HOT CORROSION IN GAS TURBINES
Hot corrosion (sulfidation) in gas turbine engines has become a major problem because of the increased use of alloys low in chromium and the operation in environments containing alkali metal salts, especially near sea water. The mechanism of attack is understood to some extent, but more work is needed. It is clear that sodium and other alkali metal salts are involved. Sodium sulfate is ingested with the combustion air or formed from the sulfur in the fuel, and reacts with the metal oxide scale acting as an Na2O sink to form a complex sodium salt. After scale breakdown, sodium sulfate may attack the underlying metal, forming sulfides. The presence of NaCl in the gas and a liquid salt film seem to be required for accelerated attack. Coatings, alloy modification, and additives to the fuel all help alleviate the immediate problem. Alloy development, dispersion hardened and fiber strengthened alloys, and rare earth additions to superalloys may offer longer-range solutions. Target performance properties are needed to focus the future research and development work. Sulfur can enter a gas turbine from the fuel, and chloride and sulfate salts from the air. There is little prospect for removal of these contaminants to such a degree as to eliminate the problem. However, from 10 to 75 percent of sea salt can be removed from the air intake to retard the attack. Data to tolerable levels of contaminants are needed. Engine testing is still the only reliable evaluation method to check improvements in the hot corrosion resistance of materials. Test rigs are commonly used for a preliminary evaluation of hot corrosion resistance. Reproducibility in test results from test rigs in different laboratories is very poor, and further effort toward test rig standardization, correlation of the data between different tests, and interpolation of tests results and extension to different testing conditions, all are needed. Specific recommendations for attacking the hot corrosion problem are detailed in the report.
National Materials Advisory BoardNational Academy of Sciences,National Academy of Engineering
Washington, DC United States 20418
- Publication Date: 1970-5
- Features: Appendices; Figures; References; Tables;
- Pagination: 70 p.
- TRT Terms: Alloys; Corrosion; Fuel additives; Gas turbines
- Old TRIS Terms: Alloy corrosion behavior; Hot corrosion; Sulfidation
- Subject Areas: Marine Transportation; Vehicles and Equipment;
- Accession Number: 00015501
- Record Type: Publication
- Report/Paper Numbers: NMAB-260 Final Rpt
- Contract Numbers: DA-49-083-OSA-3131
- Files: TRIS
- Created Date: May 13 1973 12:00AM