TW201304910A - Austenitic stainless steel pipe, boiler device, and method for processing inner surface of pipe - Google Patents

Abstract

With the present invention the inner surface (5) of an austenitic stainless steel pipe (1) is subjected to shot processing by means of shot particles (3), and the quality of the water vapor oxidation resistance of the pipe inner surface (5) is determined on the basis of the degree of hardness at a predetermined depth from the post-processing outermost surface of the steel pipe (1) which has been subjected to shot processing. In the aforementioned determination, when the roughness of the pipe inner surface (5) after the pipe inner surface (5) has been subjected to shot processing has an arithmetic mean roughness (Ra) of 2 μm or less, or when the hardness at the predetermined depth is 300 Hv or greater, it is determined that the pipe inner surface has excellent water vapor oxidation resistance. Thus, an austenitic stainless steel pipe for which the arithmetic mean roughness (Ra) of the pipe inner surface (5) is 2 μm or less or for which the hardness at the predetermined depth is 300 Hv or greater can be used as a heat transfer pipe for a boiler.

Description

Vostian iron-based stainless steel pipe, boiler device and inner surface processing method

The present invention relates to a Worthfield iron-based stainless steel pipe, a boiler device, and a method for processing the inner surface of a pipe, and more particularly to a heat transfer pipe, which is suitable for a Worthfield iron-based steel pipe in which a high-temperature, high-pressure steam flows through a portion. The method for processing the inner surface of the tube of the Worthfield iron-based steel pipe and the Worstian iron-based stainless steel pipe excellent in water vapor oxidation resistance.

In the high temperature portion of the boiler device through which the high temperature gas flows, a superheater or a reheater in which high temperature and high pressure water vapor flows in the steel pipe is provided, and the heat transfer constituting the heat is used from the viewpoint of high temperature strength and corrosion resistance. The tube uses a Worthfield iron-based stainless steel tube containing 18% or more of Cr. During the operation of the boiler, the inner surface of the steel pipe is corroded with water vapor due to contact with high temperature, high pressure water vapor flowing inside the steel pipe and reacting with the contact water vapor. The steam oxidized scale is a two-layer structure of an inner layer composed of (Cr,Fe) ₃ O ₄ and an outer layer composed of Fe ₃ O ₄ . Furthermore, the outer layer is located on the side of the steel pipe near the air layer, and the inner layer is located on the side of the base material than the outer layer.

In the case of the Worthfield iron-based stainless steel, the coefficient of linear expansion is generally large, and the steel pipe may expand or contract due to changes in the load of the boiler, the operation is stopped, or the temperature of the fluid flowing inside the steel pipe changes due to the start of the operation. At this time, if the expansion coefficient of the steel pipe itself is greatly different from the expansion coefficient of the steam oxidized scale of the inner surface layer of the steel pipe, and the temperature change occurs, the steam oxidation scale becomes easily peeled off from the inner surface of the steel pipe. If the water vapor oxidizes the scale from the steel pipe When the surface is peeled off, the water vapor rust after the peeling is deposited on the bent portion of the steel pipe, which causes the pipe to clog, and also scatters toward the steam turbine through the steam pipe, and also causes the steam turbine blade to erosion. the reason. Therefore, for the steel pipe used in the high temperature portion of the boiler, not only high temperature strength but also excellent water vapor oxidation resistance is required.

As a method for improving the steam oxidation resistance of the Worthfield iron-based stainless steel, there are the following methods: increasing the Cr content in the material; making the crystal grains fine; and spraying the inner surface of the steel pipe to form a hardened layer. Among them, the method widely used is a method in which the inner surface of the steel pipe is subjected to jet processing, and the hardened layer is formed on the inner surface of the steel pipe. For example, in the blasting process, the particles of the stainless steel are sprayed on the inner surface of the steel pipe at a predetermined pressure or more and a predetermined amount or more, and the blast processing layer having a predetermined thickness or more is formed on the inner surface of the steel pipe. Patent Document 1 describes a case where a steel pipe thus processed is used for a superheater for generating high-temperature steam, and it is presumed that an extremely thin and dense scale is formed on the inner surface of the steel pipe to prevent the growth of the water vapor-oxidized scale as a whole.

In addition, as a method of determining whether or not the spray processing of the Worthite iron-based stainless steel pipe is performed comprehensively and reliably, for example, Patent Document 2 discloses a method of causing a light source to be placed against the inner surface of the pipe from one side of the pipe that has been spray-processed. And the inside observation is carried out by the TV camera from the other end in the tube, and the area of the jet processing is measured. In this case, since the surface to be blasted becomes a non-glossy surface due to minute irregularities, and the unfinished surface becomes a glossy surface, it is possible to determine whether or not there is processing by observation. Further, Patent Document 2 selects an injection condition in which the area of the injection processing is 70% or more of the whole.

Patent Document 1: Japanese Patent Laid-Open No. 52-8930

Patent Document 2: International Publication No. WO2007/099949

Recently, the length of the Wostian iron-based stainless steel pipe used for the heater or reheater of a large-scale boiler for thermal power generation has reached several kilometers in each cylinder, and the quality of the injection processing has become a problem. However, Patent Document 1 describes that the blast processing layer is formed by blast processing to prevent the growth of the water vapor oxidized scale as a whole, but the structure or structure of the inner surface of the tube having the water vapor oxidizing resistance required as the heat transfer tube is described. The composition is not specifically described.

Further, Patent Document 2 describes a method of observing and judging by a TV camera in order to determine whether or not the blast processing is performed accurately, and the blast surface is a non-glossy surface due to irregularities, and the unprocessed surface is a glossy surface. It is only determined whether or not the construction is carried out reliably, and it is not determined whether or not the water vapor oxidation resistance required as the heat transfer tube is ensured. Further, similarly to the cited document 1, the structure of the inner surface of the tube having the water vapor oxidizing resistance required for the heat transfer tube is not particularly described.

Accordingly, an object of the present invention is to provide a Worthfield iron-based stainless steel pipe having water vapor oxidation resistance required as a heat transfer tube, and a boiler device having a heat transfer tube having Requires resistance to water vapor oxidation.

In order to solve the above problems, the present invention is a Worstian iron-based stainless steel pipe for a heat transfer tube, which is characterized by any one of the following: the inner surface of the tube of the above-mentioned Worthite iron-based stainless steel pipe is arithmetically rough The degree (Ra) is 2 μm or less, or the hardness of the outermost surface to the predetermined depth after processing of the above-mentioned Worstian iron-based stainless steel pipe is 300 Hv or more.

Moreover, the present invention is a boiler apparatus characterized by comprising a heat transfer tube composed of the above-mentioned Worthfield iron-based stainless steel pipe.

Further, the present invention relates to a method for processing an inner surface of a pipe of a Worthite iron-based stainless steel pipe, characterized in that the inner surface of the pipe of the above-mentioned Worthite iron-based stainless steel pipe is subjected to jet processing, and the inside of the pipe is subjected to jet processing. The arithmetic mean roughness (Ra) of the surface is less than 2 μm.

According to the present invention, the water vapor oxidation resistance required as a heat transfer tube can be ensured. Further, a boiler device having a heat transfer tube that ensures oxidation resistance to water vapor can be produced.

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

Fig. 1 is a view showing a processing method of a Worthfield iron-based stainless steel pipe according to an embodiment of the present invention. In the figure, the injection nozzle 2 is inserted into the inside of the Worstian iron-based stainless steel pipe 1 serving as a heat transfer tube, and the spray particles 3 are ejected from the injection nozzle 2 toward the inner surface 5 of the steel pipe. Thereby, the spray processed layer 4 is formed on the inner surface 5 of the tube.

The spraying (bead blasting) processing on the inner surface of the Worthite iron-based stainless steel pipe is made by compressing air to make sprayed particles 3 such as smaller steel sheets or steel balls made of Worthite iron-based stainless steel and the inner surface of the steel pipe 5 Collision causes a large amount of slip deformation and hardening in the crystal grains near the inner surface 5 of the steel pipe. In order to uniformly perform the jet processing on the inner surface 5 of the tube, it is necessary to make the shape of the sprayed particles, The hardness, the spray pressure of the sprayed particles, the amount of spray, the conditions of the rotational speed of the injection nozzle in the inner circumferential direction of the steel pipe 1, and the moving speed of the injection nozzle 2 in the axial direction are optimized.

In the present embodiment, a plurality of parameters can be set for the state of the inner surface 5 of the tube of the Wostian iron-based stainless steel pipe which is sprayed by the method, and the water vapor oxidation resistance is evaluated for each of the respective parameters, that is, the water resistance is judged. Whether the vapor oxidation property is excellent. Further, based on the determination result, a Worthfield iron-based stainless steel pipe having steam oxidizing resistance required as a heat transfer tube can be provided, and the Wolsfield having water vapor oxidation resistance as a heat transfer pipe can be provided. The inner surface of the iron-based stainless steel tube is processed.

Hereinafter, a plurality of examples will be described, and the evaluation criteria of the above parameters and water vapor oxidation resistance will be described. In the following description, the same or similar components are denoted by the same reference numerals, and the description thereof will be omitted as appropriate.

[Example 1]

In the first embodiment, the roughness of the inner surface 5 of the vessel of the Vostian iron-based stainless steel pipe 1 is taken as an example.

The inner surface 5 of the vessel of the Wostian iron-based stainless steel pipe 1 was spray-processed as shown in Fig. 1, and the relationship between the roughness of the inner surface of the pipe and the steam oxidation resistance after the processing was evaluated, thereby obtaining the following opinion. This insight is based on the roughness of the inner surface 5 of the tube after the blasting process and the steam rust generated on the inner surface 5 of the tube by the roughness of the inner surface 5 of the tube after the blast processing. The thickness of the skin 6 (see Fig. 3) is related. Fig. 2 shows experimental data of the correlation.

Fig. 2 is a graph showing the arithmetic mean roughness (Ra) of the inner surface 5 of the Vastfield iron-based stainless steel pipe (hereinafter, simply referred to as "steel pipe") 1 composed of 18% Cr after the injection processing, and the flow of The water vapor temperature in the steel pipe is 650 ° C and after 876 hours, the thickness of the water vapor oxidation scale 6 in the 18Cr8Ni Worth iron-based stainless steel pipe (fire SUS304J1HTB: high-strength heat-generating heat pipe for high-strength stainless steel pipe SUPER304H) And the thickness of the inner layer). Also shown in Fig. 2 is the hardness measurement at the position of the outermost surface (depth of 0 μm) at a depth of 50 μm after machining. The arithmetic mean roughness was changed and the injection processing conditions were adjusted, and the roughness was measured directly using a contact surface roughness meter. Further, the measuring device is not limited to the contact type, and a non-contact type roughness meter such as a laser microscope may be used. The actual measurement is preferably carried out over the entire length of the steel pipe. However, if the injection processing conditions are fixed, it can also be carried out by sample measurement. Further, regarding the thickness of the steam oxidized scale 6, the sample extractor was measured by a microscope by a corrosion test. Further, the outermost surface (depth: 0 μm) B0 after processing corresponds to the outermost position of the surface of the base material B after the blast processing shown in Fig. 5 below, and the depth is defined based on the position.

As a result of the measurement, when the arithmetic mean surface roughness (Ra) of the inner surface 5 of the tube is 1.97 μm or less (data G to J), the thickness of the vapor oxidized scale is 20 μm (the inner layer is 10 μm). The formation of the water vapor rust scale 6 on the inner surface 5 of the tube can be suppressed. On the other hand, when the arithmetic mean surface roughness (Ra) of the inner surface 5 of the tube is 2.06 μm or more (Comparative Example C to F), the thickness of the steam oxidized scale 6 becomes larger than 20 μm, and further The arithmetic mean surface roughness (Ra) of the inner surface 5 is 2.44 μ In the case of m or more (Comparative Examples C to E), the thickness of the water vapor rust scale 6 becomes larger than 70 μm (the inner layer is 40 μm), and the water vapor rust scale 6 cannot be suppressed on the inner surface 5 of the tube. generate. Further, in terms of data, when the arithmetic mean surface roughness (Ra) of the inner surface 5 of the tube is 1.97 μm or less (data G), the evaluation is "○", but if the data F is compared with G, and interpolation is performed When the arithmetic mean surface roughness (Ra) of the inner surface 5 of the tube is 2 μm or less, the relationship between the roughness and the hardness can be evaluated as "○". Thereby, when the arithmetic mean surface roughness (Ra) of the inner surface 5 of the tube is 2 μm or less, it is judged that the water vapor oxidation resistance is excellent. Furthermore, the inner surface 5 of the tube corresponds to a position (B0) of depth 0 here.

Further, in the non-ejection tube (Comparative Examples A and B), the thickness of the water vapor oxidized scale 6 was 150 μm (the inner layer was 75 μm). Further, the arithmetic mean surface roughness (Ra) of the inner surface 5 of the non-ejection tube was 2.44 μm (Comparative Example B) and 2.51 μm (Comparative Example A).

Further, Fig. 2 also shows the hardness measurement at the position where the outermost surface B0 depth is 50 μm after the processing, and the arithmetic mean surface roughness (Ra) of the inner surface 5 of the tube is 1.97 μm or less (data G). When the hardness was 300 Hv or more, it was found that a sprayed layer was formed. On the other hand, when the arithmetic mean surface roughness (Ra) of the inner surface 5 of the tube is 2.06 μm or more (data F), the hardness at the position of the outermost surface B0 after the processing is 50 μm (using a pyramid (pyramid) The Vickers hardness test of the material hardness of the press member was less than 300 Hv, and it was found that the spray layer capable of exhibiting water vapor oxidation resistance was not formed.

Figure 3 shows the roughness and formation of the inner surface 5 of the tube after blast processing. Description of the relationship between water vapor oxidation scales 6. Fig. 3(a) is a conceptual view showing the state of the inner surface 5 of the pipe 1 before processing. Injection processing is performed from this state. At this time, if the jet processing is uneven, as shown in FIG. 3(b), since the hardened layer formed by the jet processing is partially formed on the inner surface 5 of the tube, the surface roughness becomes thick. On the other hand, when the inner surface 5 of the tube is uniformly sprayed, as shown in FIG. 3(c), the sprayed layer 4 is integrally formed, so that the surface roughness is smooth.

If the steel pipe 1 is exposed to high-temperature steam after the blasting process, the water vapor rust is formed by forming a two-layer structure of an inner layer composed of (Cr,Fe) ₃ O ₄ and an outer layer composed of Fe ₃ O _{4 as} described above. Leather 6. At this time, on the surface of the jet-processed layer 4 which is spray-processed, the water vapor oxidizes the scale 6, and the inner layer 6a is formed only thinly, and the outer layer 6b is formed only on the outer side. Therefore, the thickness of the entire layer of the water vapor oxidized scale 6 becomes thin. On the other hand, in the portion where the blast processing is insufficient, the inner layer 6a is thickly formed as shown in Fig. 3(d), and the outer outer layer 6b is also formed thickly. Therefore, at this portion, a thicker water vapor rust scale 6 is formed as a whole. From this, it is understood that the arithmetic mean roughness is coarse and the thickness of the water vapor oxidized scale is large.

On the other hand, in the case where the inner surface 5 of the tube is uniformly subjected to the blast processing, as shown in Fig. 3(e), the blast processing layer 4 is integrally formed, so that the steam oxidized scale 6 is formed only by the thin layer. 6a, outer layer 6b. Therefore, the thickness of the entire layer of the water vapor oxidized scale 6 becomes thin. From this, it is understood that the arithmetic mean roughness is small and the thickness of the steam oxidation scale is small.

Further, the water vapor oxidized scale 6 outer layer 6b is Fe ₃ O ₄ and the inner layer 6a is (Cr, Fe) ₃ O ₄ double layer structure regardless of the presence or absence of spraying. Here, the oxide containing a large amount of Fe (Fe ₃ O ₄ , (Cr, Fe) ₃ O ₄ : (Fe>Cr)) is generally formed faster than an oxide containing more Cr (Cr ₂ O _{3 )} , (Cr, Fe) ₃ O ₄ : (Cr>Fe)). The reason for this is that the diffusion rate (moving speed) of ions (Fe, Cr, O ions) in the oxide is faster than that of the Cr oxide.

On the other hand, the blasting process has an effect of accelerating the diffusion speed of the metal (Fe, Cr) in the metal, and in the SUS steel of 18 (16) Cr or more, the diffusion rate of Cr is relatively faster than that of Fe. Therefore, when the blasting process is performed, the amount of Cr in the initial generation scale is larger than that in the case of the non-jet processing, and the growth rate of the scale is remarkably lowered, and the growth of the scale is also remarkably suppressed. Therefore, when the entire surface of the inner surface 5 of the tube is uniformly sprayed, a scale having a large amount of Cr and a small thickness is uniformly formed on the entire surface of the inner surface 5 of the tube. However, when the jet processing is uneven or local, a thick scale containing a large amount of Fe is locally generated, and therefore, the growth of the scale cannot be completely suppressed. Further, both the Cr oxide and the Fe oxide are water vapor oxidized scales formed by oxidation of a metal and a vapor.

Therefore, it is possible to determine whether or not the injection processing for suppressing the generation of the steam oxidation scale 6 is surely performed by measuring the arithmetic mean roughness of the inner surface 5 of the tube after the injection of the steel pipe 1. Further, in the present embodiment, the arithmetic mean roughness (Ra) is used for the roughness of the inner surface 5 of the tube, but it is not limited thereto. For example, other roughness such as the maximum height (Rz) or the average square root height (Rq) may be used. Degree parameter. The rationality of using these roughness parameters was confirmed by measuring the hardness at a depth of 50 μm. At this time, the reference value of each parameter is obtained in advance, and it is determined that the reference value is a threshold value.

As described above, when the arithmetic mean roughness of the inner surface 5 of the tube after the blasting is 2 μm or less, the thickness of the inner layer 6a made of (Cr,Fe) ₃ O _{4 can} be 10 μm or less. In this case, the Wristol iron-based stainless steel pipe 1 excellent in steam oxidation resistance is obtained when the arithmetic mean roughness of the inner surface 5 of the pipe after the injection processing is 2 μm or less. From this, it is understood that the Worstian iron-based stainless steel pipe 1 can be used as the heat transfer pipe of the boiler device 100 (see Fig. 8) if the arithmetic mean roughness of the inner surface 5 of the pipe after the injection processing is 2 μm or less.

[Embodiment 2]

In the second embodiment, the hardness of the inner surface 5 of the tube of the Worthite iron-based stainless steel pipe 1 is taken as an example.

In the first embodiment, the surface roughness of the inner surface 5 of the steel pipe 1 is used as a parameter to determine the water vapor oxidation resistance. However, the surface hardness may be used as a parameter to evaluate and determine the steam oxidation resistance.

Fig. 4 is a graph showing the results of comparing the inner surface hardness of the Worstian iron-based stainless steel pipe 1 composed of 18% Cr after the injection processing with the hardness of the non-jet processing. 4 is a horizontal axis showing the position (depth: micrometer) from the inner surface 5 of the tube and the vertical axis indicating hardness (Hv: Vickers hardness). As can be seen from the figure, the hardness increase after the jet processing reaches a maximum (about 380 Hv) on the inner surface (0 μm) of the tube, and the position (depth) toward the inner direction of the tube gradually decreases. Therefore, the hardness of the inner surface of the tube is not affected by the measurement position as inside the tube, so that a stable measurement result can be obtained.

In the present embodiment, if the Vickers hardness of the inner surface 5 of the tube after the blasting is 350 Hv or more, the Worth iron-based stainless steel tube excellent in water vapor oxidation resistance can be determined. As described above, in the present embodiment, since the hardness of the inner surface 5 of the tube is directly measured, the measurement becomes easier and the precision is higher than the inside of the tube which is spaced apart from the cross section of the measurement tube.

When the surface hardness of the steel pipe 1 after the blast processing is evaluated, as described above, the inner surface of the pipe can be measured and evaluated for hardness. However, if the measurement result of FIG. 4 is observed, the Worthite iron composed of 18% Cr after the blast processing is used. The hardness of the stainless steel tube 1 is maximized at the outermost surface B0 after processing, and a depth of about 200 μm from the outermost surface B0 after processing can be observed. Therefore, if the hardness is measured within a range of about 200 μm from the position of the outermost surface B0 after processing, that is, the position of 0 μm, the influence of the jet processing can be evaluated. However, what is important is the hardness near the inner surface 5 of the tube.

When the hardness in the vicinity of the inner surface 5 of the tube is measured, if the distance from the outermost surface B0 after processing becomes larger, the unevenness of the hardness value becomes larger, and there is no guarantee that it is extremely close to the outermost surface B0 after processing. In the case of the hardness of the surface, it is preferred to evaluate the hardness in the vicinity of the inner surface of the tube as much as possible.

When the inner surface hardness of the steel pipe 1 is measured by the Vickers test method, the steel pipe 1 is cut along the vertical plane in the axial direction to form a pellet shape, and the steel pipe shape of the wafer shape is measured from the inner surface 5 of the pipe toward the outer surface of the pipe. When the hardness of the inner surface 5 of the tube is 1, near the surface close to the inner surface 5 of the tube, the diamond-shaped pressing member (for example, the pressing member has a quadrangular pyramid shape and the angle is 136 degrees, and the diagonal length is 0 to A few μm) is offset from the measurement site and it is difficult to form a correct indentation. Therefore, the position at which the outermost surface B0 depth is 50 μm after the distance machining is an appropriate position for hardness measurement. With reference to Fig. 4, in the present embodiment, the hardness at the depth position of the outermost surface B0 after the processing is 50 μm is 300 Hv or more, and the Worth iron-based stainless steel pipe excellent in water vapor oxidation resistance can be determined.

Therefore, if the outermost surface B0 after processing or the outermost surface after processing The hardness is measured between B0 and 50 μm, and the hardness corresponding to the distance (depth) from the outermost surface B0 after the processing is set in advance, and the depth position of the steel pipe 1 measured from the outermost surface B0 after the processing is determined. The hardness measured at this position was judged whether or not the water vapor oxidation resistance was excellent. From this, it is understood that the Worthfield iron-based stainless steel pipe 1 is a heat transfer pipe which can be used for the boiler device 100 when it is judged that the water vapor oxidation resistance is excellent.

[Example 3]

The third embodiment is an example in which the depth of the sprayed processed layer of the inner surface 5 of the tube of the Vostian iron-based stainless steel pipe 1 is taken as a parameter.

The depth of the sprayed layer of the inner surface 5 of the tube of the Worthite iron-based stainless steel pipe 1 can be measured by the microstructure of the steel pipe 1. Fig. 5 is a photomicrograph showing the cross-sectional microstructure of the Worthfield iron-based stainless steel pipe 1 composed of 18% Cr after the blast processing. This photograph is taken after the blast processing layer 4 is clearly processed, and after the blast processing, the steel pipe 1 is heat-treated at 650 ° C for 1 hour, and then embedded as a base material B in the resin J and mirror-polished, followed by chrome. The electrolytic etching treatment is performed in the acid solution. In order to express the magnification, a scale of 50 μm is also displayed. As can be seen from the photograph, the outermost position of the base material B of the steel pipe 1 after the injection processing is the most B0 after the processing.

On the inner surface 5 of the tube, a plurality of black slip lines 7 are generated by plastic deformation due to the blast processing (see Fig. 6 below). The layer in which the slip line 7 can be observed is referred to as the spray processed layer 4. When the blast processing is actually performed, the blast processing layer 4 is uniform and deep. Figure 7 shows the number of slip lines (bar/10 μm) with a depth of 50 μm, the hardness (Hv) at the 50 μm depth of the outermost surface B0 after machining, and the evaluation (hardness at a depth of 50 μm). Experimental data on the relationship between Hv300 and above). As can be seen from the figure, the Vickers hardness is 300 or more when the outermost surface B0 after processing is at a depth of 50 μm or more from the blast layer. Therefore, in the present embodiment, when the depth of the sprayed layer from the outermost surface B0 after the processing is 50 μm or more, the Worth iron-based stainless steel pipe excellent in water vapor oxidation resistance can be determined. From this, it is understood that the Worstian iron-based stainless steel pipe 1 is suitably used for the heat transfer pipe of the boiler device 100 if the depth of the injection processed layer from the outermost surface B0 after the processing is 50 μm or more.

[Example 4]

In the fourth embodiment, the density of the slip line in the spray-processed layer of the inner surface 5 of the tube of the Vostian iron-based stainless steel pipe 1 is taken as an example.

In the same manner as in the third embodiment, the slip line of the inner surface 5 of the tube of the Worstian iron-based stainless steel pipe 1 can be measured from the microstructure of the steel pipe 1.

Fig. 6 is a micrograph showing the cross-sectional microstructure of a Wostian iron-based stainless steel tube composed of 18% Cr after the injection processing at a position where the outermost surface B0 has a depth of 50 μm after the machining. The photograph was taken after processing in the same manner as in Fig. 5 and photographed. In order to express the magnification, a scale of 25 μm is also displayed. A slip line was generated from the photograph to observe plastic deformation in the crystal grains caused by the jet processing. It is difficult to see the contrast in the photograph, and therefore, in Fig. 6, the state of the grain boundary 61 and the slip line 71 is taken out from the photograph, and is illustrated by a line graph. Here, the density (number of strips) of the slip line 71 observed in one grain boundary 61 was measured. In Figure 6, it reaches 4/10 μm.

Therefore, in Fig. 7, referring to the relationship between the number of the slip lines 71 (the length per 10 μm) and the hardness, the slip line 71 at the position of the depth of 50 μm When the number of the strips is three or less, the hardness is less than 300 Hv, and when four or more, the hard bottom is 300 Hv or more. Therefore, in the present embodiment, if the number of the slip lines 71 at the position of the outermost surface B0 after the processing is 50 μm is 4 or more per 10 μm, the Wostian iron-based stainless steel tube 1 can be determined. It is excellent in water vapor resistance. That is, it is understood that the number of the slip lines 71 at the position where the outermost surface B0 is 50 μm after the processing is four or more per 10 μm length, the Worthfield iron-based stainless steel pipe 1 is suitable for the boiler device 100. Heat transfer tube.

[Example 5]

Fig. 8 is a view showing a boiler apparatus for thermal power generation, and is an example in which the Vostian iron-based stainless steel pipe 1 described in the first to fourth embodiments is used as a heat transfer pipe of a boiler unit. In FIG. 8, the thermal power generation boiler apparatus 100 basically consists of a boiler main body 101, a burner 102, a flue 103, a heater 104, and a reheater 105. The burner 102 is provided in a large number on the lower side of the boiler body 101, and various heat exchangers such as the heater 104 and the reheater 105 are disposed in the flue 3 through which the combustion gas generated by the combustion of the burner 102 flows. The heat exchangers such as the heater 4 and the reheater 5 are configured by a combination of heat transfer plates in which a plurality of heat transfer tubes are arranged in a vertical direction at a predetermined pitch. Further, in Examples 1 to 4, a Worthfield iron-based stainless steel pipe which was judged to have excellent water vapor oxidation resistance was used as the heat transfer pipe.

When the Worstian iron-based stainless steel pipe which is judged to be excellent in water vapor oxidation resistance is used as the heat transfer pipe of the heater 104 and the reheater 105, the heat transfer pipe is not blocked in the bent portion, and it does not occur. The steam turbine wing is washed away. Thereby, the reliability and long life of the boiler operation can be achieved.

Further, in the present embodiment, the inner surface 5 of the tube corresponds to the inner surface of the steel pipe 1 which allows the unevenness after the blast processing as shown in Fig. 3(c), and the outermost surface B0 after the processing corresponds to the hardness of the base material B. The outermost surface (position) of the unevenness after the jet machining as the depth position reference. That is, the outermost surface B0 after processing is the reference position at a predetermined depth. Further, in FIGS. 2 and 7, the "depth of the inner surface of the tube" means "the depth of the outermost surface after the distance machining".

As described above, according to the present embodiment, the following effects are obtained:

1) Indirect or direct evaluation can be made by using the roughness, hardness, depth of the sprayed layer 4, and the density of the slip line in the sprayed layer 4 of the inner surface 5 of the Wolster iron-based stainless steel pipe 1 as parameters. The outer surface B0 of the Wostian iron-based stainless steel pipe 1 has a hardness of a predetermined depth from the outermost surface B0, so that it is easy to determine whether or not the water vapor oxidation resistance required as the heat transfer pipe is ensured.

2) Since the water vapor oxidizing resistance can be easily judged, the Worstian iron-based stainless steel pipe 1 which ensures the steam oxidation resistance required as the heat transfer tube can be provided if the processing satisfying the determination is performed. .

3) Alternatively, if it has the characteristics satisfying the above determination, the Worthfield iron-based stainless steel pipe 1 which is required to ensure the steam oxidation resistance required for the heat transfer tube can be used.

4) The heat transfer tube of the boiler device 100 can be ensured by using the Worthfield iron-based stainless steel pipe 1 having the characteristics satisfying the above-described determination as the heat transfer pipe of the heater 104 and the reheater 105 of the boiler device 100. It is resistant to water vapor oxidation and achieves reliability and long life of boiler operation.

5) In particular, the arithmetic of the inner surface 5 of the tube of the Vostian iron-based stainless steel tube 1 When the average roughness (Ra) is 2 μm or less, a steel pipe having steam oxidizing resistance required as a heat transfer tube can be obtained.

6) If the arithmetic mean roughness (Ra) of the inner surface 5 of the steel tube of the Vostian stainless steel tube 1 is 2 μm or less, the hardness and the density of the slip line are also satisfied, so that only the surface roughness can be used. The measurement was carried out to accurately evaluate whether or not the Worthfield iron-based stainless steel pipe 1 can be used as a heat transfer pipe.

In addition, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit and scope of the invention, and the present invention includes all technical matters of the technical idea described in the claims. The above-described embodiments are described in the preferred embodiments, but those skilled in the art can implement various alternatives, modifications, modifications, and improvements in the form of the disclosure. The technical scope.

1‧‧‧Worthian iron stainless steel pipe

2‧‧‧jet nozzle

3‧‧‧Spray particles

4‧‧‧Spray processing layer

5‧‧‧ inside surface

6‧‧‧Water vapor oxidation cortex

6a‧‧‧ inner layer

6b‧‧‧ outer layer

61‧‧‧ Grain boundary

7, 71‧‧‧ slip line

100‧‧‧Boiler installation

101‧‧‧Boiler body

102‧‧‧ burner

103‧‧‧ flue

104‧‧‧heater

105‧‧‧Reheater

B0‧‧‧ outermost surface after processing

Fig. 1 is a view showing a processing method of a Worthite iron-based stainless steel pipe according to an embodiment of the present invention.

Fig. 2 is a graph showing the results of measurement of the arithmetic mean roughness (Ra) and the thickness of the steam oxidized scale on the inner surface of the tube of the Worstian iron-based stainless steel pipe after the blast processing in the first embodiment.

Fig. 3 is a view showing the relationship between the roughness of the inner surface of the pipe after the blast processing of Example 1 and the generated steam oxidized scale.

Fig. 4 is a graph showing the results of comparing the inner surface hardness of the tube of the Worthfield iron-based stainless steel tube after the blast processing of Example 2 with the hardness of the non-jet processing.

Fig. 5 is a photomicrograph showing a cross-sectional microstructure of a Worthfield iron-based stainless steel pipe after the blasting process of the third embodiment.

Fig. 6 is a micrograph showing the cross-sectional microstructure of the Worthfield iron-based stainless steel pipe after the injection processing at a position at a depth of 50 μm from the outermost surface after the processing in Example 4.

Fig. 7 is a graph showing the relationship between the number of the slip lines having a depth of 50 μm in the examples 3 and 4, the hardness at a position at a depth of 50 μm from the outermost surface after processing, and the evaluation.

Fig. 8 is a schematic view showing a boiler apparatus for thermal power generation using the Vostian iron-based stainless steel pipes of the first to fourth embodiments as heat transfer tubes for a boiler unit.

1‧‧‧Worthian iron stainless steel pipe

3‧‧‧Spray particles

4‧‧‧Spray processing layer

5‧‧‧ inside surface

6‧‧‧Water vapor oxidation cortex

6a‧‧‧ inner layer

6b‧‧‧ outer layer

Claims (8)

A Worthfield iron-based stainless steel pipe, which is a Worstian iron-based stainless steel pipe for a heat transfer pipe, characterized in that the inner surface of the Worthite iron-based stainless steel pipe is processed by arithmetic mean roughness (Ra) It is 2 μm or less, or the hardness of the outermost surface to the predetermined depth after the processing of the Wostian iron-based stainless steel tube is 300 Hv or more. For example, the Vostian iron-based stainless steel pipe of the first application of the patent scope, wherein the predetermined depth is between 0 μm and 50 μm from the outermost surface after processing. For example, the Vostian iron-based stainless steel pipe of the first application of the patent scope, wherein the predetermined depth is the inner surface of the pipe, and the inner surface of the pipe has a hardness of 350 Hv or more. The Vostian iron-based stainless steel pipe according to the first aspect of the patent application, wherein the predetermined depth is a depth of the outermost surface of the spray-worked layer after processing, and the depth of the spray-worked layer is 50 μm or more. For example, the Vostian iron-based stainless steel pipe of the first application patent scope, wherein the predetermined depth is 50 μm from the outermost surface after machining, and the number of slip lines at the depth position is 4 pieces per 10 μm length. the above. The Vostian iron-based stainless steel pipe according to any one of claims 1 to 5, wherein when used as the heat transfer pipe, steam oxidation of the inner surface of the steel pipe of the Worthfield iron-based stainless steel pipe is used. The thickness of the inner layer 6a composed of (Cr,Fe) ₃ O ₄ in the scale layer is 10 μm or less. A boiler apparatus comprising the Worthfield iron-based stainless steel pipe of any one of claims 1 to 6 as a heat transfer pipe. The invention relates to a method for processing the inner surface of a pipe of a Worstian iron-based stainless steel pipe, which is applied to the Worthfield iron-based stainless steel pipe, which sprays the inner surface of the pipe and makes the arithmetic mean roughness of the inner surface of the pipe which has been jet-processed (Ra) is less than 2 μm.