New anticorrosion copper material for heat exchangers
The market demands durable heat exchanger material that can withstand harsh environmental conditions without corrosion. A new anticorrosion copper material developed by Luvata Rolled Products in Sweden prevents detrimental corrosion attacks in environments with condensed diesel exhaust gases. The patent has been filed for this unique metallic coating material for copper strip and test results conclude it is effective against corrosion.
Anders Falkenö, Technical Sales, Luvata Sweden, explains: “We have succeeded in developing the perfect coating to be used in corrosive environments with exhaust gas mixtures, a product without the risk of a premature failure. Traditional coating techniques have been utilized in conjunction with a standard CuproBraze® furnace brazing cycle.”
The coating can be seen in the upper part of the picture below (Fig.1). The coating together with the chromium from the alloy forms a corrosion resistant layer.
Extensive accelerated corrosion tests have been carried out and these tests show the difference between coated and uncoated copper strip in simulated exhaust environments. With coated and brazed chromium containing copper strip alloy SM0502 there are only superficial corrosion attacks in the top layer (Fig.2). When the same material without the coating was tested, it showed corrosion penetration right through the material thickness (Fig. 3).
Fig. 2 Fig. 3
Anders Falkenö indicates, “One possible application for this new product is charge air coolers in combination with Exhaust Gas Recirculation (EGR) and that initially the customers will probably be heavy vehicle and power generator manufacturers.”
Fig. 4: 1# CAC tube, 2# Brazing foil, 3# Coated turbulator
The picture above (Fig.4) shows the components for CuproBraze charge air cooler tubes. Firstly (to the right),the tube made from brass alloy SM2385. Secondly the brazing alloy foil joining the turbulators to the tubes, which makes the inner surface of the tube corrosion resistant, as well. Thirdly (to the left), the coated copper turbulator of the chromium containing alloy SM0502
Corrosion tests with the new material have been done in various environments and for different durations at low pH (<3) with nitric and sulfuric acids present. Accelerated corrosion testing has also been done in synthesized diesel exhaust at condensation temperature.
The results have been unanimous: the corrosion develops a few micrometers below and along the surface of the strip only and there is no penetration through the material.
”There is no doubt the CuproBraze technology, with the unique copper coating, offers significant promise to the design of heat exchangers for the diesel exhaust environment,” added Anders Falkenö. “Luvata is now starting pilot projects with interested customers.”