Water Well Impeller Damage

[sewerratt]

Anyone out there hear of damage to bronze impellers in water wells due to chlorinated pre-lube water? Or leaking check valves allowing chlorinated distribution water to enter the well and corrode the impeller?

 

[bimr]

Not familiar with that, but high levels of dissolved salts will do the same thing.

 

[Munequip]

Yes, but it depends on the the composition of the bronze and the chlorine residual in the water. The manufacturer would need to give the composition of the bronze and recommended limits of chlorine.

 

[strider6]

bronzes are used in seawater service. It would be necessary to define exactly the type of bronze and the type of corrosion. It could be also an erosion related mechanisms. I suggest u to make a Failure Analysis to defnie exactly the causes of the damage

Copper alloys corrosion

S.



Metal Corrosion

 

[semo]

What you are referring to is de-zincification. Many pump manufacturers changed the makeup of their bronze due to lead regulations. The lead content was eliminated and a higher zinc content was used.

Chlorine will attack and dissolve the zinc thereby pitting and eroding the bronze impeller.

I've not seen it on raw water well impellers; but, I have seen it numerous times on high service pump impellers and also on solenoid valves for chemical feed piping. The chlorine levels don't have to be that high depending on the TDS content of the water.

I've made recommendations to several clients and changed my specifications to include cast iron impellers where I think this could be a problem. Some manufacturers have different bronze alloys for this reason as well; but, it isn't always easy to find in their literature.

 

[thewellguy]

I think that Semo is correct. I've seen the same thing in well pumps. It dons't much and if the prelube leaks or the check leaks your replacing inpellors and bearings. I know that you can specify leaded bronze for some manufactuer, but you have to special order.

 

[Artisi]

Cannot see that the minute amount of water from the prelube is in any way the cause of what will be de-zincification of your bronze? impellers, it could well be your second thought of leakage from the distribution system - but even this is a long shot,how much is leaking back and surely it will be diluted by the standing water in the well.

I would suggest getting an analysis of the ground water you are pumping.

 

[chief]

There are impellers available for use where the liquid medium has harsh effects on the normal bronze alloys. They are made of a composite fibre material and are resistant to the usual scouring and cavitation. I do not have the info to hand but an internet search should produce a result.

Offshore Engineering&Design

 

[Artisi]

Cannot see how a composite material is able to withstand the destructive energy of cavitation when even 28% chrome iron with a hardness of 700+ BH cannot. If you are discussing erosion corrosion when this is a different matter altogether.

 

[BRIS]

Are you sure that the well(s) have not ben disinfected by shock chlorination/slug dosing ?

 

[bimr]

De-zincification of the impellers is common in well pumps. It has more to do with the salinity of the water than with corrosion. The well drillers around here use the same metal and get 7-10 years of service life out of the impeller. It is not economically justified to spend more for the impeller.

 

[bimr]

De-zincification actually only occurs with Brass, not Bronze. Bronze metal does not include zinc in the alloy.

Graphitization is a process where iron leaches from cast iron and weakening the cast iron.

http://www.hghouston.com/coppers/brass75.htm

Bronze is an alloy of copper, tin, zinc, phosphorus, and sometimes small amounts of other elements. Bronzes are harder than brasses. Brass is an alloy having copper (55%–90%) and zinc (10%–45%) as its essential components. The properties of brass vary with the proportion of copper and zinc and with the addition of small amounts of other elements, such as aluminum, lead, tin, or nickel.

In talking to a well driller today, it is more common to experience corrosion of the stainless shaft of the well pump rather than with the bronze impeller. This would be pitting of the stainless steel.

Wells are annually disinfected for a period of 8-24 hours with a solution of 200 to 400 mg/l of chlorine. Again, this is just one time per year disinfection. After 7-8 years of annual disinfections, there will be evidence of corrosion on the pump shaft, not the bronze impeller.

The chlorination of the water supply would consist of approximately 2 mg/l of chlorine and it would be difficult to see how this would affect the bronze when the 200-400 mg/l of chlorine does not corrode the bronze.