Is Flushing Necessary When Pump is Off?

Clearly, flushing is necessary.

Can you give me the logic plz? Thanks

Yep. The pump internals are rotten in 600 hours.

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?

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

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?

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.

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?

no chance :) We will have to consider alternative material

Ceramics would be a possibility.

As would glass.

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.....

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

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?

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

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?

don't flush with air I think...

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

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

Or leave it full of the flushing fluid.

Where is the Process Engineer in all this mess?

GA.. yes a diaphram pump would be advantageous here

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

Cheers

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?

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.

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.

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

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

http://eccentricpumps.com/index.php

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

That's a bit big for a peristaltic pump!

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

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.

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.

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,

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

Acid is leaching the slurry at high pressure,

So why not neutralise the pH before pumping it?

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

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

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.

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.

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

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.

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:

• Ceramic pump from, eg, Friatec-Rheinhuette: http://www.friatec-rheinhutte.com/ceramic-pumps.html
• Pump in SilCast from Duechting (they have been using duplex/superduplex for many years, but developed this for applications where duplex isn't good enough): http://duchting.com/en/siccast.html