Distortion. — Distortion or bowing of the linerassemblies is extremely difficult to assess when viewedthrough the borescope.If an axial streak (gutter) isobserved to be out of contour, estimate the relativedistortion in terms of dimples spanned or in relation tothe diameter of the dilution holes. If the distortion ispresent at the No. 1 band, estimate the contour changeat the dome band relative to the panel.HP TurbineInspect the HP turbine for eroded or burned areas,cracks or tears, nicks or dents, and missing blades.Knifing (erosion resulting in sharp edges) can occur onfirst-stage blades. The severity will vary according tothe cleanliness of the turbine inlet air. Check for pittingon the leading edge near the root of the second-stageblading.Cracking of the first-stage nozzle guide vanes is notvery common, but photograph and report any suspectedcracks. First-stage vane surfaces at the juncture of theinner and outer platforms have a tendency to corrode orerode. It would not be unusual for you to find severalsmall penetrations in a vane platform during its servicelife. Most of these penetrations remain small and arenot usually severe enough to warrant enginereplacement.Record any such penetrations andregularly inspect them for any changes in size orquantity.Vane HP (concave) surfaces will show gradualerosion with time, and the trailing edge slots willbecome elongated.When this degradation reachesmaximum service limits, as noted on the PMS card orin the manufacturer’s technical manual, the engine mustbe replaced.HP turbine second-stage blades have a service lifethat is dependent upon operating conditions. Cracks arethe major inspection criteria listed. You shoulddocument and report any confirmed cracks. The mostcommon form of degradation is deposit buildup anderosion; this is not usually as severe as on the first-stageblades. The most serious form of damage that you mayfind in this area is pitting in the root area, which youmust document and report. For reference to the partsnomenclature used in this section, refer to figure 2-11,sections D and E.HP TURBINE NOZZLE DAMAGE.— T h efirst-stage turbine nozzle vanes are inspectedsimultaneously with the combustor and fuel nozzles.The following paragraphs describe the common damageyou may find during the borescope inspections.Discoloration.— Normal aging of the HP turbinenozzle stage 1 vanes will result in coloration changes asoperating time is accrued. There is no limit relative todiscoloration of HP turbine nozzle vanes.Oxidation and/or burning of the vane areas isaccompanied by dark areas silhouetting the initialdistress. Cracks are shrouded in dark patches adjacentto the defect. Usually the distress starts as a crack,followed by oxidation of the shroud adjacent to thecrack Impact damage usually shows as a dark spot onthe leading edge.Leading Edge Damage.— This type of damage canbe found between the forward gill holes on the concaveand convex side of the leading edge.Axial cracks form around the leading edge.Estimate the percent of span of the leading edgeor span relative to the nose cooling hole rows todetermine the crack length.Burns and spalling on the leading edge should notbe construed as coloration only, but must haveactual metal oxidized (surface metal loss), but noholes through the leading edge. Estimate the areaboundaries by the nose cooling holes spannedboth radially (up and down the leading edge) andaxially (around or across the leading edge).Record the number of vanes affected.Blocked cooling air passages on the leading edgeis another type of damage. If multiple holeblockage is observed, record the separation of theopen cooling holes and the number of adjacentplugged holes.Airfoil Concave Surface.— Radial cracks runspanwise in the vane airfoil surface (up and down thevane). Record the relative chord position of the cracks.Record the relation of axial cracking versus radialcracking, such as axial and radial cracks that intersector join at the second row of gill holes. The intent of theservice limits are to preclude the liberation (break-out)of pressure facepieces.Other Airfoil Area Defects.— The followingparagraphs describe other airfoil area defects that youmay find during the inspections.Burns and cracks on concave and convex sides(charred). Record the area and length, estimatethe length relative to the leading edge area (gillhole to gill hole and spanwise by span of coolingor gill holes).Estimate the surface damage2-20
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business