3 replies to this topic

[mdteng]

Dear Colleagues.
I'm trying to specify the contruction materials for a cooling water pumps.
The water comes form a zeolite softening plant and is pumped to a process machine, it contains carbonates and bicarbonates of sodium (no calcium and manganese), therefore there aren´t problems of deposits.
Water temp. is 47°C (116°F), PH is between 8.5 and 10.

Standards reccomends the use of cast iron or 12% chrome steel.

Could anyone help me to know waht is the porper material for this application?.

Thanks
Martin

[Art Montemayor]

Martín:

I would select cast iron as the basic pump fabrication material of construction. I don’t see the need for 12% chrome steel.

Additionally, I would apply different logic to the associated piping. I used to use cast iron and steel piping for treated water – but that was many years ago. Today, I believe you have more practical and cost-effective options – such as Plastic piping and fittings that are corrosion-proof, low-cost, easily and quickly installed, and have an ultra-low and constant friction factor. However, there are limitations and trade-offs to be confronted with plastic piping and these should be carefully addressed to ensure a successful and lasting installation.

I would never use 12% chrome steel. I really don’t see the need for such an alloy. And I would try to avoid cast iron pipe. Cast iron is very expensive on a total, installed cost basis. The labor involved with screwed fittings, its weight and its brittle nature make it an expensive item to install and protect. Additionally, cast iron has a high friction factor. I have to assume you have what we would all call a relatively “benign” application: treated water at reasonable temperature (47 °C) and reasonable pressures (I assume approximately 50 psig). Therefore, I see this as a possible potential fit for plastic pipe.

If you are interested, look at the Excel workbook I recently posted in the Spanish Student Forum. Some issues and trade-offs associated with plastic pipe that should be considered are such items as pipe supports, allowance for thermal expansion, allowance for surge and water hammer effects, protection from physical mechanical abuse, and the application of plastic fittings and valves. If engineered and installed correctly, plastic piping will out-perform steel or cast iron piping in many applications.

[mdteng]

Tanks Art.
I think the same as you about that CI is suitable and 12% Chrome pump is more expensive and doens not add significant metalographic advantages.
Here, the pipe is simply ASTM A-106 grade B (Carbon steel) with 3mm of corrosion allowance.

This afternoon i was talking with a representative of a Pump firm, and he confirmed my that, as you said, A cast iron pump will work fine for this kind of water.

I appreciate your help.

Thanks again.
Martin

[Dev 009]

Dear Martin, 100% agreed with Art but now a days only fewer vendor can offer you CI casing ( If u don't want an API pump).

I would suggest you to go for Carbon Steel ( A 216 Gr WCB ) as basic casting material for casing and probably CI /CS as impeller MOC. I don’t see the need for 12% chrome steel

For piping you can see the economical evaluation between Plastic Piping or C.S. piping.

Regards
Rohit