JPH1122872A - Pipe fitting and method for joining pipe using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pipe fitting which is made of a material that is likely to have weld cracks, and a method for connecting the pipes. SOLUTION: This fitting part A includes a pair of fitting parts A1, A2, which comprise pipes 1, 2, having respective pipe ends 1A, 2A which are smaller in outside diameter near their pipe end faces 1a, 2a than at other parts, and sleeves 4, 5 surrounding at least the pipe ends and welded to the outer peripheries of the pipes 1, 2 at their respective rear ends 4b, 5b, and which are welded together at the ends 4a, 5a of the sleeves 4, 5 with the pipe end faces engaged with each other in such a manner as to be capable of floating in the directions of the pipe axes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pipe joint and a method of connecting the pipe using the same, and more particularly, to a pipe joint made of a material which is susceptible to welding cracks and used for transporting hot particles. The present invention relates to a joint and a pipe connecting method using the same.

[0002]

2. Description of the Related Art Since the combustion gas of a thermal power plant operating with pulverized coal as a fuel source contains hard coal ash, the coal ash is separated and recovered as follows. That is, the combustion gas is led to a cyclone, where coal ash is separated. The coal ash after separation has a temperature of 6
Since it has a high temperature of about 50 ° C., it is subsequently cooled to a temperature of about 300 ° C. through a piping structure connected to a cyclone and cooled by an air flow, and then discharged out of the system.

[0003] Here, the above-mentioned piping structure functions as a kind of heat exchanger, and usually, in terms of space saving, straight pipes are connected to each other using a U-shaped pipe or a T-shaped pipe.
A bent structure is used as a whole. And this piping structure is generally assembled by carrying necessary pipe materials to an installation location, and by connecting workers to each other at the installation location.

[0004] In the case of this piping structure, it is necessary that the connecting portion of each pipe has an airtight structure. If the airtightness is not achieved, an inconvenience such as leakage of high-heat coal ash from the connection may occur. Further, since the coal ash flowing inside each pipe is a high-heat granular material having high hardness, it is necessary that the material of the pipe used has excellent wear resistance at high temperatures. This is because in the case of a material having poor abrasion resistance, the wear of the tube wall proceeds in a short period of time, so that the operating life is shortened.

When assembling a pipe structure that satisfies the above requirements on site, a pipe made of a material having excellent wear resistance is butted at the pipe end face, and the joint is welded to form a joint between the pipes. It can be said that an airtight structure is preferable as an assembling operation. By the way, for example, 2.8%
C-27% Cr-Fe, 1.8% C-17% Cr-1.2
A tube manufactured by centrifugally casting a high chromium cast iron such as% Mo-Fe is known as a transport tube for casting sand. This high chromium cast iron has a high Vickers hardness (Hv) of 600 to 800 and is a material excellent in wear resistance.

[0006] However, this high chromium cast iron has a large carbon equivalent, and therefore is a material that is liable to cause hot cracking during welding. Therefore, it is extremely difficult to assemble the pipe structure by welding pipes of this material to each other. Therefore, when assembling a piping structure in which pipes of this material are connected to each other, the pipe ends of the pipes are butted as a flange structure, and a fastener is arranged outside the abutting portion to form a pipe structure. A method in which the flanges are tightened in the pipe axis direction and airtightly connected can be adopted.

[0007] However, it is inappropriate to apply the above-described connection structure to the piping structure that is the object of the present invention. The reason is that in the case of the piping structure targeted by the present invention,
This is because a high-heat granular material such as coal ash flows in the pipe.
That is, the high heat of the coal ash flowing in the pipe causes the inner wall side of the pipe to thermally expand, while the outer wall side in contact with the relatively low-temperature air flow does not undergo much thermal deformation. A force that opens outward is generated. Under the influence, the tightened state of the fastener is relaxed, and the airtightness of the connection portion is broken. As a result, coal ash may leak from the connection portion and cause a jetting accident.

Therefore, in the case of the above-mentioned flange structure, it is necessary to retighten. If the retightening cannot be performed, for example, the flange structure is arranged in a pressure vessel of a pressurized fluidized-bed boiler. In such cases, it cannot be adopted. In addition, if a flange structure is used for connecting the tubes in the heat exchanger, the flange portion becomes an extra space, so that the density of the tubes is reduced and the overall thermal efficiency is reduced.

[0009] Since the production cost of a pipe with a flange is high in the first place, there is a problem that the piping structure using this flange structure is disadvantageous in cost.

[0010]

DISCLOSURE OF THE INVENTION The present invention relates to a high-chromium cast iron as described above, which is made of a material which is susceptible to hot cracking during welding. It is an object to provide a pipe joint effective for connecting to a pipe and a pipe connecting method using the same.

[0011]

Means for Solving the Problems In the course of intensive studies in order to achieve the above-mentioned object, the present inventors have found that, for example, the above-mentioned high chromium cast iron is susceptible to hot cracking during welding. Under such conditions, attention is paid to the fact that welding is possible with a nickel-based alloy such as Inconel 600 (trade name), and by utilizing this fact, the pipe joint of the present invention and the The method of connecting the pipes used was developed.

That is, a pipe joint according to the present invention has a pipe having a pipe end whose outer diameter near the pipe end face is smaller than other portions, and a pipe which covers at least the pipe end and has a rear end. A pair of joints consisting of a sleeve welded to the outer circumference of the pipe are welded at the tip of the sleeve, and the pipe end faces of the pipes are engaged movably in the pipe axis direction. A pipe fitting is provided, and in the present invention,
After enclosing at least the tube end portion of a tube having a tube end portion whose outer diameter near the tube end surface is smaller than the other portion and externally fitting the sleeve to the tube, the entire temperature range is 300 to 600.
At a temperature of 900 to 1150 ° C. Then, while the tube is held in the temperature range, the rear end of the sleeve is fillet-welded to the outer periphery of the tube, and then gradually cooled, and the whole is normalized at a temperature of 900 to 1150 ° C. Tempering at a temperature of 400 to 600 [deg.] C., and then joining the ends of the sleeves and then welding the joints.

[0013]

FIG. 1 is a sectional view showing a pipe joint A of the present invention after a pair of joints A1 and A2 are connected. FIG. 2 is a sectional view showing each joint A1 and A2. is there. In FIG. 1, each of the tube ends 1A and 2A of a pair of tubes 1 and 2 to be connected has an outer diameter smaller than other portions. The pipe end faces 1a, 2a of the pipe end parts 1A, 2A are engaged with each other so as to mesh with each other as shown in the figure, and a groove is formed between the pipe end faces 1a, 2a in the circumferential direction of the pipe. Is formed.

On the outer circumference of each of the tubes 1 and 2, sleeves 4 and 5 having a length covering at least the respective tube ends 1A and 2A are arranged, and rear ends 4b and 5b of each sleeve are described later. Is fixed to the outer periphery of each of the tubes 1 and 2 via the fillet weld 6. The distal ends 4a, 5a of the sleeves 4, 5 are welded. Therefore, in the case of this pipe joint A, the pipes 1 and 2 to be connected are not welded but are merely engaged with each other. Therefore,
Each pipe is movable in the pipe axis direction. The hermetic structure is also ensured by sleeves 4, 5 whose rear ends are welded to the outer circumference of the tube and whose ends are welded to each other. One of the structural features of the pipe joint A is that a strip-shaped clearance 7 is formed in the pipe circumferential direction between the pipe ends 1A and 2A and the sleeves 4 and 5 after welding. .

The reason why the pipe joint A has such a structure will be described below. First, the pipe targeted in the present invention is a pipe made of a material which is easily weld-cracked and practically difficult to weld, such as the high chromium cast iron described above. Therefore,
Since the pipe end faces 1a and 2a cannot be directly welded in-situ, the pipe end faces are merely engaged.

In this case, when the above-mentioned high-temperature granular material flows into the tubes, the tubes 1 and 2 thermally expand in the axial direction of the tube. ,
A predetermined clearance 3 is formed between 2a and engaged so as to be freely movable in the tube axis direction. The hermetic structure of the pipe joint is ensured by the sleeves 4 and 5. In this case, when welding the distal ends 4a and 5a of the sleeves 4 and 5, in order to avoid a thermal effect on the tube ends 1A and 2A of the tubes 1 and 2 located inside, the tube ends 1A and 5A are welded. A clearance 7 is formed between the sleeves 4 and 5 by reducing the diameter of 2A.

The pipe joint A having such a structure is effective for connection of the following pipes. For example, if the C content is 0.
A material that easily causes hot cracking at the time of welding at 35% by weight or more, for example, JIS SKD61, JIS SKD1
1. Tube made of high-speed steel, powdered high-speed steel, etc.
In particular, C: 2.0-3.3% by weight, Cr: 23.0-3
0.0% by weight, Si: 1.5% by weight or less, Mn: 2.0% by weight or less, P: 0.10% by weight or less, S: 0.06% by weight
Hereinafter, it is effective for a high chromium cast iron pipe represented by a composition of not more than 1.2% by weight of Cu, not more than 2.5% by weight of Ni, and not more than 3.0% by weight of Mo.

This high chromium cast iron pipe has a hardness of HRC 56 to 64 and is excellent in abrasion resistance, so that it is suitable as the above-mentioned coal ash transport pipe. In addition, since centrifugal casting is relatively easy to manufacture, there is a great economical advantage that it is inexpensive. The sleeve is preferably made of a material whose coefficient of thermal expansion is close to the coefficient of thermal expansion of the tube and which has excellent weldability. More specifically, F having a C content of less than 0.35% by weight.
e, Ni, and Co-based alloys, for example, Inconel 600, Inconel 625, and the like are preferable examples.

When assembling the pipe joint A, first, joints A1 and A2 are manufactured at a place different from the assembly site. The manufacturing method will be described below. First, the pipes 1 and 2 to be connected are annealed, and then the pipe ends 1A and 2A.
Is machined. Annealing is performed in a temperature range of 700 to 920 ° C.

For example, when the tube 1 is made of high chromium cast iron having the above-described composition, specifically, the tube 1 is heated at a heating rate of 200 ° C.
/ Hr at a temperature of 880 ± 10 ° C., hold at that temperature for 3 hours, and cool at a rate of 50 ° C./hr of 780 ± 10 ° C.
After cooling to a temperature of 700 ° C., maintaining at that temperature for 3 hours, it is cooled again to 700 ° C. at a temperature rate of 50 ° C./hr, and then allowed to cool in the air.

By this heat treatment, the pipe 1 is softened at the same time as the processing distortion is removed. For example, 2.8% C-27
% Chromium cast iron at room temperature, HRC5
Although the hardness is as high as 6 to 64, it is softened to about 35 to 45 HRC by heating in the above temperature range. When the heating temperature is lower than 700 ° C., the softening is not sufficient, so that hot cracking is likely to occur at the time of fillet welding to the next sleeve, and when heating to a temperature exceeding 920 ° C., for example, the high chromium cast iron In this case, even if normalizing and tempering are performed after fillet welding to the sleeve described later, there is a problem that the pipe 1 does not become hard.

The pipe end faces 1a and 2a of the pipes 1 and 2 softened by the heat treatment as described above are cut into a shape such that they mesh with each other, and the outer circumferences of the pipe ends 1A and 2A are cut into a predetermined shape. To reduce the diameter by a predetermined dimension. At that time, the size of the clearance 3 between the pipe end faces 1a and 2a is
It is determined in consideration of the amount of thermal expansion due to the high-temperature powder flowing in the pipe.

Next, the sleeve 4 is fitted onto the pipe 1 from the pipe end 1A of the processed pipe 1. At this time, the length of the sleeve 4 is longer than the length of the tube end 1A, and it is necessary that the sleeve 4 surely covers the tube end 1A. Then, the whole is heated in a temperature range of 300 to 600 ° C., and while maintaining the temperature, fillet welding is performed between the rear end 4b of the sleeve 4 and the outer periphery of the pipe 1 to form a fillet welded portion 6. I do.

During this fillet welding, the temperature of the pipe 1 is 300 ° C.
When the temperature is lower than the above, welding cracks occur frequently, and when the temperature is higher than 600 ° C., workability of a worker at the time of welding is deteriorated. Then, the whole is normalized at a temperature of 900 to 1150C, further tempered at a temperature of 400 to 600C, and then left to cool.

By this heat treatment, welding distortion is removed, the structure of the tube material is refined, and its mechanical strength such as toughness and hardness is improved. When the normalizing temperature is lower than 900 ° C., the above-mentioned effects are not exhibited, and when the normalizing temperature is higher than 1150 ° C., the hardness starts to decrease and the wear resistance deteriorates. When the tempering temperature is lower than 400 ° C., the hardness becomes too high to make the finishing work difficult, and when the tempering temperature is higher than 600 ° C., the pipe starts to soften.
For example, in the case of the above-mentioned chromium cast iron of 2.8% C-27% Cr-Fe, HRC57 and tube hardening are remarkable at a temperature of 500 ° C, but HRC45 at a temperature of 700 ° C.
But rather, it softens.

Finally, the butt end surface of the sleeve 4 is subjected to a finishing process, so that the pipe joint A1 (A2) shown in FIG.
Is manufactured. When assembling the pipe joint A shown in FIG. 1, the joint parts A1 and A2 manufactured as described above are carried into an assembly site, each is fixed to a predetermined support table, and the respective pipe axes are aligned. The tube end faces 1a, 2a and the distal ends 4a, 5a of the sleeve are butted. At this time, the tubes 1 and 2 are positioned by the distal ends 4a and 5a of the sleeve.

Then, for example, joint welding is performed on the distal end portions 4a and 5a of the sleeve, and the connection of the tubes 1 and 2 is completed. At this time, since the clearance 7 is formed inside the sleeve, the thermal effect on the pipe end by welding is reduced, and, for example, the pipe end does not crack.

[0028]

As is apparent from the above description, the pipe joint of the present invention is effective when applied to a case where a pipe made of a material which is susceptible to weld cracking is welded and connected on site. In particular,
It is useful when connecting high chromium cast iron pipe of 2.8C-27Cr-Fe on site, for example, it is useful as a pipe joint when assembling a pipe structure used in a hard coal ash separation process in a thermal power plant. is there.

According to the pipe connection method of the present invention, joints are manufactured so as not to cause welding cracks at a place different from the assembly site, and they are carried into the assembly site to assemble into a target piping structure. Is extremely practical.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a pipe joint A of the present invention.

FIG. 2 is a sectional view showing joints A1 and A2 used for a pipe joint A of the present invention.

[Explanation of symbols]

 1, 2 pipe 1A, 2A pipe end 1a, 2a pipe end 3 clearance between pipe ends 4, 5 sleeve 4a, 5a sleeve tip 4b, 5b sleeve rear end 6 fillet weld 7 sleeve and pipe end Clearance between departments

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI B23K 31/00 B23K 31/00 H 33/00 33/00 A C21D 9/08 C21D 9/08 F 9/50 101 9/50 101A C22C 38/00 302 C22C 38/00 302Z 38/58 38/58 C22F 1/00 626 C22F 1/00 626 691 691A 1/10 1/10 A

Claims (4)

[Claims] 1. A pipe having a pipe end whose outer diameter in the vicinity of the pipe end face is smaller than other portions, and at least the pipe end covered and a rear end welded to the outer periphery of the pipe. And a pair of joints comprising a set sleeve and a pair of joints are welded at a distal end of the sleeve, and the end faces of the pipes are movably engaged in the axial direction of the pipe. 2. The tube according to claim 1, wherein the tube comprises a hard-to-weld material having a C content of 0.35% by weight or more, and the sleeve comprises a Fe, Ni, Co-based alloy having a C content of less than 0.35% by weight. Item 7. The pipe joint according to Item 1. 3. The fitting of claim 1 wherein said tube comprises high chromium cast iron and said sleeve comprises Inconel 600. 4. A tube having a tube end whose outside diameter near the tube end face is smaller than other places is covered with at least the tube end and a sleeve is externally fitted to the tube, and then the whole is heated. After heating at a temperature range of 300 to 600 ° C., the rear end of the sleeve was welded to the outer periphery of the tube while the tube was maintained at the temperature range, and then gradually cooled.
A method for connecting pipes, comprising normalizing at 50 ° C., tempering at a temperature of 400 to 600 ° C., and butting the ends of the sleeve, and then welding the joint.