JPH07241683A - Composite steel tube and its manufacture - Google Patents

Abstract

PURPOSE:To provide an economic composite steel tube which is formed by clad-welding method, excellent in the corrosion resistance, the heat resistance and the wear resistance, and provided with two or more multi-cladded layers, and its manufacturing method. CONSTITUTION:A plurality of plasma arc torches 10 are arranged in a row above a steel tube 1 along its axis with the axis of the steel tube 1 kept horizontal, and the powdery filler metal fed through the torches is melted with the plasma arc generated by these torches as a heat source to carry out the clad- welding on the outer circumferential surface of the steel tube 1. The cladded layer 20 to be formed by each torch arranged in a row in laminated over the whole outer circumferential surface of the steel tube by moving the plasma torches 10 in the axial direction of the tube while the torches are turned around the tube axis of this steel tube 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a long composite steel pipe having excellent corrosion resistance, heat resistance and wear resistance, which is suitable as a steel pipe for a superheater for power generation using incineration heat for incineration, and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, various methods have been devised to incinerate dust such as combustible industrial waste and municipal solid waste and utilize the heat generated at that time. For example, waste incineration heat is used for district heating and hot water pools.
It is also used as a heat source for power generation, but both are 300
It only uses heat at relatively low temperatures below ℃. Combustion gases such as industrial wastes and municipal solid wastes contain extremely strong corrosive gases such as chlorides and sulfides, and also contain hard particles, so corrosion resistance and heat resistance to withstand these combustion gases It is indispensable to develop a metal material with excellent wear resistance in order to utilize the high temperature heat in waste incineration.

As for general municipal waste, the type and collection status of dust, such as the amount of garbage and paper, the type of plastics, the mixing ratio of them, the presence or absence of separate collection, varies from region to region, so when they are incinerated. The nature of the combustion gases in is extremely diverse. However, when viewed by region,
It is known that the corrosiveness of the combustion gas shows a certain tendency, such as in areas where there are a lot of chloride-based combustion gases and areas where it becomes a sulfide-based combustion gas. If so, it is possible to some extent to select a material suitable for it. The problem is that long-term trials are required before the corrosion tendency of such combustion gas becomes clear, and it is extremely difficult to select a material to be used during that time.

On the other hand, when utilizing waste incineration heat as a heat source for power generation, a steel pipe material for a superheater is desired to have a corrosion resistance at 400 ° C., preferably 550 ° C. or higher, to withstand the combustion gas thereof. Such materials include various nickel-based superalloys, but they are expensive and, as mentioned above, due to the difficulty in selecting the optimum material due to the variety of dust incineration gas, such superalloys are overheated. It must be said that it is an extremely uneconomical method to use it as a material for steel pipes.

From the viewpoint of economy, it is conceivable to use a low-alloy steel pipe or a stainless steel pipe, which is inexpensive, and to form a coating layer of a corrosion-resistant alloy on the outer peripheral surface thereof by a method such as overlay welding. However, even in this case, it is necessary to repeat the trial to select the optimum material, and if the steel pipe for the superheater is damaged during the trial process, it is necessary to stop the entire refuse incineration system to replace it. There is a problem that the economic loss is extremely large.

As a method for solving the above problem, it is possible to use a steel pipe having a plurality of coating layers each having different characteristics. For example, a Ni-16Cr-16Mo alloy which is said to have high corrosion resistance against corrosion by sulfides, and a Ni-2 which is said to have high corrosion resistance against corrosion by chlorides.
1Cr-9Mo alloy, 50Ni which is said to have high oxidation resistance
It is expected that the corrosion resistance effect will be exhibited in any one of the coating layers by using the steel pipe laminated and coated with -50Cr alloy or the like. By the way, in the case of a steel pipe for a superheater or the like, it is desirable that such a coating layer has a thickness of at least about 2 mm or more in order to exceed the heat resistance period of 5 years.
Since it is necessary to have good adhesion to the steel pipe material of the base, the overlay welding method is suitable. However, when it is attempted to form a plurality of overlay layers on a long steel pipe by the overlay welding method, it is necessary to take a complicated step for processing bends and bead marks generated during overlay welding, which is extremely expensive. There was a problem that it became a thing.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to obtain excellent corrosion resistance, heat resistance, and wear resistance formed by the overlay welding method. Another object of the present invention is to provide an economical composite steel pipe having two or more multilayer overlay layers and a method for producing the same.

[0008]

In order to solve the above-mentioned problems, (1) a composite steel pipe of the present invention is manufactured by a plasma overlay welding method using a plasma arc as a heat source and powder as a filler metal. In a composite steel pipe having a build-up layer formed on the outer peripheral surface, build-up welding is performed by a plurality of torches arranged in the axial direction of the steel pipe, and the build-up layer formed by each of the torches is a build-up welding. A plurality of build-up layers are successively laminated in accordance with the progress of 1. and each of the formed build-up layers is made of a metal or an alloy having a different composition. Further, (2) the method for producing a composite steel pipe of the present invention is
With the tube axis of the steel tube kept horizontal, a plurality of plasma arc torches are arranged in rows above the steel tube along the tube axis, and the plasma arc generated by this torch is used as a heat source. , Melting the powdered filler material supplied through the torch, and overlay welding on the outer peripheral surface of the steel pipe material, and the steel pipe material around the pipe axis relative to the plasma arc torch row. It is characterized in that a build-up layer formed by the torches arranged in a row is formed by laminating over the entire outer peripheral surface of the steel pipe material by moving in the pipe axial direction while rotating. To do.

In the composite steel pipe of the present invention, the coating layer is formed on the outer peripheral surface of the steel pipe material because the use of the composite steel pipe of the present invention is mainly for superheaters, and the corrosiveness generated when dust is incinerated. This is to protect the outer peripheral surface of the steel pipe that comes into contact with the strong, high-temperature combustion gas. The present invention can be applied to the inner surface of the steel pipe when the inner surface of the steel pipe needs to be coated depending on the application.

In the composite steel pipe of the present invention, the coating layer is formed by a plasma overlay welding method (hereinafter referred to as PPW method) using a plasma arc as a heat source and powder as a filler material. The reason is as follows. In the PPW method, the plasma of an inert gas such as argon is used to prevent the filler material from being oxidized.

Since the powder is used as the filler material, the overlay thickness can be easily adjusted. Since it is easy to adjust the melting depth of the base metal, it is possible to reduce the composition change of the weld metal caused by the base metal melting into the weld metal. This is an important point in the constitution of the present invention, and there is an advantage that even when a plurality of built-up layers are stacked, the characteristics of each built-up layer are not impaired. Also, even hard and brittle materials that are difficult to process into welding rods or welding lines can be used as filler materials by pulverizing them, which greatly expands the degree of freedom in selecting materials that can be used as filler materials. . For example, it is possible to form a built-up layer containing a large amount of hard particles such as carbides such as VC and TiC and ceramics such as alumina and chromium oxide by mixing with metal powder.

In the present invention, for example, in forming the overlay layer 20 on the outer peripheral surface of the steel pipe material 1 as shown in FIG. 1, the steel pipe material 1 is kept with the pipe axis of the steel pipe material 1 kept substantially horizontal. A plasma arc 34 generated by a plurality of PPW torches 10 which are located above and in parallel with the tube axis of the steel tube material 1 and are arranged in a row at appropriate intervals in the tube axis direction as a heat source. The predetermined powdery filler material 31 supplied through each of the torches is melted to perform predetermined overlay welding on the outer peripheral portion of the steel pipe material 1, and the steel pipe material 1 is driven by the drive roll 2 to rotate the pipe shaft. While rotating around, the other P
By moving the PW torch 10 in the pipe axis direction, a predetermined buildup welding layer 20 is formed over the entire outer peripheral surface of the steel pipe material 1.

In the overlay welding, a first torch 11 of a plurality of PPW torches 10 arranged in the axial direction of the pipe is used to form a first first filler material on the outer peripheral surface of the steel pipe material 1.
The overlay layer 21 is formed. The second torch 12 following the first torch 11 includes a second overlay layer 22 made of a predetermined second filler material on the first overlay layer 21 formed by the first torch 11.
To form. In forming the second overlay layer 22,
The second buildup layer 22 is formed in a state where the first buildup layer 21 has been sufficiently solidified and the steel pipe material 1 is substantially free from harmful bending.

That is, if the second overlay layer 22 is to be formed on the first overlay layer 21 before the first overlay layer 21 is sufficiently solidified, the constituent elements of the overlay layers are mixed with each other. , The original characteristics of each overlay layer will be impaired. In the present invention, the goal is to exert the individual characteristics of the build-up layer formed by dividing each layer, so that the composition of the build-up layer formed should not change as much as possible from the predetermined one. Is preferred. For that purpose, it is necessary to weld the second overlay layer 22 by overlay welding after the first overlay layer 21 is sufficiently solidified.

When overlay welding is applied to the peripheral surface of the steel pipe material 1, since the welding is performed with a time lag, it is unavoidable that the temperature distribution is asymmetric with respect to the pipe axis.
Bending occurs in the steel pipe after overlaying. This bending amount varies depending on the material of the steel pipe material 1, dimensions, overlay welding conditions, overlay layer thickness, physical properties of the overlay layer, and the like, but it increases as the overlay length increases. When the bent steel pipe material 1 is rotated around the pipe axis, a large vibration is generated, which interferes with the welding torch and stable overlay welding cannot be performed.
In the composite steel pipe of the present invention, after forming the first overlay layer 21, the second overlay layer 22 is formed before the bend generated in the steel pipe material becomes a large bend that substantially hinders the execution of overlay welding.
Are formed.

Hereinafter, the third torch 13, which is appropriately arranged,
It is possible to form the third built-up layer 23, the fourth built-up layer 24, and the like in the same manner as the formation of the second built-up layer 22 by feeding the predetermined filler material with the fourth torch 14 and the like. it can.

[0017]

EXAMPLES The composite steel pipe of the present invention will be described in detail below with reference to examples. (Experiment 1) A JIS having an outer diameter of 48 mm, a wall thickness of 7 mm, and a length of 5.5 m was measured by using the apparatus whose outline is shown in FIGS. 1 and 2.
STB35 steel pipe material (0.15wt% C-0.45w
t% Mn-0.015 wt% P-0.020 wt% S)
On the outer peripheral surface of the above, the powder shown in Table 1 was piled up in four layers by the PPW method under the welding conditions shown in Table 1. The steel pipe material was rotated around the pipe axis at a speed of 1.5 rpm, and each torch was fed in the pipe axial direction at a speed of 5 to 30 mm / min to perform overlay welding.

[0018]

[Table 1]

The experimental results are shown in Table 2. In Comparative Example 1 in which overlaying was performed with only one torch, the first layer could be overlay welded up to 5 m, but a runout of 11 mm occurred, and the second layer was Pipe length 1
It became impossible to weld at the 20 mm point and was interrupted. In Example 1 and Example 2 using the first torch and the second torch, the runout was slightly large in Example 1 in which the distance between the torches was 300 mm, but overlay welding up to a pipe length of 4.5 m was performed. In Example 2 in which the distance between the torches was 100 mm, overlay welding with a pipe length of 4 m or more was possible. Example 3 is an example in which four torches were used in combination to perform four-layer overlay, but smooth build-up welding could be performed with little occurrence of runout. As shown in Table 2, the larger the number of torches to be used together and the smaller the torch spacing, the higher the appropriate torch feed speed at which a good overlay can be obtained, and therefore high-efficiency overlay welding can be performed. Is clear.

[0020]

[Table 2]

(Experiment 2) As Example 4, a JIS having the same outer diameter of 48 mm, thickness of 7 mm and length of 5.5 m as in Experimental Example 1 was used.
By the PPW method, three torches are used together on the outer peripheral surface of the STB35 steel pipe material, the purity is 99.5 wt%, and the grain size is-# 60.
/ + # 200 Ni powder was overlay welded. The welding current of each torch was 130 A, the welding voltage was 28 V, the torch interval was 100 mm, the rotation speed of the steel pipe material was 2 rpm, and the torch tube axial feed was 30 mm / min. When overlay welding was performed at a powder feed rate of 18 gr / min, the average thickness of each overlay layer was 2.4 to 2.7 mm.

The test materials were sampled from the surface side portion of each of the built-up layers, and the content of each nickel component was measured. The results are shown in Table 3. The results are shown in Table 1 for the first layer, the second layer, and the third layer. As the nickel content increases sequentially, as an embodiment of the composite steel pipe of the present invention,
It can be seen that a composite steel pipe having a pure metal layer of high purity formed on the surface of the steel pipe material can be obtained.

[0023]

[Table 3]

(Experiment 3) As Example 5, a JIS having the same outer diameter of 48 mm, wall thickness of 7 mm, and length of 5.5 m as in Experimental Example 1 was used.
STB35 steel pipe material outer peripheral surface by PPW method, using three torches together, grain size-STE of # 60 / + # 200
LLITE # 21 was overlay welded. At this time STELL
In addition to ITE # 21 powder, 16 wt% for the first layer,
A mixed powder containing 29 wt% vanadium carbide (VC) powder for the second layer and 61 wt% for the third layer was fed. As a result, it was found that a high VC content layer having a VC content rate of 61 wt% can be formed on the surface layer portion.

Table 4 shows the results of the wear test by the Ogoshi-type wear tester and the results of the corrosion resistance test. In the abrasion test, JIS SKD11 material was used as a comparative material, and the friction speed was 2.0 m /
sec, the final weight was 18 kgf, and the wear loss was measured at a friction distance of 600 m. Further, the corrosion test was performed by measuring the corrosion weight loss after exposing the test surface of 600 mm ^{2 to} the corrosion environment of NaCl-KCl-Na ₂ SO ₄ at 550 ° C. for 48 hours.

[0026]

[Table 4]

In Example 5 of the composite steel pipe according to the present invention, since the VC content of the first layer is relatively low, it is well compatible with the steel pipe material, and the VC content of the second layer having an intermediate VC content can be improved. A composite steel pipe having a strong hard layer on the surface, which has good adhesion to the metal, has good corrosion resistance, and has a strong structure by having a structure of joining to a high third layer, is presented.

[0028]

As described above, according to the method for manufacturing a composite steel pipe of the present invention, a plurality of torches are used together by the PPW method to cope with the bending that occurs during overlay welding, and a single overlay welding is performed. Combustible waste such as dust can be formed by laminating multiple types of overlay layers such as pure metal, high alloys, or hard layers containing hard particles, which have excellent corrosion resistance and heat resistance, on the outer periphery of steel pipe materials. It is possible to provide an inexpensive composite steel pipe having excellent corrosion resistance, heat resistance, and wear resistance that can withstand high-temperature combustion gas used as a steel pipe for a superheater of a power generation system that utilizes the incineration heat of the above.

[Brief description of drawings]

FIG. 1 is a schematic view showing a method for manufacturing a composite steel pipe of the present invention.

FIG. 2 is a sectional view of a main part of a plasma arc torch.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steel pipe material 2 Drive roll 10 PPW torch 11 1st torch 12 2nd torch 13 3rd torch 14 4th torch 20 Overlay layer 21 1st overlay layer 22 2nd overlay layer 23 3rd overlay layer 24 4th Overlay layer 31 Filler material 32 Center gas 33 Shield gas 34 Plasma arc 35 Carrier gas 36 Tungsten electrode 37 Plasma power supply

Claims (2)

[Claims] 1. In a composite steel pipe in which a build-up layer is formed on the outer peripheral surface of a steel pipe material by a plasma build-up welding method using a plasma arc as a heat source and powder as a filler metal, the build-up welding is performed in the axial direction of the steel pipe. It is performed by a plurality of torches arranged,
The build-up layer formed by each of the torches is formed by sequentially stacking a plurality of build-up layers as the build-up welding progresses, and each of the formed build-up layers is a metal or an alloy having a different composition. A composite steel pipe characterized by comprising: 2. A plurality of plasma arc torches are arranged in a row along the pipe axis above the steel pipe material in a state where the pipe axis is kept horizontal, and the torch is generated by the torch. Using a plasma arc as a heat source, the powdered filler material supplied through the torch is melted, and welded to the outer peripheral surface of the steel pipe material by overlay welding, and the steel pipe material is relative to the plasma arc torch row. By moving in the tube axis direction while rotating around the tube axis so that a build-up layer formed by each of the torches arranged in rows is laminated and formed over the entire outer peripheral surface of the steel pipe material. A method for manufacturing a composite steel pipe characterized by the above.