what is the suitable material for vertical treated water pump 2

[Salghetet]

Ladies and Gentlmen
we have corrosion problem with pump used for treated water in industrial area
material of wet pump is carbon steel and cast iron (casing, impellar and shaft)
i want to upgrade material of vertical Aerator Effluent Pump
i am thinking about nonmetallic material or steel lined with PTFE or SS
so please advise if you have experience

 

[micalbrch]

Plastic will be the best choice concerning corrosion and cheaper than stainless steel or any lined metal. Talk to companies like Goulds, Grundfos or Grainger. They should be able to help.

 

[Salghetet]

what about temperature damage and mechanical damage of impellar and shaft due to rotating if material is plastic

 

[micalbrch]

You did not write anything about temperature. What is the fluid temperature? Wear to impeller and shaft depends upon soldis concentration and particle size but waste water usually has a solids concentration of 1-2 % by weight and industrial waste water probably does not contain fibres which could lead to clogging.

 

[Salghetet]

fluid temperature is imbient and regarding soilds I am not sure but it is oily water from natural gas industrial at the effluent treatment stage before diposal, i think no much soilds.

 

[micalbrch]

Then you should not be scared about plastic. But talk to one of the companies I mentioned. They no better than I do.

 

[bimr]

The safest bet is probably stainless steel. Stainless steel is commonly used in wastewater treatment.

To make a rational choice, more information is needed especially on the water quality. What is the expected service life? How long has the existing pump been in service? What is the pump size? These matters will all have an effect on the selection.

Note that trace amounts of contaminants in oil may effect plastic.

 

[Salghetet]

Thanks bimr
water analysis show that
pH is 8.8 and chloride, ca, Mg and Na are high, it is corrosive and hard water, stainless steel and chloride pitting corrosion but i think pitting will not be significant problem as the scaling problem
regarding the expected service life, it is LNG company so should be long time, and existing pump it may be 15 years but with frequent maintenace due to severe corrosion
pump is vertical and size is 10cubic meter per hour and press 3.2bar

 

[bimr]

It is difficult to predict the effect that minute quantities of organic materials will have on plastics. There is no database available for prediction. The best experience will come from a similar application in the same industry.

You should not be experiencing significant scaling at a pH of 8.8. In regards to the chlorides, if the chlorides are above 200 mg/l, stainless steel will be subject to crevice corrosion. If the chloride concentration is significantly above 200 mg/l, you should consider the use of a higher grade stainless steel.

The pump in question is small so it will not be worthwhile to conduct an extensive corrosion survey. The service life of the existing pump seems to be in an acceptable range.

Your best option is probably to ask the existing supplier to quote the cost for replacing the existing pump as is and an option for the same pump in stainless steel materials.

Refer to the link for additional information on stainless steel.

http://www.nickelinstitute.org/en/N...electionAndUse/Water/WasteWaterTreatment.aspx

http://www.euro-inox.org/pdf/map/WasteWater_Installation_EN.pdf

http://www.nickelinstitute.org/~/Me...ainless SteelEquipmentPowellFassina.pdf#page=

 

[Salghetet]

Chloride is 620mg/L it may cause SCC beside crevice however in other area cast iron and steel (pump material impeller and casing) is used and no significant issues but it is horizental not vertical and different manufacture company

 

[bimr]

As the Nickel Institute articles states, type 316 stainless steel is generally considered acceptable for chloride levels up to 1000 ppm or where a greater level of confidence is required. Localised corrosion has been found to be rare below these levels. Type 316 stainless steels offer the greater resistance, due to 2-3% molybdenum content.

 

[Salghetet]

SS316 is good but we can not make usre that chloride content will not exceed 1000, for handling water I think non metallic material or lining metalic are the best regardless the price
what about low alloy steel

 

[Salghetet]

water is oily treated water from effluent area of LNG Plant and it is not waste water