JPH1030897A - Boiler high temperature pipe and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a boiler high temperature pipe a manufacturing method thereof, which is not corroded even when it comes in contact with a high temperature gas including various harmful components and prevents the generation of erosion. SOLUTION: A boiler high temperature steel pipe 1 is provided with a coating layer 6 on the outside surface of a stainless steel pipe 2 where Ni alloy including Cr or Mo is welded with the coating layer in a specified thickness. The composition of the Ni alloy includes 15 to 20wt.% of Cr, 9 to 15wt.% of Mo and the rest of Ni. The high temperature steel pipe 1 includes the serpentine-formed steel pipe 2 having the coating layer 6 in an area in contact with a high temperature gas out of straight running parts 2 and or curved parts 2b of the high temperature steel pipe. The manufacturing method of the boiler steel high temperature steel pipe proposed by this invention comprises an overlay welding process which overlays the Ni alloy in a desired area in the longitudinal direction with a specified thickness and a bending process which bends the steel pipe 2 in U shape.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-temperature pipe used for a steam pipe or a hot water pipe provided in a boiler.
In particular, the present invention relates to a high-temperature pipe that comes into contact with a high-temperature gas containing a component that easily causes corrosion and the like, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Generally, meandering hot water pipes and steam pipes are provided in a boiler to contact hot gas heated by combustion and raise the temperature of water and steam flowing through the boiler. . On the other hand, as the use of the boiler becomes widespread, the high-temperature gas used often contains a component which easily causes corrosion or the like in the pipe. For example, in a factory that incinerates garbage, in order to make effective use of the heat of the incinerated gas, high-temperature gas after incineration is passed through the boiler, and a meandering hot water pipe or steam that is piped perpendicular to the gas flow is used. It is in contact with the tube. That is, as shown in FIG. 3, the gas incinerated in the incinerator F or the gas from the rotary kiln K that heats the incinerated ash from the surroundings is supplied to the vertical boiler B as indicated by the arrow. When ascending on one side and descending on the other side, a meandering steam pipe P
And heats the steam S flowing through the inside.
Note that D in the figure indicates a discharge portion of the incinerated ash residue, E indicates a dust removing device that removes and adsorbs fine powder and the like from the gas passing through the boiler B, and C indicates a chimney that discharges such gas.

[0003] When refuse and the like are incinerated at a high temperature, soot adheres to the surface of the steel pipe constituting the steam pipe P, thereby lowering the efficiency of heat exchange and causing chlorine, oxygen,
Alternatively, there is a problem that sulfur or a compound thereof corrodes the surface of the steel pipe. The above-mentioned soot adheres much to the steam pipe P at the site where the gas contacts first. On the other hand, chlorine, oxygen, sulfur, or oxides thereof in the above-mentioned gas are contained in the steam pipe P.
Corrodes the surface. In order to solve this, it has been attempted to spray a heat-resistant, corrosion-resistant alloy steel or the like on the surface of the steel pipe, but only a porous coating layer is obtained, and the corrosion resistance to components in the gas is insufficient. there were.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a high-temperature pipe for a boiler which is hardly corroded even when it comes into contact with the high-temperature gas, and a method of manufacturing the same. .

[0005]

According to the present invention, in order to solve the above-mentioned problems, a stainless steel pipe is used for a pipe provided in a boiler, and a coating layer of a Ni alloy containing Cr and Mo is formed on the surface of the pipe by solid solution. It was made with the idea of making it adhere more closely. That is, the high temperature pipe for a boiler of the present invention is:
A stainless steel pipe is provided with a coating layer formed by welding a Ni alloy containing Cr and Mo to a predetermined thickness on an outer peripheral surface thereof.
The Ni alloy is 15-20 wt% Cr, 9-15 wt% M
o, the balance being Ni. The reasons for limiting the range of each element are as follows. Ni stands for chloride resistance, oxidation resistance,
And at least 40% by weight or more to obtain the above-mentioned properties. Cr is added in an amount of 15 wt% or more to provide heat resistance and corrosion resistance. On the other hand, when the content exceeds 20% by weight, the above-mentioned properties are saturated, the cost is increased, and disadvantages such as cracks start to be generated in the overlay welding portion. Further, Mo is added in an amount of 9 wt% or more in order to improve corrosion resistance in combination with Cr.
If it exceeds 5% by weight, there is a risk of weld cracking, so the content was made less than that. In some cases, 4 wt% or less of W is further added for improving corrosion resistance.

[0006] The coating layer is provided over substantially the entire length of the stainless steel pipe, or provided at a desired position in a linear portion and / or a curved portion at an arbitrary position. Further, for a boiler provided with the coating layer on a portion of a straight portion and / or a curved portion of a stainless steel tube having a meandering shape, and a portion of the straight portion and / or a curved portion that comes into contact with a high-temperature gas or the like that contacts the steel tube, in particular, Hot pipes are also included. Further, in order to obtain the above-mentioned high temperature pipe for boilers, N
The present invention also proposes a manufacturing method including a step of overlay-welding the i-alloy to a predetermined thickness and a step of bending the steel pipe into a U shape or the like. The order of the welding and bending is arbitrary, but in the longitudinal direction of the long stainless steel pipe, the Ni alloy is welded to a predetermined thickness only on the required portion, and then on the portion excluding the welded portion. In this case, it is desirable to bend the stainless steel pipe into a U-shape or the like sequentially at a plurality of locations in opposite directions. The overlay welding is a so-called plasma powder welding in which a metal powder is supplied together with an inert gas, the metal powder is melted by a high-temperature plasma flow from the center, and the surroundings are covered with a shielding gas using a plasma torch. (PPW)
It is desirable to use

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below together with the operation thereof. FIG. 1A is a front view showing the whole of a high-temperature pipe 1 according to the present invention, which is piped into the above-mentioned vertical boiler B. The pipe 1 has a stainless steel pipe 2 made of, for example, SUS304 in a plurality of locations, and is sequentially turned upside down. It is bent into a U-shape to exhibit a meandering shape as a whole. The meandering stainless steel pipe 2 has an inlet 3 for steam S to be heated at the lower right in the figure and an outlet 4 at the upper right, and the horizontal straight portions 2a are located at almost middle height positions. Is provided with a separating portion 5 having an increased interval. Such a pipe 1 is
A plurality of pipes are provided in the boiler B in parallel in the front-rear direction in FIG. The high-temperature gas coming into contact with the high-temperature pipe 1 is supplied so as to descend downward from above in FIG.

A coating layer 6 of a Ni alloy containing Cr and Mo is provided on the surface of the straight portion 2a and the curved portion 2b of the stainless steel tube 2. As shown in the cross-sectional view of FIG. 1B, the coating layer 6 coats the entire outer peripheral surface of the straight portion 2a or the curved portion 2b of the steel pipe 2 with the Ni alloy by overlay welding described later. Also, it is melted into the outer surface of the steel pipe 2 and integrated with the metallographic structure. The coating layer 6 is built up so as to have a thickness equal to or greater than the thickness of the steel pipe 2 as shown in a partially enlarged cross section of FIG. By the way, when the thickness of the stainless steel pipe 2 is 4 mm,
The thickness of the coating layer 6 is 4 mm even at the valley 6b between the beads 6a.
Overlay welding is performed to achieve the above thickness.

FIG. 2 relates to a method for manufacturing a high-temperature pipe 1 according to the present invention, and FIG.
(Diameter 50 mm, wall thickness 4 mm). A desired portion of the steel pipe 2 is coated with the Ni alloy. FIG. 1B shows an aspect of overlay welding for obtaining the coating. First, the stainless steel pipe 2 is rotatably mounted on a plurality of pairs of rollers (not shown), and is driven at a constant speed (1.
5 revolutions per minute). Then, the plasma torch 10 for powder overlay welding is arranged close to a predetermined position of the steel pipe 2. The torch 10 puts the Ni alloy powder (average particle size: 95 μm) in an inert gas flow such as argon, melts it into a high-temperature plasma flow from the center, and
Weld on the surface. Also, the torch 10 has a concentric multilayer cross-sectional structure such that the periphery thereof is covered with an inert shielding gas flow. The plasma torch 10 is held by a feeding means (not shown), and the stainless steel pipe 2
Along the surface at a constant speed (210 mm / min).

Further, the welding conditions are as follows: the supply amount of the Ni alloy powder is 40 g / min, the flow rate of the inert gas for supplying this powder is 1 liter / min, the plasma flow temperature is about 5000 ° C., and only one pass is used. The bead width was 10 mm and the height was 4.1 mm, and the valley where the beads overlapped was 0.1 mm lower than the top of the bead, but the thickness was 4.0 mm. On the other hand, the moving speed of the steel pipe in the longitudinal direction is 1
It was 2 mm / min. Two types of Ni alloy powder were used.
One composition is 16.5 wt% Cr-14.8 wt% Mo-
The remaining Ni was used. Other elements are C; 0.01 wt%,
S; 0.004 wt%, Fe; 0.41 wt%, W; 2.5 wt%. The addition of such W is for improving corrosion resistance and erosion resistance. The other Ni alloy powder is 1
A powder having a composition of 9% Cr-12wt% Mo-remaining Ni was used. A coating layer 6 of about 800 mm in length of each Ni alloy was provided at a plurality of positions on the two stainless steel pipes 2 by the overlay welding.

Next, as shown in FIG.
The stainless steel pipes 2 were sequentially bent into a U-shape except for the portions having the above, and the separation portions 5 were also formed in the middle, whereby two high-temperature pipes 1 were obtained. The bending is performed in such a manner that a plurality of steel balls or powders connected to one another are densely filled in the hollow portion so that the circular hollow portion does not become flat in the U-shaped portion of the steel pipe 2. . FIG. 2 (D)
In the cross section taken along the line DD in FIG. 3C, the coating layer 6 of the Ni alloy is provided on the straight portion 2a of the steel pipe 2 and is not affected at all by the bending. Incidentally, the coating layer 6 is formed by the straight portion 2a of the long stainless steel pipe 2 as described above.
When overlay welding is used, accurate and quick welding can be performed. In addition, in the part which the said steel pipe 2 bent so that it might curve gently,
Even if bending is performed after the above-mentioned overlay welding, the weld bead is less likely to be deformed or damaged. However, in the U-shaped bent portion, the weld bead can be deformed and damaged. Therefore, in order to provide the coating layer 6 in such a portion, after performing the bending process first, the overlay welding according to the bent shape is performed. It is desirable to apply.

Next, two high-temperature pipes 1 coated with the two types of Ni alloy powder of the present invention obtained by the above-mentioned method and a carbon steel (STB410) steel pipe were used. A comparative example in which a stainless steel pipe (SUS310S) was fitted was used under continuous operating conditions under the same conditions as in the same vertical boiler B shown in FIG. did. Incidentally, the temperature of the steam S is 250 to 300 ° C. at the inlet 3 of the pipe 1, but is raised to 350 ° C. or more at the outlet 4. The high-temperature gas that heats the steam pipe P is gas that has been burned from a garbage incinerator F or the like similar to that shown in FIG. 3, and contains chlorine, oxygen, sulfur released from various garbage, and Contains harmful components to steel pipes such as oxides, chlorides and sulfides. As a result, even when the two pipes 1 of the present invention were subjected to continuous heating for one year for a long period of time and cooling due to shutdown, no change was observed in the coating layer 6 and the deteriorated portions such as corrosion and erosion were observed. There were few.
On the other hand, in the pipe of the comparative example, a corroded portion was observed 150 days after the pipe was laid, and after 180 days, traces of erosion probably due to chlorides, sulfides, and the like were observed. From this result, the coating layer 6 used for each pipe 1 of the present invention was formed into a carbon steel pipe of a comparative example by the characteristics of the Ni alloy and the melting and welding to the surface of the stainless steel pipe 2 by overlay welding. Compared with the pipe in which the stainless steel pipe was inserted, it was found that the corrosion resistance and the erosion resistance were remarkably excellent.

FIG. 2 (E) is a cross-sectional view showing another example of welding of the coating layer 6. The high-temperature gas flow is directly applied to the surface of the stainless steel pipe 2 by adjusting the conditions of the overlay welding. Shown is a thicker weld bead on the contacting surface side. FIG. 2 (F) similarly shows a case in which a thick coating layer 6 is provided on the surface of the steel pipe 2 directly contacting the high-temperature gas flow, and the coating on the opposite surface is omitted. These embodiments are also included in the pipe of the present invention.

The present invention is not limited to the above embodiment. As the material of the steel pipe 2, various austenitic stainless steels other than SUS304, or various stainless steels such as a ferrite type and a two-phase type can be used. In the overlay welding, a long stainless steel pipe can be fixed, and the plasma torch can be slid in the longitudinal direction of the steel pipe while rotating around the circumference. The welding material may be TIG welding or MIG welding using a welding rod or wire of the Ni alloy instead of metal powder. And, depending on the thickness of the coating layer and the material of the stainless steel pipe, a multi-layer cladding of two or more passes is performed, or a portion where the coating layer is bent into a U shape after the overlay welding is thinned. However, this also includes overlay welding. Further, heat treatment is appropriately performed before and after the overlay welding to prevent poor welding.

The cross-sectional shape of the stainless steel pipe includes not only a circular cross section but also an elliptical cross section. Further, the bent shape may be a U shape, a concave shape, an S shape, or a V shape. The uses thereof include not only steam and hot water, but also high-temperature pipes installed in a boiler for heating a heat medium such as various oils and gases. Furthermore, the type of boiler to which high-temperature pipes are connected is not limited to the type that exchanges heat with high-temperature gas from a garbage incinerator, but the type that exchanges heat with combustion gas such as heavy oil, natural gas, coal, pulverized coal, and coke. Can also be applied.

[0016]

As described above, the high temperature pipe for a boiler of the present invention has a coating layer formed by welding a Ni alloy containing Cr and Mo to a predetermined thickness on the outer peripheral surface of a stainless steel pipe.
Even if it comes into contact with various high-temperature gases for a long time, corrosion does not occur and erosion can be prevented. Therefore, the durability of the pipe can be greatly improved, and maintenance can be significantly reduced. In addition, since the coating layer of the Ni alloy is provided by overlay welding, at a desired position on the surface of the stainless steel pipe,
A coating layer of the required length and thickness can be easily formed,
When overlay welding of alloy powder using a plasma torch,
A coating layer with excellent welding performance can be obtained accurately and quickly.

[Brief description of the drawings]

FIG. 1A is a front view of a high-temperature pipe for a boiler of the present invention,
(B) is a partially enlarged cross-sectional view of (A), and (C) is an enlarged cross-sectional view of a portion indicated by a dashed line in (B).

2A is a schematic view of a stainless steel pipe as a raw material, FIG. 2B is a schematic view showing an aspect of build-up welding to the steel pipe, FIG. 2C is a schematic front view of a pipe bent after welding, (D) is a DD sectional view in (C), and (E) and (F) are sectional views showing other covering modes.

FIG. 3 is a schematic view showing a process of a garbage incineration plant.

[Explanation of symbols]

 1 High-temperature pipe 2 Stainless steel pipe 2a Linear section 2b Linear section 6 Curved section 6 ............ Coating layer 10 Plasma torch

Claims (6)

[Claims] 1. An outer peripheral surface of a stainless steel pipe is coated with Cr and Mo.
A high-temperature pipe for a boiler, comprising a coating layer obtained by welding a Ni alloy containing Ni to a predetermined thickness. 2. The method according to claim 1, wherein the Ni alloy is 15 to 20 wt% Cr,
The high temperature pipe for a boiler according to claim 1, wherein the high temperature pipe has a composition of 9 to 15 wt% Mo and the balance of Ni. 3. The stainless steel tube has a meandering shape,
The high-temperature pipe for a boiler according to claim 1 or 2, wherein the coating layer is provided in a portion of the straight portion and / or the curved portion that comes into contact with the high-temperature gas or the like. 4. A step of overlay welding a Ni alloy containing Cr and Mo to a predetermined thickness on a required portion in a longitudinal direction of the stainless steel pipe, and a step of bending the steel pipe into a U shape or the like.
A method for producing a high-temperature pipe for a boiler, comprising: 5. A welded portion of the Ni alloy is welded to a predetermined thickness only on a required portion in a longitudinal direction of a long stainless steel pipe, and the stainless steel pipe is formed in a U-shape or the like at a portion other than the welded portion. 5. The method for producing a high-temperature pipe for a boiler according to claim 4, wherein the pipe is sequentially bent at a plurality of locations in opposite directions. 6. The build-up welding is a welding using a plasma torch that supplies a metal powder together with an inert gas, melts the metal powder with a high-temperature plasma flow from the center, and covers the periphery with a shielding gas. 6. The method for producing a high-temperature pipe for a boiler according to 4 or 5.