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Field corrosion tests were conducted on eight single tube materials and two welded overlay materials in three typical Japanese waste incineration plants in an effort to develop new corrosi...

Fireside corrosion factors in high-temperature corrosion of waterwall tubes in waste incineration boilers were investigated. Factors accelerating corrosion were considered to be heavy metal (zinc and lead) chlorides, unburned carbon in deposits, and reduction of the gas atmosphere formed by the increase of unburned gas components and the decrease of oxygen (O2). Laboratory tests confirmed that increasing these factors increased the corrosion rate of carbon steel (CS). These tendencies were in good agreement with those in actual furnaces. A gas spray coating of two-layer Al/80% Ni-20% Cr, selected after laboratory corrosion tests, was applied to waterwall tubes at the test site. The Al/80% Ni-20% Cr spray coating maintained excellent durability for > 3 years, and its effectiveness in corrosion prevention was confirmed. This coating system has been applied at seven plants. Main deterioration factors affecting the coating layer were considered to be formation of corrosion scale and a decrease in bon...

The effect of the physical properties of boiler tube deposits on high-temperature corrosion of heat-resistant alloys was quantitatively examined to clarify the corrosion mechanism and to establish the most appropriate laboratory test method for the waste incineration environment. Laboratory corrosion tests were conducted in a simulated incinerator gas on four alloys. A crucible method was compared with a coating method at 550°C using synthetic deposits composed of NaCl/KCl/Na2SO4 = 1/1/1 mole containing various amounts of alumina, that was intended to control molten phase content in the deposits (MPC). The tests were conducted with deposits from two working plants. These deposits were found to be low in MPC. In the crucible method, a bell-shaped change of corrosion mass loss was observed for all the alloys. The change is thought to be due to a competitive effect of increase in MPC. The increase in MPC accelerates and depresses the corrosion because the molten phase is aggressive but hinders gas-permeation...