JP4792355B2 - Yokoyose / stub tube welded structure and boiler apparatus including the same - Google Patents

Description

  The present invention relates to a superheater tube / stub tube welded structure in a supercritical pressure boiler (USC boiler) apparatus having a steam temperature of 600 to 650 ° C., and more particularly 9 to 12% Cr steel as a tube and stub tube material. TECHNICAL FIELD The present invention relates to a technique for preventing cracks in a welded portion between a pipe holder and a stub pipe in the case of using a steel pipe.

  In general, a boiler apparatus employs a structure in which a pipe holder and a manifold are housed in a penthouse (ceiling enclosure) above a ceiling wall, and a pendant coil is suspended in a furnace below the ceiling wall.

  In order to take this structure, the following is important regarding the ceiling wall penetration.

(A) Combustion ash should not enter the penthouse from the penetrating coil penetrating wall penetration. If combustion ash accumulates in the penthouse, the inspection period of the pressure-resistant parts and casings in the penthouse is to be inspected regularly, etc., and the period of regular inspection is limited and a large amount of work (period) is required to remove ash. It becomes.

(B) Stress must not be generated in the leg tube or stub tube in the penthouse by installing a member (box casing or the like) for preventing ash entry.

  As a structure satisfying the above conditions (a) and (b), the leg tube attached to the header is a slide structure with a gap in the ceiling wall penetrating part, and as a measure against leakage of ash into the penthouse, As shown in FIG. 8, a system in which the box casing 9 surrounds the pipe 2 and the leg tube 5 is adopted. In the figure, 1 is a pipe manifold, and 12 is a ceiling wall. As described above, a portion where the leg tube 5 penetrates the ceiling wall 12 is provided with a gap so as to be slidable. The portion of the box casing 9 that contacts the ceiling wall 12 is welded.

  Since this structure can prevent ash intrusion into the penthouse and the ceiling wall penetrating portion of the lev tube 5 is slidable, it is an excellent structure that does not generate thermal stress due to restraint with the ceiling wall 12 of the leg tube 5. is there.

  However, this structure is not without problems. FIG. 9 is a diagram for explaining this problem, and FIG. 10 is an enlarged view of a portion A in FIG. As shown in these figures, axial stress (axial stress X1 due to internal pressure, bending stress X2 due to the weight of the pendant coil) acts on the welded portion of the stub tube 3 with the header 2.

  In general, the creep rupture strength of the weld is the same as that of the base metal, the steam temperature is 550 to 580 ° C., and both the pipe holder 2 and the stub pipe 3 are made of a low alloy steel of 2.25Cr-1Mo steel. Even if the stub tube 3, the transition piece 4 and the leg tube 5 have the same inner diameter and the same wall thickness, there was no problem in the creep rupture strength of the welded portion in which the stub tube 3 was implanted and welded to the nozzle 2.

In addition, regarding the welded structure of the header, for example, the following patent documents can be cited.
Japanese Patent Laid-Open No. 7-204843 JP-A-7-214373

  In recent years, when the steam conditions are increased in temperature with the aim of improving plant efficiency, a material having higher base material strength is required.

  For example, USC (Ultra Super Critical) material includes 9Cr-12Cr steel containing W, Mo, Nb, and V, and is used for a nozzle or a stub tube in a boiler having a steam temperature of 600 to 650 ° C.

  However, a stub tube of the same material is implanted and welded to a pipe made of this material, and the stub tube, the transition piece, and the leg tube have the same inner diameter, and are connected via a transition piece between the stub tube and the leg tube. If it is configured with the same wall thickness, there arises a problem that cracks occur in the stub tube implantation weld.

  An object of the present invention is to provide a welded / stub tube welded structure and a boiler device including the welded / stub tube welded structure capable of effectively preventing a welded portion between the welded tube and the stub tube.

  In order to achieve the above object, the first means of the present invention is to implant and weld a stub tube made of the same material on a nozzle made of 9Cr-12Cr steel containing W, Mo, Nb and V, and to connect the stub tube and the leg. In a welded / stub tube welded structure in which a tube is connected via a transition piece, the inner diameters of the stub tube, transition piece, and leg tube are substantially the same, and the wall thickness of the stub tube is greater than the wall thickness of the leg tube. It is characterized by being enlarged in the range of 1.2 to 3.0 times.

  According to a second means of the present invention, in the first means, the transition piece for connecting the stub tube and the leg tube has a thin tube portion having the same inner diameter and the same thickness as the leg tube, and the stub tube. A thick tube portion having the same inner diameter and the same wall thickness, and an outer diameter changing tube portion having an outer diameter changed so that the wall thickness gradually increases from the thin tube portion to the thick tube portion. It is characterized by that.

  According to a third means of the present invention, in the first means, the nozzle and the stub tube are made of the 9Cr-12Cr martensitic stainless steel, and the transition piece and the leg tube are austenitic stainless steel. It is characterized by comprising.

  According to a fourth means of the present invention, in the third means, the stub tube and the transition piece are welded with a nickel-based alloy material.

  According to a fifth means of the present invention, in the second means, the length of the outer diameter changing tube portion of the transition piece is 2 by subtracting the outer diameter of the thin tube portion from the outer diameter of the thick tube portion. It is characterized by being at least three times larger than the divided value.

  According to a sixth means of the present invention, in the first to fifth means, the stub tube has a length of 100 mm or more.

  According to a seventh means of the present invention, there is provided a boiler apparatus including a pipe holder / stub pipe welded structure in which a stub pipe is implanted and welded to a pipe of a superheater, wherein the pipe holder / stub pipe welded structure is the first to the first. This is a welded / stub tube welded structure according to any one of the sixth means.

  The eighth means of the present invention is the seventh means, wherein the leg tube is slidable with a clearance in the ceiling wall penetrating portion, and the stub tube to the leg tube with respect to the header. A large number of series of tube bodies are attached, and these tube groups are covered with a box casing.

  The present invention is configured as described above, and by increasing the thickness of the stub tube and reducing the stress on the outer surface of the stub tube welded portion, it is possible to prevent creep cracks generated from the outer surface, By increasing the thickness, the risk of the stub tube implantation welded heat-affected zone penetrating the thickness is reduced, and the safety becomes stronger.

  Examples of 9Cr-12Cr-based materials developed as materials for steam temperature 600-650 ° C class USC boilers include Fire STPA28 (Mod. 9Cr), Fire STPA29 (NF616), and Fire SUS410J3TP (HCM12A). The chemical composition of these Cr steels is as follows. The unit is% by weight.

Fire STPA28 (Mod. 9Cr)
Cr: 9, Mo: 1, Nb: 0.08, V: 0.22, C: 0.1.

Fire STPA29 (NF616)
Cr: 9, Mo: 0.45, W: 1.75, Nb: 0.05, V: 0.2, C: 0.1.

Tue SUS410J3TP (HCM12A)
Cr: 11, Mo: 0.4, W: 2.0, Nb: 0.07, V: 0.22, Cu: 1.0, C: 0.1.

  This material can increase the high-temperature strength by adding Mo, W, Nb, V, etc., but when welded, the fine-grained area of the weld heat-affected zone softens, and the creep rupture life as the welded portion is the mother. It is greatly reduced compared to the creep rupture life of the material.

  For this reason, in the structure where a stub tube of the same material is welded to a joint using this material, there is a problem that cracks occur in the welded portion, so it is necessary to reduce the stress generated in the leg tube and prevent the cracks from occurring. is there.

  As described above, the stress that causes cracking in the welded portion of the stub tube is axial stress, and the breakdown is due to the internal pressure and the bending load due to the weight of the pendant coil. Although the axial force due to the internal pressure cannot be removed, the bending stress due to its own weight can be reduced by the structure shown in FIGS.

  That is, as shown in FIG. 11, the upper end of the suspension member 11 is connected to the pipe holder 2, the lower end is connected to the pendant coil, and the pendant coil is suspended from the pipe holder 2 via the suspension member 11. A structure that reduces the weight of the machine.

  As shown in FIG. 12, the stub tube 5 is connected to the stub tube 5 by a support member 10, thereby reducing the axial stress of the implantation welded portion of the stub tube 5 on the joint 2. .

  However, in these mechanical structures, a temperature difference is generated between the suspension member 11 and the support member 10 and the leg tube 5 at the start of the plant, and a large thermal stress is applied to the welded portion of the stub tube 3 to the header 2. There is a risk of fatigue cracking. In order to prevent the occurrence of fatigue cracks, operational restrictions such as increasing the start-up time are required, and the method has many limiting factors.

  By adopting the configuration described in detail below, the present invention can effectively reduce the axial force due to internal pressure and the bending stress due to its own weight.

  Whereas the stub tube 3 is 9Cr-12Cr martensitic stainless steel, the pendant coil and the leg tube 5 are austenitic stainless steel in the case of a plant having a steam temperature of 600-650 ° C. A transition piece 4 for joining is required.

  The material of the transition piece 4 is austenitic stainless steel, and the dimensions (outer diameter and wall thickness) on the side to be engaged with the stub tube 3 are large, while the dimensions (outer diameter and wall thickness) on the side to be engaged with the leg tube 5 are small. Thus, the following conditions can be satisfied.

(A) Although there is a high Cr steel weld heat affected zone where the creep rupture strength is reduced at the butt weld on the thick side of the transition piece 4, the stress can be reduced because the thickness is increased.

(B) The heat affected zone on the stub tube side in the welded portion of the stub tube 3 and the transition piece 4 has a weak creep rupture strength as in the case of the heat affected zone of the implanted welded portion, but this portion is also thick. Therefore, the stress is reduced and it is possible to have a sufficient creep strength.

  In addition, the thermal stress can be reduced by using the Ni-based alloy (Inconel) type | system | group of the welding rod which connects the stub tube 3 and the transition piece 4 which consists of austenitic stainless steel which has the average linear expansion coefficient of both materials.

(C) The butt weld on the thin wall side of the transition piece 4 is welded between austenitic stainless steels that originally have the same creep rupture strength as that of the base metal, and therefore has sufficient creep rupture strength even if it is thin. Is possible.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing a mounting state of a manifold, a header and a leg tube, FIG. 2 is a partially enlarged perspective view thereof, FIG. 3 is a side view showing a mounting state of the manifold, the header and a leg tube, and FIG. It is a partial cross section figure which shows the attachment state of a header, a stub pipe | tube, a transition piece, and a leg tube.

  As shown in FIG. 1, a superheater inlet manifold 1a and a superheater outlet manifold 1b installed in the width direction of the furnace are arranged in parallel. It is attached. The superheater outlet manifold 1b is connected to a turbine (not shown).

  As shown in FIG. 4, a stub tube 3 is implanted and welded to the pipe holder 2, and the stub tube 3 is connected to a leg tube 5 via a transition piece 4.

  In a plant with a steam temperature of 600 to 650 ° C., 12Cr steel (Tue SUS410J3TP) with high allowable stress and excellent steam oxidation resistance is used for the manifold 1 and the pipe holder 2, and the stub tube 3 is also the same 12Cr. Steel (fire SUS410J3TP) is used.

  The reason is that, since the welded portion 6 (see FIG. 4) of the stub tube 3 to the header 2 is structurally a stress concentration portion, the same material as that of the header 2 can be used, so that the thermal stress as a different material can be obtained. This is to avoid the problem. That is, if austenitic stainless steel is used as the stub tube 3, thermal stress (stress due to the difference in linear expansion coefficient) as a different material and stress concentration due to the shape are superimposed on the implanted welded portion 6 of the stub tube 3, which is excessive. This is because stress is generated.

  The part of the leg tube 5 that penetrates the ceiling wall 12 (see FIG. 1) has a structure (a structure that does not restrict each other) that is slidable by providing a gap for the purpose of avoiding thermal stress due to the restriction between both members. Intrusion of ash from the slide portion into the penthouse is prevented by covering the pipe holder 2 and the leg tube 5 with a box casing 9 (see FIG. 8) from the periphery thereof.

  As the pendant coil and the leg tube 5, austenitic stainless steel (for example, 18-8 stainless steel) is used from the viewpoint of allowable stress (creep strength), corrosion resistance (pipe outer surface side), and steam oxidation resistance. The dimensions (tube outer diameter, wall thickness) are determined from the thermal area, pressure loss conditions of the internal fluid (water vapor), and the like.

  When attention is paid to the implanted welded portion 6 of the stub tube 3 to the header 2, an axial stress (X1) acts as shown in FIG. 10, and there is a potential for cracking in the weld heat affected zone. The present invention aims to prevent this cracking, and its function will be described below.

  FIG. 5 is a characteristic diagram showing the relationship between the thickness of the stub tube 3 and the generated stress (axial stress: axial force due to internal pressure + bending stress due to its own weight). This figure shows tubes a, b, c, and d with the same inner diameter and gradually increased thickness. Tube a is the same thickness as leg tube 5, tube b is 1.6 times thicker than leg tube 5, and tube c is 2.2 times thicker than leg tube 5. The tube body d has a wall thickness of 2.8 times the wall thickness of the leg tube 5.

  As is clear from this figure, by increasing the thickness of the stub tube, the axial stress due to internal pressure can be reduced by the effect of increasing the cross-sectional area, and the bending stress due to its own weight can also be reduced by the effect of increasing the cross-sectional secondary moment. . On the other hand, since the creep rupture strength greatly depends on the magnitude of the stress, the life extension effect is great with a slight reduction in stress.

  If the thickness of the stub tube is less than 1.2 times the thickness of the leg tube, the life of the stub tube's implanted weld will be longer than 100,000 hours, which is the basis for setting the allowable stress even with axial stress due to internal pressure alone. On the other hand, if the thickness of the stub tube exceeds three times the wall thickness of the leg tube, the distance between the stub tubes will be shortened, making implantation welding difficult, so the thickness of the stub tube will be reduced. By enlarging the thickness within the range of 1.2 to 3.0 times, preferably 1.7 to 2.3 times the wall thickness, it is possible to achieve a significant improvement in the life of the implanted welded part and realistic welding work. However, it became clear from the various experimental results of the present inventors. For example, by making the stub tube thickness twice that of the leg tube, the creep rupture life can be improved by about 10 to 20 times, and the crack generation life can be designed to be 300,000 to 600,000 hours. It becomes.

  As shown in FIG. 4, a stub tube (12Cr steel) 3 with an increased outer diameter and thickness and a leg tube (austenitic stainless steel) 5 with a smaller outer diameter and thickness change the outer diameter in the middle of the axial direction. By using the transition piece 4 that has been made, the stub tube (12Cr steel) and the leg tube (austenitic stainless steel) 5 can be smoothly connected. Furthermore, since the wall thickness is large, the strength of the welded heat affected zone on the 12Cr steel side in the welded portion 7 of the transition piece 4 with the stub tube (12Cr steel) 3 can be improved.

As shown in FIG. 4, the transition piece 4 includes a thick tube portion 4 a having the same inner diameter and the same thickness as the stub tube 3, a thin tube portion 4 c having the same inner diameter and the same thickness as the leg tube 5, The outer diameter changing tube portion 4b has an outer diameter changed so that the wall thickness gradually increases from the tube portion 4c to the thick tube portion 4a. The ratio of the outer diameter change of the outer diameter changing pipe portion 4b is the idea of a 1/3 gradient conventionally used to reduce the stress concentration rate, that is, from the outer diameter of the thick pipe portion 4a to the thin tube portion. A method of making the length longer than three times the value obtained by subtracting the outer diameter of 4c and dividing by 2 is practical.
The material of the transition piece 4 is austenitic stainless steel, which is the same material as the leg tube 5, and the creep rupture strength of the welded portion 8 of the transition piece 4 and leg tube 5 is the same as that of the base material (stainless steel). Therefore, it is possible to avoid a decrease in weld strength, which is a problem with 9Cr steel and 12Cr steel.

  In the above-described embodiment, the welded / stub tube welded structure using 12Cr steel has been described. However, for example, a welded tube / stub tube welded structure using 9Cr martensitic stainless steel other than 12Cr steel is also used. There is a potential for cracking at the welded portion, and the present invention is applicable.

  FIGS. 6 and 7 are views showing a second embodiment of the present invention, FIG. 6 is a front view showing the attachment state of the header and the leg tube, and FIG. 7 is an enlarged sectional view of a portion B shown in FIG. is there.

  In this embodiment, the difference from the first embodiment is that a panel is configured by arranging a leg tube 5 on a header 2 installed in the furnace width direction without using the manifold 1.

  Although not shown in the figure, the third embodiment of the present invention has a structure in which the penetrating portion of the leg tube 5 with the ceiling wall 12 is restrained by an expansion or a casing. In this case, thermal stress due to the temperature difference generated between the tubes is generated instead of the stress due to its own weight. However, this thermal stress can be kept low, and the proof stress can be improved.

  Although the fourth embodiment of the present invention is not shown, automatic welding is enabled by elongating the stub tube 3 to a length applicable to the automatic welding machine. For automatic welding, it is necessary to rotate the welding torch. By making the stub tube 3 longer, the gap between the stub tubes 3 is widened, and an automatic welding machine can be applied. The length of the stub tube 3 to which the automatic welder can be applied is preferably 100 mm or more. However, if the stub tube 3 is too long, there is an adverse effect such as an unnecessary weight increase. A suitable upper limit of length is about 150 mm.

It is a perspective view which shows the attachment state of the manifold which concerns on the 1st Embodiment of this invention, a header, and a leg tube. It is a partially expanded perspective view of the attachment state of the manifold, the pipe holder, and the leg tube. It is a side view which shows the attachment state of the manifold, a header, and a leg tube. It is a partial cross section figure which shows the attachment state of the nozzle, a stub tube, a transition piece, and a leg tube. It is a characteristic view which shows the relationship between the thickness of a stub pipe | tube, and an axial direction stress. It is a front view which shows the attachment state of the header and leg tube which concern on the 2nd Embodiment of this invention. It is an expansion perspective view of the FIG. 6B section. It is a perspective view which shows the state which covered the leg tube etc. with the box casing. It is a figure for demonstrating the axial direction stress which generate | occur | produces in the welding part with the header of a stub pipe. It is an expanded sectional view of the FIG. 9A part. It is a figure for demonstrating the mechanical stress reduction method of a stub pipe welding part. It is a figure for demonstrating the other mechanical stress reduction method of a stub pipe welding part.

Explanation of symbols

  1: manifold, 2: pipe, 3: stub tube, 4: transition piece, 4a: thick tube portion, 4b: outer diameter changing tube portion, 4c: thin tube portion, 5: leg tube, 6: stub tube welding Section: 7: Welded portion of transition piece with stub tube, 8: Welded portion of transition piece with leg tube, 9: Box casing, 12: Ceiling wall.

Claims (8)

A tube / stub tube in which a stub tube of the same material is implanted and welded to a tube made of 9Cr-12Cr steel containing W, Mo, Nb and V, and this stub tube is connected to the leg tube via a transition piece. In the welded structure,
The inner diameter of the stub tube, transition piece, and leg tube is substantially the same, and the wall thickness of the stub tube is increased in the range of 1.2 to 3.0 times the wall thickness of the leg tube. / Stub tube welded structure. The welded / stub tube welded structure according to claim 1, wherein the transition piece for connecting the stub tube and the leg tube is:
A thin tube portion having the same inner diameter and the same thickness as the leg tube, a thick tube portion having the same inner diameter and the same thickness as the stub tube, and a thickness gradually from the thin tube portion to the thick tube portion. A welded / stub tube welded structure comprising an outer diameter varying pipe portion having an outer diameter changed so as to be thick.   2. The welded / stub tube welded structure according to claim 1, wherein the weld and the stub tube are made of the 9Cr-12Cr martensitic stainless steel, and the transition piece and the leg tube are austenitic stainless steel. A welded / stub tube welded structure characterized by comprising:   4. A welded / stub tube welded structure according to claim 3, wherein the stub tube and the transition piece are welded with a nickel-based alloy material.   3. The welded / stub tube welded structure according to claim 2, wherein the length of the outer diameter changing tube portion of the transition piece is 2 by subtracting the outer diameter of the thin tube portion from the outer diameter of the thick tube portion. A welded / stub tube welded structure characterized by being at least three times larger than the divided value.   6. The welded / stub tube welded structure according to claim 1, wherein the length of the stub tube is 100 mm or more.   6. A boiler apparatus comprising a pipe holder / stub pipe welded structure in which a stub pipe is implanted and welded to a pipe holder of a superheater, wherein the pipe holder / stub pipe welded structure is a pipe according to any one of claims 1 to 5. A boiler device characterized in that it is a close / stub tube welded structure. The boiler device according to claim 7, wherein the leg tube is slidable with a gap provided in the ceiling wall penetrating portion,
A boiler device, wherein a series of tube bodies from the stub tube to the leg tube are attached to the tube holder, and the tube body group is covered with a box casing.

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