JPH09262685A - Stainless steel welding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stainless steel diffusive welding method capable of obtaining a welded part provided with the corrosion resistance and sufficient mechanical properties equivalent to those of the base material under the environment of wet carbon dioxide gas containing a very small amount of hydrogen sulfide. SOLUTION: In this diffusion welding method, a material to be welded of low melting point is interposed between end faces of butted works 12, and a welding part 3 is heated, and the compressive stress is applied in the longitudinal direction 5. The works 12 are made of stainless steel containing >=9wt.% Cr, the material to be welded of low melting point is made of Ni alloy of <=1150 deg.C in the melting point containing >=5wt.% Cr of 10-80μm in thickness, the compressive stress is 0.5-2kgf/mm<2> at butted end faces, and the heating is performed in a condition where the heating length 2 of >=800 deg.C is 3-20mm, and the works are kept for 120 seconds at the temperature of a welded layer 1 not less than the melting point of the material to be welded of low melting point, and not more than the melting point of the works.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for joining stainless steel which forms a joint having high corrosion resistance in a wet carbon dioxide environment containing a trace amount of hydrogen sulfide, and more particularly to a method for joining oil well steel pipes.

[0002]

The wet carbon dioxide environment is a very important environment that materials must encounter when dealing with oil in the fields of oil drilling, oil production, oil transportation and oil refining. There are two cases in which the wet carbon dioxide gas exists in the wet carbon dioxide gas environment and a case where the wet carbon dioxide gas contains a slight amount of hydrogen sulfide. The present invention mainly focuses on the case where a trace amount of hydrogen sulfide is contained, but is also effective in an environment where a trace amount of hydrogen sulfide is not contained. In the following description, the wet carbon dioxide gas environment containing a trace amount of hydrogen sulfide includes the wet carbon dioxide gas environment not containing it.

There is an extremely strong demand for a durable material that does not damage in a humid carbon dioxide environment containing a trace amount of hydrogen sulfide, and various materials compatible with these environments, particularly various stainless steels or high-grade materials are highly demanded. Alloy steels have been developed.

When these stainless steels or high alloy steels are used for steel pipes for excavation connected by screw joints, etc., they can be used as they are as long as the steel alone has performance such as corrosion resistance in the usage environment. it can. However, the threaded joint has the following problems.

(A) Since it is necessary to cut a precise screw, a great cost is required.

(B) Since the tightening force at the time of screw tightening varies, the skill of the operator is required to secure the reliability of the screw part.

(C) The screw portion is easily damaged during transportation.

On the other hand, when the usual welding method involving melting of the base material is used for connecting a steel pipe for excavation, the base material is melted, and the following problems occur.

(A) In the case of martensitic stainless steel, the weld metal and the heat-affected zone are in a hardened state as they are quenched, resulting in severe toughness deterioration and sulfide cracking in a wet carbon dioxide environment.

(B) Duplex stainless steel has a large amount of ferrite in the weld metal, resulting in deterioration of toughness and corrosion resistance.

In recent years, a new connection method has been disclosed, which replaces the above-mentioned welding method and has a small input energy density and is capable of achieving metallic joining (Japanese Patent Laid-Open No. 5-220).
585, JP-A-5-77063, JP-A-5
-161984 and JP-A-5-169280).

According to this method, a low melting point foil (insert material) or the like is inserted between the end faces of the materials to be joined, and while applying pressure,
This is a method for achieving metallic joining by heating to a temperature higher than the melting point of the insert material and lower than the material to be joined. This method is generally called "diffusion bonding method".

As a "diffusion bonding method" which replaces the threaded joint, a method for joining a high alloy oil country tubular good which prevents deterioration in durability of the threaded joint is disclosed in Japanese Patent Laid-Open No. 6-7967. The method disclosed here is a method of preliminarily subjecting the pipe end to plastic working for the purpose of preventing softening at the joint obtained by the diffusion joining method. There is a drawback that leads to the rise of.

Further, there has not been disclosed a diffusion bonding method which can obtain a bonded portion having high corrosion resistance in a wet carbon dioxide gas environment containing hydrogen sulfide.

[0015]

SUMMARY OF THE INVENTION The present invention provides a stainless steel, especially a stainless steel, which has a high corrosion resistance in a wet carbon dioxide environment containing a small amount of hydrogen sulfide and at the same time provides a joint having sufficient mechanical performance. An object of the present invention is to provide a simple diffusion bonding method for oil well steel pipes.

[0016]

Means for Solving the Problems As a result of studying a diffusion bonding method which has sufficient corrosion resistance in the above corrosive environment and at the same time secures high mechanical properties, the present inventors have confirmed the following matters. .

(A) The proof stress (0.2% proof stress) equal to or higher than that of the base metal, which is the most difficult to achieve among the mechanical properties of the joint, is
This can be ensured by setting the length of the joint portion (hereinafter referred to as “heating length”) that is heated to 800 ° C. or more during diffusion joining to 20 mm or less.

FIG. 1 is a drawing showing a joint portion formed by applying the method of the present invention. "Joint" 3
Means a wide range that is affected by heating, and "heating length" 2
Indicates a portion heated to 800 ° C. or higher. The “diffusion layer” 4 to be described later refers to a layer in which an alloy component such as an insert material penetrates and diffuses into the end surface of stainless steel. Also,
The "bonding layer" 1 is a material that is substantially bonded by the insert material that has been deteriorated by the bonding and the end surfaces of the stainless steel on both sides of the insert material, that is, diffusion layer / trace of insert material / diffusion layer. I will indicate the part.
The “bonding layer before bonding” refers to a part including the insert material including the parts corresponding to the diffusion layers of the materials to be bonded on both sides.

(B) Similar to the proof stress, the bending performance at the joint portion, which is difficult to achieve, is such that the thickness of the low melting point joint material is 80 μm or less,
The compressive stress in the longitudinal direction 5, that is, the applied pressure is 2 kgf / m.
It can be ensured by keeping m ² or less and keeping the melting point of the low melting point material or more for 120 seconds or more.

(C) Corrosion resistance of the joint portion including the joint layer in a wet carbon dioxide environment is ensured by making the base material Cr 9% or more and the insert material Cr 5% or more. In the present specification, "%" of alloy element
Are all "% by weight".

The present invention is a method in which the above items are combined, and is completed by applying it to an actual stainless steel pipe by using an apparatus described later which enables the above-mentioned pressurization and heating and investigating the characteristics of the joint. Was done.

The gist of the present invention is the following diffusion bonding method for stainless steel (see FIG. 1).

(1) The joining portion 3 is heated by interposing a low melting point joining material between the end faces of the joined members 12 to be joined,
In the method of diffusion bonding by applying compressive stress in the longitudinal direction 5, the material to be bonded 12 is stainless steel containing 9% by weight or more of Cr, and the low melting point bonding material has a thickness of 10 to 80 μm.
m Cr: Ni-based alloy containing 5 wt% or more and having a melting point of 1150 ° C. or less, the compressive stress is 0.5 to ² kgf / mm ² at the abutted end faces, and the heating is 8
The heating length 2 to be 00 ° C. or higher is set to 3 to 20 mm, and the temperature of the bonding layer 1 is maintained for 120 seconds or more in a temperature range of the melting point of the low melting point bonding material or more and the melting point of the bonding target material or less. A method for joining stainless steel, which forms a joint having mechanical properties and carbon dioxide corrosion resistance equivalent to or higher than those of the base metal of the joined material.

In the joining method according to the present invention, while a part of the molten low melting point joining material is excluded as a molten phase, the constituent elements in the molten phase infiltrate and diffuse into the end of the stainless steel to be joined, and at the same time, This is performed based on the phenomenon that the constituent elements of stainless steel diffuse into the low melting point bonding material in the molten state and the melting point of the molten phase rises, so that the molten phase solidifies. This bonding method is referred to as "diffusion bonding method" or "liquid phase diffusion bonding method", and "low melting point bonding material" that forms a molten phase is hereinafter referred to as "bonding material". "Joining material" includes insert material that is a rapidly solidified foil, "plating" that is performed on the end surface of stainless steel, or a sprayed film whose thickness is adjusted by plasma spraying or cutting after overlay thermal spraying. .

In the present invention, "intervening" has the usual meaning, sandwiching an insert material which is a foil, and spatially interposing something originally attached to stainless steel such as "plating". It includes both of the following.

The stainless steel to be joined is a martensitic stainless steel and a two-phase (austenite and ferrite) stainless steel. Further, among the stainless steel materials, stainless steel pipes, which will be described later, and particularly seamless oil well pipes are mainly targeted, but not limited to steel pipes, and bar steel, shaped steel, or steel plates are also targeted. Among seamless oil well pipes, straight pipes and coiled seamless steel pipes called coiled tubing are also included.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION

1) Material to be bonded: The material to be bonded in the present invention is martensitic stainless steel or duplex stainless steel containing 9% or more of Cr. If the base material Cr is less than 9%, sufficient corrosion resistance cannot be ensured in a carbon dioxide gas environment of 100 ° C. or less, so the content is set to 9% or more. The upper limit of the Cr content is preferably about 32% to ensure workability. As alloy components other than Cr, C: 0.005 to 0.3%, Si: 0.02
~ 2%, Mn: 0-3%, Cu: 0-3%, Ni: 0-
10%, Mo: 0 to 4%, N: 0.001 to 0.3%,
Pb: 0 to 0.5% and, if necessary, may contain other trace elements such as Al.

The martensitic or duplex stainless steel is used to ensure both sufficient corrosion resistance and proof stress at the same time. For example, austenitic stainless steel has corrosion resistance but cannot secure sufficient proof stress.

2) Bonding material: The bonding material has a melting point of 115.
The alloy has a thickness of 10 to 80 μm at 0 ° C. or less. As described above, the joining material is an insert material which is a rapidly solidified foil, "plating" performed on the end surface of stainless steel in advance, or a sprayed film whose thickness is adjusted by plasma spraying or cutting after overlay spraying. I wish I had it. These plating or thermal spray coatings may be applied to only one end of the tube or both ends. When both ends of the pipe are plated or sprayed, the combined thickness of the plated films on both sides or the combined thickness of the sprayed films on both sides is 10-80μ.
It should be in the range of m.

In the case of the coiled tubing described above,
Insert materials are used exclusively, but other stainless steels also use plated or sprayed coatings. However, in most cases, it is desirable to use the insert material as the bonding material because of its ease of use and manufacturing cost.

The insert material is manufactured as a ribbon by dropping the melt of which components have been adjusted onto the surface of a roll which rotates at a high speed and quenching it. The thickness can be changed by adjusting the amount of molten metal supplied and the roll rotation speed. Alternatively, a commercially available product may be purchased and used.

If the thickness of the insert material is less than 10 μm, the irregularities at the joint interface cannot be completely filled, resulting in a decrease in joint strength. On the other hand, if it exceeds 80 μm, Si,
Since it takes a long time to diffuse B and the like, the bonding efficiency is reduced. In addition, if heating is performed for a short time using such a thick insert material, Si, B, and the like segregate in the bonding layer, and the corrosion resistance of the bonding portion cannot be maintained.

The reason why the Cr content of the bonding material is 5% or more is that of Cr.
This is because if it is less than 5%, sufficient corrosion resistance cannot be ensured in the bonding layer. The upper limit of Cr is not particularly set, but it is desirable to set it to 38% or less from the viewpoint of easy handling of the insert material and the like.

In order to set the melting point of the bonding material to 1150 ° C. or lower, the alloy may be, for example, a Ni alloy containing the chemical composition of the insert material described in Table 1 described later. As the range of alloy elements, Cr: 5 to 38%, Mo: 0 to 5
%, Si: 4 to 10% and B: 0.5 to 4%, and may contain other elements as necessary.

If the melting point can be set to 1150 ° C. or lower,
When the total content of B and Si does not exceed 12%, B
And the amount of Si may be changed.

3) Heating Length of the joint portion including the joint layer and heated to 800 ° C. or higher,
That is, the heating length 2 is set to 3 to 20 mm. This is 8
If the portion heated to 00 ° C. or higher is longer than 20 mm, the yield strength and toughness deteriorate due to heating during joining,
On the other hand, if the heating length is less than 3 mm, a large temperature gradient is locally generated and stable bonding becomes impossible.

The heating length of 20 mm or less is realized by suppressing the length of the coil to 20 mm or less in the case of a device for heating the joint, for example, high frequency heating. As a result, the area heated to 800 ° C or higher is about 10m on each side.
The region which can be set to m or less and is heated at the same time can be a region surrounded by a plane having the same length from the bonding layer, that is, a plane perpendicular to the length direction of the stainless steel.

In the case of joining steel pipes, as will be described later, in the portions located on both sides of the device for heating the joint,
It is desirable to mount a water cooling jacket 13 for cooling the steel pipe, which is made of a material having high thermal conductivity, so as to suppress the temperature rise and the expansion of the heating region due to the heat conduction of the steel pipe portion outside the heating device.

The heating temperature is not less than the melting point of the joining material and not more than the melting point of stainless steel in the joining layer, and the heating time is 120.
More than a second. This is because if the heating temperature is equal to or higher than the melting point of the stainless steel, a sound joint cannot be obtained, and if the heating temperature is lower than the melting point of the joining material, the liquid phase diffusion joining that enables rapid joining is not performed.

Ensure the adhesion between the abutted end faces,
Furthermore, in order to sufficiently diffuse the elements in the insert material and make the chemical composition of the bonding layer close to that of stainless steel, and to secure the bonding strength, bendability, toughness and corrosion resistance, a heating and holding time of at least 120 seconds or more. is necessary.
The upper limit does not need to be specified in particular, but heating and holding for a long time may result in an excessively long heating length.
It is desirable to set it to 0 seconds or less.

4) Compressive stress (pressurizing force) The compressive stress (pressurizing force) in the longitudinal direction 5 is a slight pressure required to hold the insert material until the temperature of the bonding layer reaches the melting point of the insert material or higher. However, above the melting point of the insert material, 0.5 at the abutting end faces
The pressure is set to ² kgf / mm ² . This pressure is 0.5
If it is less than kgf / mm ² , the adhesion at the joint interface will not be maintained at the time of joining, while if it exceeds ² kgf / mm ² , the joint will be excessively deformed and the shape will not be smooth, and retention of corrosive fluid will occur. Since local corrosion may progress, it is set to 0.5 to ² kgf / mm ² . Applied pressure is 2kgf
If the deformation exceeds / mm ² , the stress concentration occurs at the deformed portion and the bendability also deteriorates.

The pressurizing time is synchronized with the heating and is the same as the heating.
It may be held for 20 seconds or more, or may be finished when the melting point of the melted bonding material rises and a solidification phase is formed, and thereafter only heating may be performed.

[0043]

EXAMPLES Next, examples to which the present invention is applied will be shown together with comparative examples.

Table 1 is a list showing the composition of the insert material which is the bonding material used in the experiment.

The insert material is a ribbon produced by the molten metal quenching method in which the molten metal whose components are adjusted is dropped onto the surface of a rotating roll. The thickness of the ribbon is adjusted by the amount of molten metal supplied and the rotation speed of the roll, and is shown in Table 3 below.

[0046]

[Table 1]

Table 2 is a list showing the chemical compositions and yield strengths of martensitic and two-phase stainless steel pipes which are the materials to be joined. The outer diameter of each of these steel pipes is 130
mm, wall thickness: 15 mm seamless steel pipe.

[0048]

[Table 2]

FIG. 2 is a diagram showing an outline of an apparatus used for diffusion bonding. This device is made of a copper 1-turn wide heating coil and gas shield jig 11, a jacket 13 for cooling the materials (steel pipes) 12 to be joined on both outer sides thereof, a joining head comprising a pressurizing clamp 14, a high frequency power source 15 and a control. It is composed of a board 16.

The heating length 2 is 10 to 5 times the width of the heating coil.
It is adjusted to 0 mm, and further, by changing the cooling capacity of the cooling jacket 13 of the steel pipe 12 on the outside thereof (this jacket grasps the steel pipe 12 and circulates cooling water inside the jacket).

Pressurization was performed by the following two methods.

The steel pipe is clamped and the joint surface is pressurized by utilizing the thermal expansion reaction force (a spring is inserted in the clamp to release a part of the thermal expansion reaction force to adjust the applied pressure). The steel pipe is clamped and an external pressure is applied by hydraulic pressure.

A steel pipe with an insert material sandwiched between the end faces was attached to this apparatus, and heating and pressurization were held for a certain period of time for joining.

Table 3 is a list showing the conditions for combining and joining the insert material and the steel pipe in each test code.

[0055]

[Table 3]

Test pieces were sampled from these joints and subjected to a tensile test, a bending test and a corrosion cracking test for evaluation. The bending test piece and the corrosion-resistant cracking test piece were processed into a predetermined thickness by aligning the thickness center of the test piece with the wall thickness center of the steel pipe.

FIG. 3 is a drawing showing the shape of the tensile test piece.

FIG. 4A shows the shape of the bending test piece.
(B) is a drawing showing the shape of the test piece after the bending test.

FIG. 5 (a) shows the shape of the corrosion cracking test piece, and FIG. 5 (b) shows the cross section of the jig and the jig which are placed in a wet carbon dioxide environment under load in the corrosion cracking test. It is a drawing showing. Bending is applied at the center of the test piece so that a stress of 100% of the proof stress of the base material is applied.

The corrosion resistance test was carried out by a cracking test in a wet carbon dioxide gas environment containing a trace amount of hydrogen sulfide. A wet carbon dioxide environment containing a small amount of hydrogen sulfide is (0.001MP
a) H ₂ S + (3.0 MPa) CO ₂ , (5%) NaC
1 aqueous solution. The test temperature is the above-mentioned JP-A-6-796.
The temperature disclosed as having the highest crack susceptibility in Japanese Patent No. 7 is 25 ° C. for martensitic stainless steel, and 80 ° C. for duplex stainless steel.
And The test time was 336 hours in both cases, and those in which no cracking occurred after the test were regarded as pass (yes).

Table 3 is a list showing the joining conditions of the above-mentioned test bodies and the test results. In all the examples of the present invention, the yield strength exceeded the yield strength of the base material shown in Table 2, and cracks did not occur even in the bending test and the corrosion cracking test.

On the other hand, the test code B in the comparative example is
No. 1 has a high yield strength reflecting a large applied pressure, but is insufficient in bending and corrosion cracking resistance, and in the test code B2, it passes the bending test because the heating region is long, but the yield strength and It is unacceptable (No) in the corrosion cracking test.

In other comparative examples, the test code B3 has a too low heating temperature, B4 has a too short heating holding time, B5 has an excessively small pressing force, and B6 has an excessively thick insert material. Therefore, all of them have an unfavorable result in terms of yield strength, bending and corrosion cracking resistance.

From these results, it is understood that the yield strength of the joint portion to which the method of the present invention is applied exceeds that of the base metal, and the bending performance and corrosion cracking resistance performance are very good.

[0065]

The method of the present invention has a corrosion resistance equal to or higher than that of the base material in a wet carbon dioxide gas environment containing a slight amount of hydrogen sulfide by simply joining stainless steel without inputting a large energy density. At the same time, it brings a joint excellent in strength and bendability, so that it is very effective for joining oil country tubular goods, especially coiled tubing.

[Brief description of drawings]

FIG. 1 is a drawing showing a joint formed by applying the method of the present invention.

FIG. 2 is a diagram showing an outline of an apparatus used for carrying out the present invention.

FIG. 3 is a diagram showing a shape of a tensile test piece used for a tensile test of a bonded portion.

FIG. 4A is a view showing a bending test piece used for a bending test of a joint portion. FIG. (B) is a drawing showing the test piece after the bending test.

FIG. 5 (a) is a drawing showing the shape of a corrosion-resistant cracking test piece. FIG. 6B is a view showing a cross section of the test piece and the jig in a state where stress is applied.

[Explanation of symbols]

 1 ... Joining layer 2 ... Heating length 3 ... Joining part 4 ... Diffusion layer 5 ... Longitudinal direction 11 ... Heating coil and gas shield jig 12 ... Joined material 13 ... Cooling jacket 14 ... Clamp 15 ... High frequency power supply 16 ... Control Board

Claims (1)

[Claims] 1. A low-melting-point bonding material is interposed between the end faces of the materials to be bonded (12) butted together, the bonding part (3) is heated, and compression bonding is applied in the longitudinal direction (5) to perform diffusion bonding. In the method, the material to be joined (12) is stainless steel containing Cr: 9 wt% or more, and the low melting point joining material is a melting point containing Cr: 5 wt% or more with a thickness of 10 to 80 μm.
A Ni-based alloy having a temperature of 150 ° C. or lower, a compressive stress of 0.5 to ² kgf / mm ² at the abutted end faces, and a heating length (2) of 800 ° C. or higher is set to 3
It is performed under the condition that the temperature of the bonding layer (1) is set to -20 mm and the temperature of the bonding layer (1) is kept above the melting point of the low melting point bonding material and below the melting point of the bonding target material for 120 seconds or more A method for joining stainless steel to form a joint having the above mechanical properties and carbon dioxide corrosion resistance.