Erosion-corrosion behavior of alloys in chlorine containing atmospheres

摘要

The heat exchanger tubes in fluidized bed waste incinerators suffer from high temperature erosion-corrosion due to impact of sand flown by a hot air stream which contains chlorine. The combined effect of erosion and oxidation/corrosion often accelerates loss of alloy substrates during service of waste incinerators, therefore it is necessary to find/develop the alloys which are resistant for not only erosion or corrosion but also erosion-corrosion. The goal of this project is to develop the erosion-corrosion resistant coatings for the heat exchanger tubes in fluidized bed waste incinerators. In this study, we investigated the method to evaluate the erosion-corrosion behavior of different alloys, which includes the design of the test rig and experimental condition such as air flow rate, chlorine content, and angle of incidence of sands. Ni-Cr-Fe based alloys were used in this study. The surface of the specimens was finished up to 1200 grit using SiC paper. A specially designed rig was used for the erosion-corrosion experiments. The rig consists of two separated chambers, one for erosion-corrosion by sand and one for heating introducing air. The temperature of sample and sand was kept at 350°C and 700°C during erosion-corrosion test, respectively. Compressed air with a flow rate of 20-25 L/min was heated to 400°C prior to introducing the test rig, and further heating to 700°C in the bottom chamber in the rig before causing the sand to float for erosion in the upper reaction chamber. The impact angle of the sand was changed from 45° to 90° by changing the angle of specimen holder. Plain sand and sand mixed with 0.5 and 1 wt% of NaCl-KCl salt (equal in molar fraction) were used in this study to evaluate the effect of initial salt contents. To ensure a continuous supply of chlorine a crucible containing a salt mixture (Tm=546°C) was placed in the bottom chamber somewhere near the heating elements with approximate temperature of 600°C. Current results indicated that higher air flow rate and lower incident angle to surface increase the erosion-corrosion rate. The erosion-corrosion rate was significantly increased by addition of salt in sand. The alloys which are higher resistance against for high temperature corrosion in air+Cl_2 tended to show poorer erosion-corrosion resistance.