Frame 6Bs under the microscope: Cracking of S1 stator vanes, liberated S17 vanes

The sun was setting at Advanced Turbine Support LLC’s Florida headquarters last Saturday when Director of Field Services Michael Hoogsteden took a break to call the CCJ editors and report two “just-founds” during compressor inspections of Frame 6Bs—an engine that rarely makes the news.

No. 1: In the previous 48 hours, company inspectors had identified mid-chord cracking (Fig 1) on the suction side of three S1 stator vanes located in the lower half of one 6B compressor. Clashing damage, caused by contact between the leading edge of stationary vane tips with the trailing edges of rotor blades at the platform, also was in evidence.

1. Eddy-current inspection is critical for identifying mid-chord cracking, which can “hide” from dye-penetrant detection

1. Eddy-current inspection is critical for identifying mid-chord cracking, which can “hide” from dye-penetrant detection

No. 2: S17 stator vane and exit guide vane liberations (Figs 2 and 3) were found in three different units. The liberated vanes resulted in significant collateral damage and forced the engines out of service. Lesson re-learned from the aft-compressor findings was the importance of regular borescope inspections to verify both the condition of airfoils and the existence of counterbore plugs in all Model 6581 units.

2, 3. S17 stator-vane (left) and exit-guide-vane liberations (right) were easy to identify during borescope examinations

2, 3. S17 stator-vane (left) and exit-guide-vane liberations (right) were easy to identify during borescope examinations

Recall that Advanced Turbine Support has been at the forefront of the industry’s efforts to identify compressor issues for more than a decade. The company’s technicians were the first to find and report clashing damage in the 7EA fleet (2006), the first to report locating stator-vane cracks in the “area of interest” described in the OEM’s Technical Information Letter 1884, first to demonstrate the value of eddy-current inspections over dye penetrant for mid-chord crack identification, etc.

Hoogsteden and colleagues previously reported to owner/operators its findings of clashing in GE 7FAs, 6Bs, and Frame 5s, as well as in 7Es; however, this is its first report of mid-chord cracking in an engine other than a 7E.

Users can catch up with the Advanced Turbine Support experts at the Frame 6 Users Group’s 30th annual conference, June 13-16, at the PGA National Resort & Spa in Palm Beach Gardens, Fla.

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