JP2650601B2 - Manufacturing method of thick wall large diameter steel pipe by welding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for welding a large-diameter, large-diameter steel pipe, and more particularly to a method for welding a large-diameter, large-diameter steel pipe which does not show coarsening of the structure and deterioration of toughness due to large heat input.

[0002]

2. Description of the Related Art Large-diameter welded steel pipes, which have been widely used in pipelines and offshore structures, have been used in more severe environments due to the limited energy development area. Pipe specifications are changing to thicker, higher strength, and lower temperature toughness, but the problem here is the need to increase the thickness → necessity of higher efficiency → heat affected zone due to large heat input in welding (HAZ) is a coarsening of the structure and deterioration of toughness.
In particular, the low-temperature toughness is greatly deteriorated, and the specifications often cannot be satisfied.

[0003] As described above, the coarsening of the HAZ structure and the formation of island-like martensite, ferrite side plates, and upper bainite due to large heat input of welding have a bad effect on low-temperature toughness. Thus, a method of making the structure into a fine ferrite structure has been attempted. And
Conventionally, studies have been made mainly from the viewpoint of base metal performance.

[0004] For example, for the above-mentioned steel pipes having the specifications of thick wall (wall thickness ≥ 30 mm) and low temperature toughness (transition temperature ≤ -30 ° C, vE- ₃₀ ≥ 40 J), the following properties are required in order to obtain their performance. Such a method is adopted.

[0005] I) First, the heat input per pass is limited to about 30 KJ / cm, and a bond type flux is used as the flux for multi-pass welding, while the X-type opening for conventional multi-pass welding is used. After pre-processing, roll bender or C, U,
It is made into a base tube by performing O-forming and then manufactured through a series of steps of tack welding → inner surface welding → outer surface gouging → outer surface multi-layer welding, followed by final expansion and finishing.

II) Steel plate with a thickness of 38 mm (APIGr for offshore structures)
× 70, low temperature toughness -40 ° C impact value, vE _-40 ≧ 70 J) From the UO molding using the molten flux, the inner surface layer → outer surface first layer / 2 layer multi-layer welding, then I) After expanding the tube in the same way as in the case of above, finish by performing QT processing and sizing. (Literature: High Strength Pipe for Tension Leg Plat
form'92 TUBE INTERNATIONAL) III) Roll-bendering a 44mm thick steel plate (for offshore structures), then using a molten flux to perform multi-layer welding of one inner layer to the first outer layer and two outer layers. . (Reference: Development of high-efficiency welding technology for thick-walled steel pipes, '89 Welding Metallurgy Research Committee)

[0007]

However, in the above-mentioned prior art, for example, in the method I), the number of steps is large, the efficiency is low, the production cost is increased, and Inability to manufacture pipes and offshore structures.

[0008] (1) Large man-hours for groove processing (UU method x lower cutting efficiency compared to groove) (2) Large man-hours for outer gouging after inner surface welding (3) Multi-layer outer surface welding: bond type flux Using 2
In order to carry out multi-layer welding at a low electrode speed, compared to high-speed welding of three or more electrodes using ordinary molten flux,
Efficiency is significantly reduced. Also, since the number of passes is large, the incidence of welding defects increases, and repair work is required.

[0009] It is required to increase the production lot and establish a highly efficient production method while ensuring product performance. The following disadvantages are observed even in the above-mentioned method II), and are not always satisfactory.

[0010] That is, although the man-hour and the efficiency of the method I) are improved, the heat input per pass becomes 60 to 70 KJ / cm or more in the three-pass welding of a 38 mm thick tube. QT in process
It is necessary to improve the HAZ organization by processing. In addition, QT processing
Since a sizing step is added, an increase in manufacturing cost due to an increase in the number of steps is inevitable.

Further, in the above-mentioned method III), an extremely thick region
(Thickness ≥40 mm), but heat input per pass is 100 KJ / cm, and high strength (APIGr ≧ ×
65), the HAZ structure deteriorates and the toughness (vTs-3
(0 ° C or less) cannot be secured. In addition, this method is a roll bender method, and the efficiency is inevitably reduced.

It is a general object of the present invention to provide a more efficient welding of a thick-walled, large-diameter steel pipe which can exhibit a seemingly contradictory effect that the welding efficiency is further improved even when the welding heat input is reduced. Is to provide the law.

[0013] A more specific object of the present invention, in the future an increase of s stringent specifications UO forming large diameter steel pipe products, lines required for low-temperature toughness was excellent as vE _-30 ≧ 40 J at 30mm or more thick It is an object of the present invention to provide a method for manufacturing a high-performance large-diameter steel pipe which can sufficiently satisfy the specifications for pipes and offshore structures.

[0014]

Means for Solving the Problems The present inventors have studied the possibility of reducing heat input during seam welding after UO forming, that is, the possibility of increasing the efficiency at a heat input of 1 pass ≦ 60 KJ / cm. . In other words, the inevitable increase in welding heat input due to the increase in thickness, and the various disadvantages caused by it, are to be solved at once by a concept opposite to the increase in welding heat input, which was conventionally considered inevitable. It is.

FIG. 4 is a graph showing the relationship between the wall thickness and the required heat input when welding is performed in one pass on the inner surface and one pass on the outer surface.
It has conventionally been thought that it is necessary to increase the heat input as the wall thickness increases.

According to the study results of the present inventors, FIG.
Or, as shown in (b), when there is a groove gap of 3 mm or more near the weld bead, or when the angle between the weld bead and the remaining groove is 90 degrees or less, a glassy shape is formed near the weld bead. If the slag solidified firmly remains and the workability deteriorates remarkably, and if the second layer welding is carried out with the remaining slag adhered, this part cannot be completely melted and the slag is contained in the weld metal. It was found that the occurrence of welding defects was unavoidable, and based on these findings, in order to eliminate the remaining slag, the shoulders of the groove were completely or almost melted, and the depth of the groove remained By controlling the remaining angle within 3 mm and the remaining angle to 90 degrees or more, even if the welding heat input is 50-60 KJ / cm, the welding efficiency does not decrease at all and the heat input is low. HA
It was found that no coarsening of the Z structure and no deterioration in toughness were observed.
Further, they have found that it is sufficient to specify the number of passes on the inner and outer surfaces to achieve this, and have completed the present invention.

Here, the present invention relates to a UO-molded thick large-diameter steel tube having a wall thickness of 30 mm or more, using a molten flux, a welding heat input of 50 to 60 KJ / cm per pass, and Thickness 30 ~
For a 35mm large diameter steel pipe, use one pass for the inner surface and two passes for the outer surface.
A large-diameter steel pipe having a diameter of more than 35 mm is welded by a multi-electrode submerged arc welding method in which the inner surface has two passes and the outer surface has two passes, preferably in such a manner that the groove shape on the outer surface is free of attached slag. This is a manufacturing method by welding steel pipes.

More specifically, in order to prevent the adhered slag, more specifically, the shoulder portions of the groove are completely or almost melted, and the remaining depth of the groove is controlled within 3 mm and the remaining angle is controlled to 90 degrees or more. May be performed. Incidentally, conventionally, one-pass welding was performed on each of the inner and outer surfaces.

In a preferred embodiment of the present invention, the surface shape of the first layer bead is further controlled in order to facilitate slag peeling in the inner and outer first layer welding. In particular, in the second layer on the inner surface, the tip of the weld bead copying roll may be defined to have an elliptical cross section to prevent displacement during seam copying. Even in such a case, in order to obtain HAZ toughness for both the inner and outer layers, it is necessary to design the welding material for each layer in consideration of dilution from the base material and welding material.

Further, according to a preferred embodiment of the present invention,
The groove shape is a specific X shape and has two steps on the inner surface side of the steel pipe, and the groove depth on the outer surface side of the steel pipe is 15 to 18 regardless of the wall thickness.
mm, the root face on the steel pipe inner surface side and the thickness center side is 4 to 9 mm, the groove angle on the steel pipe inner surface side and the wall thickness surface side is 30 ± 5 °, and the steel pipe outer surface side Groove angle is 25 ± 5 when the wall thickness is 30 to 35 mm
°, if the wall thickness is more than 35mm, 30 ± 5 °, the groove angle on the inner side of the steel pipe and the center side of the wall thickness is 30-35mm
5 ± 3 ° in case of, 7 ± in case of thickness over 35mm
This is a method for manufacturing a thick-walled large-diameter steel pipe by welding at 3 °.

[0021]

Next, the operation of the present invention will be described in more detail with reference to the accompanying drawings. The method for manufacturing a welded steel pipe according to the present invention comprises the steps of U-press → O-press → temporary attachment → inside welding → outside welding → expansion as in the prior art. In this case, the inner and outer surfaces are welded under predetermined conditions. Other steps may be performed according to a conventional method, and there is no particular limitation in the present invention, and the description thereof is omitted in this specification.

FIG. 1 shows the transition temperature (vTs) of a welded steel pipe and the impact energy value at -30 ° C. (vE _-30 ) when welding was performed while changing the heat input under the welding conditions of Examples described later. It is a graph. As the heat input decreases, the transition temperature decreases and the impact energy increases.

The UO-formed steel tube is subjected to submerged arc welding of one pass for each of the inner and outer surfaces, thereby achieving high strength.
(APIGr. ≧ × 60) and good low temperature toughness (vTs is -30 ° C or less, vE
_-30 ≧ 40J) When trying to manufacture a thick-walled large-diameter welded steel pipe with specifications, if the wall thickness ≧ 30 mm, the welding heat input per pass is 60
It must be higher than KJ / cm, and HAZ toughness cannot be secured, and heat treatment and other additional treatments are required.

However, according to the present invention, the thickness: 30
In the case of ~ 35mm, 1 inner pass → 2 outer passes (heat input / pass:
50-60 KJ / cm), wall thickness: 35-42mm, inner surface 2 passes →
The low heat input submerged arc welding method with two external passes (heat input / pass: 50-60 KJ / cm) eliminates the need for heat treatment and other additional treatments, thus ensuring low-temperature toughness without deterioration in efficiency.

Further, according to the present invention, the reduction in workability due to the low heat input welding is further effectively achieved by using a molten flux and by making the groove shape of the outer surface free of attached slag. Can be suppressed.

On the other hand, in order to increase the efficiency and ensure the quality of the inner surface two-pass welding, the shape of the tip of the copying roll of the welding machine that contacts the bead surface or the groove during the inner surface welding is made elliptical.

The molten flux used in the present invention is obtained by blending raw ore into a predetermined composition, melting and cooling at a high temperature of, for example, 1400 ° C. or more in an electric furnace or the like, and then pulverizing to a required particle size.
This is a sized glassy flux. The use of such a molten flux in the present invention has little concern for moisture absorption, enables high-speed welding, provides excellent slag removability, and provides an excellent bead appearance. This is because the performance of the weld metal can be improved by mixing the acid agent and adjusting the alloy component from the welding wire.

FIG. 2 schematically shows the surface shape of the first layer bead. In FIG. 2 (a), the groove remaining at the end of one pass on the outer surface is shown.
Fig. 2 (b) shows a similar groove residue in another case, and Fig. 2 (c) shows the second pass welding without completely removing the attached slag. The case where the remaining slag 14 remains when the above is performed will be described. Fig. 2 (d)
Indicates a bead shape when the slag removability is good.

As described above, in consideration of the slag removability, it is necessary to avoid the residual slag adhered to the first layer bead. For this purpose, the groove 10 is left, and the groove is formed so as not to leave the adhered slag. It defines the shape.

In the present invention, the submerged welding is performed using multiple electrodes, but in this regard, it may be performed according to a conventional method, and there is no particular limitation in the present invention.
Next, the operation of the present invention will be described more specifically with reference to examples.

[0031]

EXAMPLE In this example, a steel tube was formed by a conventional UO forming method using a plate having a steel composition shown in Table 1 and a plate thickness of 30 mm or more. Submerged arc welding was performed on the thick large-diameter steel tube using a welding wire having the composition shown in Table 2. The molten flux used in this example had the following composition and had a particle size within the STM 48/145 mesh region.

SiO ₂ : 5 to 25%, Al ₂ O ₃ : 2 to 20%,
_{MnO: 0.5~15%, TiO 2:} 2~10%, CaO: 5~25
%, BaO: 1-5%, MgO: 3-15%, CaF ₂
: 25 to 60%, B ₂ O ₃ : 2% or less.

The welding conditions are summarized in Tables 3 and 5. The groove state is shown in FIG. For Run Nos. 1-3,
One pass of the inner surface and two passes of the outer surface were performed with a steel tube wall thickness t = 32 mm to produce a thick-walled large-diameter steel tube.

In the case of Run Nos. 4 to 7, the steel sheet thickness t = 38 m
m, two passes on the inner surface and two passes on the outer surface were performed to produce a thick-walled large-diameter steel pipe. The characteristics of the steel pipe manufactured as described above were evaluated. The results are summarized in Tables 4 and 6, respectively.

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

[Table 3]

[0038]

[Table 4]

[0039]

[Table 5]

[0040]

[Table 6]

[0041]

As described above, according to the present invention, while the welding heat input is limited in order to secure the HAZ toughness, the submerged arc using the molten flux is used in order to realize highly efficient welding. Multi-pass welding is performed by welding, and in order to make the welding work more efficient at that time and to obtain a high quality weld without UST defects, the groove shape and bead appearance are regulated so that no slag remains.

Therefore, if the inner and outer surfaces of a steel pipe having a wall thickness of about 30 to 42 mm are welded in a single pass as in the prior art, a heat input of 60 to 100 KJ / cm is required as shown in FIG. Although the toughness deteriorates as shown in FIG. 1, according to the method of the present invention,
Since the HAZ toughness does not deteriorate and the efficiency of the welding operation and the quality of the welded portion can be improved, the practical significance of the present invention is great.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a transition temperature and an impact energy value in an example.

FIG. 2 is a diagram schematically showing a surface shape of an initial layer bead.

FIG. 3 is a diagram showing a groove shape.

FIG. 4 is a graph showing the relationship between wall thickness and required heat input.

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Ryoyo Sato, Kashima-cho, Kashima-gun, Ibaraki 3rd, Kashima Works Sumitomo Metal Industries Co., Ltd. (56) References JP-A-63-36973 (JP, A) JP-A-5-50235 (JP, A) JP-A-63-295070 (JP, A) JP-A-58-32583 (JP, A) JP-A-6-63750 (JP, A) JP, U)

Claims (3)

(57) [Claims] 1. A UO-molded thick large-diameter steel tube having a wall thickness of 30 mm or more is welded with a welding heat input of 50-60 KJ / cm per pass and a wall thickness of 30-35 mm. A large-diameter steel pipe characterized in that it is welded by a multi-electrode submerged arc welding method in which a large-diameter steel pipe has one inner surface and two outer surfaces, and a large-diameter steel tube having a wall thickness of more than 35 mm has two inner surfaces and two outer surfaces. Manufacturing method by welding. 2. The thick-walled large-diameter steel pipe according to claim 1, wherein, during the inner surface welding performed in two passes, the tip shape of the copying roll that comes into contact with the bead surface in the first pass has an elliptical cross section. Manufacturing method by welding. 3. The groove shape has a specific X shape and has two steps on the inner surface side of the steel pipe. The groove depth on the outer surface side of the steel pipe is 15 to 18 mm regardless of the wall thickness. The root face on the inner surface side and the thickness center side is 4 to 9 mm, the groove angle on the inner surface side of the steel pipe and the thick surface side is 30 ± 5 °, and the groove angle on the outer surface side of the steel pipe. Is 25 ± 5 ° when the thickness is 30 to 35 mm, and 30 ± 5 ° when the thickness is more than 35 mm.
The groove angle on the inner side of the steel pipe and on the center side of the wall thickness is 3
3. The method according to claim 1, wherein the thickness is set to 5 ± 3 ° when the thickness is 0 to 35 mm and 7 ± 3 ° when the thickness is more than 35 mm.