JP2013151918A - Vapor turbine and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the reliability of a vapor turbine by suppressing galvanic corrosion at a contact part of a rotating blade and a rotor in a vapor turbine for thermal power generation.SOLUTION: In a vapor turbine including a rotating blade 11 and a rotor 12, the rotor 12 has a coating layer 22 at a contact part (planting part 13 of the rotating blade 11) with the rotating blade 11, and the coating layer 22 is formed of a material constituting the rotating blade 11.

Description

  The present invention relates to a steam turbine and a manufacturing method thereof, and is particularly suitable for a low-pressure steam turbine for thermal power generation.

  In recent years, in thermal power generation, it has become increasingly important to reduce the environmental load and increase the power generation efficiency.

  As one of the effective methods to reduce the environmental burden in feed water treatment of supercritical pressure once-through boilers, combined water treatment (Carbined Water Treatment (All Combined Volatile Treatment: AVT) without using hydrazine which has carcinogenicity) Conversion to Treatment (CWT) (described in Non-Patent Document 1) is underway.

CWT deliberately supplies oxygen that promotes corrosion to oxidize the eluted iron ions from divalent to trivalent with low solubility, and coat the steel surface with a stable oxide film (hematite: Fe ₂ O ₃ ) In particular, it is an effective method for suppressing corrosion in a flowing water environment such as in boiler piping.

  Patent Document 1 discloses a method in which corrosion prevention of a gap between a disk blade implantation portion of a steam turbine rotor and a blade blade root is performed using a thermosetting resin.

  Patent Document 2 discloses a turbine blade attachment structure in which a resin coating layer having electrical insulation and wear resistance is formed on at least one of an outer surface of a turbine blade attachment groove and an outer surface of a turbine blade implantation portion. Is disclosed.

  Patent Document 3 discloses that the center of a rotor blade fixing pin at the center of the wheel at the portion where the blade dovetail and the rotor blade fixing pin are coupled, and the outer periphery of the wheel at the portion where the wheel dovetail and the rotor blade fixing pin are coupled. There is disclosed a blade fixing device in which a gap is provided in the central portion of the side blade fixing pin.

  Patent Document 4 discloses a turbine rotor blade-disk coupling structure in which a lubricating film made of a thermosetting resin containing a solid lubricant is formed on a part or the entire surface of a pin.

JP-A-61-255201 JP-A-63-306206 JP 61-234206 A JP 2001-12208 A

JIS B 8223: Boiler feed water and boiler water quality

  An object of the present invention is to suppress galvanic corrosion at a connection portion between a rotor blade and a rotor of a steam turbine for thermal power generation, and to improve the reliability of the steam turbine.

  The present invention is characterized in that, in a steam turbine including a rotor blade and a rotor, a coating layer formed of a material constituting the rotor blade is provided on a surface of the rotor at a connection portion between the rotor and the rotor blade. .

  According to the present invention, corrosion prevention in water supply treatment without using hydrazine having carcinogenicity is facilitated, so that it is possible to reduce the environmental load due to hydrazine and to increase the blade length of the turbine rotor blade. It becomes possible to improve.

It is a side view which shows a low pressure steam turbine. It is a schematic cross section which shows the contact part of the moving blade of a conventional steam turbine, and a rotor. It is a partial expanded sectional view which shows the contact part of FIG. 2A. It is a schematic cross section which shows the contact part of the moving blade which is an example of a prior art, and a rotor. It is a partial expanded sectional view which shows the contact part of FIG. 3A. It is a schematic cross section which shows the contact part of the moving blade and rotor which concern on an Example. It is a partial expanded sectional view which shows the contact part of FIG. 4A. It is a schematic cross section which shows the manufacturing process of an Example. It is a partial expanded sectional view which shows the specific manufacturing process of FIG. 5A. It is a graph which shows the experimental result which measured the influence by the presence or absence of a coating layer regarding the corrosion amount of the rotor material in an AVT corrosion environment. It is a graph which shows the experimental result which measured the influence by the presence or absence of a coating layer regarding the corrosion amount of the rotor material in a CWT corrosion environment. It is a graph which shows the experimental result which measured the corrosion potential of the moving blade material and the rotor material with respect to dissolved oxygen concentration. It is a graph which shows the experimental result which measured the influence by the presence or absence of a coating layer regarding the corrosion potential difference which generate | occur | produces between a rotor material and a rotor blade material in the corrosive environment of AVT and CWT.

  The present invention relates to a steam turbine and a method for manufacturing the same, and is particularly suitable for a low-pressure steam turbine for thermal power generation.

  Hereinafter, a steam turbine and a manufacturing method thereof according to an embodiment of the present invention will be described.

  The steam turbine includes a moving blade and a rotor, and the rotor has a coating layer at a connection portion with the moving blade, and the coating layer is formed of a material constituting the moving blade.

  In the steam turbine, the coating layer preferably contains 10 to 18 wt.% Or more of Cr.

  In the steam turbine, the coating layer preferably contains 80 wt.% Or more of Ti.

  The manufacturing method of the said steam turbine has the process of forming a coating layer on the surface of the rotor in the connection part of a rotor and a moving blade using the material which comprises a moving blade.

  In the steam turbine manufacturing method, the coating layer is formed by hot-wire flame spraying, buttering, overlay welding, diffusion bonding, explosion welding, rolling cladding, or isostatic pressing.

  Hereinafter, a low-pressure steam turbine in which a rotor implantation part is formed in a bowl shape will be described as an example. However, the present invention is not limited to this, and can also be applied to cases where the planting portion has a Christmas tree shape, a fork shape, a T shape, or the like. Further, the present invention can be similarly applied to a steam turbine using a high / medium pressure rotor or each water supply treatment. It is particularly effective for steam turbines that use 12Cr steel or Ti alloy for the rotor blade material and 3.5NiCrMoV steel for the rotor material.

  FIG. 1 is a side view showing a low-pressure steam turbine.

  In this figure, the steam turbine 1 is composed of a moving blade 11 and a rotor 12. The moving blade 11 is fixed to the rotor 12 at the implantation portion 13. The moving blade 11 receives the collision of steam generated in the boiler, absorbs the kinetic energy, and rotates the rotor 12. Thereby, the energy of the steam is converted into the rotational energy of the rotor 12. Here, the implantation part 13 is also called a connection part between the moving blade 11 and the rotor 12.

  The rotor blade 11 is made of 12Cr steel, which is a material having both high temperature strength and corrosion resistance. The rotor 12 is formed of 3.5NiCrMoV steel, which is a material having both normal temperature strength, large-scale casting manufacturability, and fatigue strength.

  The implantation part 13 has a bowl shape. This improves the resistance of the rotor blade to centrifugal force and vibration stress.

  FIG. 2A is a schematic cross-sectional view showing a contact portion between a rotor blade and a rotor of a conventional steam turbine.

  2B is an enlarged cross-sectional view showing the contact portion of FIG. 2A.

  In these drawings, the moving blade 11 and the rotor 12 are in direct contact.

In the steam turbine downstream of the boiler, water tends to stay in the gap of the implantation portion 13 where the moving blade 11 and the rotor 12 are in contact. In the implanted portion 13, the moving blade 11 and a part of the rotor 12 are in contact with each other, so that the moving blade 11 having a noble electrode potential serves as a cathode and the rotor 12 having a low electrode potential serves as an anode. Therefore, a potential difference is generated between the rotor blade 11 and the rotor 12, and a corrosion current (e ⁻ ) flows as shown in FIG. 2B. Thereby, metal components such as iron (Fe) are ionized from the rotor 12 and eluted into water, and corrosion proceeds. Therefore, sufficient corrosion resistance must be imparted to the surface of the rotor 12 serving as the anode.

  As a conventional technique for improving the corrosion resistance and reliability of the surface of the rotor 12 in the implanted portion 13, there is a means for electrically insulating the rotor blade 11 and the rotor 12. One of them is one in which at least one of the surfaces of the rotor blade 11 and the rotor 12 is covered with a thermosetting resin having electrical insulation (described in Patent Documents 1 and 2).

  FIG. 3A is a schematic cross-sectional view showing a contact portion between a rotor blade and a rotor, which is an example of the prior art. 3B is an enlarged cross-sectional view showing the contact portion of FIG. 3A.

  In FIG. 3A, the steam turbine is composed of a moving blade 11 and a rotor 12. The gap between the rotor blade 11 and the rotor 12 is filled with a thermosetting resin 21.

  However, as shown in FIG. 3B, as a result of the use of the steam turbine, the thermosetting resin 21 is partially peeled off, and solid foreign matter 14 (scattered matter) is likely to be generated. In general, the thermosetting resin 21 has an elastic modulus smaller than that of a metal. For this reason, the thermosetting resin 21 (resin layer) sandwiched between the moving blade 11 and the rotor 12 is subjected to strong centrifugal force or vibration stress by the moving blade 11 and is cracked or broken. Moisture may flow into the surface of the rotor 12 from this portion, and local corrosion may occur. Therefore, the coating on the surface of the rotor 12 in the implanted portion 13 needs to have sufficient strength against the centrifugal force and vibration stress of the rotor blade 11.

  In the case of insulating with resin, the method is roughly composed of two steps: (1) applying a thermosetting resin, and then (2) curing the resin by heating with a ribbon heater or the like. . In order to maintain the adhesion of the coated thermosetting resin, it is necessary to uniformly heat the thermosetting resin at a predetermined temperature. However, as the heat capacity increases and the structure of the turbine increases due to the increase in size of the turbine, heat treatment becomes difficult, and it is not necessarily a suitable method.

  As another conventional technique, in a coupling structure in which a fork and a rotor, which are part of a moving blade, are fixed by a plurality of pins, means for covering the fixing pins with ceramic or solid lubricant (Patent Documents 3 and 4) is there.

  However, ceramics and solid lubricants have a low modulus of elasticity and adhesion to metals, similar to the thermosetting resin described above, and may crack and scatter when operated for a long time under high surface pressure. The scattered ceramic and solid lubricant collide with the lower rotor blade and induce erosion of the rotor blade surface. Moreover, when it flows into a downstream condenser as a foreign material, it adheres as a scale and causes a reduction in heat transfer efficiency and an increase in differential pressure between the boiler and the feed water heater. In order to avoid this, although there is a power generation facility in which a filter for removing solids is installed upstream of the double water condenser, it is desirable to reduce the scattered matter generated from the turbine because of the high cost of maintenance.

  FIG. 4A is a schematic cross-sectional view illustrating a contact portion between a rotor blade and a rotor according to an embodiment. 4B is an enlarged cross-sectional view showing the contact portion of FIG. 4A.

  As shown in these drawings, in the implanted portion 13, a coating layer 22 (corrosion-resistant coating layer) formed of a blade material is provided on the surface of the rotor 12 that faces or contacts the blade 11. It is. As a result, the potential generated on the contact surface between the rotor blade 11 and the rotor 12 can be made the same potential, and galvanic corrosion can be prevented.

  The coating layer 22 is not a ceramic or an insulator, but a metal with a high elastic modulus. By using a blade material that is the original structural material, a turbine that combines high pressure adhesion and reliability is provided. can do. In addition, the surface of the rotor blade 11 is not coated with the rotor material having poor corrosion resistance, but the surface of the rotor 12 is coated with the blade material excellent in the formation of a passive film, thereby improving the corrosion resistance against crevice corrosion. it can.

  The coating layer 22 preferably contains 10 to 18 wt.% Cr. The covering layer 22 preferably contains 80 wt.% Or more of Ti.

  Next, a method for forming the corrosion-resistant coating layer will be described.

  FIG. 5A is a schematic cross-sectional view illustrating the manufacturing process of the example. FIG. 5B is a partially enlarged cross-sectional view showing a specific manufacturing process of FIG. 5A.

  A coating layer 22 made of a moving blade material is formed on the surface of the rotor 12 facing the moving blade. FIG. 5A shows the middle of film formation.

  For forming the coating layer 22, it is desirable to use a thermal spraying apparatus or an ion sheath film forming apparatus capable of forming a large area. Here, hot flame flame spraying was used in which the material to be sprayed is not easily altered and there is little loss of Cr compared to arc spraying. Then, the spray gun 31 was formed to pass through the surface of the rotor 12 at a constant speed while maintaining the same film formation conditions (gas pressure and film formation power).

  In the present example, the film thickness was made uniform in the plane and 50 μm or more for the purpose of uniformizing the stress applied to the coating layer 22 and reducing defects in the coating layer 22. The thermal spray rod 32 is preferably an alloy having the same composition as the blade material. The reason why the alloy having the same composition is used is that the smaller the potential difference between the outer surface of the implanted portion of the rotor 12 and the moving blade, the more the corrosion current is reduced, which is effective in preventing galvanic corrosion.

  As a specific spray rod 32, 12Cr steel is effective if the blade material is 12Cr steel, and Ti-6Al-4V is effective if the blade material is Ti-6Al-4V (titanium alloy). is there. In addition, 13Cr steel and 12Cr—Mo—V steel can be cited as common materials used as the spray rod 32 and the blade material.

  After the film formation as described above, the sprayed surface was naturally cooled to stabilize the film formation surface, and then the moving blade 11 was assembled into the implanted portion 13 of the rotor 12 as shown in FIG. 4A.

  Through the above steps, corrosion of the implanted portion 13 of the rotor 12 is suppressed, and a highly reliable steam turbine can be obtained.

  Next, a corrosion resistance test was performed using a rotor blade material made of 12Cr steel and a rotor material made of 3.5NiCrMoV steel. The results are shown in FIGS.

  FIG. 6 is a test in an AVT corrosive environment (pH 9.5, dissolved oxygen concentration is less than 7 ppb), and FIG. 7 is a test in a CWT corrosive environment (pH 8.5, dissolved oxygen concentration is 100 ppb).

  In order to make an accelerated test, a clearance test piece (Example) in which a blade material and a rotor material provided with a coating layer were brought into contact with an aqueous solution containing 0.01 mol / l of sodium chloride as a corrosion promoting compound, and a blade A gap test piece (comparative example) in which a material and a rotor material not provided with a coating layer were brought into contact was immersed, and the immersion bath was heated to 90 ° C. and then held for 400 hours and 800 hours.

  As shown in FIGS. 6 and 7, in any corrosive environment, the amount of corrosion was lower in the example than in the comparative example. And the amount of corrosion decreased greatly in the test piece to which the acceleration test of CWT was applied rather than AVT. From this, it can be seen that AVT is suitable for anticorrosion in a corrosive environment as well as CWT.

  Here, in the case of the example, the reason why the corrosion can be suppressed particularly in the corrosive environment of CWT will be described.

Corrosion is a phenomenon in which metal exposed to a certain environment reacts with water, oxygen, etc. in the environment and the metal surface is thinned. Corrosion forms that occur up to the crevice occurring in the rotor blade implant are mainly (1) galvanic corrosion and (2) crevice corrosion. Among these, (1) galvanic corrosion, as described above, the electrode potential difference generated by the contact of different metals becomes a driving force, and the metal having a lower electrode potential is selectively corroded among these different metals. On the other hand, (2) crevice corrosion, the electromotive force becomes the driving force by the density difference between the dissolved oxygen and ions in and out of the gap, the anion having entered from the outside (in particular Cl ^-) the oxide layer is formed on the surface of the gap section Generated by destruction.

  Therefore, in order to suppress corrosion in gaps composed of different metal surfaces such as moving blade implants, (1) the electrode potential difference between the contacting metals approaches 0V, and the passive film is destroyed. (2) A structure in which the entire surface is covered with a metal with an increased amount of Cr is preferable in order to make it difficult to be done.

  In order to estimate the galvanic corrosion susceptibility of rotor materials in AVT and CWT, the corrosion potentials of the blade material and rotor material in a corrosive environment using an aqueous solution containing 0.01 mol / l of the above-mentioned corrosion promoting compound sodium chloride The dissolved oxygen concentration dependence was evaluated. The result is shown in FIG. The temperature of the aqueous solution is 90 ° C. and the pH is 8.5.

  Here, the test piece of the rotor blade material or rotor material is immersed in an aqueous solution containing the above sodium chloride alone, and degassed by injecting nitrogen gas to evaluate the dependency of dissolved oxygen. The dissolved oxygen inside was suppressed to about 0 ppb. Thereafter, the corrosion potential up to 120 ppb was measured while increasing the dissolved oxygen concentration at a rate of 15 ppb / hour.

  As shown in FIG. 8, the corrosion potential difference between the rotor blade material and the rotor material is small when the dissolved oxygen is around 0 ppb, but as the dissolved oxygen increases, each corrosion potential becomes noble, and the corrosion potential difference suddenly increases in the range of 20 ppb to 40 ppb. To be high.

  Therefore, it can be seen that in a corrosive environment containing sodium chloride, dissolved oxygen increases the sensitivity of the rotor material to galvanic corrosion. It can be estimated that the corrosion amount of the rotor material in the CWT in FIG. 7 is higher than the AVT in FIG. 6 because the galvanic corrosion has progressed.

  FIG. 9 is a graph showing experimental results obtained by measuring the influence of the presence or absence of a coating layer on the corrosion potential difference generated between the rotor material and the blade material in the corrosive environment of AVT and CWT.

  As shown in this figure, the difference in corrosion potential when the coating layer was provided on the rotor material decreased in both AVT and CWT. This effect is particularly noticeable with CWT.

  From the above measurement results of the corrosion amount and the corrosion potential difference, it was proved that a steam turbine capable of suppressing the corrosion of the rotor in the implanted portion can be provided.

  In this example, a rotor blade made of 12Cr steel and a rotor made of 3.5NiCrMoV steel were used, but the present invention is not limited to this, and low alloy steel, Ti alloy, etc. are used. It can also be applied to existing rotor blades and rotors.

  Further, the method for forming the coating layer is not limited to the hot wire flame spraying used in the present embodiment, but can be applied to buttering, overlay welding, diffusion bonding, explosion welding, rolling cladding, isostatic pressing, and the like. .

  1: Steam turbine, 11: Rotor blade, 12: Rotor, 13: Implanted part, 14: Solid foreign substance, 21: Thermosetting resin, 22: Coating layer, 31: Thermal spray gun, 32: Thermal spray rod.

Claims (5)

  A steam turbine including a moving blade and a rotor, wherein the rotor has a coating layer at a connection portion with the moving blade, and the coating layer is formed of a material constituting the moving blade. A steam turbine characterized by   The steam turbine according to claim 1, wherein the coating layer contains 10 to 18 wt.% Or more of Cr.   The steam turbine according to claim 1, wherein the coating layer contains 80 wt.% Or more of Ti.   A method of manufacturing a steam turbine including a moving blade and a rotor, wherein a coating layer is formed on a surface of the rotor at a connection portion between the rotor and the moving blade using a material constituting the moving blade. A method for manufacturing a steam turbine, comprising:   The steam turbine manufacturing method according to claim 4, wherein the coating layer is formed by hot wire flame spraying, buttering, overlay welding, diffusion bonding, explosion welding, rolling cladding, or isostatic pressing.

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