A modern gas turbine consists of many components that constantly operate under increased mechanical and thermal loads. They require periodic replacement or repair. The service life of combustion chambers, blades and other components operating under increased loads and temperatures is not always observed due to the peculiarities of operation.
Repair of gas turbine units is a laborious and expensive process that requires highly qualified specialists to be involved with the use of special measuring equipment and tools. They may include vibration analyzers, laser systems for controlling the flow path geometry and shaft alignment.
Repair of turbine blades
Turbine performance and service life are largely dependent on the condition of the gas turbine blades. The blades are exposed to high loads and temperatures and they corrode and deform.
The most common types of blades damage are:
- Corrosion and wear along the edges, pitting on the surface of the blades due to increased temperature. All this leads to a change in aerodynamic parameters and to decrease in strength.
- Cracks on the edges and in some cases even more serious damage to the blades due to the penetration of foreign bodies into the flow path of the turbine.
- Mechanical cracks and damage to the blades due to the thermal fatigue of the material.
- Disturbance in the structure of heat-resistant alloys due to overheating and high mechanical stress.
The process of the gas turbine blades repair includes the following operations and technologies:
- Study of the metal alloy structure using metallography methods.
- Assessment of the metal coating integrity and condition.
- Coating removal in the affected area by means of sandblasting and subsequent polishing of the affected areas.
- Preliminary preparation for the repair of nicks and cracks.
- Damage repair by welding and building-up.
- Heat treatment, application, and restoration of the protective coating.
Repair of fuel valves
Any irregularities in the operation of the fuel valves can change the temperature conditions of the gas turbine unit and cause uneven heating of individual components. It often results in the wear and failure of individual turbine components. Timely replacement and repair of fuel valves increase the reliability of the turbine and the service life of the gas turbine unit.
Accurate and efficient operation of bypass valves extends the bearings service life and improves the gas turbines efficiency.
Maintenance and repair of fuel and bypass valves is performed in strict accordance with the manufacturer's recommendations. The products of such companies as Meggitt and Woodward are most widely represented on the domestic market.
Repair of cracks in turbine nozzles
Crack formation in turbine body parts is caused by recurrent heating-cooling cycles. To assess the scope of defects, the cracking areas are cleaned and then the extent of the damage is determined by means of non-destructive testing (MPI, ultrasonic inspection, dye penetrant inspection, eddy-current method, etc.).
If the crack size exceeds the dimensions permissible according to the standard, an unscheduled replacement of the part is performed. In a part removed for repair, a similar defect can be eliminated by cutting out the metal around the crack and then welding. After that, mechanical and heat treatment of the weld is performed followed by the application of thermal-protective coating. The repaired part is then sent to the repair pool and can later be used to replace another damaged part.
Timely replacement and repair of stator guides and adjustable vanes (IGV and VSV) allows to enhance the gas turbine performance.
The pumping equipment used in gas turbine units has outstanding reliability and durability, but at the same time it needs to be maintained in accordance with the manufacturer's requirements.
Among other most frequent malfunctions of the gas turbine unit is contamination in fuel pipelines and burners due to insufficient gas purification. This leads to a disturbance of the temperature conditions at the turbine outlet and may also be followed by breakage of the blades.
Timely routine inspection of the gas turbine unit as well as a complete repair of individual components are necessary technical procedures during the operation of gas turbine equipment.