JP2017129164A - Piping support structure and method for forming the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piping support structure having a structure with high-corrosion resistance against stress corrosion, and to provide a method for forming the same.SOLUTION: The piping support structure includes: piping 1; and a hollow columnar support member connected to the outside of the piping. The support member has one end of which outer periphery is connected to the piping, where the piping and the columnar support member are integrally formed by casting.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a pipe support structure mainly used in an outdoor chemical plant or the like and a method for forming the same.

  Piping used in a chemical plant or the like may have a complicated shape depending on the application. In addition, the installation location may be a narrow location where installation, repair, inspection, and the like are difficult. On the other hand, since the piping structure in a plant requires high safety, it is necessary to install support members for supporting the piping at various places.

  FIG. 5 shows a pipe support structure 110 in which a general pipe 101 is supported by a column 102. In general, a support member such as the support column 102 is often welded to the pipe by welding. Also in this example, the outer periphery of the upper end of the support column 102 is welded to the pipe 101.

  Moreover, stainless steel is often used as a material for such piping. In stainless steel, chromium (Cr) in the component combines with oxygen in the air to form a dense and highly adhesive film (passive film) having a thickness of several nanometers on the surface. For this reason, this film prevents the progress of corrosion inside the steel material, and has the property of being less susceptible to rusting than other steel materials.

  However, even in stainless steel, when three factors of the stress condition, the material component, and the environmental condition are prepared, a special form of corrosion called stress corrosion may occur. The crack generated by this special corrosion is called stress corrosion cracking (SCC).

  In order to prevent stress corrosion cracking, at least one of the above three factors may be excluded. For example, there is a method of relaxing the stress condition and eliminating the stress factor by applying a heat of about 850 ° C. or more to the steel material to remove the residual stress. However, this method is often difficult to apply to piping installed in a narrow place in the plant. Further, in this method, a region (HAZ: Heat Affected Zone) having a temperature of about 450 ° C. to about 850 ° C. may occur around the heat treatment. In this case, chromium in the crystal grains of the stainless steel precipitates as chromium carbides at the grain boundaries, and the chromium concentration in the vicinity of the crystal grain boundaries decreases, thereby reducing corrosion resistance (sensitization). .

  Among the above-mentioned factors, as a method for eliminating environmental factors, for example, in Patent Document 1 (Japanese Patent Laid-Open No. 8-254594), a method of applying electrical corrosion protection by controlling the potential of stainless steel is given. It has been. However, this method requires a separate configuration for measuring and controlling the potential.

JP-A-8-254594

  In view of the above circumstances, an object of the present invention is to provide a pipe support structure having high corrosion resistance against stress corrosion and a method for forming the same.

  In order to achieve the above object, a pipe support structure according to the present invention includes a pipe and a hollow columnar support member connected to the outside of the pipe, and the support member has an outer periphery connected to the pipe. The pipe and the columnar support member are integrally formed by casting.

  Further, the pipe support structure according to the present invention is another embodiment, and includes a pipe and a hollow columnar support member connected to the outside of the pipe, and the support member has an outer periphery welded to the pipe. The welded welded portion may be subjected to a solution treatment.

  Moreover, the said columnar support member can be made into the form which has a length of at least 50 mm from the junction part of the said piping.

  Another aspect of the present invention is a method for forming a pipe support structure, which includes a pipe and a hollow columnar support member connected to the outside of the pipe, and the support member has an outer periphery at one end. The pipe and the columnar support member of the pipe support structure connected to the pipe are integrally formed by casting.

  Further, the pipe support structure forming method according to the present invention is such that the outer periphery of one end of a hollow columnar support member is welded to the outside of the pipe, and a solution treatment is further applied to the welded welded portion. Also good.

  ADVANTAGE OF THE INVENTION According to this invention, the piping support structure with high corrosion resistance with respect to stress corrosion, and its formation method are provided.

It is a mimetic diagram showing a 1st embodiment of piping support structure concerning the present invention. It is a schematic diagram which shows 2nd Embodiment of the piping support structure which concerns on this invention, and its formation method. It is a schematic diagram which shows 3rd Embodiment of the piping support structure which concerns on this invention, and its formation method. It is a schematic diagram which shows 4th Embodiment of the piping support structure which concerns on this invention, and its formation method. It is a schematic diagram which shows the form of a general piping support structure. It is a schematic diagram which shows the piping in a general piping support structure. It is a schematic diagram which expands and shows the crack which generate | occur | produced in the piping in a general piping support structure.

  Embodiments of a pipe support structure according to the present invention will be described below with reference to the accompanying drawings.

  First, a general structure 110 for supporting a pipe used in a chemical plant or the like will be described in more detail with reference to FIG.

  In the pipe 101, the direction of the pipe is bent from the vertical direction to the horizontal direction. A pipe having such a shape is generally called an elbow pipe. The support column 102 has a hollow cylindrical shape. The upper end of the support column 102 has a shape that follows the shape of the outer wall of the bent portion of the pipe 101. Therefore, the outer periphery of the upper end surface of the support column 102 is in close contact with the outside of the bent portion of the pipe 101 over the entire periphery. In general, stainless steel is often used as the material of the pipe 101 and the column 102.

  As a method of forming such a pipe support structure, welding the pipe 101 and the hollow column 102 in the welded portion 103 is performed. This welding is performed over the entire upper end of the support column 102.

  Next, the special stress corrosion cracking that occurs at the welded portion between the pipe 101 and the hollow column 102 and the solution thereof will be described.

  The chemical plant that employs the pipe support structure according to the present invention may be assumed to be constructed in a coastal area or the like near the coast. Under such circumstances, rainwater and garbage containing sea salt particles may accumulate in the piping. In particular, they tend to accumulate relatively easily in places with complicated shapes such as bent portions of piping. Further, as shown in FIG. 5, when a support column is welded to a bent portion of a pipe, the shape becomes more complicated, and rainwater, dust, and the like are easily collected. Furthermore, as shown in FIG. 5, when a support column is joined to the lower part of an elbow-shaped pipe, rainwater and dust tend to gather at the welded part 103 along the outer periphery from the upper part of the pipe.

  In general, most of the particles such as dirt and sea salt once accumulated on the outer wall of the pipe are often swept away by stronger rain or wind, and therefore rarely continue to accumulate for a long time. However, there are cases in which fine gaps, cracks, scratches, and the like are formed in the welded part of the pipe due to a temperature change of the pipe accompanying the welding process or plant operation. The sea salt particles that enter this gap may not be washed away by rain or wind, and may continue to accumulate on the spot.

  Furthermore, in the pipe support structure 110 as shown in FIG. 5, since the support column 102 has a hollow shape, sea salt particles or the like may enter the hollow interior. In this case, the sea salt particles that have entered the hollow interior adhere to the inner wall surface of the column 102 and the outer wall surface of the pipe 101 located inside the column 102 and may continue to accumulate without being washed away by rain or wind. .

  Also, such pipes 101 and struts 102 are generally often welded at a plant construction site. In this case, complicated welding may be performed in an environment where workability is poor, and there is a possibility that defects such as a poor welding state and generation of residual stress due to this may occur. The residual stress generated in the pipe in this way can be a stress factor that causes stress corrosion cracking of the pipe 101. Further, in the vicinity of the joint portion 103, temperature unevenness may occur during welding, and the structure of the stainless steel may be sensitized. This sensitized structure can be a material factor that causes stress corrosion cracking.

  Here, FIG. 6 shows the pipe 101 after the support column 102 is removed from the pipe support structure 110 shown in FIG. The welding position 111 is a portion where the upper end surface of the support column 102 has been welded. The cavity position 112 is a portion located in the cavity inside the support column 102 when the support column 102 is welded to the pipe 101.

  FIG. 7 is an enlarged schematic view showing a crack generated in the pipe 101 in a general pipe support structure. The range shown in FIG. 7 is the welded portion of the column 102 in the pipe 101. In addition, the support | pillar 102 is not illustrated in this figure.

  The crack 107 and the crack 108 shown in FIG. 7 indicate cracks generated in a pipe support structure used for about two years in an outdoor plant in a coastal area. The crack 107 generated near the welding position 111 has many crack-like cracks, and the crack 108 generated near the center of the cavity position 112 has many turtle-shell-like cracks.

[First Embodiment]
Next, the piping support structure according to the first embodiment will be described with reference to FIG.

  In FIG. 1, a pipe 1 and a support column 2 are made of stainless steel (for example, austenitic stainless steel such as SUS321, SUS316, SUS304, etc.) and are integrally formed by casting. The support column 2 has a hollow shape.

  As described above, when the pipe support structure 10 is formed by integrally casting the pipe 1 and the support column 2 in advance by casting, a fine gap between the members that occurs in the welding process does not occur. Thereby, sea salt particles can be prevented from entering and accumulating in the gap. Further, it is possible to prevent sea salt particles from flowing into the cavity of the hollow support column 2 (corresponding to the cavity position 112 in FIG. 5). Therefore, environmental factors that cause stress corrosion cracking can be eliminated.

  In addition, by integrally forming the pipe 1 and the support column 2 in advance by casting in this way, it is possible to suppress the occurrence of residual stress in the vicinity of the welded portion, which occurs due to temperature unevenness or a cooling process. Therefore, stress factors that cause stress corrosion cracking can be eliminated.

  Even in the pipe support structure 10 that is integrally formed by casting, residual stress may be generated by cooling in the casting process. In order to remove this, the integrally formed pipe support structure 1 may be heat-treated again in a furnace at 850 ° C. or higher. Thereby, a residual stress can be eliminated more effectively.

  As a result of these, in the pipe support structure 10 in the present embodiment, environmental factors and stress factors are eliminated, and the occurrence of special forms of stress corrosion cracking can be prevented. That is, when the above-described general pipe support structure 110 is used, sea salt particles or the like that have flowed due to rainwater or the like may accumulate and concentrate in the regions of the welding position 111 and the cavity position 112. However, according to the present embodiment, such a stress factor can be eliminated by preventing sea salt particles and the like from entering the joint.

[Second Embodiment]
A pipe support structure and a method for forming the pipe support structure according to the second embodiment will be described with reference to FIG.

  In order to form the pipe support structure according to the present embodiment, first, the pipe 1a and the support column 2a are welded at the welded portion 3. Thereafter, the entire furnace 4 is heated and subjected to a solution treatment, whereby the pipe support structure 10a can be formed.

  When the pipe 1 and the column 2 are joined by welding, a structure in which stainless steel is sensitized around the welded portion 3 may be generated. According to the present embodiment, since the pipe support structure 10a is formed by performing the solution treatment, the chromium carbide precipitated from the stainless steel can be dissolved again in the crystal grains. As a result of this treatment, the corrosion resistance of the sensitized tissue can be recovered again.

  As a heating condition in the solution treatment, for example, in the case of a pipe support structure in which a strut having a thickness of about 2.5 mm using SUS304 is welded to a pipe having a thickness of about 2.5 mm using SUS304, from 1000 ° C. It is desirable to heat at a temperature of 1200 ° C. for about 60 minutes. Further, in the cooling process of the solution treatment, it is preferable to forcibly cool by providing a blower or the like in order to remove 450 ° C. to 850 ° C., which is a temperature range where SUS304 is sensitized, as quickly as possible.

[Third Embodiment]
The piping support structure according to the third embodiment will be described with reference to FIG. Since the third embodiment is a modification of the first embodiment (FIG. 1), the same portions or similar portions are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 3 shows a pipe support structure 20 and a method for forming the same in the third embodiment.

  First, in the form of FIG. 3, the pipe 21 and the support column 22 are integrally formed by casting. At this time, the length L of the column 22 is longer than at least 50 mm. The “length” here means the distance from the connecting portion with the pipe 21 to the axial end of the column 22. Moreover, the connection part here means all the places in the boundary of the outer wall of the piping 21, and the support | pillar 22. As shown in FIG.

  The piping support structure 20 according to the present embodiment assumes that, for example, a column extension member 26 is further welded to an end 25 opposite to the piping in the column 22. In the present embodiment, the transmission of heat to the pipe 21 is reduced by setting the length L to at least 50 mm. In this case, at the time of welding of the extension member, heat can be mitigated from reaching the pipe 21 through the support column 22. Thereby, the sensitization of the stainless steel structure can be prevented and the material factor of stress corrosion cracking can be eliminated.

[Fourth Embodiment]
A pipe support structure according to the fourth embodiment will be described with reference to FIG. Since the fourth embodiment is a modification of the second embodiment (FIG. 2) and the embodiment of FIG. 3 (FIG. 3), the same or similar parts are denoted by the same reference numerals. Thus, redundant description is omitted.

  FIG. 4 shows a pipe support structure 30 and a formation method thereof in the fourth embodiment.

  First, in FIG. 4, the pipe 31 and the support column 32 are joined by welding at the welded portion 33. At this time, the length L of the support column 32 is longer than at least 50 mm as in the case of FIG. Furthermore, solution treatment is performed in the furnace 4. Thereby, the residual stress produced by welding is removed from the formed pipe support structure 30.

  When large heat energy is transmitted to the periphery of the welded part 3 during welding of the pipe 31 and the support column 32, the member may be deformed in the vicinity of the welded part 3. Due to this deformation, stress is generated inside the material, which may become a stress factor of stress corrosion cracking. However, as in the present embodiment, by applying the solution treatment, the stress caused by the deformation can be removed, so that the stress factor can be eliminated.

  Also in the pipe support structure 30 in the present embodiment, it is assumed that, for example, an extension member 36 of a support column is further welded to an end portion 35 opposite to the piping of the support column 32. In this case, when the extension member is welded, heat may reach the pipe 32 through the support column 32. As a result, sensitization of the stainless steel structure occurs, which can be a material factor for stress corrosion cracking, which is not desirable. However, this can be prevented by reducing the transfer of heat to the pipe 31 by setting the length L to at least 50 mm as in this embodiment.

[Other aspects]
The description of the embodiment described above is an example for explaining the pipe support structure according to the present invention, and does not limit the invention described in the claims. Moreover, each part structure of this invention is not restricted to embodiment mentioned above, A various deformation | transformation is possible within the technical scope as described in a claim.

  For example, in the above-described embodiment, the support column is attached to the outside of the bent portion of the pipe, but the configuration may be attached to the inside of the bent portion. Further, the support column is not limited to a vertical attachment, and may be a horizontal attachment or an oblique attachment. In the present embodiment, the support column is described using a configuration in which the pipe is supported from below, but may be configured to be supported from above.

  Further, the cross-sectional shapes of the pipe and the support are not limited to a circle, but may be other shapes such as a square. In addition, you may attach the support | pillar which does not have a cavity inside instead of a hollow support | pillar. Further, the thickness of the pipe may be about 1 mm to about 50 mm, and similarly, the thickness of the support column may be about 1 mm to about 500 mm.

DESCRIPTION OF SYMBOLS 1 Piping 1a Piping 2 Strut 2a Strut 3 Welding part 4 Furnace 10 Piping support structure 10a Piping support structure 20 Piping support structure 20a Piping support structure 21 Piping 22 Strut 25 End 26 Extension member 30 Piping support structure 31 Piping 32 Strut 33 Welding part 35 End 36 Extension member 100 Piping support structure 101 Piping 102 Strut 103 Welding portion 107 Crack 108 Crack 111 Welding position 112 Cavity position L Length

Claims (5)

  A pipe and a hollow columnar support member connected to the outside of the pipe are provided, and the support member has an outer periphery connected to the pipe at one end, and the pipe and the columnar support member are integrally formed by casting. Piping support structure.   A pipe and a hollow columnar support member connected to the outside of the pipe, and the support member has an outer periphery welded to the pipe, and the welded welded portion is subjected to a solution treatment. Piping support structure.   The exhaust pipe support structure according to claim 1 or 2, wherein the columnar support member has a length of at least 50 mm from a connection portion with the pipe.   The method for forming a pipe support structure according to claim 1, wherein the pipe and the columnar support member are integrally formed by casting.   A method for forming a pipe support structure, wherein an outer periphery of one end of a hollow columnar support member is welded to the outside of a pipe, and a solution treatment is further performed on the welded portion.

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