JP4711779B2 - Method for suppressing oxidation of steam pipe and steam supply device - Google Patents

Description

  The present invention relates to a technique for suppressing oxidation of a steam pipe for supplying steam.

Thermal power plants are known as plants that use steam. A schematic configuration of an example of a thermal power plant is shown in FIG.
The thermal power plant shown in FIG. 8 includes a boiler, a steam turbine, a generator, a condenser, and the like. The steam turbine includes a high-pressure turbine, an intermediate-pressure turbine, and a low-pressure turbine, and is connected to a generator.
The thermal power plant shown in FIG. 8 operates as follows.
The steam generated in the boiler is heated by the superheater and then supplied to the high-pressure turbine. The steam discharged from the high-pressure turbine is re-superheated by the reheater and then supplied to the intermediate-pressure turbine. The steam discharged from the intermediate pressure turbine is supplied to the low pressure turbine. The generator is driven by a steam turbine to generate electric power, and supplies the generated electric power to an electric power system or the like. Steam discharged from the low-pressure turbine is returned to the boiler via the condenser.
Steam pipes for supplying steam (for example, main steam pipes for supplying superheated steam and reheat steam pipes for supplying reheated steam) are made of high-temperature heat-resistant materials (for example, Cr-Mo steel). Has been.
On the other hand, in such a water vapor pipe, when the high temperature and high pressure water vapor passes, the water vapor passage side is oxidized. For example, in the case of a steam pipe formed of Cr—Mo steel, an oxide scale (steam oxide scale) is generated on the steam passage side (inner surface side) of the base material forming the steam pipe as shown in FIG. The oxide scale has, for example, a two-layer structure of an outer layer scale generated on the inner surface side and an inner layer scale generated on the outer surface side. The outer scale includes iron oxide (mainly Fe ₃ O ₄ ), and the inner scale includes oxides such as Cr. The oxide scale grows through the passage of water vapor.

In such a thermal power plant, when the steam turbine is started, the temperature of the steam pipe changes from a low temperature to a high temperature, and when the steam turbine is stopped, the temperature of the steam pipe changes from a high temperature to a low temperature. The base material and the oxide scale expand or contract due to the temperature change of the water vapor pipe. Here, since the base material and the oxide scale have different thermal expansion coefficients, stress is generated in the oxide scale due to the difference in the thermal expansion coefficient between the base material and the oxide scale when the steam turbine is started or stopped.
For this reason, when the start and stop of the steam turbine are repeated, the oxide scale is peeled off from the base material, and the peeled oxide scale may damage the high-pressure turbine and the intermediate-pressure turbine.
Therefore, a method for suppressing the oxidation of the inner surface of the steam pipe by applying a coating for suppressing the generation of oxide scale to the inner surface of the steam pipe, or a chemical cleaning of the inside of the steam pipe is generated on the inner surface of the steam pipe. A method of removing the oxidized scale is used.
In addition, an electron conductive layer is formed on the surface of the carbon-based substrate in order to provide oxidation resistance to the carbon-based substrate that is formed of a carbon-based material such as carbon or silicon carbide and is used in a high temperature environment exceeding 1100 ° C. In addition, a technique for forming an oxide layer on the surface of the electron conductive layer has been proposed. (See Patent Document 1)
JP 2005-8497 A

In the method of suppressing the oxidation of the inner surface of the steam pipe using the method of coating the inner surface of the steam pipe, the effect of suppressing the oxidation of the inner surface of the steam pipe has a limit.
In addition, the method of chemically cleaning the inside of the steam pipe is costly, and furthermore, the oxide scale generated on the inner surface of the steam pipe cannot be sufficiently removed.
The technique described in Patent Document 1 is a technique for imparting oxidation resistance to a carbon-based substrate formed of a carbon-based material, and also forms an electron conductive layer on the surface of the carbon-based substrate. An oxide layer is formed on the surface of the electron conductive layer. For this reason, it is necessary to form an electron conductive layer and an oxide layer, and the work load is large and the cost is high.
The present invention was devised in view of the above points, and effectively suppresses the growth of oxide scale generated on the inner surface of a water vapor pipe formed of Cr-Mo steel simply and inexpensively. It is an object of the present invention to provide a method for suppressing oxidation of a water vapor pipe and a water vapor supply device.

The technology of each of the following inventions is a water vapor pipe for supplying water vapor at 400 ° C. to 600 ° C., which is formed of Cr—Mo steel, and an oxide scale is formed on the inner surface by supplying water vapor at 400 ° C. to 600 ° C. It is used suitably as a technique for suppressing the growth of oxide scale generated on the inner surface of such a steam pipe.
1st invention of this invention is the oxidation suppression method of water vapor piping as described in Claim 1. FIG.
In the present invention, the potential D on the inner surface side of the water vapor pipe formed of Cr—Mo steel and generating an oxide scale on the inner surface by supplying steam at 400 ° C. to 600 ° C. is set to [−10V ≦ D ≦ −0. .5V].
The “inner surface side of the steam pipe” means the inner face side of the base material excluding the oxide scale generated on the inner face of the steam pipe. In the present invention, it is only necessary that the inner surface side of the steam pipe is set to a negative potential, and the entire steam pipe (for example, the inner surface side and the outer surface side of the steam pipe) may be set to a negative potential.
As the Cr-Mo steel forming the steam pipe, [1.25Cr-0.5Mo steel] (STPA23, STBA23) or [2.25Cr-1Mo steel] (STPA24, STBA24) is preferably used.
In the steam pipe formed of Cr-Mo steel, the oxide ions generated by the steam diffuse on the outer surface side of the base material of the steam pipe on the inner surface in contact with the steam, and an oxide scale composed of an outer layer scale and an inner layer scale is generated and grow up. In the present invention, by setting the inner surface side of the steam pipe to a negative potential, the diffusion of oxide ions to the outer surface side of the steam pipe is suppressed. Thereby, the growth of the oxide scale produced | generated on the inner surface of a water vapor piping is suppressed, ie, the oxidation of the inner surface of a water vapor piping is suppressed.
Furthermore, in the present invention, the electric potential D on the inner surface side of the steam pipe is set in the range of [-10V≤D≤-0.5V]. By setting the potential D on the inner surface side of the steam pipe to a negative potential within this range, the adhesion strength of the oxide scale and the non-peelability against thermal shock of the oxide scale can be improved, and the oxide scale can be effectively peeled off. Can be prevented.
Various methods can be used as a method of setting the inner surface side of the steam pipe to a negative potential.

The second invention of the present invention is a method for inhibiting oxidation of a steam pipe as described in claim 2.
In the present invention, the electric potential D on the inner surface side of the steam pipe is set in a range of [−5V <D ≦ −0.5V].
By setting the electric potential D on the inner surface side of the water vapor pipe in the range of [−10 V ≦ D ≦ −0.5 V], it is possible to improve the adhesion of the oxide scale and the non-peelability to the thermal shock of the oxide scale. However, the thickness of the oxide scale can be reduced by setting in the range of [−5V <D ≦ −0.5V]. Thereby, the growth of oxide scale can be more effectively suppressed, and peeling of the oxide scale can be more effectively prevented.

A third invention of the present invention is a method for inhibiting oxidation of a steam pipe as described in claim 3.
In the present invention, by arranging a DC power source between the steam pipe and the ground electrode so that the negative electrode is connected to the steam pipe and the positive electrode is connected to the ground electrode, the inner surface side of the steam pipe is set to a negative potential. It is set.
Various DC power supply devices can be used as the DC power supply device.
The negative electrode and the positive electrode of the DC power supply device may be directly connected to the water vapor pipe and the ground electrode, respectively, or may be connected indirectly (for example, via a resistor).

A fourth aspect of the present invention is a method for inhibiting oxidation of a steam pipe as described in claim 4.
In the present invention, an electrode is disposed in the steam pipe in an insulated state from the steam pipe, and the direct current power supply device is connected between the steam pipe and the electrode so that the negative electrode is connected to the steam pipe and the positive electrode is connected to the electrode. By disposing, the inner surface side of the steam pipe is set to a negative potential.
In the present invention, the inner surface side of the steam pipe is set to a negative potential by electrostatic induction action by an electrode connected to the positive electrode of the DC power source and insulated from the steam pipe in the steam pipe.
The shape and position of the electrode disposed in the steam pipe are appropriately determined according to the position and area on the inner surface side of the steam pipe set to a negative potential.
The negative electrode and the positive electrode of the DC power supply device may be connected directly or indirectly to the water vapor pipe and the electrode, respectively.

A fifth aspect of the present invention is a water vapor supply device as set forth in the fifth aspect.
The present invention is a steam pipe formed of Cr-Mo steel for supplying a steam generator and steam at 400 ° C to 600 ° C generated by the steam generator, and supplying steam at 400 ° C to 600 ° C. Thus, a water vapor pipe for generating an oxide scale on the inner surface is provided. Furthermore, a negative potential setting device is provided for setting the potential D on the inner surface side of the steam pipe in a range of [−10 V ≦ D ≦ −0.5 V].
As the Cr—Mo steel forming the steam pipe, the same Cr—Mo steel as in the first invention is preferably used.
The negative potential setting device of the present invention only needs to be able to set the inner surface side of the steam pipe to a negative potential, and may set the entire steam pipe to a negative potential.
Furthermore, by setting the potential D on the inner surface side of the steam pipe to a range of [-10 V ≦ D ≦ −0.5 V], the adhesion strength of the oxide scale and the non-peelability against the thermal shock of the oxide scale are improved. And the oxide scale can be effectively prevented from peeling off.
Various negative potential setting devices can be used as a negative potential setting device that sets the inner surface side of the steam pipe to a negative potential.

A sixth aspect of the present invention is a water vapor supply device as set forth in the sixth aspect.
In the present invention, the negative potential setting device sets the potential D on the inner surface side of the steam pipe in a range of [−5V <D ≦ −0.5V].
By setting the potential D on the inner surface side of the water vapor pipe to the range of [-5V <D ≦ -0.5V], the growth of the oxide scale can be more effectively suppressed, and the oxide scale can be further peeled off. It can be effectively prevented.

A seventh aspect of the present invention is a water vapor supply device as set forth in the seventh aspect.
In the present invention, the negative potential setting device has a DC power supply device in which the negative electrode is connected to the water vapor pipe and the positive electrode is connected to the ground electrode.
Various DC power supply devices can be used as the DC power supply device.
The negative electrode and the positive electrode of the DC power supply device may be connected directly or indirectly to the water vapor pipe and the ground electrode, respectively.

An eighth aspect of the present invention is a water vapor supply device as set forth in the eighth aspect.
In the present invention, the negative potential setting device includes an electrode disposed in a state where the water vapor pipe is insulated from the water vapor pipe, a DC power supply device in which the negative electrode is connected to the water vapor pipe and the positive electrode is connected to the electrode. Have.
In the present invention, the inner surface side of the steam pipe is set to a negative potential by the electrostatic induction action by the electrode set to a positive potential.
The shape and position of the electrode disposed in the steam pipe are appropriately determined according to the position and area on the inner surface side of the steam pipe set to a negative potential.
The negative electrode and the positive electrode of the DC power supply device may be connected directly or indirectly to the water vapor pipe and the electrode, respectively.

  By using the method for suppressing oxidation of a steam pipe according to any one of claims 1 to 4 and the steam supply device according to claims 5 to 8, it is formed of Cr-Mo steel and by supplying steam at 400 ° C to 600 ° C. Oxidation of the water vapor piping in which an oxide scale is generated on the inner surface can be effectively suppressed simply, inexpensively. Thereby, the erosion (thickness reduction by damage) of the blade | wing of a high pressure turbine or an intermediate pressure turbine can be suppressed.

Embodiments of the present invention will be described below with reference to the drawings.
Steam pipe for supplying steam, for example, a main steam pipe for supplying steam heated by a superheater of a thermal power plant to a high-pressure turbine, or a reheat steam pipe for supplying steam reheated by a reheater to an intermediate pressure turbine Is often formed of Cr-Mo steel.
The water vapor supplied from the superheater or the reheater usually has a pressure of 17 MPa or more at a temperature of 400 ° C. to 600 ° C.
Typically, [1.25Cr-0.5Mo steel] (STPA23, STBA23) or [2.25Cr-1Mo steel] (STPA24, STBA24) is used as the Cr-Mo steel forming such a steam pipe. Used.
When water vapor passes through a water vapor pipe formed of Cr—Mo steel, the water vapor generates oxide ions (oxygen ions O ²⁻ and hydroxyl ions OH ⁻ ) on the inner surface of the water vapor pipe, and the water vapor pipe is generated by the oxide ions. An oxide scale is generated on the inner surface of the substrate. As shown in FIG. 9, the oxide scale has a two-layer structure of an outer layer scale containing an iron oxide and an inner layer scale containing a chromium oxide. When oxide ions diffuse from the inner surface side of the water vapor pipe to the outer surface side of the water vapor pipe, an oxide scale grows.
When the steam turbine is started, stopped, or when the load of the steam turbine is increased or decreased, stress is generated in the oxide scale due to thermal expansion or contraction of the steam pipe and the oxide scale, and the boundary portion between the inner scale and the base material. The number of voids (cavities) generated near the inner scale side increases, and the voids increase. For this reason, there exists a possibility that an oxide scale may peel from water vapor piping. In this case, the greater the number of voids generated at the location on the inner layer scale side in the vicinity of the boundary between the inner layer scale and the base material, and the greater the void, the higher the risk that the oxide scale will peel off.
Therefore, in this embodiment, the inner surface side of the base material of the steam pipe is set to a negative potential. In this case, an electric repulsive force is generated between the oxidized ions generated on the inner surface of the water vapor pipe and the electrons at the negative potential on the inner surface side of the water vapor pipe. Diffusion to the outer surface side is suppressed. Thereby, the growth of the oxide scale, that is, the oxidation of the steam pipe can be suppressed.

Here, in order to confirm the effect of suppressing the growth of oxide scale generated on the inner surface of the steam pipe by passing the steam in a state where the inner surface side of the steam pipe is set to a negative potential, The experiment was conducted.
A schematic diagram of the test apparatus used is shown in FIG.
The test apparatus shown in FIG. 1 includes a water tank 10, a pump 11, a water vapor generator 20, a reaction tube 30, a DC power supply device 34, and the like.
The water accumulated in the water tank 10 is supplied by the pump 11 to the pipe 40c through the pipe 40a and the valve 50a. Air is supplied to the pipe 40c via the pipe 40b and the valve 50b. The pipe 40c mixes the water supplied through the valve 50a and the air supplied through the valve 50b and supplies the mixed water to the water vapor generator 20.
The steam generator 20 is provided with a heater 21, and the steam generated by the steam generator 20 is heated by the heater 21. The water vapor heated by the heater 21 is supplied to the reaction tube 30 through the pipe 40d and the insulating ring 60a. The reaction tube 30 is made of stainless steel (SUS304).
The reaction tube 30 is provided with a heater 31, and the water vapor supplied to the reaction tube 30 is heated by the heater 31. The water vapor discharged from the reaction tube 30 is returned to the water tank 10 through the valve 50c, the insulating ring 60b, and the piping 40c.
The insulating ring 60a and the insulating ring 60b are for insulating the reaction tube 30 from the piping 40d and the piping 40c.

The test was performed by the following method using the test apparatus shown in FIG.
As the test pieces (1) to (6), actual machine use test pieces corresponding to steam pipes (for example, a superheater pipe and a reheater pipe) in a state where an oxide scale (steam oxidation scale) was generated were prepared. And the alumina container 32 was arrange | positioned in the reaction tube 30 in the state which accommodated the test pieces (1)-(6) in the alumina container 32. FIG.
In addition, an insulating alumina tube 33 was inserted into the reaction tube 30, one end side was connected to each of the test pieces (1) to (6), and the other end side was connected to the negative electrode of the DC power supply 34. A plurality of lead wires were provided. Further, the positive electrode of the DC power supply 34 was connected to the reaction tube 30. Thereby, each test piece (1) to (6) is set to a negative potential with respect to the reaction tube 30. The potentials D of the test pieces (1) to (6) are [0V], [−0.5V], [−2V], [−5V], [−10V], and [−20V], respectively. Have been adjusted so that.
Then, with the test temperature in the reaction tube 30 set to 550 ° C. and the test pressure set to 1 atm, a test for 500 hours, which is a time interval in which the growth of the oxide scale (water vapor scale) can be confirmed in an actual machine environment, is performed. It was.

Next, with respect to the test pieces (1) to (6) tested as described above, the adhesion strength of the oxide scale generated in each of the test pieces (1) to (6) and the non-peelability of the oxide scale. Evaluated.
Evaluation of the adhesion strength of the oxide scale generated in each of the test pieces (1) to (6) was performed by the method shown in FIG. That is, the tensile member was bonded to the oxide scale generated on the test piece (surface area: 5.86 cm ² ) with an adhesive (adhesion area: 0.785 cm ² ), and the test piece was fixed to the fixing member. A tensile load was applied by the member. And the tensile load (N) when an oxide scale peeled was measured.
Moreover, evaluation of the non-peelability of the oxide scale produced | generated by each test piece (1)-(6) was performed with the following method. That is, the number of times that the operation of dropping a water droplet after holding the test piece at 500 ° C. for 1 hour (operation for applying a thermal shock) until the oxide scale was peeled off by dropping the water droplet was measured (however, 10 was the upper limit).

FIG. 3 shows the results of the evaluation of the adhesion strength of the oxide scale to each of the test pieces (1) to (6). Here, when a tensile load exceeds 400N, it is estimated that it can endure use of an actual machine. From FIG. 3, the tensile load (the adhesion force of the oxide scale) when the potential D of the test piece is set in the range of [−10 V ≦ D ≦ −0.5 V] is any tensile load 400 N that can withstand the actual use. I can understand that
In this way, by setting the potential D of the test piece in the range of [−10 V ≦ D ≦ −0.5 V], the stress due to thermal expansion or contraction is reduced when the steam turbine is started or stopped. When it acts on, it can prevent that an oxide scale peels from water vapor | steam piping.
In addition, that the tensile load of an oxide scale is large means that the oxidation of water vapor piping is suppressed and the densification of the inner layer scale is promoted.

FIG. 4 shows the results of evaluating the non-peelability of each test piece (1) to (6) against the thermal shock of the oxide scale. Here, when the number of thermal shocks exceeds two, it is presumed that it can withstand the actual use. From FIG. 4, it is understood that by setting the potential D of the test piece within the range of [−10 V ≦ D ≦ −0.5 V], the number of thermal shocks that can withstand use of the actual machine exceeds both. it can.
As described above, by setting the potential D of the test piece in the range of [−10 V ≦ D ≦ −0.5 V], the oxide scale is peeled off from the steam pipe when a thermal shock is applied to the steam pipe. Can be prevented.
A large number of thermal shocks required to peel the oxide scale means that the oxidation of the steam pipe is suppressed and the densification of the inner scale is promoted.

  From the above evaluation of the adhesion strength of the oxide scale and the evaluation result of the non-peelability of the oxide scale, by setting the potential D of the test piece in the range of [−10 V ≦ D ≦ −0.5 V], It is possible to suppress the oxidation and promote the densification of the inner scale, and it is possible to prevent the oxide scale generated in the water vapor pipe from being peeled off due to stress and thermal shock.

Furthermore, cross-sectional microstructure observation was performed about test piece (1)-(6) which tested.
As a result, when compared with the test piece (1) tested in the state where the potential D is set to the actual state D [0V], the potential D is set to [−5V] and [−10V]. In the test pieces (4) and (5) in which the test was performed, it was found that the void (cavity) generated in the inner layer scale was repaired and the oxide scale was thickened.
In addition, in the test piece (6) that was tested in the state where the potential D of the steam pipe was set to [−20V], it was found that the number of voids in the inner layer scale increased and the voids increased. It was. Furthermore, in the test piece (6), it was found that the oxide scale was peeled off.
On the other hand, in the test pieces (2) and (3) in which the potential D of the steam pipe is set to [−0.5 V] and [−2 V], voids (cavities) on the inner layer scale are repaired and oxidation is performed. It was found that the thickness of the scale was decreasing. A decrease in the thickness of the oxide scale indicates that the oxidation suppression effect of the steam pipe is particularly great.
Thus, by setting the potential D of the steam pipe to a range that is [−0.5V] or less and greater than [−5V], that is, a range of [−5V <D ≦ −0.5V], the steam pipe Can be further suppressed.
Further, considering the evaluation result of the adhesion strength of the oxide scale shown in FIG. 3 and the evaluation result of the non-peelability of the oxide scale shown in FIG. 4, the potential D of the water vapor pipe is in the range of [−5V <D ≦ −2V]. It is preferable to set to. By setting the potential of the steam pipe to a range of [−5V <D ≦ −2V], oxidation of the steam pipe can be remarkably suppressed.

Next, an example of a method for setting the potential D of the steam pipe to a negative potential is shown in FIG.
In the method shown in FIG. 5, a conductive water vapor pipe (usually formed in a cylindrical shape) is provided in an insulated state with another pipe through an insulating member such as an insulating ring. Then, a DC power supply device is connected between the water vapor pipe and the ground electrode (ground electrode). At this time, the negative electrode of the DC power supply device is connected to the steam pipe, and the positive electrode is connected to the ground electrode. Then, by adjusting the voltage of the DC power supply device, the potential D of the steam pipe (potential D on the inner surface side of the steam pipe) is set to the negative potential described above.
In this case, as shown in FIG. 5, the amount of electrons in the base material of the steam pipe increases. As a result, an electrical repulsive force acts between the oxidized ions generated on the inner surface of the steam pipe and the electrons in the base material of the steam pipe, so that the oxidized ions diffuse to the outer surface side of the base material of the steam pipe. Can be suppressed. Therefore, the oxidation of the steam pipe can be suppressed.
The negative electrode and the positive electrode of the DC power supply device may be directly connected to the steam pipe and the ground electrode, or may be indirectly connected.
Moreover, the position which connects the negative electrode of a direct-current power supply device to water vapor | steam piping can be selected suitably.

Another example of a method for setting the potential D of the steam pipe to a negative potential is shown in FIG.
In the method shown in FIG. 6, the electrode is disposed in the water vapor pipe while being insulated from the water vapor pipe. For example, a cylindrical electrode is fixed to the inner surface of the water vapor pipe via a ring-shaped support portion made of an insulating material. As a method for joining the electrode and the support portion or a method for joining the electrode and the steam pipe, a joining method by welding, a joining method using an adhesive, or the like can be used.
And while connecting a direct-current power supply device between this electrode and a ground electrode, water vapor piping is connected to a ground electrode. At this time, the positive electrode of the DC power supply device is connected to the electrode, and the negative electrode is connected to the ground electrode. Further, the lead wire connecting the positive electrode of the DC power supply device and the steam pipe is insulated from the steam pipe.
In this case, as shown in FIG. 6, due to the electrode set to a positive potential, the potential (potential on the inner surface side of the steam pipe) D of the base material of the steam pipe facing the electrode becomes a negative potential. Then, by adjusting the voltage of the DC power supply device, the potential D (potential D on the inner surface side of the steam pipe) of the base material of the steam pipe facing the electrode is set to the negative potential described above.
As a result, an electrical repulsive force acts between the oxide ions generated on the inner surface of the water vapor pipe and the electrons collected on the side of the base material of the water vapor pipe facing the electrode. Diffusion to the outer surface side of the base material can be suppressed. Therefore, the oxidation of the steam pipe can be suppressed.

The negative electrode and the positive electrode of the DC power supply device may be directly connected to the electrode and the ground electrode, or may be indirectly connected. Further, the water vapor pipe may be directly connected to the ground electrode or may be indirectly connected.
The position where the electrode is disposed and the shape of the electrode can be appropriately selected. For example, a cylindrical electrode having a circular shape is used when the surface facing the inner surface of the water vapor pipe is viewed in a cross section perpendicular to the axial direction of the water vapor pipe, but an electrode having an arc shape or an electrode having a linear shape is used. It can also be used. In this case, one electrode can be arranged at a desired position along the circumferential direction of the inner surface of the steam pipe, or a plurality of electrodes are discretely arranged at a plurality of positions along the circumferential direction of the inner face of the steam pipe. You can also Moreover, although one electrode was arrange | positioned along the axial direction of water vapor piping, a some electrode can also be arrange | positioned in the several position along the axial direction of water vapor piping. In any case, it is preferable to select the shape and the arrangement position of the electrode so that the distance between the surface of the electrode facing the inner surface of the water vapor pipe and the inner surface of the water vapor pipe is substantially equal. By selecting the shape and arrangement position of the electrodes, it is possible to set the location and area where electrons are collected in the base material of the steam pipe to a desired location and area.
Moreover, you may connect the negative electrode of a DC power supply device to water vapor piping, without passing through a ground electrode. Also in this case, the negative electrode and the positive electrode of the DC power supply device may be directly connected to the electrode and the steam pipe, or may be indirectly connected.

In FIG. 6, as electrodes arranged in the steam pipe, electrodes facing the inner surface of the steam pipe are formed in a planar shape extending along the circumferential direction of the inner face of the steam pipe and the axial direction of the steam pipe. Although used, an electrode formed in a dot shape can also be used.
For example, as shown in FIG. 7, a plurality of needle-shaped electrodes are fixed to the inner surface of the water vapor pipe via a ring-shaped support portion made of an insulating material. As a method for joining the electrode and the support portion, a joining method for inserting the electrode into a hole formed in the support portion, a joining method by welding, or a joining method using an adhesive can be used. As a method for joining the electrode and the steam pipe, a joining method by welding, a joining method using an adhesive, or the like can be used. The needle-like electrode is preferably arranged so that the axial direction of the needle-like electrode is substantially perpendicular to the inner surface of the steam pipe (in the radial direction). Then, a DC power supply device is connected between the electrode and the steam pipe by the method described above.
In this case, electrons are collected by electrostatic induction around the portion of the base material of the steam pipe that faces the tip of the needle-like electrode. Thereby, the electric potential of the vicinity of the location which opposes the front-end | tip part of an electrode of the preform | base_material of water vapor piping becomes a negative electric potential. Then, by adjusting the voltage of the DC power supply device, the potential D (potential D on the inner surface side of the steam pipe) of the base material of the steam pipe facing the electrode is set to the negative potential described above.
By using such an electrode, a desired location on the inner surface side of the steam pipe can be set to a negative potential.
In addition, although the needle-shaped electrode was used, a rod-shaped electrode can also be used. Further, the number of needle-shaped electrodes disposed in the water vapor pipe can be appropriately selected including one. In addition, as a method of arranging a plurality of needle-shaped electrodes, a method of arranging along the circumferential direction of the inner surface of the steam pipe, a method of arranging along the axial direction of the steam pipe, a circumference of the inner surface of the steam pipe The method of arrange | positioning along the direction and the axial direction of water vapor | steam piping can be used.

As described above, the present embodiment arranges electrons on the inner surface side of the steam pipe by setting the inner surface side (side through which the steam passes) of the steam pipe formed of Cr-Mo steel to a negative potential. It is configured. Thereby, the oxide ion generated on the inner surface of the water vapor pipe receives an electric repulsion force generated between electrons on the inner surface side of the water vapor pipe. Therefore, it is possible to suppress the diffusion of oxide ions to the outer surface side of the steam pipe, and to suppress the oxidation of the steam pipe where oxide scale is generated by supplying steam on the inner surface of the Cr-Mo steel at low cost and easily. be able to. Thereby, the erosion (thickness reduction by damage) of the blade | wing of a high pressure turbine or an intermediate pressure turbine can be suppressed.
Moreover, in this Embodiment, since it is only necessary to set the inner surface side of the steam pipe to a negative potential, oxidation of the steam pipe can be easily suppressed at a low cost.
Moreover, the oxidation of the inner surface of the steam pipe can be effectively suppressed by setting the potential D on the inner face side of the steam pipe in the range of [-10V ≦ D ≦ −0.5V].
Further, by setting the potential D on the inner surface side of the steam pipe to a range of [−5V <D ≦ −0.5V] and further [-5V <D ≦ −2V], the inner surface of the steam pipe is oxidized. It can suppress more effectively.
In addition, the oxidation suppression technique of this invention can be used suitably in order to suppress the oxidation of the steam piping which is formed with Cr-Mo steel and supplies 400 to 600 degreeC steam.

The present invention is not limited to the configuration described in the embodiment, and various changes, additions, and deletions are possible.
For example, by placing an electrode in the steam pipe and connecting a DC power supply device between the electrode and the steam pipe so that the electrode has a positive potential, the side of the steam pipe facing the electrode is set to a negative potential. As the negative potential setting method and negative potential setting device to be set, various negative potential setting methods and negative potential setting devices other than the negative potential setting method described in the embodiment and other than the negative potential setting device can be used.
Moreover, although the case where the oxidation of the steam piping used in the thermal power plant was suppressed was described, the present invention is applied to the case where the oxidation of the steam piping used in various facilities using steam is suppressed. be able to.
Moreover, as Cr-Mo steel which forms water vapor piping, it is not limited to [1.25Cr-0.5Mo] steel or [2.25Cr-1Mo] steel, Various Cr-Mo steel can be used.

It is a schematic block diagram of the test apparatus which tests the test piece of water vapor piping in the state set to different electric potential. It is a schematic block diagram of the apparatus which measures the adhesive force of the oxide scale produced | generated by each test piece tested in the state set to a different electric potential. It is a graph which shows the evaluation result of the adhesive force of the oxide scale produced | generated to the test piece tested in the state set to different electric potential. It is a graph which shows the evaluation result of the non-peelability with respect to the thermal shock of the oxide scale produced | generated in the test piece tested in the state set to different electric potential. It is a figure which shows an example of the method of setting the inner surface side of water vapor piping to a negative potential by connecting a DC power supply device between water vapor piping and a ground electrode. It is a figure which shows an example of the method which sets the inner surface side of water vapor piping to a negative potential by arrange | positioning an electrode in water vapor piping and connecting a DC power supply device between an electrode and water vapor piping. It is a figure which shows the other example of the method which sets the inner surface side of water vapor piping to a negative potential by arrange | positioning an electrode in water vapor piping and connecting a DC power supply device between an electrode and water vapor piping. It is a figure which shows schematic structure of an example of a thermal power plant. It is a figure which shows the production | generation condition of the oxidation scale in water vapor piping.

Explanation of symbols

10 Water tank 20 Steam generator 30 Reaction tube 33 Alumina tube (insulating tube)
34 DC power supply 60a, 60b Insulating ring 70 Test piece

Claims (8)

Oxidation suppression of a steam pipe that is formed of Cr-Mo steel and that supplies steam at a temperature of 400 ° C. to 600 ° C. generated by a steam generator, and that generates an oxide scale on the inner surface by supplying the steam. A method,
A method for suppressing oxidation of a steam pipe, wherein the potential on the inner surface side of the steam pipe is set in a range of [-10V ≦ potential on the inner face side of the steam pipe ≦ −0.5V]. A method for inhibiting oxidation of a steam pipe according to claim 1,
A method for inhibiting oxidation of a steam pipe, wherein the potential on the inner face side of the steam pipe is set within a range of [-5V < potential on the inner face side of the steam pipe ≦ -0, 5V]. A method for inhibiting oxidation of a steam pipe according to claim 1 or 2,
Between the steam pipe and the ground electrode, a DC power supply device, the anode is connected to the steam pipe, by the positive electrode is disposed so as to be connected to the ground electrode, the inner surface of the steam pipe potential Is set to a negative potential in the above range, the method for inhibiting oxidation of water vapor piping. A method for inhibiting oxidation of a steam pipe according to claim 1 or 2,
An electrode is disposed in the steam pipe in an insulated state from the steam pipe, a direct current power supply device is connected between the steam pipe and the electrode, a negative electrode is connected to the steam pipe, and a positive electrode is connected to the electrode By arranging as described above, the method for suppressing oxidation of the steam pipe is characterized in that the potential on the inner surface side of the steam pipe is set to a negative potential within the above range . A steam generator,
A water vapor pipe formed of Cr-Mo steel for supplying water vapor at 400 ° C. to 600 ° C. generated by the water vapor generator, and a water vapor pipe for generating an oxide scale on the inner surface by supplying the water vapor;
A steam supply device comprising: a negative potential setting device for setting the potential on the inner surface side of the steam pipe in a range of [-10V≤potential on the inner face side of the steam pipe≤-0.5V]. The water vapor supply device according to claim 5,
The said negative electric potential setting apparatus sets the electric potential of the inner surface side of the said steam piping in the range of [-5V < potential of the inner surface side of steam piping <=-0.5V], The steam supply device characterized by the above-mentioned. The steam supply device according to claim 5 or 6,
The negative potential setting device has a DC power supply device,
The DC power supply device is characterized in that a negative electrode is connected to the water vapor pipe and a positive electrode is connected to a ground electrode. The steam supply device according to claim 5 or 6,
The negative potential setting device has an electrode disposed in the steam pipe in a state insulated from the steam pipe, and a DC power supply device,
The direct current power supply device has a negative electrode connected to the water vapor pipe and a positive electrode connected to the electrode.

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