JP4984447B2 - Manufacturing method of low YR ERW steel pipe for line pipe - Google Patents

Description

The present invention relates to a method for manufacturing a low YR electric resistance welded steel pipe for line pipes, and more specifically, low YR electric resistance welded steel pipe for line pipes that is less likely to buckle when laid as a pipeline and has excellent earthquake resistance after laying. It relates to the manufacturing method.
Here, YR is the yield ratio, which is defined by the yield strength (YS) to tensile strength (TS) ratio (= YS / TS) measured by a tensile test. However, YS is one of the following: yield stress (LYS), 0.2% yield strength (0.2% PS) by the offset method, 0.5% yield strength (0.5% PS) by the underload method (full elongation method). In particular, in the case of pipes, the tensile test is performed using full-thickness test pieces in the pipe length (pipe length (L)) direction defined in various industrial standards related to steel pipes such as API, JIS, and ASTM. In addition, the “low YR electric resistance welded pipe” referred to in the present invention means an electric resistance welded pipe having a YR of 0.90 or less (90% or less in percentage display) at any position on the entire circumference or the entire length of the product. .

  Traditionally, seamless steel pipes have been used for reel barge line pipes that are bent and unbent at the time of laying in terms of quality and strength. Attempts have been made to use ERW steel pipes. In such ERW steel pipes for reel barges, local buckling due to bending strain when laying and the breakage of pipes starting from this are problems. In addition to reel barges, ERW steel pipes with a size exceeding Φ200mm are widely used as alternatives to UOE steel pipes, and local buckling occurs due to distortion caused by ground fluctuations such as earthquakes after laying. It has become a problem in recent years that the pipe breaks starting from this. Therefore, as a material design of a pipe for preventing breakage due to local buckling, it has been required to lower YR in the L direction tensile properties, and in recent years, it is necessary to satisfy YR ≦ 90%. .

However, since the ERW steel pipe is given tensile strain in the L direction at the time of pipe forming, the L direction YR tends to increase. In particular, in recent years, there has been a demand for further improvement in sour performance, resulting in a low-C composition compared to past ERW steel pipes, and a significantly higher YR at the material stage (80% or more). It is becoming difficult to satisfy YR ≦ 90% after the tube.
In addition, in the low YR steel pipe for line pipes, for example, for reel barge, a method of substantially setting the carbon amount to 0.1% or more as shown in Patent Document 1 is known. On the other hand, in the UOE steel pipe, a technique of applying a compressive strain in the L direction by expanding the pipe after welding and reducing the YR is used (for example, Patent Document 2).
JP-A-3-21255 Japanese Patent Laid-Open No. 10-310821

However, in the technique described in Patent Document 1, although the characteristics of the electric resistance welded portion are improved by adjusting the components, excellent sour resistance that has been requested by customers in recent years is not taken into consideration. Further, the tensile characteristics shown in the examples are the results of a tensile test of a welded joint including a circumferential weld, and are different from the tensile characteristics of the base material, and thus are not helpful.
On the other hand, in order to apply the pipe expansion process in UOE steel pipe manufacturing to ERW steel pipe manufacturing that generally does not perform pipe expansion, in addition to the need for additional pipe expansion equipment, the pipe expansion process is a batch process that is performed one by one after pipe forming In addition, since heat treatment may be necessary, the production by high-speed welding such as an ERW steel pipe has a drawback that it leads to a significant reduction in production efficiency.

  In view of such circumstances, the present invention provides a method for producing a low YR electric-welded steel pipe for line pipes, which can produce a low-YR electric-welded steel pipe for line pipes without adding equipment or reducing production efficiency. The purpose is to do.

  In order to achieve the above-mentioned object, the present inventors have made correction processing in a rotation correction process that is appropriately performed after pipe forming and ERW welding from the viewpoint of reducing the YR of the ERW steel pipe for line pipe after pipe forming. As a result of diligent examination of the conditions, as a result, using a material with a composition designed to meet the sour resistance, repeatedly bending strain in the tube thickness direction or compressing in the tube longitudinal direction in the rotation correction process It has been found that by imparting strain, excellent sour resistance and low YR after pipe forming can be achieved at once.

  More specifically, the material is made of a specific steel composition of low C system to ensure sour resistance, and in the rotation correction process after ERW welding, 0.1-7.0% of the pipe is obtained by bending and unbending the entire pipe. Conditions (1) for imparting average strain in the thickness direction, conditions (2) for imparting compressive strain in the pipe length direction of 0.1 to 7.0% due to reduced diameter without increasing / decreasing the length in the pipe length direction, 0.1 by direct compression in the pipe length direction without reducing diameter Conditions to give pipe length direction compressive strain of ~ 7.0% (3), Conditions to give pipe length direction compressive strain of 0.1 to 7.0% by diameter reduction and pipe length direction direct compression (4), Condition (1) and Condition (2) The present inventors have found that the effect can be maximized by performing rotation correction processing so that any one of the conditions (5) in combination with any one of (4) is satisfied.

The present invention has been made based on the above findings, and the gist thereof is as follows.
[Claim 1] A steel strip is continuously formed into a substantially cylindrical open pipe, and a pair of upper and lower rolls are intersected with a pipe formed by electro-welding the circumferential ends of the open pipe with their roll axes intersecting each other. In addition, in the method for manufacturing an electric resistance welded steel pipe, the roll stand that is held in a slanted arrangement with respect to the pass line is arranged in a plurality of tandems, and the outer shape is adjusted by performing rotation correction processing. The composition of the steel strip is in mass%, C: 0.02 to 0.1%, Si: 0.01 to 0.5%, Mn: 0.6 to 2.3%, P: 0.01% or less, S: 0.01% or less, Al: 0.1% or less The balance is essentially composed of Fe, and the entire tube is repeatedly bent and bent back, reduced in length without increasing or decreasing the length in the tube length, directly compressed in the tube length without shrinking, and directly compressed in the tube length direction. one of the rotation correction processing, the following condition (2) to (5) of any to one is satisfied Method of manufacturing a line pipe for low YR electric resistance welded steel pipe and wherein the subjecting.

Condition (1): A condition in which an average strain in the pipe thickness direction of 0.1 to 7.0% is given by repeated bending and unbending of the whole pipe.
Condition (2): A condition in which a compressive strain in the pipe length direction of 0.1 to 7.0% is imparted by a diameter reduction without increasing or decreasing the length in the pipe length direction.
Condition (3): A condition in which a compression strain in the tube length direction of 0.1 to 7.0% is imparted by direct compression in the tube length direction without reducing the diameter.
Condition (4): A condition in which a compression strain in the tube length direction of 0.1 to 7.0% is imparted by reducing the diameter and directly compressing in the tube length direction.
Condition (5): A condition in which the condition (1) is combined with any one of the conditions (2) to (4).

[Claim 2] The method for producing a low YR ERW steel pipe for a line pipe according to claim 1, wherein the composition has a carbon equivalent Ceq defined by the following formula of less than 0.44%.
Record
Ceq = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14
However, the element symbol term on the right side is the component content (% by mass) in the steel of the same element, and the term of the component element not contained is ignored.

[Claim 3] Instead of a part of the Fe, one or two kinds selected from Cu: 0.5% or less and Ni: 0.5% or less are contained in mass%. The manufacturing method of the low YR ERW steel pipe for line pipes of 1 or 2.
[Claim 4] The present invention is characterized in that, instead of a part of the Fe, one or two elements selected from Cr: 0.5% or less and Mo: 0.5% or less are contained in mass%. The manufacturing method of the low YR ERW steel pipe for line pipes in any one of 1-3.

[Claim 5] Instead of a part of the Fe, by mass%, Nb: 0.1% or less, V: 0.1% or less, Ti: 0.1% or less selected from one or two or more selected from The manufacturing method of the low YR ERW steel pipe for line pipes in any one of Claims 1-4 characterized by the above-mentioned.
[Claim 6] The low YR electro-sewing for line pipes according to any one of claims 1 to 5, wherein Ca is contained in 0.005% or less by mass% instead of part of the Fe. Steel pipe manufacturing method.

  According to the present invention, it is possible to manufacture a low YR ERW steel pipe for line pipes by appropriately combining the material composition and rotation correction processing conditions without requiring additional equipment and without reducing the production efficiency. it can.

  The present invention provides a tube forming process for continuously forming a steel strip into a substantially cylindrical open pipe, a joining process for electrowelding the circumferential ends of the open pipe, and a pipe after the electrosealing welding. And a rotation correction process for adjusting the external dimensions by performing rotation correction processing. In the tube-forming process, the steel strip that has been continuously discharged from the coiled roll is passed through roll forming means in which a plurality of breakdown roll devices, cage roll devices, fin pass roll devices, etc. are arranged in series. Form continuously into a tube. In the joining step, the V-shaped convergence point of the open pipe is continuously joined by using an electric seam welding means including a high-frequency energization (or induction) heating device and a squeeze roll device. What is necessary is just to implement a pipe-forming shaping | molding process and a joining process by a conventional method.

  The present invention has a great feature in that a low YR can be realized by using a rotation correction process. Therefore, the rotation correction process will be described prior to the description of the material composition. The rotation correction processing is performed using, for example, a rotation correction machine as shown in FIG. 1 in order to adjust the outer dimensions and shape of the tube 1 after pipe forming and electro-welding and improve the product dimensional accuracy. This is made up of a plurality of roll stands 3 arranged in tandem for holding a pair of upper and lower rolls 2 and 2 'in a form in which their roll axes cross each other and are obliquely arranged with respect to the pass line. 3, 3, 3, 3, 3, 3, and 3 can be corrected by bending and bending back. As shown in FIG. 1, when the rolls 2 and 2 'are rotated in the directions indicated by arrows 4 and 4', the tube 1 is conveyed in the direction indicated by arrows 5 while rotating in the direction indicated by arrows 6. At this time, by setting operation factors such as roll rotation speed, roll gap, pass line height position, etc. for each roll stand 3, 3,... Can be controlled.

Conventionally, the rotation correction process is intended only for improving the dimensional accuracy of the product, and there has been no technical idea of using it for controlling the material of the product. On the other hand, according to the present invention, the YR of the product can be advantageously reduced by using the rotation correction process. The operation will be described.
When a rotational straightening machine as shown in FIG. 1 is used to repeatedly apply bending strain to a pipe after ERW welding, a YR related to tensile characteristics in the pipe length direction occurs due to the Bauschinger effect. In addition, when the diameter is reduced without increasing or decreasing the length in the tube length direction, the strain that is subjected to the compressive strain in the tube circumferential direction and tends to extend in the tube length direction is suppressed, so that the compressive strain acts in the tube length direction. The effect causes a reduction in YR related to tensile properties in the tube length direction. Furthermore, depending on the setting method of the operating factor, it is possible to directly apply compressive strain in the tube length direction without reducing the diameter, and in this case as well, low YR is possible through changes in the tube direction tensile properties due to the Bauschinger effect. It becomes.

If the average strain in the tube thickness direction given by repeated bending and unbending of the entire tube is 0.1% or more, it is sufficient to reduce YR. On the other hand, if it exceeds 7.0%, the bausinger in the tube length direction by work hardening Since the effect is offset, it is important to set the content to 0.1 to 7.0%.
In addition, the compression strain in the tube length direction is 0.1% or more, regardless of whether the application method is reduced diameter or direct compression in the tube length direction, and is sufficient to reduce YR due to the Bauschinger effect, while 7.0% If it exceeds 1, the bausinger effect in the tube length direction is offset by work hardening, so it is important to set it to 0.1 to 7.0% or less.

Pipe thickness direction average strain imparted by repeated bending and unbending, pipe length direction compressive strain imparted by reduced diameter, and pipe length direction compressive strain imparted by direct compression in the pipe length direction are reduced YR both when performed individually and in combination. The effect is obtained.
The quantitative relationship between the control amount and the set operation amount of the operation factor necessary for controlling the tube thickness direction average strain or the tube length direction compression strain to the target value is appropriately determined based on the elasto-plastic deformation theory of the tube. This can be determined using a model formula that has been verified by experiment.

  Next, the reason for limiting the composition (chemical component) of the material will be described. In addition, although mass% is used for the unit of chemical component content, it is abbreviated as% below. The electric resistance welded steel pipe for line pipes which is the subject of the present invention needs to have excellent sour resistance in order to withstand use in various laying environments and in particular to meet customer demands in recent years. Accordingly, the material composition according to the present invention was designed based on the sour resistant adaptive composition.

  C is 0.02 to 0.1%. C is an element that contributes to precipitation strengthening as a carbide. However, if it exceeds 0.1%, the fraction of the second phase of pearlite, bainite, martensite, etc. increases, ensuring the excellent sour resistance required for line pipes. become unable. For this reason, C was limited to 0.1% or less. On the other hand, if the C content is less than 0.02%, sufficient strength as a line pipe cannot be secured. For this reason, C is contained by 0.02% or more. Preferably it is 0.02 to 0.07%.

Si is 0.01 to 0.5%. Si is added for deoxidation, but if it is less than 0.01%, the deoxidation effect is not sufficient, and if it exceeds 0.5%, the ERW weldability is deteriorated, so the Si content is specified to be 0.01 to 0.5%.
Mn is 0.6 to 2.3%. Mn is added to ensure strength and toughness, but if it is less than 0.6%, the effect is not sufficient, and if it exceeds 2.3%, the second phase fraction increases and the excellent material toughness required as a line pipe cannot be secured. Therefore, the Mn content is specified to be 0.6 to 2.3%.

P is 0.01% or less. Since P is an element that degrades electroweldability, the upper limit of the P content is specified to be 0.01%.
S is 0.01% or less. S is generally better in the steel because it becomes MnS inclusions in steel and the origin of hydrogen-induced cracking (HIC). However, since there is no problem if it is 0.01% or less, the upper limit of the S content is specified as 0.01%.

On the other hand, as an index of the weldability of steel materials, the carbon equivalent Ceq of the following formula derived from experimental data analysis on the influence of component elements on the maximum hardness of the weld heat affected zone of structural steel materials is often used.
Ceq = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14
However, the element symbol term on the right side is the component content (% by mass) in the steel of the same element, and the term of the component element not contained is ignored. If Ceq is less than 0.44%, defects such as cracks are unlikely to occur in various welding operations of ERW steel pipes. Therefore, in the present invention, Ceq is preferably less than 0.44%. It should be noted that the embodiment relating to the Ceq regulation is desirably applied even when it contains a selective additive component described later.

The remainder other than the above consists essentially of Fe. That the balance is substantially composed of Fe means that an element containing an inevitable impurity and other trace additive elements is included in the scope of the present invention unless the effects of the present invention are lost. The content of inevitable impurities is preferably 0.05% or less in total. The content of other trace additive elements is preferably 5% or less in total.
Furthermore, in the present invention, in order to further improve the strength and yield ratio of the ERW steel pipe for line pipe, toughness, instead of a part of Fe in the composition,
-Cu: 0.5% or less, Ni: 1 or 2 types selected from 0.5% or less,
・ One or two selected from Cr: 0.5% or less, Mo: 0.5% or less,
-Nb: 0.1% or less, V: 0.1% or less, Ti: 0.1% or less selected from the following,
・ Ca: 0.005% or less,
Can be added selectively.

Cu should be 0.5% or less. Cu is an effective element for improving toughness and increasing strength, but if added in large quantities, weldability deteriorates, so when added, the upper limit is 0.5%. Preferably it is 0.05 to 0.5%.
Ni should be 0.5% or less. Ni is an element effective for improving toughness and increasing strength. However, if added in a large amount, a hardened second phase tends to be formed, leading to a decrease in sour resistance. Therefore, when added, the upper limit is 0.5%. Preferably it is 0.05 to 0.5%.

Cr is preferably 0.5% or less. Like Mn, Cr is an element effective for obtaining sufficient strength even at low C. However, if added in a large amount, the second phase tends to form and the sour resistance is lowered. And Preferably it is 0.1 to 0.5%.
Mo should be 0.5% or less. Mo is an element effective for obtaining sufficient strength even at low C like Mn and Cr, but if added in a large amount, the second phase tends to form and lowers sour resistance, so 0.5% when added. Is the upper limit. Preferably it is 0.05 to 0.5%.

Nb is preferably 0.1% or less. Nb improves strength and toughness by fine precipitation of carbonitride and fine graining of the structure. However, if it exceeds 0.1%, the cured second phase tends to increase, and sour resistance is remarkably deteriorated. Preferably it is 0.01 to 0.1%.
V should be 0.1% or less. V, like Nb, contributes to strength increase by fine precipitation of carbonitride. However, if it exceeds 0.1%, the cured second phase fraction increases in the same manner as Nb and the sour resistance is remarkably deteriorated. Preferably it is 0.05 to 0.1%.

Ti should be 0.1% or less. Ti, like Nb and V, contributes to strength increase by fine precipitation of carbonitride. However, if it exceeds 0.1%, the cured second phase fraction increases in the same manner as Nb and the sour resistance is remarkably deteriorated. Preferably it is 0.005-0.1%.
Ca is preferably 0.005% or less. Ca is an element necessary for controlling the morphology of elongated MnS, which tends to be the starting point of hydrogen-induced cracking. However, if added over 0.005%, excessive Ca oxides and sulfides are generated, leading to toughness deterioration. Therefore, when added, the content is specified to be 0.005% or less. Preferably it is 0.002 to 0.005%.

  A steel strip (coiled hot-rolled steel plate) having the composition, thickness, YS, TS, and YR shown in Table 1 is obtained by the tube forming step and the subsequent joining step (heating method is a high-frequency current heating method). The obtained tube was subjected to rotation correction treatment using a rotation straightening machine under any of the conditions shown in Table 2 to produce an X65 electric resistance steel tube having an outer diameter of 18 inches (457 mmφ). In the present embodiment, the joining process is performed by a high-frequency current heating method, but other heating methods such as a high-frequency induction heating method are also applicable.

  Using JIS No. 5 full-thickness tensile test specimens collected so that the test direction is the L direction from the position 180 degrees away from the seam portion of the obtained ERW steel pipe (product) in the circumferential direction, A YS (LYS or 0.2% PS) and TS were measured by performing a compliant tensile test, and YS was calculated. Then, in consideration of manufacturing variations, products having a YS of 88% or less were evaluated as pass (◯) in terms of excellent low yield ratio, and the rest were evaluated as fail (×).

  In addition, a corrosion test piece (size: 20W x total thickness x 100L [mm]) collected from the product is used to conduct an HIC test in accordance with the NACE Standard TM0284, and after immersion, the test piece is cut in accordance with the same. After polishing, the crack length was measured, and the crack length ratio (CLR) was determined. And the thing with CLR of 10% or less was evaluated by the point which is excellent in sour resistance ((circle)), and the remainder was rejected (x).

  Furthermore, as a comprehensive evaluation of the low yield ratio and sour resistance, “good” indicates that both of these are acceptable and “×” indicates the rest. The obtained results are shown in Table 3.

From Table 3, all steel pipes (No. 1 to 5) made of steel strip A whose C content is outside the claimed range are ferrite-bainite based on the structure and pass the low yield ratio. It does not accept sourness. Steel pipes (steel pipe Nos. 6 to 15) made of steel strips B and C whose Mn or Nb content is outside the scope of claims are not acceptable for not only sour resistance but also low yield ratio. .
In the case of steel pipes (steel pipes Nos. 16 to 41) made of steel strips D to J whose composition is within the claimed range, they all pass sour resistance. However, condition No. 1 in which rotation correction processing is not performed, condition No. 2 in which the average strain in the pipe thickness direction by repeated bending-bending is less than 0.1%, condition No. 3 in which the strain exceeds 7.0%, pipe length direction Although the diameter was reduced without increasing the length of the tube, the tube length direction compression strain was relatively less than 0.1%, condition No. 5, the strain was over 7.0%, condition No. 6, and the tube length direction compression was performed without shrinkage, but the tube length direction compression. In condition No. 8 in which the strain is less than 0.1% and condition No. 9 in which the strain exceeds 7.0%, the low yield ratio is not acceptable. On the other hand, in conditions No. 4, 7, 10, 11, 12, and 13 in which the rotation correction treatment is within the claimed range, YR is lower than that of the material strip steel, and the low yield ratio is passed.

It is the schematic which shows one example of a rotation correction machine.

Explanation of symbols

1 tube 2, 2 'roll 3 roll stand 4 arrow in the roll rotation direction 5 arrow in the tube transport direction 6 arrow in the tube rotation direction

Claims (6)

A steel strip is continuously formed into a substantially cylindrical open pipe, and a pair of upper and lower rolls are joined to a pipe formed by electro-welding the circumferential ends of the open pipe with their roll axes crossing each other and passing lines. On the other hand, in a method of manufacturing an ERW steel pipe that uses a rotation straightening machine in which a plurality of roll stands that are held in an oblique arrangement are arranged in tandem, the rotation dimension is adjusted to adjust the outer shape and shape. , C: 0.02 to 0.1%, Si: 0.01 to 0.5%, Mn: 0.6 to 2.3%, P: 0.01% or less, S: 0.01% or less, Al: 0.1% or less, with the balance being substantially In general, the composition is composed of Fe, and the entire pipe is repeatedly bent and unbent, reduced in diameter in the tube length direction without any increase or decrease in length, directly compressed in the tube length direction without diameter reduction, and reduced in rotation or directly compressed in the tube length direction. The processing is performed so that any one of the following conditions (2) to (5) is satisfied. A manufacturing method of low YR ERW steel pipes for line pipes.
Condition (1): A condition in which an average strain in the tube thickness direction of 0.1 to 7.0% is given by repeated bending and unbending of the entire tube.
Condition (2): A condition in which a compressive strain in the pipe length direction of 0.1 to 7.0% is imparted by a diameter reduction without increasing or decreasing the length in the pipe length direction.
Condition (3): A condition in which a compression strain in the tube length direction of 0.1 to 7.0% is imparted by direct compression in the tube length direction without reducing the diameter.
Condition (4): A condition in which a compression strain in the tube length direction of 0.1 to 7.0% is imparted by reducing the diameter and directly compressing in the tube length direction.
Condition (5): A condition in which the condition (1) is combined with any one of the conditions (2) to (4). The method for producing a low YR electric resistance welded steel pipe for a line pipe according to claim 1, wherein the composition is such that the carbon equivalent Ceq defined by the following formula is less than 0.44%.
Record
Ceq = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14
However, the element symbol term on the right side is the component content (% by mass) in the steel of the same element, and the term of the component element not contained is ignored.   It replaces with a part of said Fe, and contained 1 type or 2 types chosen from Cu: 0.5% or less and Ni: 0.5% or less in the mass%, The Claim 1 or 2 characterized by the above-mentioned. Of low YR ERW steel pipes for line pipes.   4. Instead of a part of the Fe, one or two selected from Cr: 0.5% or less and Mo: 0.5% or less are contained by mass%. A method for producing a low YR electric resistance welded steel pipe for a line pipe according to claim 1.   Instead of a part of the Fe, it is characterized by containing one or more selected from the group consisting of Nb: 0.1% or less, V: 0.1% or less, Ti: 0.1% or less in mass%. The manufacturing method of the low YR ERW steel pipe for line pipes in any one of Claims 1-4.   The method for producing a low YR ERW steel pipe for a line pipe according to any one of claims 1 to 5, wherein Ca is contained by 0.005% or less in mass% instead of a part of the Fe.

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