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What is the Testing and Commissioning of Gas Turbine?
The Testing and Commissioning of Gas Turbine entails an extensive series of assessments to ensure that the turbines operate as efficiently as possible in accordance with their design specifications. This crucial stage involves operational and inspection tests, component alignment, control system verification, and adherence to safety procedures.
Before the turbine is put into full operational mode, tests are conducted under various loads to mimic operational situations, evaluate vibration and temperature levels to anticipate any mechanical problems, and ensure the turbine’s dependability and efficiency. The objective is to ensure that the gas turbines satisfy all safety and technical requirements, offering a strong and dependable power source for the planned use.
Unit Testing and Shop Inspections
Gas turbines and their auxiliary systems are subject to individual shop testing and inspection; eventually, before the package is delivered, it is best to have a complete unit test performed, in which all job auxiliaries are tested for integrated functionality while the gas turbine shaftline is operating at full load, partial load, or no load.
Some shop auxiliaries, like fuel gas filters, may be permitted to be used throughout the complete unit test for pragmatic reasons.
Integration of Expert Insights
Excerpts from Emmanuel Bustos, Michael Hotho, Mounir Mossolly, and Alfredo Mastropasqua’s paper “Gas turbines and associated auxiliary systems in oil and gas applications,” which was delivered at the 2017 Turbomachinery Pump and Symposia by TechnipFMC Paris, are included in this article.
Qualification and Individual Component Testing
Newly released gas turbines must pass a qualification process that involves testing that is more thorough and unique than standard shop tests. Major gas turbine components could have their mechanical integrity and/or performance verified during the individual testing cycle.
To verify the vibration levels, for example, the power turbine of an aero-derivative gas turbine will be subjected to a mechanical run test (MRT). To verify that the operational parameters are within the permitted ranges or limits, a performance test would be performed on the gas generator.
Complete Assembly Performance Assessment
According to ASME PTC22 guidelines, the performance of the entire gas turbine assembly is performed. But all auxiliary systems would be fully tested for operation at the sub-suppliers’ shops.
The actions that must be performed during this integrated test must be mutually agreed upon by the supplier and the contractor/ end-user for the complete unit test. The shaftline should always be operating at full speed, but it is possible to choose between full load full speed, half load full speed, or no-load complete unit test depending on the project context and test bed limits.
Verification of Vibration Levels and Noise Emissions
Vibration levels should be measured and verified in accordance with the relevant international regulations and standards during the complete unit test (or string test if no off-skid auxiliaries are present).
During the complete unit test, the package’s overall noise level should be measured, and the torsional behavior of the connected shaft line may be verified. Furthermore, a validation is performed on the combined sequences and integrated functionalities of all the auxiliary systems.
Utility Consumption and System Pressure Checks
Utility consumption guarantees are examined. Similar to how the exhaust system’s pressure drop affects the gas turbine’s output power, the inlet air system’s pressure drop is likewise monitored. Additionally, the pressure inside the enclosure is measured and the gas turbine’s ventilation system is verified.
Lastly, inside the gas turbine cage, the fire and gas system is tested by turning it on. A gas generator replacement, for example, might be demonstrated during the complete unit test. Complete unit test lowers the execution risks in projects, particularly for sites that are offshore or in remote locations, despite the fact that full load tests are expensive, may cost several million euros, and would require several months of planning.
Structural Support and Mounting Preparations for Offshore Installations
Gas turbine drivers and the driven equipment can be mounted on a shared 3-point mount skid in offshore applications. A strong structural beam may be required to support the load in some situations where the 3-point mounting creates a significant point load on the structure. Precise shimming preparations must then be made in accordance with this need.
Shimming beneath each point of a three-point mount installation should be done in accordance with the complete skid’s reference level. To ensure that the leveling is unaffected by water movement for floating applications, this can only be performed onshore.
Throughout the installation process, the skid must not experience any stress. After the skid has been leveled and positioned within small tolerances, a full welding job can be performed on each attachment point to meet the supplier’s specifications.
The standards for flatness and levelness at the interface between the gimbals and the structure must also be adhered to. The quality of the weld will then be controlled by applying a full non-destructive examination (NDE).
Modular Design Considerations for Offshore Gas Turbine Skids
Gas turbine main skids for offshore projects utilizing modular design must be provided with jacking pads in order to raise the skid if necessary during installation adjustments when using a crane with slings traversing the decks above is not an option.
Then, in a predetermined order, auxiliary structures including ventilation ducts, exhaust stacks, and inlet air filter houses must be built, starting at the bottom and working upward.
All of the ducting’s expansion joints permit some installation tolerances. As specified by the supplier, silencers must be installed (for instance, in the exhaust stack) and occasionally, specialized guiding tools will need to be used.
Certain duct components will need to be assembled/connected horizontally at the ground, then tilted and raised for the final installation in order to ease the build-up/erection of the ducting.
Pre-Commissioning Instrument and Electrical Checks
All instruments and electrical auxiliaries must be verified for correct operability during the pre-commissioning process. All instruments installed in the gas turbine package, including the auxiliaries, must have a complete loop inspection performed. Further calibration might be required to verify the instrument’s dependability.
To verify the cable connection and motor rotation, all motor solo runs should be performed (with pump/fan disconnected). Every piping network surrounding the gas turbine and its auxiliaries needs to be cleaned as thoroughly as feasible. A full oil flushing procedure needs to be performed for the oil line. To perform this flushing, the lubricating oil pump of the oil console could be utilized.
To collect solid particles and other oil pollutants, filters with fine mesh should be installed on the return lines in accordance with the specifications provided by the gas turbine manufacturer. Gas turbine oil lines are cut off and bearings are avoided to perform this type of oil cleansing. During the pre-commissioning stages, the gas turbine must also undergo boroscopy inspections.
To ensure that the physical equipment is in full compliance with the engineering documentation, such as the Piping & Instrumentation Diagram (PID) and hook-up drawings, etc., a final inspection must be performed.
Commissioning Phase and Fuel Considerations
Unless the gas turbine is dual fuel, commissioning of the turbine can be done with liquid fuel (diesel, for example). Gas turbines are typically commissioned with site fuel gas. All auxiliary systems, including control and power panels, must be commissioned and proven to be completely operational prior to starting any full test runs of the gas turbine.
The commissioning team must strictly adhere to the commissioning instructions provided in the commissioning handbook by the gas turbine supplier. Every auxiliary system needs to be independently commissioned.
To ensure safety throughout the commissioning process, the fire and gas system (F&G), including enclosure systems like fire dampers, etc., shall be the first system to be commissioned.
All permissive-to-start commissioning must then be performed.
Stability Testing and Operational Readiness
Systems could be commissioned in the following order:
- Panels for power and control units;
- The F&G System
- Mineral and synthetic lubricant systems;
- launching the system;
- ventilation system for enclosures;
- Gas System for Fuel;
- system of inlet air filters;
- gas turbine motoring/cracking system; after that
- Systems pertinent to the machinery being driven. Testing the emergency trip system comes first once the gas turbine is operational:
- Examination of the emergency push button that is installed outside the gas turbine enclosure
- Test the remote trip signal; Vibration control must be performed to ensure a good stability after some running time. The gas turbine is deemed ready for operation if the vibration has steadied within a reasonable range.
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