JPH0641679A - Electric-resistance-welded steel tube excellent in sulphide stress corrosion cracking resistance - Google Patents

Abstract

(57) [Summary] [Object] The present invention provides an electric resistance welded steel pipe used in an environment containing moist hydrogen sulfide such as an oil well or a gas well. [Structure] Of the oxide inclusions contained within 100 μm on both sides of the electric resistance welded surface 2 of the electric resistance welded pipe 1, the shape of the inclusions as seen in a cross section in the cross section is the length in the thickness direction and the circumferential direction. The number of inclusions with a length ratio of 2 or more and a major axis of 10 μm or more that cuts the cross section per 1 mm ² is 5 or less, and the hardness measurement value within 30 mm on both sides centering on the electric resistance abutting surface The electric resistance welded steel pipe 1 has a maximum value of 250 or less in Vickers hardness and a difference between the maximum value and the minimum value of 30 or less in Vickers hardness. [Effect] It is possible to provide a steel pipe that has excellent sulfide stress corrosion cracking resistance even in a low pH and severe environment and is suitable as a structural member used in an oil well or the like.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric resistance welded steel pipe having high resistance to sulfide stress corrosion cracking (hereinafter referred to as SSC) caused by an environment containing moist hydrogen sulfide, and particularly to oil wells and gas wells. The present invention relates to a structural member used in, for example, an electric resistance welded steel pipe suitable as an oil well pipe or a line pipe.

[0002]

2. Description of the Related Art In recent years, in the development of oil and gas fields, due to the rapidly increasing demand and the progress of technology to meet the demand, it has been buried deep in the earth, which has been left unattended or difficult to develop. In addition, oil and gas in so-called sour environments, which are considerably contaminated with sulfides such as hydrogen sulfide, are gradually being developed.

Therefore, in the field of oil and natural gas production, it withstands external pressure (pressure in the formation), internal pressure (pressure of oil or gas), or the tensile load due to the weight of the steel material, and can be used in a sour environment. There is a further demand for the development of a steel having high strength and excellent sulfide stress corrosion cracking resistance (hereinafter referred to as SSC characteristics) that can sufficiently exhibit desired performance.

Since 1950, various studies have been made on means for improving the sulfide stress corrosion cracking resistance of steel.
At present, for example, NACE Standard MR-0
It is said that suppressing the strength of steel below the upper limit of hardness (strength) shown in 1-75 is the most effective for improving SSC characteristics, and in order to meet the needs of users, L-8 based on this is satisfied.
0 has been added to the API standard.

However, it is naturally understood that the SSC characteristics cannot be improved only by the upper limit of the hardness, and there are some other factors. As one of the factors for improving the SSC characteristic, improvement of the sour characteristic can be considered. The improvement of the sour property is to reduce hydrogen blistering cracks in an environment containing hydrogen sulfide, and this fracture can be recognized even without an external load stress.

When stress is applied in a sour environment, hydrogen blistering cracks may occur in parallel with the stress axis, and the connection of these may lead to fracture, so that the occurrence of hydrogen blistering cracks should be prevented. The idea is to improve the SSC characteristics.

By the way, hydrogen blistering is an M that extends in the rolling direction when hydrogen invading from the environment exists in the base material.
It is generated by the gas pressure by accumulating at the boundary between A-type sulfide-based inclusions such as nS and the base metal, and is generated by the gas pressure. Parallel cracks on the plate surface using A-type sulfide-based inclusions such as MnS as the nucleus of the crack. And the parallel cracks in the plate surface are connected in the plate thickness direction. A-type sulfide inclusions such as MnS tend to become nuclei for cracks because the shape elongated in the rolling direction forms sharp notches, and is said to be the most harmful to this type of fracture.

[0008] Various studies have hitherto been made on steel having a high resistance to hydrogen blistering and various proposals have been proposed. They are, for example, Japanese Patent Publication No. 57-17.
As typical examples thereof are found in Japanese Patent Publication No. 065 and Japanese Patent Publication No. 57-16184, cracking prevention by addition of Ca or Co, reduction of MnS by extremely low S, fixation of S by addition of Ca or rare earth element, etc. Etc., and steels capable of withstanding considerably severe environments have been developed up to now by these technologies. Further, it is possible to improve the SSC resistance by using various means for improving the sour property.

[0009]

By the way, the electric resistance welded steel pipe is one in which a steel plate such as a hot coil is formed and electric resistance welding is performed. Needless to say, the decisive difference from the steel plate is that the welded portion and the weld heat affected zone are To exist. However, heretofore, almost no example has been found in which the SSC resistance characteristic of the peripheral portion of the electric resistance welded portion, and also the C direction is examined.

In the ordinary manufacturing process, the large amount of A-based sulfide inclusions such as MnS are present in the reverse segregation part and the V segregation part in the large steel ingot, and in the central segregation part in the continuous cast piece. In addition, the edge portion of the steel sheet is extremely small, and the microsegregation of Mn and P that promotes parallel cracking of the sheet surface is severe.
It is the same as the site where many A-based sulfide inclusions such as nS are present, and is almost not present at the edge part. This is because it has been understood that the single-width material has a good SSC resistance property in the peripheral portion of the electric resistance welded portion.

Further, in a so-called multi-strand electric resistance welded steel pipe manufactured by dividing one hot coil into two or more in the width direction, an inverse V segregation portion, a center segregation portion or the like is formed on one or both of the electric resistance welded portions. Since the part with high SSC sensitivity of
There was recognition for SSC. However, also in this case, the same measure as that of the base material has been taken mainly as a measure, such as reduction of A-based sulfide-based inclusions such as MnS.

The present invention has been made in view of the above problems,
Provided is an electric resistance welded steel pipe having excellent resistance to sulfide stress corrosion cracking.

[0013]

In order to solve the above problems, the present inventor has conducted a detailed investigation of the SSC resistance characteristics of the electric resistance welded steel pipe in the direction of the electric resistance welded portion C. As a result, sulfide inclusions such as MnS do not exist. It has been found that the SSC characteristics of the electric resistance welded portion may deteriorate even in some cases. However, in the case of the electric resistance welded part, it is different from the base metal part that the hydrogen swelling crack of the vertical type on the plate surface is the starting point of the SSC. There is a concern that it will easily occur.

Further, it has been found that SSC originating from this kind of hydrogen blistering crack is generated even in the case of a mono-width material having essentially less microsegregation at the steel plate edge portion. SS of the electric resistance welded part starting from hydrogen blistering perpendicular to this plate surface
C has not been known so far, and is a more serious problem than SSC originating from hydrogen blistering cracks parallel to the plate surface of the base material. However, it has been found that this crack also occurs in the electric resistance welded steel pipe using the conventional countermeasure steel against hydrogen blistering crack and cannot be prevented by the conventional technique.

The inventors of the present invention continued their research with the aim of developing a steel pipe having a high resistance to SSC originating from such a completely new type of plate vertical vertical hydrogen blistering crack.
The cause of hydrogen swelling crack which is the starting point of SSC of the electric resistance welded portion of the electric resistance welded steel pipe 1 schematically shown in FIG. 1 is that the electric resistance welded portion 2 and the heat affected zone 3 where Z1 and Z2 on both sides thereof are within 100 μm.
It was found that they are plate-like oxide-based inclusions existing in the.

Further, among these plate-shaped oxide-based inclusions, both sides Z1 of the abutting portion 2 of the electric resistance welded steel pipe 1 shown in FIG. 1 =
As for the shape of inclusions in a cross section within Z2 = 100 μm, inclusions having a ratio of the length in the plate thickness direction to the length in the circumferential direction of 2 or more and a major axis of 10 μm or more are cores of hydrogen blistering cracking. That is, the ratio of the length in the plate thickness direction to the length in the circumferential direction is 2 or more, and the inclusion having a major axis of 10 μm or more is 1 mm.
When the density of oxide-based inclusions exceeds 5 in the cross section of ^2, the hydrogen swelling cracks that have been nucleated combine with each other and grow into macroscopic cracks, resulting in SSC.
Found to cause.

Further, according to the research conducted by the present inventor, in these plate-shaped oxide inclusions, the near-spherical oxide inclusions pre-existing in the base metal are included in the heat-affected zone 3 during electric resistance welding. It was revealed that the material was heated to near the melting point of the steel due to the influence and was pressed from both sides by the squeeze rolls, so that it deformed into a plate shape and was generated. In addition, it has also been found that when the oxide inclusions are complex, for example, Ca is contained in the oxide inclusions, the oxide inclusions are significantly deformed.

Further, as a result of detailed examination of the factors that deteriorate the SSC characteristics of the electric resistance welded portion other than hydrogen blistering cracks caused by the above inclusions, the present inventors have found that the electric resistance welded surface is the center and both sides are within 30 mm. It has been found that the maximum value of the hardness measurement value in Vickers hardness is 250 or less, and the difference between the maximum value and the minimum value is 30 or less in Vickers hardness.

Although the regulation of the maximum value of hardness is a conventional finding, regarding the necessity of regulation of the hardness distribution, the occurrence of cracks due to stress concentration at the portions having different hardness distribution deteriorates the SSC characteristics. It is thought to be to do.

The present invention was made based on the above findings, and the gist of the invention is as follows.

The first aspect of the present invention is C: 0.05 to 0.35.
%, Si: 0.02 to 0.50%, Mn: 0.30
Ca in addition to 2.00% 0.0005 to 0.0080
% And Al 0.005 to 0.100%, balance Fe
In an electric resistance welded steel pipe made of a steel made of, the shape of the inclusions within 100 μm on both sides centering on the electric resistance abutting surface as seen in cross section is the length in the plate thickness direction and the circumferential direction. The ratio of the length of 2 is 2 or more, and the number of inclusions with a major axis of 10 μm or more that cuts the cross section per 1 mm ² is 5 or less, and the hardness measurement value within 30 mm on both sides centering on the electric resistance abutting surface. Is a Vickers hardness of 250 or less, and the difference between the maximum value and the minimum value is Vickers hardness of 30 or less, which is an electric resistance welded steel pipe excellent in sulfide stress corrosion cracking resistance. .

The second aspect of the present invention is C: 0.05 to 0.35.
%, Si: 0.02 to 0.50%, Mn: 0.30
Ca in addition to 2.00% 0.0005 to 0.0080
% And Al 0.005 to 0.100%, and M
o: 0.1 to 2.0%, Nb: 0.01 to 0.15%,
V: 0.01 to 0.30%, Ti: 0.001 to 0.0
50%, B: 0.0003 to 0.0040%, one or two or more of them, in an electric resistance welded steel pipe made of a steel composed of the balance Fe, with 100 on both sides centering on the electric resistance contact surface.
Among the oxide inclusions contained within μm, the inclusions having a ratio of the length in the plate thickness direction to the length in the circumferential direction of 2 or more and the major axis of 10 μm or more as a shape of the inclusions in a cross section are 1 mm ²
The number of cross-sections per unit is 5 or less, and the maximum hardness measurement value within 30 mm on both sides of the electric resistance welding surface is 250 or less in Vickers hardness, and the maximum and minimum values Is a Vickers hardness within 30 and is an electric resistance welded steel pipe excellent in sulfide stress corrosion cracking resistance.

The third aspect of the present invention is C: 0.05 to 0.35.
%, Si: 0.02 to 0.50%, Mn: 0.30
Ca in addition to 2.00% 0.0005 to 0.0080
% And Al of 0.005 to 0.100%, and further C
u: 0.1 to 2.0%, Ni: 0.1 to 9.5%, C
r: an electric resistance welded steel pipe made of steel containing the balance Fe, containing one or more of 0.1 to 3.0%, and
Of the oxide inclusions contained within 100 μm on both sides of the electric resistance abutting surface, the shape of the inclusions as viewed in cross section has a ratio of the length in the plate thickness direction to the length in the circumferential direction of 2 or more and the major axis. The number of inclusions of 10 μm or more that cuts the cross section per 1 mm ² is 5 or less, and the maximum hardness measurement value within 30 mm on both sides of the electric resistance joint surface is Vickers hardness of 250 or less. It is an electric resistance welded steel pipe excellent in sulfide stress corrosion cracking resistance, characterized in that the difference between the maximum value and the minimum value is within 30 in Vickers hardness.

In the fourth aspect of the present invention, C: 0.05-0.
35%, Si: 0.02 to 0.50%, Mn: 0.30
~ 0.000% and 0.0005 to 0.008 Ca
0% and 0.005 to 0.100% Al, Mo: 0.1 to 2.0%, Nb: 0.01 to 0.15
%, V: 0.01 to 0.30%, Ti: 0.001 to
0.050%, B: 0.0005 to 0.0040%, one or more kinds, and Cu: 0.1 to 2.0%,
In an electric resistance welded steel pipe made of a steel containing one or more of Ni: 0.1 to 9.5% and Cr: 0.1 to 3.0% and the balance Fe, an electric resistance contact surface Among oxide inclusions included within 100 μm on both sides with respect to the center, inclusions having a ratio of the length in the plate thickness direction to the length in the circumferential direction of 2 or more and the major axis of 10 μm or more as the shape of the inclusions as viewed in a cross section. Is 1
The number of cross-sections per mm ² is 5 or less, and the maximum hardness measurement value within 30 mm on both sides of the electric resistance contact surface is 250 or less in Vickers hardness, and the maximum value It is an electric resistance welded steel pipe excellent in sulfide stress corrosion cracking resistance, characterized in that the difference in the minimum value is within 30 in Vickers hardness.

[0025]

The present invention will be described in detail below along with its operation.

First, the present invention is intended for all electric resistance welded steel pipes excellent in sulfide stress corrosion corrosion resistance, and the reasons for defining the above components are as follows.

C has the effect of increasing the strength of the steel material, and C.
Although it is added in an amount of 0.05% or more, if it is added in an amount of more than 0.35%, the toughness is significantly deteriorated.
Was set to 0.35%.

Si has a solid solution strengthening effect and an effect of improving the strength and ductility of the steel material, and is added in an amount of 0.02% or more, but if added in excess of 0.50%, the toughness of the steel material is deteriorated. Therefore, the content is set to 0.02 to 0.50%.

Similar to C, Mn also has the effect of increasing the strength of the steel material and is added in an amount of 0.30% or more, but its content is 2.
If it exceeds 0%, not only is it economically difficult to make steel making work, but also the weldability is impaired.
It was set to 30 to 2.0%.

Ca is S by controlling the morphology of sulfide inclusions.
It is effective in preventing hydrogen blistering cracks, which is the starting point of SC, and is added in an amount of 0.0005% or more. However, if the content increases, it forms inclusions in the steel and deteriorates the properties of the steel. ˜0.0080%.

Al is necessary for deoxidation at the steelmaking stage, and its lower limit was made 0.005%. Further, if added over 0.10%, the amount of inclusions increases and the cleanliness of the steel is lost, and it interferes with the steelmaking work. Therefore, the range is set to 0.005 to 0. It was set to 10%.

Mo is useful for increasing the strength and is added in an amount of 0.10% or more. However, if it increases, the weldability is impaired. Therefore, the range is set to 0.10 to 2.0%.

Nb is useful for refining the austenite grains and increasing the strength, and is added in an amount of 0.01% or more. However, if it increases, the weldability is impaired.
And

V is useful for precipitation strengthening and is added in an amount of 0.1% or more. However, if it is too large, the weldability is impaired, so the range was made 0.01 to 0.30%.

Ti is useful for refining austenite grains and is added in an amount of 0.001% or more. However, if it increases, the weldability is impaired, so the range is made 0.001 to 0.050%.

B has the effect of significantly increasing the hardenability of steel by the addition of a trace amount. To obtain this effect effectively, at least 0.0003% of B is necessary, but if added in excess, it forms a B compound and deteriorates the toughness of the steel, so the range is 0.0003 to 0.0040. %.

Cu is effective in increasing strength and corrosion resistance, and has a Cu content of 0.
1% or more is added, but even if added over 2.0%, there is almost no increase in strength, so the range is set to 0.1.
˜2.0%.

Ni is effective for improving the low temperature toughness and is added in an amount of 0.1% or more. However, since it is an expensive element, the range is set to 0.1 to 9.5%.

Cr is effective in increasing the strength and improving the corrosion resistance.
1% or more is added, but if it increases, the low temperature toughness and weldability are impaired, so the range was made 0.1 to 3.0%.

P is an element that facilitates the propagation of hydrogen blistering cracks in the base material, and should be 0.03% or less.
Further, S combines with Mn to form MnS which becomes a starting point of hydrogen swelling cracks in the base material portion, so S should be suppressed to 0.005% or less.

Next, the maximum skeleton of the present invention is 100 μm on both sides of the electric resistance abutting surface as a center as described above.
Of the oxide-based inclusions included within, the shape of the inclusions as viewed in cross section has a ratio of the length in the plate thickness direction to the length in the circumferential direction of 2 or more, and the inclusions with a major axis of 10 μm per 1 mm ^2. The number of cuts in the cross section of 5 is 5 or less. This is based on the following reason.

First, the range defining the inclusions was set within 100 μm on both sides of the electric resistance abutting part as a center, because many SSC resistance tests and detailed observations were conducted on the test piece including the electric resistance abutting part. As a result, hydrogen blistering cracks, which are the starting points of SSC generation, are within 100 μm, and the plate-like oxide inclusions, which are the starting points, are mostly aggregated within 100 μm. This is because it exists very rarely in the range exceeding 0, and even if cracks nucleate, they do not connect, so that they cannot grow into macroscopic cracks.

Next, attention was paid to the oxide-based inclusions as the target inclusions. As described above, the oxide-based inclusions are deformed due to the thermal effect of welding and the pressure applied by the squeeze roll to cause hydrogen blistering cracks. This is the cause.

Here, the oxide-based inclusions in the present invention refer to inclusions composed of oxides and composites mainly containing oxides and a small amount of sulfides. In addition, if it is added as a reference, the amount of sulfide-based inclusions was significantly reduced to secure the sour resistance of the base metal, and the main object is steel, so we focused on the amount of oxide-based inclusions. It is a thing.

As a shape of the inclusions, the ratio of the length in the plate thickness direction to the length in the circumferential direction is set to 2 or more. As a result of detailed observation, the inclusions deformed into such a plate shape generate crack nuclei. However, it was revealed from the results of the experiment that inclusions having a ratio of the length in the plate thickness direction to the length in the circumferential direction of less than 2 are not harmful for cracking. .

In the present invention, the direction of deformation of the oxide inclusions is defined in the plate thickness direction and the circumferential direction. However, since the deformation of the inclusions is caused by the heating during welding heating, Material inclusions do not always extend correctly in the plate thickness direction, and some of them may have some inclination, but of course, even if they are slightly inclined, they can be the starting points of cracks at all. .

In the present invention, it is considered that such inclusions have a ratio of the length in the longest direction which is oblique to the length in the direction perpendicular thereto to be 2 or more. The major axis 10
The inclusions having a size of μm or more are based on the finding by experiments that even if the length ratio is 2 or more, fine inclusions having a major axis of less than 10 μm do not become the starting point of cracking.

Furthermore, in the present invention, these inclusions are 1
The number of cross-sections cut per mm ² is 5 or less,
It is based on the fact that it was found by experiments that nucleated hydrogen blistering cracks are interconnected when the number of inclusions having the above-mentioned shape and size exceeds 5 cross sections per 1 mm ^2. .

In order to satisfy the above requirements,
This can be achieved, for example, by applying the technique described below. First, deoxidation, desulfurization or Ca of molten steel
It is effective to thoroughly remove the oxide-based inclusions remaining after the treatment such as addition, for example, by blowing the inert gas from the bottom of the molten steel container to promote the floating of the molten steel inclusions. realizable.

Further, a large amount of an element forming a high melting point oxide such as Al or Ti is added to change the oxide inclusions in the steel into a single component and a high melting point compound, and the welding is performed. Sometimes it is effective to make it difficult to deform.

Alternatively, the pressure applied by the squeeze roll during electric resistance welding is reduced to prevent the change of oxide inclusions,
Alternatively, it is extremely effective to reduce the amount. However, in this case, needless to say, it is necessary to control welding conditions and applied pressure so as not to cause electric resistance welding defects.

Various other techniques can be applied, but in short, oxide-based inclusions in the base material, which cause plate-like inclusions, are reduced or inclusions having a composition that is difficult to deform during welding are used. It is possible to satisfy the requirements of the present invention, for example, by positively forming or by welding with less deformation during electric resistance welding.

As the manufacturing process of the steel of the present invention, hot rolling may be performed as it is, or a process of normalizing, tempering or quenching and tempering a rolled material may be applied. After electric resistance welding, a step of normalizing, tempering, or quenching and tempering only the vicinity of the electric resistance welded portion or the entire steel pipe may be applied.

At this time, in order to prevent the occurrence of cracks due to stress concentration in the areas having different hardness distributions as described above, the maximum value of the hardness values measured within 30 mm on both sides of the electric resistance abutting surface as a center. Must have a Vickers hardness of 250 or less, and the difference between the maximum value and the minimum value must be 30 or less in Vickers hardness. Whether or not to heat treat steel or steel pipe depends on
In addition to the above requirements for hardness, it may be determined according to the need to secure other mechanical properties such as strength and toughness.

[0055]

EXAMPLES The effects of the present invention will be described in more detail below with reference to examples. Table 1 shows the composition of the steel from which the ERW steel pipe was manufactured, and Table 2 shows the test results.

[0056]

[Table 1]

[0057]

[Table 2]

In Table 2, Note 1) Among the number of inclusions (pieces) within 1 μm ² within 100 μm from the electric resistance abutting portion, inclusions having a major diameter / minor diameter ratio of 2 or more and a major diameter of 10 μm or more. Number Note 2) Number of inclusions that cut the cross section within 1 mm ² within 100 μm from the electric resistance joint, and have a major axis / minor axis ratio of 2 or more and a major axis of less than 10 μm Note 3) ERW Out of the number of inclusions (pieces) that cut the cross section within 1 mm ² within 100 μm from the joint, the number of inclusions with a major axis / minor axis ratio of less than 2 Note 4) Hv _max- Hv _min Note 5) Unit is Kgf / mm ² Note 6) In the table, Q is the one that was hardened only after the electric resistance welding and has been hardened and tempered. QT is the one that has been hardened and tempered only at the electric resistance welded part.
N is a tube processed by electric resistance welding and subjected to a normal process.

Steel of the composition shown in Table 1 was hot-rolled into a steel plate having a thickness of 13 mm, and then an electric resistance welded steel pipe was prepared in the conventional process. In particular, Steel Nos. A, B, and C are those in which inclusions in molten steel have been sufficiently removed by blowing an inert gas.
In E and F, the inclusions in the steel are almost completely converted to Al ₂ O ₃ by adding a large amount of Al.

Next, from the direction of the electric resistance welded portion C of these electric resistance welded steel pipes, a constant load type sulfide stress corrosion test piece 5 was sampled according to the collecting procedure shown in FIG. At that time, the electric resistance welded portion was made to cross the central portion of the sample.

As a test for evaluating the sulfide stress corrosion resistance property, a test is carried out by the NACE TM-01-77 standard test method, and the ratio of the critical stress (σth) to the yield strength (σy) in the C direction of the electric resistance welded portion is used. It was evaluated, and if σth / σy ≧ 0.75, it was determined to be good.

In the test results shown in Table 2, A1 and B
1, C1, D1, E1, and F1 are the steels of the present invention, and the major axis / short axis among the number of inclusions (pieces) cutting the cross section per 1 mm ² within 100 μm from the electric resistance abutting portion represented by inclusion 1 Since the number of inclusions having a diameter ratio of 2 or more and a major axis of 10 μm or more is 5 or less and ΔHv is 30 or less, excellent sulfide stress corrosion cracking resistance (σth / σy ≧ 0.75) is exhibited.

On the other hand, A2, B2, C2, D2, E
Although the inclusions 1 and 2 of F2 and F2 are 5 or less, since ΔHv exceeds 30, deterioration of sulfide stress corrosion cracking resistance is observed. Further, G1, H1, I1, J1, and K1 have ΔHv of 30 or less, but since the inclusion 1 exceeds 5,
Degradation of sulfide stress corrosion corrosion cracking resistance is observed.

[0064]

As described above, the electric resistance welded steel pipe of the present invention has high strength and excellent sulfide stress corrosion cracking resistance even in a severe environment of low pH and is used in oil wells and gas wells. It is possible to provide a suitable steel pipe as a pipe material or a structural member.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an abutting portion of an electric resistance welded steel pipe and regions on both sides thereof where the amount of oxide inclusions is limited.

FIG. 2 is a drawing showing a procedure for collecting test pieces in Examples.

[Explanation of symbols]

 1 ERW steel pipe 2 Abutting part 3 Heat affected zone 4 Welding direction 5 Test piece

Claims (4)

[Claims] 1. C: 0.05 to 0.35%, Si: 0.
02 to 0.50%, Mn: 0.30 to 2.00%, 0.0005 to 0.0080% of Ca and 0.0 of Al.
In an electric resistance welded steel pipe made of a steel containing 0.05 to 0.100% and the balance being Fe, both sides 1 with the electric resistance contact surface as the center
Among the oxide inclusions contained within 00 μm, the inclusions having a ratio of the length in the plate thickness direction to the length in the circumferential direction of 2 or more and the major axis of 10 μm or more as a shape of the inclusions in a cross section are 1 m.
The number of cross-sections per m ² is 5 or less, and the maximum hardness measurement value within 30 mm on both sides of the electric resistance abutting surface is 250 or less in Vickers hardness and the maximum value. ERW steel pipe excellent in sulfide stress corrosion cracking resistance, characterized in that the difference in the minimum value is 30 or less in Vickers hardness. 2. C: 0.05 to 0.35%, Si: 0.
02 to 0.50%, Mn: 0.30 to 2.00%, 0.0005 to 0.0080% of Ca and 0.0 of Al.
05: 0.100%, and Mo: 0.1-2.
0%, Nb: 0.01 to 0.15%, V: 0.01 to
0.30%, Ti: 0.001 to 0.050%, B:
In an electric resistance welded steel pipe manufactured from a steel composed of the balance Fe, containing one or more of 0.0003 to 0.0040%, an oxide-based inclusion included within 100 μm on both sides of the electric resistance contact surface. As for the shape of inclusions in the cross section, the ratio of the length in the plate thickness direction to the length in the circumferential direction is 2 or more, and the number of inclusions having a major axis of 10 μm or more cuts the cross section per 1 mm ² is 5 or less. In addition, the maximum value of hardness measured within 30 mm on both sides of the electric resistance contact surface is Vickers hardness of 250 or less, and the difference between the maximum value and the minimum value is within 30 Vickers hardness. ERW steel pipe with excellent sulfide stress corrosion cracking resistance, which is characterized by 3. C: 0.05 to 0.35%, Si: 0.
02 to 0.50%, Mn: 0.30 to 2.00%, 0.0005 to 0.0080% of Ca and 0.0 of Al.
05: 0.100%, and further Cu: 0.1-2.
0%, Ni: 0.1 to 9.5%, Cr: 0.1 to 3.0
% Of the oxide inclusions contained within 100 μm on both sides of the electric resistance welded surface as a center, in the electric resistance welded steel pipe manufactured from the steel containing the balance Fe and containing one or more of The shape of the inclusions is such that the ratio of the length in the plate thickness direction to the length in the circumferential direction is 2 or more, and the number of inclusions having a major axis of 10 μm or more cuts the cross-section per 1 mm ^{2 and} is 5 or less. The maximum value of hardness measured within 30 mm on both sides of the mating surface is Vickers hardness of 250 or less, and the difference between the maximum value and the minimum value is Vickers hardness of 30 or less. ERW steel pipe with excellent sulfide stress corrosion cracking resistance. 4. C: 0.05 to 0.35%, Si: 0.
02 to 0.50%, Mn: 0.30 to 2.00%, 0.0005 to 0.0080% of Ca and 0.0 of Al.
05: 0.100%, and Mo: 0.1-2.
0%, Nb: 0.01 to 0.15%, V: 0.01 to
0.30%, Ti: 0.001 to 0.050%, B:
One or two or more of 0.0005 to 0.0040%, Cu: 0.1 to 2.0%, Ni: 0.1 to 9.
5%, Cr: 0.1 to 3.0% of 1 or 2 or more, and in the electric resistance welded steel pipe manufactured from the steel consisting of the balance Fe, within 100 μm on both sides of the electric resistance contact surface Among the oxide-based inclusions, the inclusions with a ratio of the length in the plate thickness direction to the length in the circumferential direction of 2 or more and the major axis of 10 μm or more have a cross-section per 1 mm ² as the shape of the inclusions in the cross-section. The number of cuts is 5 or less, and the maximum value of hardness measured within 30 mm on both sides of the electric resistance contact surface is Vickers hardness of 250 or less, and the difference between the maximum value and the minimum value is Vickers hardness. ERW steel pipe excellent in sulfide stress corrosion cracking resistance, characterized in that it is within 30 in length.