JP5891859B2 - Steam piping and manufacturing method thereof - Google Patents

Description

  The present invention relates to steam piping.

  In the steam piping, high-speed droplets are formed in the downstream portion of the orifice of the drain piping or the steam transport piping. Since the generated droplet collides with the pipe wall at a high speed, erosion (droplet impact erosion) occurs in the pipe due to the impact. As measures against such erosion, conventionally used carbon steel pipes are replaced with pipes made of alloy steel or stainless steel having high erosion resistance. Moreover, in order to improve erosion resistance, such as a turbine blade, it is also known to perform coating by alumina spraying (see Patent Documents 1 and 2).

JP 7-11416 A Japanese Patent Laid-Open No. 9-279364

  However, the portion where the droplet impact erosion is likely to occur in the piping of the steam system is a portion where a small diameter piping where the flow velocity is increased is used, or a bent portion where the steam flow collides. Construction by alumina spraying described in Patent Documents 1 and 2 has been extremely difficult for these small diameter pipes and bent portions of the pipes.

  The present invention has been made in view of the above-described problems of the prior art, and an object of the present invention is to provide a steam pipe that can suppress thinning due to droplet impact erosion and has excellent workability.

The steam pipe of the present invention is characterized in that a protective layer having an alumina layer formed through an aluminum diffusion / permeation layer is provided on the inner surface of the pipe.
The steam pipe of the present invention is characterized in that a protective layer having a chromium compound layer formed through a chromium diffusion / permeation layer is provided on the inner surface of the pipe.
The steam pipe of the present invention is characterized in that a protective layer having a Ni-PB plating layer is provided on the inner surface of the pipe.
The steam pipe of the present invention is characterized in that a protective layer having a nitride layer formed via a nitrogen diffusion layer is provided on the inner surface of the pipe.

  According to the steam pipe having the above-described configuration, excellent durability against droplet impact erosion can be obtained by forming the protective layer of the above material on the inner surface of the pipe. Moreover, said protective layer can be formed by the heat processing in the state embedded in powder, or a liquid phase process. Therefore, the protective layer can be easily applied even to a small-diameter pipe or a bent pipe such as an elbow joint, which cannot be formed by a conventional thermal spraying process.

The pipe may have an inner diameter of 60 mm or less.
The protective layer may be provided in the pipe bending portion.
The protective layer may be provided in a range within 100 mm downstream from the orifice.

  ADVANTAGE OF THE INVENTION According to this invention, the piping for steam which can suppress the thinning by droplet impact erosion and was excellent also in workability is provided.

The fragmentary sectional view of piping for steam of an embodiment. Sectional drawing which shows the steam piping structure which can apply the piping for steam of embodiment. The figure which shows the water jet apparatus used for erosion resistance evaluation. The graph which plotted the damage depth with respect to test time in an Example.

  Hereinafter, embodiments of steam piping will be described with reference to the drawings.

FIG. 1 is a partial cross-sectional view of the steam pipe of the present embodiment.
As shown in FIG. 1, the steam pipe 10 includes a pipe 11 and a protective layer 12 formed on the inner surface of the pipe 11. The steam pipe 10 is used for pipes and joints constituting a steam pipe structure for transporting steam generated by a steam boiler or the like to a demand section.

  The pipe 11 is made of, for example, carbon steel, alloy steel, or stainless steel. The material of the pipe 11 can be selected according to the use of the steam pipe 10. Although the shape of the pipe 11 is not particularly limited, it can be preferably applied to a small-diameter pipe, an elbow joint, a bent pipe, or the like where droplet impact erosion easily occurs.

  The protective layer 12 is made of any one of an alumina layer formed by an aluminum diffusion penetration treatment, a chromium compound layer formed by a chromium diffusion penetration treatment, a Ni-P-B plating layer, and a nitride layer formed by a nitridation treatment. Become. In the present embodiment, the protective layer 12 may be formed as a separate coating from the pipe 11, or may be a layer formed by diffusing a substance on the surface of the pipe 11. In addition, as the protective layer 12, each of the four types listed above may be used alone, or layers other than the above may be laminated as necessary.

  When the protective layer 12 is an alumina layer, it is formed using an aluminum diffusion permeation process. The aluminum diffusion and penetration treatment in the present embodiment is a treatment for forming an alumina layer on the surface while diffusing and penetrating aluminum on the steel material surface. For example, the pipe 11 that is the object to be processed is buried in a mixed powder containing alumina powder and ammonium chloride powder (treatment agent) in a container, and the temperature is about 900 ° C. to 1100 ° C. for a predetermined time (for example, 24 hours). Heat. As a result, aluminum diffuses on the surface of the pipe 11 to form an aluminum diffusion layer. Moreover, an aluminum layer (protective layer 12) is formed on the aluminum diffusion / permeation layer by oxidizing aluminum in the surface layer portion of the aluminum diffusion / permeation layer.

  When the protective layer 12 is a chromium compound layer, it is formed using a chromium diffusion penetration process. In the chromium diffusion permeation treatment, for example, the pipe 11 that is an object to be treated is buried in a mixed powder containing chromium powder and ammonium chloride powder (treatment agent) in the container, and the inside of the container is set to a hydrogen gas atmosphere, and 900 ° C. to 1100 Heating is performed for a predetermined time (for example, 24 hours) under a temperature condition of about ° C. Thereby, chromium diffuses on the surface of the pipe 11 to form a chromium diffusion / permeation layer. Further, a chromium compound layer (protective layer 12) made of, for example, iron chromium carbide is formed on the chromium diffusion and penetration layer. The composition of the chromium compound layer to be formed depends on the composition of the pipe 11.

  When the protective layer 12 is a Ni—P—B plating layer, it can be formed by a known plating process. That is, the pipe 11 that is the object to be processed is immersed in an aqueous solution of hypophosphorous acid and dimethylamine borane containing nickel ions. Nickel ions, hypophosphorous acid, and dimethylamine borane are reduced by electrons released by oxidation of the reducing agent in the aqueous solution. As a result, a Ni coating containing phosphorus and boron is deposited on the surface of the pipe 11, and a Ni—P—B plating layer as the protective layer 12 is formed.

  When the protective layer 12 is a nitride layer, it can be formed by a known nitriding treatment of a steel material. That is, the pipe 11 as the object to be processed is immersed in a salt bath mainly composed of alkali metal cyanide and carbonate, and maintained at a temperature of about 600 ° C. Thus, an iron nitride layer (nitride layer, protective layer 12) is formed on the surface of the pipe 11, and nitrogen is also diffused into the surface layer portion of the pipe 11 to form a nitrogen diffusion layer. As the nitriding treatment, a vapor phase treatment using nitrogen gas or ammonia gas may be used.

FIG. 2 is a cross-sectional view showing a steam pipe structure to which the steam pipe 10 of the present embodiment can be applied.
The steam pipe structure 100 shown in FIG. 2A is a structure in which an orifice 103 is interposed between two steam pipes 101 and 102. A steam pipe structure 110 shown in FIG. 2B is a structure in which two steam pipes 104 and 105 are connected via a 90 ° elbow joint 106.

  First, when the orifice 103 is provided in the piping structure as in the steam piping structure 100 shown in FIG. 2A, the pressure when flowing into the steam pipe 102 from the reduced diameter passage of the orifice 103. Decreases. As a result, droplets that move at high speed are formed in the steam flowing into the steam pipe 102. The formed droplets collide with the inner wall of the steam pipe 102 by the steam flow spreading in the radial direction of the pipe at the inlet of the steam pipe 102. This collision of droplets causes thinning (droplet impact erosion) in the steam pipe 102.

  Further, as shown in FIG. 2A, droplet impact erosion in the downstream portion of the orifice 103 is likely to occur on the inner wall surface E1 of the steam pipe 102 at a position slightly away from the orifice 103. The position at which droplet impact erosion occurs varies depending on the inner diameter of the pipe, the flow velocity of the steam, and the shape of the orifice.

  On the other hand, when the steam flow is bent using the elbow joint (pipe bent portion) 106 as in the steam pipe structure 110 shown in FIG. 2B, the steam flow flowing into the elbow joint 106 from the steam pipe 104 is reduced. Droplet impact erosion is likely to occur on the inner wall surface E2 of the elbow joint 106 in the front direction.

  The droplet impact erosion at the elbow joint 106 is caused by the collision of the droplets contained in the vapor flow with respect to the inner wall surface E2 from the front, and the vapor flow diameter reduction similar to that of the orifice at the bending angle of the vapor flow. It is considered that this is because droplets are likely to be generated due to a decrease in pressure at the radially outer periphery of the joint 106. The above phenomenon is the same in a bending pipe that does not use the elbow joint 106.

  Further, in the structure illustrated in FIG. 2, when the inner diameter of the pipe is small, droplet impact erosion is likely to occur. This is thought to be because the steam velocity tends to increase compared to the case where the pipe inner diameter is large. In the case of a small-diameter pipe, it is difficult to apply a protective layer by thermal spraying, and in particular, if the pipe inner diameter is 60 mm or less, the construction is almost impossible.

  The steam pipe 10 of the present embodiment can be applied to the steam pipes 101, 102, 104, 105, the orifice 103, and the elbow joint 106 that constitute the steam pipe structures 100, 110 shown in FIG. In the steam pipe 10 of the present embodiment, the protective layer 12 is formed on the inner surface of the pipe 11, so that even when a droplet flying at high speed in the pipe collides with the inner wall surface, the pipe 11 (steam The pipes 101, 102, 104, 105, the orifice 103, and the elbow joint 106) can be effectively protected.

  The steam pipe 10 of this embodiment has good erosion resistance because the alumina layer, the chromium compound layer, the Ni—P—B plating layer, and the nitride layer that constitute the protective layer 12 are in hardness. This is considered to be due to the excellent coating and excellent toughness. That is, the protective layer 12 of the present embodiment can suppress the generation and development of cracks due to the impact of droplets that repeatedly enter at high speed. Thereby, generation | occurrence | production of droplet impact erosion can be suppressed and the steam piping structure excellent in reliability can be comprised.

  Further, the protective layer 12 used in the steam pipe 10 of the present embodiment can be formed by heat treatment or liquid phase treatment in a state of being buried in powder. Therefore, the protective layer 12 can be easily applied even to a small-diameter pipe (pipe having a diameter of 60 mm or less) or a bent pipe such as an elbow joint, which cannot be formed by a conventional thermal spraying process.

  In the present embodiment, the protective layer 12 may be formed on the entire inner surface of the pipe 11 or may be formed only on a part thereof. For example, it may be formed only on the inner surface of the elbow joint 106 where droplet impact erosion is particularly likely to occur, or may be formed only on the inner surface of the steam pipe 102 on the downstream side of the orifice 103. Furthermore, the protective layer 12 may be formed only in the range of 100 mm or less from the downstream end of the orifice.

  Hereinafter, the steam pipe of the present embodiment will be described in more detail by way of examples.

  In this example, a plurality of types of protective layers were formed on the inner surface of an STPA 23 pipe (chromium molybdenum steel pipe) having a nominal diameter of 50A, and the durability against droplet impact erosion was evaluated. In this example, the following five types of test pieces were prepared and used for testing and evaluation.

  The alumina layer of Sample 1 was formed by heating at 900 ° C. for 24 hours with a test piece embedded in a mixed powder of alumina powder and ammonium chloride powder. When the test piece was subjected to EDX analysis, it was confirmed that an Al—Fe—C intermetallic compound layer (aluminum diffusion permeation layer) was formed at the interface between the alumina layer and the base material (STPA 23).

The chromium compound layer of Sample 2 was formed by holding a test piece in a mixed powder of chromium powder and ammonium chloride powder in an H ₂ atmosphere and heating at 900 ° C. for 24 hours. A chromium diffusion / permeation layer formed by diffusing chromium on the surface layer of the substrate (STPA23) is formed, and an iron chromium carbide layer (chromium compound layer) is formed on the chromium diffusion / permeation layer. confirmed.

  The nitride layer of Sample 3 was formed by immersing the test piece in a salt bath containing alkali metal cyanide oxide and carbonate as main components and maintaining the specimen at 600 ° C. The formed nitride layer was an iron nitride layer in which iron of the base material (STPA23) was nitrided. Moreover, the nitrogen diffusion layer which nitrogen diffused in the base material was formed in the lower layer side of the iron nitride layer of the surface.

  The Ni—P—B plating layer of Sample 4 was formed by immersing the test piece in a plating solution (an aqueous solution of hypophosphorous acid and dimethylamine borane containing nickel ions).

  FIG. 3 is a diagram showing a water jet apparatus 200 used for erosion resistance evaluation. The water jet apparatus 200 includes a nozzle 201, a nozzle support portion 202 that supports the nozzle 201, and a stage portion 203 that supports the test piece S. Water W is pumped to the nozzle 201 from a pump (not shown). A nozzle opening having a diameter of 0.4 mm is formed on the lower surface of the nozzle 201 in the figure. The water W pumped into the nozzle 201 is jetted as a water jet WJ from the nozzle opening. The water jet WJ is jetted so as to enter the surface of the test piece S at a predetermined angle (for example, 90 °).

  In this embodiment, the jet pressure in the water jet device 200 is 30 MPa, the test time is 1 second to 5400 seconds, the test distance D from the nozzle 201 to the surface of the test piece S is 200 mm, and the surface of the test piece S of the water jet WJ is The angle was 90 °. The droplet collision speed with respect to the test piece S was 148 m / s.

  The evaluation of each sample was performed by measuring the damage depth by the depth of focus of the metal microscope after the surface damage test of the test piece S by the water jet device 200 and obtaining the damage depth with respect to the test time.

FIG. 4 is a graph plotting damage depth versus test time for samples 1-4 and control samples.
As shown in FIG. 4, in the test pieces of Samples 1 to 4 in which the protective layer is formed, the slope of the degree of increase in damage depth (damage depth speed) with respect to the test time is small. That is, it was confirmed that the progress of damage by the water jet was slow with respect to the control sample STPA23 in which the protective layer was not formed.

  In particular, the damage depth rate in the specimen in which the alumina layer is formed by the aluminum diffusion treatment of Sample 1 is 0.22 μm / s, which is about 1/44 of the damage depth rate of 9.7 μm / s in the control sample. It dropped to. In addition, in the test piece in which the nitride layer was formed by nitriding treatment of Sample 3, the damage depth rate was 0.89 μm / s, and the damage depth rate was reduced to about 1/10 compared to the control sample. It was confirmed that the durability against droplet impact erosion was remarkably improved by using these materials as a protective layer.

  10, 101, 102, 104, 105 ... steam piping, 11 ... piping, 12 ... protective layer, 103 ... orifice, 106 ... elbow joint (bending portion of piping)

Claims (4)

  A protective layer having an alumina layer formed through an aluminum diffusion / permeation layer is provided on the inner surface of a pipe made of steel, the inner diameter of the pipe is 60 mm or less, and the aluminum diffusion / permeation layer is made of Al-Fe-C metal. Steam piping characterized by being an intermetallic layer.   The steam pipe according to claim 1, wherein the protective layer is provided at a pipe bending portion.   The steam pipe according to claim 1 or 2, wherein the protective layer is provided in a range within 100 mm downstream from the orifice. It is a manufacturing method of the piping for steam according to any one of claims 1 to 3,
A pipe made of steel, by heating at a temperature of 900 ° C. C. to 1100 ° C. in a state of being buried in a mixed powder comprising alumina powder and ammonium chloride powder, an aluminum diffusion coating layer is formed on the surface of the pipe, the A method for producing a steam pipe, wherein the alumina layer is formed by oxidizing aluminum in a surface layer portion of an aluminum diffusion layer.

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