Ductile Iron Impeller or SS?

[bulkhandling]

In a few projects, I met the problem. Some bidders proposed duplex stainless steel CD4MCu for impellers while some other bidders proposed ductile iron impellers. The applications are for water with no or little solids. Normally the bids with CD4MCu is about 10% higher than the DI bids. I like the CD4MCu but could not justify the 10% extra cost.
What's your opinion and if any disadvantage of ductile iron impellers in water application?

 

[Artisi]

For clean water ordinary grey cast iron is more than sufficient, in fact, ductile iron in itself is an over-kill and CD4MCu which is a great material is certainly way over the top for this application.
Guess the only advantage of CD4MCu is that in 100 years when the casing etc have been replaced 3 - 4 times you will still have a near new impeller.

Naresuan University
Phitsanulok
Thailand

 

[pumpkind]

I fully subscribe to Artisi's opinion - Duplex stainless is definitely not the effective solution

 

[bulkhandling]

How do you understand that some major pump manufacturers (FS and SZ)supply duplex SS impellers as their standard design, which make them inevitably the higher bidders than their competitors?

 

[cub3bead]

When you say water with little or no solids do you mean that it is demineralized?

If your water is demineralized and is fully oxygeneated then the ductile and cast are unsuitable for the application. Nor are any of the "yellow" alloys.

 

[bulkhandling]

I do not mean any special treatment other than just being clarified or maybe sand-filtered. Oy say, just natural water from a lake.

 

[Artisi]

If a manufacturer is suppling duplex SS as standard this will naturally make their manufacturing costs marginally higher and it becomes a marketing decision if they want an order to cut their margins. You should also bear in mind that the initial cost should not be the main factor in deciding on the best bid.
But your question was - to compare ductile iron with CD4MCu which has been done.

Naresuan University
Phitsanulok
Thailand