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PIPING NOISE PROBLEMS
2

PIPING NOISE PROBLEMS

PIPING NOISE PROBLEMS

(OP)
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.

RE: PIPING NOISE PROBLEMS

You picture is missing. Maybe you can provide a sketch?

RE: PIPING NOISE PROBLEMS

Maybe the flow of demin water to user is low; so recirculation rate is high and recirculation line velocity is too high ? At max recirc flow (which should be total pumping rate when demand is zero), velocity should not be more than 3-4m/sec. Meanwhile, better engg practice is to return the recirc demin water back to tank and not to suction line. Noise can also be generated at the globe valve if it is pinching down a lot at low demand. Why do you have a globe valve on the discharge line?

RE: PIPING NOISE PROBLEMS

Is it possible that noise is related to some trapped air, somewhere in the line?
As bimr said, a sketch will be helpful.

RE: PIPING NOISE PROBLEMS

(OP)
Dear ALL

Total flow rate is 170m^3/h(App. 30%) into Recirculation line from Discharge rate, and Globe v/v control this Rec. rate, Let me show you picture as attached. Recirculation orifice should be used in order to keep Discharge pressure, otherwise, Discharge pressure will be decreased.

RE: PIPING NOISE PROBLEMS

(OP)
As for pipe minimum thickness, especially stainless Steel in case of thin thickness and restriction orifice installed, it should be considered with pipe noise for velocity of orifice flow.

RE: PIPING NOISE PROBLEMS

You are showing the recirculation piping with a flow of 170 m/h. That provides a velocity of 8.5 ft/sec which is acceptable.

However, the 54 mm orifice plate is extremely small.

Do you have flow meters on the piping? The head loss across the 54 mm orifice plate should be about 60 m to pass the 170m/h flow.

You need to determine the flow in the pipe sections and where the pump is operating on the pump curve.

The noise is most likely generated at the orifice plate, valve, and pump. You should reevaluate the pump recirculation design. It does not look feasible. With a cost for power of $0.10 /kw hour, that recirculation system will cost around $40,000 per year to operate.

What type of plant is this? What is the pressure requirement for the demin water?

RE: PIPING NOISE PROBLEMS

(OP)
Dear Bimr

I also agree with your orifice required hole diameter, However, What I'm talking is about thin stainless steel pipe may cause piping noise rather than restriction orifice.
We already have changed RO hole size and experience to install Dual type as well, multi type orifice.
However, nevertheless that noise could not be able to remove as to criterial.
So I strong believe that thin S.S pipe is the reason for this noise.

RE: PIPING NOISE PROBLEMS

When you are in precomm mode, demin water flow to user may be zero (?), and all flow may be going through recirc ( 170 / 0.3 = 570m3/hr), so a lot of the noise may be from the globe valve, and some from high velocity at 8.5 / 0.3 = 29fps = 9m/sec ?

RE: PIPING NOISE PROBLEMS

(OP)
Dear sir,

As I noticed previous giving information, Recircultaion of flow rate(170m^3/h) is about 30% of total rate.

RE: PIPING NOISE PROBLEMS

Large pressure drop may cause flashing through the orifice.

RE: PIPING NOISE PROBLEMS

I agree that the thin walled pipe may have more noise, but don't think that it is the main problem.

One fix for noise is to insulate the piping. Have you considered insulation?

RE: PIPING NOISE PROBLEMS

(OP)

Dear Bimr

No piping insulation is doned for Demi-water piping.

RE: PIPING NOISE PROBLEMS

Okay, in that case pls check that the Q-h curve is not flat around the operating region.

RE: PIPING NOISE PROBLEMS

(OP)
Dear ALL

This paper has been prepared by PES-ENG(http://www.pes21.com) for the guidance in decision of required thickness for piping design based on related CODE rule and industrial practice. Especially, this paper would like to indicate additional consideration in stage of minimum required thickness particularly, when Stainless Steel is to be selected rather than Carbon steel because relatively Stainless Steel thickness more thinner than that of Carbon steel. Those by, this may cause noise and vibration on piping line in case of restriction orifice installed at recirculation line due to pressure drop at back side of orifice, which means that front side cause back pressure where have to be keeping discharge pressure through Pump discharge pressure.
Therefore, the velocity will be increased as much as decreased pressure at rear side of orifice. Generally this velocity would be one of the reason cause of noise and vibration in piping line.
Specially, in case of thin thickness of stainless steel pipe would cause noise and vibration due to dynamic force of fluid velocity in case of which is passing through Elbow. Herewith, the dynamic force may be calculated as F={(P*A)^2+(eQV)^2}^0.5).
Even though, required minimum thickness should consider not only various external force but also additional thickness at the time of thickness selection in accordance with Code rule such as ASME B31.1 or EN13480-3, As well, where existing Fluid dynamic force such as Elbow flow would not be easy to apply to optimum thickness selection.

RE: PIPING NOISE PROBLEMS

If the restriction orifice is close to the tank and has 60m of pressure drop, probably there is cavitation in the orifice. If the orifice has cavitation also has noise. The noise is transmitted outside the pipe and the pipe wall reduces the noise because it produces tranamission loss. This noise reduction increases with the pipe thickness.
In any case if you have cavitation you must eliminate it to eliminate the noise.
You say that have changed the orifice plate by two in series or by a multi-hole plate. With a total pressure drop of 60m and with no appreciable back pressure in the orifice, that is the orifice outlet pressure similar to the tank pressure, probably you need an orifice with more than 2 stages to eliminate the cavitation and the noise.
casflo

RE: PIPING NOISE PROBLEMS


In addition to look thoroughly into the flow over the restriction orifice, which probably is (one of ?) the main contribution(s?)of noise, it could be sensible to look into other possible additional causes.

Question: from the picture it seems that this is one of several parallell constructions. If yes, is the problem and noise-level and operational data equal for all?

In my opinion the piping construction seems to be mostly self-bearing, lacking support near this (now problematic) construction. Perhaps extra support and extra fundaments could improve the noise level or at least alter the resonance characteristic of the system. Sharp 90 deg. bends, T's and short straight stretches do not improve the noise level.

The globevalve might also contribute to the noise, as well as the distance between the valve and orifice.

Replace the globevalve with suitable regulation valve and remove orifice restriction?

RE: PIPING NOISE PROBLEMS

Regarding: "No piping insulation is done for Demi-water piping."

The point being made is that you may add insulation to the piping to reduce the noise.

RE: PIPING NOISE PROBLEMS

(OP)
Dear gerhardl

This pump is parallel installed for 3 sets, noise is nearly same for each single set.

RE: PIPING NOISE PROBLEMS

You need to check the pressure at the inlet of the pumps. Noise may be generated by the high cavitation due to the low pressure.

RE: PIPING NOISE PROBLEMS

(OP)
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.

RE: PIPING NOISE PROBLEMS

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.

RE: PIPING NOISE PROBLEMS

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.

RE: PIPING NOISE PROBLEMS

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.

RE: PIPING NOISE PROBLEMS

(OP)
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.

RE: PIPING NOISE PROBLEMS

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?

RE: PIPING NOISE PROBLEMS

(OP)
Dear Bimr,

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

RE: PIPING NOISE PROBLEMS


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.

RE: PIPING NOISE PROBLEMS

(OP)
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.

RE: PIPING NOISE PROBLEMS

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/uploads/68-vibration_... . 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.

RE: PIPING NOISE PROBLEMS

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.

RE: PIPING NOISE PROBLEMS

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.

RE: PIPING NOISE PROBLEMS

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.

RE: PIPING NOISE PROBLEMS

(OP)
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.

RE: PIPING NOISE PROBLEMS

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

RE: PIPING NOISE PROBLEMS

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.

RE: PIPING NOISE PROBLEMS

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

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