Pump Impeller

[Giray Veli]

Hi everyone, we are using this pump to transfer sulphuric acid. Our concentration is %85 and this impeller MOC is PVDF. This impeller got some damage but we don’t know the reason. There is no particule on fluid it is clean and closed system. I have faced this problem 3 times and I want to know reason to solve problem. I have calculated the NPSHa and it is almost 6m, NPSHr is 3m hence there is no cavitation. What can be the reason could u help me?

 

[Artisi]

Have the previous failure looked to be similar?
A few more photos at better quality of the failure site, the impeller hub and along the periphery of the impeller.
There are areas that look like damage but unclear in the current photo.

 

[Giray Veli]

Have the previous failure looked to be similar?
A few more photos at better quality of the failure site, the impeller hub and along the periphery of the impeller.
There are areas that look like damage but unclear in the current photo.

We have 2 pump and one of standby, both pump’s impellers got damaged and this is the standby pumps impeller photos and the cracks part is same but, the body of impeller has wave shape I don’t know why. I think can not be appropriate for fluid but the vendor said it is manufactured for sulphuric acid.

 

[MintJulep]

Have you considered that the material might not be PVDF.

A different material provided by mistake.

Counterfeit material.

 

[Giray Veli]

Have you considered that the material might not be PVDF.

A different material provided by mistake.

Counterfeit material.

I have used 3 different pump in here and all pump’s impeller got the damaged. We have bought all pumps a reliable vendor.

 

[Artisi]

Temperature problem?

 

[pierreick]

Hi,
Consider the resources attached to support your work.
Who are the reputable suppliers? Can you share their names and proposals for your application?
From the documents shared you will see that "PVDF" is not the recommended material, prone to rupture, lack of mechanical strength?
Alloy 20 or Steel coated Teflon could be a better option.

BTW, no indication about the temperature.

Pierre

 

[goutam_freelance]

he body of impeller has wave shape I don’t know why

It could be due to fatigue failure arising from fluid dynamic forces. Please check the type of crack.

It is better to have an impeller with a smooth streamline flow.

 

[innovativepumps]

Although a sealless positive displacement pump guy, I have seen my share of damaged impellers; definitely need to double check your temperature to ensure you do not have an upset condition and in such an upset condition you might also have insufficient NPSHa, so you end-up with both temperature and cavitation stress on the impeller. Also, is it possible that there are any solids getting into the pump? It is very difficult to thoroughly trouble-shoot a pump application in a forum, here's how I try to guide the conversation: 1st, did the application ever work correctly - without such damage? If so, what has changed since then? If this has been an issue from day 1, it is likely not a pump problem as much as an inlet condition issue. Transient upset conditions such as a clogged inlet filter, miscalculation of NPSHa, temperature upsets etc... the material is reacting physically and perhaps chemically to your application. Hopefully your vendor will take the time to walk through your system and provide ideas to aid with identifying the root cause of damage. It might be that a centrifugal pump is not the best type for your application.

 

[Artisi]

Although a sealless positive displacement pump guy, I have seen my share of damaged impellers; definitely need to double check your temperature to ensure you do not have an upset condition and in such an upset condition you might also have insufficient NPSHa, so you end-up with both temperature and cavitation stress on the impeller. Also, is it possible that there are any solids getting into the pump? It is very difficult to thoroughly trouble-shoot a pump application in a forum, here's how I try to guide the conversation: 1st, did the application ever work correctly - without such damage? If so, what has changed since then? If this has been an issue from day 1, it is likely not a pump problem as much as an inlet condition issue. Transient upset conditions such as a clogged inlet filter, miscalculation of NPSHa, temperature upsets etc... the material is reacting physically and perhaps chemically to your application. Hopefully your vendor will take the time to walk through your system and provide ideas to aid with identifying the root cause of damage. It might be that a centrifugal pump is not the best type for your application.

Sealless positive displacement pump????????

 

[innovativepumps]

Sealless positive displacement pump????????

Yes. Typically used for pressures >30 PSIG and up to maximums 3500+PSIG depending upon model. Flow range from fractions GPH conforming to API 675 metering pump standards up to 330 GPM for the largest size. Can operate dry, self-prime, handle temperatures in the 200F range and since they do not have dynamic seals they pump reclaimed/abrasive/non-librication liquids reliably.

 

[EdStainless]

Either the plastic is softening because of high temp or it is suffering chemical attack.
You can find a lab that does plastic work and them test a used impeller to see if it is attack or not.
Here is a list of metals:
Tantalum, Gold, Platinum, Impervious graphite and lead up to 80°C (176°F) and 96% sulfuric, Glass
High-silicon cast iron (14.5% Si)
Hastelloy® B, B-2, and D, not up to BP 20Cb3 up to 66°C (150°F)
CW12MW and 2507 also are used.

If your impeller is actually PVDF then I suspect that is a poor grade or that the injection is very poorly controlled.
ECTFE and ETFE are also options as well as the thermoset Furane.

 

[LittleInch]

Looks to me like the material is softening and then tearing. Is there a tear on that first photo at the next impellor down from the damaged one?

Also NPHR is NOT a cavitation limit. It is a point where the differential pressure drops by 3%. Cavitation limit can be several metres higher and "almost 6m" means you have about 2.5m spare. Not a lot and Sulphuric acid is strange stuff. You might be getting some gas bubbles of something rather odd attacking the plastic.

Is the temperature in the range you put on the data sheet to the vendors?

 

[Giray Veli]

Temperature problem?

When ı checked the tempretaru ıt was 40 C and ıt ıs normal.

 

[Giray Veli]

Hi,
Consider the resources attached to support your work.
Who are the reputable suppliers? Can you share their names and proposals for your application?
From the documents shared you will see that "PVDF" is not the recommended material, prone to rupture, lack of mechanical strength?
Alloy 20 or Steel coated Teflon could be a better option.

BTW, no indication about the temperature.

Pierre

Hi, the supplier is Hydroo pump and when we ask them they have recommended this PVDF pumps. I think so they were wrong bcz our 2 PVDF pumps had this damaged. Now we ordered Teflon impeller pumps, hopefully they can run proper.
The temperature is 40 C.

 

[Giray Veli]

Although a sealless positive displacement pump guy, I have seen my share of damaged impellers; definitely need to double check your temperature to ensure you do not have an upset condition and in such an upset condition you might also have insufficient NPSHa, so you end-up with both temperature and cavitation stress on the impeller. Also, is it possible that there are any solids getting into the pump? It is very difficult to thoroughly trouble-shoot a pump application in a forum, here's how I try to guide the conversation: 1st, did the application ever work correctly - without such damage? If so, what has changed since then? If this has been an issue from day 1, it is likely not a pump problem as much as an inlet condition issue. Transient upset conditions such as a clogged inlet filter, miscalculation of NPSHa, temperature upsets etc... the material is reacting physically and perhaps chemically to your application. Hopefully your vendor will take the time to walk through your system and provide ideas to aid with identifying the root cause of damage. It might be that a centrifugal pump is not the best type for your application.

Hi, you have mentioned many different situations and ı want to make it narrow, The temperature was always same nothing changed. I have calculated the NPSH and NPSHA is 5,9m NPSHr is 3m. I dont think so ıt ıs wrong.
The application has work correctly 6 months without damage. We changed the pump and new pump ran 4 month than we faced same problem again. And assemblied 3, pump, ıt has worked 3 month. the process is closed system and when we check the system, There was no any particule or small material. Therefore ı think the problem ıs material of ımpeller bcz other probabilities are week.

 

[Giray Veli]

Looks to me like the material is softening and then tearing. Is there a tear on that first photo at the next impellor down from the damaged one?

Also NPHR is NOT a cavitation limit. It is a point where the differential pressure drops by 3%. Cavitation limit can be several metres higher and "almost 6m" means you have about 2.5m spare. Not a lot and Sulphuric acid is strange stuff. You might be getting some gas bubbles of something rather odd attacking the plastic.

Is the temperature in the range you put on the data sheet to the vendors?

I have faced 3 times that impellers has cracked.
The temperature is in the range.

 

[Giray Veli]

Either the plastic is softening because of high temp or it is suffering chemical attack.
You can find a lab that does plastic work and them test a used impeller to see if it is attack or not.
Here is a list of metals:
Tantalum, Gold, Platinum, Impervious graphite and lead up to 80°C (176°F) and 96% sulfuric, Glass
High-silicon cast iron (14.5% Si)
Hastelloy® B, B-2, and D, not up to BP 20Cb3 up to 66°C (150°F)
CW12MW and 2507 also are used.

If your impeller is actually PVDF then I suspect that is a poor grade or that the injection is very poorly controlled.
ECTFE and ETFE are also options as well as the thermoset Furane.

Some of the materials for impeller hard to find. I will searched other materials and inform you.

 

[EdStainless]

20Cb3 and CW12MW should be available.
Just make sure that the castings have been annealed and come with corrosion test certification.
I would be surprised if you cannot find Furan also.

 

[Giray Veli]

Thank you for all comments I am appreciate. We decide to change pump impeller. First we will use Teflon coated impeller because it is easy to provide for us. If we face again same problem we will use Alloy 20Cb3.