Effect of HCI on the corrosion of waterwall tubes in a waste incineration plant

Abstract

The corrosion behavior of a carbon steel and Type 347H coated with 50mol%NaCl-50mol%KCl mixture has been investigated under reducing and oxidizing atmospheres containing HCI. It has become clear that HCI and H2O content have a great influence on the corrosion rate of the carbon steel covered with NaCl-KCl in the reducing atmosphere. When the HCl and H2O content in the reducing gas was 0.2% and 20% respectively, a severe corrosion attack was observed at 350 and 400°C. This corrosion is considered to be due to NaCl-KCl-FeCl2 hot corrosion. H2O acts as an oxidant in molten chlorides. However, in the oxidizing atmosphere containing 0.2%HCl the corrosion was slight at all temperatures tested. Although CuO, PbO or ZnO additions to the NaCl-KCl salt mixture did not accelerate the corrosion in the reducing atmospheres, these oxides remarkably increased the corrosion rate in the oxidizing atmospheres. These oxides catalyze the oxidation of HCl, and the formation of FeCl2 was promoted. The corrosion rates of Type 347H were negligibly small in the both atmospheres even at 400°C. However, significant corrosion took place in the oxidizing atmosphere at 400°C when 10%CuO or 10%ZnO was added to the salt mixture.