Method for manufacturing test specimen for evaluating protective layer

Abstract

To provide a method for manufacturing a test piece which is capable of evaluating the performance of a protective layer on an inner wall of a combustion furnace of a boiler with respect to combustion ash accumulated on the inner wall without using the inner wall and the combustion ash as test subjects.SOLUTION: A method for manufacturing a protective layer evaluation test piece includes mixing simulated ash and solvent to form slurry, forming a pellet 33 having a predetermined thickness by compression molding of the slurry, and heating the pellet 33 and a metal plate 31 covered by the protective layer 32 inside simulated gas at a predetermined temperature in the state where the pellet 33 is mounted on the metal plate 31. The simulated gas contains components of high-temperature gas created inside a boiler. The predetermined temperature is the temperature of an inner wall while the boiler is being operated. The simulated ash includes a main component containing silicon dioxide, aluminum oxide and ferric oxide, and a corrosive component containing sulfur oxide and chloride. The molar ratio of chlorine for sulfur is 0 to 1 in the corrosive component, and the molar ratio of the corrosive component for the total sum of the main component and the corrosive component is 0.2 to 0.5.SELECTED DRAWING: Figure 3A

Description

[Technical field]

[0001] The present disclosure relates to a method for producing a test specimen for evaluating a protective layer to which combustion ash adheres. [Background technology]

[0002] Boilers such as pulverized coal boilers are equipped with a combustion furnace, whose inner wall is composed of heat transfer water tubes that extend continuously in a spiral shape. The inner wall is covered with a protective layer to protect the combustion furnace from combustion gas. Meanwhile, the combustion gas contains combustion ash, which adheres to the protective layer and gradually accumulates. Since the combustion ash has a lower thermal conductivity than the material (e.g., metal) that constitutes the inner wall of the combustion furnace, as the accumulation of combustion ash on the inner wall progresses, the efficiency of heat transfer from the combustion furnace to the heat transfer water tube decreases.

[0003] For this reason, the combustion furnace is provided with a soot blower (ash removal device). When the amount of combustion ash adhering to the heat transfer water tube exceeds a predetermined threshold, the soot blower removes the combustion ash by blowing steam or compressed air onto the inner wall of the heat transfer water tube, etc. (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2012-52740 A Summary of the Invention [Problem to be solved by the invention]

[0005] When combustion ash is exposed to the combustion furnace for a long time, corrosion occurs on the inner walls of the heat transfer tubes, etc., and as this corrosion progresses, the adhesion of the combustion ash becomes stronger. In order to prevent the adhesion of the combustion ash, the inner walls of the combustion furnace are covered with a protective layer. The protective layer suppresses the above-mentioned corrosion reaction and makes it easier for the combustion ash to fall off.

[0006] One method for evaluating the performance of a protective layer against combustion ash is to install a probe simulating the inner wall of a combustion furnace inside the furnace. Combustion ash adheres to the protective layer of the probe while the furnace is operating. Therefore, a tensile test is performed to peel the combustion ash from the probe, and the adhesion strength of the combustion ash can be calculated by measuring the tension at the time of peeling. However, while the boiler operation needs to be temporarily stopped when the probe is removed from the combustion furnace, the boiler is operated continuously for several months. Therefore, it is practically difficult to remove the probe frequently.

[0007] In addition, fuels for pulverized coal-fired boilers and other boilers are becoming more diverse, and not only conventional coal but also low-grade fuels such as subbituminous coal, lignite, and biomass are beginning to be used. In other words, the components that corrode the inner walls of combustion furnaces are also becoming more diverse.

[0008] The present disclosure has been made in consideration of the above circumstances, and aims to provide a method for manufacturing a test specimen that makes it possible to evaluate the performance of the protective layer of the inner wall against combustion ash, without using the inner wall of a boiler combustion furnace and the combustion ash accumulated on the inner wall as test subjects. [Means for solving the problem]

[0009] A method for manufacturing a test specimen for evaluating a protective layer according to one embodiment of the present disclosure includes mixing simulated ash and a solvent to form a slurry, forming a pellet having a predetermined thickness by compression molding the slurry, and heating the pellet and the metal plate at a predetermined temperature in a simulated gas while the pellet is placed on a metal plate covered with a protective layer. The simulated gas contains components of high-temperature gas generated in a boiler. The predetermined temperature is equal to the temperature of the inner wall during operation of the boiler. The simulated ash contains a main component including silicon dioxide, aluminum oxide, and ferric oxide, and a corrosive component including sulfur oxide and chloride. In the corrosive component, the molar ratio of chlorine to sulfur is 0 to 1. The molar ratio of the corrosive component to the sum of the main component and the corrosive component is 0.2 to 0.5.

[0010] The sulfur oxide may include at least one of sodium sulfate and potassium sulfate. The chloride may include potassium chloride. The solvent may be an aqueous polyvinyl alcohol solution. The temperature may be 400°C to 700°C. Effect of the Invention

[0011] According to the present disclosure, a method for manufacturing a test specimen can be provided that enables evaluation of the performance of a protective layer on an inner wall against combustion ash without using the inner wall of a boiler combustion furnace and the combustion ash accumulated on the inner wall as test subjects. [Brief description of the drawings]

[0012] [Figure 1] FIG. 2 is a schematic explanatory diagram of a boiler. [Diagram 2] FIG. 2 is a cross-sectional view of a wall of a combustion furnace. [Figure 3A] FIG. 2 is a perspective view of a test specimen according to the present embodiment. [Figure 3B] FIG. 2 is a cross-sectional view of a test specimen according to the present embodiment. [Figure 3C] FIG. 11 is a cross-sectional view of a modified example of the test specimen. [Figure 4] FIG. 2 is a side view showing a test specimen attached to a tensile tester. [Diagram 5] FIG. 1 is a schematic configuration diagram illustrating an example of a heat treatment system. [Figure 6] 3 is a flowchart showing each step of a manufacturing method according to the present embodiment. [Figure 7A] FIG. 2 is a diagram for explaining one step of the manufacturing method according to the present embodiment. [Figure 7B] FIG. 2 is a diagram for explaining one step of the manufacturing method according to the present embodiment. [Figure 7C] FIG. 2 is a diagram for explaining one step of the manufacturing method according to the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, a test specimen according to an embodiment of the present disclosure will be described with reference to the accompanying drawings. Note that common parts in the various drawings are given the same reference numerals, and duplicated explanations will be omitted.

[0014] 1 is a schematic diagram of a boiler 10. As shown in this figure, the boiler 10 has a combustion furnace 11 and a heat transfer water tube 12. The heat transfer water tube 12 is formed in an S-shape, a U-shape, or the like, and is located in an upper part of the combustion furnace 11.

[0015] A plurality of burners 13 are provided at the bottom of the combustion furnace 11. A mixed gas of fuel and air is supplied to each burner 13. The fuel is appropriately selected depending on the type of the boiler 10. For example, when the boiler 10 is a pulverized coal-fired boiler, the fuel is pulverized coal made of subbituminous coal, lignite, biomass, or the like.

[0016] The burner 13 burns fuel in the lower part of the combustion furnace 11. The heat transfer water tube 12 is heated by radiant heat and combustion gas generated by this combustion, and the water flowing inside the heat transfer water tube 12 is heated. The combustion gas is discharged through an exhaust passage 14 to an exhaust gas treatment system (not shown) provided downstream of the combustion furnace 11.

[0017] 2 is a cross-sectional view of a wall 17 of the combustion furnace 11. As shown in this figure, the combustion furnace 11 is configured with a double-structure wall 17 consisting of an inner wall 15 and an outer wall 16. The inner wall 15 has a heat transfer water tube 18 that extends continuously in a spiral shape, and a connecting portion 19 that connects two of the heat transfer water tubes 18 that run parallel in a spiral shape. The outer wall 16 is located outside the inner wall 15 so as to surround the inner wall 15. A heat insulating material (not shown) is arranged between the inner wall 15 and the outer wall 16.

[0018] The inner wall 15 (i.e., the heat transfer water tube 18 and the connection portion 19) is made of a heat-resistant metal such as carbon steel (e.g., STB (carbon steel tube for boilers and heat exchangers)) or stainless steel (e.g., SUS310S). The inner wall 15 is covered with a protective layer 20 to protect the combustion furnace 11 from the combustion gas. The combustion gas contains combustion ash 21, which adheres to the protective layer 20 and gradually accumulates while the boiler 10 is in operation.

[0019] The test specimen 30 according to this embodiment simulates the inner wall 15, the protective layer 20, and the combustion ash 21 of the combustion furnace 11 described above, and is used as a sample for a tensile test, for example. As described below, the test specimen 30 is used as a test specimen for evaluating the protective layer.

[0020] Fig. 3A is a perspective view of a test specimen 30 according to this embodiment, and Fig. 3B is a cross-sectional view of the test specimen 30. Fig. 3C is a cross-sectional view of a modified example of the test specimen 30. As shown in Fig. 3A, the test specimen 30 includes a metal plate (metal piece) 31 covered with a protective layer 32, and a pellet 33.

[0021] As shown in Fig. 3B, the pellet 33 is placed on the protective layer 32 and adhered to the protective layer 32 by heating using a heat treatment system 50 (see Fig. 5) described later. The outer shape of the test specimen 30 is arbitrary as long as a tensile test can be performed, and for example, it has a cylindrical shape as shown in Fig. 3A.

[0022] The metal plate 31 is a metallic plate member, and is made of the same material as the inner wall 15 of the combustion furnace 11. That is, the material of the metal plate 31 is a heat-resistant metal such as stainless steel (for example, SUS310S).

[0023] The metal plate 31 has a sufficient thickness so that deformation or breakage is unlikely to occur during a tensile test. The shape of the metal plate 31 may be circular as shown in Fig. 3A, rectangular or other shapes. The metal plate 31 is covered with a protective layer 32 and has an upper surface 31a on which a pellet 33 is placed.

[0024] The upper surface 31a of the metal plate 31 is covered with a protective layer 32 having corrosion resistance and heat resistance. The protective layer 32 is formed of the same material as the protective layer 32 covering the inner wall 15 of the combustion furnace 11. For example, the protective layer 32 includes ceramics such as aluminum oxide (alumina) or a thermal spray material. The protective layer 32 is formed by coating the upper surface 31a, for example.

[0025] The pellet 33 is a solid material containing simulated ash (described later) of the combustion ash 21 as an ingredient. The shape of the pellet 33 may be a cylinder having a predetermined height (thickness) as shown in FIG. 3A, or may be a prism or other shape. In either case, the pellet 33 has an upper surface 33a that is attached to a jig 41 of a tensile tester (not shown) and a lower surface 33b that is in contact with the protective layer 32. The lower surface 33b of the pellet 33 is attached to the protective layer 32 by heating under a corrosive gas in the manufacturing process of the test specimen 30.

[0026] In addition, the surface of the metal plate 31 facing the pellet 33 (i.e., the upper surface 31a) and the surface of the pellet 33 facing the metal plate 31 (i.e., the lower surface 33b) may have shapes that determine the relative positions between the metal plate 31 and the pellet 33. For example, as shown in FIG. 3C, the upper surface 31a of the metal plate 31 is formed as an axisymmetric convex surface, and the lower surface 33b of the pellet 33 is formed as an axisymmetric concave surface having a shape complementary to the upper surface 31a, which is a convex surface. Conversely, the upper surface 31a of the metal plate 31 may be formed as a concave surface, and the lower surface 33b of the pellet 33 may be formed as a convex surface. These shapes can be formed by using a mold having a corresponding shape for the pellet 33 and processing the metal plate 31 into a corresponding shape in advance. In either case, the centers of pressure generated by tensile force are made to coincide with each other on the upper surface 31a of the metal plate 31 and the lower surface 33b of the pellet 33, respectively, and the moment can be easily reduced by the positional deviation of the centers.

[0027] The simulated ash, which is the material of the pellets 33, will now be described. Table 1 shows examples of the components of combustion ash obtained by X-ray fluorescence analysis (XRF). Cases 1 and 2 show the components of combustion ash when the boiler fuel is coal, and cases 3 and 4 show the components of combustion ash when the boiler fuel is biomass. Note that each component value is an oxide equivalent value. Also, the gas temperature in the table is the temperature of the combustion gas, and the metal temperature is the surface temperature of the heat transfer water tube 18 (see Figure 2). The initial layer in the table is the layer of ash that is deposited on the heat transfer water tube at the beginning of the formation of the combustion ash, in other words, the layer of ash distributed at the interface between the combustion ash and the heat transfer water tube. On the other hand, the bulk layer is the layer of ash that is deposited further from the initial layer. [Table 1]

[0028] The simulated ash according to this embodiment contains ferric oxide, aluminum oxide, and silicon dioxide as main components. These are, for example, in the same amount in molar terms. As shown in Table 1, the main components of the combustion ash in Case 1 and Case 2 are silicon dioxide, aluminum oxide, and ferric oxide. The main components of the combustion ash in Case 3 and Case 4 are potassium oxide, magnesium oxide, and calcium oxide. Therefore, the ratios of ferric oxide, aluminum oxide, and silicon dioxide, which are the main components of the simulated ash, are changed and mixed according to the fuel to be evaluated.

[0029] The simulated ash according to this embodiment contains sulfur oxides and chlorides as corrosive components. The sulfur oxides include, for example, at least one of sodium sulfate, potassium sulfate, calcium sulfate, and magnesium sulfate. The chlorides include, for example, at least one of potassium chloride, calcium chloride, and magnesium chloride. As shown in Table 1, in Case 1 and Case 2, sulfur oxides are found in the components of the combustion ash, but chlorides are not found. On the other hand, in Case 3 and Case 4, both sulfur oxides and chlorides are found in the components of the combustion ash. In this way, the corrosive components are divided into cases where sulfur oxides are included and cases where sulfur oxides and chlorides are included, depending on the fuel components of the boiler. Therefore, the corrosive components of the test specimen 30 may be selected as "sulfur oxides only" or "sulfur oxides and chlorides" depending on the fuel components of the boiler.

[0030] The initial layer of the accumulated combustion ash is the layer that affects the adhesion of the combustion ash and the corrosion caused by the combustion ash. Therefore, the component ratio of the corrosive components in the simulated ash is set to match the component ratio of the corrosive components in the initial layer of the combustion ash.

[0031] In addition, the molar ratio of chlorine to sulfur in the corrosive components is set to 0 to 1. That is, the corrosive components of the simulated ash contain at least sulfur oxides. Furthermore, when the corrosive components contain chlorides, the amount of chlorine contained in the corrosive components of the combustion gas does not exceed the amount of sulfur oxides in molar terms.

[0032] For example, if the fuel for the boiler 10 contains only coal-derived components, the combustion gas does not contain chlorides. Therefore, the corrosive components of the simulated ash do not need to contain chlorides (i.e., the molar ratio of chlorine to sulfur is 0). On the other hand, if the fuel for the boiler 10 contains biomass-derived components, the combustion gas contains sulfur oxides and chlorides. Therefore, the corrosive components of the simulated ash contain sulfur oxides and chlorides (i.e., the molar ratio of chlorine to sulfur is greater than 0 and less than or equal to 1).

[0033] Furthermore, the molar ratio of the corrosive components to the sum of the main components and the corrosive components is set to 0.2 to 0.5. As described later, the pellets 33 are heated to 400°C to 700°C, which simulates the metal temperature, for several tens to several hundreds of hours in a simulated gas containing components of high-temperature gas (exhaust gas) generated in the boiler 10. By setting the molar ratio within the above range, it is possible to prevent excessive deformation such as melting when the pellets 33 are heated, regardless of the above-mentioned molar ratio of chlorine to sulfur.

[0034] The above-mentioned molar ratio can be confirmed by using a known analytical method such as X-ray fluorescence analysis, wet analysis such as atomic absorption spectrometry or ICP (inductively coupled plasma) emission spectrometry, or water-soluble component analysis on the test specimen 30 after preparation.

[0035] 4 is a side view showing a test piece 30 attached to a tensile tester. As shown in this figure, in a tensile test, a metal plate 31 is attached to a jig 42 of the tensile tester by adhesion or the like, and a pellet 33 is attached to a jig 41 of the tensile tester by adhesion or the like. The jig 41 and the jig 42 move away from each other. As a result, the pellet 33 and the metal plate 31 are pulled in opposite directions, and when this tension exceeds the adhesive force of the pellet 33, the pellet 33 peels off from the metal plate 31. The configuration of the tensile tester and the tensile test method comply with the Japanese Industrial Standards (JIS) "Testing Method for Coating Adhesion Strength of Thermal Spray Coating" (JIS H 8402).

[0036] The adhesive force of the pellets 33 is calculated from the tension when the pellets 33 are peeled off from the metal plate 31. The adhesive force changes depending on the degree of deterioration of the protective layer 32 due to the corrosive components of the pellets 33 and the progress of corrosion of the metal plate 31. Therefore, from the adhesive force of the pellets 33, it is possible to evaluate the influence on the adhesive force depending on the progress of corrosion of the metal plate 31. It is also possible to evaluate the performance of the protective layer 32, such as adhesion resistance, durability, and corrosion resistance.

[0037] The metal plate 31 is formed of the same material as the inner wall 15 of the combustion furnace 11, such as the heat transfer water tube 18, and simulates the inner wall 15 of the combustion furnace 11. The protective layer 32 is formed of the same material as the protective layer 20 formed on the inner wall 15, and simulates the protective layer 20. Furthermore, the pellet 33 is formed of simulated ash, which is the combustion ash 21, and among the components of the simulated ash, the corrosion components of the metal plate 31 include the corrosion components in the combustion ash 21 that adhere to the inner wall 15. That is, the pellet 33 simulates the combustion ash 21 in that at least the same corrosion reaction occurs. Therefore, the performance of the protective layer 20 formed on the inner wall 15 of the combustion furnace 11, such as adhesion resistance, durability, and corrosion resistance, can be evaluated from the results of the tensile test on the test piece 30 without using the inner wall 15 and the combustion ash 21 deposited on the inner wall 15 as direct test subjects.

[0038] Next, a method for manufacturing the test specimen 30 will be described. First, there will be described a heat treatment system 50 used in manufacturing the test specimen 30. The configuration of the heat treatment system 50 and the treatment using this system comply with the Japanese Industrial Standards (JIS) "General rules for high temperature corrosion test methods for metallic materials" (JIS Z 2290).

[0039] 5 is a schematic diagram showing an example of a heat treatment system 50. As shown in this figure, the heat treatment system 50 includes a heating device 51, a simulated gas supply system 52, and a simulated gas exhaust system 53. The heating device 51 includes a quartz tube 54 and a tubular furnace 55 for heating the quartz tube 54. The quartz tube 54 is inserted into the tubular furnace 55, and the test specimen 30 is placed on an alumina boat 56 and installed in the quartz tube 54.

[0040] The heating device 51 further includes a thermometer 57 and a controller 58. The thermometer 57 is configured with a thermocouple or the like, and measures the temperature inside the quartz tube 54. The controller 58 controls the heating by the tubular furnace 55 based on the temperature measured by the thermometer 57 so that the temperature inside the quartz tube 54 becomes the set temperature.

[0041] The supply system 52 is connected to one end (upstream side) of the quartz tube 54, and supplies the simulant gas to the quartz tube 54. The simulant gas contains components of high-temperature gas (exhaust gas) generated in the boiler 10. The simulant gas is generated by uniformly mixing oxygen, carbon dioxide, sulfur dioxide (sulfur dioxide gas), water vapor, and nitrogen in the mixer 59b. For example, the respective concentrations are 3.5 vol% oxygen, 18 vol% carbon dioxide, 150 ppm sulfur dioxide (sulfur dioxide gas), 10 vol% water vapor, and the remainder nitrogen. Note that the water vapor and nitrogen gas are humidified by a bubbling method using heated pure water, and then mixed with other gases. The temperature of the pure water is controlled according to the concentration of the water vapor to be humidified. The flow rate of the simulant gas is controlled by the control of the mass flow controller 59a. For example, the flow rate of the simulant gas is set to 660 cc / min, and the flow rate of the simulant gas is 3.4 mm / s.

[0042] The exhaust system 53 is connected to the other end (downstream side) of the quartz tube 54. The exhaust system 53 is equipped with treatment devices such as a sublimate trap 60 and an exhaust gas trap 61. These treatment devices treat the simulated gas discharged from the quartz tube 54 and the reaction product gas generated by corrosion and the like.

[0043] Next, a manufacturing process using the heat treatment system 50 will be described. Fig. 6 is a flow chart showing each step of the method for manufacturing a test specimen according to this embodiment, and Figs. 7A to 7C are diagrams for explaining the steps. An example of producing one pellet 33 will be described below.

[0044] First, 2.3 g of simulated ash and 0.8 g of solvent are mixed to form a slurry (paste) (step S10). The solvent is, for example, a polyvinyl alcohol aqueous solution. The solvent is dropped onto the simulated ash in multiple batches and mixed with the simulated ash. During this mixing, the simulated ash may be further pulverized.

[0045] Next, the slurry is compression molded to form pellets (step S20). For example, the slurry is put into a conventional pellet molding machine (not shown) to form pellets. For example, as shown in FIG. 7A, the slurry 34 is filled into a cylindrical mold (lower mold) 45, and then pressurized by a pin (upper mold) 46 inserted into the mold 45. The slurry 34 is held under a pressure of 12 MPa for about three minutes, and then removed from the mold 45 to form a pellet 33. The formed pellet 33 is cylindrical, with a diameter of, for example, 12 mm and a thickness (height) of, for example, 25 mm.

[0046] Next, the pellet 33 is dried (step S30). For example, the pellet 33 is dried by placing it in a conventional dryer (not shown) at 250° C. for about 12 hours. After drying the pellet 33, the lower surface 33b (see FIG. 3B) of the pellet 33 may be polished. The surface roughness after polishing is, for example, 0.4 to 1.6 in terms of arithmetic mean roughness (Ra).

[0047] Next, the pellets 33 are placed on the metal plate 31 covered with the protective layer 32 (see FIG. 7B). In this state, the pellets 33 and the metal plate 31 are heated to a predetermined temperature in the simulated gas (step S40). Specifically, the pellets 33 and the metal plate 31 are placed on an alumina boat 56, which are then installed in a quartz tube 54 of a heat treatment system 50. Then, the simulated gas is supplied from a supply system 52 to the quartz tube 54. With the simulated gas flowing from the upstream side to the downstream side of the quartz tube 54, the controller 58 starts heating by the tubular furnace 55, and the pellets 33 and the metal plate 31 are heated to a predetermined temperature. This predetermined temperature is equal to the temperature of the inner wall 15 of the boiler 10 during operation.

[0048] As shown in Table 1, the temperature of the initial layer of combustion ash, i.e., the metal temperature, is sufficiently lower than the gas temperature due to the flow of water in the heat transfer tube. In other words, a temperature gradient is generated inside the combustion ash that drops from the gas temperature to the metal temperature, and it can be seen that the corrosion reaction proceeds at temperatures of 400°C to 700°C, which is sufficiently lower than the gas temperature. Therefore, the heating temperatures of the pellets 33 and the metal plate 31 are also set to 400°C to 700°C.

[0049] The heating time is set to a value necessary for evaluating the performance of the protective layer 32. That is, the heating time is set within a range from a time shorter than the time at which corrosion of the metal plate 31 occurs due to the corrosive components of the pellets 33 to a time at which the corrosion of the metal plate 31 progresses sufficiently. The heating time is, for example, 50 hours to 700 hours. In some cases, it may be set even longer.

[0050] After the heating time has elapsed, the heating by the tubular furnace 55 is stopped, and the pellets 33 and the metal plate 31 are gradually cooled in the simulant gas (step S50). Through the above steps, the test specimen 30 in which the pellets 33 are attached to the metal plate 31 is completed (see FIG. 7C).

[0051] The present disclosure is not limited to the above-described embodiment, but is defined by the claims, and includes all modifications within the meaning and scope equivalent to the claims. [Explanation of symbols]

[0052] 10... boiler, 11... combustion furnace, 12... heat transfer tube, 13... burner, 14... exhaust channel, 15... inner wall, 16... outer wall, 17... wall, 18... heat transfer tube, 19... connection part, 20... protective layer, 21... combustion ash, 30... test specimen, 31... metal plate (metal piece), 31a... upper surface, 32... protective layer, 33... pellet, 33a... upper surface, 33b... lower surface, 34... slurry, 41... jig, 42... jig, 45... mold (lower mold), 46... pin (upper mold), 50... heat treatment system, 51... heating device, 52... supply system, 53... exhaust system, 54... quartz tube, 55... tubular furnace, 56... alumina boat, 57... thermometer, 58... controller, 59a... mass flow controller, 59b... mixer, 60... sublimate trap, 61... exhaust gas trap

Claims

1. Mixing the simulated ash with a solvent to form a slurry; forming a pellet having a predetermined thickness by compression molding the slurry; The pellet is placed on a metal plate covered with a protective layer, and the pellet and the metal plate are heated at a predetermined temperature in a simulated gas. Including, The simulated gas contains components of high-temperature gas generated in a boiler, The predetermined temperature is equal to the temperature of the inner wall of the boiler during operation, The simulated ash is A main component including silicon dioxide, aluminum oxide, and ferric oxide; Corrosive components including sulfur oxides and chlorides Including, The molar ratio of chlorine to sulfur in the corrosive component is 0 to 1; The molar ratio of the corrosive component to the sum of the main component and the corrosive component is 0.2 to 0.

5. A method for manufacturing a test specimen for evaluating a protective layer.

2. The sulfur oxides include at least one of sodium sulfate, potassium sulfate, calcium sulfate, and magnesium sulfate. A method for producing a test specimen for evaluating a protective layer according to claim 1.

3. The chloride includes at least one of potassium chloride, calcium chloride, and magnesium chloride. A method for producing a test specimen for evaluating a protective layer according to claim 1 or 2.

4. The solvent is an aqueous polyvinyl alcohol solution. A method for producing a test specimen for evaluating a protective layer according to any one of claims 1 to 3.

5. The temperature is between 400° C. and 700° C. A method for producing a test specimen for evaluating a protective layer according to any one of claims 1 to 4.

6. The surface of the metal plate facing the pellet and the surface of the pellet facing the metal plate have shapes that determine the relative position between the metal plate and the pellet. A method for producing a test specimen for evaluating a protective layer according to any one of claims 1 to 5.

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