Cavitation Resistant Coating for Pumps

[crradovan]

Hey guys!

We have this problem on our plant. Severe cavitation damage are incurred in our pumps and we are currently studying the cause of it. For the mean time we are in the process of repairing the pump since operation of the pump is critical in the process.

We are looking into cavitation/erosion resistant lining to be applied as mitigation to prevent further damage to the pump internal components while we are finding an effective solution to eliminate the cause. I would like to consult if this method will be effective in preventing or at least minimizing the damage caused by cavitation.

Are there other considerations that i should be looking at? The pump is water service with 316SS impeller and CS volute.

Regards,
CR Radovan

 

[EdStainless]

Look at an elastomer or polymer coating.
I don't think that your part would support a harder overlay.
And this is just temporary.

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P.E. Metallurgy, Plymouth Tube

 

[SJones]

Something like this for instance:

http://www.belzona.com/en/products/2000/2141.aspx

I haven't used it, and thus I can't vouch for it. The coating manufacturer will have to convince you of its performance and efficacy.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[crradovan]

EdStainless

May I know why elastomer or polymer coating?
Most of the articles I have read suggested to upgrade to a harder material or conduct surface hardening. However, what do you mean by "our part cannot support a harder overlay"?

I apologize for the questions but i am eager to know why.

regards,
CR Radovan

 

[crradovan]

SJones,

Yes, I am actually looking into that product by Belzona as it is also one of the product stating it follows ASTM G32-92 testing. But there is the "modified" word in the description for that.

However, my question is - are linings be enough to prevent damage to the newly repaired pumps?

Regards,
CR Radovan

 

[EdStainless]

soft surfaces (rubber) resist erosion and cavitation damage by flexing under the impact.
If you hard coat then the substrate needs to be strong enough to assure that you don't flex (and fail) the coating.

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P.E. Metallurgy, Plymouth Tube

 

[SJones]

.....changing to a more corrosion resistant and/or higher hardness material may not improve cavitation resistance. Excessively hard
materials may not be suitable if they lack the toughness required to withstand the high local pressures and impact (shear loads) of the collapsing bubbles.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[bimr]

The first plan of attack should be to correct the improper pump application parameters that are the root of the problem.

 

[corrosionguru]

The short answer is yes. The right coating, applied properly, will solve these issues. Another company you may want to look at is Enecon. However, when 85% of all coating failures and reduced performance characteristics are due to application error, identifying the optimal material is only a part of the equation. Further, there are powder coating and other alternatives which, depending on the size of the part, etc., would be a better, less-costly solution. From Warren Brand - owner of Chicago Corrosion Group.

 

[crradovan]

bimr,

We are on it. But process needs the pump to be operating and can only give a short period of time. So for the mean time we are to operate it with a mitigation to minimize the damage.

Thank you and regards,
CR Radovan

 

[crradovan]

EdStainless,

I never thought of it that way. Thank you for the additional information. We'll look on to these materials and methods of application.

regards,
CR Radovan

 

[crradovan]

SJones,

Again, thank you for the reference and information.

Regards,
CR Radovan

 

[crradovan]

corrosionguru,

Thank you for the information. I believe we have Enecon here locally.

As you said application is one factor to consider, I have read studies with results of the coat chipping off concluding that there was a fault in the adhesion. I guess the company will be the one to guarantee this. We'll also look onto the application methods you mentioned. Thank you for this.

Regards,
CR Radovan

 

[KyleFlanagan]

Morning all,

I agree with bimr in the first instance, mitigation of cavitation should first be examined through change in process conditions which have resulted in the cavitation. However, in the event that this is not possible or that the spectrum across which cavitation is occurring is too broad to design out then use of polymeric coatings such as the Belzona 2141 is the next option. As EdStainless correctly pointed out, these materials resist cavitation by absorbing the implosion forces of the vapour bubbles. Cavitation causes damage by impacting the substrate with a high velocity force. If this force exceeds the elastic limit of the material then damage occurs in the form of small pits. Use of harder materials therefore will not solve this problem. Belzona 2141 has a high elastic limit allowing it to absorb the high velocity forces.

In response to the question of the 'modified' version of ASTM G32-92. The modification was to coat the sample instead of the vibrating probe. It was found that coating the probe with the elastomers resulted in heat build up in the elastomers and a measurement of the heating of elastomers through vibration instead of actual cavitation resistance. By coating a sample under the probe, cavitation was induced and the Belzona 2141 tested for 'true' cavitation resistance.

- Kyle

 

[EdStainless]

There are metallic options for high cavitation environments. A high strength steel or cast iron that is overlayed with a Co based hard facing (either Stellite or a WC) works well. The other option is a Co based alloy. Even 'soft' Co alloys (Ultimet) resist cavitation very well.

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P.E. Metallurgy, Plymouth Tube