THE EROSION-CORROSION OF ALLOYS UNDER OXIDIZING-SULFIDIZING CONDITIONS AT HIGH-TEMPERATURE

A whirling-arm erosion-corrosion rig has been designed and constructed to allow studies under gaseous conditions of high-sulphur, low-oxygen activities at high temperatures; these environments are pertinent in processes such as gasification of coal and catalytic cracking of oil. The system can operate at particle impact velocities up to 30 m s(-1), particle impact fluxes up to 1 g cm(-2) s(-1) and temperatures up to 800 degrees C. The particles are carried to the specimen chamber in a stream of nitrogen and mixed with hydrogen, hydrogen sulphide and, if necessary, water vapour to attain the required sulphur and oxygen activities. In this paper, results are presented for two commercial austenitic high-temperature alloys, 310 stainless steel and Alloy 800HT, during impact erosion by 25 mu m alumina particles at velocities of 10-25 m s(-1) and particle fluxes in the ranges 0.06-0.16 g cm(-2) s(-1) and 0.38-0.95 g cm(-2) s(-1) at 500 degrees C. The gaseous environment resulted in the development of sulphide scales on the alloys during exposures in the absence of the erodent particles. The erosion-corrosion damage was determined in terms of mean thickness-change measurements obtained every 5 h and overall metal-recession rates obtained by cross-sectional examination at the end of the 35 h or 70 h exposure periods. The results are discussed in terms of the synergistic interactions of growth of metal sulphides and removal of such phases by the impacting particles.