7EA S1 liberations occur on units with no history of clashing

7EA owner/operators have been conditioned to look for clashing damage in compressor stages 1 and 2 during inspections. Numerous presentations at the 7EA Users Group and CTOTF meetings by plant personnel, the OEM, Rod Shidler and Mike Hoogsteden of Advanced Turbine Support LLC, and others have kept the fleet on alert. Although the bases of some vanes, and the tips of some rotating blades, have been banged up by contact, there have been no public reports of vane and/or blade liberations traced to clashing—at least not yet.

The lesson here is the importance of inspecting the entire airfoil, not just where you would expect to find problems based on the experience of colleagues. Case in point: Users were surprised to learn of several full-chord S1 stator-vane tip liberations in the last few weeks. Information from one incident is shown in Figs 1-4. The top 1.25 in. of an S1 vane located at the 12 o’clock position went downstream, causing significant compressor damage. Note the nominal half-inch crack in the area of the vane where the liberation occurred (Fig 3).

Advanced Turbine Support’s Field Service Manager Hoogsteden told the editors this failure occurred after only about 12,000 operating hours and 184 total starts. The gas-fired unit had experienced 21 trips during its operational lifetime.

The service manager said he knew of another five 7EAs that recently had suffered S1 tip liberations from vanes located in the 1 to 2 o’clock position. All incidents led to catastrophic compressor wrecks. Leading-edge corrosion pitting was identified as the root cause of the failure in each of these cases.

Interestingly, all six units that were damaged are located outside the US and in close proximity to saltwater. At least one unit also was installed close to a refinery.

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