JPH0751743A - Band steel having different thicknesses in longitudinal direction and steel pipe using same as base stock - Google Patents

Abstract

PURPOSE:To obtain a band steel and a steel pipe gradually increasing the thickness toward the longitudinal direction. CONSTITUTION:The band steel 1-1 varying the thickness toward the longitudinal direction and having the range of 1.6-4.5mm the min. thickness t1 and the max. thickness t2 and the fixed value of <=22% variation ratio alpha of the thickness shown in the following equation, is used. alpha=[(t2-t1)/t1]x 100%. Further, the steel containing 0.09-0.18wt.% C, 0.25-0.45% Si, 0.70-1.00% Mn, 0.20-0.30% Cu, 0.05-0.20% Ni, 0.50-0.80% Cr, <=0.002% S and the balance Fe with inevitable impurities is used as the base stock. The pipe is manufactured by using this band steel to form the steel pipe varying the thickness at the fixed ratio toward the longitudinal direction. This steel pipes 3-1, 3-2 can be welded without a step on the outer periphery and are available to the steel pipe for cleaning the inner surface of an oil well pipe.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a strip steel whose plate thickness varies in the longitudinal direction at a constant rate, and a steel pipe manufactured from the strip steel whose wall thickness varies at a constant rate in the longitudinal direction.

[0002]

2. Description of the Related Art Usually, a hot-rolled steel sheet (a hot-rolled steel sheet and a product obtained by slitting the hot-rolled steel sheet in the longitudinal direction are referred to as "band steel" in the present specification, and a coiled product thereof is referred to as a coil) Has a constant strip thickness, and rolling is performed in one coil so that the variation in strip thickness is as small as possible.

However, as a raw material for producing a special product as described below, a strip steel whose plate thickness varies in the longitudinal direction is desired.

FIG. 4 shows a steel pipe for cleaning the inner surface of an oil well pipe, which is lowered into an oil well pipe deeply buried in the ground, for example, at a depth of several thousand meters. It is used for pouring a cleaning liquid to clean the inner surface of the oil well pipe. In addition, FIG. 4 and FIG.
To clarify the characteristics, the longitudinal direction is drawn smaller than the radial direction of the tube.

FIG. 5 is a schematic diagram for explaining a method of suspending the above oil well pipe cleaning steel pipe in the oil well pipe 8. The oil well cleaning steel pipe 5'is, as shown in the drawing, a winding / rewinding device 9
It is wound into a coil and transported to the oil field. Then, it is unwound in the horizontal direction, suspended in the oil well pipe 8 while curving the steel pipe by the guide roll 10, and wound up and pulled out after the cleaning work is completed.

As shown in FIG. 4, a conventional steel pipe 5'for cleaning oil country tubular goods is an electric resistance welded steel pipe manufactured by forming strip steels for several coils having different plate thicknesses and electric resistance welding the widthwise ends thereof. 7-1, 7-
Used as a joined steel pipe with a constant inner diameter by butt-welding a large number of ,. As shown in FIG. 4, the reason why the wall thickness becomes smaller as it goes downward is to reduce the suspended weight because a steel pipe having a long pipe length is used in a suspended state.

As described above, the conventional steel pipe for cleaning oil country tubular goods 5 '
Since a large number of steel pipes made of strip steel having a constant plate thickness are connected to each other, a step is formed in the butt welding portion 6.
As shown in FIG. 5, when such a steel pipe is wound into a coil and put into and taken out from the oil country tubular goods 8, when the bending portion 11 and the winding / rewinding device 9 undergo bending and bending back processing, the welded portion Since 6 has the above-mentioned step, the notch effect is generated, and the step easily starts cracking. To avoid this, if steel pipes made of hot-rolled steel of the same plate thickness are butt-welded and used, the suspension weight increases, so the steel pipe material must be upgraded to increase its strength. Equipment such as winding and rewinding devices must also be large-scale.

[0008]

DISCLOSURE OF THE INVENTION An object of the present invention is to provide a steel strip which can be used in various applications in the longitudinal direction and whose plate thickness is changed at a constant ratio, and a longitudinal direction produced by using the steel strip as a raw material. The purpose is to provide a steel pipe whose wall thickness is changed at a constant ratio. This steel pipe is connected by butt welding and is suitable for use as the above-mentioned oil well pipe cleaning steel pipe.

[0009]

Means for Solving the Problems The gist of the present invention is the following strip steels (1) and (2) and steel pipes (3) below using them as raw materials.

(1) A strip steel having a plate thickness varying in the longitudinal direction, and the minimum strip thickness t ₁ and the maximum strip thickness t _{2 in the} strip are both within the range of 1.6 to 4.5 mm. And, a strip steel characterized in that the plate thickness change rate α represented by the following formula is a constant value of 22% or less.

Plate thickness change rate α (%) = [(t ₂ −t ₁ ) / t ₁ ] × 100 (%), where t ₁ is the minimum plate thickness (mm) t ₂ in the same strip steel. : Maximum plate thickness (mm) in the same strip steel (2)% by weight, C: 0.09 to 0.18%, Si: 0.25 to 0.45%,
Mn: 0.70 to 1.00%, Cu: 0.20 to 0.30%, Ni: 0.05 to 0.20
%, Cr: 0.50 to 0.80%, S: 0.002% or less, the balance Fe
The steel strip according to (1) above, which is manufactured from steel consisting of unavoidable impurities.

(3) A steel pipe produced by using the strip steel according to the above (1) or (2), and having a wall thickness varying at a constant ratio in the longitudinal direction.

The strip steel of the present invention according to the above (1) and (2),
It includes a steel plate as hot-rolled, a steel plate having a plurality of slits formed in the longitudinal direction (rolling direction), and a steel plate obtained by cutting these into a predetermined length. In addition, this strip steel is usually 600 ~
It is about 1600 m long.

The strip steel of the present invention can be manufactured by a method of continuously changing the rolling reduction of the finish rolling mill of the hot rolling mill. For example, by the integration control of the plate thickness X-ray monitor,
Rolling is performed while adjusting the plate thickness on the rolling top side to be thin and the plate thickness on the rolling bottom side to be thick according to the reference plate thickness and the thickness change rate (α).

FIG. 1 is a perspective view of a steel strip of the present invention (showing two types of steel strips having different reference plate thicknesses, 1-1 and 1-2). In this figure, the longitudinal direction of the plate is shown to be smaller than the width direction. As shown in this figure, the steel strip 1-1 of the present invention
Has a minimum plate thickness t ₁ and a maximum plate thickness t _2, and from this t ₂ to t ₁ , the plate thickness decreases at a constant ratio α in the longitudinal direction of the strip steel. Similarly, the steel strip 1-2 also has a minimum strip thickness t ₁ 'and a maximum strip thickness t ₂ ', and from this t ₂ 'to t ₁ ', the strip thickness has a constant ratio in the longitudinal direction of the strip steel. It decreases with α.

FIG. 2 is a perspective view of the steel pipes 3-1 and 3-2 of the present invention produced by forming the above-mentioned strip steels 1-1 and 1-2 into a circular shape in the longitudinal direction and joining the ends in the width direction. It is a figure. For the production of this steel pipe, a well-known method for producing a so-called ERW steel pipe, in which a band steel is formed and welded, can be adopted. The manufactured steel pipe has a length corresponding to the length of the strip steel of the raw material, and this is wound into a coil and stored and transported. A long steel pipe with a predetermined length is made by welding.

The steel pipe 3-1 shown in FIG. 2 is made of a strip steel 1-1, and therefore its wall thickness varies in the longitudinal direction at a constant ratio, and the minimum wall thickness T ₁ is the above. equal to t ₁ ,
Also, the maximum wall thickness T ₂ is equal to t ₂ . On the other hand, steel pipe 3-2
Is made of strip steel 1-2, and its minimum wall thickness T
₁ 'is the t _1' equal to, also, the maximum thickness T ₂ 'is t _2' is equal to. The inner diameters d ₁ and d ₂ are manufactured to be equal.

The minimum thickness t _{1 of the} steel strip 1-1 shown in FIG.
2-1) and the maximum thickness t ₂ 'of the steel strip 1-2 (the thickness of the end 2-2) are made equal, the minimum wall thickness of the steel pipe 3-1 shown in Fig. 2 is obtained. The thickness T ₁ is equal to the maximum wall thickness T ₂ ′ of the steel pipe 3-2.
Therefore, connect the steel pipes 3-1 and 3-2 to the ends 4-1 and 4-
If the connection is made by butt welding at step 2, there will be no step at the connection. FIG. 3 shows the state.

FIG. 3 is a cross-sectional view of a steel pipe for oil well pipe cleaning in which the steel pipes (3 pipes) of the present invention are butt welded. As is apparent from comparison with FIG. 4 described above, the outer diameter of the steel pipe 5 for cleaning oil country tubular goods gradually decreases without interruption, and the joint 6 has no step. Therefore, even when this connecting pipe is used as the above-mentioned oil well pipe cleaning steel pipe as shown in FIG. 5, there is no risk of cracks or the like due to steps.

[0020]

As described above, the strip according to the present invention changes in plate thickness at a constant rate α (%). This α is 21% or less, and the minimum strip thickness t in the strip steel is t. ₁ and maximum plate thickness t ₂
Are in the range of 1.6 to 4.5 mm. Further, it is desirable that the chemical composition of the steel used as the material of the strip steel be as described above. The reason for defining these conditions will be described together with the operational effects.

(A) Plate thickness change rate: The reason why the plate thickness change rate α (%) expressed by the above formula must be 22% or less is as follows.

(1) It is not necessary to change the opening degree (roll interval) of the finishing roll during rolling in the case of ordinary rolling of a strip steel having a constant plate thickness, but when rolling the strip of the present invention, ,
It is necessary to change the opening of the finishing roll during rolling.
At this time, the larger the rate of change of the plate thickness, the greater the amount of change in the roll opening during rolling, making it difficult to adjust the reduction load load balance of the finishing rolls in each stand, and the variation of the reduction load load balance becomes difficult. growing.
As a result, there is a risk that a narrowing variation of the sheet thickness (the sheet thickness varies due to a localized concentrated load in the width direction) or a sheet passing trouble such as a break of the sheet during rolling.

(2) In the strip rolling of the present invention, the strip thickness is changed in the length direction of the strip by rolling so that the strip top side is thin and the strip bottom side is thick. Although the reverse is also possible, the above rolling method is preferable from the viewpoint of stabilizing the mill load and reducing the variation in strip thickness of the steel strip.

At this time, if the rate of change in plate thickness is too large,
Opening degree of the pinch roll installed in front of the coil winder
(Roll interval) The followability of the adjustment becomes insufficient, the pinch roll is excessively pressed, and the roll is easily scratched, and the coil surface is easily scratched. Further, if the pinch roll is excessively reduced, the tension between the final finishing roll and the pinch roll is likely to fluctuate, and the coil shape becomes unstable. As a result, a defective shape such as a camber that is laterally bent in the rolling direction when the coil is unfolded or a defective winding shape due to uneven coil edges may occur.

From the results of a large number of tests, the limit of the plate thickness reduction rate at which the above problems (1) and (2) do not occur was calculated.
It became clear that it was%.

(B) Range of strip thickness of strip steel: The minimum strip thickness t ₁ and the maximum strip thickness t ₂ of the strip according to the present invention are 1.6 to 4.5 mm.
Must be within the range. The reason is as follows. That is, when the rolled plate thickness becomes thinner than 1.6 mm,
The pressing load becomes large and it becomes difficult to pass the plate. Furthermore, in rolling that changes the strip thickness during rolling, the load balance in the axial direction of the roll is more likely to be uneven than in the case of rolling steel strips where the strip thickness is constant, and localized concentrated loads are applied in the width direction. As a result, the thickness of the sheet may be narrowed and the sheet may break during rolling. On the other hand, if the plate thickness is thicker than 4.5 mm, the bending performance in the curved portion of the steel pipe cannot be ensured in the welded steel pipe with a long pipe length used in a suspended state by the method shown in FIG.

(C) Chemical composition of raw steel: The steel strip and the steel pipe of the present invention can be used for various purposes, and the steel type of the raw material may be selected according to the use. However, when the steel pipe of the present invention is used as a steel pipe for cleaning oil country tubular goods, the environment in which it is used is highly corrosive, it requires strength because a long pipe is suspended, and since it is joined by welding, Considering the fact that excellent weldability is required, etc., it is desirable to consider the component contents of the raw steel as follows. Hereinafter,% relating to the content means% by weight.

C, Si, Mn: C, Si and Mn have the function of improving the strength of steel. If their contents are low, the desired strength cannot be secured, so the lower limit contents are preferably 0.09% for C, 0.25% for Si, and 0.70% for Mn. On the other hand, if the contents of C, Si and Mn increase, the weldability deteriorates, so the upper limits of the contents are preferably 0.18% for C, 0.45% for Si and 1.00% for Mn.

S (Sulfur): S is an unavoidable impurity of steel. If the content is high, the amount of sulfide inclusions increases, and the resistance to hydrogen sulfide cracking that occurs in the oil well environment deteriorates. Therefore, it is desirable to keep S to 0.002% or less.

Cu: Cu improves the corrosion resistance of steel. To obtain this effect, it is necessary to contain 0.20% or more. On the other hand, when Cu-added steel is heated, a Cu-rich solid solution having a low melting point is formed immediately below the scale on the surface of the rolled material, and surface defects occur during hot rolling. This phenomenon can be mitigated by the addition of Ni described below.
As the content of Ni increases, the amount of expensive Ni used must be increased. Therefore, considering economic efficiency, the Cu content is
It should be up to 0.30%.

Ni: Ni has the effect of preventing the occurrence of surface defects due to the addition of Cu. If Cu is 0.20 to 0.30% steel, by adding Ni to 0.05 to 0.20%,
The melting point of the Cu-enriched solid solution is increased, and surface defects are prevented from occurring during hot rolling.

Cr: A component that improves the strength and corrosion resistance of steel. 0.50% or more is required to fully exhibit this effect. On the other hand, considering economic efficiency, the content of Cr is 0.
It is desirable to limit it to 80%.

(D) Steel pipes whose wall thickness changes at a constant change rate in the longitudinal direction: When the strip steel of the present invention is used, for example, it is possible to manufacture a steel pipe whose inner diameter is constant and whose wall thickness changes in the longitudinal direction. it can. The inner diameter can be adjusted by changing the width of the strip steel (hot-rolled steel plate or its slit material).

By connecting the above steel pipes by butt welding of the end portions, a long joined steel pipe having a constant inner diameter and a gradually decreasing (or gradually increasing) outer diameter can be manufactured. As shown in FIG. 3, since there is no step at the joint portion of this joined steel pipe, handling is easy, and the step does not become a notch and is not destroyed. Further, when the pipe is extended and used in a suspended state, the suspended weight can be reduced by reducing the wall thickness toward the tip (downward).

In the above-mentioned connected steel pipe, the material of each steel pipe constituting the same may be the same or different. For example, when used for cleaning the inner surface of the oil well pipe described above, it is possible to make the steel pipe on which the load is applied higher in strength or to make the steel pipe on the tip end side particularly excellent in corrosion resistance.

[0036]

EXAMPLES As examples, examples of manufacturing the steel strip and the steel pipe of the present invention as a material for a steel pipe for cleaning oil country tubular goods will be described below.

Continuously cast slabs of steel having various chemical compositions shown in Table 1 were hot-rolled to produce steel strips having a thickness changed in the longitudinal direction as shown in Table 2. The hot rolling conditions were that the rolling finishing temperature was 860 ° C and the coil winding temperature was 560 ° C.
The state of occurrence of surface defects and the flatness of the manufactured steel strip were investigated, and the results are shown in Table 2. The circles are those with almost no flaws and good flatness.

Next, after roll-forming the strip steel obtained by slitting the above strip steel in the longitudinal direction, electric resistance welding (E
Welding by the RW method, the wall thickness changes in the longitudinal direction and the inner diameter
A steel pipe with a length of 26.5 mm and a length of 850 m was manufactured.

First, in order to evaluate the strength characteristics, a tensile test was performed using JIS No. 5 test pieces in the strip rolling direction. The results are shown in Table 3. Here, the value of the yield point (YP) marked with ◯ means that it is 343 N / mm ² or more and satisfies the level required as a steel pipe for cleaning oil country tubular goods.

On the other hand, in order to evaluate the corrosion resistance, an acid corrosion resistance test was conducted under the following conditions to examine the corrosion weight loss.

Corrosion test liquid: 60% by volume H ₂ SO ₄ aqueous solution Test temperature: 80 ° C. Immersion time: 16 hours Specimen size: thickness 2.3 mm, width 100 mm, length 150 mm The test results are also shown in Table 3. Here, the value with ○ is
It means that the weight residual ratio is 80% or more and satisfies the level required as a steel pipe for cleaning oil country tubular goods.

Further, in order to evaluate the weldability of the steel pipe, steel pipes of the same steel type were butted and welded under the following conditions, and the maximum hardness of the weld heat affected zone was measured.

Welding method: TIG welding Current: 130 A Welding speed: 15 cm / min The measurement results are also shown in Table 3. Here, as the butt weldability of the steel pipe for cleaning oil country tubular goods is good, the maximum hardness Hv (Vickers hardness) of the weld heat affected zone is 210 or less is marked with a circle.

Table 4 shows the results of a bending test conducted to evaluate the bending performance of the butt welded portion of the steel pipe of the present invention. That is, several steel strips were selected from those shown in Table 2, and using these as raw materials, pipes were manufactured under the above-mentioned pipe making conditions, and butt welding was performed to perform a bending test. This butt welding method is the TIG welding method.

6A and 6B are views showing a bending test method. FIG. 6A is a front view and FIG. 6B is a side view. As shown in the figure,
The press fitting 12 and the support 13 are provided with a groove having a cross section close to a semicircle with which the outer diameter of the test tube 14 circumscribes so that the steel tube can be smoothly bent.

The bending performance is such that the bending angle is constant at 90 °,
Change the bending radius by an integral multiple of the pipe inner diameter (d = 26.5 mm),
It was evaluated by whether or not cracks were generated in the weld. The smaller the bending radius that can be bent without causing cracking, the better the bending performance.

In Tables 2 and 3, the rank A indicates that the chemical composition of the raw steel is within the desirable range described above, and the plate thickness and the plate thickness change rate are within the range of the present invention. belongs to. Rank B indicates that the content of the component marked with * deviates from the desirable range among the components of the material steel, and Comparative Example shows that the plate thickness or the plate thickness change rate is outside the range of the present invention. is there. The conventional example is an example of a strip steel having a constant plate thickness.

From the results shown in Tables 2 and 3, the band steel of rank A and the steel pipe made of the same are sufficiently satisfied with the mechanical properties, corrosion resistance and weldability required for the steel pipe for cleaning oil country tubular goods. You can see that Although those of rank B have insufficient properties in any of these properties, they can be used in applications other than steel pipes for cleaning oil country tubular goods.

In the comparative example, there is a problem in the plate thickness or the plate thickness change rate, and there are problems in the surface properties and flatness of the strip steel.

Looking at the results in Table 4 showing the bending performance after the butt welding of the steel pipes, it was found that the excellent bending performance was obtained in the joining of the steel pipes of rank A, while the steel pipes of the comparative example having no change in wall thickness were obtained. It can be seen that the bending performance is remarkably inferior in the joints (a step is formed on the outer periphery as shown in FIG. 4).

[0051]

[Table 1]

[0052]

[Table 2]

[0053]

[Table 3]

[0054]

[Table 4]

[0055]

EFFECT OF THE INVENTION The strip steel of the present invention having a varied thickness can be used, for example, for manufacturing a steel pipe having a varied thickness. This steel pipe can be butt-welded to form a long steel pipe having no step on the outer periphery of the connection portion. Furthermore, by appropriately selecting the chemical composition of the material, it is possible to obtain a strip steel or steel pipe having good weldability, corrosion resistance and high strength.
It is extremely excellent for being used in a suspended state in a corrosive environment like a steel pipe for cleaning the inner surface of an oil well pipe.

[Brief description of drawings]

FIG. 1 is a perspective view of a steel strip according to the present invention in which the plate thickness is changed at a constant ratio.

2 is a perspective view of a steel pipe of the present invention manufactured from the steel strip of FIG. 1 and having a variable wall thickness.

FIG. 3 is a longitudinal sectional view of a connection steel pipe obtained by butt welding the steel pipes of the present invention.

FIG. 4 is a vertical cross-sectional view of a connection steel pipe obtained by butt welding conventional steel pipes having a constant wall thickness.

FIG. 5 is a schematic diagram illustrating a method of suspending the connection steel pipe of FIG. 4 in an oil well pipe for cleaning the oil well pipe.

6A and 6B are views showing a bending test method for butt-welded steel pipes, in which FIG. 6A is a front view and FIG. 6B is a side view.

[Explanation of symbols]

1-1 and 1-2: strip steel of the present invention t ₁ : minimum strip thickness of steel strip 1-1, t ₂ : same maximum strip thickness 3-1 and 3-2: steel pipe of the present invention T ₁ : steel pipe 3 minimum thickness of -1, T _2: likewise the maximum thickness 5 and 5 ': oil well pipe cleaning steel, 6: junctions, 7-1 and 7-2: conventional constant thickness of the steel pipe, 8: OCTG 9: Winding / rewinding device

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[Procedure amendment]

[Submission date] September 7, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Claim 2

[Correction method] Change

[Correction content]

Claims (3)

[Claims] 1. A strip steel having a strip thickness varying in the longitudinal direction, wherein both the minimum strip thickness t ₁ and the maximum strip thickness t ₂ in the strip steel are within a range of 1.6 to 4.5 mm, Further, the strip steel characterized in that the plate thickness change rate α represented by the following formula is a constant value of 22% or less. Plate thickness change rate α (%) = [(t ₂ −t ₁ ) / t ₁ ] × 100 (%), where t ₁ is the minimum plate thickness in the same strip steel (mm) t ₂ : the same strip Maximum plate thickness in steel (mm) 2. C: 0.09 to 0.18% by weight, Si: 0.25 to
0.45%, Mn: 0.70 to 1.00%, Cu: 0.20 to 0.30%, Ni: 0.
05 to 0.20%, Cr: 0.50 to 0.80%, S: 0.002% or less,
The strip steel according to any one of claims 1 to 3, which is manufactured from a steel having the balance being Fe and inevitable impurities. 3. A steel pipe produced by using the strip steel according to claim 1 or 2, and having a wall thickness varying at a constant ratio in the longitudinal direction.