JP5471380B2 - High-efficiency manufacturing method for large welded steel pipes for offshore wind power towers - Google Patents

Description

The present invention relates to high-efficiency production method of a large welded steel pipes for use in the construction of offshore wind power tower.

In recent years, attempts have been actively made to use natural energy in order to cope with the reduction of CO ₂ gas that contributes to global warming and the future depletion of fossil fuels such as oil. Wind power generation is one of them, and it is spreading worldwide. The best areas for wind power generation are areas where constant strong winds can be expected. Therefore, offshore wind power generation has been realized (see Patent Documents 1 to 6), and large-scale offshore wind power generation is planned on a global scale.

  When constructing a wind power tower on the ocean, it is necessary to drive a foundation structure into the seabed ground in order to stabilize the wind power tower. In addition, in order to stably maintain the turbine blades of the wind power generator at a sufficiently high position from the sea level, the foundation structure and the steel pipe columns installed on the foundation structure must have a sufficient height. I need. Eventually, the height of the wind power tower reaches over 80m.

  Thus, the offshore wind power generation tower is a huge steel structure including the foundation structure, but when constructing, a large thick steel plate or a steel pipe can be simply and at the construction site or the coast near the construction site, It is required to weld with high efficiency.

  In general, high energy density beam welding, such as electron beam welding and laser beam welding, is suitable for the construction of giant steel structures such as offshore wind power generation towers because welding materials can be welded easily and efficiently. Although it is a welding method, since it is necessary to weld in a high vacuum chamber, there exists a limit in the magnitude | size of the steel plate or steel pipe which can be welded.

  Based on this, in recent years, a welding method (RPEBW: Reduced Pressure Electron Beam Welding) that can efficiently weld an extremely thick steel plate having a thickness of about 100 mm on-site has been proposed (Patent Document 7, reference).

  If the RPEBW method is used, when a large steel structure such as a wind power tower is constructed, it is expected that a thick steel plate can be efficiently welded by locally maintaining a welding point in a vacuum.

  However, the RPEBW method has a problem that the toughness of the weld metal part formed by solidification after melting is inferior because welding is performed in an atmosphere having a low degree of vacuum as compared with welding in a high vacuum chamber.

The offshore wind power tower is constantly exposed to strong winds and vibrates at a repetition rate in the gigacycle (10 ⁹ to 10 ¹⁰ ) region. Stress is concentrated. For this reason, the welded portion is required to have fatigue resistance characteristics that can withstand vibrations in a gigacycle region whose order is different from the normal fatigue cycle (10 ⁶ to 10 ⁷ ).

JP 2008-111406 A JP 2007-092406 A JP 2007-322400 A JP 2006-037397 A JP 2005-194792 A JP 2005-180239 A International Publication No. 99/16101 Pamphlet

  Large steel pipe columns used for offshore wind turbine monopile foundations (underwater) or power generation towers (ocean) are usually produced by first producing unit steel pipes (for example, 5 m in diameter x 3 m in length). Accordingly, the unit steel pipe is manufactured by joining in the circumferential direction. For example, if the length of the steel pipe column is 60 m and the length of the unit steel pipe is 3 m, 20 unit steel pipes are welded in the circumferential direction (see FIG. 1).

  And conventionally, each unit steel pipe is manufactured by arc-welding two end portions in the width direction of two steel materials formed into a semi-cylindrical shape with the rolling direction (longitudinal direction) of the steel material as a circumferential direction. (See FIG. 2). 1 and 2 will be described later.

  Thus, in order to manufacture one large steel pipe column used for offshore wind power generation, many welding times are required, and each welding becomes multi-layer welding, so that the larger the steel pipe column is, the more it is completed. Welding time is increased.

  Further, before the unit steel pipes are welded in the circumferential direction, it is necessary to correct the unit steel pipes to ensure the required roundness in order to ensure the accuracy of the groove. A large press machine is required to straighten the unit steel pipe to ensure the required roundness. Usually, the roundness is corrected for each unit steel pipe with a large press, so the correction of the unit steel pipe is a bottleneck process in the manufacture of the steel pipe column.

  Therefore, in order to improve the productivity of large steel pipe columns for offshore wind power generation, the welding length should be as short as possible, especially circumferential welding that requires the required roundness and requires high-precision welding. How to reduce this is a very important issue. Further, as described above, the welded portion of the offshore wind power generation tower is required to have sufficient fracture toughness to ensure safety.

  Accordingly, the present invention processes a steel plate having an extremely thick thickness (for example, a thickness of more than 50 mm) and welds to produce a large steel pipe column, and (i) shortens the weld length and (ii) circumferential welding. It is an object of the present invention to significantly improve the productivity of a large-sized steel pipe column and to provide a large-sized steel pipe column provided with a weld having sufficient fracture toughness.

The present inventors diligently studied a processing method and a welding method that achieve the above object. As a result, (x) an arc-shaped long steel material that is long in the rolling direction of the steel sheet and has an arc shape in the width direction perpendicular to the rolling direction is prepared, and (y) a plurality of arc-shaped long steel materials are prepared in the rolling direction. When the butted surfaces are welded by high energy density beam welding, (z-1) a welded portion having fatigue characteristics that can withstand vibrations in the gigacycle region and sufficient fracture toughness is obtained. It was found that (z-2) a large welded steel pipe with excellent fatigue resistance can be provided.

  This invention was made | formed based on the said knowledge, and the summary is as follows.

( 1 ) Three or more arc-shaped long steel materials having a thickness of more than 50 mm, which are long in the rolling direction of the steel sheet and arc-shaped in the width direction perpendicular to the rolling direction , are end faces parallel to the rolling direction. And the butted surfaces are welded by high energy density beam welding to form unit steel pipes, and the obtained unit steel pipes are welded in the circumferential direction by high energy density beam welding . High-efficiency manufacturing method for large welded steel pipes.

( 2 ) The high-efficiency manufacturing method for large welded steel pipes for offshore wind power generation towers according to ( 1) above, wherein the arc-shaped long steel material has a width of 2 m or more.

( 3 ) The high-efficiency manufacturing method for large-scale welded steel pipes for offshore wind power towers according to ( 1 ) or ( 2), wherein the arc-shaped long steel material has a tensile strength of 355 MPa or more.

  According to the present invention, a large-sized welded steel pipe for offshore wind power towers having fatigue characteristics that can withstand vibrations in the gigacycle region and having sufficient fracture toughness is manufactured and provided with high production efficiency. can do.

It is a figure which shows an offshore wind power generation tower. It is a figure which shows the aspect of the conventional large sized steel pipe. It is a figure which shows the aspect of the large sized welded steel pipe of this invention. It is a figure which contrasts the manufacturing process of the conventional large-sized welded steel pipe, and the manufacturing process of the large-sized welded steel pipe of this invention. (A) shows the manufacturing process of the large sized steel pipe by the conventional arc welding, (b) shows the manufacturing process of the large sized steel pipe which applied the high energy density beam welding of this invention. The weight of the steel material is 18 tons and the length of the steel pipe is 60 m. (I) Steel pipe diameter 7 m, plate thickness 120 mm, (ii) Steel pipe diameter 5 m, plate thickness 100 mm, and (iii) Steel pipe diameter 3.5 m, plate thickness It is a figure which shows the relationship of the circumferential direction division | segmentation number (piece) of a unit steel pipe, and the welding length (m) in the case of setting it as 50 mm.

In the present invention, a plurality of arc-shaped long steel materials that are long in the rolling direction of the steel sheet and arc-shaped in the width direction perpendicular to the rolling direction are butted at the end faces parallel to the rolling direction. It is characterized by welding by energy density beam welding. Hereinafter, the present invention will be described with reference to the drawings.

  FIG. 1 shows an offshore wind power generation tower. In the offshore wind power generation tower, a monopile foundation structure 1 and a power generation tower 2 and a nacelle 3 including turbine blades 4 are mounted thereon. The monopile foundation structure 1 and the power generation tower 2 are both large steel pipe columns, which are large steel pipe columns that reach a pipe diameter of 3.5 to 7 m, a thickness of 50 to 120 mm, and a length of 30 to 80 m. Usually, the monopile foundation structure 1 installed under the sea surface has a larger pipe diameter, thickness, and length than the power generation tower 2 installed on the sea.

  FIG. 2 shows an aspect of a large welded steel pipe (conventional steel pipe) having a length l (m) and a diameter k (m), which is a constituent unit of a steel pipe column. In general, the length 1 is 2 to 4 m and the diameter k is 3.5 to 7 m.

  As shown in FIG. 2, the large welded steel pipe 5 includes a unit steel pipe 5c formed by joining semi-cylindrical steel materials 5a and 5b curved in the rolling direction of the steel sheet (see arrows in the figure) at the end face arc welded portion 5x. The three unit steel pipes 5c arranged so that the end face arc welded portions 5x are not on the same line are joined by the circumferential arc welded portion 5y.

  In FIG. 4, the manufacturing process of the conventional large welded steel pipe and the manufacturing process of the large welded steel pipe of this invention are shown in contrast. FIG. 4A shows a manufacturing process of a large welded steel pipe by conventional arc welding, and FIG. 4B shows a manufacturing process of a large welded steel pipe to which the high energy density beam welding of the present invention is applied.

  As shown in FIG. 4 (a), conventionally, the steel sheet is cut so that the rolling direction of the steel sheet is the circumferential direction of the steel pipe (see FIG. 2), and formed into a semi-cylindrical steel material. Next, the end surfaces in the tube axis direction of the two semicylindrical steel materials are brought into contact with each other and tack welded, and the inner surface side is arc welded. Then, after machining the groove by machining or the like, multi-layer arc welding on the outer surface side is performed to manufacture a unit steel pipe.

  For this arc welding, multilayer prime welding by a submerged arc welding method is usually used. The number of passes increases in proportion to the plate thickness. For example, the number of passes when the plate thickness is 50 mm is around 20 passes. MAG welding may be used for welding on the inner surface side and tack welding.

  Normally, the shape of the unit steel pipe is distorted, and in the pre-process of circumferential welding to connect the unit steel pipes, the unit steel pipe is straightened to increase the roundness, and the groove accuracy when matching is not increased must not. In order to correct the roundness, a large press is required, and usually the roundness is corrected for each unit steel pipe, so this straightening process becomes a bottleneck in the manufacturing process of the large steel pipe column.

  After straightening the unit steel pipe, the unit steel pipes are butted together at the circumference and arc welding of the inner and outer surfaces is performed. Compared to welding of unit steel pipes (seam welding), circumferential welding requires much time for preparation and requires much higher welding accuracy, so in order to improve productivity, as much as possible It is better to reduce the number or time of circumferential welding.

  After welding, it is usually left for 48 hours to check for cold cracking, and the quality of the arc welded part is inspected (for example, ultrasonic inspection) to confirm that there are no defects before shipment.

  As described above, the conventional method for producing a large welded steel pipe requires many steps until the product is shipped, and the productivity is low.

  In the welding process, the number of weldings is large, and the entire length of the weld line is extremely long. For example, when the length of the steel pipe column is 60 m, the plate thickness is 75 mm, the steel pipe diameter is k = 4.5 m, and the length of the unit steel pipe is l = 4.1 m, the weld line reaches 312 m.

  Offshore wind turbines are expected to increase in size in the future, and the length, diameter and thickness of steel pipe columns will increase. When the unit weight of the steel material is constant, (a) if the plate thickness is 100 mm and the steel pipe diameter k = 5 m, the weld line is 444 m, and (b) if the plate thickness is 120 mm and the steel pipe diameter k = 7 m, The weld line can be as long as 896m.

  In normal arc welding, the amount of welding per one pass of welding is determined, and as the plate thickness increases, the number of passes increases accordingly, so the time required for the actual welding process is proportional to the plate thickness, To increase.

  In addition, when the steel material is procured from the market, there is a restriction on the unit weight and the width. Therefore, when the steel pipe diameter and the plate thickness are increased, the plate width, that is, the length of the unit steel pipe is shortened. As a result, the number of roundness corrections required before performing circumferential welding between unit steel pipes increases.

  Here, the aspect of the large sized welded steel pipe 6 of this invention is shown in FIG. The large welded steel pipe 6 has a thickness of 100 mm, a steel pipe diameter k = 5 m, and a unit steel pipe length l = 5.5 m. As shown in FIG. 3, the large welded steel pipe 6 has four long arcs that are long in the rolling direction of the steel sheet (see arrows in the figure) and arc in the width direction perpendicular to the rolling direction. The steel material 6a is abutted at the end face in the longitudinal direction, and the abutting surface is joined by the high energy density beam weld 6z.

  FIG. 4B shows a manufacturing process of the large welded steel pipe of the present invention. As shown in FIG. 4B, the steel sheet is cut so that the longitudinal direction of the steel sheet coincides with the rolling direction (see FIG. 3), and is curved along the direction (width direction) perpendicular to the longitudinal direction. Form an arc-shaped long steel material.

  Next, three or more arc-shaped long steel materials are butted at the end faces in the longitudinal direction, and the butted surfaces are welded in one pass through the plate thickness by high energy density beam welding to produce a unit steel pipe. As the high energy density beam welding, electron beam welding or laser beam welding is used.

  In the present invention, for example, if (a) the plate thickness is 100 mm, the steel pipe diameter is k = 5 m, and the number of long steel materials is 3, the weld line is 390 m (444 m for arc welding), and (b) the plate thickness is 120 mm. When the steel pipe diameter k = 7 m and the number of long steel materials is 5, the weld line is about 597 m (896 m for arc welding), and the weld line can be significantly shortened compared to arc welding.

  Table 1 shows a comparison of welding conditions and indices when a large welded steel pipe is manufactured by submerged arc welding (conventional) and when manufactured by local exhaust vacuum electron beam welding (invention). From Table 1, it can be seen that the manufacturing method of the present invention is remarkably superior in welding efficiency.

  Since the high energy density beam welding of the present invention can perform one-pass through welding regardless of the plate thickness, when compared with the total weld line length (number of passes × weld line), as the plate thickness increases, The effect of the present invention will be enhanced.

  5, a steel material unit weight is 18 tons and a steel pipe length is 60 m, (i) a steel pipe diameter of 7 m, a plate thickness of 120 mm, (ii) a steel pipe diameter of 5 m, a plate thickness of 100 mm, and (iii) a steel pipe diameter. The relationship between the number of divisions (pieces) in the circumferential direction of the unit steel pipe and the weld length (m) when the thickness is 5 m and the plate thickness is 50 mm is shown. The number of divisions 1 and the number of divisions 2 are when manufactured by a conventional manufacturing method.

  From FIG. 5, it can be seen that according to the manufacturing method of the present invention, the effect of shortening the weld length increases as the steel pipe diameter and the plate thickness increase.

  The steel material for producing the large welded steel pipe of the present invention is not limited to a steel material having a specific component composition.

  In the manufacturing method of the present invention, when the unit weight of the steel material is constant, the number of long steel materials can be increased, and the length of the unit steel pipe can be increased. Therefore, roundness correction is necessary and the degree of difficulty is high. The number of circumferential weldings can be reduced. In the case of arc welding, if the number of long steel materials is increased, the roundness of the unit steel pipe is reduced and the roundness correction time per unit steel pipe is greatly increased. Increasing the value does not make much sense.

  In the manufacturing method of the present invention, since high energy density beam welding is used, a waiting time for confirming low temperature cracking before quality inspection of the welded portion is unnecessary after manufacturing, and inspection and shipping can be performed as they are. it can. After all, in the manufacturing method of the present invention, as shown in FIG. 4, since the “* step” in the conventional manufacturing method shown in FIG. Compared with the manufacturing method, the productivity is extremely good.

And the manufacturing method of the large-sized welded steel pipe of this invention is long in the rolling direction of a steel plate, and makes 3 or more arc-shaped long steel materials which make circular arc shape in the width direction perpendicular | vertical to a rolling direction, and is parallel to a rolling direction . a butt at the end face, a projecting mating surface where, is characterized in that the welding with high energy density beam welding, on the basis of the feature, has a good fracture toughness value, large welding for offshore wind tower The steel pipe can be manufactured and provided with high production efficiency.

  Next, examples of the present invention will be described. The conditions in the examples are one example of conditions used for confirming the feasibility and effects of the present invention, and the present invention is based on this one example of conditions. It is not limited. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

(Example)
Table 2 uses steel materials (B1 to B3) showing the component composition and mechanical properties, welding is performed under the electron beam welding conditions (W1 to W4) shown in Table 3 or arc welding conditions shown in Table 4, and large welding A steel pipe was manufactured. Table 5 shows the specifications of the manufactured large welded steel pipe.

  Fracture toughness of large welded steel pipes was evaluated by a three-point bending CTOD test at a test temperature of 0 ° C by collecting CTOD specimens from welded joints, but equal to or higher than that of conventional steel pipes (see circles in the table). Met.

  As described above, according to the present invention, a large welded steel pipe used for construction of an offshore wind power generation tower having a fatigue characteristic that can withstand vibrations in the gigacycle region and having a sufficient fracture toughness, It can be manufactured and provided with high production efficiency. Therefore, the present invention has high applicability in the large structure construction industry.

DESCRIPTION OF SYMBOLS 1 Monopile foundation structure 2 Power generation tower 2a Steel pipe 3 Nacelle 4 Turbine blade 5 Large welded steel pipe (conventional steel pipe)
5a, 5b Semi-cylindrical steel 5c Unit steel pipe 5x End face arc welded part 5y Circumferential arc welded part 6 Large welded steel pipe (invented steel pipe)
6a Arc-shaped long steel 6z High energy density beam weld

Claims (3)

Three or more arc-shaped long steel materials having a thickness of more than 50 mm, which are long in the rolling direction of the steel sheet and arc-shaped in the width direction perpendicular to the rolling direction , are butted at end faces parallel to the rolling direction, A large-sized welded steel pipe for an offshore wind power tower characterized in that the abutting surfaces are welded by high energy density beam welding to form unit steel pipes, and the obtained unit steel pipes are welded in the circumferential direction by high energy density beam welding. High-efficiency manufacturing method. The width of the arc-shaped long steel material is 2 m or more, and the high-efficiency manufacturing method for large-sized welded steel pipes for offshore wind power towers according to claim 1 . The high-efficiency manufacturing method for large-scale welded steel pipes for offshore wind power generation towers according to claim 1 or 2 , wherein the arc-shaped long steel material has a tensile strength of 355 MPa or more.

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