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turbine. The combustion chamber positions as well as the actual chambersor baskets should be permanently numbered， and a complete record shouldbe made for each basket regarding hours of service， repairs or replacementsmade， and their location in the turbine at each inspection date. The basketends， or at places where they are supported， should be inspected for excessivewear fromvibration， or expansion and contraction movement. Repair of these parts should be made by cutting out and welding in new materials or replacing spring seals if necessary. The first-stage turbine stationary blades or nozzles can be superficially inspected for warps or sags by entering the turbine through the combustion chamber areas or by removing inspectionplates. In certain size turbines (and by somewhat difficult maneuvering)， the last row or turbine rotating blades can be inspected by entering through the turbine discharge duct. The opportunity should be taken tomeasure， ifpossible， the blade tip clearance at four points on the circumference. Com-parison of these clearance readings with those at installation or at some previous time will indicate if rubs have occurred and whether or not the seal ring is warped and out of round. It will also indicate whether or not the rotor is below its original position and requires further investigation at the over-haul period.
As the hot sections become exposed， preliminary inspection for cracks or warping should be undertaken to estimate work to be done. The bearings require inspection for wear and alignment for the same reason. The transi-tion pieces should be inspected for cracking and wear at points of contact. Wear usually occurs between the transition piece and the combustion linersleeve， and also at the first-stage nozzle fit. The cylindrical section of the transition piece may be replaced if the wear is excessive; wear at the nozzle-end of the transition piece is more serious because it allows excessive vibra-tion of the transitionpiece， which might lead to cracking. Transition pieces should be replaced if 50% of the inner or outer seal is reduced to half theoriginal thickness. If the transition piece is in otherwise excellent condition， the seals may be ground off and replaced. The new floating seals have been found to be more reliable than the old fixed seals. Transition pieces should be replaced if cracks are found in the body.
Turbine blades should be closely inspected for erosion and cracks.The most critical areas in the turbine rotor are the fir-tree section， where theblades are attached to therotor， and the trailing edge of the blade near the hub. The trailing edge of the turbine blade is usually the hottest section of the blade. These areas should be carefully cleaned and checked for cracks with spray penetrant. First-stage inlet vanes and rotating blades should be removed and blasted clean with a No. 200 grit aluminum oxide or other approved blasting material. They should then be inspected minutely for cracks by means of red dye or black light. The first-stage inlet vanes willprobably need attention， which can be done on the job. Vane warpage on thetrailingedge， ifany， can be taken out by inserting a spacer piece of correctcross-sectional area between the vanes， heating the top vane to red heat with atorch， and forging the vane edge flat with a hammer and flatter. Thecracks， if less than 1.5 incheslong， can be grooved out and welded， providingthe crack does not run under the end-supporting rings. In this case， the vane must be removed and welded or a new vane fitted in place. As the vanes arewelded， they must be continually checked for newcracks， which in turn must be grooved and welded and checked again.
While repairing the first-stage inletvanes， the upper-and lower-vanesection should be bolted or clampedtogether， and the entire ring should beplaced on aflat， level surface， or sufficiently supported in the horizontal plane to prevent heat warpage of the ring due to heating of the vanes during their repair.
After straightening or taking out any warpage in the trailing edges of thevanes (partitions)， perpendicular distances between the trailing edges of each vane and the surface of the next should be carefully measured. An average of these distances should be made and then corrected to a plus or minus percentage approved by the manufacturer. This method will help to assure equal distribution of gas flow to the first-stage rotating blades for elimin-ation of blade vibration.
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燃气涡轮工程手册 Gas Turbine Engineering Handbook 3(87)
