KR20130135353A - Austenitic stainless steel pipe, boiler device, and method for processing inner surface of pipe - Google Patents

Abstract

According to the present invention, the inner surface 5 of the austenitic stainless steel pipe 1 is shot processed by shot particles 3, and the outermost surface after the shot processed steel pipe 1 is processed. It is to determine the superiority of the water vapor oxidative resistance of the inner surface 5 of the tube according to the depth hardness set in advance. In the above judgment, when the roughness of the inner surface 5 after shot processing of the inner surface of the inner tube 5 is 2 µm or less as the arithmetic mean roughness Ra or when the predetermined depth hardness is 300 Hv or higher, it is determined that the water vapor oxidation resistance is excellent. In this way, the austenitic stainless steel pipe having an arithmetic mean roughness Ra of the inner surface of the pipe 5 of 2 μm or less or a predetermined depth hardness of 300 Hv or more can be used as a boiler heat pipe.

Description

Austenitic stainless steel pipe, boiler equipment and inner surface processing method {AUSTENITIC STAINLESS STEEL PIPE, BOILER DEVICE, AND METHOD FOR PROCESSING INNER SURFACE OF PIPE}

TECHNICAL FIELD The present invention relates to an austenitic stainless steel pipe, a boiler apparatus, and a surface processing method of an inner tube. In particular, the present invention relates to an austenitic stainless steel pipe, which is suitable for use in a region where high temperature and high pressure steam flows as a heat transfer tube. A method for processing the inner surface of a tube of a nitrous steel pipe, a boiler device having the austenitic steel pipe, and an austenitic stainless steel pipe excellent in water vapor oxidation resistance.

The superheater and reheater through which hot and high pressure steam flows in a steel pipe is installed in the high temperature part through which the high temperature gas of a boiler apparatus flows, and the heat exchanger tube which comprises these high temperature strength and corrosion resistance ( In view of the nature, an austenitic stainless steel pipe containing 18% or more of Cr is used. During the operation of the boiler, a steam oxidation scale is generated on the inner surface of the steel pipe by the contact with the high temperature and high pressure water vapor flowing through the steel pipe and the reaction with the contacted water vapor. This water vapor oxidation scale has a two-layer structure of an inner layer made of (Cr, Fe) ₃ O ₄ and an outer layer made of Fe ₃ O ₄ . The outer layer is located closer to the air layer on the surface of the steel pipe, and the inner layer is located at the base metal side than the outer layer.

Since austenitic stainless steels generally have a large coefficient of linear expansion, the steel pipe expands or contracts in response to changes in the temperature of the fluid flowing inside the steel pipe due to changes in the load of the boiler, shutdown, or startup. At this time, there is a big difference between the expansion coefficient of the steel pipe itself and the expansion coefficient of the water vapor oxidation scale forming a layer on the inner surface of the steel pipe. When the temperature change occurs, the water vapor oxidation scale is likely to peel off from the inner surface of the steel pipe. When the water vapor oxidation scale is peeled off from the inner surface of the steel pipe, the water vapor oxidation scale that is peeled off is deposited on the bent portion of the steel pipe, causing the blockage of the pipe, and also scattering through the steam pipe to the steam turbine part, It may also cause turbine blade corrosion. Therefore, in addition to the high temperature strength, the steel pipes used in the high temperature portion of the boiler require excellent water vapor oxidation resistance.

As a method of improving the water vapor oxidation resistance of an austenitic stainless steel, there are a method of increasing the Cr content in the material, miniaturizing the crystal grains, or shot processing the inner surface of the steel pipe to form a hardened layer. Among these, the method generally adopted widely is a method of performing a shot process on the inner surface of a steel pipe, and forming a hardened layer on the inner surface of a steel pipe. For example, as shown in Patent Literature 1, shot processing is performed by spraying particles made of stainless steel on the inner surface of a steel pipe to a working surface at a predetermined pressure or more and a predetermined injection amount or more, and shot processing having a predetermined thickness or more on the inner surface of the steel pipe. To form a layer. Patent Document 1 describes that when the steel pipe thus processed is used for a superheater for generating high temperature steam, an extremely thin and dense scale is formed on the inner surface of the steel pipe, and it is assumed that it prevents the growth of the entire water vapor oxidation scale. .

In addition, as a method for determining whether shot processing in an austenitic stainless steel pipe is reliably applied to the entire surface, Patent Document 2, for example, allows a light source to reach the inner surface of a tube from one side of the shot processed tube. Thus, a method of measuring the shot processed area while moving the TV camera for observing the inner surface from the other end in the tube is described. In this case, the shot-processed surface becomes a non-gloss surface due to minute unevenness, and the unprocessed surface becomes a gloss surface, so that the presence or absence of processing can be determined by visual observation. In this patent document 2, a shot condition is selected in which the shot processed area becomes 70% or more of the whole.

Japanese Laid-Open Patent Publication No. 52-8930 International publication number WO2007 / 099949 publication

In recent large-scale boilers for thermal power generation, the length of the austenitic stainless steel pipes used for superheaters and reheaters is thousands of meters or more per can, and the problem of good or poor shot processing is a problem. However, although Patent Document 1 describes the prevention of growth of the entire water vapor oxidation scale by forming the shot processing layer by shot processing, the structure or structure of the inner surface of the tube having water vapor oxidation resistance required as a heat transfer tube. It is not specifically described about.

Further, in Patent Document 2, in order to determine whether shot processing is reliably constructed, the shot processing surface is observed to be a non-gloss surface due to irregularities, and the unprocessed surface is used as a gloss surface to observe with a TV camera. Although the method of determination is described, it is only to judge whether it is constructively, but it is not determining whether the water vapor oxidation resistance required as a heat exchanger tube is ensured. In addition, the structure of the inner surface of a pipe | tube which has the water vapor oxidation resistance required as a heat exchanger tube like a reference document 1 is not specifically described.

Then, the problem which this invention is going to solve is to provide the austenitic stainless steel pipe which has the water vapor oxidation resistance required as a heat exchanger tube, and to provide the boiler apparatus provided with the heat exchanger tube which has required water vapor oxidation resistance.

In order to solve the above problems, the present invention, in the austenitic stainless steel pipe for heat transfer pipe, the inner surface of the tube of the austenitic stainless steel pipe is 2㎛ or less in the arithmetic mean roughness (Ra), or the austenitic stainless steel pipe After the processing of the steel pipe is characterized in that the hardness from the outermost (most outer surface) to a predetermined depth is any one of 300Hv or more.

Moreover, this invention is characterized by the boiler apparatus provided with the heat exchanger tube which consists of said austenitic stainless steel pipes.

In addition, the present invention, the austenitic stainless steel pipe in the tube surface of the austenitic stainless steel pipe shot, and the arithmetic mean roughness (Ra) of the inner surface of the tube is shortened to 2 ㎛ or less in the tube of the austenitic stainless steel pipe It is characterized by the surface processing method.

According to the present invention, the water vapor oxidation resistance required as the heat transfer tube can be ensured. Moreover, it can be set as the boiler apparatus which has a heat exchanger tube which ensured water vapor oxidation resistance.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the processing method of an austenitic stainless steel pipe in embodiment of this invention.
It is a figure which shows the measurement result of the arithmetic mean roughness Ra of the inner surface of the tube of the austenitic stainless steel pipe after shot processing in Example 1, and the thickness of the water vapor oxidation scale.
It is explanatory drawing which shows the relationship between the roughness of the inner surface of a pipe | tube after shot processing in Example 1, and the produced | generated water vapor oxidation scale.
It is a figure which shows the result of having compared the hardness of the inner surface hardness of the austenitic stainless steel pipe after shot processing in Example 2, and the shotless process.
5 is a micrograph showing a cross-sectional microstructure of an austenitic stainless steel pipe after shot processing in Example 3. FIG.
6 is a micrograph showing a cross-sectional microstructure of an austenitic stainless steel pipe after shot processing at a depth of 50 µm from the outermost surface after processing in Example 4. FIG.
It is a figure which shows the relationship of the number of slip lines of 50 micrometers in depth in Example 3, and 4, the hardness in the position of 50 micrometers in depth from the outermost surface after processing, and evaluation.
FIG. 8 is a view showing an outline of a thermal power plant boiler apparatus using the austenitic stainless steel pipes of Examples 1 to 4 as heat transfer tubes of a boiler apparatus.

Embodiments of the present invention will be described with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the processing method of an austenitic stainless steel pipe in embodiment of this invention. In the figure, the shot nozzle 2 is inserted inside the austenitic stainless steel pipe 1 used as the heat transfer pipe, and the shot particles 3 are ejected from the shot nozzle 2 toward the inner surface 5 of the steel pipe. do. As a result, the shot processing layer 4 is formed on the tube inner surface 5.

Shot (blasting) processing on the inner surface of an austenitic stainless steel pipe is performed by compressing the shot particles (3) such as small pieces of steel or steel balls of austenitic stainless steel into compressed air. This impinges on the inner surface of the steel pipe 5, causes a large number of slip deformations in the crystal grains near the inner surface of the steel pipe 5, and hardens it. In order to uniformly apply shot processing to the inner surface of the tube 5, the shape, hardness, injection pressure of the shot particles, injection amount, rotation speed of the shot nozzle in the inner circumferential direction of the steel pipe 1, shot nozzle ( It is necessary to optimize the conditions of the moving speed in the axial direction of 2).

In this embodiment, a plurality of parameters are set for the state of the inner surface of the tube 5 of the austenitic stainless steel pipe shot by the method described above, and the water vapor oxidation resistance is evaluated for each of the parameters, that is, the water resistance. It was possible to determine whether or not the vapor oxidizing property was excellent. And based on this determination result, it becomes possible to provide the austenitic stainless steel pipe which has the water vapor oxidation resistance required as a heat exchanger tube, and to process the inner surface of the tube of an austenitic stainless steel pipe which has the water vapor oxidation resistance required as a heat exchanger tube. It became possible.

Hereinafter, the said parameter and the evaluation criteria of water vapor oxidation resistance are demonstrated for several Example. In addition, in the following description, the same code | symbol is attached | subjected to the component which can be regarded as the same or the same, and the overlapping description is abbreviate | omitted suitably.

Example 1

Example 1 is an example in which the roughness of the inner surface 5 of the tube of the austenitic stainless steel pipe 1 was parameterized.

The inner surface 5 of the austenitic stainless steel pipe 1 was shot as shown in FIG. 1, and the following findings were obtained by evaluating the relationship between the roughness of the inner surface of the tube after processing and the water vapor oxidation resistance. . The knowledge is that in the austenitic stainless steel made of 16 to 23% Cr, the water vapor oxidation generated on the inner surface 5 of the tube 5 whose roughness of the inner surface 5 after shot processing is an index of water vapor oxidative resistance It is related to the thickness of the scale 6 (see FIG. 3). 2 is experimental data showing the relationship.

Fig. 2 shows the arithmetic mean roughness Ra of the inner surface of the tube 5 of the austenitic stainless steel pipe (hereinafter, simply referred to as "steel pipe") 1 made of 18% Cr after shot processing, and water vapor flowing through the steel pipe. Thickness of the steam oxidation scale 6 (all layers and inner layers) in an 18Cr-8Ni austenitic stainless steel pipe (KA-SUS304J1HTB: high-strength stainless steel pipe SUPER304H for high-efficiency thermal power plants) after 876 hours at 650 ° C. Thickness]. In FIG. 2, the measured value of the hardness of the position of 50 micrometers in depth from the outermost surface (0 micrometer in depth) after processing is also shown in parallel. Arithmetic mean roughness was adjusted by changing shot processing conditions, and the roughness was measured by direct measurement using a contact surface roughness measuring instrument. And about a measuring apparatus, it is not limited to a contact type, You may use non-contact roughness measuring instruments, such as a laser microscope. It is preferable to perform an actual measurement over the full length of a steel pipe, but if shot processing conditions are constant, it can also be performed by sample measurement. In addition, what sampled about the thickness of the water vapor oxidation scale 6 was measured by the microscope by the corrosion test. In addition, outermost surface (0 micrometer in depth) B0 after a process corresponds to the outermost position of the surface of the base material B after the shot process shown in FIG. 5 mentioned later, and defines depth based on this position.

As a result of the measurement, when the arithmetic mean surface roughness Ra of the inner surface of the tube 5 is 1.97 µm or less (data G to J), the thickness of the steam oxidation scale is 20 µm (inner layer 10 µm), and the inner surface of the tube Generation of the water vapor oxidation scale 6 into (5) can be suppressed. In contrast, when the arithmetic mean surface roughness Ra of the tube inner surface 5 is 2.06 µm or more (Comparative Examples C to F), the thickness of the water vapor oxidation scale 6 becomes larger than 20 µm, and the tube inner surface 5 When the arithmetic mean surface roughness Ra of () is 2.44 μm or more (Comparative Examples C to E), the thickness of the water vapor oxidation scale 6 becomes larger than 70 μm (inner layer 40 μm), and the water vapor to the inner surface of the tube 5. The production of the oxidation scale 6 could not be suppressed. In addition, on the data, although the arithmetic mean surface roughness Ra of the inner surface of the pipe | tube 5 is 1.97 micrometers or less (data G), evaluation is "(circle)", but the relationship between roughness and hardness is compared by comparing data F and G. Interpolation can be made into evaluation "(circle)" when the arithmetic mean surface roughness Ra of the tube surface 5 is 2 micrometers or less. Thereby, when the arithmetic mean surface roughness Ra of the pipe | tube inner surface 5 is 2 micrometers or less, it can be judged that it is excellent in water vapor oxidation resistance. In addition, the tube surface 5 corresponds to the position B0 of depth 0 here.

In the non-shot tube (Comparative Examples A and B), the thickness of the water vapor oxidation scale 6 was 150 µm (inner layer 75 µm). And the arithmetic mean surface roughness Ra of the inner surface 5 of the non-shot tube was 2.44 micrometers (comparative example B), and 2.51 micrometers (comparative example A).

In addition, although the measured value of the hardness of the position where the depth from the outermost surface B0 after processing is 50 micrometers is also shown in parallel in FIG. 2, the arithmetic mean surface roughness Ra of the inner surface of the tube 5 is 1.97 micrometers or less. In the case (document G), the hardness is 300 Hv or more, and it turns out that a shot layer is formed reliably. In contrast, when the arithmetic mean surface roughness Ra of the inner surface of the tube 5 is 2.06 µm or more (document F), the hardness at a position of 50 µm in depth from the outermost surface B0 after processing [pyramid indenter] (Vickers hardness test) of the material hardness using ()) is less than 300 Hv, it can be seen that a short layer that can reliably exhibit the water vapor oxidation resistance is not formed.

3 is an explanatory view showing the relationship between the roughness of the inner surface 5 of the tube after shot processing and the generated water vapor oxidation scale 6. FIG. 3A is a diagram conceptually showing a state of the inner surface 5 of the pipe 1 of the steel pipe 1 before processing. Shot processing is performed from this state. At this time, if shot processing is nonuniform, as shown in FIG.3 (b), since the hardened layer by shot processing partially forms in the inner surface 5 of a pipe | tube, surface roughness will be loose. On the other hand, when shot processing is uniformly applied to the inner surface 5 of a tube, as shown in FIG.3 (c), since the shot processing layer 4 is formed in the whole, surface roughness becomes smooth.

When the steel pipe 1 is exposed to high-temperature steam after shot processing, the formation of the two-layered water vapor oxidation scale 6 between the inner layer made of (Cr, Fe) ₃ O ₄ and the outer layer made of Fe ₃ O ₄ is described above. Same as one. At this time, only the inner layer 6a of the steam oxidation scale 6 is formed on the surface of the shot processing layer 4 subjected to the shot processing, and only the outer layer 6b generated outside thereof is also formed thin. . Therefore, the entire layer thickness of the water vapor oxidation scale 6 becomes thin. On the other hand, as shown in FIG.3 (d), the inner layer 6a is thickly formed and the outer layer 6b of its outer side is also thickly formed in the site | parts whose shot processing is insufficient. Therefore, at this site, a totally thick steam oxidation scale 6 is produced. Therefore, it can be seen that if the arithmetic mean roughness is rough, the water vapor oxidation scale thickness is large.

On the other hand, when shot processing is uniformly applied to the inner surface 5 of the tube, the shot processing layer 4 is formed as a whole as shown in Fig. 3E, so that the water vapor oxidation scale 6 is formed on the inner layer. Both 6a and outer layer 6b are produced only thinly. Therefore, the entire layer thickness of the water vapor oxidation scale 6 becomes thin. Therefore, when the arithmetic mean roughness is fine, it can be seen that the thickness of the water vapor oxidation scale is small.

In the water vapor oxidation scale 6, the outer layer 6b is Fe ₃ O ₄ , and the inner layer 6a is a two-layer structure of (Cr, Fe) ₃ O ₄ , with or without a shot. Here, an oxide containing a lot of Fe [Fe ₃ O ₄ , (Cr, Fe) ₃ O ₄ : (Fe> Cr)] is generally faster than the Cr-containing oxides {Cr ₂ O ₃ , [(Cr, Fe) ₃ O ₄ : (Cr> Fe)]}. This is because the diffusion rate (moving rate) of ions (Fe, Cr, O ions) in the oxide is faster than that of the Cr oxide.

On the other hand, shot processing has an effect of speeding up the diffusion rate of metals (Fe, Cr) in the metal, and in SUS steel of 18 (16) Cr or more, the diffusion rate of Cr is relatively faster than Fe. Therefore, when shot processing is performed, a scale with a large amount of Cr in the scale is initially generated as compared with the case of no shot processing, the scale growth rate is remarkably lowered, and growth of the scale is significantly suppressed. Therefore, when shot processing is uniformly constructed on the whole surface of the tube surface 5, the amount of Cr is largely uniformly in the whole surface of the tube surface 5, and the thickness is thin. However, when the shot processing was uneven or partial, a thick scale partially containing a large amount of Fe is produced, so that scale growth cannot be completely suppressed. Both Cr oxides and Fe oxides are water vapor oxidation scales produced by oxidation of metals with steam.

Therefore, by measuring the arithmetic mean roughness of the inner surface 5 of the pipe after shot processing of the steel pipe 1, it is possible to determine whether or not the shot processing for suppressing the generation of the water vapor oxidation scale 6 is reliably constructed. Can be. In addition, in this embodiment, although the arithmetic mean roughness Ra was used for the roughness of the inner surface of the pipe | tube 5, it is not limited to this, For example, other, such as a maximum height Rz, an average square root height Rq, etc. Roughness parameters may be used. The validity of using these roughness parameters was confirmed by measuring the hardness in the depth of 50 micrometers position. At this time, the reference value by each parameter is calculated | required previously, and this reference value is determined as a threshold value.

Thus, when the arithmetic average roughness of the inner surface of the short tube (5) after processing 2㎛ or less, (Cr, Fe) can be the thickness of the inner layer (6a) composed of a ₃ O ₄ to 10㎛ below. This means that if the arithmetic mean roughness of the inner surface 5 of the tube after shot processing is 2 µm or less, it is an austenitic stainless steel pipe 1 having excellent water vapor oxidation resistance. Thereby, it turns out that this austenite stainless steel pipe 1 can be used as a heat exchanger tube of the boiler apparatus 100 (refer FIG. 8), if the arithmetic mean roughness of the inner surface 5 of a pipe after shot processing is 2 micrometers or less. .

[Example 2]

Example 2 is an example in which the hardness of the inner surface 5 of the austenitic stainless steel pipe 1 was used as a parameter.

In Example 1, the water vapor oxidation resistance is determined by using the surface roughness of the inner surface 5 of the pipe 1 as a parameter, but the water vapor oxidation resistance can be evaluated and determined using the hardness of the surface as a parameter.

Fig. 4 is a diagram showing the result of comparing the hardness of the inner surface of the austenitic stainless steel pipe 1 made of 18% Cr after shot processing with the hardness without shot processing. 4 shows the position (depth: micron) from the tube inner surface 5 on the horizontal axis, and the hardness (Hv: Vickers hardness) on the vertical axis. As can be seen from the figure, the increase in hardness due to shot processing becomes maximum (about 380 Hv) at the inner surface of the tube (0 µm), and gradually decreases at the position (depth) in the inner direction of the tube. Therefore, since the hardness of the inner surface of the tube is not affected by the measurement position as in the inner tube, stable measurement results are obtained.

In the present embodiment, when the Vickers hardness of the tube inner surface 5 after shot processing is 350 Hv or more, it can be judged that it is an austenitic stainless steel pipe excellent in water vapor oxidation resistance. As described above, in the present embodiment, in order to directly measure the hardness of the inner surface of the tube 5, the measurement is easier and the accuracy is higher than that of the inside of the tube from the tube cross section.

When evaluating the surface hardness of the steel pipe 1 after shot processing, it is also possible to measure and evaluate the hardness with respect to the inner surface of a pipe as mentioned above, but when measuring the result of FIG. 4, it is 18% Cr after shot processing. The hardness of the austenitic stainless steel pipe 1 formed becomes the maximum at the outermost surface B0 after processing, and can be observed from the outermost surface B0 after processing to a depth position of about 200 μm. Therefore, when hardness is measured within the range of the position of about 200 micrometers in depth from the position of 0 micrometer which is outermost surface B0 after a process, the influence of shot processing can be evaluated. However, what is important is the hardness in the vicinity of the inner surface 5 of the tube.

In the case of measuring the hardness in the vicinity of the inner surface of the pipe 5, when the distance from the outermost surface B0 increases after processing, the nonuniformity of the hardness value also increases, and the hardness of the surface extremely close to the outermost surface B0 after the processing is guaranteed. Since it may not be possible, it is preferable to evaluate by hardness in the tube surface vicinity as much as possible.

When measuring the internal hardness of the steel pipe 1 using the Vickers test method, the steel pipe 1 is cut and sliced in a plane perpendicular to the axial direction, and this cutting and slicing shape steel pipe When the hardness of the tube inner surface 5 of (1) is measured from the tube inner surface 5 toward the tube outer surface, a diamond-shaped indenter (for example, in the vicinity of the surface very close to the tube inner surface 5) The indenter shape is a square pyramid, and an angle of 136 ° and a diagonal length of 0 to several μm) is displaced from the measurement site, so that it is difficult to form an accurate indentation. Therefore, the minimum depth is 50 from the outermost surface B0 after processing. The position in μm is the proper position for the hardness measurement. Referring to FIG. 4, in the present embodiment, when the hardness at the position of a depth of 50 μm from the outermost surface B0 after processing is 300 Hv or more, it can be determined that the austenitic stainless steel pipe has excellent water vapor oxidation resistance. .

From this, when hardness is measured between 50 micrometers from the outermost surface B0 after a process or the outermost surface B0 after a process, the hardness according to the distance (depth) from the outermost surface B0 after a process will be set previously. From the depth position from the outermost surface B0 after processing of the measured steel pipe 1 and the hardness measured at that position, it can be determined whether the water vapor oxidation resistance is excellent. Thereby, when it is judged that water vapor oxidation resistance is excellent, it turns out that this austenitic stainless steel pipe 1 can be used for the heat exchanger tube of the boiler apparatus 100. FIG.

[Example 3]

Example 3 is an example in which the depth of the shot process layer of the inner surface 5 of the austenitic stainless steel pipe 1 was used as a parameter.

The depth of the shot processing layer of the inner surface 5 of the austenitic stainless steel pipe 1 can be measured from the microstructure of the steel pipe 1. FIG. 5 is a micrograph showing a cross-sectional microstructure of an austenitic stainless steel pipe 1 made of 18% Cr after shot processing. In order to make the shot processing layer 4 clear, this photo is heat treated at 650 ° C. for 1 hour, and then embedded in a resin (J) as a base material (B), followed by mirror polishing. It is image | photographed by the electrolytic etching process in the chromic acid solution. The scale of 50 micrometers is also shown in order to specify magnification. As can be seen from this photograph, the outermost position after shot processing of the base material B of the steel pipe 1 becomes the outermost surface B0 after processing.

On the inner surface 5 of the tube, a large number of slip lines 7 (see FIG. 6 to be described later) produced by plastic deformation due to shot processing are observed black. The layer in which this slip line 7 is seen is called the shot processing layer 4. This shot processing layer 4 becomes uniform and deep when shot processing is reliably constructed. 7 shows the number of slip lines having a depth of 50 μm (open / 10 μm), hardness Hv at a depth of 50 μm from the outermost surface B0 after processing, and evaluation (more than hardness Hv300 at a depth of 50 μm). Experimental data showing the relationship between From the same figure, it turns out that Vickers hardness is 300 or more as the depth of the shot process layer from the outermost surface B0 after processing is 50 micrometers or more. Therefore, in the present embodiment, when the shot processing layer depth from the outermost surface B0 after processing is 50 µm or more, it can be determined that the austenitic stainless steel pipe has excellent water vapor oxidation resistance. Thereby, it turns out that this austenitic stainless steel pipe 1 is suitable for use of the heat exchanger tube of the boiler apparatus 100, if the depth of a shot process layer from outermost surface B0 after processing is 50 micrometers or more.

Example 4

Example 4 is an example which made the density of the slip line in the shot process layer of the inner surface 5 of the austenitic stainless steel pipe 1 the parameter. The slip line of the inner surface 5 of the austenitic stainless steel pipe 1 can be measured from the microstructure of the steel pipe 1 in the same manner as in the third embodiment.

FIG. 6 is a micrograph showing a cross-sectional microstructure of an austenitic stainless steel pipe made of 18% Cr after shot processing at a depth of 50 µm from the outermost surface B0 after processing. This photograph is processed and photographed by the same processing method as in FIG. 5. The scale of 25 micrometers is also shown in order to specify magnification. From this photograph, the slip line produced by the plastic deformation by shot processing in the crystal grains is observed. Since the contrast is difficult to understand in the photograph, the state of the grain boundary 61 and the slip line 71 is drawn out from the photograph in a diagram in FIG. 6. Here, the density (number) of the slip lines 71 shown at one grain boundary 61 is measured. In FIG. 6, it is four / 10 micrometers.

Therefore, in Fig. 7, referring to the relationship between the number of slip lines 71 (per 10 m length) and the hardness, when the number of slip lines 71 at a depth of 50 m is 3 or less, the hardness is It is less than 300 Hv, and in four or more, it is 300 Hv or more. Therefore, in the present embodiment, if the number of slip lines 71 at a depth of 50 µm from the outermost surface B0 after processing is 4 or more per 10 µm length, the austenitic stainless steel pipe 1 is It can be judged that water vapor oxidation resistance is excellent. That is, if the number of slip lines 71 at a depth of 50 µm from the outermost surface B0 after processing is 4 or more per 10 µm length, the austenitic stainless steel pipe 1 is formed of the boiler apparatus 100. It turns out that it is preferable to use a heat exchanger tube.

[Example 5]

FIG. 8 is a view showing a boiler device for thermal power generation, and is an example in which the austenitic stainless steel pipe 1 described in Examples 1 to 4 is used as a heat transfer tube of a boiler device. In FIG. 8, the boiler apparatus 100 for thermal power generation is basically composed of a boiler body 101, a burner 102, a flue 103, a superheater 104, and a reheater 105. It is. A plurality of burners 102 are installed on the lower side of the boiler body 101, such as the superheater 104 and the reheater 105 in the flue 103 through which the combustion gas generated by the combustion of the burner 102 flows. Various heat exchangers are installed. Heat exchangers such as the superheater 104 and the reheater 105 are constituted by a combination of heat transfer panels in which a plurality of heat transfer tubes are arranged in a vertical direction at a predetermined pitch. And in Examples 1-4, the austenitic stainless steel pipe judged to be excellent in water vapor oxidation resistance is used as said heat exchanger tube.

Thus, when the austenitic stainless steel pipe determined to be excellent in water vapor oxidation resistance is used as the heat transfer tubes of the superheater 104 and the reheater 105, the heat transfer tube is not blocked at the bent portion and no steam turbine blade corrosion occurs. . Thereby, the reliability and long life of a boiler operation can be aimed at.

In addition, in this embodiment, the inner surface 5 of the pipe corresponds to the inner surface of the steel pipe 1 which allowed the unevenness | corrugation after a shot process, as shown to Fig.3 (c), and the outermost surface B0 after a process is It corresponds to the outermost surface (position) of the unevenness | corrugation after shot processing used as a reference | standard of the depth position at the time of evaluating the hardness of a base material B. That is, the outermost surface B0 after a process is a reference position at the time of defining a depth. In addition, in FIG.2 and FIG.7, "depth from the tube inner surface" means the "depth from the outermost surface after processing."

As described above, according to the present embodiment,

1) The austenitic stainless steel pipes have parameters of austenitic stainless steel pipes 1 having roughness, hardness, depth of shot processing layer 4 and density of slip lines in shot processing layer 4 as parameters. By indirectly or directly evaluating the hardness of the predetermined depth from the outermost surface B0 after the processing of the steel pipe 1, it is possible to easily determine whether or not the water vapor oxidation resistance required as the heat transfer pipe is secured.

2) In addition, since the superior and poor heat resistance of the water vapor oxidizing property can be easily determined, the austenitic stainless steel pipe 1 having the water vapor oxidation resistance required as the heat transfer pipe can be provided by performing the processing that satisfies the determination.

3) Or if it has the characteristic which satisfy | fills the said determination, it can be used as an austenitic stainless steel pipe 1 which ensured the water vapor oxidation resistance required as a heat exchanger tube.

4) By using the austenitic stainless steel pipe 1 having the characteristic of satisfying the above determination as the heat transfer tubes of the superheater 104 and the reheater 105 of the boiler apparatus 100, the water resistance of the heat transfer tube of the boiler apparatus 100 is The steam oxidizing property can be ensured, and the reliability and long life of a boiler operation can be aimed at.

5) In particular, if the arithmetic mean roughness Ra of the inner surface 5 of the austenitic stainless steel pipe 1 is 2 µm or less, it can be a steel pipe having water vapor oxidation resistance required as a heat transfer pipe.

6) If the arithmetic mean roughness Ra of the inner surface 5 of the austenitic stainless steel pipe 1 is 2 µm or less, the hardness and the density of the slip line are also satisfied, so that the austenitic stainless steel pipe is measured only by measuring the surface roughness. Whether or not it is used as the heat transfer tube of (1) can be evaluated with good accuracy.

Has the same effect.

In addition, this invention is not limited to embodiment mentioned above, A various deformation | transformation is possible in the range which does not deviate from the summary of this invention, and all the technical matters contained in the technical idea described in the claim are object of this invention. do. Although the said embodiment showed the preferable example, those skilled in the art can implement | achieve various alternative, modification, modification, or improvement from the content disclosed in this specification, and these are in the technical scope as described in the attached claim. Included.

1: austenitic stainless steel pipe
2: shot nozzle
3: shot particles
4: shot processing layer
5: inner surface of pipe
6: water vapor oxidation scale layer
7, 71: slip line
100: boiler device
B0: outermost surface after machining

Claims (8)

Austenitic stainless steel pipe for heat transfer pipe,
The inner surface of the tube after shot processing of the austenitic stainless steel pipe is 2 µm or less in terms of arithmetic mean roughness Ra, or
The hardness from the outermost surface to the predetermined depth after processing after shot processing of the austenitic stainless steel pipe is 300 Hv or more.
One of the austenitic stainless steel pipe. The method of claim 1,
Austenitic stainless steel pipe, wherein the predetermined depth is between 0 μm and 50 μm from the outermost surface after processing. The method of claim 1,
An austenitic stainless steel pipe, wherein the predetermined depth is an inner surface of the tube and the hardness of the inner surface of the tube is 350 Hv or more. The method of claim 1,
And said predetermined depth is the depth of the shot working layer from the outermost surface after processing, and the depth of the shot working layer is 50 micrometers or more. The method of claim 1,
And said predetermined depth is 50 [mu] m from the outermost surface after processing, and the number of slip lines at the depth position is 4 or more per 10 [mu] m length. The method according to any one of claims 1 to 5,
Or less, when used as the heat transfer tubes the thickness of the inner layer (6a) composed of a (Cr, Fe) ₃ O ₄ wherein the austenitic steam oxidation scale layer is generated on the steel pipe inner surface of the stainless steel pipe (scale layer) 10㎛, austenite Based stainless steel pipe. A boiler apparatus comprising the austenitic stainless steel pipe according to any one of claims 1 to 6 as a heat transfer pipe. As the inner surface processing method of austenitic stainless steel pipe,
A method of processing the inner surface of an austenitic stainless steel pipe by shot processing an inner surface of the austenitic stainless steel pipe so that the arithmetic mean roughness Ra of the shot inner surface of the tube is 2 µm or less.

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