JP2002102931A - Manufacturing method of uoe steel pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of an UOE steel pipe capable of improving compression strength in the process of UOE pipe manufacture without changing conditions of pipe stock. SOLUTION: In the manufacturing method of the UOE steel pipe, in which a plate is bent in an U shape by means of an U-shape forming press and is next formed tubular in form by means of an O-shape forming press having a press tool arranged in tiers and then the welded pipe is entirely expanded by an expander after seam-welding a connecting portion of the tubular plate, compressibility in O-shape forming press is set bigger than the pipe-expanding ratio in the expander.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for manufacturing a UOE steel pipe.

[0002]

2. Description of the Related Art UOE steel pipes are known as steel pipes used in deep sea pipelines and the like. UOE steel pipe is generally formed by bending a steel plate (steel plate) into a U-shape by a U-press, and then forming the tube by an O-press equipped with a step press tool.
After the seam welding of the parts to be joined, it is manufactured through a tube expansion process using an expander. FIG. 3 shows a schematic view of the manufacturing process of the UOE steel pipe.

On the other hand, a steel pipe used in an environment where the external pressure is high, such as a deep sea pipeline, is subjected to a high compressive force due to the external pressure, so that the steel pipe may be crushed. For this reason, it is necessary to maintain the required compressive strength in a pipe-formed state. However, as a method of increasing the compressive strength of a UOE steel pipe, a conventional method of increasing the pipe thickness or forming a steel pipe of a high-strength material as a material has been used. Such a method is adopted.

[0004]

However, the above-mentioned method of increasing the thickness of the tube necessarily causes an economic disadvantage.
Further, in the method of using a high-strength steel sheet as a pipe-forming material, strict control of components is required for the steel sheet used as the pipe-forming material, and strict control is also required for manufacturing conditions of the steel sheet. For this reason, the productivity of the steel sheet may be degraded, resulting in an economic problem.

An object of the present invention is to provide a method of manufacturing a UOE steel pipe capable of improving the compressive strength in the process of forming a UOE steel pipe without changing the strength conditions of the steel sheet used as the material for pipe making. I do.

[0006]

According to the present invention, a plate is bent into a U-shape by a U-press, then formed into a tubular shape by an O-press equipped with a stepwise pressing tool, and the joined parts are seam-welded and then extracted. A method of manufacturing a UOE steel pipe which expands with a panda, wherein a compression ratio in an O-press is set to be larger than an expansion ratio in an expander.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, in a UOE pipe forming process as shown in FIG. 3, for example, the compression ratio in the O press is set to be larger than the expansion ratio in the expander. O
The compression ratio in the press is expressed by the formula: (1-D2 / D1) or the value of the above formula, where D1 is the tube outer diameter at the time of bending back (compression start) by the O-press, and D2 is the tube outer diameter at the time of compression completion. Defined as × 100 (%). The expansion rate in the expander is defined as: D3 is the outer diameter of the pipe at the start of expansion by the expander, and D4 is the outer diameter of the pipe at the completion of expansion, and the equation: (D4 / D3-1) or the value of the equation x 100 (% ). Thereby, the compression characteristics of the product steel pipe base material can be improved without changing the chemical composition and structure of the raw steel sheet.

[0008] In order to make the present invention, the inventor conducted a UOE pipe making experiment in a laboratory with various processing histories, and based on the results, the final stress state when the compression ratio and the expansion ratio were changed. The prediction calculation model of the compressive strength in was made. FIGS. 1 and 2 show a first example and a second example of the calculation result by this model.
Shown in FIG. 1 and FIG. 2 are stress-strain history curves of a tube forming process and a process of applying a compressive force after the tube forming, with the inner side of the U-shaped bottom in the U press as a target portion. In the first example, the compression ratio in the O-press is 0.9%, and the expansion ratio in the expander is 0.7%.
In the second example, the compression ratio in the O-press was 0.9%, and the expansion ratio in the expander was 1.1%. Other conditions (material yield strength, etc.) were the same in the first example and the second example.

In FIGS. 1 and 2, points A and B are U-press, points B and C are bent back by O-press, points CD are compression by O-press, and points D to E are expander by expander. Expansion, point E
ＦF corresponds to each step of the compression test, and the black circles correspond to 0.5% compression strength. As a result, the 0.5% compression proof stress was 510 MPa (FIG. 2) in the second example, whereas it was 551 MPa (FIG. 1), which was higher than that in the first example.

[0010] From these results, by setting the compression ratio in the O-press larger than the expansion ratio in the expander,
Since the compressive strength was expected to increase, a test tube was produced on an actual machine, and the expected result was obtained.

[0011]

EXAMPLE In the UOE pipe forming process shown in FIG. 3, using a steel plate having the same chemical composition, the same structure and the same strength level as the material, the compression ratio in the O-press was set to 0.6%, and the expansion ratio in the expander was set to 0.95. % (Comparative example) and 0.50% (example), and six UOE steel pipes (thickness 31.8%)
mm x 610 mm in outer diameter and compressive strength (0.5%) for each product
The compression strength was examined, and the results shown in Table 1 were obtained. Compressive strength was obtained by taking a round bar test piece from a UOE steel pipe product so that the circumferential direction of the steel pipe almost coincides with the axial direction of the test piece as shown in FIG. 4 and performing a compression test using this. I asked. Table 1
Thus, in the examples of the present invention, significantly higher compressive strength was obtained than in the comparative examples.

[0012]

[Table 1]

[0013]

According to the present invention, it is possible to improve the compression characteristics of a UOE steel pipe without changing the conditions such as the chemical composition and structure of the base steel sheet, thereby reducing the production cost and responding to strict compression characteristics requirements. It has an excellent effect that it becomes possible.

[Brief description of the drawings]

FIG. 1 is a graph showing a first example of a calculation result by a compression strength prediction model.

FIG. 2 is a graph showing a second example of a calculation result by a compression strength prediction model.

FIG. 3 is a schematic view showing an example of a UOE pipe forming process.

FIG. 4 is a schematic view showing a sampling position of a round bar test piece.

Claims (1)

[Claims] 1. Production of a UOE steel pipe in which a plate is bent into a U-shape by a U-press, then formed into a tube by an O-press equipped with a step-wise press tool, and a welded portion is seam-welded and expanded by an expander. A method for producing a UOE steel pipe, wherein the compression ratio in the O-press is set to be larger than the expansion ratio in the expander.