MONITORING FATIGUE IN STEAM TURBINE ROTOR

Abstract

 A rotor (1) for a rotary machine (10) includes a monitor portion (100) which is designed for being exposed during operations to a maximum strain range, and at least one operating portion (30, 40) subject to being coupled or covered during operations by another component (31, 41) of the rotary machine. The monitor portion (100) is adjacent to or distanced from the at least one operating portion (30, 40).

Description

Field of invention

[0001] The present invention relates to a rotor of a rotary machine, in particular a steam turbine, including a device for monitoring or detecting damages due to thermal fatigue. The present invention relates to a method for monitoring or detecting damages due to thermal fatigue in a rotor of a rotary machine, in particular a steam turbine.

Art Background

[0002] In the field of rotary machine, and in particular of steam turbine, it is desirable to detecting in advance if the rotor of a rotary machine is close to a thermal fatigue damage due to thermal load may be critical.

[0003] This is critical in particular for turbines where the rotor is the highest thermally loaded component, due to many and/or to fast starts or stops and to load cycling.

[0004] The thermal load in such situations constitutes a combination of creep and low cycle fatigue of the material which constitutes the rotor. The creep is caused by long term operation at high temperatures with strained material, the low cycle fatigue is caused by regular high peaks of material strains when the turbine is loaded and unloaded. Cracks in the material are initiated in the highly strained regions when a certain limit of load cycles is exceeded. This limit depends on the magnitude of the strain peaks (strain range), the passed duration of high temperature operation (creep) and the local material properties.

[0005] The strain range itself is not only dependent on the thermal conditions provided by the steam flow, but also on the local geometry. Main geometry parameters are the material thickness, i.e. the diameter of the rotor itself and radii of the notches, which cause local stress and strain concentrations.

[0006] A physical supervision of the fatigue condition caused by this thermal load collective is presently not possible or very difficult, due to the following reasons:

• the initiated crack caused by this thermal load collective often starts from a location, which is very difficult to inspect. Typically these locations are in the notches and grooves of the hot rotor parts, which may be often covered by seals, blades, or inner casings;
• the initiated crack may not be dangerous in all cases, depending on how the crack grows at the specific geometry location. A supervision of the crack growth would be wished, but due to safety considerations this may not be allowed in highly loaded regions of the rotor;
• before the crack is initiated, there is no indication in the material on the level of fatigue, i.e. how long the rotary machine could be operated further until a crack will build. Therefore, a rotor inspection in the normal maintenance schedule will not give a clear answer on the thermal fatigue condition of the rotor.

[0007] A solution to the above problem has been provided by specifying an allowed number of load cycles based on theoretical fatigue calculations and evaluations. After this number has been defined, some turbines are equipped with a life time counter, which indicates the theoretically consumed life time, i.e. cycles, based on operation data.

[0008] The main inconvenient of this method is that it needs to be conservative in order to ensure integrity of the components during the design life time.

[0009] A further solution is that of periodically inspecting the rotor for identifying cracks. However, only already initiated cracks can be detected, close-to-crack situations are instead impossible to determine by means of inspection.

[0010] It is therefore still desirable to provide a system for detecting in advance if the rotor of a rotary machine is close to a thermal fatigue damage in an efficient way and in particular solving the above mentioned problem.

Summary of the Invention

[0011] It may be an object of the present invention to provide a rotor of a rotary machine, in particular a steam turbine, including a device for monitoring or detecting damages due to thermal fatigue, in order to achieve, with respect to the prior art, an improved level of confidence in determining the residual available life time of the rotor.

[0012] Further objects of the present invention to provide a rotary machine, in particular a steam turbine, including a rotor of the type above specified and a method for monitoring fatigue in a rotor, which may be capable to achieve, with respect to the prior art, an improved level of confidence in determining the residual available life time of the rotor.

[0013] In order to achieve the objects defined above, a rotor of a rotary machine and method for monitoring fatigue are provided in accordance to the independent claims. The dependent claims describe advantageous developments and modifications of the invention.

[0014] According to a first aspect of the present invention, a rotor for a rotary machine includes a monitor portion, which is designed for being exposed during operations to a maximum strain range, and at least one operating portion subject to being coupled or covered during operations by another component of the rotary machine, wherein such monitor portion is adjacent to or distanced from the at least one operating portion.

[0015] According to a second aspect of the present invention, a rotary machine, in particular a steam turbine, includes a rotor and at least one of:

• a seal,
• a plurality of blades,

the having a monitor portion which is designed for being exposed during operations to a maximum strain range and at least one operating portion subject to being coupled or covered during operations by one of said seal or plurality of blades or other internal component, wherein such monitor portion is adjacent to or distanced from the at least one operating portion.

[0016] According to a third aspect of the present invention, a method for monitoring fatigue in a rotor of a rotary machine, the method comprising the step of:

• providing at least one operating portion subject to being coupled or covered during operations by another component of the rotary machine,
• providing a monitor portion on the rotor, designed for being exposed during operations to a maximum strain range, the monitor portion being adjacent to or distanced from the at least one operating portion,
• monitoring periodically the monitor portion up to when a crack is generated,
• supervising the crack growth in order to determine a correspondent fatigue level.

[0017] The technical solution provided by this invention foresees to design the rotor such that highest thermal stress due to load cycling occurs on a location which is easy to monitor for crack initiation.

[0018] Advantageously, the maximum thermal stress in the rotor is not increased by the monitoring portion. Furthermore, the chosen location is not critical regarding other loads, i.e. it is sufficiently remote from operating locations, so that crack initiation will not pose a risk for further operation. The detection of a crack initiation in the monitor location may, according to a possible implementation of the method of the present invention, demand more careful operation until an overhaul of the rotor has mitigated the fatigue issue.

[0019] The present invention can be particularly used to monitor damages caused by low cycle fatigue. This allows a more rapid load cycling, thus providing capability for faster starts of steam turbines equipped with this invention.

[0020] According to possible embodiments of the present invention, the operating portion is one of:

• a bearing portion, subject to being coupled during operations by a bearing of the rotary machine,
• a sealing portion, subject to being coupled during operations by one or more seals of the rotary machine,
• a blade portion having a blade grove and subject being covered during operations by a plurality of blades of the rotary machine.

[0021] All the above operating portions are difficult to be reached and inspected by an operator of the rotary machine. Advantageously, the monitoring portion is placed immediately adjacent to or distanced from one of the above described operating portion.

[0022] Namely, according to possible embodiments of the present invention, the monitor portion of the rotor is provided:

• between two of seals of the sealing portions, and/or
• between a sealing portion and the blade portion, and/or
• at one end of the rotor, protruding from the bearing portion and opposite to the other end of the rotor, where momentum is transmitted.

[0023] In the latter case, when the rotary machine is a steam turbine, the casing of the steam turbine and the monitor portion are both connected to the same main supply of steam. Advantageously, this allows the monitor portion and the operating portion to be subject to the same thermal source, i.e. the steam entering the steam turbine.

[0024] According to possible embodiments of the present invention, the monitor portion comprises at least a notch. Advantageously, such geometry allows concentrating the thermal stress on a notch, i.e. on a very limited and controlled portion of the rotor, which is would be also the point where a crack would preferably initiate.

[0025] According to possible embodiments of the present invention, the monitor portion comprises one or more grooves. Advantageously, such geometry allows concentrating the thermal stress on a groove, i.e. on a very limited and controlled portion of the rotor, which is would be also the point where a crack would preferably initiate.

[0026] It has to be noted that embodiments of the invention have been described with reference to different subject matters. In particular, some embodiments have been described with reference to apparatus type claims (claims about a rotor and a steam turbine) whereas other embodiments have been described with reference to method (claims about a method for monitoring fatigue) type claims. However, a person skilled in the art will gather from the above and the following description that, unless other notified, in addition to any combination of features belonging to one type of subject matter also any combination between features relating to different subject matters, in particular between features of the apparatus type claims and features of the method type claims is considered as to be disclosed with this document.

Brief Description of the Drawings

[0027] The aspects defined above and further aspects of the present invention are apparent from the examples of embodiment to be described hereinafter and are explained with reference to the examples of embodiment. The invention will be described in more detail hereinafter with reference to examples of embodiment but to which the invention is not limited.

Fig. 1 is a sectional schematic view of a steam turbine having a rotor according to the present invention,

Fig. 2 is a magnified view of a first embodiment of monitoring device according to the present invention,

Fig. 3 is a magnified view of a second embodiment of monitoring device according to the present invention,

Fig. 4 is a magnified view of a third embodiment of monitoring device according to the present invention.

Detailed Description

[0028] The illustration in the drawing is schematically. It is noted that in different figures, similar or identical elements or features are provided with the same reference signs. In order to avoid unnecessary repetitions elements or features which have already been elucidated with respect to a previously described embodiment are not elucidated again at a later position of the description.

[0029] Figures 1 and 2 schematically show a rotary machine 10 constituted by a steam turbine.

[0030] The steam turbine 10 comprises a rotor 1, which in operation rotates about a rotation axis X, and a casing 60, at least partially housing the rotor 1. The rotor 1 comprises at least a bearing portion 20 (two bearing portions 20 in the embodiment of figure 1 at two opposite ends of the rotor 1, respectively) to which one or more bearings 21 are internally coupled. The bearings 21 support the rotation of the rotor 1 about its rotary axis X.

[0031] In the embodiment of figure 1, the rotor 1 further comprises a free end portion 50 protruding from the casing 60 and including a first bearing portion 20.

[0032] According to another embodiment of the present invention (not shown) the free end portion 50 of the rotor 1 is not present, i.e. the rotor 1 does not comprise any portion protruding from the casing 60 and the bearings 21 of the first bearing portion 20 are adjacent to the casing 60 or interposed between the rotor 1 and the casing 60.

[0033] The rotor 1 comprises a momentum end portion 52, opposite to the free end portion 50, where the momentum generated by the steam turbine 10 is externally transmitted, for example for generating electricity by means of a connection with an electrical generator. At the momentum end portion 52, a second bearing portion 20 is provided. The second bearing portion 20 comprises one or more bearings 21, between the rotor 1 and the casing 60, for supporting the rotation of the rotor 1 at the momentum end portion 52. Adjacent to the second bearing portion 20 a seal 31 is provided for preventing the steam flowing in the turbine 10 to exit the casing 60.

[0034] Between the free end portion 50 and the momentum end portion 52, the rotor further comprises:

• a sealing portion 30, which is subject to being coupled during operations by one or more seals 31. In the embodiment of figure 1, two seals 31 are provided, respectively coupled with the casing 60 for preventing the steam flowing in the turbine 10 to exit the casing 60 and coupled with another inner casing 61, for preventing internal leakages;
• an intermediate portion 35 adjacent to the sealing portion 30;
• a blade portion 40, interposed between the intermediate and portion 35 and the momentum end portion 52. The blade portion 40 has a plurality of blade groves 42 and is subject to being covered during operations by a plurality of blades 41 of the steam turbine 10.

[0035] The sealing portion 30, the seals 31, the intermediate portion 35, the blade portion 40 and the blades 41 are housed inside the casing 60. The casing 60 further comprises a connection to a main supply of steam 70, from which a flow of steam enters the steam turbine 10 to be directed towards the blades 41. The flow of steam causes the blades 41 and the rotor 1 to rotate about the rotation axis X, thus generating the momentum at the momentum end 52 of the rotor 1.

[0036] The sealing portion 30 and the blade portion 40 are difficult to be reached and inspected by an operator of the steam turbine 10, because they are covered by the seals 31 and the blades 41, respectively. Even if these portions of the rotor 1 may be the most thermally stressed, it is therefore impossible or difficult to identify on them the occurrence of a thermal fatigue damage, for example a crack of significant magnitude due to low cycle fatigue.

[0037] According to the present invention, the rotor 1 further includes a monitor portion 100 which is designed for being exposed during operations to a maximum strain range. The monitor portion 100 is adjacent to or distanced from the operating portions, 30, 40, which are subject to being coupled or covered during operations by another component 31, 41 of the steam turbine 10.

[0038] In the embodiment of figure 1, the operating portions are constituted by the sealing portion 30 and the blade portion 40, which are respectively coupled or covered by the seals 31 and the blades 41.

[0039] According to other embodiments of the present invention, in particular for rotors of other rotary machines, for example a gas turbine, the operating portions may be different.

[0040] In all cases, the present invention characterizes itself for the fact that the monitoring portion 100, further to be designed to for being exposed during operations to a maximum strain range, is also placed not in coincidence with the above defined operating portion.

[0041] Possible locations for the monitor portion 100 are;

• between the two seals 31 of said sealing portions 30,
• in the intermediate portion 35, between the sealing portion 30 and the blade portion 40.

[0042] In the embodiment of figure 1, inspection holes 90 are provided on the casing 60 for visually inspecting the monitoring portions 100 of the rotor 1, i.e. in correspondence between the two seals 31 of said sealing portions 30 and /or in the intermediate portion 35.

[0043] In the embodiment of figure 1, where the end portion 50 of the rotor 1 protrudes from the casing 60, the monitor portion 100 is also possibly located on the end portion 50. In such a case the steam machine 10 comprises a connection 80 between the end portion 50 of the rotor 1 and the main supply of steam 70, in order that also the monitor portion 100 on the end portion 50 is subject to the same thermal load condition of at least one of the other portions, 30, 35, 40 of the rotor 1. The steam flowing from the main supply 70 to the end portion 50 is then re -injected inside the casing 60 through the recirculation piping 81. According to another embodiment of the present invention (not shown), the recirculation piping 81 is not present and the steam flowing in the connection 80 towards the end portion 50 is therefore lost. In the embodiment of figure 1, the rotor 1 comprises three monitor portion 100 in three different locations, i.e. at the free end portion 50, between the seals 31 and in the intermediate portion 35, between the sealing portion 30 and the blade portion 40.

[0044] According to other embodiments (not shown), a different number of monitor portions 100 may be present, for example only one at the free end portion 50.

[0045] With reference to figures 2 to 4, three different possible embodiments of a monitor portion 100 are shown.

[0046] In the embodiment of figure 2, the monitor portion 100 is defined by a portion 101 of the rotor 1 having a greater diameter with respect to the adjacent portion. In the two points where the diameter is changed two notches 110, 111 are respectively defined. This allows concentrating the thermal stress on the notches 110, 111, i.e. on a very limited and controlled portion of the rotor 1, which is would be also the point where a crack would preferably initiate.

[0047] In the embodiment of figure 3, the monitor portion 100 comprises a stress relief groove 120 in the intermediate portion 35. The stress relief groove 120 may also be positioned, according to other respective embodiments of the invention, between the seals 31 or end portion 50 of the rotor 1. The stress relief groove 120 allows concentrating the thermal stress on a very limited and controlled portion of the rotor 1, which is would be also the point where a crack would preferably initiate.

[0048] In the embodiment of figure 4, the monitor portion 100 comprises a first bigger groove 120 and a second smaller groove 121, inside the first groove 120. This allows concentrating the thermal stress on a very limited and controlled portion, i.e. on the smaller groove 121, which is would be also the point where a crack would preferably initiate. The latter embodiment is preferably used outside the casing 60, on the end portion 50 of the rotor 1, to avoid that the smaller groove 121 may mechanical weaken the rotor 1.

[0049] According to the present invention, after one or more monitor portions 100 have been defined on the rotor 1, such portions 100 can be periodically monitored, at least up to when a crack is generated.

[0050] After the crack is generated, the accessibility of the monitor portions 100 allow supervising the crack growth in order to determine a correspondent fatigue level, i.e. a residual available life time of the rotor.

[0051] Corrective actions may be taken, for example overhauling of the rotor.

[0052] In all cases, the present invention provides an improved confidence, with respect to low cycle fatigue, in operating the rotary machine 10. This will allow more rapid load cycling, i.e. faster starts of the machine.

Claims

1. A rotor (1) for a rotary machine (10) including a monitor portion (100) which is designed for being exposed during operations to a maximum strain range, and at least one operating portion (30, 40) subject to being coupled or covered during operations by another component (21, 31, 41) of the rotary machine, wherein such monitor portion (100) is adjacent to or distanced from the at least one operating portion (20, 30, 40).

2. The rotor (1) according to claim 1, wherein the operating portion (30, 40) is one of:

- a sealing portion (30), subject to being coupled during operations by one or more seals (31) of the rotary machine

- a blade portion (40) having at least a blade grove (42) and subject to being covered during operations by a plurality of blades (41) of the rotary machine.

3. The rotor (1) according to claim 2, wherein the monitor portion (100) is provided between two seals (31) of the sealing portions (30).

4. The rotor (1) according to claim 2, wherein the monitor portion (100) is provided between a sealing portion (30) and the blade portion (40).

5. The rotor (1) according to claim 1 or 2, wherein the monitor portion (100) is provided at one end (50) of the rotor (1), protruding from the bearing portion (20).

6. The rotor (1) according to any of the preceding claims, wherein the monitor portion (100) comprises at least a notch (110, 111).

7. The rotor (1) according to any of the preceding claims, wherein the monitor portion (100) comprises at least a groove (120, 121).

8. A rotary machine (10) including a rotor (1) and at least one of:

- a seal (31),

- a plurality of blades (41),
the having a monitor portion (100) which is designed for being exposed during operations to a maximum strain range and at least one operating portion (30, 40) subject to being coupled or covered during operations by one of said seal (31) or plurality of blades (41),
wherein such monitor portion (100) is adjacent to or distanced from the at least one operating portion (30, 40).

9. The rotary machine (10) according to claim 8, further including a casing (60) inside which a part of the rotor (1), one or more seal (31) and the plurality of blades (41) are housed, the monitor portion (100) being housed inside the casing (60).

10. The rotary machine (10) according to claim 8, further including a casing (60) and an end (50) of the rotor (1) protruding from the casing (60), the monitor portion (100) being positioned on said rotor end (50).

11. The rotary machine (10) according to claim 9, wherein said rotary machine (10) is a steam turbine, the casing (60) being connected to a main supply of steam (70).

12. The rotary machine (10) according to claim 10, wherein said rotary machine (10) is a steam turbine, the casing (60) and the monitor portion (100) being both connected to the same main supply of steam (70).

13. The rotary machine (10) according to any of the claims 9 to 12, wherein the casing (60) comprises at least an inspection hole (90) for visually inspecting the monitor portion (100).

14. A method for monitoring fatigue in a rotor (1) of a rotary machine (10), the method comprising the step of:

- providing at least one operating portion (30, 40) subject to being coupled or covered during operations by another component (31, 41) of the rotary machine,

- providing a monitor portion (100) on the rotor (1), designed for being exposed during operations to a maximum strain range, the monitor portion (100) being adjacent to or distanced from the at least one operating portion (30, 40),

- monitoring periodically the monitor portion (100) up to when a crack is generated,

- supervising the crack growth in order to determine a correspondent fatigue level.

Drawing