Second And Third Stage Buckets - GE MS-6001B Maintenance Instructions Manual

Hot Gas Path Inspection — Inspection Procedures
2. Dents — Dents are permissible with the following limits:
a. The dent must not contain any cracks per the above paragraph.
b. The dent must not obstruct the diameter of, or penetrate into a cooling air hole. The cooling
hole closest to the leading edge, should pass a 0.067 in. diameter wire or next larger standard
ball to be acceptable. Holes 2 through 12 must pass a 0.050 in. diameter wire or a next larger
standard ball to be acceptable. The trailing edge hole must pass a 0.034 in. diameter wire or
next larger standard ball to be acceptable.
c. A dent must not be more than 0.090 in. deep. Therefore in areas where metal thickness to a
cooling hole is not the limiting factor, a dent may be blended to remove resulting cracks or
metal displacement, providing the 0.090 in. limit is not exceeded.
3. Missing Metal — Missing metal on first stage buckets occurring in the squealer portion can be
repaired by blending. Missing metal or radial cracks in the squealer portions can be corrected with-
in the following limits:
a. The squealer tip wall may be removed for a surface distance of 1.0 in. from the leading edge
on the suction side of the bucket.
The squealer tip wall may be removed for a surface distance of 0.50 in. from the leading edge
on the pressure side of the bucket. See Figure HGP-I.11 Squealer Tip Repair Limit.
b. Missing metal, dents and blending cracks in the leading edge must not extend more than 0.750
in. down from the top edge of the bucket. No more than five buckets total may have leading
edge blending below the squealer section without a resultant loss in performance. See Figure
HGP-I.11 Leading Edge Repair Limits.
4. Corrosion — First stage buckets are more susceptible to damage by corrosion, erosion, and oxida-
tion than second or third stage buckets. This condition usually first appears on the leading edge
of the airfoil as a flattening and roughening of the surface; however, the entire airfoil is susceptible
to corrosion, erosion or oxidation attack.
Direct measurement of this wearing is difficult, if not impossible; however, a general criteria can
be established. The cooling hole closest to the leading edge is approximately 0.15 in. from the lead-
ing edge and about 0.06 in. from the airfoil suction side surface. The corrosion pattern on the lead-
ing edge will allow a maximum of 0.088 in. corrosion before a breakdown of the hole closest to
the leading edge occurs. This breakdown appears as a depression on the suction side surface, near
the leading edge. If this condition appears on the first stage buckets, replacement is required.
If some lesser amount of corrosion is observed, judgment is required to weigh the possibility of
a corrosion related failure against the cost of replacement of buckets at the time of inspection.
Realize the 0.088 in. of corrosion constitute a total corrosion life. The fraction of 0.088 in. removed
is the fraction of the life used (it is assumed that corrosion progresses linearly with time). Replace
the buckets if total corrosion life is predicted before the next planned inspection.

Second and Third Stage Buckets

1. Cracks — Cracks also occur in the second and third stage buckets due to foreign object damage.
These cracks usually occur at the airfoil leading edge in the outer span sections.
HGP-I-10
Inspection and Maintenance — GEK 107048