JPH03285770A - Manufacture of large diameter steel pipe excellent in sour gas resistance - Google Patents

Abstract

PURPOSE:To obtain the large diameter steel pipe excellent in sour gas resistance by subjecting base metals having specified chemical composition to one-pass submerged arc welding on the inside and outside by using low oxygen-base flux and an extra low carbon-base high Mn-low N-Ti-base welding wire to obtain weld metal having specified composition. CONSTITUTION:In the UOE steel pipe, the chemical composition of the base metals contains, by weight %, 0.02-0.05% C, 0.01-0. 05% Nb, 0.01-0.025% Ti, 0.002-0.005% Ca, 0.05-0.3% Mo and 0.01-0.08% V and ESSP of the expression I satisfies 1.5-6.0. These base metals are subjected to one-pass submerged arc welding on the inside and outside by using the low oxygen-base flux end the extra low carbon-base high Mn-low N-Ti-base welding wire. The weld metal contains 0.02-0.06% C, Ti, Al, Mo, B, etc., and PWM of the expression II is regulated to 0.13-0.16 and alpha of the expression III is regulated to (-10)-(+10). Consequently, the maximum hardness of a weld zone is suppressed and high toughness thereof is attained.

Description

[Detailed description of the invention]

(Field of Industrial Application) The present invention relates to a method for manufacturing large-diameter steel pipes with excellent sour gas resistance, and particularly relates to circumferential welding (hereinafter referred to as on-site welding) of steel pipes on-site when the steel pipes are laid on the seabed, etc. , and girth welding), low hardening of the intersection of large-diameter steel pipe seam welds (usually referred to as T-cross for convenience) and excellent toughness for the seam weld metal. The present invention relates to a welding manufacturing method for the large-diameter steel pipe, comprising: (Conventional technology) In recent years, UO line pipes installed in the development of offshore gas wells and oil fields are required to have high strength, high toughness, and HIC resistance, as well as SSC resistance, based on the assumption that they will be used in sour gas environments. ing. Raybarge underwashing is used for laying line pipes on the seabed, and highly efficient gas metal arc welding is usually used for girth welding. However, this welding method has a low welding heat input and is intended to significantly improve efficiency, so it requires free preheating, which increases the hardness of the intersection between girth welding and steel pipe seam welding, and The hardness of reheated submerged arc welded (SAW) metal increases significantly, with the highest hardness in that area. The hardness of such a welded part "1 increase" is SS
This is not preferable because it acts to increase C sensitivity. Therefore, it is customary to regulate the maximum hardness of welded parts from the viewpoint of SSC resistance. In general, methods for reducing the hardness of the weld include post-heat treatment of the girth weld, or methods of lowering the alloy content of the seam weld metal to suppress the increase in hardness of the reheated seam weld metal. It will be done. However, the former method is impractical due to lower on-site work efficiency and higher costs. In addition, the latter method is a method of lowering the alloy components through component adjustment, that is, a method of minimizing the hardenability of the weld metal, and may become the most practical method. However, if the hardenability of the weld metal is lowered, even if it is possible to lower the hardness, there is a concern that the toughness, which is another important property, will decrease. Usually, welding metal is different from manufacturing steel materials.
Since it is required to have properties comparable to those of steel even when solidified, these properties are achieved by designing alloys that are higher than those of the base material in terms of strength and toughness, that is, by improving hardenability. Japanese Patent Publication No. 57'-+ 7637 discloses a method of adjusting the composition of the weld metal in order to improve the notch toughness of the weld. In other words, there is a trace amount of B or Ti in the weld metal.
The purpose is to improve notch toughness by adding Ti, fixing oxygen and nitrogen in the steel with Ti, and dissolving B as a solid solution. However, this publication does not mention the hardness of the welded portion. (Problem to be solved by the invention) As mentioned above, the girth welded part of large diameter steel pipes for sour gas resistance needs to have a low hardness, especially in order to be resistant to hydrogen sulfide and to reduce the susceptibility to stress corrosion cracking. , currently H
v (10 kg) max≦248 is generally required from the viewpoint of SSC resistance. In particular, the surface layer of the girth weld where the cooling rate is fast at the intersection of the pipe-making seam and the girth weld, and the heat-affected zone where the pipe-making seam weld metal is reheated by girth welding tend to have the highest hardness, so the above requirements are met. is big. However, reducing the hardness also reduces the toughness, making it impossible to obtain a large-diameter steel pipe that simultaneously has the desired low hardenability and high toughness and has excellent sour gas resistance. The present invention aims to improve these contradictory characteristics, and is characterized by suppressing the maximum hardness Hv (10 kg) of the welded part to 248 or less and further increasing the toughness. The objective is to provide a large-diameter steel pipe with excellent sour gas properties. (Means for Solving the Problems) The present inventors have discovered that the girth welds of steel pipes manufactured by the UOE method, particularly the intersections of the UO tube welds and the girth welds (hereinafter referred to as T-cross parts), have low hardness. The following knowledge was obtained regarding the improvement of the toughness of pipe-making seam weld metal. That is, welds obtained by girth welds, especially T-
The surface welding part (the part that is reheated by girth welding of submerged arc welding metal and does not receive afterheating) at the cross section is rapidly cooled, and since there is no afterheating, it becomes a quenched structure and increases in hardness. Therefore, in order to lower the hardness, it is necessary to create a structure that is difficult to harden.■ To achieve this, the component parameters (in the present invention, expressed as PMW) in the weld metal should be adjusted to a low value, and the CB
) It is effective to reduce the concentration as low as possible, and to prevent the decrease in toughness that accompanies such a decrease in hardness, and to achieve even higher toughness. O] By lowering ffi to a range where Ti can form a solid solution, that is, by adding Ti to form Ti2O3, fine acicular ferrite is formed in the austenite grains with this Ti2O3 as a core during the transformation from austenite to ferrite. necessary for the generation of such T1□03.

[0] It is preferable to keep the concentration up to. and () the above-mentioned trace amounts of CB) can be effectively utilized and dissolved in the weld metal to suppress the generation of ferrite at the austenite grain boundaries during transformation and prevent the formation of a coarse structure. ), it was found that it is important to keep the amount of Ti added within a narrow range by considering the balance between [Aρ), [0), and (N)]. The present invention was completed based on this knowledge, and its gist is as follows. In UOE steel pipes, the chemical composition of the base metal in weight% is C: 0.020~O, []550% Sl, 05% or less, Mn: 1.0~1.5%, P: 0.02% or less, S: 0.0OL5%v)X), Nb
:O,0L. 05%, Ti: 0.010-0.025%
, Al: 0.05% or less, N: 0.005% or less,
O: 0.0025% Bo 1, Ca: 0.002-0
．． 005%, and further contains one or more kinds of Mo and V, Mo: 0.05 to 0.30%,
:0. ESSP containing old-o, og%, and of the following formula
satisfies 1.5 to 6.0, and the remainder consists of unavoidable impurities and Fc. One-pass submerged arc welding was performed, and in weight percent, C: 0.020 to 0.060%, Si: 0.5% or less,
Mn: 1.35-1.85%, P: 0.03%
Below, S: 0.006% below, Tj: 0.00
5-0.025%, Al: 0.005-0.030%,
Mo: 0.30% or less, B: 0.0004 to 0.00
12%, 0.0.015-0.025%, N: 0.0
To obtain a weld metal containing 0.04% or less, and having a PWM of the following formula of 0.13 to 0.16, satisfying α of the following formula of -10 to +10, and the remainder consisting of unavoidable impurities and Fe. A method for manufacturing large diameter steel pipes with excellent sour gas resistance. ESSP=CaN, -124(0))/1.25
SPWM =C+Si/30+ (Mn+Cu+Cr
)/2010N+/60+MO/+5+V/10 α= C1,,5 (0~0,89Al) +3.4N-
Tt]XIO3 The above base material components include Ni: 0.
05-0.3%, Cu: 0.05-0.30%, Cr:
One or more types of 0.05-1.0% can be contained. The present invention will be explained in detail below. The large-diameter steel pipe manufactured by the present invention is a steel pipe with excellent sour gas resistance properties that is manufactured by UOE forming in a factory and joining the seam part by submerged arc welding, etc.
The base material is high toughness and high tensile strength steel of X-65 or higher specified by the standard X series. In other words, it is a low-alloy steel with a predetermined amount of alloying elements added and a low carbon content in order to impart the desired strength and toughness.
In addition, Ti is added to improve the toughness of the heat-affected zone of the weld, and the oxygen contained in the steel is converted into oxides such as Tl2O3.

[7
In addition to removing harmful oxygen, the Ti2O3 becomes the austenite→ferrite transformation point during the welding cooling process, and becomes pro-eutectoid ferrite formation nuclei within the austenite grains, thereby refining the structure. On the other hand, S in steel forms Mn and MnS, but this MnS
easily combines with hydrogen, forming hydrogen sulfide in this region, causing stress corrosion cracking. In the present invention, S is reduced to M as much as possible.
Ca is added to prevent it from combining with n, thereby changing the form of the sulfide. Ca combines with oxygen, but adding too much is not preferable because other inclusions may be formed or the size may increase. Therefore, in addition to the amount that binds to the remaining oxygen, it is necessary to make the amount sufficient to fix S. For this purpose, in the present invention, E S S P (El″rec
tiveSulfide 5shape Parameter
er) is established and managed. In the present invention, large-diameter pipes are manufactured using the UOE method from the above-mentioned base material, and these are joined on-site. During transportation, joints and heat-affected zones are more susceptible to SSC than the base material. That is, this is because the hardness is high, and the maximum hardness appears particularly in the T-cross portion as described above. When girth welding is used to join steel pipes, the inner side of the groove is heated layer by layer in a multi-layer build-up, and toughness is restored, but the outer circumference and inner surface (outermost layer) cool quickly. Moreover, the hardness of this weld increases due to the fact that it is a dwarf heat weld. Especially steel pipe seam welds and intersections (T-
(Cross), the seam weld metal is heated again, and combined with rapid cooling due to dwarf heat welding, the hardness of that part increases significantly. The present invention aims to reduce the hardness of this T-cross part and prevent the accompanying decrease in toughness by setting a range of PWM, which is the minimum index of hardenability, and by adding elements for refining the structure. The greatest feature is that it is configured by setting an α value to be used effectively and adjusting the concentration balance of Al-Ti -0 to N within a narrow range. For the welding material to obtain the weld metal of the part, a low carbon flux is selected, and it is preferable to use an extremely low carbon high Mn-low N-Ti wire for the welding rod. A flux consisting of the components disclosed in Publication No. 1-18836 is adopted.The reason why a low carbon type flux is preferable is that too much oxygen increases inclusions and reduces toughness. In addition, the components of the welding wire are preferably as follows: c: 0.01 to 0.10%, Si: 0.5% or less, Mn: 1 .5 to 3.5%, Pro, below old %,
S: 0.01% or less, Ni: 0.1-2.
0%, Ti20.01-0.2%, Aj7+0.
5% or less, N + o, +% or less, the balance consisting of Fe and unavoidable impurities. The reason why the welding wire used in the present invention is set in the above component range will be explained below. C: C is the element that most improves the hardenability in the weld metal.The smaller the amount, the easier it is to achieve lower hardness, or if the amount is too small, the CO reaction weakens and N in the atmosphere is drawn in.
The toughness of the weld metal deteriorates due to the adverse effects of oxidation, and problems arise in the manufacture of welding wires, so the above range was set. Si: Si is not a main component and enters the weld metal through the flux used or dilution of the base material, so in order to obtain high toughness, it is preferably 0.5% or less. Mn+Mn is one of the main components of the weld metal of the present invention. That is, the aim is to keep the C content low and to supplement the hardenability necessary for toughness with Mn. Therefore, if Ml is too low, the necessary hardenability cannot be ensured, and if it is too high, the hardenability is improved like C, so the above range was set. P, S-P, and S are contained as impurities and are preferably as small as possible, preferably 0.01% or less. Ti: Ti combines with O to form Tl2O3, and is one of the main components for obtaining the weld metal of the present invention to obtain high toughness.If TIN is too low, the necessary Tl2O3 will be insufficient, or if it is too high. Since there is a concern that toughness may deteriorate due to excessive Tj, the above range was set. Ag: Ag is a deoxidizer like Ti, but as mentioned above, the formation of Tl2O3 is very important in the weld metal of the present invention, and in combination with a low oxygen flux, it is more likely that Δ
It is preferable that the amount of Ω is less than 0.5%. N: Since a large amount of N reduces toughness, the upper limit was set to 0.1% or less. In the present invention, the PWM is 0.13 to 0. ] The reason why the range is limited to 6 is as follows. PWM is CE (
This is a formula that indicates hardenability similar to carbon equivalent (carbon equivalent), and a large value indicates high hardenability, that is, high hardness. As a result of various studies, it was confirmed that PWMO is more appropriate than CE. If the PWM value is 0.13 or less, sufficient quenching property cannot be obtained] 5. Hardenability cannot be obtained, and although it is easy to achieve low hardness, necessary toughness cannot be ensured. On the other hand, if the PWM value is 016 or more, the hardenability becomes excessive, so it is difficult to achieve low hardness (Hv
(1,0kg) max≦248) is not expected. In addition, by setting the above PWM value in the range of 013 to 0.16, the target hardness Hv (IOkg) maX≦2
48 is possible, but the toughness of the weld metal is not necessarily satisfactory. In order to stabilize the toughness at a high level, it is necessary to further refine the structure. The present invention uses Tj-B as a method of increasing toughness, and in particular, B has the effect of significantly increasing the hardenability of the weld metal and has the effect of suppressing the formation of ferrite at grain boundaries. The present inventors attempted to increase the toughness on the premise of effectively utilizing a small amount of B. In other words, by introducing the α value (formula), the toughness of weld metal has been dramatically improved within a limited range of PWM values. The reason is as follows. α is composed of the elements O, N, Ag, and Ti, and can be used as an index for preventing embrittlement due to excessive T1. That is, this formula is 0. N. The stoichiometric excess or deficiency between Ag and TI is shown as Ti equivalent. In other words, for example, a significant shift in the α value to the + side indicates that the amount of Ag and N is insufficient for 0 JfL, and excessive O combines with other elements, increases inclusions, etc., and high toughness is not expected. Can not. On the other hand, a large deviation to one side indicates that 8Ω, Tjm is excessive with respect to the amount of O, and the excess Ti combines with C to form TiC.
This results in unfavorable results such as the formation of hardness. The reasons for limiting the components of the present invention will be explained below. Concerning the base metal components, 0.020% or more of C is required to ensure the desired strength of the base metal, but if the amount increases, weldability and HAZ toughness deteriorate. Also, since it affects the low-temperature toughness of the base material,
．． The upper limit was set at 0.050%. St is an element contained in deoxidized steel, but when added to steel, it deteriorates HAZ toughness. Therefore, the content was set at 0.5% or less. Mn is an element necessary to ensure strength and toughness,
For this purpose, add 1.0% or more. Furthermore, Mn suppresses the formation of coarse pro-eutectoid ferrite at the γ grain boundaries and has the effect of improving HAZ toughness, but when the amount is large, hardenability increases, resulting in improved weldability and HAZ toughness. Therefore, the upper limit was set at 1.5%. P is contained as an impurity, and in order to prevent weld toughness and cracking due to micro-segregation, the content should be kept as low as possible, and should be 0.02% or less. Although S is also an impurity element, the inclusion of a large amount of S forms coarse sulfide-based inclusions and reduces the toughness of the base material. In particular, it forms MnS and adsorbs hydrogen, causing cracking, which is harmful to steel that requires sour gas resistance. Therefore, it is preferable to reduce it as much as possible, 0.00+,
It was set to 5% or less. Nl) is an essential element for obtaining excellent HAZ toughness, suppresses ferrite generated at the γ grain boundaries, and suppresses Ti20.
It has the effect of promoting the formation of fine acicular ferrite with . For that purpose, it is necessary to have 0, old% or more. However, if the amount exceeds 0.05%, the above effects tend to be hindered. Ti forms fine TiN in steel, suppresses austenite grain coarsening during slag heating, and is effective in improving base metal toughness and HAZ toughness, but no effect can be expected if it is less than 0.01%. However, if the amount is too large, TiC and the like will be formed, resulting in negative effects. Therefore, the upper limit was set at 0.025%. Ag is usually added as a deoxidizing agent, but Ti, S
j is also possible, and it is not necessary to add sushi. On the contrary, if the Ag content exceeds 0.05%, Ag-based nonmetallic inclusions will increase and impair the cleanliness of the steel, so the upper limit was set at 0.05%. N is an impurity element, which is less than 0.00.
5% indicates the upper limit of tolerance. O is also an element that is inevitably mixed. As mentioned above, A
90 When present in large amounts, various large inclusions (oxides) are formed,
It has a great influence on properties, especially HAZ toughness. Therefore, the less the content, the better, and the allowable amount should be 0.0025% or less. Ca is one of the characteristics of the base material component of the present invention, and is an effective element for improving low-temperature toughness and hydrogen-induced cracking resistance. S usually combines with Mn to form MnS, but hydrogen easily enters MnS, producing H2S and making the steel brittle. Ca controls the morphology of this MnS, prevents embrittlement, and provides the above effects. For this purpose, 0.002% is necessary. The amount of Ca added is determined in consideration of the oxygen content. In other words, Ca also has a strong deoxidizing effect, and Ca added to deoxidizing
As mentioned above (in the explanation of ESSP), it is necessary to exceed the amount consumed, but if the amount is too large, it will become large inclusions, which will harm not only the toughness of the steel but also its cleanliness, which will also have a negative effect on weldability. coming out. Therefore, the content was set at 0.005% or less. Mo and V increase the strength of the base material and effectively act on toughness, but for this purpose, the amount of 0.05.0. Although it requires more than the old %,
On the other hand, addition of a large amount leads to deterioration of the toughness of the base metal and welded zone, which is also unfavorable for weldability. Therefore 0.3.0.08 respectively
%, and one or two of these may be selected and added together as required. Ni, Cu, and Cr are elements that are added as necessary.N1 improves the strength and toughness of the base metal, and Cu is also effective for corrosion resistance and hydrogen-induced cracking resistance.
are elements that increase the strength of the base metal and weld zone, and are added at least 0.05% each for these purposes, but the upper limit is 0.3% each to avoid deterioration of weldability and HAZ toughness. , 0.3%, 1.0% or less. Next, the reason for specifying the components of the weld metal is as follows. Regarding C, Si, Mn, and Mo, the reason for adding them is the same as the above-mentioned base metal component, and the upper and lower limits of these elements are slightly different from those of the base metal. Because it's good. That is, by setting the addition amount of each of the above elements to 013≦PMW≦0,16, the hardness of the weld metal can be adjusted to Hv (1
0kg)≦248. N and O are elements that are unavoidably mixed into the weld metal, or their mixing in large amounts significantly deteriorates the toughness of the weld metal. Therefore, it is necessary to keep the amount of N as low as possible, below 0.004%, and the amount of O, below 0.025%. When these elements, especially O, are deoxidized with Ti,
Af! Considering the balance with etc., it is preferable to keep the content low enough to be equivalent to a small amount of addition T1,
This makes it possible to secure the solid solution B required for toughness. The lower limit of O was set at 0.001.5% because Ti
, 03. AI is a deoxidizing element that fixes N, 0 and fine Al
The content is 0.005 to 0.030% to form N and Al203 and improve the toughness of the weld metal. This AI is T1
Is it necessary to add it in balance? Ti is a deoxidizing and denitrifying element, and is one of the characteristics of the weld metal constituents of the present invention.
O3 is formed, and T is formed in the γ grains during the γ-α transformation of the weld metal.
i20. This has the effect of improving toughness by producing fine intragranular pro-eutectoid ferrite with ferrite as the nucleus. For that purpose, Al
, N, and O in the required amount. but,
Less than 0.005% has no effect. If the excess Ti amount exceeds 0.025%, the weld metal becomes brittle. B is a characteristic component of the weld metal of the present invention together with Ti, and by adjusting Ti to balance within the α value, (O), CN
) is sufficiently fixed to form a solid solution of B in the weld metal. Solid solution B suppresses coarse ferrite generated from γ grain boundaries during γ-α transformation, and promotes the formation of fine acicular ferrite through γ intragranular transformation with Ti2O3 as a nucleus. That is, a certain degree of hardenability is required to generate the above-mentioned acicular ferrite, and the solid solution B also serves to ensure this hardenability. As a result, a fine structure is formed and high toughness is obtained. In order to bring about the effects described in 1., the amount of B added must be at least 0.0.
0.004% is necessary, and if the amount is too large, the hardness will increase due to excessive hardenability. Therefore, the upper limit was set at 0.0012%. Note that P and S are unavoidable impurities and should be kept as low as possible for the same reason as the base material components described above, but the allowable upper limit is set to 0.03% and 0.006%, respectively. The above-mentioned weld metal components can be varied depending on the welding wire and flux components used, or can be kept within a specific range by adjusting the welding wire and flux component ranges described above. (Example) Next, an example of the present invention will be described. Steel tapped on site shown in Table 1]), 2) (Plate thickness: 12
．． 27 +nm t 44'), the hypoxic flux shown in Table 2, the comparative flux, and the third
Welded joints were produced by performing one-pass submerged arc welding on the inner and outer surfaces using the combinations of ultra-low carbon high Mn to low N-Ti welding wires shown in the table in the same manner as when manufacturing large diameter pipes in the UOT field. However, when welding joints, it is limited to changing the weld metal components by using only the combinations shown in the table above. Therefore, in order to study the influence of trace components, it is necessary to prepare carbon powder, Ti, etc. , All wire, and other metal powders were sprinkled or placed in the test. An impact test piece of the welded metal part and a test piece of the size shown in FIG. 1 were taken from the outside of the welded joint in order to simulate the maximum hardness of the on-site weld part. The method for the maximum hardness test is shown in Figure 1. In other words, for the maximum hardness test, remove the latent arc weld bead reinforcement on the outer surface side to the plate surface, and apply a test bead (10kJ/cm) using CO2 welding to cross the latent arc weld bead part (A) at a temperature of 10 kJ/cm. B) was placed, and a hardness measurement sample (C) was taken from the test weld. The hardness measurement position is the surface of the submerged arc weld (B),
The heat affected zone (D) of the submerged arc weld reheated by test welding was measured at a position within the diagonal distance of the normal rotation from the weld boundary by micro-Vickers hardness measurement, and the highest hardness value was measured. was evaluated as the highest hardness. Table 4 shows the weld metal components, weld metal toughness, and maximum hardness simulation results of the on-site weld. JP-A-3 285770 (8) JP-A-3 285770 (9) In the weld metal component system obtained by the uninvented method, weld metal properties including good toughness and low hardness were obtained. However, conventional weld metal components that are not based on the present invention have incompatible properties and are not suitable for sour resistance. In conventional weld metals, implementation No. II has too much Cm, so even if Mn is lowered, the PWM of the weld metal increases, and although toughness can be ensured, hardenability is extremely high. Furthermore, in Example No. 12.13, Cm was lowered, and even with a relatively high Mn content, the PWM was similarly high and the hardness was high. No. 14 has a good PWM value of -30°C
Although the toughness was not a problem, the hardness was higher than that of the weld metal of the present invention. This is because the BJi was higher than that of the invention metal and acted to increase the hardenability of the weld metal, which is not appropriate from the viewpoint of hardenability. No. 15.16 is also P
Although the WM value is at an appropriate level and the toughness is good, No.
Like No. 14, it has high hardness and is not suitable. This is because the α value went too far to the negative side, and No, I
5 is excessive Ti, No. 8 is because precipitation embrittlement due to excessive Aρ acts to increase the hardness of the weld metal. On the other hand, No. I7 showed an appropriate PWM value and low hardness or significantly low toughness. No. No. Only the material was tested using a comparative flux, and the oxygen content was higher than the other results. Therefore, T for the amount of O
Since the amounts of i and Ω are small, the toughness is significantly reduced due to excess oxygen, and the properties are not as good as those of the weld metal of the present invention. Further, in No. + 8, the PWM value is too low, and although a reduction in hardness is achieved, the toughness is low due to insufficient hardenability of the weld metal. (Effects of the Invention) As explained above, the girth welded portion of the UOE method large-diameter steel pipe obtained by the method of the present invention has a target hardness of Hv (1
0kg) It has a low hardness characteristic that satisfactorily achieves max≦248, and has high toughness without causing the deterioration in toughness that would normally occur with such a reduction in hardness. Therefore, the joint part (especially the T-cross part) is extremely stable even during girth welding on site where the heat input is small.
It is possible to obtain large diameter steel pipes with excellent sour gas resistance. 9 0

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a hardness test hole for a welded joint, and FIG. 2 is a diagram showing a hardness test specimen cut out from FIG. 1.

Claims (1)

[Claims] (1) In UOE steel pipes, the chemical components of the base metal are: C: 0.020 to 0.050%, Si: 0.5% or less,
Mn: 1.0-1.5%, P: 0.02% or less, S: 0
．． 0015% or less, Nb: 0.01-0.05%, Ti
: 0.010 to 0.025%, Al: 0.05% or less,
N: 0.005% or less, O: 0.0025% or less, Ca
: 0.002 to 0.005%, and further contains one or more of Mo and V, Mo:
0.05 to 0.30%, V: 0.01 to 0.08%, and the ESSP of the following formula satisfies 1.5 to 6.0, the balance consists of inevitable impurities and Fe, and the above The base material is low oxygen flux and ultra-low carbon high Mn-low N-Ti.
One-pass submerged arc welding was performed on the inner and outer surfaces using a system welding wire, and in weight percent, C: 0.020 to 0.060%, Si: 0.5% or less,
Mn: 1.35-1.65%, P: 0.03% or less, S
: 0.006% or less, Ti: 0.005 to 0.025%
, Al: 0.005-0.030%, Mo: 0.30%
Below, B: 0.0004-0.0012%, O: 0.0
15 to 0.025%, N: 0.004% or less, and PWM of the following formula is 0.13 to 0.16, α of the following formula satisfies -10 to +10, and the remainder is unavoidable. A method for producing a large-diameter steel pipe with excellent sour gas resistance, the method comprising obtaining a weld metal containing impurities and Fe. ESSP=Ca[1-124(O)]/1.25SPW
M=C+Si/30+(Mn+Cu+Cr)/20+N
i/60+Mo/15+V/10 α=[1.5(O-0.89Al)+3.4N-Ti]
×10^3 (2) In UOE steel pipe, the chemical composition of the base material is in weight%: C: 0.020 to 0.050%, Si: 0.5% or less,
Mn: 1.0-1.5%, P: 0.02% or less, S: 0
．． 0015% or less, Nb: 0.01-0.05%, Ti
: 0.010 to 0.025%, Al: 0.05% or less,
N: 0.005% or less, O: 0.0025% or less, Ca
: 0.002 to 0.005%, and further contains one or more of Mo and V, Mo:
Contains 0.05 to 0.30%, V: 0, 01 to 0.08%, and further Ni: 0.05 to 0.30%, Cu: 0.05 to 0.3.
0%, Cr: 0.05 to 1.0%, and ESSP of the following formula satisfies 1.5 to 6.0, the remainder consists of inevitable impurities and Fe, and the above-mentioned The base material is low oxygen flux and ultra-low carbon high Mn-low N-T.
One-pass submerged arc welding was performed on the inner and outer surfaces using an i-series welding wire, and in weight percent, C: 0.020 to 0.060%, Si: 0.5% or less,
Mn: 1.35-1.65%, P: 0.03% or less, S
: 0.006% or less, Ti: 0.005 to 0.025%
, Al: 0.005-0030%, Mo: 0.30% or less, B: 0.0004-0.0012%, O: 0.01
5 to 0.025%, N: 0.004% or less, and PWM of the following formula is 0.13 to 0.16, α of the following formula satisfies -10 to +10, and the remainder is unavoidable. A method for producing a large-diameter steel pipe with excellent sour gas resistance, characterized by obtaining a weld metal containing impurities and Fe. ESSP=Ca
[1-124(O)]/1.25SPWM=C+Si/
30+(Mn+Cu+Cr)/20+Ni/60+Mo
/15+V/10 α=[1.5(O-0.89Al)+3.4N-Ti]
×10^3