Emergency Rebuild for the Power Generation Industry Case Study

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Emergency Rebuild for the Power Generation Industry

Background

A major city in the Southeastern United States had been using six Philadelphia Gear gas turbine generators - typically rated from 16 to 30 megawatts - to supplement their power grid during times of peak usage. Installed nearly three decades ago, the city neglected to maintain and service the units - not uncommon for users of these types of generators. This lack of equipment predictive maintenance procedures can often become problematic, as was the case with the city's six units.

Metal-on-metal parts require lubrication to prevent premature wear, metal fatigue, and potentially catastrophic failure. Over a period of time the oil is consumed and must be refilled. Additionally, every 3-5 years (depending on usage and environmental factors) the units require a complete oil change - approximately 3,000 gallons each for units this size. In this case, only periodic refills had been administered, though not on a routine basis. This lack of lubrication caused metal fatigue and severe pitting, as well as brittle gears.

The Problem

The generators were in use for nearly 30 years and had never undergone a complete oil change - oil had been topped off occasionally, but not as part of a planned predictive maintenance schedule. Adding to the problem, the city upgraded their performance efficiency from 24 to 29 megawatts, placing even more wear and tear on the mechanical components - particularly the gear sets. Eventually the bearings failed in one of these units, causing excessive vibration that destroyed the gears and shut the unit down in the process.

The Solution

The gearbox was sent to the Philadelphia Gear Eastern Regional Service and Manufacturing Facility in New Castle, Delaware for inspect and cost/benefit analysis to determine whether a repair of the existing unit was feasible. The alternative was to manufacture a completely new gas turbine generator. The on-site team of technicians and engineers determined that the repair would cost $100,000, compared to a replacement cost of $200-250,000. In addition to cost savings, the advantage of such a refurbishment would be time - 18-20 weeks for the rebuild versus a manufacturing time of 26-30 weeks. The decision was easy

At the Service and Manufacturing Facility, the unit underwent a series
of tests, including:

• Magnetic particle inspection of all gear elements and quill shaft (this is a sophisticated black light test that reveals pits, cracks, etc.)

• Check of quill shaft for straightness

• Measurement and charting of current tooth geometry per design specifications

• Calculation of stress levels in damaged pinion, bearing journal and design bushing

• Visual inspection of bearings to evaluate cause of failure

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Power Generation Emergency Rebuild

Power Generation Emergency Rebuild Solution

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