The interactions of sulphidation and particle erosion at high temperatures

Although there have been many studies of erosion-corrosion of alloys involving impact by solid particles in air or oxygen at high temperatures, there have been very few, if any, in gases of high-sulphur, low-oxygen activities. As these environments are pertinent in processes such as coal gasification and catalytic cracking of oil, there is a need for some basic studies of the interactions of erosion and corrosion in oxidizing/sulphidizing gases. Thus, a whirling-arm rig has been designed and constructed; it can operate under a range of erosion conditions (velocities to 30 m s(-1), particles fluxes to 1 g m(-2) s(-1)) in gaseous environments consisting of mixtures of nitrogen, hydrogen, hydrogen sulphide and water vapour as necessary, at temperatures to 800 degrees C.

Some preliminary tests have been carried out using 310 stainless steel and Alloy 800HT at 500 and 700 degrees C and Fe-2.25Cr-1Mo and 410 stainless steel at 500 degrees C. Erosion particles were 25 mu m alumina, with impact velocities of 10 to 25 m s(-1) and fluxes of 0.06 to 0.16 g cm(-2) s(-1). The gaseous environment was a mixture of hydrogen, hydrogen sulphide and nitrogen; this caused sulphidation of all the alloys at both temperatures. The extents of erosion-corrosion damage were determined by thickness-change measurements taken every 5 h and overall metal-recession measurements taken at the end of the full test period of 35 h.

The extents of damage were increased significantly with increasing impact velocity for the austenitic alloys at 700 degrees C; similar trends were observed at 500 degrees C for Fe-2.25Cr-1Mo and 410 stainless steel, although the presence of impacting particles had only a small effect on the austenitic alloys at the lower temperature. These initial results are discussed in terms of the interactions of growth of the sulphide scale and removal of scale by the particles.