JP5463863B2 - UOE steel pipe manufacturing method - Google Patents

Description

  The present invention relates to a method for manufacturing a UOE steel pipe. Specifically, the present invention relates to a UOE steel pipe manufacturing method that can prevent weld cracking in the vicinity of a seam welded portion of a high-strength UOE steel pipe.

  In recent years, UOE steel pipes used for line pipes are subjected to high-pressure transportation for the purpose of reducing transportation costs. For this reason, in this UOE steel pipe, an increase in diameter, a reduction in thickness, and an increase in strength are promoted. Under such circumstances, development of a high-strength UOE steel pipe having a tensile strength of 800 MPa or more, an outer diameter of 500 mm or more, and a wall thickness of 6 mm or more is promoted as a line pipe material.

  In recent years, in the manufacture of UOE steel pipes having such tensile strength, outer diameter, and wall thickness, it is a new problem that transverse cracks (cracks in the circumferential direction of the steel pipe) frequently occur in the seam welds in the manufacturing process. It has become apparent. In a welded UOE steel pipe, it is required that the tensile strength of the weld heat-affected zone and the weld metal be equal to or higher than the tensile strength of the base metal, so that the base metal fractures in the tensile test. However, in a high-strength UOE steel pipe having a tensile strength of 800 MPa or more, for example, in the case of pipe expansion after welding, a transverse crack at the position of the weld heat-affected zone is likely to occur due to the increased strength of the weld metal.

  From the above investigations, UOE steel pipes have transverse cracks because of (a) hydrogen embrittlement caused by diffusible hydrogen in weld metal, (b) increased crack susceptibility, and (c) added tensile stress. It is said that it is a crack. Until now, several inventions for preventing lateral cracking in the manufacturing process of a high-strength UOE steel pipe have been proposed.

  For example, in Patent Document 1, when manufacturing a high-strength UOE steel pipe having a tensile strength of 800 MPa or more, an outer diameter of 406 mm or more, and a wall thickness of 10 mm or more, a butt portion of a steel plate as a raw material is tack welded, and then a welding material is used. An invention relating to a method for preventing transverse cracking is disclosed by performing seam welding after limiting the amount of diffusible hydrogen of a welding flux to 20 ml / 100 g or less and then expanding the tube at a tube expansion rate of 5% or less.

  Further, in Patent Document 2, when a steel plate having a tensile strength of 850 MPa or more is formed into an open pipe and a butt portion is manufactured by submerged arc welding from the inner surface and the outer surface to produce a high strength welded steel pipe, over the entire length in the welding direction, An invention relating to a method for preventing embrittlement cracking of a weld metal by reducing the height in the thickness direction of the weld metal by 0.2 to 10% is disclosed.

Japanese Patent No. 3896031 JP 2007-210023 A

  The present inventor cannot deny the productivity of the UOE steel pipe when the inventions disclosed in Patent Documents 1 and 2 are carried out, so that not only the manufacturing cost of the UOE steel pipe is increased, but also according to these inventions, the tensile strength is increased. It was found that transverse cracks frequently occur during the production of a high-strength UOE steel pipe of 800 MPa or more.

  The present invention has been made in view of such problems of the prior art, and is not accompanied by management of welding materials or press working after welding, and after welding of a UOE steel pipe having a tensile strength of 800 MPa or more. It aims at providing the manufacturing method of the UOE steel pipe which can reduce the amount of diffusible hydrogen in a weld metal, and can prevent generation | occurrence | production of the transverse crack of a welding part reliably by this.

  As a result of intensive studies, the present inventor has found that when manufacturing a UOE steel pipe by performing inner surface welding and outer surface welding on a groove processed portion formed at an edge of an open pipe having a tensile strength of 800 MPa or more. A welded portion of a UOE steel pipe having a tensile strength of 800 MPa or more is obtained by removing the scale in a predetermined region adjacent to the grooved portion in the circumferential direction of the pipe and then performing inner surface welding and outer surface welding of the grooved portion. Knowing that the occurrence of transverse cracks in can be reliably prevented, the present invention has been completed.

The present invention relates to an open pipe peripheral surface on the outer surface and / or inner surface of the open pipe before the inner surface welding and the outer surface welding are performed on the groove processed portion formed at the edge of the open pipe having a tensile strength of 800 MPa or more. From the position of the end portion of the groove processed portion in the circumferential direction of the open pipe, which is a predetermined region continuous to the groove processed portion in the direction, from the end of the steel plate that is the base material of the open pipe, After removing the scale in the region up to a position of 30 mm in the circumferential direction so that the removal rate of the scale defined as the degree of rust removal in ISO 8501 is reduced to Sa2 (67%) or more , inner surface welding and outer surface welding This is a method for manufacturing a UOE steel pipe having an outer diameter of 500 mm or more and a wall thickness of 6 mm or more .

In the present invention, the “predetermined region continuous with the groove processing portion in the circumferential direction of the open pipe” refers to the base material of the open pipe from the position of the end portion of the groove processing portion in the circumferential direction of the open pipe. It means the region from the end of the steel plate to the position that is 30 mm in the circumferential direction of the open pipe, in other words, the region that is 10 mm from the position of the end portion of the groove processing portion in the circumferential direction of the open pipe. To do. Prior to the filing of the present application, such a region has not been descaled.

  Further, in the present invention, “removing the scale” means not only the case where the scale existing in the vicinity is completely removed, but also the scale existing in the vicinity reduces the amount of diffusible hydrogen in the weld metal. The case of reducing to a certain extent is also included. Specifically, it means that the scale removal rate defined as the degree of rust removal in ISO 8501 is reduced to Sa2 (67%) or more.

  Furthermore, as a technique for “removing the scale” in the present invention, for example, (a) physical removal by a grinder or blast is the most general and simple, but it is not limited thereto. For example, (b) removal by pickling treatment using chemicals (sulfuric acid or the like), (c) removal by high-pressure washing at the time of rolling the steel plate, etc. are exemplified.

  According to the present invention, it is possible to reliably and easily suppress transverse cracks that frequently occur in the manufacturing process of a high-strength UOE steel pipe having a tensile strength of 800 MPa or more, without involving management of welding materials and extra pressing. become.

FIG. 1 is a perspective view showing an open pipe in the manufacturing process of a UOE steel pipe. FIG. 2 is a graph showing the relationship between the scale removal rate and the amount of diffused hydrogen. FIG. 3 is a graph showing the relationship between the scale removal rate and the occurrence rate of transverse cracks.

A mode for carrying out the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a perspective view showing an open pipe 1 in a manufacturing process of a UOE steel pipe.
In the present invention, a UOE steel pipe having a base material having a tensile strength of 800 MPa or more, an outer diameter of 500 mm or more and a wall thickness of 6 mm or more is a C press for bending a steel sheet as a material into a C-section, By performing a U press that bends into a U shape and an O press that bends into a cross section O shape, an open pipe 1 shown in FIG. 1 is obtained, and then a groove processing portion 2 formed at the edge of the open pipe 1. A UOE steel pipe is manufactured by performing inner surface welding and outer surface welding.

  As shown in the enlarged view in FIG. 1, in the present invention, the circumferential direction of the open pipe 1 on the outer surface 1 a and / or the inner surface 1 b of the open pipe 1 is performed before the inner surface welding and the outer surface welding are performed on the groove processing portion 2. The scale of the predetermined region 3 continuous to the groove processing portion 2 is removed, and then the inner surface welding and the outer surface welding are performed on the groove processing portion 2.

  In the present invention, the predetermined region 3 that is continuous with the groove processing portion 2 in the circumferential direction of the open pipe 1 refers to the groove processing portion 2 in the circumferential direction of the open pipe 1 as shown in the enlarged view of FIG. It means the region A from the position of the terminal end 4 to the position 6 that is 30 mm in the circumferential direction of the open pipe 1 from the end of the steel plate 5 (indicated by the alternate long and short dash line) that is the base material of the open pipe. In the circumferential direction of the open pipe 1, it means a region that is 10 mm from the position of the end portion 4 of the groove processing portion 2. Prior to the filing of the present application, the scale removal for the region A has not been performed.

  In the present invention, the range of the region A is determined from the end of the steel plate 5 to the position 6 that is 30 mm in the circumferential direction of the open pipe 1 because it is a range that is caught in the welding surplus. In other words, the influence of the scale is only on the portion related to the weld surplus, and if the scale of the weld surplus portion is removed, transverse cracks can be prevented. Therefore, the predetermined region A is a range where the welding surplus is applied, and is determined to be equal to or greater than the range indicated by the following formula that defines the relationship between the wall thickness and the welding surplus width.

W = (0.7 × T + 12) / 2 W: welding weld width on one side, T: wall thickness Although the weld welding width varies depending on the wall thickness of the open pipe 1, for example, when the wall thickness is 16 mm, 11.6 mm or more.

  For example, (a) physically removing with a grinder or blast, (b) removing by a pickling treatment using chemicals (sulfuric acid, etc.), and (c) The removal by high-pressure washing at the time of rolling the steel plate is exemplified, but it is not limited to these, and any means that can remove this kind of scale is equally applicable.

In the present invention, the reason why the inner surface welding and the outer surface welding are performed on the groove processing portion 2 after the scale removal for the region A will be described.
As described above, it is effective to reduce the amount of diffusible hydrogen in the weld metal in order to prevent lateral cracking of the UOE steel pipe. Then, it has been found that it is important to remove the cause of hydrogen contamination in the weld metal in order to reduce the amount of diffusible hydrogen in the weld metal.

  As a result of earnest examination of the cause of hydrogen mixing into the weld metal, the present inventor has introduced hydrogen into the weld metal not only from the welding flux but also from the scale formed in the vicinity of the weld, and in particular, the tensile strength of the base metal It has been found that in a high strength UOE steel pipe having a strength of 800 MPa or more, the occurrence of transverse cracks becomes significant due to the mixing of hydrogen from the scale generated in the vicinity of the weld.

In the present invention, the amount of diffusible hydrogen to the weld metal is reduced by removing the scale formed in the vicinity of the weld before welding, thereby preventing lateral cracking.
Table 1 shows the case where scale removal of area A was performed by a grinder before the inner surface welding and outer surface welding of an open pipe having a tensile strength of 960 MPa (scale removal performed in Table 1), and scale removal was performed before welding. An example of the actual measurement of the amount of diffusible hydrogen in the weld metal is shown for the case where there is no (no scale removal in Table 1).

As shown in Table 1, the amount of diffusible hydrogen in the weld metal can be remarkably reduced to about (1/6) by removing the scale in the region A before performing the inner surface welding and the outer surface welding.
In this invention, after performing the removal process of the scale with respect to the area | region A in this way, the inner surface welding and the outer surface welding of the groove processing part 2 are performed, and a UOE steel pipe is manufactured.

  Note that the scale removal process for the region A may be performed before the groove processing is performed on the steel plate that is the material of the open pipe 1 or after the groove processing is performed. The scale removal process may be performed after the open pipe 1 is used, but it is preferable to perform the scale removal process at the stage of the steel plate that is the material of the open pipe 1 from the viewpoint of workability.

  Furthermore, although the scale removal process for the region A can be performed only on either the outer surface 1a or the inner surface 1b of the open pipe 1, the amount of diffusible hydrogen in the weld metal can be reduced, but is performed on both the outer surface 1a or the inner surface 1b. It goes without saying that it is desirable.

  In this way, according to the present invention, transverse cracks that frequently occur in the manufacturing process of high strength UOE steel pipes with a tensile strength of 800 MPa or more are reliably and easily suppressed without management of welding materials and unnecessary pressing. Will be able to.

The present invention will be specifically described with reference to examples.
The scale existing on the front and back surfaces of the steel plate (tensile strength: 970 MPa, wall thickness: 16 mm) as the material for the UOE steel pipe is equivalent to ISO8501Sa2 using a grinder and NP wheel (trade name: air straight grinder). In accordance with (rust removal rate: 67% or more), almost completely removed.

  Thereafter, the steel plate is sequentially subjected to C press, U press and O press to form an open pipe, and by performing tack welding, inner surface welding and outer surface welding, the tensile strength is 1000 MPa, the outer diameter is 914 mm and the meat is Twenty UOE steel pipes with a thickness of 16 mm were produced.

  And the presence or absence of a transverse crack was confirmed by performing the ultrasonic test and X-ray imaging of the welding part of each of these 20 UOE steel pipes. Table 2 shows the rate of occurrence of lateral cracks {(number of lateral cracks generated / 20) × 100} (%) with and without scale removal before welding. Table 3 and FIGS. 2 and 3 collectively show the relationship between the scale removal rate and the amount of diffused hydrogen or the rate of occurrence of transverse cracks.

  As shown in Table 2, the rate of transverse cracking was reduced to (1/3) or less by removing the scale as specified in the present invention.

DESCRIPTION OF SYMBOLS 1 Open pipe 1a Outer surface 1b Inner surface 2 Groove processing part 3 Predetermined area | region 4 Termination part 5 Steel plate 6 Position A area | region

Claims (1)

Before performing inner surface welding and outer surface welding on the grooved portion formed at the edge of the open pipe having a tensile strength of 800 MPa or more, the outer surface of the open pipe and / or the inner surface, the circumferential direction of the open pipe From the position of the end portion of the groove processed portion in the circumferential direction of the open pipe, which is a predetermined region continuous to the groove processed portion, from the end of the steel plate that is the base material of the open pipe, After removing the scale of the area up to a position of 30 mm in the direction so that the scale removal rate defined as the degree of rust removal in ISO 8501 is reduced to Sa2 (67%) or more, the inner surface welding and the outer surface welding are performed. A method for manufacturing a UOE steel pipe having an outer diameter of 500 mm or more and a wall thickness of 6 mm or more .

Images