Performance of heat exchanger materials
Earlier it was assumed that copper-nickel alloys provided sufficient corrosion resistance in the fresh waters while use in the heat exchanger services. The materials like austenitic stainless steels and nickel-chromium-iron alloys were mentioned essential only while operation in the brackish water or sulfide polluted water, because these were very costly for use in ordinary fresh water conditions. It was found that Incoloy 800, Inconel 600 and stainless steel 304 were not prone to attack in fresh waters up to 70oC. However in an Ontario Hydro Pickering Nuclear Generation Station, where Incoloy 800 moderate heat exchanger tubes were installed, a premature failure of copper-nickel alloy 70/30 was noticed because of pitting and crevice corrosion.
It is already accepted that Stainless steel 304 and 316 grades withstand extremely high chloride conditions. I-800 would be assumed to achieve better corrosion resistance as compare to SS 316. The nickel based superalloys such as Incoloy 800, Inconel 600, Inconel 690, Stainless steel 304, Monel 400, Copper-nickel alloy 70/30 and 90/10 and brass have outstanding corrosion resistance in the natural fresh waters. However in alloy 70/30 Cu-Ni alloy and 90/10 CU-Ni alloy, corrosion risk increases with increase in temperature. Incoloy 825 doesn’t suffer from any pitting attack however alloy 800 suffers from pitting at 76oC. Stainless steel 904l rarely gets pitting.
The corrosion occurs in the heat transfer tubes is of dark green or black layers which produce on the tube slit, evaluations of such dark spots showed that these contain calcium, sulfur and chlorine and considerable magnitudes of chromium. Following the heat transfer conditions, many alloys are prone to pitting corrosion that occurs in salt water. Only Titanium and Incoloy 825 are resistant to pitting in these environments.
Heanjia Super-Metals attempts to serve needs of heat exchanger or heat transfer based applications by manufacturing high performance nickel based alloys. For more information, reach us at email@example.com