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Is Flushing Necessary When Pump is Off?

08/31/2011 4:16 AM

Hi,

We are facing frequent failure of centrifugal pump dealing with dense slurry, wet end parts rotten after 600 hours. Pur pump specialist told me there shouldn't be any slurry inside when its off. Does that make any sense? Pump material is supposed to be dealing with slurry so whether its off or on, it doesn't matter. please shre your experience

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#1

Re: Is flushing necessary when pump is off?

08/31/2011 4:19 AM

Clearly, flushing is necessary.

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#2
In reply to #1

Re: Is flushing necessary when pump is off?

08/31/2011 4:24 AM

Can you give me the logic plz? Thanks

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#3
In reply to #2

Re: Is flushing necessary when pump is off?

08/31/2011 4:30 AM

Yep. The pump internals are rotten in 600 hours.

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#4

Re: Is flushing necessary when pump is off?

08/31/2011 4:32 AM

Can you tell how the pump is failing? Is the slurry corrosive or abrasive? Or, when the pump is idle, does the slurry "cake" in the pump and simply clog it?

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#5
In reply to #4

Re: Is flushing necessary when pump is off?

08/31/2011 4:37 AM

Its corroded badly. Slurry is corrosive and abrasive, high chloride, Sulphuric Acid.

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#6
In reply to #5

Re: Is flushing necessary when pump is off?

08/31/2011 4:41 AM

Then the wetted materials of the pump are incorrectly selected.

  • What opportunities are there to change the wet end for more appropriate materials?
  • What opportunities are there to change the process to produce a less aggressive fluid for pumping?
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#7
In reply to #6

Re: Is flushing necessary when pump is off?

08/31/2011 4:43 AM

The material is duplex C26 and I'm already in the process of upgrading it to C19 Super duplex but still trying to determine the reason of failure.

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#8
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Re: Is flushing necessary when pump is off?

08/31/2011 4:48 AM

The reason for the failures is that the wetted materials of the pump were incorrectly selected and the pump has not been flushed.

What scope is there to change the process so that less aggressive fluids are present?

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#9
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Re: Is flushing necessary when pump is off?

08/31/2011 4:54 AM

no chance :) We will have to consider alternative material

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#10
In reply to #9

Re: Is flushing necessary when pump is off?

08/31/2011 5:13 AM

Ceramics would be a possibility.

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#12
In reply to #9

Re: Is flushing necessary when pump is off?

08/31/2011 10:23 AM

As would glass.

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#13
In reply to #5

Re: Is flushing necessary when pump is off?

08/31/2011 7:05 PM

High chlorides and sulfuric acid ???...... sounds like you have a "worst case" witches brew to pump!!!

What is your flow rate, temperature and pressure ?

What materials are being used for all of the upstream piping, tanks etc ?

I suggest you consider a pump made from the highly corrosion resistant (and highly expensive) "bad-boy" of nickel alloys........ C276

Also set up a flushing sequence in your operations logic.

If your temperature is not too high, you might consider a PTFE lined pump.

Consider cooling your witches brew before pumping.....

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#14
In reply to #13

Re: Is flushing necessary when pump is off?

08/31/2011 8:28 PM

The temperature is 90degC. We are going to try C19 and will instroduce flushing sequence

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#11

Re: Is flushing necessary when pump is off?

08/31/2011 5:46 AM

600 hours is about 4 weeks.

  • Is this a recent problem or has it been a repeating problem every four weeks or so since the process was first commissioned?
  • If it is a recent problem, what else may have changed to provoke the problem?
  • What is the Process Engineer's input on the problem?
  • Is the process running as originally commissioned or has there been a change that has provoked the problem? If so, then what?
  • What scope is there to take the process back to the as-commissioned state and re-start it from there?
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#15

Re: Is Flushing Necessary When Pump is Off?

08/31/2011 10:27 PM

it is easier to flush when it is off...

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#16
In reply to #15

Re: Is Flushing Necessary When Pump is Off?

08/31/2011 10:45 PM

Yes, but there are concerns like if we flush out, it will fill with Air and may cause line hammer. So what would be the remedy of this problem?

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#17
In reply to #16

Re: Is Flushing Necessary When Pump is Off?

08/31/2011 10:56 PM

don't flush with air I think...

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#18
In reply to #17

Re: Is Flushing Necessary When Pump is Off?

08/31/2011 11:40 PM

Nice suggestion :) So either we need to flush and dont worry about Air filling in or leave it as it is.

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#21
In reply to #18

Re: Is Flushing Necessary When Pump is Off?

09/01/2011 12:05 AM

It sounds like the pump materials have been chosen to deal with the corrosive fluid, they cannot tolerate the grit. What you do is buy a pressurized labyrinth gland into which you pump a slow steady amount of the fluid (with no solid). The outer seal keeps it from leaking out and the flow into the labyrinth prevents any grit from getting into the bearing. This may be the flushing spoken of? A simple flush with not exclude grit from the bearings

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#25
In reply to #18

Re: Is Flushing Necessary When Pump is Off?

09/01/2011 3:57 AM

Or leave it full of the flushing fluid.

Where is the Process Engineer in all this mess?

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#19

Re: Is Flushing Necessary When Pump is Off?

08/31/2011 11:59 PM

my 10 cents ...

Agree, the current material selection is poor. High Chloride, low pH fluid is difficult to pump if it is also abrasive (assuming slurry means it is abrasive).

Even a higher grade of duplex, may not solve your problem. Nor introducing a flush, once high chlorides cause pitting, they are difficult to stop (even with flushing).

Can I suggest you consider other pump materials, and pumping styles.

I have to question why you are pumping a dense slurry using a centrifical pump. I believe something like a positive displacement pump might have been a better selection.

For example, a pneumatic diaphram pump, can be manufactured from reistant materials, and can handle quite dense solids. The abrasive material causes wear on parts that are designed for frequent replacement.

Just a suggestion, hope it helps.

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#22
In reply to #19

Re: Is Flushing Necessary When Pump is Off?

09/01/2011 12:09 AM

GA.. yes a diaphram pump would be advantageous here

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#23
In reply to #19

Re: Is Flushing Necessary When Pump is Off?

09/01/2011 12:44 AM

This is just one supplier of pneumatic diaphram pump, of materials resistant to acid/high chlorides.

http://www.verder.com/Liquidshandling/Pumps/Double_diaphragm_pumps/Verderair_Non_Metallic

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#20

Re: Is Flushing Necessary When Pump is Off?

09/01/2011 12:03 AM

you need to look at the material the pump is made of, ask your supplier for a different material like high grade stainless steel for the WHOLE pump NOT just the impellers, if you are pumping acid.

As for flushing, great idea, back flush with water, providing you do not have a NRV at the bottom or in the line, and if that fails think about after each pumping operation lift the pump out of the mix and wash/back flush.

As for your comment of air in the line, nothing to worry about for both the pump and the line, as the air what little there will be will quickly be compressed in the line and with a centrifugal pump it does not need priming once submerged.

Ceramics have been suggested,but if you have dense slurry, then that material might prove to be fragile if dealing with heavy solids and large particles.

What exactly is failing in the pump, the bearings, the impellers, the defusers or some other part, how deeply submerged is the pump, and can it be pulled out/up for cleaning, is the pumping process continuous?

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#24
In reply to #20

Re: Is Flushing Necessary When Pump is Off?

09/01/2011 3:55 AM

What about peristaltic pump for this solution? You can freely choose the flexible tube out of materials that are tolerant for most wigorious fluids and it tolerates solid particles of quit large dimension as well. Units are available for most capasities.

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#26
In reply to #24

Re: Is Flushing Necessary When Pump is Off?

09/01/2011 3:59 AM

Good bet, however the original poster has stated nothing about heads and florates.

They may well appear before the remaining readers get fed up with this thread.

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#27
In reply to #26

Re: Is Flushing Necessary When Pump is Off?

09/01/2011 4:19 AM

had enuf now..NEXT!!

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#28
In reply to #24

Re: Is Flushing Necessary When Pump is Off?

09/01/2011 4:21 AM

It may a be a good idea..how about a link to date/info on these pumps for all AND the OP to read??

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#29
In reply to #28

Re: Is Flushing Necessary When Pump is Off?

09/01/2011 5:03 AM

info and manufacturers for peristaltic pumping units are easily found through google, but here is one of them:

http://eccentricpumps.com/index.php

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#30
In reply to #28

Re: Is Flushing Necessary When Pump is Off?

09/01/2011 5:07 AM

Yes, the flow rate is 245 m3/hr and density is 1400kg/m3. Process Engineers have also started looking into and flishing seems to be the available solution in our case, defnitiely we will change the material to Super Duplex but implement flushing as a precaution

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#31
In reply to #30

Re: Is Flushing Necessary When Pump is Off?

09/01/2011 8:06 AM

That's a bit big for a peristaltic pump!

Come on, original poster. Share the delivery pressure as well. It won't hurt.

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#32
In reply to #30

Re: Is Flushing Necessary When Pump is Off?

09/01/2011 8:21 AM

Super duplex pump materials may or may not be your best choice...

Flushing, of course, would help any material

The point I was trying to make above is that your pumpage is the "worst of the worst"......acid, chlorides and abrasive slurry.

I suggest that you consider a study involving corrosion coupons (with different candidate materials) in the pumped stream. ASTM has much information about this.

You did not answer my earlier question.

Don't you have corrosion problems upstream of the pump?

Isn't there a tank/pipe/bin or a something leaking upstream ?

What are the MOCs upstream ??

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#33
In reply to #32

Re: Is Flushing Necessary When Pump is Off?

09/01/2011 8:25 AM

Good point. The pump needs to be of similar materials to the pipelines both sides of it as a first choice, as the pipeline materials haven't seen the same corrosion in 600 hours - unless the original poster has not disclosed the fact.

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#35
In reply to #33

Re: Is Flushing Necessary When Pump is Off?

09/01/2011 9:15 AM

Connecting low direct current to the wet end of the pump with the other electrode in the slurry - anode or cathode depending of the chemical consistense of the slurry - gives you one possibility to move the corrosion from the pump to the electrode, which ought to be cheaper and easier to change. The material for the electrode must be optimized by the slurry.

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#39
In reply to #32

Re: Is Flushing Necessary When Pump is Off?

09/01/2011 6:02 PM

These are the only pumps after adding Sulphuric Acid to slurry, after that, we pump the slurry to our Neutralizer and it doesn't cause any problem over there. Vessel material where Suphuric acid adds in Slurry is Ceramic lines, piping is mostly titanium and SAF 2507 (Its Super duplex), Discharge pressure is 247kpa,solid sp gravity 2.68, PH is 0-1, temp is around 90,

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#40
In reply to #39

Re: Is Flushing Necessary When Pump is Off?

09/02/2011 3:53 AM

What does the sulphuric acid do, apart from add to the corrosion problems, then?

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#41
In reply to #40

Re: Is Flushing Necessary When Pump is Off?

09/02/2011 3:55 AM

Acid is leaching the slurry at high pressure,

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#42
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Re: Is Flushing Necessary When Pump is Off?

09/02/2011 3:56 AM

So why not neutralise the pH before pumping it?

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#43
In reply to #42

Re: Is Flushing Necessary When Pump is Off?

09/02/2011 4:03 AM

We do, we pump the slurry to the neutralization pit after this pump but they are 250m away from it and we dont have any plans to setup a system to neutralize them before this pump

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#44
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Re: Is Flushing Necessary When Pump is Off?

09/02/2011 5:11 AM

There is scope for a Process Engineer to look at the operation to see what could be done to improve it.

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#45
In reply to #30

Re: Is Flushing Necessary When Pump is Off?

09/06/2011 6:46 AM

Many experts have voted in favour of flushing, I'm also one of them. I believe that over 50% of your problem will just evaporate after adding flushing operation before or after stopping the pump, without changing any other item. It means you may get over 1200 hrs life. Why because, (1) rate of corrosion is many times faster in standstill corrosive fluid, (2) when you start next, the settled solid particles at bottom cause havoc while accelerating, resulting extensive damage due to erosion on moving parts, seals, volute etc.

Your process engineer is the best person to define a proper flushing method suiting to your operation. If flushing fluid is water, then will the little addition of water in process fluid cause any process problem in down stream? If no effect, you can programme like this:

Water lines with automatic on/off valves are to be connected with 'T' pipes (at least half the size of process fluid) at suction and discharge of pump. When you stop pump, first its suction valve closes and water valve at suction side opens. After 5 seconds (with timer) pump discharge valve closes and water valve opens at discharge side. After 10 seconds (with timer since stopping command) pump stops and both water valves closes. This method will address environmental issues also by not allowing dangerous process fluid to come out during flushing.

This is an example, you can select flushing fluid, flushing time, line sizes etc. which best suits to your process. Even you can adopt stationary flushing after stopping the pump, but pump rotor is to be rotated for better flushing.

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#34

Re: Is Flushing Necessary When Pump is Off?

09/01/2011 9:03 AM

Yes, it is necessary but, I want to know what is the chemical properties of that slurry.we use 4adpa in our plant when it came it atmosphere it is sticky once it is hard it need heating.so, it may be something like that in urs chemical.

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#36

Re: Is Flushing Necessary When Pump is Off?

09/01/2011 9:51 AM

Dear Mr. sam12,

Pl. inform what type of FAILURE you are facing. Is it ELECTRICAL FAILURE ALSO EXPERIENCED.? What is the consistency of the slurry ? What is the viscosity ? What is the pH ? and what is the material for pump impeller and pump body ? whether rubber lining or glass lining is required ? all these details are required for understanding the problem and examined.

When the pump is stopped, the slurry tends to settle down at the bottom and once settled you can not start the pump and it is to be cleard physically. If you try to start the pump, it will not start, and the starter will trip or fuses may blow-out.

Thanks.

RAJESWARI.

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#37

Re: Is Flushing Necessary When Pump is Off?

09/01/2011 1:48 PM

As everyone said, with that product FLUSH the system including the pump, else your corrosion problems will be in the pipes, vessels, and pumps.

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#38

Re: Is Flushing Necessary When Pump is Off?

09/01/2011 4:21 PM

We use a Moyno pump for a corrosive slurry.

http://www.moyno.com/meteringpumps.html

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#46

Re: Is Flushing Necessary When Pump is Off?

09/06/2011 12:29 PM

As some people have pointed out, 600 hours is a very short life and there is a flaw (in my opinion it sounds like ill suited materials not the operation of it).

I'd suggest scrapping the centrifugal pumps and the pump rep you have now (and seeing that you're replacing them every 600 hours that shouldn't be painful except to the salesman who is making a good profit off you). The last plant I worked for used hose pumps to transfer chemicals. They're great in terms of reliability and will work fine for an acid slurry.

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#47

Re: Is Flushing Necessary When Pump is Off?

09/06/2011 1:42 PM

As MJCronin says, this is a right witches brew, with corrosion, abrasion, attack from chlorides, and the temperature of 90degC doesn't help. Flushing the pump might help matters, but ideally you should have the most suitable pump type in the most compatible materials.

Normally alternative pump technologies would be a good consideration, but perhaps not in this instance. I am not aware of any diaphragm or peristaltic pumps that would come close to the 245 m3/hr flowrate required, they usually don't go much beyond 90 m3/hr. Progressive cavity pumps can easily meet the flowrate, but I would still be concerned about the materials. It's not just the rotor and stator that need to be compatible as wetted parts also include the casing, shaft and joint sleeves.

I am not convinced that Superduplex will be that much better than Duplex ss. The relatively elevated temperature will rule out certain non-metallics, linings, coatings, etc that could otherwise be considered.

Two possibilities that might be expensive, but certainly worth considering:

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