Figure 2-26.—HP turbine blade flaking and buildup.Record the magnitude and span location relative to thenumber of gill holes spanned. Estimate the out ofcontour as percent of the leading edge frontal area widthor relative to the lateral spanning of the leading edgecooling hole rows.Blade Tip Nibbling.— The HP turbine rotor stage1 blade tip nibbling is associated with hot runningengines. Momentary overtemperature operation (suchas experienced during compressor stalls) has exhibitedthis type of deterioration. This area of the blade is abovethe tip cap and located about two-thirds of the chord aftfrom the leading edge. Figure 2-27 shows a typical“nibbled tip” as a result of a severe stall.Blade Leading Edge Impact Damage.— Figures2-28 and 2-29 show an impacted and distorted leadingedge of a stage 1 HP turbine rotor blade. (Note thecracking condition leading from the impact area into theairfoil surface.) The critical part of this type of damageis the axial or chord wire cracking. If this crackingprogresses from the impacted damaged area into theFigure 2-27.—HP turbine blade tip nibbling.convex or concave airfoil surface, the damage can besevere.HP Turbine Blade Coating Failure.— The HPturbine protective coating is the key factor in the service2-22
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