JPS6225069B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a high-efficiency welding method for thick-walled bending roll steel pipes, and more particularly, to a welding method for highly efficient welding of thick-walled bending-roll steel pipes and for obtaining a welded portion free of weld defects. ,
This invention relates to a method for forming an initial layer in internal welding. Methods for manufacturing large diameter steel pipes include the UOE method, spiral method, and bending roll method. Among these, the bending roll method involves bending both ends of the steel plate using a hydraulic press, etc. to improve the roundness after bending, and then pressure-forming with rolls, usually 6 to 10 revolutions, to obtain the specified pipe diameter. This method involves welding and welding, and is suitable for manufacturing comparatively thick-walled steel pipes. In general, 1 is an inner beveling, 2 is an end bending,
3 is bending roll forming, 4 is external partial tacking, 5 is internal multilayer welding, 6 is external gouging,
The pipe is manufactured using the following steps: 7. External multilayer welding, 8. Dimension correction. The submerged arc welding method is used as the welding method because it has deep penetration, high welding speed, and is suitable for obtaining beads with good appearance. However, since multiple layers must be welded on both the inner and outer surfaces, the time required for welding is extremely long, which limits productivity. In the case of UOE pipes and spiral pipes,
Double-sided layer welding by multi-electrode submerged arc welding is commonly performed, and the welding speed is fast, so welding efficiency is very high compared to those requiring multi-layer welding. In order to enable such double-sided single-layer welding, the groove precision must be as good as in UOE pipes.In this respect, bending roll steel pipes cannot be said to have good groove butt precision, and the Since the thickness is large, multi-layer welding is inevitably required, but since the groove shape is point contact as shown in Figure 2 and there is almost no root, the following steps are required to perform multi-layer welding. There are problems with the street. When making a pipe by the bending roll method, as shown in FIG. 1, a steel plate 1 is provided with an inner groove 4 at an angle α, and then formed using a bending roll or the like. As shown in FIG. 2, the groove shape after molding is of a type in which the two contact only at one point, and a gap of an angle θ is created at the abutting portion on the outer surface side 3. This clearance θ varies depending on how the press is applied, but as shown in Fig. 1, it is geometrically difficult to avoid as long as inner bevels are provided at both ends of the raw steel plate 1. As shown, the conditions for welding the first layer on the inner surface are greatly influenced by the shape of the groove with which the root portion makes point contact. That is, the groove of the shape shown in FIG.
When the first layer is welded, it is a point contact and there is almost no root part, so burn-through is likely to occur depending on the welding conditions.For this reason, the first layer welding is performed under low current and low heat input to prevent melting. This will prevent it from falling,
Usually, a one-electrode method is used and a low current is used. However, in the inner first layer bead formed in this way, the amount of weld metal is small, and if the heat input in the second layer is increased too much, the arc will penetrate the first layer weld metal.
Burn-through occurs in the second layer. Therefore, when welding the first layer with a low current using the first electrode method, the second
Low current welding was also performed for the layers using the one-electrode method, and welding with a large amount of heat input had to be carried out from the third layer onwards, posing the problem of extremely poor welding efficiency. Therefore, in order to increase the welding speed and reduce the number of welding passes in order to improve the welding efficiency of bending roll steel pipes, the present inventors applied a multi-electrode submerged arc to the inner surface of the groove as shown in Figure 2. Welding was performed, and the welding conditions were examined in detail in relation to the groove shape. The results showed that even in multi-electrode welding, by changing the welding conditions according to the groove shape, especially the gap angle θ, it was possible to prevent burn-through and form a bead with a large amount of welding at high speed. . First, when welding the first layer from the inner surface of a groove shape as shown in FIG. 2, the amount of welding heat input must be controlled according to the size of the gap angle θ in order to prevent burn-through. Next, if the current in the leading electrode is made too large, even if the welding speed is high and the welding heat input is reduced,
The digging action of the arc is too strong and it burns through easily.
For this reason, it is important that the preceding current is not too large. Furthermore, even if the current is small, if a wire with a small diameter is used, the current density will increase, resulting in the same result as passing a large current. For this reason, it is advantageous to use a wire having a diameter greater than a certain value. Next, in multi-electrode welding, it is important to set the current ratio of each electrode within a certain range in order to prevent defects such as slag entrainment and to obtain a well-shaped bead. The present invention has been made based on the above findings. Therefore, the present invention will be explained below through initial layer welding conditions and the like. First, in the present invention, 0.4 mm of the plate thickness is applied only to the inner surface of a relatively thick steel pipe material, such as a plate thickness of 25 to 60 mm.
~0.6x, beveled at an angle of 25° to 40°,
This is molded using a bending roll method, the outer surface is partially tacked, the inner surface is subjected to multi-electrode submerged arc welding, the outer surface is peeled off, and the outer surface is welded to form a pipe. In other words, in pipe manufacturing methods such as the UOE method and the spiral method, which are mainly used for steel pipes whose plate thickness is not very thick, it is more efficient to weld the inner and outer surfaces in one pass without lifting the back. In fact, such a method has been adopted. In particular, UOE steel pipes have good groove precision and single-layer welding on the inner and outer surfaces with relatively high heat input. On the other hand, the bending roll method is capable of making pipes from thin to thick materials, but it is inevitably less efficient than the UOE method when producing relatively thin products.
Furthermore, when comparing steel pipes manufactured using the same bending roll method, the number of welding passes is not so large for thin products, so welding efficiency is rarely a problem. Welding efficiency becomes a problem when it comes to thick steel plates, but for thick steel plates that are close to extremely thick, such as those over 60 mm, even if the first layer is welded under the welding conditions described below, Since the total number of passes becomes very large, the effect of improving welding efficiency for the first and second layers is relatively small from the overall perspective.For this reason, the present invention targets plates with a thickness in the range of 25 mm to 60 mm. shall be. By the way, in order to increase welding efficiency with thick materials,
It is desirable to improve the butt precision of the root face as a groove on the inner and outer surfaces and to prevent burn-through even with large heat input, but expensive equipment is required to prepare the groove on both sides mechanically. Attempting to create a double-sided bevel using gas cutting is extremely time consuming. Therefore, when forming pipes by the bending roll method in the method of the present invention, as shown in FIG. No drilling is performed, but at this time the depth of the inner groove is determined by the thickness of the plate.
Make the groove depth about 0.4 to 0.6 times. In other words, internal welding is performed with a groove depth less than 0.4 times the plate thickness,
If an attempt is made to weld the outer surface by cutting the outer surface, the groove area on the outer surface will become larger, and as a result, the time required for welding will become longer, which is undesirable from the standpoint of improving welding performance. Moreover, if the depth exceeds 0.6 times, the inner surface side butt groove area S shown in FIG. 3 becomes large, and the time required for welding becomes longer in this case as well, which is not preferable. Further, if the inner surface groove angle α (see Fig. 1) is less than 25°, the following problems occur. In other words, when raw steel plates are formed into a steel tube, the actual butt angle β on the inner surface shown in Figure 2 is β = (2α - θ), and if α is less than 25°, the butt angle will be quite narrow. . The narrower the groove angle, the more advantageous it is to reducing the number of passes, but if the angle is narrow, the slag after welding tends to peel off, and its removal becomes an extremely serious problem, especially on the inner surface of the pipe. Moreover, when welding with a large heat input at a narrow angle, the bead 5
The cross section becomes pear-shaped as shown in FIG. 4, and solidification cracks 5a are likely to occur. Therefore, the groove angle of the raw steel plate must be 25° or more. On the other hand, if the value exceeds 40°, there is no fear of slag separation or solidification cracking, but the groove area after forming becomes wider, leading to an increase in the number of welding passes. Therefore, when processing into a raw steel plate, the inner surface groove angle is preferably in the range of 25° to 40°. In addition, as mentioned above, when forming the first layer by multi-electrode submerged arc welding on the inner surface, the diameter
Using a 4.0 to 4.8 mm electrode wire, set the first electrode current to 750 A or less, set the second and subsequent electrode currents to 0.70 to 0.90 times the previous electrode current, and further, as shown in Figure 2. The initial layer bead is formed by adjusting the amount of heat input within the range described below by adjusting the clearance angle θ. First, as an electrode wire, its diameter is 4.0 to 4.8.
It is preferable to use a diameter of approximately mmφ. In relation to the electrode current described later, the wire diameter is 4.0mmφ
If the current density is less than 4.8mmφ, the current density will become too large, and as a result, the digging action of the arc will also become stronger, leading to the risk of burn-through.On the other hand, if the welding current exceeds 4.8mmφ, the welding current described below will be short and stable. There is a problem that welding cannot be performed. Therefore, the wire diameter is preferably 4.0 to 4.8 mmφ in relation to the welding current described later. Next, regarding electrode current, the role of the first electrode in multi-electrode welding is to ensure sufficient penetration depth, and for this purpose, a high current is generally passed.
In the present invention, if such conditions are adopted, burn-through occurs easily, so the current of the first electrode needs to be 750 A or less. As mentioned above, the first electrode excavates the base material by the docking action of the arc, so a large number of slags remain at the bottom of the bead formed by the first electrode, but these slags are floated by the second and subsequent electrodes. At the same time, the bead shape is adjusted, but if the second electrode current is made too large, the penetration depth increases too much, increasing the risk of burn-through, and even if burn-through does not occur, the second electrode However, a large amount of slag remains. Furthermore, if the second electrode current is too small, the slag remaining at the bottom of the bead formed by the first electrode will not float, resulting in a slag entrainment defect. In order to prevent these defects and obtain beads with good shape, it is necessary to set the second electrode current to 0.70 to 0.90 times that of the first electrode. In addition, in the case of three-electrode welding, in order to obtain a bead with a good shape and no defects, the third electrode current must be
It should be set to 0.70-0.90 times the electrode current,
Furthermore, even when using subsequent electrodes, the current is set to 0.70 to 0.90 times the previous electrode current. Next, since the groove shape is as shown in Figure 2, the clearance angle θ on the outer surface side that occurs during forming is determined, and from this angle θ, the welding heat input (HI KJ/cm ). When θ≦10° -3.67θ+69≦HI≦−3.67θ+99 When 10°≦θ≦18° 32≦HI≦−3.67θ+99 When 18°≦θ HI≦32. The reason for this is as follows. Welding heat input is a function of current, voltage, and welding speed, and the heat input is determined by these conditions. However, in the present invention, the groove shape is as shown in Fig. 2, and the conditions for not causing burn-through when welding this groove are as described above, by adjusting the heat input in relation to the clearance angle θ. Therefore, when we specifically sought this relationship, we found that
The relationship shown in FIG. 5 was obtained. Figure 5 shows the relationship between the clearance angle θ and the amount of welding heat input that can be input.The areas A and B surrounded by diagonal lines in Figure 5 are the ranges where inner first layer welding can be performed with high efficiency and without burn-through. It is. At this time, if the upper limit is exceeded, burn-through occurs, and if the lower limit is exceeded, the welding efficiency decreases. In other words, if the welding heat input (HI KJ/cm) satisfies the relationship HI≦−3.67θ+99, it is possible to obtain a bead with good shape without burn-through. Therefore, it is sufficient to perform welding with a heat input amount less than or equal to the amount of heat determined by θ. However, in addition to this, it is necessary to consider the welding efficiency due to the multi-electrode method, and when this is combined, when θ≦10° -3.67θ+69≦HI≦−3.67θ+99θ When 10°≦θ≦18° 32≦HI ≦−3.67θ+99θ When 18°≦θ, it is necessary to satisfy the relationship HI≦32. In other words, when θ is less than 10°, the welding heat input is -3.67θ + 69 (KJ/
cm), the benefits of high-speed welding due to multiple electrodes cannot be expected. In addition, when 10°≦θ≦18°, the minimum welding heat input for the inner first layer is 32KJ/cm, and the maximum welding heat input is -3.67θ+
It can be changed up to 99KJ/cm. θ≧18
The probability of burn-through becomes extremely high when the temperature is 32 KJ/cm or less, but burn-through can be prevented by the surface tension of the molten iron if the heat input is kept below 32 KJ/cm. After welding the first layer under the above conditions, if it is necessary to weld the second layer or later, set the amount of heat input according to the plate thickness and weld. This multi-electrode welding method can achieve high efficiency. Internal welding can be performed. As described above, according to the method of the present invention, internal welding of bending roll steel pipes, which has conventionally been inefficient, can be performed with high efficiency. Next, the present invention will be explained in more detail with reference to Examples. Example 1 As shown in Figure 6, plate thickness (t = 38 mm), length 1 m
According to the API standard of ×-60 grade steel plate, an angle β (equivalent to 2α in Fig. 1) and a depth (t ₁ ) of 20 mm are taken on the inner surface, and a gap with an angle θ is created on the outer surface. Si
Multi-electrode submerged arc welding was performed using -Mn wire and SiO ₂ -TiO ₂ -AlO ₃ fused flux. All welding was performed using the three-electrode method, and the burn-through phenomenon during welding was investigated. The welding conditions and results are shown in Table 1 (however, the welding heat input is the total amount of the three electrodes L, M, and T). In the method of the present invention, the welding heat input is determined by the wire diameter, welding current, and θ. Since all of the required conditions were met, a good bead was obtained in all cases, and a sufficient amount of welding was obtained to prevent burn-through even when the next layer was welded. On the other hand, in the comparative examples, burn-through occurred in the first layer welding in all cases, making it impossible to weld all the way to the end. That is, in B1, although the welding heat input range determined by θ was satisfied, burn-through occurred because the welding current was too large. In B2, although the welding current and welding heat input satisfied the necessary conditions, the wire diameter was small, resulting in a high current density, resulting in a large penetration depth and burn-through. B3, B4
was too large than the heat input required by θ, so it burned through.

[Table] Example 2 A steel plate similar to the steel plate used in Example 1 was welded with an inner groove β of 55° and an angle θ formed on the outer surface of the groove with a depth of 20 mm constant at 8°. . In this case, the inner first layer welding conditions were varied, and after the second layer was heaped up, an X-ray transmission inspection was conducted. The wire flux used was also the same as in Example 1. Table 2 shows welding conditions and welding results (however, the amount of heat input is the total amount of the three electrodes L, M, and T).

[Table] In the method of the present invention, the bead appearance was good even when the first and second layers were welded, and no defects were observed even by X-ray inspection. On the other hand, various problems arose in the comparative example. That is, in D1, the first layer was welded using the one-electrode method, and the second layer was welded on top of it, but because the amount of weld metal in the first layer was small, burn-through occurred in the second layer. In D2, the welding conditions of the first layer three-electrode welding method are poor, that is, the current of the M pole (second electrode) is larger than the current of the first electrode, and the penetration depth becomes large, resulting in melting in the first layer welding. It fell. In D3, a good bead appearance was obtained even after welding the second layer, but due to the poor current ratio of each electrode in the first layer welding, an X-ray transmission inspection revealed that there were many slag coils on the first layer bead. Containment was recognized. In D4, the initial layer heat input was small, so the amount of weld metal was small and burned through when the second layer was welded. Example 3 Using a steel plate similar to that used in Example 2, wire, and flux, internal welding was performed up to the final pass, and the number of passes and time taken to complete welding were measured and compared with the conventional method. Table 3 shows the welding conditions, and in the case of the method of the present invention, everything from the first layer to the final pass was performed using a three-electrode method. However, the heat input in Table 3 is for the three electrodes L, M, T.
is the total amount of

[Table] On the other hand, in the comparative example, the first layer and the second layer were formed using the one-electrode method, and the third and subsequent passes were performed using the three-electrode method, as was conventionally done. All wires used were 4.0 mmφ. Table 4 shows the groove shape, lamination method, and welding results.

[Table] The method of the present invention has a high welding speed and a small number of passes, so it is efficient and completed in 29 minutes at an interpass temperature of 150°, whereas it took 45 minutes in the comparative example. As shown in the examples above, according to the present invention, thick-walled bending roll steel pipes can be welded more efficiently than conventional methods, and the time required for welding can be significantly shortened, making it possible to weld industrially. This is a great contribution.

[Brief explanation of the drawing]

Figure 1 is a side view of the bending roll material for steel pipes, Figure 2 is an explanatory diagram of the groove butting situation after the bending roll, Figure 3 is an explanatory diagram of the groove area after the bending roll, and Figure 4 is an illustration of the groove area after the bending roll. is an explanatory diagram of solidification cracking in the first layer weld metal, FIG. 5 is a graph showing the relationship between the clearance angle θ of the outer surface side abutment part and the amount of heat that can be input for inner first layer welding, and FIG. It is an explanatory view of an example of tip shape. Code, 1... Steel plate for steel pipe, 2... Inner surface, 3... Outer surface, 4... Inner groove, 5...
...Bead, 5a...Initial solidification crack, α...Inner surface groove angle of raw steel plate, β...Inner surface groove angle at butt, θ
...External clearance angle at butt, S...Inner butt groove area.

Claims (1)

[Scope of Claims] 1. After groove-processing the inner side of a raw steel plate for steel pipes, it is formed using a bending roll method and partially tacked on the outer side, and then a butt angle β is formed on the inner side, and a butt angle β is formed on the outer side. When making a pipe by welding grooves that butt together with their roots in point contact, creating a clearance angle θ from the inner and outer surfaces, the initial bead of butt welding from the inner surface is welded using a multi-electrode It is formed by submerged arc welding, and when forming this first layer, the first electrode current value is adjusted to 750 A or less, the current value of the second electrode and subsequent electrodes is adjusted to 0.70 to 0.90 times the immediately preceding electrode current value, and the above-mentioned gap is adjusted. Based on the angle θ, the following relational expression
Within the range of (1), (2), and (3), when θ≦10°, −3.67θ+69≦Welding heat input (HI KJ/cm) ≦−3.67θ+99 …(1) 10°≦θ≦18° When 32≦Welding heat input (HI KJ/cm) ≦−3.67θ+99 …(2) When 16°≦θ Welding heat input (HI KJ/cm)≦32 …(3) Welding heat input (HI KJ/cm) ) A high-efficiency welding method for thick-walled bending roll steel pipes.