Cathodic Protection with Impressed Current for Heat Exchanger of Salt-Making Evaporator
Studies on the Corrosion of Metals in a Stalt-Making Apparatus and Its Protection (XIII)
1974 Volume 27 Issue 5 Pages 285-294
Details
1974 Volume 27 Issue 5 Pages 285-294
Experiments were carried out to establish the technique of cathodic protection with impressed current for the heat exchanger of the salt-making evaporator consisted of different metals. The results obtained were as follows:
1. The protection potential of copper, naval brass, and stainless steel in mother liquid at 30°C under static condition was assumed to exist near -500mV, -650mV, and -800mV (SCE), respectively.
2. A corrosion protection test was conducted by using a model evaporator (outside heating type) with a stainless steel water box, naval brass tube plate, and a copper heating tube in mother liquid containing 15 volume % salt crystals at 112°C under dynamic condition of the flow rate of 2m/sec. for 120 hours. This test showed that the water box, the tube plate and the end of the heating tube were perfectly protected from corrosion at a cathodic potential of -800mV (current density 0.8A/m2).
3. From the potential distribution over the internal surface of the tube in a basic test and from the distribution of corrosion rate in a corrosion protection test, the protection of the heating tube seemed to be limited to the length of 100mm from the tube plate. The distribution of corrosion rate was found to correspond to the deposit by electrolysis.
4. Most of the Mg (OH) 2 and CaCO3 deposits were observed at the end of the tube, but the speed of scale deposition was under the critical value (0.03g/m2hr). 5. The concentration of free Cl2 by electrolysis was 0.1ppm at 2.2-3.0 Volt of bath voltage, and there seemed to be no corrosion problem for this apparatus.
