Corrosion protection of pumps

[shantanu]

Hi all,

For pumps handling extreme grade salinated water; upto 700-800 ppm, what would you recommend for corrosion protection of pump casings and impellers:

cr2o3
Or
WCCoCr- HVOF sprayed
Or any other coating?

Regards

Shantanu

[djewell]

There are lots of coatings which can protect the pump casings from corrosion. The key is getting full density of the coating in order to prevent the saltwater from getting to the base metal. WCCoCr and Cr2O3 would only be necessary if you also have an abrasion problem as well.

[MichiganMan]

More information needed.
What kind of pumps are you dealing with (most likely centrifugal, but it bears asking)?
What is the temperature of the process fluid (it makes a big difference)?
Are there solids in the process fluid? Any indication of abrasion (even fine particle)?
What are the pumps made of (most likely cast or ductile iron)?

Sealer is likely a good idea depending on the above. Even minimum porosity will lead to under coating corrosion and ultimately delamination in the case of most iron alloys in this type of solution.

[shantanu]

More information needed.
What kind of pumps are you dealing with (most likely centrifugal, but it bears asking)?
What is the temperature of the process fluid (it makes a big difference)?
Are there solids in the process fluid? Any indication of abrasion (even fine particle)?
What are the pumps made of (most likely cast or ductile iron)?

Sealer is likely a good idea depending on the above. Even minimum porosity will lead to under coating corrosion and ultimately delamination in the case of most iron alloys in this type of solution.

Dear Michiganman,

Pump type: centrifugal
Temp of process fluid: ambient
Solids in process fluids: NO
Pump MOC: Cast iron

Understanding that any porosity is unadvisable, HVOF then should be the ideal process....and what sealer would you recommend? Will a standard loctite be ok?

Shantanu

[MichiganMan]

I'm a bit confused by the 700-800 ppm being referred to as "extreme grade". Perhaps this is (or will be) medical grade saline you are handling, or perhaps I am misinterpreting what you mean by 7-800 ppm? Typical saltwater from the ocean is more than 35000 ppm, so maybe I am not using consistent units of measure compared to your statements. If it is a medical (or even a food grade) application for the water, then I would suggest being careful to choose a sealer that will not leech chemical into the process over time (something with NSF 61 or similar approval).

At any rate, at ambient temps most of the common organic sealers will do fine in a saline environment and you can easily determine it viability for your application by consulting the item's product data sheet. Frankly, I would be more likely to use a ceramic filled composite coating (probably epoxy based) for this application than a TSC, because with no abrasion in the evironment it would last forever and give a smoother finish offering better pump efficiency and it would cost a fraction of the price.

I haven't considered the resistance to corrosion in a saline environment of the alloys you are thinking of here, so I can't say I would recommend either specifically, but I have used both in immersion environments before, and both do just fine. Even with the HVOF I would recommend use of a sealer though, otherwise one tiny pore can cause a whole lot of damage to the integrity of the coating (a phenomenon similar to crevice corroion takes place beneath the coating and it gets real bad real fast sometimes).

[k09]

We have sprayed many pump sleeves with densified Chrome Oxide coating which has worked very well. To check the endurance of the coating in corrosive saline conditions we have validated our coatings in Salt spray test. However I have also been told that a dense WC-Co-Cr coatings work equally well in such corrosive conditions.

Regards
K09