of Distance, This will reduce vibration and Noise to have reinforcement of pipe's thin thickness.

 

[rconner]

While I do not know exactly what is going on here, I have understood vibration and noise (modal effects?), and maybe particularly in dynamic piping systems with low stiffness and wall thicknesses as you have noted little more than an eighth of an inch thick, can be a complex subject. In a nutshell it would appear such conditions along with infrequent supports and other factors maximize pipe wall/system deflections and movements in response to various acoustical or mechanical loads and "excitations". You may be interested in reading the paper "Vibrations in Reciprocating Machinery and Piping Systems" e.g. from portal

http://www.engdyn.com/images/upload...ng_machinery_and_piping_systems_-_jcw&jdt.pdf

. In looking at the image of the piping without a whole lot of external restraints or supports as Gerhardt notes, the following may be of interest,

"The piping layout and supports should be designed such that the piping mechanical natural frequencies are well above the frequencies of significant pulsation induced forces.” Also, “Long, unsupported spans with low support stiffness could result in low mechanical natural frequencies. Piping spans with unsupported block valves or other heavy masses can also have low response frequencies.”

As you are alas faced with pipe, fittings and valves/control structures etc. that are already there, perhaps some systematic "diagnostic" procedures like mentioned in this paper, or others from these or similar authors, might be helpful in determining if you have a critical problerm that must be corrected, and then in determining effective re-fit measures to make any behavior of concrn more palatable? [As to "orifice plates" as referred to by another, I also read, "Orifice plates can be very effective in attenuating specific acoutical natural frquencies if they are located near the maximum acoutical velocity."

While it is perhaps a terible analogy, there may be reason "reeds" of musical instruments are made as they are, and closer in thickness to the SS piping in your image than that of say some greater thickness legacy metal pipes in such sizes? All have a good weekend.

 

[LittleInch]

ryuchang,

I beginning to wonder why you are on this site as in your last two posts, you have come on with a very fixed idea of what the issue/problem/solution is, most people then tell you, you are not correct or offer alternatives to your course of action and then you ignore them.

With noise it is not easy to pin down sources and emission of noise can occur some distance from the source. Sure, with a thin pipe, it will resonate and transmit noise better than a thick one, but first eliminate the source of the noise, which is undoubtedly your orifice. Then if its still noisy decide if its actually a problem and then acoustically lag the pipe.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[BigInch]

He's the doctor that doesn't know what disease the patient has and carries a big bag of cures, because what he really likes is just to treat the symptoms.

 

[LittleInch]

And then sometimes you find the patient is already dead....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[ryuchangmyong]

Let me give you more clarification on piping noise, I posted this issue regarding for only Restriction orifice and Noise firstly.
And then I tried to reduce noise with change of Orifice in a Single double type (Installed 2 place, Multi hole double type(7 holes one plate installed 2 places) with CFD analysis.
Absolutely, I could decreased noise with Multi hole type, but cost nearly two times of piping construction. I believe that restriction orifice line would be enough less than 5 meter from discharge line, Let me consider weight and cost.
-6" SCH 10S-57kg
-6" SCH, STD (7.1mm)- 132kg
And when we install double stage, additional flange should be increased thin thickness piping and engineering cost of manufacturing would be 2 times of piping cost.

When we use pipe thickness of SCH.10S, as I said weight will be of 57kg, Let me know how about material cost, it would be around USD 200, and multiply by 5 times of this material, construction cost will not be more than USD 1,000.
And compare this to SCH. STD, total construction cost would be USD 2,000.

Finally, considering additional cost of Flange and Engineering cost of multi orifice never less than SCH. STD.
This is why I said we have to consider minimum thickness in piping where restriction orifice should be installed.

I also posted this recommendation in my engineering web site(

http://www.pes21.com),

I'm a professional engineer in mechanical engineering with more than 30 years of experience in static and rotating engineering.

 

[BigInch]

You already spent more than $2000 of our time listening to you discussing it.

 

[bimr]

You should have the process engineer or whoever designed this system review the design.

If you are interested in a fix, the most cost effective fix will not be changing the piping.

With a cost for power of $0.10 /kw hour, that recirculation system will cost around $40,000 per year to operate.

You should really be looking for a method to eliminate the orifice plate as it costs a small fortune to operate it.

 

[ryuchangmyong]

I got a realized that refinement is much more important than technology.