A used gas turbine's remaining life cannot be established from fired hours alone. Match the engine, installed parts, operating history, and completed work to the applicable OEM maintenance method. Then price the next required intervention, package completion, and service support before comparing the machine with another offer.
“Recently serviced” is a starting point for document review. It can describe anything from routine work to an extensive engine overhaul. The buyer needs to know which components were inspected, repaired, replaced, or retained, and which limits govern their next intervention.
The useful output is a dated condition-and-scope assessment for the offered equipment. It should show the next maintenance event, the evidence behind it, and the costed work needed to place the package into its intended service.
Key Takeaways
- Establish the OEM maintenance method before converting operating history into remaining interval.
- Keep hours and starts separate where the OEM uses independent limits; the earlier limit governs.
- Verify component history as well as engine history, including the scope of any overhaul or exchange.
- Compare complete generating packages on the same delivery and commissioning basis.
- Value documented maintenance position alongside parts support, service terms, and suitability for the new duty.
100 factored starts — the worked example below has this remaining allowance to its assumed hot-gas-path intervention; under the assumed duty, the starts criterion is reached before the hours criterion.
Establish exactly what is included in the offer#
Start with an equipment schedule identifying the engine, generator, gearbox where applicable, controls, auxiliaries, inlet, exhaust, and emissions equipment. Record the serial identity and supplied documentation for each major assembly. Describe exclusions as carefully as inclusions.
The expressions “gas generator,” “engine,” “core,” and “package” require particular care. Ask the seller to define the offered assembly against a bill of materials and general arrangement. A gas-generator or engine listing may exclude components needed to deliver electricity, including a power turbine where applicable. It cannot be compared directly with a complete generating installation.
Establish the boundary of the asset being priced#
| Offered scope | Evidence to request | Work to include in the comparison |
|---|---|---|
| Engine, core, or module | Assembly identity, configuration, installed-parts records, preservation history | Missing generating equipment, integration, controls, installation and testing |
| Packaged generating set | Complete equipment list, interfaces, condition reports for engine and package | Excluded auxiliaries, emissions treatment, civil and electrical connections |
| Installed plant offered for relocation | Plant drawings, operating records, dismantling scope, ownership and release documents | Removal, preservation, transport, reconstruction, new-site approvals and commissioning |
Use the gas turbine catalogue to establish the candidate family. Then move to the exact unit documents. The LM6000, GE 7F, and SGT-800 require different maintenance enquiries; their names alone do not establish the offered configuration.
Resolve frequency, generator voltage, fuel system, control interfaces, and intended duty before commissioning an extensive condition review. If the package cannot be adapted to the project on acceptable terms, an attractive position in its inspection cycle may have little purchasing value.
Use the OEM's maintenance method before calculating remaining hours#
Fired hours, starts, trips, and operating severity are inputs to maintenance assessment. They do not combine through one industry-wide equation. Ask the OEM or responsible service organization to identify the applicable manual revision, hardware configuration, calculation method, and governing limits.
For relevant heavy-duty GE machines, GER-3620 Rev P treats factored hours and factored starts as independent inspection criteria. It discusses operating factors including fuel, loading, injection, trips, and start cycles. The first applicable limit reached determines the inspection position; rotor maintenance has separate criteria.
For the GE 7F.04 example below, Figures 41 and 42 describe separate hot gas path (HGP) calculations. Factored hours sum fired hours in each mode, weighted for fuel, load, and water/steam injection severity. Factored starts weight start/stop cycles and add applicable fast-start, trip, and load-step adjustments. Those cycle adjustments belong to the HGP starts calculation. Use the OEM coefficients and qualifications for the installed hardware.
Request the calculation as an auditable worksheet. It should identify the source logs, factor applied to each operating category, event classifications, component history, and treatment of missing data. A total labelled “equivalent operating hours” without that supporting method is insufficient for a purchase decision.
Maintenance questions that differ by turbine family#
| Candidate | What the assessment must establish | Comparison error to avoid |
|---|---|---|
| GE 7F heavy-duty machine | Applicable factored-hours and starts limits for its installed hardware | Converting every start to an arbitrary fixed number of hours |
| GE LM6000 aeroderivative | Engine- and module-specific service schedule, life-limited parts, repair or exchange scope | Applying a heavy-duty combustion/HGP/major schedule to the aero engine |
| Siemens Energy SGT-800 | Applicable equivalent-hours or cycle-based maintenance plan and configuration | Treating a family-level advertised overhaul capability as the unit's remaining allowance |
| Solar Taurus 60 | Engine history, condition assessment, and agreed maintenance programme | Assuming a fixed interval from another industrial turbine family |
GE's aeroderivative service programme includes engine and module exchanges. That service architecture changes the records and commercial scope the buyer needs. Follow the identity and history of the delivered assembly, including any parts retained during repair.
For an SGT-800, obtain the maintenance plan that applies to the actual rating, fuel, and proposed dispatch. Its public service description offers time- or cycle-based concepts; it cannot certify the remaining life of an individual used machine.
Read inspection intervals with their hardware and duty basis#
An OEM baseline is useful for screening records. It becomes a unit-level maintenance position only after the installed hardware and operating history have been reconciled against it. Keep that distinction visible in the assessment.
The numerical interval table and worked example here cover a heavy-duty turbine only. An aeroderivative assessment follows the applicable engine and module maintenance instructions, including component limits and exchange history. The heavy-duty example cannot establish an LM6000 interval; obtain its configuration-specific schedule before calculating the next intervention.
Published reference intervals for GE 7F.04 heavy-duty turbines#
| Inspection | Factored hours | Factored starts | Published basis |
|---|---|---|---|
| Combustion, DLN | 32,000 | 950 | 60 Hz; base load; natural gas; no water/steam injection; applicable hardware qualifications |
| Hot gas path | 32,000 | 1,250 | Same baseline; separate hours and starts criteria |
| Major | 64,000 | 2,500 | Same baseline; rotor assessment remains separate |
Source: GER-3620 Rev P, Figure 36, printed page 29; frequency identification from GE's 7F product specifications. The maintenance figure qualifies hardware generations and upgrades; these reference intervals are not a guarantee for every used 7F.04.
Do not silently transpose this table to another suffix, an uprated combustion system, or an aeroderivative. Ask the service organization to state which published baseline applies and which unit-specific instructions supersede it. Keep the answer with the engine configuration record.
For an aeroderivative, request the separate hot-section, overhaul, module, and life-limited-part requirements that apply to the offered engine. Public sales tables can list service intervals without enough information to reproduce the maintenance assessment. Require the underlying schedule before assigning a remaining allowance to an LM6000 offer.
Also ask what each named event includes. Inspection, repair, replacement, overhaul, and exchange can describe different scopes. A completed intervention establishes only the work documented in its release records. It does not establish that every component in the generating package has begun a new life cycle.
The commercial question is therefore specific: which intervention is due next under the new owner's intended operation, what evidence establishes that position, and what is included in the quotation to complete it?
Calculate the next intervention under the proposed duty#
Use a consistent assessment date and project the relevant counters under the new operating schedule. Keep assumptions separate from recorded history. If the new duty is more cyclic, a generous hours allowance can coexist with a near-term starts limit.
The following calculation is an editorial example for a hypothetical 7F.04 HGP assessment. It assumes the published baseline above has been confirmed for the installed hardware. It also assumes the current counters and future annual increments have already been factored correctly by the responsible service organization. The example tracks exposure since the applicable HGP event and assumes intervening combustion inspections are current; each inspection counter needs the correct starting point. It describes no actual SecondWatt listing.
Worked example: independent hours and starts allowances#
| Calculation | Hours criterion | Starts criterion |
|---|---|---|
| Assumed applicable HGP interval | 32,000 factored hours | 1,250 factored starts |
| Assumed accumulated position | 24,000 factored hours | 1,150 factored starts |
| Remaining allowance | 32,000 − 24,000 = 8,000 hours | 1,250 − 1,150 = 100 starts |
| Assumed future accumulation | 4,000 factored hours/year | 200 factored starts/year |
| Time to criterion | 8,000 ÷ 4,000 = 2 years | 100 ÷ 200 = 0.5 years |
The starts criterion governs this example: min(2, 0.5) = 0.5 years. This is time to the assumed HGP criterion, not the remaining useful life of the turbine. Another component limit, condition finding, or inspection requirement could bring work forward.
Repeat the exercise for other governing events and assemble an outage schedule. Include access, removal, replacement parts, service availability, and the plant's ability to carry load while the unit is unavailable. The earliest counter limit identifies a planning need; it does not by itself describe the entire outage.
Where records are incomplete, do not fill the gap with a favourable average factor. Ask for a documented conservative assessment, further inspection, or a price and contract structure that reflects the uncertainty. If the uncertainty cannot be bounded, remove the unit from the comparable set.
Build the evidence file around components and completed work#
Begin with operating logs and the engine's lifetime history, then reconcile the counters against overhaul, module-exchange, and controls-change dates. A reset display should have an explanation. The chain must follow the physical assembly through previous owners and service organizations.
Records to request before accepting a remaining-life claim#
| Record | What the buyer should establish |
|---|---|
| Engine and major-assembly identities | Which physical components are included and whether records follow them |
| Fired-hours, starts, trips, and fuel logs | Source data for the applicable maintenance calculation |
| Borescope reports and original images | Inspection date, areas examined, findings, limitations, and disposition |
| Overhaul work packs and release documents | Work actually completed, tests performed, retained parts, and exclusions |
| Parts installation and repair history | Part identities, accumulated exposure, repair cycles, and applicable restrictions |
| Controls hardware and software history | Counter continuity, configuration changes, and supportability |
| Storage and preservation records | Condition during inactivity and the recommissioning work required |
| Outstanding recommendations | Unclosed findings, service instructions, and quoted corrective work |
A borescope report is one part of this evidence. Ask what the inspection could see, which areas were inaccessible, and whether the report explains the significance of each finding. A clean image does not establish unseen component history.
Solar's service programme describes combining machine data with physical condition evidence for maintenance planning. The purchasing implication is to require both records and inspection findings, with a named party responsible for their interpretation.
Rotor condition deserves its own review, separate from the most recent hot-section work. Siemens Energy's field-service offering includes nondestructive testing and independent inspection evaluation. Require the assessor to explain how the rotor's history, findings, and applicable limitations support the engineering conclusion.
Treat provenance precisely. Record who performed the work, the scope of any OEM authorization, and the warranty issued. An invoice headed “overhaul” is weaker evidence than the supporting work pack. Verify an authorization claim with the organization said to have granted it.
Compare purchase offers after completing the missing scope#
Build a comparison on the same equipment boundary, delivery condition, currency date, and intended service. State whether dismantling, transport, taxes, installation, emissions treatment, testing, and commissioning are included. Record exclusions before calculating a total.
Use SecondWatt's pricing tool as a starting point for examining the available observations. For any figure carried into a purchase memo, retain its evidence type, sample count, observation date, and equipment scope. Asking prices describe offers. A listing marked sold does not establish its clearing price. This article makes no claim about SecondWatt transaction prices.
Comparison worksheet for two used-equipment offers#
| Cost or risk item | Required comparison basis |
|---|---|
| Equipment consideration | Same included assemblies and delivery condition |
| Immediate maintenance | Written scope, parts assumptions, service slot, and acceptance criteria |
| Package completion | Quoted missing or incompatible components and integration work |
| Relocation and installation | Removal condition, preservation, shipping, civil and electrical scope |
| Emissions and site suitability | Costed changes needed for the intended operation |
| Commissioning and testing | Defined output and emissions test responsibilities |
| Uncertainty allowance | Explicit scenario tied to an unresolved finding, with its rationale |
Calculate the subtotal from those comparable quotations, then assess outage and schedule exposure separately to avoid double counting. A machine with more documented interval remaining can justify a different offer, but the premium should be tied to work and risk the buyer actually avoids.
Read the procurement roadmap alongside that comparison. The project's usable-power date depends on more than equipment availability. Where the application allows alternatives, the fuel-cell and turbine comparison provides a separate technology-selection discussion. Preserve the same load and project boundaries when comparing options.
Build the used gas turbine relocation scope alongside the condition assessment so dismantling, transport, site adaptation and commissioning appear in the same purchase comparison.
Secure service support and prepare an owner-side evidence package#
Ask for written parts and service availability for the next expected intervention. Identify which items are stocked, reserved, repairable, or subject to manufacturing lead time. A general statement that a model is supported does not establish availability for a particular outage.
For a proposed exchange, clarify the delivered assembly, condition standard, retained equipment, core-return obligations, inspection charges, and acceptance terms. Solar's overhaul and exchange offering illustrates why an exchange is a defined engine transaction. The existing generator and other package systems still need their own condition review.
Read any long-term service agreement before attaching value to it. Check transfer consent, coverage, exclusions, minimum payments, escalation, operating assumptions, and treatment of pre-existing findings. Request confirmation that the agreement will support the new owner's location and duty. Identify the commercial effect if it cannot be transferred.
An owner preparing to sell should assemble the same evidence before marketing the unit. Summarize configuration, included scope, supported maintenance position, outstanding findings, and availability. Keep detailed serial records and location information in controlled diligence material.
Solar's authorized pre-owned programme describes OEM inspection, service, and warranty options. It is a useful example of claims that should have documents behind them. It does not establish equivalent coverage for a separately offered machine.
For the broader reserve-power decision, use the backup-power procurement discussion to connect the turbine outage plan with the campus's required service. Avoid assuming that spare generation can carry the site until its capacity, controls, and operating permissions have been checked.
SecondWatt publishes independent equipment intelligence and connects buyers with sellers without taking equipment into inventory. Turbine owners can contact info@secondwatt.com to discuss the appropriate next step and document scope before sharing identifying records.
FAQ: used gas turbine remaining life and overhaul position#
How many hours are left in a used gas turbine?#
There is no reliable family-wide answer. Establish the applicable OEM maintenance method, component history, condition findings, and proposed duty. The resulting assessment should identify the next interventions and any component limits, rather than reducing the whole package to one remaining-hours figure.
Is a low-hour turbine always the better purchase?#
No. Starts, trips, operating severity, preservation, missing equipment, and service support can change the decision. Compare the work needed to achieve the same operating scope. Low recorded hours are useful only when the records and physical condition support them.
Does a major overhaul reset all component life?#
Read the completed work scope and installed-parts record. Some components may have been replaced, others repaired or retained. Establish the applicable history and limitations for each governing assembly. The package's controls, generator, auxiliaries, and emissions equipment require separate attention.
Can I convert starts into equivalent hours myself?#
Only through the method applicable to that machine and hardware. Some OEM approaches use independent hours and starts criteria. An arbitrary conversion can conceal the earlier intervention. Have the responsible service organization document the calculation and its source records.
What is an acceptable substitute for missing service records?#
Ask the OEM or qualified assessor what inspections, documentation recovery, or replacement scope would establish an acceptable position. There may be no practical substitute for some missing history. Price the defined recovery work and uncertainty before deciding whether to proceed.
Should an owner overhaul the turbine before selling it?#
Compare a documented as-is offer with the cost, schedule, and commercial effect of a specified overhaul. The next buyer may require a different duty or configuration. Obtain a service quotation and assess whether the proposed work improves the sale terms enough to justify doing it first.