Performance Degradation Tracker — Output & Heat Rate Loss

Baseline corrected output (MW)

Baseline corrected heat rate (kJ/kWh)

Current corrected output (MW)

Current corrected heat rate (kJ/kWh)

Operating hours since baseline

Quantity	Value
Output degradation	–
Output loss in MW	–
Heat-rate degradation	–
Degradation rates (per 1,000 operating hours)	–
Extra fuel at current output	–
Extra fuel energy	–

The Calculation, Explained

What degradation is — and is not

Degradation is the loss of corrected performance between two points in a machine's life:

Output degradation % = ( P_current,corr − P_{baseline,corr} ) / P_{baseline,corr} × 100

Heat-rate degradation % = ( HR_current,corr − HR_{baseline,corr} ) / HR_{baseline,corr} × 100

The word corrected does all the work in those formulas. Both points must first be corrected to the same reference conditions — otherwise you are comparing a July afternoon with a January morning and calling the weather "wear". Get both points corrected with the Performance Correction Calculator, then come back here.

Recoverable and non-recoverable

Recoverable degradation — compressor fouling, fouled heat-exchange surfaces, dirty filters. Restored by washing and cleaning; on a gas turbine this is commonly 1–3% of output over a fouling cycle.
Non-recoverable degradation — erosion, corrosion, seal and tip-clearance wear, hot-gas-path ageing. Restored only by overhaul. Typically accumulates at a fraction of a percent per thousand hours and is what the per-1,000-hour rates above are for: a plant losing heat rate much faster than its historical rate is telling you something specific has happened, not that time has passed.

Assumptions and applicability

Baseline and current points at the same load setting and boundary, both corrected identically. A baseline from the acceptance test is ideal; a post-overhaul test is the practical alternative.
The fuel penalty is computed at the current output: extra fuel = P₁ × 24 h × (HR₁ − HR₀). It answers "what does today's condition cost per day", not "what would the old machine have saved at full load".
A single pair of points shows change, not trend. Two-point snapshots carry the full measurement noise of both tests; monthly corrected points on a trend line are worth ten arguments.

Worked example (the defaults above)

Baseline (acceptance test, corrected): 420.0 MW at 9,866 kJ/kWh. Today, 8,500 operating hours later, corrected: 402.5 MW at 10,240 kJ/kWh. Output degradation = −4.17% (17.5 MW missing); heat-rate degradation = +3.79%; rates of −0.49% and +0.45% per 1,000 hours. The fuel penalty at today's output: 402,500 kW × 24 h × 374 kJ/kWh = ≈ 3,613 GJ (3,424 MMBTU) of extra fuel every day — the number that turns a performance discussion into a maintenance-budget approval.

Practitioner's note. When degradation appears suddenly, suspect the measurements before the machine: a drifting inlet-temperature sensor manufactures "degradation" more reliably than any fouled compressor. Check instrument plausibility first — it is the cheapest overhaul you will ever do.

References

ASME PTC 46 / PTC 22 (correction methodology prerequisite); ISO 2314 (acceptance tests and degradation allowances in gas turbine contracts).

Related reading: What a Performance Test Really Proves.

Related calculators: Performance Correction · Vibration Severity

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