FIELD OF THE INVENTION:
The present invention relates to a design of test rig for high temperature turbine
rotors made up of super alloys. More particularly, the invention relates to a
mechanism for integrated heating and cooling of rotor at extreme temperature
and pressure conditions, in an enclosure to simulate accelerated LCF (Low Cycle
Fatigue) and creep damage. The invention also relates to the parameters to be
controlled for attaining creep and LCF vis-à-vis thermal loading. The invention
further relates to a detailed control mechanism to attain desired heating, cooling
rates with control and instrumentation.
BACKGROUND OF THE INVENTION:
Coal based thermal power plants operating in sub-critical conditions have lower
efficiency and higher emissions compared to those operating in supercritical
conditions. In order to reduce CO2 emissions and meet global environmental
norms, efforts are directed to improve technology for achieving higher efficiencies
as well as reduce emissions. Design of Advanced Ultra Super Critical designs is
directed in achieving the desired goals discussed. These operate at higher
temperatures (~=7OO°C) and pressures (~= 300 Bar).
Contemporary research, directed to use of advanced material to withstand these
extreme temperature and pressures, is in nascent stages. Materials like IN617
or its equivalents are proposed for steam turbine rotor, a critical component of a
thermal power plant. These rotors undergo severe thermal transients during
start up and shut down. During steam turbine start-up, temperature of rotor
surface gradually rises with the incoming steam. During this process, rate of
temperature rise of the rotor central portion is lower than that of rotor surface,
resulting in formation of severe thermal stresses within the rotor.
Likewise, the rotor surface is subjected to tensile stresses during the cooling
down during shut down stage. After a certain number of such cycles, surface or
core of rotor may develop cracks due to LCF.

An embodiment of invention relates to designing a specialized test rig consisting
heating and cooling cycle arrangement that can facilitate an accelerated testing
of segment of an actual rotor. It is an objective that accelerated creep and low
cycle fatigue be simulated to assess damage fraction and validate design. It
further relates to the control mechanism to set parameters for achieving the
desired thermal gradients during heating and cooling cycles.
Another embodiment of the invention relates to heat radiation by electric heaters
and convective cooling by gas flow and their disposition.
Patent No. EP 2 902 594 81 describes a control system for a cooling fluid flow in
a high pressure turbine section of a steam turbine system. The invention resides
in a cooling fluid flow control system for a turbine section of a steam turbine
system and a program product stored on a computer readable storage medium
of a computer system.
Patent No. US 6,642,682 81 discusses a method to preheat the rotor of a motor-
generator device by principle of induction heating. A high frequency current is
to be passed through armature windings of the motor-generating circuitry to
induce surface currents into the periphery of the rotor. In this concept, the
motor-generator circuitry of a flywheel energy conversion device can be utilized
to preheat the rotor of the flywheel device.
Patent No. US 7,985,045 82 (US) describes a control method for heating and
cooling of flanges of seals in steam turbine by displacement detector. A
displacement detector for measuring a difference in thermal expansion in the
rotor axis direction between the casing and the rotor is proposed. A controller to
make the flanges heated or cooled by the heating/cooling devices until a
measured value obtained by the displacement detector reaches a preset value.
The prior art envisages either isolated heating or cooling and also lacks mention
of control mechanism to regulate parameters.

They are inadequate in their method to incorporate an integrated approach for
heating and cooling of rotor meeting specified thermal gradients and profiles.
There is also limited work on regulating of temperatures within a rotor in a
transient manner. The present invention addresses a mechanism consisting of
heating and cooling cycles to simulate the requirements of LCF and creep
damage. In addition, a gradient wise heating and cooling is established in an
integrated enclosure. Furthermore, temperature and flow control mechanism
and its arrangement in the system is also discussed.
OBJECTS OF THE INVENTION:
It is an object of the invention to provide an apparatus for integrated heating and
cooling of large superalloy turbine rotors in the same enclosure, with
independent operation in order to simulate accelerated LCF and creep damage
of test rotors.
Another object of the invention is to provide a heating arrangement and have
radiative heating in vacuum controlled conditions to attain desired rotor
temperatures with specified temperature gradient between bulk-mean of rotor
and surface of rotor.
Another object of the invention is to provide a cooling arrangement of forced
convective cooling by gas in a controlled manner to attain desired temperatures,
with specified temperature gradient between bulk mean of rotor and surface of
rotor.
Another object of the invention is to provide a heat exchanger system for cooling
the gas exiting the enclosure.
Another object of the invention is to provide a method for re-injecting the cooled
gas into the circuit in order to complete the cycle.

A further object of the invention is to heat the rotor, maintain at steady state and
cool it in a particular number of pre-determined cycles so as to simulate LCF
and creep in an accelerated manner.
A further object of the invention is to have a vacuum system, a gas storage, safety
and protection system and a blower system.
A further embodiment of invention is to have a specialized control and
instrumentation mechanism for operation of said systems.
SUMMARY OF THE INVENTION:
A test apparatus is provided to study creep and LCF phenomena of the super
alloy rotor. Considering equivalent cold starts obtained from actual cold, warm
and hot starts of the steam turbine, temperature difference to be maintained
between rotor surface and bulk mean temperature during transient thermal
loadings in the rotor is computed. It is deliberated that this simulates damage in
accelerated manner as envisaged in actual rotor.
On attaining steady-state temperature, the test rotor undergoes creep
phenomena. Hence, the principal of apparatus is to arrive at a suitable test cycle
comprising of transient thermal loading, steady state thermal loading followed
by transient cooling. This completes one cycle. The process repeats for a specific
number of cycles.
According to a first aspect of the invention, the heater arrangement is so as to
attain desired ramp rate of rotor temperature. The electric heater elements are
arranged circumferentially on the enclosure surface for optimized radiative
heating. The medium in the enclosure is maintained as vacuum. After the rotor
attains desired steady state temperature, it is let to soak. The cooling of rotor is
carried out by gas flow on the outer surface of rotor. A controlled gradient is
maintained between the rotor surface and mean temperatures. The gas flow rate,
pressure and rotor rotational speed are sustained so as to meet this temperature

gradient. The heated gas is cooled at the exit of the enclosure by means of an
external heat exchanger and recirculated back to the test enclosure apparatus
by means of a blower system. Gas storage system supplies the make-up cooling
gas lost due to leakage in the circuit. Control logic and mechanism, for regulating
electric heaters operation and gas flow parameters, is developed. For heating
cycle, it is accomplished by means of thermostat or regulating current by varying
the voltage across heater elements. For cooling cycle, cooling rate is adjusted by
variation of rotational speed of rotor and mass flow of gas.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
It is to be noted, however, that the appended drawings illustrate only typical
embodiments of the present subject matter and are therefore not to be
considered for limiting of its scope, for the invention may admit to other equally
effective embodiments. Detailed description is provided with reference to the
accompanying figures. The same numbers are used throughout the figures to
reference like features and components. Some embodiments of system or
methods in accordance with embodiments of the present subject matter are now
described, by way of example, and with reference to the accompanying figures,
in which:
Figure 1 illustrates an arrangement of heating system for the rotor assembly in
accordance to the invention.
Figure 2 illustrates an arrangement of cooling system for the rotor assembly in
accordance to the invention.
Figure 3 shows an external heat exchanger circuit for cooling the hot gas
assembly in accordance to the invention.
Figure 4 shows the interface to control and instrumentation of the system in
accordance to the invention.
Figure 5 depicts the overall system arrangement in accordance to the invention.

Figure 6 depicts the graphical representation of sequence and period of heating
and cooling cycles in accordance to the invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION:-
A sectional view of heating arrangement of a superalloy test rotor (1), for the
purpose of evaluating LCF and creep properties by thermal loading, is depicted
in figure 1. The superalloy test rotor (1) is hung from top by means of a support
and rotational arrangement not forming aspects of this invention. The rotor
enclosure (13) housing and the superalloy test rotor (1) has an electric heating
element arrangement (14) on its inner surface in a circumferential manner. The
vacuum system (8) is required for maintaining design vacuum pressure in
enclosure. The line has a pressure indicator (11) to monitor anticipated
conditions. The superalloy test rotor (1) is heated from ambient to the desired
steady state temperature, by meeting the design temperature gradient between
surface and core. The temperature sensors (9) detect and display temperatures
of the heaters. The control and instrumentation system (23) varies the operation
of heaters and determines the number of heaters to be on at any instant of
operation. This is attained by governing current, by means of varying voltage
across heating elements. On attaining steady state temperature, superalloy test
rotor (1) is let to soak for a predetermined time duration. It is cooled by
maintaining a temperature gradient between surface and bulk mean of rotor.
The cooling system is integrated to the same circuit as shown in figure 2. The
gas inlet header (2) sources the rotor enclosure (13) with cold gas. The flow
element and flow indicator (10) present on the gas inlet header (2) monitor the
flow of gas. The rate of gas flow, pressure of gas at entry, rotational speed of the
rotor are regulated to control the temperature gradient between surface and bulk
mean of superalloy test rotor (1). The gas flows into the outlet header (3) after
exiting the rotor enclosure (13) with blower system (5). In order to reutilize the

gas, it is proposed to cool it and recycle. It is cooled to the desired inlet
temperature by means of an external heat exchanger (4).
A heat exchanger system (21) is shown in figure 3. The hot gas is cooled by means
of another fluid and the heat is rejected through an air cooled heat exchanger or
a cooling tower (15). The cooled gas is then supplied to the inlet header (2) though
the blower (5). The inlet header (2) supplies gas to the rotor enclosure (13) and
the cooling cycle is established. It can so happen that the system encounters a
leak. The gas storage system (7) is the back-up supply for the cycle. It sources
the supply header (6) which in turn delivers to the blower (5) and then gas enters
the inlet header (2). The pressure indicators (11) display the operating pressure
in the cycle. The pressure sensors (12) positioned after the supply header (6)
maintain the system pressure. The signal for the quantum of gas to be present
in the enclosure at different time periods, for efficient heat transfer is regulated
control and instrumentation system (23) as shown in figure 4. The flow in the
piping is controlled by means of isolation, control and non-return valves and
suitable instrumentation for monitoring them. The back-up blower system (5),
vacuum system (8) and gas storage systems (7) have adequate redundancies to
meet contingencies.
An AC supply and generator support (17) to ensure uninterrupted operation is
provided. During the period when cooling occurs, the heaters are safeguarded by
circumferentially collapsible shields (16). The rotor surface is in contact with the
axial gas flow but not the heating elements (14). At the end of the cooling cycle,
the circumferentially collapsible shields (16) withdraws and the heater elements
are exposed to the rotor (1) again. The heating and cooling systems are integrated
and their operation is established.
Auxiliary support systems like vacuum, safety and protection, gas storage,
supply form part of overall system as depicted in figure 5. The cycle depicts
temperatures during transient heating (25), steady state operation (26) and

transient cooling (27) with respect to time, in figure 6. This cycle repeats for a
predetermined number of design cycles to simulate accelerated LCF and creep
criteria of superalloy test rotor (1).

WE CLAIM:
1. A testing apparatus for testing super alloy turbine rotor (1) by heating and
cooling, the apparatus comprising of:
- a heating system (22) that comprises of an electric heater arrangement
(14) in an enclosure (13), a vacuum system (8) to sustain pressure and allow
heat transfer, an operational logic to control the heat flow of the heating system
and control the vacuum system (8), associated electronics to monitor the heating
process;
- a cooling system (20) comprising a gas inlet header (2) to stream cold gas
monitored and controlled by a flow indicator (10), a gas outlet header (3) to
receive the gas expelled from the super alloy turbine rotor (1) by means of a
blower (5), an operational logic to control the flow of cooling;
- a heat exchanger (21) to cool and reutilize the exiting gas;
- a gas storage system (7);
- protection means to prevent explosion;
- wherein the heating and cooling of the super alloy turbine rotor (1)
simulates accelerated low cycle fatigue and creep damage.
2. The testing apparatus of super alloy turbine rotor (1) as claimed in claim 1,
wherein the protection means comprises of an enclosure (13) and a pressure
relief valve (24).
3. The testing apparatus of super alloy turbine rotor (1) as claimed in claim 1,
wherein the operational logic calculates the heating and cooling cycle.
4. The testing apparatus of super alloy turbine rotor (1) as claimed in claim 1,
wherein the operational logic controls the temperature gradient between surface
and bulk mean of the rotor during heating cycle.

5. The testing apparatus of super alloy turbine rotor as substantially described
and illustrated herein with reference to the accompanying drawings.