Most of the maintenance ideas presented in Chapter 5 are also applicable to the axial. Concentricity of the rotor clearances in the stator is again stressed. Rotor tip clearances allow a reasonable tolerance. A 10% clearance change is not greatly significant.

When an axial is taken out of service, the blading should be carefully cleaned and inspected. If minor damage is noted, the blade should be repaired or, if the damage is significant, it should be replaced. In most cases, minor, foreign-object "dings" or cracks can be ground out and blended. If several blades in a row show cracking, a note of the accrued operating time of that row should be made and the manufacturer consulted to ensure that a more serious problem isn't beginning to show. With

Figure 6-11. Adjustable stator blade linkage. (Courtesy of Elliott Company)

reasonable operation, not too many hours in surge, or no gross upsets, blading should last 50,000 hours or more. If no cracks are detected, blades should be randomly selected and examined by one of the NDT methods. Should any cracks be detected, very strong consideration should be given to replacing the entire blade row in which the cracked blade was located.

If movable stator blades were used, the linkage should be checked for binding and wear. If a clean gas purge was used to keep the linkage clean and dry, the source and supply lines should be inspected to make sure they all work as intended when the compressor is restarted.

Beyond these items, the balance of the maintenance procedure should include the customary bearing and seal checks.

1. NASA SP-36, Aerodynamic Design of Axial-Flow Compressors, NASA,

2. Alleyne, C. D., Carter, D. R., and Watson, A. P., Cleaning Turbomachinery Without Disassembly, Online and Offline, Proceedings of the 24th Turbo-machinery Symposium, Texas A&M University, College Station, TX,

3. Horlock, J. H., Axial Flow Compressors, Malabar, FL: R. E. Kreiger Pub-

4. Shepherd, D. G., Principles of Turbomachinery, Toronto, Ontario, Canada:

5. Boyee, M. P., Gas Turbine Engineering Handbook, Houston, TX: Gulf

6. Lieblein, Seymour, "Analysis of Experimental Low-Speed Loss and Stall Characteristics of Two-Dimensional Compressor Blade Cascades," RM E57A28, NACA (NASA) 3-19-57, Declassified 6-24-58.

7. Emery, J. C., Herrig, L. J., Erwin, J. R., and Felix, A. R., Systematic Two-Dimensional Cascade Tests of NACA 65-Series Compressor Blades at Low

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