JP2007044710A - Method for manufacturing uo-formed steel pipe having excellent low temperature cracking resistance, and uo-formed steel pipe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a UO-formed steel pipe, which method can prevent low temperature cracks caused in a weld metal in the seam welding portion of the UO-formed steel pipe without imposing any restrictions on the chemical composition of the weld metal, and further without lowering the efficiency of a manufacturing process. <P>SOLUTION: In the seam welding portion of the UO-formed steel pipe formed by a preceding seam welding operation and the following seam welding operation, the upper limit of the amount of diffusible hydrogen in the preceding seam welding portion is restricted, and also a tensile stress caused in the weld metal in the preceding seam welding is reduced by specifying a ratio W2/W1 so as to satisfy the following expressions: 0.6≤W2/W1≤0.8 or 1.2≤W2/W1≤2.5, where W1 shows the thickness of the weld metal in the preceding seam welding, and W2 shows the thickness of the weld metal in the following seam welding. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a weld metal having a tensile strength of 850 MPa or more and 1200 MPa or less after forming a steel plate having a tensile strength of 850 MPa or more and 1200 MPa or less used in a natural gas / crude oil transportation line pipe or the like into a cylindrical shape. For UO steel pipes that are manufactured by straightening seam welding one layer at a time from both the inner and outer surfaces of the butted part and then correcting or expanding the pipe, etc. And a UO steel pipe manufactured by the manufacturing method thereof.

  UO steel pipe is generally used as a large-sized steel pipe for a line pipe that transports natural gas or the like. A UO steel pipe is formed into a cylindrical shape by forming a steel sheet into a U shape, further forming an O shape into a cylindrical shape, and joining the butted portions by welding. This welding is generally called seam welding. For the welding of the butt portion, submerged arc welding having a high welding speed and good weld quality is used. However, there is no problem if gas shield arc welding or laser beam welding is used. Also, generally, the first seam welding is performed from the inner surface of the cylindrically formed steel pipe, and then the subsequent seam welding is performed from the outer surface, thereby welding one layer each from the inner surface side and the outer surface side to perform seam welding. Although complete, it is also possible to perform the preceding seam welding from the outer surface in the reverse order and the subsequent seam welding from the inner surface. Furthermore, generally, prior to seam welding, a butt portion of a steel plate formed into a cylindrical shape is preliminarily welded in advance by gas shield welding or the like. At this time, generally, the temporarily welded portion is melted by seam welding and does not remain in the final seam welded portion.

  The steel pipe formed and welded into the cylinder as described above is further subjected to straightening processing such as expansion or contraction, and finally a UO steel pipe as a product is manufactured. Therefore, it is sometimes called UOE steel pipe.

  Conventionally, X65 and X80 grades (American Petroleum Institute Standards, API Standards) have been used, but in recent years, for the purpose of improving transportation efficiency, reducing line pipe construction costs or transportation costs, Development of a high-strength UO steel pipe with a tensile strength of 850 MPa or more, from X100 to X120, is in progress.

  Since the weld metal used for seam welding of these high-strength UO steel pipes is naturally required to have a tensile strength equal to or higher than that of the base metal, a high-strength weld metal is employed.

  However, a high-strength weld metal causes low-temperature cracking caused by three factors: the hardness of the weld metal, the diffusible hydrogen contained in the weld metal, and the tensile weld residual stress generated in the weld during welding. Therefore, low temperature cracking also occurs in the seam welded portion of the high-strength UO steel pipe.

  For such a problem of cold cracking, for example, in Patent Document 1, the chemical composition of the weld metal used, Pcm obtained by calculation from the chemical composition of the weld metal, and the cooling time of the weld metal part to 100 ° C. are defined as Pcm. A method for preventing cold cracking by limiting to a cooling time calculated from diffusible hydrogen has been proposed.

  Patent Document 2 proposes a method for preventing cold cracking by limiting the upper limit of the transformation temperature obtained by calculation from the tensile strength of the weld metal or the chemical composition of the weld metal to 375 ° C. or lower.

  Furthermore, Patent Document 3 proposes a method for preventing cold cracking by setting the time until diffusion forming to 30 minutes or longer after seam welding of a UO steel pipe is completed.

JP 2003-33876 A JP 2001-71176 A JP 2003-313121 A

  However, in any of the methods disclosed in Patent Document 1 or Patent Document 2, the Pcm or transformation temperature that needs to be controlled to prevent cold cracking is determined by the chemical composition of the weld metal, which is the chemical composition of the weld metal. It becomes a limit in designing. That is, the weld metal is required to have properties such as strength, low temperature toughness, and deformability, and it is not preferable to add unnecessary restrictions in determining the chemical composition of the weld metal.

  Moreover, in patent document 1, the cooling time to 100 degreeC is lengthened more than the cooling time calculated from Pcm and diffusible hydrogen, and in patent document 3, the time to pipe expansion forming after seam welding is set to 30 minutes or more. In this case, the manufacturing process takes a long time, which is problematic for application to industrial production where improvement in production efficiency is required.

  The present invention provides a manufacturing method for preventing low-temperature cracking that occurs in the weld metal of a seam welded portion of a UO steel pipe without any limitation on the chemical composition of the weld metal and without lowering the efficiency in the manufacturing process. Moreover, the UO steel pipe manufactured by the manufacturing method is provided.

  In order to achieve the above object, the present inventors have examined in detail the occurrence of cold cracks during seam welding of UO steel pipes. As a result, cold cracks occurring in seam weld metal occur in the weld metal of the preceding seam weld. Turned out to be. Furthermore, as a result of detailed examination, the upper limit of the amount of diffusible hydrogen existing in the weld metal of the previous seam weld is specified, and the residual stress generated in the weld metal of the previous seam weld is controlled in the welding conditions or groove shape. It was found that the low temperature cracking generated in the seam welded portion of the UO steel pipe can be prevented by reducing the amount of the crack.

  That is, the first feature of the present invention is that, after a steel sheet having a tensile strength of 850 MPa or more and 1200 MPa or less is formed into a cylindrical shape, the butt portion of the steel sheet is butted using a weld metal having a tensile strength of 850 MPa or more and 1200 MPa or less. In a method of manufacturing a UO steel pipe by performing seam welding in order of one layer each from both the inner and outer surfaces of the part and then performing straightening processing such as expansion or contraction, the amount of diffusible hydrogen in the weld metal of the preceding seam welding is When the thickness of the weld metal of the preceding seam weld is W1 and the thickness of the weld metal of the subsequent seam weld is W2, the ratio of W2 / W1 is 0.6 ≦ W2. /W1≦0.8 or 1.4 ≦ W2 / W1 ≦ 2.5 is generated in the weld metal of the preceding seam welding by performing seam welding. UO steel pipe manufacturing method with excellent low temperature cracking resistance, characterized by reducing the tensile stress is.

The second feature of the present invention is that, after a steel sheet having a tensile strength of 850 MPa or more and 1200 MPa or less is formed into a cylindrical shape, the butt portion of the steel sheet is formed by using a weld metal having a tensile strength of 850 MPa or more and 1200 MPa or less. In the method of manufacturing UO steel pipe by performing seam welding in order of one layer each from both the inner and outer surfaces and then performing straightening processing such as expansion or contraction, the amount of diffusible hydrogen in the weld metal of the preceding seam welding is the weld metal 2.0cc or less per 100 g, and in carrying out the subsequent seam welding, preceding the maximum temperature of the weld metal surface of the seam welding T1, the Ac ₁ transformation temperature of the weld metal of the preceding seam welding Ac ₁ when the seam is preceded by the T1 / Ac ₁ performs is satisfied seam welding 0.65 ≦ T1 / Ac ₁ ≦ 1.2 Process for producing a superior UO pipes in low-temperature cracking resistance, characterized by reducing the tensile stress generated in the weld metal of the contact is.

  The third feature of the present invention includes a base material portion having a tensile strength of 850 MPa to 1200 MPa and a seam weld portion having a tensile strength of 850 MPa to 1200 MPa formed by seam welding of one layer from each of the inner and outer surfaces. In the UO steel pipe, the amount of diffusible hydrogen in the weld metal formed by the preceding seam welding is 2.0 cc or less per 100 g of the weld metal, and the thickness of the weld metal formed by the preceding seam welding is W1, followed by When the thickness of the weld metal formed by seam welding is W2, the relationship 0.6 ≦ W2 / W1 ≦ 0.8 or 1.2 ≦ W2 / W1 ≦ 2.5 is satisfied. It is a characteristic UO steel pipe excellent in cold cracking resistance.

  The fourth feature of the present invention consists of a base material portion having a tensile strength of 850 MPa to 1200 MPa, and a seam weld portion having a tensile strength of 850 MPa to 1200 MPa formed by seam welding of one layer from each of the inner and outer surfaces. In a UO steel pipe, the amount of diffusible hydrogen in the weld metal formed by the preceding seam welding is 2.0 cc or less per 100 g of the weld metal, and the thickness of the weld metal formed by the preceding seam welding is W1. Satisfy the relationship of 0.1 ≦ f / W1 ≦ 1.0, where f is the width of the weld heat affected zone formed by subsequent seam welding in the weld metal formed by seam welding. This is a UO steel pipe excellent in cold cracking resistance characterized by the following.

  The present invention relates to a weld metal having a tensile strength of 850 MPa or more and 1200 MPa or less after forming a steel plate having a tensile strength of 850 MPa or more and 1200 MPa or less used in a natural gas / crude oil transportation line pipe or the like into a cylindrical shape. In the method of manufacturing UO steel pipe by performing seam welding from the inner and outer surfaces using a pipe, and then performing straightening processing such as pipe expansion or contraction, prior seam welding without any restriction on the chemical composition of the weld metal By controlling the ratio of the diffusible hydrogen upper limit of the weld metal and the thickness of the weld metal thickness of the seam weld, or the surface temperature of the preceding seam weld metal, or the ratio of the seam weld metal to the weld heat affected zone, It prevents cold cracking that occurs in seam weld metal. Therefore, the freedom degree of the component design for obtaining the characteristic required for a weld metal increases. Furthermore, since there is no limitation on the time until the start of the process after seam welding is performed, there is no influence on the manufacturing process. From these facts, according to the present invention, a UO steel pipe having a welded portion having high performance without a low temperature crack in the seam welded portion can be manufactured with high productivity.

  The present invention is described in detail below.

  In the present invention, the range of the strength of the base material and the weld metal to be applied is limited to 850 MPa to 1200 MPa. The reason for this is outside the scope of the present invention because when the tensile strength of the weld metal is less than 850 MPa, the strength is low and cold cracking does not occur in the weld metal and is likely to occur in the weld heat affected zone of the base metal. On the other hand, when the strength is 1200 MPa or more, it is difficult to obtain low temperature toughness necessary for UO steel pipe.

  It is desirable to use the steel sheet as a base material of the UO steel pipe to which the present invention is applied, the chemical composition of the weld metal, the welding method, and the welding material for creating the weld metal described below.

  The chemical composition of the steel sheet used as the base material is mass%, C: 0.02 to 0.10%, Si: 0.01 to 0.6%, Mn: 1.5 to 2.5%, P: 0 0.015% or less, S: 0.003% or less, Ni: 0.1 to 2.0%, Mo: 0.15 to 0.60%, Nb: 0.001 to 0.10%, Ti: 0.0. 005 to 0.03%, Al: 0.06% or less, if necessary, B: 0.0001 to 0.005%, N: 0.006% or less, V: 0.10% or less, Cu: 1.0% or less, Cr: 1.0% or less, Zr: 0.005% or less, Ta: 0.005% or less, Ca: 0.01% or less, REM: 0.01% or less, Mg: One or two or more of 0.006% or less is contained, and the balance is obtained by hot rolling steel composed of Fe and inevitable impurities.

  Moreover, the chemical composition of the weld metal is C: 0.03 to 0.10%, Si: 0.04 to 0.4%, Mn: 0.5 to 3.0%, P: 0.010 in mass%. % Or less, S: 0.010% or less, Cr: 0.01 to 1.5%, Ni: 4.5% or less, Mo: 2.0% or less, Nb: 0.020% or less, Ti: 0.0. 005 to 0.030%, Al: 0.05% or less, O: 0.0100 to 0.0500%, B: 0.005% or less, N: 0.010% or less, V: 0.04% or less, Cu: 0.40% or less is contained, and the balance is made of Fe and inevitable impurities.

  In addition, as a welding method for forming a weld metal, submerged arc welding is desirable in terms of productivity and quality in UO steel pipes, but gas shield arc welding, laser beam arc welding, and the like can also be used. .

  The chemical composition of the weld metal is determined by the dilution ratio of the base material determined by the welding method and the welding conditions, and the chemical composition of the base material and the welding material. Therefore, if the base material to be used, the welding method, and the welding conditions are determined, the desired chemical composition of the weld metal can be obtained by preparing a welding material having such a chemical composition that the desired chemical composition of the weld metal can be obtained.

  In submerged arc welding, a welding wire and flux are used as welding materials. Since welding can be easily performed using a plurality of wires as electrodes in the welding, a desired weld metal can be obtained by appropriately selecting an existing welding wire. However, by using a dedicated welding wire, a desired weld metal can be obtained more accurately.

  Therefore, in submerged arc welding, the desirable chemical composition of the welding material is mass%, C: 0.03-0.15%, Si: 0.01-0.40%, Mn: 1.0-3.0%. P: 0.010% or less, S: 0.010% or less, Cr: 3.5% or less, Ni: 12.0% or less, Mo: 4.5% or less, Nb: 0.05% or less, Ti : 0.005-0.05%, Al: 0.03% or less, O: 0.010% or less B: 0.005% or less, N: 0.010% or less, the balance is made of Fe and inevitable impurities Is.

Although the submerged arc welding amount of oxygen in the weld metal can be controlled by the flux used, the composition of the desired flux, by _{mass%, CaF 2: 15~55%,} SiO 2: 2~25%, Al 2 O 3 15 to 45%, MgO: 1 to 8%, CaO: 5 to 30%, Li ₂ O: 3.0% or less, K ₂ O: 2.0% or less, if necessary, balance is inevitable impurity It consists of

  The inventors actually perform submerged arc welding on both sides of the steel sheet using these base materials and welding materials to create a welded joint. Next, the inventors actually made a UO steel pipe on a trial basis and examined a method for preventing cold cracking.

  Table 1 shows the chemical composition of the base material used. Table 2 shows the chemical composition of the welding wire used. Table 3 shows the chemical composition of the flux used. Table 4 shows the groove shape conditions used. Table 5 shows the welding conditions used. In the present invention, all welding uses a three-electrode submerged arc welding method. Table 6 shows the chemical composition of the weld metal used. The weld metal shown in Table 6 was produced by combining the wires shown in Table 2 and the flux shown in Table 3 with the heat input shown in Table 6. Although the chemical composition of the weld metal is slightly different depending on the welding conditions even if the heat input is the same, it has been confirmed that there is no significant difference within the range of the welding conditions shown in Table 5, and Table 6 shows an example of the chemical composition. It is shown.

  As has been said in the past, cold cracking is caused by the overlap of three types of factors: the hardness of the weld metal, the amount of diffusible hydrogen in the weld metal, and the tensile stress applied to the weld metal. For this reason, generation | occurrence | production of a low temperature crack can be prevented by relieving any one or more types of factors by three types of factors.

  Of these three types of factors, the hardness of the weld metal is an important factor that affects the mechanical properties of the weld metal, and it is not preferable to regulate it easily. Therefore, a method for reducing both diffusible hydrogen and tensile residual stress was investigated.

  First, the present inventors investigated the relationship between the occurrence of cold cracking and the amount of diffusible hydrogen and stress. As the weld metal, among the weld metals shown in Table 6, weld metal I having a tensile strength of 855 MPa and weld metal V having a tensile strength of 1015 MPa were used. As a base material, a base material corresponding to the weld metal shown in Table 6 was used. As the welding conditions, for weld metal I, the groove shape no shown in Table 4 and the welding conditions 33 shown in Table 5 were used. For the weld metal V, the groove shape shown in Table 4 and the welding conditions 25 shown in Table 5 were used.

  Hydrogen was enclosed by electrolytic charging in a round bar type test piece cut out from the prepared weld metal so that the tangential direction and the tensile axis were parallel to each other. This round bar type tensile test was pulled with various stresses, and the occurrence of cold cracking after 72 hours was examined. FIG. 1 shows the result of a weld metal of 1015 MPa. It can be seen that the higher the applied stress, the more cracking occurs with less diffusible hydrogen. The results for the 855 MPa weld metal are shown in FIG. 2, but the trend was similar to the 1015 MPa weld metal.

  Next, the present inventors observed and examined in detail the cold cracks that occurred in the seam welds of UO steel pipes welded under various conditions. As a result, it has been found that in seam welds where one layer is welded from both sides, cold cracking always occurs from the inside of the preceding seam weld metal. Under conditions where cold cracking is likely to occur, cold cracking was observed even in the following seam weld metal. However, when the occurrence point of cold cracking was investigated in detail, the occurrence point of cold cracking was the same as that of the preceding seam welding. It was found that it was in the weld metal and propagated to the weld metal of the subsequent seam weld. It was also found that the low temperature cracks generated in the weld metal of the preceding seam weld progressed in the direction perpendicular to the weld line direction.

  Furthermore, the present inventors examined the generation | occurrence | production state of the tensile residual stress in a seam weld metal. The stress generated in the seam weld metal of the UO steel pipe is a welding residual stress (hereinafter simply referred to as a residual stress in the present invention) resulting from a thermal cycle during welding. Since it is difficult to actually measure the distribution of residual stress generated in the seam weld metal, the direction of the weld line at the center of the weld bead width is determined by numerical analysis simulation by the finite element method (hereinafter referred to as FEM in the present invention). The distribution of residual stress in the plate thickness direction was estimated. The residual stress in the weld line direction was determined because the low-temperature cracks generated in the seam welds of the UO steel pipe propagated in the direction perpendicular to the weld line as described above, and the stress in the weld line direction contributed to the low-temperature cracks. This is because it was judged. Seam welding, which is a premise of calculation, is a welded portion obtained by performing submerged arc welding on each side of a steel plate having a thickness of 20 mm from one side. The tensile strength of the steel sheet was 950 MPa, and the tensile strength of the weld metal was 1000 MPa. The welding heat input is 3.4 kJ / mm for the preceding seam welding and 3.4 kJ / mm for the following seam welding. Further, a seam welded portion with one layer on both sides was created by combining the steel plate B shown in Table 1 with the base metal and the weld metal V shown in Table 6, and the residual stress on the surface of the weld bead was measured. The validity of numerical analysis was verified. The welding conditions were the same heat input as that used in the numerical calculation, the groove shape was groove shape E in Table 4, and the welding condition 25 in Table 5 was used as the welding condition.

  FIG. 3 shows the results of numerical analysis and actual measurement. The residual tensile stress is shown as a positive value. Hereinafter, in the present invention, the stress in the tensile direction is positive. Since the numerical calculation result on the surface of the weld metal coincides with the actual measurement value, it can be judged that the numerical analysis is appropriate.

  From FIG. 3, the tensile residual stress showed the maximum value in the preceding seam weld metal, and its position coincided with the position of the cold crack starting point.

  From the above investigation results, the present inventors have come to the result that cold cracks occurring in UO steel pipes can be prevented by preventing cold cracks occurring in the weld metal of the preceding seam welding. This means that in two-layer welding, in which subsequent seam welding is performed following the preceding seam welding, measures for preventing low temperature cracks need to be concentrated only on the preceding seam welding. It means that it can be very simple in preventing.

  Therefore, the present inventors conducted a numerical analysis in more detail to investigate the change in the residual stress in the weld line direction generated in the weld metal of the preceding seam welding. As a result, the weld line direction generated in the weld metal of the preceding seam weld is shown in FIG. 4 by the ratio of the weld seam thickness W1 of the preceding seam weld and the thickness W2 of the weld seam of the subsequent seam weld. It was found that the residual stress changed. FIG. 5 shows the relationship between W2 / W1 and the maximum residual stress in the weld line direction generated in the weld metal of the preceding seam weld, which was obtained by numerical analysis. The tensile strength of the weld metal on both sides is assumed to be 1000 MPa. The maximum tensile stress in the weld line direction changed with W2 / W1, and W2 / W1 showed a maximum value at about 0.9. FIG. 6 shows the result of calculation under the assumption that the tensile strength of the weld metal on both sides is 850 MPa, and shows the same tendency as 1000 MPa.

  The reason why there is a difference in stress in the weld line direction due to the difference in W2 / W1 was considered. As a result, we inferred as follows. The preceding seam weld is heated by the heat of the subsequent seam weld. Therefore, thermal expansion and contraction occur in the preceding seam welding due to the heat of the subsequent seam welding, and tensile stress is generated again in the weld line direction. The tensile stress resulting from this increases as W2 / W1 increases. However, on the other hand, a tensile residual stress is generated in the direction of the weld line in the subsequent seam welding. The preceding seam weld is compressed by this tensile stress, and the tensile stress in the weld line direction generated in the weld metal of the preceding seam weld is relaxed. Therefore, the tensile stress in the weld line direction in the preceding seam welding is reduced as W2 / W1 increases. Since the sum of both becomes the tensile stress in the weld line direction generated in the weld metal of the preceding seam weld, as W2 / W1 increases, the tensile stress in the weld line direction initially increases due to the former effect. However, it is considered that when W2 / W1 is near 1, the latter effect becomes stronger and the tensile stress in the weld line direction is reduced.

  The present inventors further studied a method for reducing the tensile stress in the weld line direction generated in the subsequent seam welding. As a result, attention is paid to the fact that high-strength weld metal undergoes transformation expansion during cooling, and it is considered to effectively reduce the tensile stress in the weld line direction that occurs in the weld metal of the preceding seam weld. It was.

In order to effectively cause transformation expansion, the temperature of the weld metal of the preceding seam welding is important. Therefore, the relationship between the surface temperature of the weld metal in the preceding seam welding and the residual stress in the weld line direction was examined. FIG. 7 shows the case where the tensile strength of the weld metal on both sides is 1000 MPa. The maximum surface temperature of the preceding seam weld metal and the weld metal of the preceding seam weld obtained by numerical analysis, as determined by numerical analysis. The relationship of the maximum axial tensile stress generated in the interior is shown. The temperature of the weld metal surface of the preceding seam welding referred to here is the temperature at the position of H1, which is the apex of the weld metal of the preceding seam weld shown in FIG. In FIG. 7, the weld metal surface temperature of the preceding seam weld is made dimensionless from the weld metal surface temperature T1 of the preceding seam weld by the Ac ₁ temperature of the weld metal. For the Ac ₁ temperature, the value used in the numerical calculation is used. According T1 / Ac ₁ increases from FIG. 7, the weld line direction of the tensile stress in the weld metal of the preceding seam welding, it is seen that the smaller. FIG. 8 shows the numerical analysis results for the weld metal having a tensile strength of 850 MPa on both sides. As can be seen from FIG. 8, even in the case of 850 MPa, the same tendency as in the case of the weld metal of 1000 MPa was shown.

Next, the present inventors examined whether it was possible to determine whether T1 / Ac ₁ was maintained at 0.65 or more from the shape of the welded portion after seam welding. As a result, T1 / Ac ₁ of 0.65 or more is intended to increase the area of the region heated to Ac ₁ or more. Therefore, by knowing the region affected by welding heat, T1 / Ac 1 It has been found that it can be determined whether ₁ is heated to 0.65 or higher. Specifically, T1 / Ac ₁ is 0.65 by measuring the ratio of the width of the welding seam effect due to the subsequent seam welding in the weld metal of the preceding seam weld and the thickness W1 of the preceding seam weld. It came to the knowledge that it was possible to know whether it was above. Here, the width of the weld heat affected zone is the length of f shown in FIG. f can be easily measured by corroding the weld metal with a corrosive liquid such as nital.

Figure 9 shows the relationship between T1 / Ac ₁ and f / W1. If the 9 of T1 / Ac ₁ is less than 0.65, f / W1 is seen that less than 0.1. That is, if f / W1 is not less than 0.1 to find that T1 / Ac ₁ is 0.65 or more. From this fact, it can be determined whether or not the present invention has been reliably implemented from the macro structure after manufacture.

  Next, the present inventors paid attention to the minimum value of the tensile stress in the weld line direction generated in the weld metal of the preceding seam weld. FIG. 10 shows the result of calculating the minimum stress in the weld line direction generated in the weld metal of the preceding seam weld by numerical analysis by changing the strength of the weld metal. As a result of numerical analysis, the minimum tensile stress in the weld line direction generated in the weld metal of the preceding seam welding was about 520 MPa to 550 MPa. Further, it was considered that the maximum tensile stress in the weld line direction generated in the weld metal of the preceding seam welding was about 830 MPa.

  Based on the above examination results, the present inventors devised a method for preventing cold cracking without limiting the chemical composition of the weld metal and without affecting the process after seam welding.

  The contents of the present invention will be described in detail below.

  First, the amount of diffusible hydrogen in the weld metal of the preceding seam welding was limited to 2.0 cc or less per 100 g of weld metal. As shown in FIG. 10, a tensile stress in the weld line direction of at least about 520 MPa to 550 MPa is generated in the weld metal of the preceding seam welding as shown in FIG. In order not to cause cold cracking even in this tensile stress, the diffusible hydrogen content of the weld metal needs to be 2.0 cc or less per 100 g of weld metal from FIGS. It has been found that due to the expansion or contraction of the pipe, large plastic deformation is applied to the seam welded portion of the UO steel pipe and stress is redistributed, and as a result, the tensile stress in the weld line direction is reduced to 500 MPa or less. That is, after correcting the expansion or contraction, cold cracking does not occur.

  Examples of the method for reducing the diffusible hydrogen in the seam welded portion to 2.0 cc or less per 100 g of the weld metal include drying of the welding material amount, cleaning of the groove, preheating or postheating during welding. In submerged arc welding, which is desirable in the present invention, since flux is used, drying the flux is effective in reducing diffusible hydrogen. For example, diffusible hydrogen brought into the weld metal from the flux can be reduced by spreading the flux to a thickness of about 30 mm and drying in a furnace heated to 250 to 350 ° C. for 2 hours. However, diffusible hydrogen in the weld metal may increase during welding. That is, dirt on the groove surface and surrounding moisture are also sources of diffusible hydrogen into the weld metal. Correspondingly, there are the following methods for reducing diffusible hydrogen during welding. The dirt on the groove surface to be welded includes iron powder and dust, which can be removed by washing with water. In addition, water-soluble liquids, oils and fats that can be suspended in water, or small amounts of oils and fats that are not suspended in water can be removed by spraying water or high-pressure water on the groove surface. Removal of dirt with a volatile solvent or alcohol completely removes the groove surface. In addition, diffusible hydrogen that increases when brought in from the atmosphere can be reduced by heating after heating at 250 ° C. for 20 to 30 minutes after welding, and diffusible hydrogen in the weld metal can be further stably reduced. . The diffusible hydrogen content in the weld metal varies depending on the ease of moisture absorption of the welding material used and the ambient humidity during welding, but by combining these measures, the amount of diffusible hydrogen in the weld metal is reduced. be able to.

  Next, a method for measuring diffusible hydrogen in the weld metal of the preceding seam welding used in the present invention will be described. In general, in the field of welding, a method for measuring diffusible hydrogen when discussing low temperature cracking is a method for measuring the amount of hydrogen in a steel weld according to JIS Z 3118. This is a method for measuring diffusible hydrogen in a weld metal. is there. In the present invention, the amount of diffusible hydrogen in the weld metal is used as a reference in order to make it more realistic. In this method, after actually welding the steel sheets one by one from both sides, when the seam weld reaches 100 ° C., a specimen for measuring diffusible hydrogen of about 5 mm × 40 mm is cut out from the preceding seam weld, It measured based on the diffusible hydrogen measuring method by the gas chromatograph method described in JISZ3118. Of course, the amount of diffusible hydrogen in the weld metal of the subsequent seam welding can be measured in the same manner.

  Moreover, in this invention, the diffusible hydrogen when it reaches 100 degreeC is measured. This is because diffusible hydrogen at 100 ° C. was measured because cold cracking occurred at about 100 ° C. or less. In the pipe making of UO steel pipe, the diffusible hydrogen in the weld metal of the preceding seam welding decreases monotonously after welding. Therefore, after seam welding, if the diffusible hydrogen at the time when the welded portion is cooled to 100 ° C. is 2.0 cc or less, cold cracking does not occur. Therefore, diffusible hydrogen at this temperature was measured.

  If the above-mentioned method is used, the amount of diffusible hydrogen remaining in the welded part closer to the work can be measured. Furthermore, even if adopting a method to control the diffusible hydrogen of the weld metal of the preceding seam welding by methods such as drying of welding material, cleaning of groove, preheating, postheating, etc., the effect can be confirmed directly, It is an effective method.

  Next, the reason for limiting the range of W2 / W1, which is the ratio of the height W1 of the weld metal of the preceding seam weld to the height W2 of the weld metal of the subsequent seam weld will be described. 1 and 2, it can be estimated that when the amount of diffusible hydrogen in the weld metal is 2.0 cc or less per 100 g of weld metal, cold cracking does not occur when the tensile stress is less than about 700 MPa. From FIG. 5 and FIG. 6, the tensile stress in the weld line direction generated in the weld metal of the preceding seam welding should be less than 700 MPa in the range of W2 / W11 ≦ 0.8 and 1.2 ≦ W2 / W1. I know I can do it.

  Next, the reasons for limiting the upper and lower limits of W2 / W1 will be described below. Excellent low temperature toughness is required for seam welds of UO steel pipes. However, when the toughness of the heat-affected zone of the preceding seam weld that is reheated by the subsequent seam welding is measured in the double-sided single-layer seam welded portion of the high-strength UO steel pipe, if the welding conditions are not appropriate, the toughness is low. There is a problem that it is likely to occur. FIG. 11 shows a low value of the absorbed energy of −30 ° C. of the weld metal W2 / W1 and the weld heat affected zone of the double-sided single-layer seam weld zone having the weld metal V shown in Table 3 for the steel plate B shown in Table 1. The relationship of incidence is shown. As shown in FIG. 12, the impact test piece was sampled so that the notch of the impact test piece was located at the position where the heat affected zone of the preceding seam weld and the heat affected zone of the subsequent seam weld overlapped. 27 impact test pieces were carried out under the condition of one W2 / W1, and the generation rate of absorbed energy of 40 J or less was shown as a percentage. W2 / W1 was adjusted by selecting the groove shape and welding conditions shown in Tables 4 and 5. As shown in FIG. 12, the occurrence frequency of the low value increases rapidly when W2 / W1 is less than 0.6 and more than 2.5. When W2 / W1 is more than 2.5, the meltdown phenomenon (hereinafter referred to as the present seam welding), in which the preceding seam welding is heated too much by the subsequent seam welding and becomes high temperature, and the weld metal of the preceding seam welding melts. (In the invention, it is abbreviated as MD)). From this viewpoint, W2 / W1 is preferably 2.5 or less.

  From the above examination, the range of W2 / W1 was set to 0.6 ≦ W2 / W1 ≦ 0.8 and 1.2 ≦ W2 / W1 ≦ 2.5.

  A method for controlling W2 / W1 will be described. W1 and W2 can be controlled by controlling the size and shape of the weld metal. The size referred to here is the cross-sectional area S of the weld metal shown in FIG. 13, and the shape is the height h and width b when the weld metal is viewed in a cross section perpendicular to the welding direction. W1 is a value obtained by subtracting the intersecting length of the preceding seam weld metal and the subsequent seam weld metal from h of the preceding seam weld metal. On the other hand, W2 is the same value as h of the weld metal of the subsequent seam welding.

  Generally, in welding, the welding conditions are determined so that the groove can be sufficiently filled with a welding material melted by a heat source such as an arc. Therefore, if a groove shape having a large cross-sectional area is created, a weld metal S having a large cross-sectional area can be obtained. On the other hand, if a groove having a small cross-sectional area is created, a weld metal having a small cross-sectional area S can be obtained. That is, since the area of the weld metal can be easily controlled by welding heat input, setting W2 / W1 to a value within the required range is possible if the groove shape on both sides is designed to be the required W2 / W1. Easily possible.

  FIG. 14 schematically illustrates this. FIG. 14B shows an example in which the groove of the preceding seam welding is processed to be substantially the same as the groove of the subsequent seam welding. Therefore, W1 and W2 are almost the same value. On the other hand, FIG. 14A is processed so that the groove of the preceding seam welding is larger than the groove of the subsequent seam welding. Therefore, W1 is larger than W2 and W2 / W1 is less than 1. On the other hand, FIG. 14 (c) shows an example in which the groove of the preceding seam welding is smaller than the groove of the subsequent seam welding. In this case, W1 is smaller than W2, so W2 / W1 is The value exceeds 1. Since the ratio of the groove dimensions is important, it can be designed in the same manner even if the thickness of the steel sheet used is different.

  Furthermore, it is possible to increase the height h and reduce the width b even under the same weld metal area under welding conditions. That is, as the welding current increases, the penetration d shown in FIG. 13 increases. Of course, the height h also increases. When the welding current increases, the welding heat input increases. However, if you want to keep the welding heat input constant, increasing the welding speed makes the welding heat input constant, and increases the height h without changing the welding heat input. be able to. When the heat input is kept constant and the welding speed is increased, the width b is generally reduced. FIG. 14D is a schematic diagram of an example in which W2 / W1 is increased by this method. Even if the groove shape is the same as in FIG. 14B, by increasing the welding current, a deep weld metal having a large penetration d can be obtained. When the heat input is kept constant and the welding speed is increased, FIG. A vertically long weld metal is obtained as shown in FIG.

  In this manner, W2 / W1 can be easily controlled by appropriately selecting the welding conditions and the groove shape. Further, the chemical composition of the weld metal can be predicted by the dilution rate of the base material determined by the welding conditions, the chemical composition of the welding material, and the chemical composition of the base material. The strength and toughness of the weld metal are almost determined by this chemical composition. Therefore, even if the welding conditions and the base metal are fixed, the chemical composition of the weld metal can be freely adjusted by appropriately selecting the welding material. Therefore, the design of W2 / W1 for any characteristics of the weld metal. Will not interfere.

Next, the reasons for limiting T1 / Ac ₁ will be described. The purpose of limiting T1 / Ac ₁ is to reduce the tensile stress in the weld line direction generated in the weld metal of the preceding seam weld with the same purpose as the limitation of 1.4 ≦ W2 / W1. That is, by increasing the area of transformation expansion in the weld metal of the seam welding the preceding increase the T1 / Ac _1, it is to reduce the tensile stress from occurring in the axial direction.

As described above, when the tensile stress in the weld line direction generated in the weld metal of the preceding seam weld is less than 700 MPa, when the amount of diffusible hydrogen per 100 g of weld metal is 2.0 cc or less, cold cracking occurs. Occurrence can be prevented. 7 and 8, by setting T1 / Ac ₁ to 0.65 or more, the tensile stress in the weld line direction generated in the weld metal of the preceding seam welding can be made less than 700 MPa. Therefore, the T1 / Ac ₁ 0.65 or more. Next, as with the upper limit of the limit of the upper limit of W2 / W1, if the temperature of the weld metal surface of the preceding seam weld becomes too high, the previous seam weld reheated by the subsequent seam weld The frequency of occurrence of low values in the toughness of the heat affected zone increases. In addition, when performing the subsequent seam welding, the upper limit is set to 1.2 because there is a high risk of occurrence of MD in which the weld metal of the preceding seam welding is melted.

Next, the reason for limiting f / W1 will be described. As shown in FIG. 9, in order to the T1 / Ac ₁ to 0.65 or more f / W1 is required to be 0.1 or more. For T1 is Ac ₁ or more, since from the cross section of the seam weld f can not measure the upper limit of f / W1 is 1.0. Therefore, T1 / Ac ₁ reaches 1.2 or more from the cross-section of the seam welded portion, and the control of whether there is a risk of causing a decrease in toughness of the weld heat affected zone and further MD occurs is W1 / W2 ≦ 2.5. The conditions will be adopted.

Next, a method of controlling T1 / Ac ₁ will be specifically described. T1 is the maximum heating temperature of the surface of the weld metal when performing the subsequent seam welding, and becomes higher as W1 is smaller than W2. That is, the control method of T1 can be easily controlled by the welding conditions and the groove shape, similarly to the control method of W2 / W1. On the other hand, Ac ₁ is a measurable value determined by the chemical composition of the weld metal. Since the chemical composition of the weld metal can be adjusted independently of the welding conditions as described above, first, after determining the chemical composition of the weld metal to obtain the characteristics required for the weld metal, the Ac ₁ is measured. , easily present invention by designing the welding conditions or groove shape as that from the value T1 / Ac ₁ are within the scope of the present invention can be carried out. Furthermore, it is also effective to use a method in which the preceding seam weld is heated with an auxiliary heat source such as a burner or the like, or heat is retained by a method such as protecting the preceding seam weld with a heat insulating material. The maximum heating temperature of the welded metal surface of the preceding seam welding can be confirmed by performing a test weld using a preset groove shape, welding conditions or heat treatment, and these can be confirmed during actual seam welding. If the set welding conditions are reproduced, the maximum heating temperature of the weld metal surface of the preceding seam welding can also be reproduced. Of course, it may be confirmed by measuring the temperature individually in the actual pipe making, which is a more desirable direction in terms of quality control.

  Next, the effects of the present invention will be described in detail using examples.

  A UO steel pipe was manufactured using the steel plate shown in Table 1 and the welding material for submerged arc welding shown in Table 2 and Table 3. The groove shapes used at that time are already shown in Table 4. Also, the welding conditions used are already shown in Table 5. W1 / W1 and T1 were adjusted by combining these groove shapes and welding conditions. The flux used for submerged arc welding was dried at 300 ° C. for 2 hours for the preceding seam welding, but it was not purchased for the subsequent seam welding. used. The groove surface was wiped with a cloth soaked with acetone to remove dust and grease, and then the groove surface was maintained so as not to be contaminated, and the welding process was started. Therefore, basically, preheating and post heat treatment were not performed, but in some pipe making, the preceding seam weld was preheated from 100 ° C. to 150 ° C. when performing the subsequent seam welding. This is to increase the weld metal surface temperature of the preceding seam welding, but also has the effect of reducing diffusible hydrogen.

  On the other hand, a steel pipe with intentionally increased diffusible hydrogen was also made. In some pipes, the amount of diffusible hydrogen in the weld metal was increased by absorbing the preceding seam welding flux. Furthermore, in actual production, oil or the like may be attached to the groove surface. Therefore, a water-soluble lubricating oil used for pipe making is intentionally applied to the groove surface that has been cleaned by simulating them. Manufactured.

In seam welding, first, tack welding is performed with a commercially available 50 kg class CO ₂ welding wire, then preceding seam welding is performed from the inner surface by submerged arc welding, and then subsequent seam welding is performed from the outer surface by submerged arc welding. It was. In this example, the temperature of the weld metal surface of the preceding seam weld during the subsequent seam welding was measured by joining a thermocouple to the weld metal surface of the preceding seam weld by resistance welding.

  For the amount of diffusible hydrogen in the weld metal, a test piece for measurement was taken when the seam welded portion was cooled to 100 ° C. after the UO steel pipe was formed, and the amount of diffusible hydrogen in the weld metal was measured.

After that, tube expansion was corrected. After finishing the expansion of the pipe, a non-destructive inspection was performed on the whole seam welded portion with X-rays to confirm the occurrence of cold cracking. Then, the impact test piece was extract | collected in the way shown in FIG. 12 from the both ends and center part of the UO steel pipe, and the toughness of the welding heat affected zone was measured. The tensile strength of the weld metal was measured by collecting a JIS round bar type A2 tensile test piece in the weld line direction from the weld metal of the preceding seam weld. The Ac ₁ temperature of the weld metal can be estimated from the chemical composition of the weld metal, but in this example, for the sake of accuracy, a test piece is taken from the weld metal of the preceding seam weld and is expanded and contracted during heating and cooling. The Ac ₁ temperature was measured by measuring the amount. Tables 7 and 8 (continued in Table 7) show examples of the invention of the UO steel pipe according to the present invention.

  Invention Examples 1 to 7 are invention examples in which W1 / W2 is in the range of 0.6 to 0.8. The strength of the weld metal varies from 855 MPa to 1195 MPa. The amount of diffusible hydrogen in the weld metal of the preceding seam weld when the seam weld is cooled to 100 ° C after seam welding is 2.0 cc or less in 100 g of weld metal, and the groove shape and welding conditions are appropriate. Since W1 / W2 is within the range of the present invention, the low temperature cracking does not occur. Furthermore, the frequency of occurrence of low values of the toughness of the weld heat affected zone is low and good.

  Invention Example 1 and Invention Example 2 are invention examples in which the base metal, the groove shape, and the welding conditions are the same, but the strength of the weld metal is different.

  Invention Example 3 is an invention example in which the plate thickness is 20 mm and the strength of the weld metal exceeds 1000 MPa.

  Invention Example 4 and Invention Example 5 are invention examples in which the base material, the groove shape, and the weld metal are the same, but the welding conditions are different. Therefore, W2 / W1 is different.

  Invention Example 6 is an invention example having the same base material and groove shape as Invention Example 4 and Invention Example 5, but different welding conditions and weld metal strength.

  Invention Example 7 is an invention example of a high-strength seam welded portion, in which the welding conditions are the same as in Invention Example 4, but the base material, the groove shape, and the weld metal are different.

  Invention Examples 8 to 26 are invention examples in which W1 / W2 is in the range of 1.2 to 2.5 and f / W1 is in the range of 0.1 or more.

The strength of the weld metal varies from 856 MPa to 1179 MPa. The amount of diffusible hydrogen in the weld metal of the preceding seam weld when the seam weld is cooled to 100 ° C. after seam welding is 2.0 cc or less in 100 g of weld metal, and the groove shape and welding conditions are By selecting appropriately, since W1 / W2 is within the range of the present invention, no cold cracking occurs. Furthermore, the value of T1 / Ac ₁ also 0.65 or more and 1.2 or less. The value of f / W1 is also 0.1 or more. Furthermore, since the welded part is not excessively heated, the occurrence frequency of the low value of the welded part heat affected zone is low and good.

  Invention Example 8, Invention Example 9 and Invention Example 10 are invention examples in which the base metal, the weld metal and the groove shape are the same, but the welding conditions are different. Therefore, although W2 / W1 is different, both are within the scope of the present invention. Also, T1 / AC1 is a value of 0.65 or more and 1.2 or less. Moreover, f / W1 is 0.1 or more.

Invention Example 11 has the same base material, weld metal, and welding conditions as Invention Example 8, but the groove shape is different. Since the groove of the preceding seam welding is deepened, the value of W2 / W1 is small. However, within the scope of the present invention, both the T1 / Ac _1, 0.65 or more, and is 1.2 or less of the value. Moreover, f / W1 is 0.1 or more.

Invention Example 12 and Invention Example 13 are examples in which the present invention is applied to a combination of a base material A and a weld metal I. Although welding conditions and groove shapes are different from those of Invention Examples 8 to 11, both W1 / W2, T1 / Ac ₁ and f / W1 are the values of the present invention because appropriate welding conditions and groove shapes are selected. It is included in the range, and a sound weld with no cold cracking is obtained.

Inventive Example 14, Inventive Example 15, Inventive Example 16 and Inventive Example 17 are inventive examples in which the base metal and the weld metal are the same, but the welding conditions or the groove shape are different. W2 / W1 is being changed by the welding conditions and groove shape, within the scope of the present invention, both the T1 / Ac _1, 0.65 or more, and is 1.2 or less of the value. Moreover, f / W1 is 0.1 or more.

  Invention Example 18 is an example in which the base metal, groove shape and welding conditions are the same as Invention Example 15, but the tensile strength of the weld metal is about 940 MPa. No cracks occurred even at this tensile strength.

Invention Example 19 is an invention example in which the welding conditions are different from those of Invention Example 18 and the value of W2 / W1 is increased. However, cold cracking does not occur and the toughness of the weld heat affected zone is also good. T1 / Ac ₁ also 0.65 or more, are included in the range of 1.2 or less. Moreover, f / W1 is 0.1 or more.

Invention Example 20, Invention Example 21 and Invention Example 22 are invention examples in which the base metal, the weld metal and the groove shape are the same, but the welding conditions are different. Therefore, W2 / W1 is different, in any of the welding conditions, W2 / W1 is within the scope of the present invention, T1 / Ac ₁ also 0.65 or more, 2.5 or less, f / W1 also 0. 1 or more. Therefore, there is no cold cracking and the toughness of the weld heat affected zone is good.

Invention Example 23 has the same base material, groove shape, and welding conditions as Invention Example 21, but the tensile strength of the weld metal is as high as 1185 MPa. However, W2 / W1 is within the scope of the present invention, T1 / Ac ₁ also 0.65 or more, 2.5 or less, f / W1 even 0.1 or more. Therefore, there is no cold cracking and the toughness of the weld heat affected zone is good.

Invention Example 24 is an invention example in which the groove shape and welding conditions of Invention Example 23 are changed. W2 / W1 is within the scope of the present invention, T1 / Ac ₁ also 0.65 or more and 1.2 or less, f / W1 even 0.1 or more. Therefore, there is no cold cracking and the toughness of the weld heat affected zone is good.

Invention Example 25 is an invention example using the base material D. W2 / W1 is within the scope of the present invention, T1 / Ac ₁ also 0.65 or more and 1.2 or less, f / W1 even 0.1 or more. Therefore, there is no cold cracking and the toughness of the weld heat affected zone is good.

Invention Example 26 is also an invention example using the base material D. The strength of the weld metal is 1194 MPa, which is even higher. W2 / W1 is within the scope of the present invention, T1 / Ac ₁ also 0.65 or more and 1.2 or less, f / W1 even 0.1 or more. Therefore, there is no cold cracking and the toughness of the weld heat affected zone is good.

  Invention Example 27 to Invention Example 32 are examples in which W1 / W2 is less than 1.2, but low temperature cracking is prevented by heat treatment to increase the T1 temperature. The amount of diffusible hydrogen in the weld metal of the preceding seam weld when the seam weld is cooled to 100 ° C. after seam welding is 2.0 cc or less in 100 g of weld metal.

In Invention Example 27, T1 / Ac _{1 is set} to 0.74 by preheating the preceding seam welded portion at 150 ° C. immediately before performing the subsequent seam welding. f / W1 is also 0.1 or more.

Inventive Example 28 preheats the preceding seam weld immediately before performing the subsequent seam welding at 100 ° C., and further keeps the preceding seam weld with a heat insulating material during the subsequent seam welding. T1 / Ac _{1 is set} to 0.69. f / W1 is also 0.1 or more.

Invention Example 29 is an example in which the tensile strength of the weld metal is 865 MPa. Immediately before the subsequent seam welding is performed, the preceding seam weld is preheated at 150 ° C., whereby T1 / Ac _{1 is set} to 0.70. f / W1 is also 0.1 or more.

Inventive Example 30 by heating the seam weld preceding in implementing the subsequent seam welding with a burner, and a T1 / Ac ₁ and 0.71. f / W1 is also 0.1 or more.

In Invention Example 31, T1 / Ac _{1 is set} to 0.68 by keeping the preceding seam welded portion with a heat insulating material during the subsequent seam welding. f / W1 is also 0.1 or more.

In Invention Example 32, T1 / Ac _{1 is set} to 0.70 by preheating the preceding seam welded portion at 100 ° C. immediately before performing the subsequent seam welding. f / W1 is also 0.1 or more.

By these means, Invention Example 27 to Invention Example 32 do not cause cold cracking. Also, T1 / Ac ₁ is 2.5 or less, and W1 / W2 is 2.5 or less, and the welded part is not excessively heated. Therefore, the occurrence frequency of the low value of the toughness of the weld heat affected zone is low and good. MD is not generated. Further, these heat treatments also reduce the amount of diffusible hydrogen in the weld metal of the preceding seam welding.

  Next, a comparative example will be described. Tables 9 and 10 (continued in Table 9) show comparative examples of the present invention.

Comparative Examples 1 to 7 are examples in which W2 / W1 is more than 0.8 and less than 1.2. The strength of the weld metal is changed from 862 MPa to 1184 MPa. Further, the amount of diffusible hydrogen in the weld metal of the preceding seam weld when the seam weld is cooled to 100 ° C. after the seam weld is 2.0 cc or less in 100 g of the weld metal. However, since the welding conditions are inappropriate for the groove, W2 / W1 is out of the scope of the present invention. Since the heat-retaining and heat treatment also is not performed, T1 / Ac ₁ be less than 0.65, f / W1 is less than 0.1. From these facts, although the amount of diffusible hydrogen in the weld metal is small, cold cracking occurs in the weld metal of the preceding seam welding.

  Comparative Examples 8 to 10 are examples in which W2 / W1 is less than 0.6. The strength of the weld metal is changed from 860 MPa to 1181 MPa. Since the value of W2 / W1 is small, cold cracking does not occur, but the occurrence rate of the low value of the toughness of the weld heat affected zone frequently occurs at 15% or more.

Comparative Examples 11 to 15 are examples in which W2 / W1 exceeds 2.5. The strength of the weld metal is changed from 865 MPa to 1178 MPa. In either case, W2 / W1 exceeds 2.5 because the welding conditions are inappropriate for the groove. In addition, it has become even greater than 1.2 T1 / Ac _1. Therefore, although the low temperature crack does not generate | occur | produce in the preceding seam weld metal, the low value occurs frequently in the toughness of a welding heat affected zone. Furthermore, in Comparative Example 12, Comparative Example 14, and Comparative Example 15, MD occurred because the weld metal of the preceding seam welding was excessively heated.

  Comparative Examples 16 to 22 are comparative examples when the amount of diffusible hydrogen in the weld metal is large.

  Comparative Example 16 has the same conditions as Invention Example 1, but because the dirt adhered to the groove surface and the flux absorbed moisture, the preceding seam when the seam weld was cooled to 100 ° C. after seam welding. The amount of diffusible hydrogen in the weld metal of welding is more than 2.0 cc in 100 g of weld metal. Therefore, cold cracking has occurred in the preceding seam weld metal. Furthermore, this cold crack had propagated into the weld metal of the subsequent seam weld.

  Comparative Example 17 has the same conditions as Invention Example 4, but because the flux absorbed moisture, the amount of diffusible hydrogen in the weld metal of the preceding seam weld when the seam weld was cooled to 100 ° C after seam welding. Is over 2.0 cc in 100 g of weld metal. Therefore, cold cracking has occurred in the preceding seam weld metal.

  Comparative Example 18 has the same conditions as Invention Example 7, but because the flux absorbed moisture, the amount of diffusible hydrogen in the weld metal of the preceding seam weld when the seam weld was cooled to 100 ° C after seam welding. Is over 2.0 cc in 100 g of weld metal. Therefore, cold cracking has occurred in the preceding seam weld metal.

  Comparative Example 19 has the same conditions as Invention Example 9, but the front seam at the time when the seam weld was cooled to 100 ° C. after seam welding because dirt adhered to the groove surface and the flux absorbed moisture. The amount of diffusible hydrogen in the weld metal of welding is more than 2.0 cc in 100 g of weld metal. Therefore, cold cracking has occurred in the preceding seam weld metal. Furthermore, this cold crack had propagated into the weld metal of the subsequent seam weld.

  Comparative Example 20 has the same conditions as Invention Example 20, but because the flux absorbed moisture, the amount of diffusible hydrogen in the weld metal of the preceding seam weld when the seam weld was cooled to 100 ° C after seam welding. Is over 2.0 cc in 100 g of weld metal. Therefore, cold cracking has occurred in the preceding seam weld metal.

  Comparative Example 21 has the same conditions as Invention Example 15, but because the flux absorbed moisture, the amount of diffusible hydrogen in the weld metal of the preceding seam weld when the seam weld was cooled to 100 ° C after seam welding. Is over 2.0 cc in 100 g of weld metal. Therefore, cold cracking has occurred in the preceding seam weld metal.

  Comparative Example 22 has the same conditions as Invention Example 24, but because the flux absorbed moisture, the amount of diffusible hydrogen in the weld metal of the preceding seam weld when the seam weld was cooled to 100 ° C after seam welding. Is over 2.0 cc in 100 g of weld metal. Therefore, cold cracking has occurred in the preceding seam weld metal.

The figure which shows the result of the numerical analysis by a finite element method. The figure explaining W1 and W2. The figure which shows the relationship between W2 / W1 and the residual stress which generate | occur | produces in the weld metal of seam welding. The schematic diagram of a seam welding part. The figure which shows the relationship between W2 / W1 and the residual stress of a weld line direction in the weld metal whose tensile strength is 1000 MPa. The figure which shows the relationship between W2 / W1 and the residual stress of a weld line direction in the weld metal whose tensile strength is 850 Mpa. The figure which shows the relationship between T1 / AC1 and the residual stress of a weld line direction in the weld metal whose tensile strength is 1000 MPa. The figure which shows the relationship between T1 / AC1 and the residual stress of a weld line direction in the weld metal whose tensile strength is 850 MPa. It shows the ratio relationship of T1 / Ac ₁ and f / W1. The figure which shows the relationship between the tensile strength of a weld metal, and the maximum and minimum tensile stress residual stress of the weld line direction which generate | occur | produces in the preceding seam weld metal. The figure which shows the relationship between the generation frequency of the low value of W2 / W1 and the toughness of a welding heat affected zone. The figure which shows the impact test piece collection position of a seam welding part. The schematic diagram of the shape of a welding part. The schematic diagram which shows the adjustment method of W2 / W1.

Explanation of symbols

B1 Weld metal of the preceding seam weld B2 Weld metal of the subsequent seam weld a Distance from the weld metal surface of the preceding seam weld W1 Height of the weld metal of the preceding seam weld referred to in the present invention W2 Followed in the present invention Height of weld metal of seam weld H1 Maximum heating temperature measurement position of weld metal of preceding seam weld S Area of weld metal h Thickness of weld metal b Width of weld metal d Depth of penetration f Thermal effect of preceding seam weld Width of part

Claims (4)

After forming a steel plate having a tensile strength of 850 MPa or more and 1200 MPa or less into a cylindrical shape, the butt portion of the steel plate is sequentially layered from both inner and outer surfaces of the butt portion of the steel plate using a weld metal having a tensile strength of 850 MPa to 1200 MPa. In a method of manufacturing a UO steel pipe by performing straightening processing such as pipe expansion or contraction after seam welding to
The diffusible hydrogen amount of the weld metal of the preceding seam weld is 2.0 cc or less per 100 g of weld metal, the thickness of the weld metal of the preceding seam weld is W1, and the thickness of the weld metal of the subsequent seam weld is W2. In the weld metal of the preceding seam welding by performing seam welding with W2 / W1 defined as 0.6 ≦ W2 / W1 ≦ 0.8 or 1.2 ≦ W2 / W1 ≦ 2.5 The manufacturing method of the UO steel pipe excellent in the low temperature cracking resistance characterized by reducing the tensile stress which generate | occur | produces. After forming a steel plate having a tensile strength of 850 MPa or more and 1200 MPa or less into a cylindrical shape, the butt portion of the steel plate is sequentially layered from both inner and outer surfaces of the butt portion of the steel plate using a weld metal having a tensile strength of 850 MPa to 1200 MPa. In a method of manufacturing a UO steel pipe by performing straightening processing such as pipe expansion or contraction after seam welding to
The amount of diffusible hydrogen in the weld metal of the preceding seam weld is 2.0 cc or less per 100 g of weld metal, and when the subsequent seam weld is performed, the highest temperature of the weld metal surface of the preceding seam weld is T1, When the Ac ₁ transformation temperature of the weld seam of the preceding seam welding is Ac ₁ , T1 / Ac ₁ satisfies 0.65 ≦ T1 / Ac ₁ ≦ 1.2, and the preceding seam welding is performed. The manufacturing method of the UO steel pipe excellent in the cold cracking resistance characterized by reducing the tensile stress which generate | occur | produces in this weld metal. In a UO steel pipe composed of a base metal part having a tensile strength of 850 MPa to 1200 MPa and a seam weld part having a tensile strength of 850 MPa to 1200 MPa formed by seam welding of one layer each from both inner and outer surfaces,
The amount of diffusible hydrogen in the weld metal formed by the preceding seam welding is 2.0 cc or less per 100 g of the weld metal, and the thickness of the weld metal formed by the preceding seam welding is W1, and by the subsequent seam welding When the thickness of the formed weld metal is W2, the relationship 0.6 ≦ W2 / W1 ≦ 0.8 or 1.2 ≦ W2 / W1 ≦ 2.5 is satisfied. UO steel pipe with excellent cold cracking property. In a UO steel pipe composed of a base metal part having a tensile strength of 850 MPa to 1200 MPa and a seam weld part having a tensile strength of 850 MPa to 1200 MPa formed by seam welding of one layer each from both inner and outer surfaces,
The amount of diffusible hydrogen in the weld metal formed by the preceding seam welding is 2.0 cc or less per 100 g of the weld metal, and the thickness of the weld metal formed by the preceding seam welding is W1, and by the preceding seam welding In the formed weld metal, when the width of the weld heat affected zone formed by the subsequent seam welding is defined as f, the relationship of 0.1 ≦ f / W1 ≦ 1.0 is satisfied. UO steel pipe with excellent cold cracking resistance.

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