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copper & stainless steel with water
07-06-2011, 04:14 AM
Post: #1
copper & stainless steel with water
we are considering the following option for our solar Energy Water piping

1) Passing the hot water through the solar cell of Copper construction and then the same water will be passed through stainless steel-304 or plastic Piping . Again re-circulation will be done through copper.
Hot water temperature : 90-100 deg C at 2.5 bar pressure
Will it cause the Galvanic corrosion. What issues may come up?


2) Which piping material shall be used for Hot water temperature : 90-100 deg C at 2.5 bar pressure
Also we want to use the control valves , circulation pumps in this pipeline, which material shall be used.
Can we use the plastic? if yes which type?

Regards,
Tushar Deshmukh
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07-07-2011, 05:03 PM
Post: #2
RE: copper & stainless steel with water
(07-06-2011 04:14 AM)tndeshmukh Wrote:  we are considering the following option for our solar Energy Water piping

1) Passing the hot water through the solar cell of Copper construction and then the same water will be passed through stainless steel-304 or plastic Piping . Again re-circulation will be done through copper.
Hot water temperature : 90-100 deg C at 2.5 bar pressure
Will it cause the Galvanic corrosion. What issues may come up?


2) Which piping material shall be used for Hot water temperature : 90-100 deg C at 2.5 bar pressure
Also we want to use the control valves , circulation pumps in this pipeline, which material shall be used.
Can we use the plastic? if yes which type?

Regards,
Tushar Deshmukh
Tushar

As a general rule if you connect two dissimilar metals that are bridged by an electrolyte, as in this case fresh water, there is a good chance to have galvanic corrosion.

There are several factors to be considered

-the galvanic series of metals in freshwater is different from the one in seawater and copper / stainless steel show approx the same potential.

-even if the potential is similar copper can suffer severe corrosion if coupled to a large area of stainless steel.

-the current between different materials change with temperature and the hardness of water.

Based on the above our suggestion is to avoid as fas as possible to join different materials and if you have to do it use an isolation joint or use a spool of plastic pipe.

Regarding the corrosion resistance at high temperature it should not be a problem for copper even if in the past there have been cases of pitting corrosion in copper tube in solar water heaters (see the doc below).

The resistance of stainless steel in water at that temperature depends on the water chemistry and in particular the chloride content.

You should try to obtain a water analysis and see if in you area there have been cases of copper corrosion.

We have find some document that deal with material selection in solar water heater system.
http://www.branz.co.nz/cms_show_download...b73b520541

http://www.thyssenkrupp-nirosta.de/filea...ution1.pdf

http://www.bld-specialists.com/documents...allest.pdf

There is also an ISO standard that gives guidelines for material selection:

Solar energy -- Water heating systems -- Guide to material selection with regard to internal corrosion
http://www.iso.org/iso/iso_catalogue/cat...mber=18251

hope this help

Corrosionist Team
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