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Figure  2-16.Compressor  blade  midspan  shroud  wear.
Figure  2-19.Combustion  liner  dome  band  and  plate  cracks.

Gas Turbine Systems Supervisor - Supervisor manual for Gas Turbine Engines
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shrouding   over   the   blade   tips   and   the   rotor   drum   area under  the  stator  vanes.  tip  rubs  of  either  the  blades  or the  vanes  will  rub  off  the  aluminum  coating.  As  time  is accrued  on  the  compressor  assembly,  the  after  stages  of the  rotor  release  or  flake  the  aluminum  coating.  This deterioration   is   a   normal   progression.   Flaking   occurs because   of   the   differences   in   thermal   expansion   of dissimilar   metals   and   the   differences   in   the   size   and configuration   of   the   various   parts.   The   released aluminum  flakes  enter  the  airstream,  impact  the  rotor blades   or   vanes,   and   splatter   the   airfoils.   Aluminum splatter  observed  forward  of  stage  11  can  be  caused  by object   damage   or   aluminum   flakes   that   are   rubbed   out of  the  compressor  case  coating.  This  condition  requires a  thorough  inspection  of  the  forward  compressor  stages. Leading  Edge  Buildup.—  Aluminum   buildup   on the  leading  edges  of  blades  is  usually  observed  in  stages 11  through  16.  The  buildup  changes  the  contour  of  the airfoil  and  can  alter  the  stall  margin.  You  should  report the   presence   of   leading   edge   buildup   in   the   inspection report.   This   type   of   buildup   may   occur   on   low-time compressors. The   compressor   blades   tend   to   “self clean”  or  lose  this  leading  edge  buildup  as  the  assembly accrues  time. Airfoil   Powdering.—   Compressor  rotor  blades  may have   aluminum   particles   visible   on   the   airfoils   in varying   degrees   (from   stage   to   stage).   This   powder   is indicative  of  a  possible  compressor  stall  or  a  hard  blade tip  rub. Combustion   Section Inspect   the   combustor   for   eroded   or   burned   areas, cracks,  nicks,  dents,  hot  streaks,  flatness  of  liners  caused by  hot  spots,  blocked  air  passages,  and  carbon  buildup. If  damage  is  found  in  the  combustion  section,  it  usually consists  of  a  burn-through  in  the  dome  area  adjacent  to a   fuel   nozzle.   The   problem   can   usually   be   traced   to   a loss  of  film-cooling  air  caused  by  upstream  debris  or  to a   faulty   fuel   nozzle. Cracking   is   not   normally   a problem,   but   you   should   photograph   and   report   any suspected   or   confirmed   cracks.   Carbon   deposits   around the   fuel   nozzles   occur   on   all   engines   and   are   not considered  serious.  These  deposits  build  up  only  on  the venturi   and   swirl   cup   rather   than   on   the   shroud   or discharge  orifice.  They  do  not  usually  interfere  with  the fuel   spray   pattern.   If   you   find   cracking,   evaluate   it   to ensure   that   no   pieces   will   detach   and   cause   any secondary   damage   to   the   HP   turbine.   For   reference   to parts   nomenclature   used   in   the   following   section,   refer to  figure  2-11,  sections  B  and  C. COMBUSTION   SECTION   DAMAGE.—   In  the following  paragraphs,  we  describe  some  of  the  damage that  you  might  find  during  a  borescope  inspection  of  the combustion  section.  Because  the  dark  surfaces  in  the combustion   section   absorb   light,   you   will   need   a 1,000-watt  light  source  for  a  proper  inspection. Discoloration. —  Normal   aging   of   the   combustor components   will   show   a   wide   range   of   color   changes. This   is   not   a   cause   for   concern.   As   operating   time   is accrued   on   the   combustor   assembly,   an   axial   streaking pattern   running   aft   of   every   other   circumferential   fuel nozzle  will  occur. On   low-time   assemblies,   the coloration  is  random  and  has  little  or  no  information  to aid   you   during   the   inspection.   As   operating   time increases   on   the   assembly,   you   will   observe   significant deterioration   at   the   edges   of   the   streaking   patterns. Cracking  will  begin  in  the  forward  inner  liner  panels  and will  propagate  aft.  The  axial  cracks  tend  to  follow  the light   streaks.   Panel   overhang   cracking   and   liberation usually  occur  at  the  edge  of  the  streaks. Riveted   Joints.— The  dome  band  and  the  inner  and outer  liner  assemblies  are  joined  by  rivets  as  shown  in figure  2-18.  The  presence  and  condition  of  the  rivet heads  and  rivet  holes  are  easily  assessed  because  of  their position   in   relationship   to   the   borescope   ports.   Record any  missing  rivets  and  torn  or  cracked  hole  edges. Dome   Assembly. —   Distortion   of   the   trumpets and/or  swirl  cups  is  random  and  occurs  on  high-time assemblies.   Record   the   distortion   (in   percent)   of   the edge   and/or   span   of   the   trumpet   and   the   percent   of circumference   versus   diameter   of   the   swirlers. Figure  2-18.—Combustion  liner  dome  rivet  joint. 2-15







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