JPS6113899B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for butt welding the bottom plate of a steel storage tank with a backing metal.

For welded joints on the bottom plates of crude oil tanks, etc., for those with a bottom plate thickness exceeding 9 mm, butt joints with backing metals are used for strength reasons. It has been confirmed that horizontal cracks 8 occur in the weld bead 2 from the gap a between the mutually abutting portions of the adjacent backing metals 1 and 1', as shown in FIG. It is assumed that the cause of this horizontal cracking is that the gap a between the adjacent backing metals 1 and 1' becomes a kind of notch, and stress concentration occurs in this part when the weld metal solidifies and shrinks. There is.

In order to prevent this horizontal cracking, the conventional method has been to widen the gap between the backing metals and butt weld the bottom plates together so that a bead is formed in this gap. However, this method cannot completely prevent the occurrence of welding defects. That is, Fig. 2 shows a cross section of the welded part constructed by this method, where 4 and 4' are the backing metals, 5 is the bottom plate, and 6 is the welded part.
is a weld bead, which is welded in the direction of the arrow. However, since an acute angle is formed at the end of the backing metal 4' (section A in the figure), this becomes a notch, and when the weld metal solidifies and contracts, , there is a risk that welding defects will occur in this area, resulting in horizontal cracking.

This invention was proposed in order to solve the above-mentioned conventional drawbacks.
In butt welding of storage tank bottom plates with backing metal, in which two bottom plates arranged on the left and right with a gap between their ends are welded together with a backing metal, the bottom plate is welded at the abutting part of the backing metal. The object of the present invention is to provide a welding method that can prevent horizontal cracks from occurring in welded joints.

An embodiment of the present invention will be described below with reference to the drawings.

First, a plurality of backing metals are arranged on the storage tank foundation in a straight line back and forth according to the shape of the bottom plate with gaps between them, and the ends are placed on top of the backing metals and the ends of each other are placed. Arrange the two bottom plates on the left and right with a gap between them. In this case, as shown in FIG.
is preferably 10 mm or more. Note that 11 is a bottom plate.

Next, FIGS. 4 and 5 show the portions where the backing metals 10 and 10' are located in the abutment area between the backing metals 10 and 10', that is, the portions near the respective ends of the backing metals 10 and 10'. As shown in the figure, the first layer welding is performed on the butt portions of the bottom plates 11 and 11', and the backing metal 10 (or 10') and the left and right bottom plates 1 are welded.
1 and 11' are welded together. Reference numerals 12 and 12' indicate weld beads of this initial layer. In this case, the welding direction is as shown by arrows A and B in Fig. 4.
0' end, the backing metal 10,
This is good because it prevents insufficient melting at the ends of 10' (arrows C and D). Further, if the welding length L is, for example, about 50 mm to 100 mm, it is sufficient to prevent welding defects from occurring at the abutting portions of the backing metals 10 and 10'. Due to the weld beads 12, 12' of the first layer, there are no notches in the portions C and D.

Next, as shown in FIG. 6 and FIG.
For the gap between 0 and 10', the bottom plate 11,
The bottom plate 11,
11' are welded together. In this case, welding is carried out using the previously welded bead 12 or 1.
2' end, i.e. C (or D) in Fig. 4.
Welding is carried out from part 2 (or part 3) to other part 2 (or 3).
Thoroughly melt it into the ends C and D of 12', and
It is best to weld so that a sufficient amount of undulations can be produced, and if it is difficult to produce undulations with one-pass welding, two-pass welding may be used. 13 indicates the weld bead. In this way, the ends of the weld beads 12, 12'
Since the weld bead 13 is provided between the ends H,
There is no notch in the weld bead 13.
Since the backing waves are formed, the backing metals 10, 10'
The abutting portions are in the same state as a completely melted state, and this prevents the occurrence of transverse cracks.

Next, the remaining butt portions of the bottom plates 11 and 11', that is, the first layer of butt welding between the bottom plates 11 and 11' where the backing metals 10 and 10' are present is performed. Thereafter, welding is performed for the entire butt portion of the bottom plates 11, 11' from the second layer onward to the final layer.

When butt welding of the bottom plates 11 and 11' is performed in the above-described manner, the first layer welding is carried out on the parts where the backing metals 10 and 10' are not present, and the first layer welding is performed on the parts with the backing metals 10 and 10'. Since this is done later, sufficient penetration occurs at the ends of the backing metals 10, 10' (arrows H and F in Figure 6), and a defect-free weld bead is formed, preventing the occurrence of transverse cracks. is prevented.

In addition, in the embodiment, the root spacing l of the abutting portions of the backing metals 10 and 10' was set to 10 mm or more because the above dimension was This is because if l is too short, welding with sufficient penetration will not be performed and welding defects will likely occur.

Note that the first layer welding of the intermediate portion of the backing metals 10, 10' and the welding of the second and subsequent layers on the entire backing metals 10, 10' are not limited to the order of the embodiments, The first layer welding and the second layer and subsequent welding may be performed on the middle part of the backing metals 10, 10' after the second layer and subsequent layers are welded on the first layer.In short, first,
First layer welding is performed on the part where the backing metals 10, 10' are present in the abutment area between the backing metals 10, 10', and then first layer welding is performed on the areas where the backing metals 10, 10' are not present. If so, the order after that is not particularly limited.

Next, a comparison test between the method of butt welding a storage tank bottom plate with a backing metal according to the present invention and a conventional method and the results thereof will be described.

Figures 8 to 10 show the arrangement and dimensions (unit: mm) of the test piece, thickness: 6 mm, width: 100 mm.
mm, length: approx. 200 mm (3 pieces), approx. 75 mm (2 pieces) backing metal 10 made of mild steel (JIS G3101 SS41),
10' at the part of ,, 10mm,
Arrange them at intervals of 20 mm, 30 mm, and 3 mm, and on top of that, two bottom plates 1 made of mild steel (JIS G3101 SS41) with a thickness of 12 mm, a width of about 200 mm, and a length of about 750 mm.
1, 11', root gap: 5mm, bevel angle: 40
The welding method of the present invention was applied to the sections , , and the conventional method was applied to the other sections.

In other words, the area near the backing metal joint (portion L in Figure 4) is approximately 30mm
Welding rod for mild steel with a diameter of 4.0φ (JIS Z3201
D4316), the first layer was welded in the directions of arrows A and B in Figure 4 at a current of 170 A, a voltage of 26 V, and a welding speed of 11 cm per minute.

Next, the joint part between the backing metals (10 mm, 20
mm, 30 mm interval) were welded in the first layer using the same welding rod as above and under the same welding conditions in the same manner as Uranami welding. After that, the first layer welding of the remaining parts of the bottom plates 11, 11' was performed under the same conditions as above, and the second layer and the final layer were welded using a mild steel welding rod (JIS
Z3201 D4316), current 230A, voltage 27V,
Welding speed: welded at 10-15cm per minute.

For the part shown in Fig. 2, the conventional welding method is used, and the first layer is welded in only one direction from one backing metal to the other backing metal, and then the second and subsequent layers are welded in sequence. Welded and completed welding.

The results of the cross-sectional macro test of each joint in the above test,
Cracks were observed in the conventionally welded joints.

On the other hand, the joint parts where the welding method according to the present invention was applied had no cracks at all.
It was in extremely good condition.

As explained above, according to the present invention, in butt welding of a storage tank bottom plate with a backing metal, the abutting portion of the backing metal can be welded so that sufficient penetration occurs, and therefore, this part It is possible to prevent horizontal cracks from occurring in the welded joint of the bottom plate.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the occurrence of transverse cracking by a conventional welding method, Fig. 2 is an explanatory diagram of the welding situation by another conventional welding method, and Fig. 3 and subsequent figures are explanatory diagrams of each stage of the welding process of the method of the present invention. FIGS. 3, 4, and 6 are cross-sectional views of the vicinity of the backing metal abutting portion, and FIGS. 5 and 7 are plan views thereof. Also, Figures 8 to 1
Figure 0 shows the arrangement of the backing metal and bottom plate in the welding test, Figure 8 is a plan view, Figure 9 is a side view,
FIG. 10 is a side view showing the groove state of the two bottom plates. 10, 10'... Backing metal, 11, 11'... Bottom plate, 12, 12', 13... Welding bead.

Claims (1)

[Claims] 1. Two bottom plates whose ends rest on backing metals arranged in a straight line in the front and back with a space between them, and which are arranged on the left and right with a space between the ends. In the butt welding method of storage tank bottom plate with backing metal, in which the backing metal is welded together with the backing metal, the first layer welding is performed at the butt part of the bottom plate on the part where the backing metal is in contact with the backing metal, and then the backing metal is welded. The gold and left and right bottom plates are welded together, then the first layer welding is performed on the butt part of the bottom plate where there is no backing metal, the bottom plates are welded together, and the two bottom plates are welded together with the backing metal. A method of butt welding a storage tank bottom plate with a backing metal, which is characterized by integral welding.