JPH0224629B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a method of butt welding a bottom plate in a steel plate storage tank having a welded structure.

As is well known, in welded steel plate storage tanks for storing petroleum and other liquids, strict quality is required for the welding of the bottom plate from the standpoint of safety.

In particular, for specified outdoor storage tanks that store petroleum with a capacity of 1000Kl or more, welding of the annular plates (the side plates are joined at the outer circumferential bottom plate of the storage tank bottom plate) must be by butt welding using a backing metal or by welding. It is regulated that welding must be performed using a welding method that has the same or higher welding strength, and the welding inspection is also required to sufficiently confirm its safety.

In response to such demands, this invention proposes a welding method that does not cause welding defects, and in particular, it is an object of the present invention to propose a welding method that does not cause welding defects. This invention relates to an improvement in the method of butt welding a storage tank bottom plate using gold.

Conventionally, due to the above-mentioned regulations, welding of the annular plates constituting the storage tank bottom plate to each other has generally been carried out by butt welding from one side using a backing metal.

FIG. 1 shows a cross section of the welded joint. As understood from this figure, since the backing metal 1 is in close contact with the lower surface of the joint, the lower surface of the joint is in a sealed state.

Normally, before welding begins, the welding area is cleaned to remove moisture and oil, as well as to completely remove impurities.

However, as mentioned above, in single-sided welding with a backing metal, the bottom surface of the joint is sealed, so moisture, oil, and other foreign substances tend to accumulate.
Another drawback is that it is difficult to completely remove even when cleaned, and the problem is that moisture, oil, etc. adhering to the joint become gasified by the welding heat during welding, which can cause blowholes. ing.

However, these blowhole welding defects are difficult to detect using color checks, magnifier tests, vacuum tests, etc., and unfortunately are often overlooked. However, non-destructive inspection using X-Ray is impossible due to the fact that one side is in contact with the foundation surface, and in order to prevent this type of welding defect, blowholes must occur at the welding stage. It is important to select a welding method that prevents this from occurring.

Therefore, in order to prevent the occurrence of such welding defects called blowholes, the present invention is designed to prevent the occurrence of welding defects such as blowholes by welding along the edges of the base materials A, A of the flat bottom plates to be welded together, that is, along the lower surfaces of the root edges 2, 2. After forming the protrusion 7 linearly, the protrusion 7 is in contact with the upper surface of the backing metal 1, and a gap 5 is provided between the bottom plate lower surface 3 and the backing metal 1 to form a welded joint, The joint portion is welded from one side.

FIG. 2 shows a cross section of an annular plate welded joint showing one embodiment of the present invention. According to this method, as can be understood from the above diagram, the backing metal 1 does not come into close contact with the lower surface of the welding base metals A and A, forming a gap 5, which prevents moisture and oil from accumulating in the joint. Even if moisture and oil have accumulated in the joint, the welding heat will gasify the moisture and oil that has accumulated in the joint, and the moisture and oil will be released as gas from the gap 5. It does not cause welding defects such as blowholes. In particular, if cleaning is done thoroughly before welding, moisture and oil that can cause welding defects can be easily removed because of the gap 5, compared to the conventional tightly sealed type shown in Figure 1. This allows for welding work without welding defects such as blowholes.

As a method of linearly forming the protrusion 7 by the weld bead 4 along the lower surface of the root edge 2 of the groove of the base material A, as shown in FIG. 4 is placed in a series along the lower surface of the edge of the base materials A and A for mutual welding of the bottom plates, and then cut as shown by the cutting line 6 to perform bevel processing.

In addition, as a method of forming a linear protrusion 7 along the lower surface of the root edge 2 instead of the weld bead 4, as shown in FIG. It is sufficient to perform the bending process, then cut along the cutting line 6 as in the case of FIG. 3, and perform the beveling process so that the root edge 2 of the bevel is located at the bent part.

In this way, after the weld bead 4 is linearly built up along the lower surface of the edge of the weld base material A, or after the bending process is performed, the groove surface 8 is provided by cutting the bevel, so that the protrusion 7 Defects generated in the weld bead 4 and defects generated during bending are removed from the welding groove including the welding groove, resulting in a welded joint having a groove free of defects.

In any case, before butt welding, a linear protrusion 7 is made to protrude downward from the lower surface of the base material A for base plate welding along the lower surface of the groove root edge 2 of the base metal A, and in this state, the protrusion 7 is By applying the backing metal 1 to 7 and welding a welded joint having a defect-free groove, it is possible to prevent the occurrence of welding defects due to blowholes as described above, and to obtain a sound welded part. It is possible.

Furthermore, with respect to the fact that a gap 5 is formed between the root edges 2, 2 and the backing metal 1, and undercuts are expected to occur at the root edges 2, 2, according to the method of the present invention, the root edge can be removed. 2, welding is performed by providing a protrusion 7 linearly along the lower surface of the weld base material A, and welding is carried out in a weld shape that protrudes from the lower surface of the weld base material A. Therefore, even if an undercut occurs, the depth of the cut is It remains within the protruding weld shape and has no effect on joint strength.

As described above, according to the method of the present invention, the occurrence of blowholes that were previously overlooked can be prevented,
Furthermore, even undercuts that are expected to occur at the root edge portion do not affect the joint strength in any way, allowing for higher quality welding work.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a butt joint in a conventional welding method, FIG. 2 is a sectional view of a butt joint in an embodiment of the method of the present invention, and FIGS. 3 and 4 show how to prepare a groove. FIG. 1...Backing metal, 2...Root edge, 3...Bottom plate bottom surface, 4...Welding bead, 5...Gap, 6...
Cutting line, 7... protrusion, 8... groove surface.

Claims (1)

[Scope of Claims] 1. In a bottom plate butt welding method using a backing metal for a flat bottom welded structure storage tank for storing petroleum etc., the edges of flat bottom plates to be welded to each other are cut to form a bevel. a step of forming a surface, a step of forming a protrusion linearly along the lower surface of the root edge of the edge of the mutually welded base material of the bottom plate, and a step of arranging the root edge of the mutually grooved surface of the bottom plate at regular intervals. After forming a welded joint by a process of providing a band-shaped backing metal with a gap in which the linear protrusion and the top surface are in contact and separated from the bottom surface of the bottom plate, the joint is covered with a backing metal. A method of butt welding a storage tank bottom plate, which is characterized by welding one side from the top surface facing the metal. 2. After providing a weld bead linearly along the edge of the lower surface of the base material for mutual welding of the bottom plates to be welded, the weld bead is cut and beveled to form a weld bead along the lower surface of the root edge of the end of the mutually grooved surface of the bottom plate. 2. The method of butt welding a storage tank bottom plate according to item 1, in which a protrusion is formed in a straight line. 3. By bending each of the edges of the welding base material of the base plate to be welded downward, and then cutting the groove so that the root edge of the groove is located at the bent part, the bottom plate is 2. The method for butt welding a storage tank bottom plate according to item 1, wherein a protrusion is formed linearly along the lower surface of the root edge of the mutually grooved surface end.