JPH0386367A - Method for joining clad steel pipe - Google Patents

Abstract

PURPOSE:To efficiently join clad steel pipes and to obtain a defectless joint part by interposing a specific inserting material into the mutually butting parts of the steel pipes consisting of an outside pipe consisting of a carbon steel, etc., and an inside pipe consisting of a stainless steel, etc., and subjecting the butting parts to induction heating under specific conditions. CONSTITUTION:The steel pipes consisting of the outside pipe consisting of the carbon steel or low-alloy steel, etc., and the inside pipe consisting of the stainless steel, etc., or high-Ni alloy steel are butted against each other. The inserting material is interposed into the mutually butting parts. The inserting material consists of <=8wt.% Si, <=4% B, 5 to 40% Cr, <=10% or 0% Mo and the balance unavoidable impurities and Fe or Ni and has <=1,150 deg.C m. p. and 10 to 80mum thickness. While the butting parts are pressurized under 0.5 to 2kgf/ mm<2>, the butting parts are subjected to the induction heating for >=120 second at 1,150 to 1,250 deg.C by a high frequency current of 100 to 400kHz in an atmo sphere of <=200ppm oxygen. Thus, the above-mentioned inserting material is melted, by which the above-mentioned clad steel pipes are joined easily in a short period of time and the secure jointing part free from crazing, cracking, etc., is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method of joining clad steel pipes by butt-joining internally clad steel pipes or externally clad steel pipes to each other.

[Conventional technology]

Inner stainless steel clad steel pipes that combine an outer pipe made of carbon steel or low-alloy steel with an inner pipe made of stainless steel, the corrosion resistance of the inner side that comes into contact with the carrier fluid is ensured by the stainless steel, and the strength of the entire steel pipe is achieved by using inexpensive carbon. Since it is made of steel pipes, it is widely used in chemical industry plants, line vanes, etc. due to its economic efficiency and high practicality. Also,
External stainless steel clad steel pipes with an inner pipe made of carbon steel or low alloy steel and an outer pipe made of stainless steel are also widely used in chemical industry plants, etc., just like the inner stainless steel clad steel pipes.

Such stainless clad steel pipes are broadly classified into welded pipes and seamless pipes depending on the manufacturing method. Welded pipes are manufactured by butt welding joints of stainless clad steel pipes shaped into tubular bottoms using various welding methods, and seamless pipes are manufactured by extrusion and rolling from a multilayer material. When producing long lengths of any stainless clad steel pipe, a method of interconnecting and extending the stainless clad steel pipes is often used due to equipment constraints and economical considerations.

As a method for interconnecting stainless clad steel pipes, circumferential welding is mainly used in which the butt portions of stainless clad steel pipes are arc welded over the entire circumference.

However, applying conventional general techniques to welding will cause various problems, so special consideration is required. A joint welding method is disclosed in which an inner layer containing the same type of alloying element as that of the mating material, an intermediate layer, and an outer layer containing the same type of alloying element as the base material are sequentially formed on the side of the base material. However, even with such a welding method, there are still many difficulties involved in circumferential welding of clad steel pipes.Problems in circumferential welding of stainless steel clad steel pipes will be described below with respect to internal stainless clad steel pipes.

[Problem to be solved by the invention]

Circumferential welding of steel pipes is usually done from the outside.
Co-metal thread material is used as the welding material.

When welding an inner stainless steel clad steel pipe from the outer side on one side, if you use stainless steel welding consumables to weld the mating material of the inner tube and carbon steel welding consumables to weld the base metal of the outer tube, when welding the base metal, the A portion of the stainless steel weld metal of the formed laminate is remelted, and the stainless steel weld metal is diluted by the carbon steel weld metal, resulting in a hardened layer. As a result, cracks may be induced in the welds and stainless steel
, high temperature welding cracks may occur. On the other hand, if the entire weld metal is made of high-alloy welding material, not only is there a concern that the joint strength will be insufficient, but the stainless steel will be exposed on the outer surface, and this part will be made of dissimilar metals such as stainless steel and carbon steel. Since contact occurs, this is not preferable in terms of galvanic corrosion, etc.

Furthermore, in circumferential welding of external stainless clad steel pipes, when one side is welded from the external surface side, the same problem as in the case of the internal stainless clad steel pipes occurs. In other words, when welding an external stainless clad steel pipe from the outside,
If the carbon steel of the inner tube is welded with carbon steel welding material and then stainless steel weld metal is laminated thereon, a hardened layer may be formed due to dilution, which is not preferable.

As a solution to such problems, Japanese Patent Application Laid-Open No. 58-1670
Even if the welding method disclosed in Publication No. 94 is adopted, the welding materials and welding conditions must be changed sequentially for the inner layer, intermediate layer, and outer layer, which makes the welding work complicated. Since the soundness of the joint is affected by the skill of the individual builder, there is a problem that the quality becomes unstable. An even bigger problem is that the welding speed must be suppressed to prevent welding defects, resulting in extremely poor construction efficiency.

The present invention was made in view of the above situation, and its purpose is to provide a method for joining clad steel pipes that can efficiently join stainless clad steel pipes and obtain a sound joint.

[Means to solve the problem]

As a method of joining steel pipes, a method of diffusion joining the abutted portions using an insert material is known. According to this method, joining can be performed simply by controlling the atmosphere and heating and pressurizing the abutting portions of steel pipes, and it is conceivable that this easy-to-implement diffusion joining method can also be applied to joining stainless clad steel pipes. However, when joining stainless clad steel pipes, unlike when joining solid steel pipes, there are the following problems.

In the case of solid steel pipes, it is sufficient to join a single material and give the joint the characteristics equivalent to the steel pipe material.
In the case of stainless clad steel pipes, it is necessary to join two types of materials with a common insert material, and for the base metal side of the joint and the joint down, a single insert with different characteristics corresponding to the base material and the joint material is used. It is necessary to provide it with wood. In addition, considering workability, atmosphere control during bonding must be easy, and an even bigger problem is that
This is because a temperature difference occurs between the base material and the bonded material as the abutted portion is heated.

In other words, because the thermal conductivity, magnetic permeability, and specific resistance of the base material carbon steel or low-alloy steel and the austenitic stainless steel or Ni alloy used for the laminate differ, high-frequency induction heating or resistance heating is performed. In many cases, the base material and the laminate material are not at the same temperature.

If a temperature difference occurs between the base material and the mating material, the insert material may not melt or the steel pipe itself may melt.

The inventors of the present invention conducted various experimental studies to solve these problems, and as a result, the following findings were obtained regarding a diffusion bonding method for internally clad steel pipes and externally clad steel pipes.

In order to easily butt join clad steel pipes, it is essential to melt the insert material. In order to provide sufficient joint strength to the joint, it is necessary to break up and decompose the oxide at the joint interface, and for this purpose it is effective to add Si and B to the insert material to lower its melting point. It is. Adding St and B to the insert material lowers the melting point of the insert material and widens the permissible range of atmosphere control. At the same time, these added elements diffuse into the material to be joined during heat bonding, and the addition of St and B Embrittlement of the bonding layer caused by this is also prevented.

In order to ensure the corrosion resistance of the bonded joint, it is necessary to limit the thickness of the insert material, add Cr to the insert material, add B and Si, which diffuse quickly, and heat the material at an appropriate temperature and for an appropriate time to reduce B and St. It is effective to sufficiently diffuse the In order to alleviate the temperature difference between the base material and the cladding material during heat welding, it is necessary to
Hz, and for externally clad steel pipes, high frequency induction heating using high frequencies of 10 kHz or less is effective.

The present invention was made based on such knowledge, and the mutual butt portions of clad steel pipes are coated with Si: 8% or less and B: 8% or less by weight.
4% or less, Cr: 5 to 40%, and further Mo as necessary.
: Contains 10% or less, the remainder being unavoidable impurities and Fe
Or made of Ni, melting point 1150℃ or less, thickness 1O~8
With insert material of 0IJm, oxygen amount is 200p
In an atmosphere below pm, the butt part is 0.5 to 2
While pressurizing at a pressure of kgf/kaku 8, if the clad steel pipe is an internally clad steel pipe, a high frequency current of 100 to 400 kHz is applied, or if the clad steel pipe is an externally clad steel pipe, a high frequency of 10 kHz or less is applied to 1150 ° C. ~1
The gist of the present invention is a method for joining clad steel pipes, which is characterized in that the insert material is melted by induction heating at a temperature of 250° C. for 120 seconds or more.

[For production]

The joining method of the present invention targets clad steel pipes in which the base material is carbon steel or low alloy steel and the cladding material is stainless steel or high Ni alloy steel, and the cladding material is located on either the inner tube side or the outer tube side. However, when the cladding material is located on the outer pipe side, that is, the heating frequency of the outer clamp steel pipe is 10
kHz or less, and when the cladding material is located on the inner pipe side, that is, the heating frequency of the inner clad steel pipe is 100 to 400 kHz.
Let it be z.

As insert material, Si: 8% or less, B:
An Fe-based or Ni-based alloy containing Cr: 4% or less, Cr: 5 to 40%, or an Fe-based or Ni-based alloy containing M0: 10% or less in the above components is used.

Si and B are melting point lowering elements for lowering the melting point of the insert material, and are elements that easily diffuse into the clad steel pipe. The reason why the Si content is 8% or less is that St is 8%.
This is because if the content exceeds 1%, the bonding layer becomes brittle due to SL remaining in the bonding layer without being able to diffuse into the materials to be bonded.

The reason why the B content is set to 4% or less is that if B is contained in an amount exceeding 4%, the bonding layer becomes brittle in the same way as with St.

The lower limit of the content of Si and B is the minimum amount that can cause the melting point of the insert material to be 1150° C. or lower. However, B
When the content of Si is at the upper limit (4%), there is no problem even if it does not contain Si.
This is because the bonding is carried out at temperatures above

Cr and Mo are contained in order to improve the corrosion resistance of the joint. The reason for setting the Cr content to 5 to 40% is that if the Cr content is less than 5%, the corrosion resistance of the joint will be significantly reduced.
This is because if Mo is contained in an amount exceeding 40%, the bonding layer becomes brittle like Si and B. Mo is contained as appropriate depending on the steel type of the cladding material, and the content is set to 10% or less because
This is because if Mo is contained in an amount exceeding 10%, the bonding layer becomes brittle like Si and B.

If the insert material is Ni-based or Fe-based, either is fine if the mating material is stainless steel, but high N
In the case of i-alloy steel, Ni-based steel is desirable from the viewpoint of corrosion resistance.

The insert material preferably has an amorphous structure.

This is because, in the above-mentioned insert material component system, by making the insert material amorphous, it becomes easier to handle the insert material, and also because the amorphous material is cheaper and easier to manufacture.

The thickness of the insert material is 10 to 80 μm.

The main purpose of using an insert material is to widen the tolerance limits for the bonding atmosphere and bonding surface roughness compared to diffusion bonding without an insert material, and when the thickness is less than 10 μm, the effect of expanding these tolerance ranges is However, on the other hand,
Considering the corrosion resistance of the bonding layer, it is desirable to transfer alloy components such as Cr and Mo from the craft steel bonding material to the bonding layer to enrich the alloy components in the bonding layer. However, when the laminated material becomes thick, the enrichment of this alloy component does not progress due to dilution by the insert material.Therefore, it is necessary to set an upper limit on the thickness of the insert material, and the thickness of the insert material must be set at 80 μm.
The following shall apply.

High-frequency induction heating is used to heat the butt part during bonding.
The frequency is 100 if the outer tube is carbon steel or low alloy steel, the inner tube is stainless steel, or the inner clad steel tube is high Ni alloy steel.
~400 kHz, and in the opposite case, that is, when the outer tube is made of stainless steel or high Ni alloy steel, and the inner tube is made of carbon steel or low alloy steel, the outer clad steel tube is made to be 10 kHz or less.

High-frequency induction heating was adopted because it is the easiest and quickest way to heat the joints.

The frequency in high-frequency induction heating is an important point in the method of the present invention.

That is, in the method of the present invention, the heating frequency differs depending on whether the mating material and base material of the clamped steel pipes to be joined are located in the inner pipe or the outer pipe. This will be explained in detail below.

When steel pipes are butted against each other and joined by high frequency heating, the outer surface of the steel pipes is intensively heated due to skin hardening that is unique to high frequencies.

First, we will discuss the case of an outer clad steel tube in which the outer tube is made of carbon steel or low alloy steel as a base material, and the inner tube is made of stainless steel or high Ni alloy steel as a mating material.

Originally, the outer tube was made of carbon steel, and the inner tube was made of stainless steel.
It has higher thermal conductivity than high-Ni alloy steel and is easily heated. When heated in this state with high frequency waves of 100 to 400 kHz, it is possible to heat it to a temperature at which both the outer tube and the inner tube can be joined, and the insert material can also be sufficiently melted. However, LOOkHz
If it is lower than The alloy steel will be heated too much and the melt will fall.

In addition, if heating exceeds 400kHz, please follow the instructions in 1 above.
Contrary to when the frequency is less than 00kHz, the skin effect of the high frequency is greater for the carbon steel and low alloy steel of the outer tube, and only the outer tube is heated, while the stainless steel and high Ni alloy of the inner tube are not heated much. , the insert material is also insufficiently melted, making it impossible to properly join.

Therefore, the joining of inner clad steel pipes where the outer tube is made of carbon steel and low alloy steel and the inner tube is made of stainless steel and high Ni alloy steel is as follows:
It is performed at a high frequency of 100 to 400 kHz.

Next, the conditions for high-frequency heating will be described in the opposite case to the above, that is, in the case where the outer tube is an outer clad steel tube made of stainless steel or high Ni alloy steel and the inner tube is made of carbon steel or low alloy steel.

In this case, heating is performed using high frequency heating of 10kHz or less.

This is due to the high-frequency skin effect and thermal conductivity when heated above 10kHz.
This is because only the i-alloy steel is heated, and the carbon steel and low-alloy steel of the inner tube are difficult to heat, resulting in insufficient heating, and the insert material is not sufficiently melted, making it impossible to properly join.

Note that the lower limit is not particularly limited, but desirably a high frequency of 1 kHz is preferable from an economical point of view.

Regarding the bonding atmosphere, the oxygen content was set to 200 ppm or less. This is to prevent oxides from forming at the bonding interface and causing defects.

It is more economical to lower the heating temperature during bonding.

However, if the heating temperature is lower than 1150°C, the insert material may not be completely melted, and even if the insert material melts, the melting point lowering elements contained in the insert material will not diffuse sufficiently into the clad steel. , the bondability decreases.

Therefore, the heating temperature was set at 1150'C or higher. However, if the heating temperature exceeds 1250'C, not only will the economic efficiency deteriorate, but also the crystal grains around the joint will become coarser, leading to a decrease in toughness, so 1250°C is the upper limit of the heating temperature. do.

The time to maintain the heating temperature at 1150-1250℃ is 12
0 seconds or more. This is to ensure that the melting point-depressing element contained in the insert material is sufficiently diffused into the clamped steel pipe that is the joining base. Although there is no particular upper limit to the heating holding time, a shorter heating time is more economical as long as bonding and diffusion are sufficiently promoted.

Pressure force during bonding is 0.5kgf/w for bonding surfaces.
In other words, if the pressing force is less than 0.5 kgf/m, the adhesion between the liquid-phase insert material and the clad steel pipe is insufficient, resulting in poor bonding. On the other hand, if the pressure is too high, the joints tend to deform, so the upper limit was set at 2 kgf/kaku2.

Note that depending on the material of the clad steel pipe, the joint portion may be heat-treated at a temperature of 500 to 700° C. after joining.

〔Example〕

Examples of the joining method of the present invention will be described below.

A clad steel pipe with an outer diameter of 91+s, an inner diameter of 67 cm, a wall thickness of 12 am, and a length of 1500 am was used as the material to be welded. There were two types of clad steel pipes: an inner clad steel pipe with an outer pipe as the base material and an inner pipe as the cladding material, and an outer clad steel pipe with the inner pipe as the base material and an outer pipe as the cladding material.

The base material of the clad steel pipe is 9 mm thick and made of carbon 11 (C3) or low alloy steel (CM), and the carbon steel is 50 kgf.
/m” Handled copper, low alloy steel T-Ha2 Va Cr-IM
The 0 mating material using o steel is 3mm thick and made of stainless steel or high Ni alloy steel.The stainless steel is 5US316L and the high Ni alloy steel is A11oy62.
5 or A11oy825, respectively. Table 1 shows the ingredients and precepts for each.

Table 1 (wt%) Table (wt%) □Joining outside the scope of the present invention involves cutting each of the above-mentioned clad steel pipes at right angles to the pipe axis direction, polishing the end faces of the pipes to 5071 mR■ax, and then I sandwiched the insert material.

The insert material is 25μ thick and made by rapid solidification method.
m or 50 μm amorphous alloy ribbon.

Its component NIi precepts are shown in Table 2. In addition, the first
As shown in the figure, an annular heating pad 2 was used to butt and fix a pair of test materials 1a and lb.

The heating head 2 has a half-split shape, and the test material 1a is attached to both ends.

It is provided with restraint parts 3a and 3b for lb, and an inductor 4 between them. Then, by this heating Herad 2, 1
A set of specimens 1a and lb was sandwiched and fixed between the end faces of the insert material, and heated in an atmosphere with an oxygen content of 200 ppm or less while flowing N2 gas into the inner surfaces of specimens 1a and lb and into the heating pad 2. The abutted portions of the test materials 1a and lb were heated by an inductor 4. Due to this heating, the insert material between the end faces is melted and extends in the tube axis direction of the sample material, and a pressure is applied between the joining surfaces to perform diffusion bonding between the end faces. The pressing force was adjusted by relaxing it by the reaction force caused by the thermal expansion of the restraining parts 3a and 3b. The heating temperature and heating holding time were determined by operating the high frequency power source 5 of the inductor 4. Note that the clad steel pipes using low alloy steel as the base material were subjected to post-AC heat treatment at 700° C. for 15 minutes after joining.

The soundness of the joint was evaluated by joint strength and corrosion resistance tests. The joint strength was determined by performing a bending test using the bending test piece 6 shown in Fig. 2 at a bend diameter of 14 m (2 tons), and also investigating the presence or absence of cracks around the joint 7 of the bending test piece 6. , those with no cracks were evaluated as good, and those with cracks were evaluated as not good.
O represents a laminate material. The corrosion resistance of the joint 7 can be determined by taking a pitting corrosion test piece 8 shown in FIG. The evaluation was made by determining the ratio of The test liquid was artificial seawater, and its temperature was 5US316L.
In the case of 60°C, Al1oy625, AIIoy
In the case of 825, it was set to 100'C.

The test results are shown in Table 3 along with the bonding conditions.

A1 to A6 are examples in which clad steel tubes in which the outer tube is made of carbon steel and the inner tube is made of 5US316L are joined together using insert materials (1) to (5). Insert material! 1 to ■5 are Si:8
% or less, B: 4% or less, and Cr: 5% or more and 40% or less. Other conditions are also appropriate. Therefore, it shows excellent bondability and corrosion resistance.

A7 is an example in which the outer tube is made of low-alloy steel and the inner tube is made of 5US316L clad steel tube, which are joined together using insert material I2, and other conditions are also appropriate and exhibits excellent bondability and corrosion resistance.

88 is A11 where the outer tube is carbon steel and the inner tube is high Ni alloy steel.
Insert material is clad steel pipe made of oy825! 2 is an example of mutually joining, A9 has an outer tube made of carbon steel and an inner tube made of high N.
An example in which clad steel pipes made of A11oy625, which is i-alloy steel, are joined together using insert material I4.AIO is an example in which clad steel pipes in which the outer tube is made of low alloy steel and the inner tube is made of A11oy625 are joined using insert material I4. , Al
1 is an example in which an outer tube made of 5US316L and an inner tube made of carbon steel are joined using insert material I2. In both cases, the thickness of the insert material is 25 μm, the heating time is 300 seconds, and the pressing force is 1 kgf/■! , the power supply frequency shows excellent bonding performance and corrosion resistance of the bonded portion under the conditions of the present invention.

Also, like A2, A12 has an outer tube of carbon steel and an inner tube of 5U.
A clad steel pipe made of S316L is inserted into insert material A2.
This is an example in which bonding was performed at a heating temperature of 1250° C., and it still shows excellent bonding properties and corrosion resistance.

On the other hand, B1 does not use insert material,
Poor bonding is occurring. Although B2 uses an insert material, the heating temperature is too low, resulting in poor bonding. In B3, the pressing force was too small, resulting in poor bonding. In B4, the power supply frequency was too high, resulting in poor bonding even though other conditions were appropriate. This is because even if the carbon steel of the outer tube is heated to 1200° C., the AIIoy825 inner tube is not easily heated and is about 100° C. lower than the carbon steel of the outer tube.

Also, B5. B6. In case of B7, defective bonding occurred because the insert material used had a composition outside the scope of the present invention.

B8 is Al1 where the outer tube is carbon steel and the inner tube is high Ni alloy steel.
Insert material I2 is a clamped steel pipe made of oy 825.
In the example of B9, the outer tube is 5US31SL,
The insert material is a clad steel tube whose inner tube is made of carbon steel! 2
This is an example in which they are joined to each other. In both cases, the power supply frequency was outside the conditions of the present invention, resulting in poor bonding.

〔Effect of the invention〕

As is clear from the above explanation, the joining method of the present invention
Clad steel pipes can be firmly joined to each other, and there is no risk of cracks caused by the formation of a hardened layer, high-temperature weld cracking, or galvanic corrosion caused by contact with dissimilar metals, which is a problem with welding methods.

Therefore, excellent bondability and corrosion resistance can be imparted to the bonded portion. Furthermore, it is easier to work with than welding, takes less time to join, and has significantly better workability. Furthermore, since the soundness of the joint is affected by the skill of each individual builder, it is possible to eliminate variations in quality.

Therefore, the joining method of the present invention can easily and inexpensively lengthen a clad steel pipe, for example, even at a piping site.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of a joining apparatus used in the joining method of the present invention, FIG. 2 is a diagram illustrating the shape of a bent test piece, and FIG. 3 is a diagram illustrating the shape of a pitting test piece. In the figure, la, ltz sample material, 2: heating head, 3a, 3
b: restraint part, 4: inductor, 5: high frequency power supply, 6: bending test piece, 7: joint part, 8: pitting test piece, 9: base material, lO:
Laminating material. Figure Figure Figure

Claims (2)

[Claims] (1) Si: 8% or less, B: 4% or less by weight,
Contains Cr: 5 to 40%, Mo: 10% or less, and the remainder consists of inevitable impurities and Fe or Ni, melting point 1150
℃ or less, insert material with a thickness of 10 to 80 μm, or weight% Si: 8% or less, B: 4% or less, Cr: 5 to 40
%, the balance being unavoidable impurities and Fe or Ni, with a melting point of 1150°C or less and a thickness of 10 to 80 pm interposed, and the abutted portion is heated at 0.5 to 2 kgf/mm^ in an atmosphere with an oxygen content of 200 ppm or less. A method for joining clad steel pipes, characterized in that the insert material is melted by induction heating at a temperature of 1150 to 1250° C. for 120 seconds or more with a high frequency current of 100 to 400 kHz while pressurizing at a pressure of 2. (2) Si: 8% or less in weight percent, B: 4 at the mutual butt part of the clad steel tube where the outer tube is made of stainless steel or high Ni alloy steel and the inner tube is made of carbon steel or low alloy steel.
% or less, Cr: 5 to 40%, Mo: 10% or less,
An insert material with a melting point of 1150°C or less and a thickness of 10 to 80 μm, the remainder consisting of unavoidable impurities and Fe or Ni,
Or Si: 8% or less, B: 4% or less, Cr:
5-40%, the balance being unavoidable impurities and Fe or Ni
An insert material with a melting point of 1150°C or less and a thickness of 10 to 80 μm is interposed, and the butt part is heated at 0.5 to 2 kgf/mm in an atmosphere with an oxygen content of 200 ppm or less.
A method for joining clad steel pipes, characterized in that the insert material is melted by induction heating at a temperature of 1150 to 1250° C. for 120 seconds or more using a high frequency current of 10 kHz or less while pressurizing at a pressure of ^2.