TL;DR
Wide exhaust temperature spread with high firing temperature points to combustion non-uniformity or blocked bucket cooling. Perform a borescope inspection and check fuel nozzle balance.
What you might see
- exhaust temperature spread above alarm limit
- firing temperature higher than normal for the same load
- visible discoloration on first-stage buckets at borescope inspection
- combustion dynamics alarms from the DCS
Likely causes
Plugged or partially blocked turbine bucket cooling holes reducing blade cooling effectiveness
Fuel nozzle flow imbalance creating hot streaks through the turbine
Combustor liner damage allowing hot gas bypass to the first-stage blade row
Firing temperature control error from a failed thermocouple biasing the control system high
Required tools
- Borescope (video borescope preferred for documentation)
- DCS exhaust temperature spread trend
- Combustion dynamics data if available
Safety first
- Hot section temperatures can exceed 1400 degrees C during operation. The turbine must be offline and cooled to safe temperature before any internal access.
- Lock out the turbine turning gear and confirm zero gas pressure before opening any combustor or hot-section access panel.
Procedure
- 1
Review exhaust thermocouple spread data. A spread above the alarm limit (typically 30-50 degrees F depending on the machine rating) indicates uneven combustion or a cooling issue.[1]
- 2
Check for any failed or out-of-range exhaust thermocouples. A single thermocouple failure can falsely indicate spread if the control system averages its value.
Warning: All hot-section inspections require the turbine to be offline, cooled, and locked out. No internal inspection is possible on a running unit. - 3
Review combustion dynamics data for any can showing elevated pressure oscillations, which indicates a fuel-air mixture problem in that can.
- 4
At the next available outage, perform a borescope inspection of the first-stage buckets, nozzles, and combustor liners per the OEM inspection procedure.
- 5
Document any oxidation, cracking, or coating spallation on the buckets. Compare finding severity to the OEM's accept/reject criteria.
- 6
Inspect fuel nozzles for wear or plugging. Send nozzles for flow-check and cleaning if any show more than 5% flow deviation from nominal.
- 7
Return to service only if borescope findings are within the OEM run/repair limits. Otherwise, pull the affected stage hardware for refurbishment.
Sources
GE Vernova GE 7HA.02 / 7F.05 Gas Turbine (Heavy / Aero) general technical documentation, GE Vernova
Gas turbine hot-section inspection, exhaust temperature spread analysis, general power generation references (general)
More guides for GE Vernova GE 7HA.02 / 7F.05
How to reduce combustion dynamics and pressure oscillations on a GE Vernova GE 7HA.02 / 7F.05 gas turbine
High combustion dynamics come from fuel-air ratio instability in the combustion can. Verify fuel nozzle pilot split, check for blocked nozzles, and compare fuel heating value to the turbine control system's expected value.
How to recover power output loss from compressor fouling on a GE Vernova GE 7HA.02 / 7F.05 gas turbine
Compressor fouling reduces airflow and raises heat rate. Perform an online water wash first. If performance does not recover, plan an offline crank wash at the next available outage.
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