JP2008202128A - ERW steel pipe for expanded oil well with excellent pipe expansion performance and corrosion resistance and method for producing the same - Google Patents

Abstract

The present invention provides an electric-welded steel pipe for an expanded oil well that can be expanded at a high expansion ratio and has excellent resistance to sulfide stress cracking in a corrosive environment in the oil well after the expansion, and a method for manufacturing the same.
SOLUTION: In mass%, C: 0.01 to 0.3%, Si: 0.01 to 0.7%, Mn: 0.5 to 2.0%, Nb: 0.005 to 0.1 %, Ti: 0.005-0.05%, Al: 0.002-0.1%, Ca: 0.0005-0.008%, P: 0.10% or less, S: 0.0. 005% or less, O: 0.0040% or less, Si / Mn: 0.005 to 1.5 is satisfied, and the balance is composed of Fe and inevitable impurities. Excellent tube expansion performance and corrosion resistance ERW steel pipe for expanded oil wells. Furthermore, it is preferable to contain Cr: 0.5% or less and to satisfy Si / (Mn + Cr): 0.005-1.5.
[Selection figure] None

Description

  The present invention relates to an electric resistance steel pipe used for an oil well or a gas well (hereinafter collectively referred to simply as “oil well”), and more specifically, the steel pipe is expanded in the oil well and used as a casing or tubing as it is. The present invention relates to an electric resistance welded steel pipe for a pipe expansion well that is excellent in pipe expansion performance and corrosion resistance.

  Conventionally, excavation of an oil well starts from the surface layer portion of the formation, and when a predetermined depth is reached, a casing is inserted, and insertion of a casing having a small outer diameter is repeated while digging. Therefore, when deep drilling is necessary, the drilling area in the outer diameter direction of the oil well is widened, and the drilling cost and construction period are increased, which is economically disadvantageous. In recent years, a construction method has been proposed in which a casing inserted into an oil well is expanded in the well to reduce a drilling area and significantly shorten a drilling period.

This is a technique called expandable tubular, and a steel pipe excellent in pipe expansion performance and corrosion resistance has been proposed as a steel pipe suitable for a casing (for example, Patent Document 1). In this steel pipe, the relationship between the crystal grain size and the yield strength is in an appropriate range. Patent Document 1 is a technique for improving the corrosion resistance of seamless steel pipes, and although it is suggested to be applied to ERW steel pipes, pipe expansion performance of ERW steel pipes having ERW welds, and ERW after pipe expansion It does not take into account cracks in the corrosive environment of the weld.
JP 2002-266055 A

  The present invention provides an electric resistance welded steel pipe used for an expandable tubular casing, that is, an electric resistance welded steel pipe for expanded oil wells having excellent pipe expansion performance, and a method for producing the same. In particular, it provides an electric resistance welded steel pipe for expanded oil wells that has excellent corrosion resistance and does not cause sulfide stress cracking in an electric resistance welded part even if it is used in a corrosive environment in an oil well after pipe expansion. is there.

The present invention limits the amount of oxygen in steel, the ratio between the Si amount and the Mn amount, and the ratio of the Si amount, the Mn amount and the Cr amount when selectively containing Cr as a specific range. This is an electric resistance steel pipe that controls the form of oxide in the seam welded portion, has excellent pipe expansion performance, and further prevents the occurrence of sulfide stress cracking when used in a severe corrosive environment in an oil well after pipe expansion. Yes, the summary is as follows.
(1) By mass%, C: 0.01 to 0.30%, Si: 0.01 to 0.70%, Mn: 0.5 to 2.0%, Nb: 0.005 to 0.100% Ti: 0.005 to 0.050%, Al: 0.002 to 0.100%, Ca: 0.0005 to 0.0080%, P: 0.10% or less, S: 0.005 %, O: 0.0040% or less, Si / Mn: 0.02 to 1.50 is satisfied, the balance is made of Fe and inevitable impurities, and the weld defect area ratio of the electro-welding joint is An electric-welded steel pipe for an expanded oil well having excellent pipe expansion performance and corrosion resistance, characterized by being 0.10% or less.
(2) By mass%, C: 0.01 to 0.30%, Si: 0.01 to 0.70%, Mn: 0.5 to 2.0%, Nb: 0.005 to 0.100% Ti: 0.005 to 0.050%, Al: 0.002 to 0.100%, Ca: 0.0005 to 0.0080%, P: 0.10% or less, S: 0.005 %, O: 0.0040% or less, further containing Cr: 0.50% or less, satisfying Si / (Mn + Cr): 0.02-1.50, An electric resistance welded steel pipe for expanded oil wells having excellent pipe expansion performance and corrosion resistance, wherein the weld defect area ratio is 0.10% or less.
(3) The electric-welded steel pipe for an expanded oil well having excellent pipe expansion performance and corrosion resistance according to the above (1) or (2), characterized by containing B: 0.0035% or less by mass%.
(4) The composition according to any one of the above (1) to (3), wherein one or both of Cu: 0.50% or less and Ni: 0.50% or less are contained. ERW steel pipe for pipe expansion well with excellent pipe expansion performance and corrosion resistance.
(5) The above-mentioned, characterized by containing one or more of Mo: 1.00% or less, W: 0.50% or less, and V: 0.005 to 0.200% by mass% ( The electric resistance welded steel pipe for an expanded oil well having excellent pipe expansion performance and corrosion resistance according to any one of 1) to (4).
(6) A pipe expansion well having excellent pipe expansion performance and corrosion resistance according to any one of the above (1) to (5), characterized by containing REM: 0.0005 to 0.0100% in mass%. ERW steel pipe.
(7) The ferrite fraction of the metal structure of the base material is 50 to 95%, and is for a pipe expansion well excellent in pipe expansion performance and corrosion resistance according to any one of (1) to (6) above ERW steel pipe.
(8) A method for producing an electric resistance welded steel pipe according to (7) above, in which a steel plate comprising the component according to any one of (1) to (6) is formed into a tubular shape, and the butt portion is electrically connected. A method for producing an electric-welded steel pipe for an expanded oil well having excellent pipe expansion performance and corrosion resistance, characterized by sewing welding, heating to an Ac ₁ transformation point to an Ac ₃ transformation point, and cooling.

  According to the present invention, it is possible to expand at a high expansion ratio, and even after being expanded, even if it is used in a severe corrosive environment such as in an oil well, it does not cause sulfide stress cracking in the ERW weld, and has excellent corrosion resistance. It is possible to provide an electric well welded steel pipe and a method for producing the same, and the industrial contribution is extremely remarkable.

  The present inventor is concerned with the pipe expansion performance that is particularly problematic when using an electric resistance welded steel pipe, which is cheaper to manufacture than a seamless steel pipe, as a steel pipe for expanded oil wells, and cracks in the corrosive environment of the electric resistance welded portion after the pipe expansion. Study was carried out. First, C: 0.01 to 0.30%, Si: 0.01 to 0.70%, Mn: 0.5 to 2.0%, Nb: 0.005 to 0.100%, Ti: 0.00. 005 to 0.050%, Al: 0.002 to 0.10%, Ca: 0.0005 to 0.0080%, P: 0.10% or less, S: 0.005% or less, O: A steel plate restricted to 0.0040% or less and further a steel plate containing Cr: 0.50% or less were electro-welded to produce an electric-welded steel pipe.

  Next, a conical test jig was pushed into the end portions of these electric resistance welded steel pipes, and the pipe expansion ratios of the inner diameter of the steel pipe end portions before and after the pipe expansion were expanded to 10%, 17%, and 28%. After pipe expansion, the presence or absence of cracks in the ERW welded portion of the steel pipe, that is, pipe expansion cracks, was visually confirmed. Furthermore, the test piece was extract | collected from the edge part of the steel pipe which has not generate | occur | produced the crack in an electric-welding welding part so that the circumferential direction may be made into the longitudinal direction and a welding part may become a center. The test piece was immersed in a solution simulating the corrosive environment in the oil well, and the presence or absence of sulfide stress cracking was confirmed.

  The solution simulating the corrosive environment in the oil well is a NACE environment in which hydrogen sulfide gas is saturated at a partial pressure of 0.1 MPa in a 0.5% acetic acid solution containing 5% NaCl. The presence or absence of sulfide stress cracking was confirmed after applying a stress of 397 MPa in a NACE environment and holding it for 720 hours.

  1 and 2 show Si / (Mn + Cr), the presence or absence of occurrence of pipe expansion cracks, and the presence or absence of occurrence of sulfide stress cracks in the ERW welds after pipe expansion. 1 and 2, the vertical axis represents the tube expansion ratio, the horizontal axis represents Si / (Mn + Cr), x indicates that cracking occurred due to expansion, and x indicates that no cracking occurred due to expansion and sulfide stress cracking occurred. Those that have not occurred are indicated by ○. 1 and 2, the Si / (Mn + Cr) of the steel not containing Cr was calculated by setting Cr to 0.

  FIGS. 1 and 2 show the lower and upper limits of Si / Mn or Si / (Mn + Cr), respectively, which do not cause expansion cracking and sulfide stress cracking in a corrosive environment. From FIG. 1, if the lower limit of Si / Mn or Si / (Mn + Cr) is 0.02 or more, and if the upper limit of Si / Mn or Si / (Mn + Cr) is 1.50 or less from FIG. It can be seen that no sulfide stress cracking occurs. Furthermore, in order to suppress the occurrence of pipe expansion cracks and improve the pipe expansion performance, Si / Mn or Si / (Mn + Cr) is preferably 0.03 to 1.00, and more preferably 0.05 to It turns out that it is 0.50.

In order to clarify the influence of Si / Mn or Si / (Mn + Cr) on the pipe expansion performance and corrosion resistance, the structure of the ERW welded portion of the ERW steel pipe was observed with an optical microscope. As a result, it was found that if the Si / Mn is 0.02 to 1.50 with Cr-free steel, the residual of the binary mixed oxide of SiO ₂ and MnO in the ERW weld can be suppressed. . Similarly, in steel containing Cr, by setting Si / (Mn + Cr) to 0.02 to 1.50, a ternary mixed oxide of SiO ₂ , MnO, and Cr ₂ O ₃ to the ERW weld is used. It was found that the residual of can be suppressed.

This is because steel containing no Cr has a Si / Mn ratio of 0.02 to 1.50, so that the melting point of the binary mixed oxide of SiO ₂ and MnO is lowered to 1600 ° C. or less. This is because the liquid phase is discharged from the welded portion during the sewing welding. Similarly, in steel containing Cr, the melting point of the ternary mixed oxide of SiO ₂ , MnO, and Cr ₂ O ₃ is 1600 ° C. or less by setting Si / (Mn + Cr) to 0.02 to 1.50. Thus, it is discharged from the ERW weld as a liquid phase, and the residual oxide can be suppressed.

  In addition, when Si / Mn and Si / (Mn + Cr) are controlled within a more suitable range, the melting point of the oxide is lowered, and the oxide can be discharged reliably from the ERW welded portion, improving the pipe expansion performance. And even if it raises a pipe expansion rate, favorable corrosion resistance can be maintained. If Si / Mn and Si / (Mn + Cr) are set to 0.03 to 1.00, more preferably 0.05 to 0.50, it is possible to reliably prevent oxide from remaining in the ERW weld. As a result, tube expansion performance is improved.

  In the ERW steel pipe in which Si / Mn or Si / (Mn + Cr) is controlled within an appropriate range, the residual oxide is suppressed, so that the generation of defects due to the oxide is suppressed. That is, the residue of the oxide in the electric seam welded portion can be determined by the weld defect area ratio of the electric seam abutting portion. The cracks in the electric seam abutting portion are caused by oxides, and if the weld defect area ratio is 0.10% or less, excellent pipe expansion performance and corrosion resistance can be obtained. Therefore, the weld defect area ratio is set to 0.10% or less. Further, when the weld defect area ratio is more than 0.10%, the mechanical characteristics of the electro-welding abutting portion are not sufficiently satisfied, and further, there is a possibility of rupture in various tests.

  A method for measuring the weld defect area ratio of the electric seam abutting portion will be described. A Charpy impact test piece provided with a notch in the ERW weld is prepared so that the fracture surface is parallel to the welding direction, and the Charpy impact test is performed at a temperature at which the ductile fracture surface ratio becomes 100%. The fracture surface of the Charpy specimen after fracture is observed with an optical microscope, and the area of the crack is measured. A value obtained by dividing the area of the crack by the area of the observation surface in percentage is the weld defect area ratio.

  Hereinafter, the component composition of the present invention will be described.

  C is a basic element that improves the hardenability of the steel and increases the strength, and it is necessary to add 0.01% or more. On the other hand, if the amount of C is too large, a cracking is induced, so the upper limit is made 0.30% or less.

  Si is a deoxidizing element. If the content is less than 0.01%, the amount of oxygen in the steel increases, and coarse oxide-based inclusions are generated in the ERW weld. On the other hand, even if the amount of Si is more than 0.70%, an oxide is generated in the welded portion and cracks are generated in the oil well. Therefore, the Si amount is set to 0.01 to 0.70%.

  Mn is an element that renders S harmless as MnS, and contributes to improvement of hardenability. In order to obtain this effect, it is necessary to add 0.5% or more of Mn. On the other hand, Mn is harmful to the resistance to sulfide stress cracking, so the upper limit is made 2.0% or less.

  As described above, Si and Mn are extremely important elements for controlling the form of inclusions in the ERW weld, and Si / Mn needs to be in the range of 0.02 to 1.50. is there. Moreover, in order to improve pipe expansion performance, maintaining corrosion resistance, it is preferable to make Si / Mn 0.03-1.00, and a more suitable range is 0.05-0.50.

  Nb and Ti generate carbides and nitrides, and by containing appropriate amounts, TiN and NbC are formed, preventing coarsening of the crystal grains in the ERW welds, pipe expansion performance and sulfidation resistance after pipe expansion It is an effective element for improving physical stress cracking. On the other hand, if it is contained excessively beyond the appropriate amount, carbides and nitrides become coarse and toughness is impaired. Therefore, the addition amounts of Nb and Ti are 0.005 to 0.100% and 0.005 to 0.050%, respectively.

  Al is an element used as a deoxidizer, and it is necessary to add 0.002% or more in order to reduce the amount of oxygen and suppress the formation of oxide in the ERW weld. On the other hand, if excessive Al exceeding 0.100% is contained, coarse inclusions are produced and the expansion performance and the resistance to sulfide stress cracking after expansion are reduced. is required.

  Ca is an element that generates CaS and contributes to the control of the form of sulfide, and is effective in improving the resistance to sulfide stress cracking. In order to acquire this effect, it is necessary to contain 0.0005% or more of Ca. On the other hand, if Ca is contained in excess of 0.0080%, a large amount of inclusions are generated, which becomes a starting point of pitting corrosion, and the corrosion resistance is lowered, so the upper limit is made 0.0080% or less.

  S is an impurity, and forms MnS to impair sulfide stress cracking resistance. Therefore, the upper limit is limited to 0.005% or less.

  P is also an impurity, and segregates at the grain boundaries to reduce the resistance to sulfide stress cracking, so the upper limit is limited to 0.10% or less.

  O particularly needs to be limited to 0.0040% or less in order to reduce the resistance to sulfide stress cracking by generating an oxide in the ERW weld and consequently forming a weld defect. In addition, when oxygen exceeds 0.0040%, Ca added to fix S becomes an oxide, and non-metallic inclusions extending in the rolling direction, for example, sulfides such as MnS, are generated in the base material. , The resistance to sulfide stress cracking is reduced. When the amount of oxygen is limited to 0.0025% or less, it becomes possible to reduce the maximum major axis of non-metallic inclusions generated in the base material, and to prevent the occurrence of sulfide stress cracking from the base material. Therefore, it is more preferable to limit the oxygen amount to 0.0025% or less.

  Cr is an effective element for improving hardenability and ensuring strength. When Cr is added excessively, the toughness of HAZ deteriorates, so the upper limit is preferably made 0.50% or less. In addition, when adding Cr, it is preferable to add Si / (Mn + Cr) in the range of 0.02 to 1.50 in order to suppress residual oxide in the ERW weld. Further, when Si / (Mn + Cr) is set to 0.03 to 1.00, more preferably 0.05 to 0.50, the pipe expansion performance can be improved while maintaining the corrosion resistance.

Furthermore, B may be added to improve the tube expansion performance.
B is an element that enhances hardenability and is effective in improving the pipe expansion performance. However, when it exceeds 0.0035%, the toughness may be deteriorated. Therefore, the upper limit of the B addition amount is preferably 0.0035% or less.

  Further, in order to improve sulfide stress cracking resistance, one or more of Cu, Ni, Mo, W, V, and REM may be added.

  Cu and Ni form a sulfide film in a corrosive environment, thereby suppressing hydrogen intrusion into the steel and improving sulfide stress cracking resistance. On the other hand, if more than 0.50% is added, slab cracking may occur, so addition of 0.50% or less is preferable.

Mo is an element that enhances the resistance to sulfide stress cracking and improves the hardenability, but the effect is saturated even if added over 1.00%. Further, the addition 0.50 percent, since the toughness Mo ₂ C is precipitated sometimes deteriorates, so the upper limit is preferably made 0.50% or less. In addition, in order to improve sulfide stress cracking resistance, addition of 0.15% or more is preferable.

  W is an element that generates carbides and traps diffusible hydrogen, improves resistance to sulfide stress cracking, and improves hardenability, but if added over 0.50%, toughness may be reduced. Therefore, the upper limit is preferably 0.50% or less.

  V is an element that forms fine carbides and nitrides to capture diffusible hydrogen and is effective in improving the resistance to sulfide stress cracking. In order to acquire this effect, it is preferable to add V 0.005% or more. On the other hand, if V is added in excess of 0.200%, carbides and nitrides are coarsened and the toughness may be impaired, so the upper limit is preferably made 0.200% or less.

  REM is an element added for the purpose of controlling the form of impurity elements (P, S, O) and their precipitates (inclusions). In order to fix impurities as stable and harmless precipitates and improve strength and toughness, it is preferable to add REM 0.0005% or more. On the other hand, if the amount of REM added exceeds 0.0100%, inclusions may increase and the toughness may be impaired. Therefore, the REM content is preferably 0.0005 to 0.0100% or less.

  Non-metallic inclusions present in the base material can be the starting point of fracture during corrosion resistance tests such as mechanical properties and SSC. When the maximum major axis of the non-metallic inclusions present in the base material exceeds 300 μm, if the corrosive environment becomes severe, it may become a starting point of occurrence of breakage and may impair the stress corrosion cracking resistance. Therefore, the maximum major axis of the nonmetallic inclusion is preferably 300 μm or less. Nonmetallic inclusions extending in the rolling direction are mainly MnS, and the maximum major axis can be shortened by generating CaS and fixing S effectively. Therefore, in order to make the maximum major axis of the non-metallic inclusions 300 μm or less, the oxygen amount is reduced to 0.0040 or less, and an appropriate amount of Ca may be added.

  The area ratio of ferrite of the base material was analyzed by image processing of the structure observed with an optical microscope. If the ferrite fraction is less than 50%, uniform and sufficient tube expansion cannot be performed, and the limit tube expansion rate may be lowered. On the other hand, if the ferrite fraction exceeds 95%, the tensile strength and compressive strength required for oil well pipes may not be obtained. Therefore, the ferrite fraction is preferably 50 to 95%. As described later, the ferrite fraction of the base material can be 50 to 95% depending on the heat treatment conditions of the ERW steel pipe.

  Next, the manufacturing method of the ERW steel pipe of this invention is demonstrated.

  The steel plate used as the material of the electric resistance welded steel pipe can be manufactured by a conventional method. That is, melting and casting of steel is performed by a conventional method, and the obtained steel piece is hot-rolled and cooled to obtain a steel plate. The casting is preferably continuous casting from the viewpoint of productivity. The hot rolling conditions do not need to be specified in particular, and the conditions may be determined in consideration of the shape and thickness of the steel slab, the thickness of the steel sheet after hot rolling, and the desired mechanical properties. . Although air cooling may be performed after hot rolling, accelerated cooling is preferably performed. Accelerated cooling can be appropriately selected in consideration of target mechanical characteristics such as water cooling, mist cooling, and air blowing.

  A steel plate obtained by the above-described method is piped, and the butt portion is electro-welded and an electric-welded steel pipe is manufactured. In pipe making of ERW steel pipe, hot rolled steel sheet is formed into a tube by cold bending process such as roll forming, and heat input, butt angle (V angle) of steel sheet, sheet feeding speed of steel sheet, etc. are controlled, ERW welding.

Furthermore, it is preferable to heat-treat the ERW steel pipe. The heating temperature is preferably in a temperature region in which the steel structure has two phases of ferrite and austenite, that is, between the Ac ₁ transformation point and the Ac ₃ transformation point. The ferrite fraction can be adjusted by the heating temperature, and when heated between the Ac ₁ transformation point and the Ac ₃ transformation point, the ferrite fraction can be 50 to 95%. What is necessary is just to cool so that the ferrite fraction produced | generated by heating and holding | maintenance may be maintained at the time of subsequent cooling. Therefore, it is preferable to perform accelerated cooling after heating and holding. Accelerated cooling can be appropriately selected in consideration of target mechanical characteristics such as water cooling, mist cooling, and air blowing.

The Ac ₁ transformation point and the Ac ₃ transformation point can be obtained by the following calculation formulas depending on the alloy element content.
Ac ₁ = 723-10.7Mn-16.9Ni + 29.1Si + 16.9Cr
+ 6.38W
Ac ₃ = 910-203C ^1/2 -15.2Ni + 44.7Si + 104V
+ 31.5Mo + 13.1W

  Steel pieces obtained by melting and casting the chemical components shown in Table 1 were hot-rolled into steel plates, and the steel plates were formed into a tubular shape, and the butt joints were electro-welded. The blank in Table 1 means that the selected element is not added, and the underline means outside the scope of the present invention. Steels with steel numbers N to T in Table 1 are examples containing excessively added selectively added Cr, B, Cu, Ni, Mo, W, and V. In addition, depending on whether Cr was added or not, either Si / Mn or Si / (Cr + Mn) was determined and shown in Table 1. In Table 1, “-” is shown in the “Si / Mn” column of steel containing Cr and the “Si / (Cr + Mn)” column of steel not containing Cr.

  The outer diameter of the obtained electric resistance welded steel pipe was 193 mm, and these were heated to the temperatures shown in Table 2 and cooled. A Charpy impact test piece with a notch in the ERW weld is taken from the ERW steel pipe after the heat treatment, and a Charpy impact test is conducted at a temperature at which the ductile fracture surface ratio becomes 100%. The fracture surface was observed with an optical microscope, and the weld defect area ratio was measured. Further, the metal structure of the base material was observed with an optical microscope, the major axis of the stretched nonmetallic inclusion was measured, and the maximum value was obtained and shown in the “inclusion length” column of Table 2.

  A conical tube expansion jig was inserted into the inner surface from the end of the ERW steel tube, and the tube was expanded at a tube expansion rate of 10%, 17%, and 28%. The maximum tube expansion rate at which no cracks occurred (referred to as the limit tube expansion rate) is shown in Table 2 as “tube expansion rate”. From the end of the steel pipe expanded at the limit expansion rate shown in Table 2, the circumferential direction was taken as the longitudinal direction, and tensile specimens were collected from the base material. A tensile test was performed to measure the 0.2% proof stress, and the results are shown in “YS after tube expansion” in Table 2.

  Furthermore, from the end of the steel pipe expanded at the limit expansion ratio shown in Table 2, the constant direction SSC with the outer diameter of the parallel part being 6 mm so that the circumferential direction is the longitudinal direction and the welded part is the center part of the test piece A test piece was collected and a constant load SSC test was performed with a gauge length of 30 mm. The test environment was the above-mentioned NACE environment, a stress of 397 MPa was applied and held for 720 hours, and the presence or absence of fracture was evaluated. In the column of corrosion resistance in Table 2, those that were not broken after being held for 720 hours were indicated by “◯”, and those that were broken were indicated by “x”.

  As shown in Table 2, the production No. Reference numerals 1 to 13 are examples of the present invention, the limit tube expansion rate is as high as 17% or more, the YS after tube expansion is 550 MPa or more, and the corrosion resistance after tube expansion, that is, the stress corrosion resistance is good. On the other hand, production No. 14-22 is a comparative example, the limit pipe expansion rate is low, the crack has arisen in the SSC test after pipe expansion, and corrosion resistance is also falling.

It is a figure which shows the minimum of Si / (Mn + Cr) with favorable sulfide stress cracking resistance. It is a figure which shows the upper limit of Si / (Mn + Cr) with favorable sulfide stress cracking resistance.

Claims (8)

% By mass
C: 0.01 to 0.30%
Si: 0.01-0.70%,
Mn: 0.5 to 2.0%
Nb: 0.005 to 0.100%,
Ti: 0.005 to 0.050%,
Al: 0.002 to 0.100%,
Ca: 0.0005 to 0.0080%
Containing
P: 0.10% or less,
S: 0.005% or less,
O: limited to 0.0040% or less,
Si / Mn: 0.02-1.50
, The balance is Fe and inevitable impurities, and the weld defect area ratio of the electro-welding joint is 0.10% or less. . % By mass
C: 0.01 to 0.30%
Si: 0.01-0.70%,
Mn: 0.5 to 2.0%
Nb: 0.005 to 0.100%,
Ti: 0.005 to 0.050%,
Al: 0.002 to 0.100%,
Ca: 0.0005 to 0.0080%
Containing
P: 0.10% or less,
S: 0.005% or less,
O: limited to 0.0040% or less, and
Cr: 0.50% or less,
Si / (Mn + Cr): 0.02-1.50
Satisfying the above, and the weld defect area ratio of the ERW abutting portion is 0.10% or less, and an ERW steel pipe for expanded oil wells having excellent pipe expansion performance and corrosion resistance. % By mass
B: 0.0035% or less, The electric-welded steel pipe for pipe expansion wells having excellent pipe expansion performance and corrosion resistance according to claim 1 or 2. % By mass
Cu: 0.50% or less,
Ni: 0.50% or less of one or both are contained, The electric resistance welded steel pipe for pipe expansion wells excellent in pipe expansion performance and corrosion resistance of any one of Claims 1-3 characterized by the above-mentioned. % By mass
Mo: 1.00% or less,
W: 0.50% or less,
V: 0.005 to 0.200%
1 type or 2 types or more of these are contained, The electric-welding steel pipe for pipe expansion wells excellent in pipe expansion performance and corrosion resistance of any one of Claims 1-4 characterized by the above-mentioned. % By mass
REM: 0.0005 to 0.0100%
The electric-welded steel pipe for expanded oil wells according to any one of claims 1 to 5, which has excellent expanded performance and corrosion resistance.   The electric resistance steel pipe for an expanded oil well having excellent pipe expansion performance and corrosion resistance according to any one of claims 1 to 6, wherein the ferrite fraction of the metal structure of the base material is 50 to 95%. A method for producing an ERW steel pipe according to claim 7, wherein the steel sheet comprising the component according to any one of claims 1 to 6 is formed into a tubular shape, and the butt portion is electro-welded, and the Ac ₁ transformation is performed. A method for producing an electric-welded steel pipe for pipe expansion wells excellent in pipe expansion performance and corrosion resistance, characterized by heating to point to Ac ₃ transformation point and cooling.

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