Understanding the lingo of LM engine component dispositions

MT R&O LLC’s Rick Kowalski, PE, presented at the WTUI’s special technical session, Mar 17, 2015 on topic of interest to most attendees: “Maintaining an Ageing Fleet through Parts Repairs.” He opened by saying that repair and overhaul (R&O) are key components in serviceability strategies used throughout the four aero fleets served by the Western Turbine Users: LM2500, LM5000, LM6000, and LMS 100. Component salvage options are available for the proportionate extension of part serviceability, he continued, with material-add constituting the largest portion of component R&O—through standard joining, plating, thermal spray, coating, and custom mods. 

The speaker learned through discussions with LM owner/operators the following influences on repair decisions:

      • OEM guidelines and recommendations can drive decisions for replacement versus repair for serviceability.

      • Access to inventory is controlled and can be limited.

      • There is finite availability for replacement parts in the market.

      • There is an expressed need for salvage options with existing engine components.

Kowalski reviewed the attributes of the repair technologies identified in the opening paragraph for extending part serviceability and offered a couple of examples—including bearing journal restoration by use of thermal spray, and replacement of the wear strip on the No. 3 bearing stationary seal with an improved component.

The need for evaluation and disposition follows every aspect of engine and component review and processing, he continued—including visual and borescope inspection, engine teardown reviews, component reviews, and standard R&O in-process.

The portion of Kowalski’s presentation concerning dispositions and how to use them was particularly instructive, in the editor’s opinion. He began by identifying five functionally available dispositions cited in military standards:

      • Accept/use as is.

      • Rework.

      • Repair.

      • Reject.

      • Scrap.

The speaker said the primary purposes of the corrective action and disposition system, as spelled out in MIL-STD-1520, are to identify and correct causes of nonconformances (including those identified in engine-run hardware), prevent the recurrence of wasteful practices, reduce the cost of manufacturing, and foster quality and productivity improvement.

Accept/use as is, despite one or more minor nonconformaces, is a decision that should be made by an individual qualified to evaluate the usability of a part for its intended purpose in its existing condition. Kowalski stressed that the decision-maker must understand how the part impacts the system and know that the as-found condition is benign to any system effects in its “as-is” state.

Rework is a disposition applied to a nonconformance that will eliminate it and result in a characteristic that conforms completely to the drawings, specifications, or contractual requirements.

Repair reduces but does not completely eliminate a nonconformance but has been reviewed and concurred by an owner or its authorizing agent. Repair is distinguished from rework in that the characteristic after repair still does not completely conform to the applicable specs, drawings, or contractual requirements.

Reject is a temporary disposition allowing the part condition to be accepted or corrected at a later date or by way of alternative repair development.

Scrap is a permanent disposition and requires part destruction to prevent its further availability for engine duty. This disposition only can be made by the hardware owner, unless the owner formally authorizes a representative to act on its behalf.

Kowalski closed out his presentation with a series of case histories illustrating the various dispositions. They included a nick on a bearing journal that was disposed as a reject; pitting of components in the low-pressure compressor (LPC); and cracks, nits and scratches, and dents in the LPC case.

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