Depending on the volume and periodicity, scheduled repair works are divided into A, B, and C-inspection.
- A-inspection (borescopic) is performed without disassembling of the unit. While carrying out of the A-inspection the condition of the hot gas path elements, combustion chamber, blades, and the compressor inlet are studied using an optical device – borescope. A-Inspection is often used to obtain data on the basis of which a checklist for B and C-inspections is compiled.
- is used to obtain information about the condition of the combustion chamber and the hot gas path and is characterized by an increased volume of work compared to the A-inspection. For certain gas turbine units, B-inspection is performed using a borescope, for many other units during the inspection it is also planned to replace a number of elements of the combustion chamber and hot gas path.
- is carried out with disassembly of the turbine. All internal parts and components are checked. Replacements of the parts specified in the schedule and parts with the detected defects are made.
An overhaul is characterized by a large volume of works, as it is associated with the disassembly and inspection of the unit, including its individual parts. An overhaul includes troubleshooting, condition assessment of the parts and assemblies. Performed operations covers the removal of the upper part of the turbine housing, inspection and cleaning of the air-gas channel, removal of the rotor blades, nondestructive inspection of the blades, restoration of the coatings, inspection of inserts and bearings, checking of the compressor assembly, coaxiality examination of the turbine with the onboard equipment, replacement of the individual elements and parts specified in the schedule.
For an efficient overhaul it is important to have corresponding technical documentation, necessary set of tools, equipment and accessories.