material for pump impeller

[upm]

Gents,
we have a duble suction pump for tar service (dirty) fitted with ductile iron material. last inspection , the impeller were erroded very badly and pin holes were on the wearing ring location. the inlet blad tips are toptaly erroded and the discharge blade tips are erroded as well.
this pump is operted at cavitation condtions and pumping polymer sluges.
is SS316 or 410 adequate for the service?
upm

 

[stanweld]

Alloy CA6NM should prove effective.

 

[arunmrao]

NiHard material can be used with some modifications in central bore.
If the above is not possible then CA6NM can beused instead of 410 or316.

Ductile iron is a wrong selection of material for such an application.

 

[upm]

gents,
thanks for the information and sorry for the reply delay.
i need to work out the running clearances for the new material. any idea where can i find the thermal expansion constant
upm

 

[JimMetalsCeramics]

Is the metal eroding from physical impact or is it corroding?

 

[upm]

The material is erroding due to abrasive wear based on the sludge being pumped with the process stream. you even can see the abrasive wear marks on the impeller back shroud and the casing volute. do you think Bronze is a good abrasive wera resistance?
thanx
upm

 

[JimMetalsCeramics]

You should harden the impeller surface. Your choices are:

-Simple electroplating of chromium.
-Thermal spray coatings (e. g., Cr, MCrAlY, ceramic).
-Conversion coating (furnace carburizing, nitriding or boronizing, or plasma nitriding).

With a good coating, you might avoid the need for stainless steel. A quench-hardened steel would be a plus.

NO, on the bronze.

 

[arunmrao]

Certainly a NO NO for pump impeller. It would just vanish even before you settle down.You should consider only the wear resistant alloys for this application. In some instances I am aware that plain grey iron is used though it wears out fast for ease of manufacture and cost. All surface treatments will be superficial and would get worn out or peeled off for the application being suggested.

 

[JimMetalsCeramics]

Even if you have excessive, worst-case wear, thermal sprayed coating can be put on thick. Ceramics or superalloys, for example, can extend useful wear life several fold.

 

[upm]

Gents,
Thanks for the great help. ceramic spry coating would be the best as we can do it locally. can we do the coating with brush or it needs to be spray coating?
do i need to coat the impeller only or the impeller and the wearing rings? if so , i need to work out the new running clearances as the thermal expantion will be different, am i correct?
thx. gents and hope to hear from you
upm

 

[JimMetalsCeramics]

You should coat all mating wear surfaces. You should use very high temperature spray deposition to get maximum ceramic densification and adhesion.

 

[upm]

Thanx Jimmetalceramics for the great help.
can you tell me pls. how can i get the coating procedure for the spry ceramic coating? we are shortage of coating againts here and i need to explain to the local againt the way it should be
thanx again
upm

 

[tmtresearch]

If erosion is due to abrasive wear then a hard coating or surface treatment would be advisable. We find that boronizing work extremely well in combination with both CA6NM and CA=15/410 to protect against erosion. Unlike a spray coating, boronizing will harden all surfaces not just what is easily accessible by line of sight.

Feel free to contact me directly if you would like some additional information (matt.hinckley@tmtresearch.com)

 

[JimMetalsCeramics]

Where are you located?

 

[upm]

JimMetalsCeramics ,
i am located in the middle east where such a specilized application is very limited.
upm

 

[JimMetalsCeramics]

The only places I know of there would be in Israel like:

http://metalock.co.il/

Ceramic coatings are applied through high deperature spraying (above the meting point of the ceamic). Such processes include:

HVOF, Super D-Gun, and Vacuum Plasma Spraying. If you have enough volume, you might purchase a system.

 

[upm]

JimMetalsCeramics ,
Thanks for the info.

 

[iitmpal]

weld overlay of manganese can be tried.