Progress being made in combatting accelerated high-temperature corrosion caused by combustion products of residual fuel oils is reviewed. Results of laboratory investigations cannot be compared strictly because of wide differences in testing procedures used. No effective and economical method for removing all offending ash components has been found, although lowering of sodium content by washing with magnesium sulfate solution has been applied successfully to gas turbine operation. Available high-temperature alloys do not have adequate resistance to oil-ash attack at temperatures above 1200 F. Improved corrosion resistance has been attained with certain experimental alloys but some of these are difficult to fabricate into the required form and have inferior mechanical properties. Surface treatments such as aluminizing, chromizing and siliconizing appear to have some inherent protective value, but further development of procedures for applying impervious and adherent coatings is needed.
Investigation of oil additives has received the most attention in recent years. A great many inorganic, or metal-organic compounds are effective oil-ash corrosion inhibitors but only a few have been found to be economically feasible. Additives raise melting point of ash components so they will be solid at operating temperatures in boilers and gas turbines. Under certain conditions some additives reduce corrosion but increase deposit formation.
Progress is being made in basic studies to identify reactions taking place during combustion of oil and in appplication of this knowledge to establish mechanism of the corrosion reaction. 4.3.3
