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3.3 The high pressure turbine, operation behavior and operation load
There are some parts where during the life of a car several exchanges can be expected. Included are the exhaust pipe, tires, battery and brakes. When those parts have to be exchanged depends not at last how we treated them during operation. The replacement takes place accordant the observable condition or an in time noticed malfunction. This is called a condition depending approach („on condition“).
But there are also components that have to be exchanged after an operation time, that is defined by the manufacturer (OEM), regardless how gentle we treated them. Otherwise we must reckon with serious failures and possibly losing the guarantee. To this belongs the replacement of the V-belt. Especially the exchange of the synchronous belt, is prescribed in case this principle is used in our car. It drives the camshaft. In case of a failure it can come to a damaging contact between valves and pistons with a catastrophic motor failing.
The blades of the high pressure turbine normally are the life time determinative components of our gas turbine. They are subject, like the synchronous belt of the motor, by the OEM limited lifetime. What is truely not worth in case of the synchronous belt can be possible for the costly blades. Premise is a verifiable lower life consumption as it was underlying the exchange. It is thinkable that in this case the OEM gives his approval for a time limited further use or repair. Crucial are normally in the manual defined deterioration limits.
Multi shaft engines ( "Ill. 3.1-2") possess a separate high pressure turbine (HPT). It drives the (high pressure) compressor, and normally is part of the gas generator. That delivers the hot gas for the power turbine (low pressure turbine, LPT).
Two thirds of the overall power of the engine is transmitted as inner performance ( "Ill. 2.1-3.1"). The delivered power output is produced by the low pressure turbine. The high pressure turbine is exposed to a gas flow, often showing temperatures above softening of the blade material (ca. 1200 °C). This demands an intensive cooling of blades ( "Ill. 3.3-3" and "Ill. 3.3-6"). Even the centrifugal load of the blades and disks are, because of the relatively high (high pressure-) rotor speed at the limit of material strength. The high cyclic and static load of the HPT is responsible that this component group ( "Ill. 3.3-5"), particularly the HPT rotor blades ( "Ill. 3.3-10"), is creep life ( "Ill. 2.3-1" and 2.3-2) limited and has normally to be exchanged first.
The thermally very high loaded turbine guide vanes ( "Ill. 3.3-9") are life limited mainly by thermal fatigue and oxidation. As static components they are subject to thermal stresses and gas bending loads. Crack propagation by those stresses can be controlled in limits, allowed by the OEM ( "Ill. 3.3-17"). In addition direct at the combustion chamber exit located vanes (nozzles) can be better inspectet by borescope and evaluated than the rotor blades ( "Ill. 4.1-6"). So a failure can be easier captured than on rotor blades. New part acquisitions and repair efforts for these components determine the operation costs.
