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A full hot gas path components major inspection can take up to 368 hours, which is equivalent to 46 8 hour shifts. These inspections are necessary as it is common for hot gas path components to wear, even when used properly. These inspections will require the hot gas path components to be inspected along with other parts of the turbine engine. During an inspection of this type, these things will be checked and/or removed:
- The discharge case, upper inlet, and mid cases are all removed.
- Inspection of the inlet and compressor cases for any erosion, corrosion, leakage, and fouling.
- The stator and rotor compression blades are checked for rubs, bowing, tip clearances, cracking and warping.
- The hook fits and seals are all checked for rubs, fretting, erosion and thermal deterioration of nozzles and diaphragms.
- Turbine buckets are inspected for foreign object damage, cracking and erosion and corrosion. To do this properly they will have to be removed.
- Seals and bearings are inspected for wear and clearance.
- All clearances will be compared to which will ensure they are at their original values.
Recommendations for hot gas path components inspections
It is recommended that a major hot gas path components inspection be done every four years. But, every 2 years, you should perform a less intense hot gas path components inspection that will check the major components. The major components of the engine will last much longer than the turbine. Because of this, you can expect that the gearbox and the electric generator will certainly outlast the turbine itself. When doing a lighter inspection, it will take approx. 176 hours or 22 eight hour shifts, so the inspection is still pretty intense.
During this time there will be a combustion inspection along with a detailed inspection of the shrouds and turbine nozzles. The top half of the turbine will have to be removed in order to perform this inspection properly. The shrouds, diaphragms and nozzles are removed and the turbine buckets are inspected but not removed.
Some things that you should keep in mind are the environment in which the turbine is used. Some things such as the airfoils can be really affected in some environments. Other factors that should be taken into consideration when you are drawing up a maintenance plan of your hot gas path components turbine is the downtime, type of fuel, environment, Utilization need, reliability need, on-site capability, manufacturer’s recommended maintenance program, duty cycle, and Design features. In order to limit the number of inspections needed it is important to get the highest quality components like those found on this website.
Things to Consider
As we have said, the engine should go through a major inspection every four years but this is dependent on many factors. One major factor is how long or how much the engine is actually being used and is running, along with the environment and other things. Of course, if you suspect there is something wrong, you should have a major inspection done as well. A hot gas path component should be done around 24k hours or 1200 starts and a Major inspection should be done at 48K or 2400 starts. These hours also take into account the peak load, fuel type and diluent (steam injection or water).