Zinc free Bronze Impeller for chilled water pumping

[vecnaj1978]

Dear All

I request your expert advice on the below

For one of the chilled water pumping requirement, we are proposing a pump with CI casing and bronze impeller.
The consultant on the project wants the impeller to be Zinc Free.
Our bronze impeller contains 5% zinc in it.

I kindly request you to help me know on why Zinc is added in the bronze impeller.

what is the advantage of zinc free impeller over impeller with zinc

upto what percentage of zinc is recommended in the bronze impeller


please help me with your expert advise

regards

 

[Artisi]

Ask the consultant why he wants zinc free bronze.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[vecnaj1978]

Dear Sir

This is the problem, even he does not know I guess

he is just following the specs written by some one

please let me know if we can help him on this

regards

 

[micalbrch]

Bronze containing zinc is less resistant against corrosion than bronze without zinc.

 

[Artisi]

Only in a zinc aggressive environment, otherwise bronze is ok.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[TenPenny]

Some people will specify low or no zinc impellers for chlorinated water service, it's possible that the person writing the spec was using something based on that concept.

If he/she doesn't know why they're putting something in the spec, he/she shouldn't be writing it.

 

[Artisi]

If only that were true about knowing and writing specs, and it doesn't end there - as they will argue their point even though they are wrong.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[DubMac]

Unfortunately, Specs have become the lazy man's way out of work. Beware of engineers and users that send listing of ALL applicable specs they can find, and then make a statement such as: Products shall comply with all listed specs.

 

[EdStainless]

Traditional bronze has no Zn in it (but most have lead).
But most commercial bronze alloys do have some Zn.
Zn alone is no indication of resistance to corrosion or even de-zincification.


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P.E. Metallurgy, Plymouth Tube

 

[vecnaj1978]

Dear Sir

Thanks for you responses

I had a meeting this morning with the consultant regarding this matter and he informed that they will be using these pumps for drinking water transfer pumps.

he has no justification for the zinc free bronze but insisting in having them as he wants to follow the specifications.

regards

 

[Artisi]

Well in that case comply, if there is a major difference on price and delivery, put in an alternate price for standard bronze and let the consultant / end-user make the decision.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[EdStainless]

Does he have an industry spec that he is using or is this his own?
There are alloys listed in NSF for drinking water service.
Artisi is correct, all that you do is provide options.


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P.E. Metallurgy, Plymouth Tube

 

[1gibson]

Options, and firm position on scope, if this is a new requirement or new interpretation of a vague requirement.

 

[bimr]

Bronze is an alloy consisting primarily of copper, commonly with about 12% tin and often with the addition of other metals (such as aluminium, manganese, nickel or zinc) and sometimes non-metals or metalloids such as arsenic, phosphorus or silicon. These additions produce a range of alloys that may be harder than copper alone, or have other useful properties, such as stiffness, ductility or machinability.

Bronze tends to be a generic term. Many manufacturers stopped using the SAE-40 bronze (a common alloy used for impellers) 20 years ago because it contained 4.5% lead content. The SAE-40 bronze alloy was replaced with other bronze alloys that caused dezincification problems with impellers.

Since one does not know the exact chemical composition of the generic bronze that the pump manufacturers are selling, it is easier to specify zinc free to avoid the problem of dezincification.