2. Decrease in air compressor discharge pressure

3. Change in lube oil temperatures or pressure

4. Air or combustion gases blowing out at the shaft seals

5. Incorrectly reading thermocouples

6. Change in wheel space temperatures

.. Fuel oil or gas leakage
8. Fuel control valves operate satisfactorily

9. Hydraulic control oil pressures changed

10. The turbine governor ""hunts""

11. Change in sound level of gear boxes

12.  Overspeed devices operate satisfactorily

13.  Babbitt or other material found on lubricating oil screens

14.  Lube oil analysis shows corrosion factor increase

15.  Change in pressure drop across heat exchangers

16.  Turbogenerator reaches rated load at design ambient and exhaust temperature conditions

Preparation for shutdown should be made as complete as possible to eliminate lost time and confusion at the beginning of the job.
A list should be made of all major items that are to be inspected or repairs to be made if they are known at the time. This list should be prepared with the manufacturer"s engineer present. A detailed schedule should be formu-lated from this list including the time allotted for the shutdown and the maintenance crew available. Plan the work with the expectation of finding the worst conditions-the unexpected work found after the machine is opened will then be compensated. This procedure will greatly reduce the possible need for costly overtime.
Tools on-site should be reviewed by the manufacturer"s engineer. All special or regular equipment not on hand that is necessary or required to do any part of the work should be ordered and on-site before shutdown.
Exact outage time should be arranged， and the turbine prepared for the contracting crew or plant maintenance crew. All personnel should be on the job or available to meet the starting date.
Facilities， such asconvenient air and electrical connections， should beprearranged for operating tools， etc. Sufficient hose lengths and connectors are required as well as electrical extension cords. Install air driers or waterseparators in the air system， since dry air is necessary for successful grit blasting of turbine parts.
Before removing turbine flange bolts or disturbing the normal turbinesetting， clearance readings between the last row of turbine rotating blades and their wheel shroud should be made at both horizontal and vertical positions. Evidence of the main turbine flange spreading or warping should be checked with feeler gauges between each of the flange bolts. Elevation checks at each of the turbine supports should be made for comparison with original readings to determine if there has been movement at these points.When all outside checks have beenmade， structural beam supports should be placed under the turbine at the midpoints between the normal turbine supports. Screw jacks must then be used to bring pressure under the turbineuntil a slight deflection on dial has been reached. For this purpose， use onlyscrewjacks， not hydraulic or lift jacks. Flange bolts can then be removed as well as the top half of the turbine casing.
8orescope Inspection
Borescope inspection is carried out because of the following benefits it can provide in the maintenance program:
1.  Internal on-site visual checks without disassembly

2.  External periods between scheduled inspection

3.  Allows accurate planning and scheduling of maintenance actions

4.  Monitors condition of internal components

5. 
Increased ability to predict required parts， specialtools， and skilled manpower

Figure 21-. shows the time savings one may obtain by the proper use of borescopic inspection for planned maintenance.
The borescope contains its own light source throughout the engine inter-nal passages. Onceinserted， the flexible borescope can be maneuvered to inspect the complete hot-section flow path. The results of the visual inspec-tion can be used to assist in planning scheduled disassembly of the gasturbine. It must be remembered that a borescope is a monocular device， and it is extremely difficult to estimate size or distance. Maintenance per-sonnel should be well trained to use a borescope effectively. Photographs，especiallycolored， can be utilized as a reference on the history of a machine.In addition to performing inspections while the gas turbine is not operating， some research has been conducted to develop methods for inspection during operations by providing a film of cooling air around the borescope tube. Ifthis system is developed， it will enable visual inspections of the hot sections up to the first-stage turbine blades without shutting down the unit.
　
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