Corrosion Prevention by Deaeration of Materials for Salt-making Apparatus

Studies on the Corrosion of Metals in a Salt-making Apparatus and It's Protection (XI)

Abstract

In order to study effects of corrosion prevention by deaeration upon those materials which are used for salt-making apparatus, experiments were carried out under static condition in sea water, brine and mother liquid at room temperature for 144 hours with mild steel, copper and stainless steel, and under dynamic condition of the flow rate of 1, 2, 3.5 m/sec in saturated brine and 25-30% slurry of salts at 40°C for 240 hours with copper, aluminium brass and cupro-nickel. Results obtained were as follows.
1. In the static test, the corrosion rate of mild steel showed a decrease in proportion to the increase of concentration of dissolved oxygen, notwithstanding the kind of liquids. The corrosion rate of copper declined in line with the increase of the concentration of dissolved oxygen, but the limited concentration of dissolved oxygen showed a tendency of controlling corrosion. The corrosion rate of stainless steel proved to be low regardless of the concentration of dissolved oxygen.
2. In the dynamic test of saturated brine, the corrosion rate of each material showed a decline with an increase in the concentration of dissolved oxygen. The corrosion prevention rate by deaeration of copper, aluminium brass and cupro-nickel turned out to be 90, 40, 20%, respectively.
3. In the dynamic test of 25-30% slurry, the corrosion rate of materials except copper at atmosphere showed a rise of 8-9 times, and the effect of crrosion prevention was very low. This was considered to be attributable to the fact that erosion was promoted by the abrasive action of flowing salt crystals.
4. Ferrous sulfate was found to have corrosion controlling effects on copper and copper alloys.