information relative to the stage, location on the blade(estimate the percent of chord and span), and thecondition of the surrounding airfoil. You do not have torecord the appearance of the defect (sharpness andcontour). Compressor stall is one of the worst thingsthat can happen to an engine. tip clang damage isdifficult to spot and gives the appearance of minordamage. The V-shaped notch on the top of a bladecaused by tip clang is only an indicator; it in itself is notthe damage. The damage is at the blade root andnormally cannot be seen.If a blade has beenoverstressed, it must be replaced.Platform Distortion.— Compressor blade platformfretting or shingling (fig. 2-14) can be observed on someafter stage blades. These distortions are the overlappingof one blade platform mating edge with the adjacentplatform edge. When shingling is found, the platformswill be distorted and bowed (fig. 2-15). When theplatforms are shingled, only the locking lug blades willexhibit this defect. Monitor this condition to see if aplatform crack develops. Also look for missing piecesaround the locking lugs. You must report and record anycracks in the platform. Be sure you have included thefollowing information:The stageThe number of bladesFigure 2-14.—Platform fretting or shingling.Figure 2-15.—Platform bowing.The spacing of the blade numbers separating theshingled blade platformsThe platform gap observation (estimate gap aspercent of circumferential span of the platform)The condition of the shingled edge (bent, fretted,or stepped as per table 2-1)Midspan Shroud Wear.— Some stage 1compressor blades show wear at the mating surfaces ofthe midspan damper shrouds. (See figs. 2-16 and 2-17.)Wearing of the tungsten-carbide wear coat causes themating face contour to change from a straight line to astepped line.This occurs at the after edge of theclockwise blade midspan (trailing edge) and the forwardedge of the counterclockwise blade midspan shroud(leading edge). In the step area, some metal maybeturned or protruding from the midspan shroud matingline (mushrooming). This protrusion is indicative ofwear-through. A missing pad on one face would initiatean accelerated failure of the mating surfaces.BLADE DEPOSITS.— Compressor blades andstator vanes exhibit varying degrees of cleanliness.Variables such as air-inlet configuration, ambientatmospheric conditions, and air contaminants(chemicals, salt, dirt, water, and so forth) all tend toaffect the surface condition of the compressor rotor andstator blades.A l u m i n u m D e p o s i t s . — Two areas in thecompressor assembly are coated with aluminum, the2-13
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