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Hot Gas Path Inspection — Inspection Procedures
Nozzle Cracking
Nozzles experience several thermal gradients during starting as well as high temperatures during
loading operation. Such conditions frequently cause nozzle cracking and, in fact, cracking is ex-
pected. With certain exceptions, this cracking does not impair the efficiency or the mechanical integri-
ty of the nozzle. Figures HGP-I.1 through HGP-I.5 display typical cracking patterns. The cracks
shown are acceptable and do not require immediate repair. If uncertainty arises in regard to any cracks,
such as types not represented by Figures HGP-I.1 through HGP-I.5 contact your General Electric
Company Field Service Representative for disposition. Obtain specific advice prior to making repairs
when nozzle condition is considered beyond established limits.
Although to date we have found very few cracks that could impair the mechanical integrity, they can
exist. The inspector should be alert for the following which may require immediate disposition (i.e.,
repair or scrap):
1. Open cracks in critical areas: Open cracks can permit ingestion of hot gases. An open crack is
defined as a crack sufficiently open to pass a 0.005 in. feeler gauge and having a length of 1.0 in.
or more. The critical areas are certain regions of the vane and inner sidewalls and are shown in
Figure HGP-I.6.
2. Cracks that could cause part breakout: Cracks whose orientation and growth rate are such as to
raise questions of the dislodgement of significant portions of the nozzle must be evaluated. See
Figures HGP-I.7 and HGP-I.8 for more details.
3. Continuous fillet cracks on one vane side: Cracks such as this can cause air-foil separation. See
Figure HGP-I.8 for further details.
Nozzle Foreign Object Damage
Nozzles can be severely damaged by foreign objects in the gas stream. This damage can impair the
structural integrity and aerodynamic performance of the nozzle. Such damage should be evaluated
by the following criteria:
1. All tears and breaks must be evaluated by the same criteria given above for cracks.
2. Raised metal must be blended to the adjacent surface contours.
3. Nicks and chips must not exceed 50% of the wall thickness.
4. Cooling holes must be open, capable of passing a 0.050 in. wire.
Corrosion or Erosion of Nozzles
There have been no cases of severe corrosion or erosion of nozzles to date. The following guidelines
are provided, however, in the event that such cases develop:
1. The allowable amount of vane region metal removal is 50% of the wall thickness (0.100 in.).
2. Sufficient trailing edge material must be maintained to prevent nozzle cooling hole exposure.
3. Area and harmonic checks must be performed where significant material removal has occurred.
HGP-I-2
Inspection and Maintenance — GEK 107048
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