JPS6272477A - Welding method for thin steel plate - Google Patents

Abstract

PURPOSE:To reduce the cross sectional area of a groove part and to increase the work efficiency and quality by subjecting the initial layer to the full automatic TIG welding at overhead position as well as to butt weld. CONSTITUTION:The groove shape of a weld zone is made X shape and the root gap is made narrow as well. A binding plate 3 is welded on the upper face respectively of the thin steel plates 1 adjoining like stepping over the butt part, a sealing plate 4 is placed on the upper face of the thin steel plate 1 to cover the upper part of the butt part and by driving a wedge 5 between the binding plate 3 and sealing plate 4 the sealing plate 4 is closely fitted to the thin steel plate 1. The welding of the groove part 6 at the lower face side is performed in an inert gas at overhead position by full automatic TIG arc welding as the initial layer welding. The cross sectional area of the groove part is thus reduced, the welding time is shortened, the welding heat input quantity is less as well and the toughness is increased.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method of welding thin steel plates, and in particular, to a method for welding thin steel plates, particularly at -162°
Liquefied natural gas (LNG) is used at extremely low temperatures around C.
) Tank and low temperature around -45℃! In low-temperature tanks such as liquefied petroleum gas (LPG) tanks used in plastic tanks, thin steel plates are horizontally formed to form bottom plates and roof plates! This relates to a welding method for butt welding in a state of D or close to it.

[Conventional technology] In order to ensure sufficient structural safety in low-temperature tanks for storing LNG and LPG, the materials used and welded parts must be of high quality and high performance with particular emphasis on low-temperature properties. is required.

Therefore, in LNG tanks, 9% nickel steel, LP
In G tanks, low-temperature aluminum quilt steel is generally used as a material, and the type of welded joints for roof plates, bottom plates, etc. made of such material is often a butt weld.

Low-temperature thin steel plates are placed in a horizontal or nearly horizontal position to form roof plates, bottom plates, etc. in low-temperature tanks! Conventionally, when butt welding is performed in a downward position, a backing material 2, a restraining jig 3, etc. are attached to the lower surface of a thin steel plate 1, and welding is performed in a downward position, as shown in Fig. 3. Furthermore, automatic welding such as submerged arc welding, fully automatic MTG welding, or fully automatic TIG welding is used to ensure the stability and reliability of welded parts. In the welding method,
It has various problems as described below.

[Problems to be Solved by the Invention] First, in the welding method according to the above-mentioned prior art, when a backing metal made of #l is used as a true backing material, blowholes tend to occur frequently in the root part. There is.

Further, when performing Uranami welding using a copper-made bracing material, if a high current welding method such as submerged arc welding is used, copper may be mixed into the weld metal and cause weld cracks.

In addition, in order to ensure a healthy urana wave shape, the groove angle in the ■-shaped groove shape must be 60 degrees or more, and the root gap must be wide, but such a groove shape must be welded. It is very difficult to maintain this before and during welding, and in addition, performing welding at a wide angle and wide root gap leads to an increase in welding materials and welding work time. Furthermore, under these conditions, since the groove cross-sectional area is large, the amount of welding heat input is inevitably large, and as a result, the low-temperature toughness of the weld zone may deteriorate. Fourth
The figure shows the Charpy impact test results of thin steel plates welded by this conventional method, and as can be understood from this figure, there is a constant if'! from the fusion line. Embrittlement points occur at distant locations.

Furthermore, since one-sided butt welding causes large welding deformation and distortion, many restraint jigs are required to prevent this, and
It is necessary to install the jigs necessary for welding, such as the restraining jigs and the jigs for attaching the true support material, to the lower surface of the thin steel plate so that they do not interfere with downward welding. There were problems such as poor work efficiency as the removal work after completion and inspection of jig marks after removal had to be done in an upward position.

Accordingly, an object of the present invention is to provide a welding method that can solve these problems and provide a high-quality welded joint with high work efficiency.

Means for Solving Problem L] The method for welding thin steel plates according to the present invention, when butt welding thin steel plates together in a horizontal position or a state close to it,
The groove shape of the overhang between the JgA plates will be X-shaped and welded from both sides, at least in the welding of the first layer.
It is characterized in that a sealing plate is brought into close contact with the upper surface of the thin steel plate so as to cover the upper groove, and the lower groove is welded in an upward position by fully automatic TIG welding.

[Function] In the method for welding thin steel plates according to the present invention described above, the cross-sectional area of the groove is smaller than that of the conventional method, and the first layer is welded by fully automatic T and IQ welding in an upward position. ,
The Ura wave shape becomes flat.

Other objects, features and advantages of the invention will become apparent from the detailed description below, taken in conjunction with the accompanying drawings.

[Example] Fig. 1 of the drawings shows an embodiment of the welding method according to the present invention. When butt welding the thin steel plate 1 in an almost horizontal position in order to
The groove shape of the welded part is X-shaped, the groove angle at least on the lower surface side is 60 degrees or less, and the root gap is narrower than in the case of the conventional method. 6 For example, if the thickness of the thin steel plate 1 is If it is 9mm, conventionally the root gap had to be 6 to 8IIIfi, but according to this invention, the root gap can be 3fflI11.
In order to maintain the groove shape of the thin steel plate 1 processed in this way and to prevent welding distortion, the U-shaped restraining plate 3 is placed across the abutting portion of each adjacent thin steel plate 1. Weld to the top surface. Next, the seal plate 4 is placed on the top surface of the thin steel plate 1 to cover the upper part of the butt part, and the seal plate 4 is brought into close contact with the thin steel plate 1 by driving a metal hole 5 between the restraint plate 3 and the seal plate 4. . As the material of the seal plate 4, a material such as a metal plate or glass cloth that can actually cut off the atmosphere by four parts is used.

When the welding preparations are completed as described above, the lower surface side groove portion 6 is welded in an upward position by fully automatic T'IG welding as the first layer welding. TIG welding is performed in an inert gas,
The seal plate 4 prevents the release of inert gas,
Also, since it is shielded from the atmosphere, the acid f of the Uranami bead is
Hi is prevented. In addition, even with a narrow root gap, the molten metal is forcibly pushed up by the strong arc force of T I G welding, and due to the action of gravity, a flat and good Uranami shape can be obtained even without the use of a backing material. It looks like this. Therefore, it is not necessary to perform a shaping operation using a grinder or the like before performing downward welding of the upper groove portion 7. After welding on the bottom side is completed, welding on the groove part 7 on the top side is fully automatic TI.
The welding work is completed by G welding.

In this example, all welding was done by fully automatic TIG/8 welding in consideration of the quality of the welded part 6.7.
Other than welding the first layer, it is also possible to use MTG welding, manual welding, etc., depending on the situation. Moreover, both the lower surface side groove part 6 and the upper surface side groove part 7 may be formed into a single layer, or one or both may be formed into a multilayer structure.

It goes without saying that the present invention is not limited to low-temperature tanks, but can be applied to butt welding of thin steel plates in other structures.

[Effects of the Invention] As described above, according to the present invention, by performing both side thrust welding and fully automatic TIG welding in an upward position for the first layer, the groove shape can be formed with a narrow groove angle and a narrow route. X of the gap
It can be made into a mold, and the cross-sectional area of the groove can be reduced. Therefore, the time required for l6 contact is shortened, so
The welding heat input is also small and the toughness is improved. 6 Figure 2 of the drawings shows the Charpy impact test results of thin steel plates butt welded by the welding method according to the present invention. It will be understood from this figure that no points are generated.

Furthermore, since the cross-sectional area of the groove is small, fewer molds of welding material are needed, resulting in lower material costs.

Furthermore, since the amount of weld metal is small and welding is performed from both the upper and lower sides, welding deformation is small and the number of restraint jigs can be significantly reduced.

Furthermore, since all the jigs are attached to the top surface, the burden on the operator in the work of removing and sizing them is significantly reduced.

Further, since the first layer is welded in an upward position, a good back wave shape can be obtained without using a backing material, and there is no need for fitting or removing the backing material or shaping work using a grinder.

As described above, according to the present invention, it is possible to achieve a significant improvement in work efficiency and quality, and it is particularly suitable for forming roof plates, bottom plates, etc. of low-temperature tanks.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram showing a method for welding thin steel plates according to the present invention, FIG. 2 is a diagram showing the results of a Charpy impact test on thin steel plates welded according to the present invention, and FIG. 3 is a diagram showing a conventional welding method. FIG. 4 is a diagram showing the results of a Charpy impact test of a thin steel plate welded by the conventional method shown in FIG. In the figure, 1: thin steel plate, 2: backing material, 3: restraint jig, 4: seal plate, 5: missing metal, 6: bottom groove, 7, top groove. Patent applicant: Toyo Kanetsu Co., Ltd. Figure 1 1 Woman Hyakkin wire Torimushi line Riki et al.'s distance scale Figure 3

Claims (1)

[Claims] When butt welding thin steel plates to each other in a horizontal state or a state close to it, the groove shape of the butt part of the thin steel plates is set to be X-shaped and welded from both sides, and at least in the welding of the first layer, the upper surface side is open. The seal plate is brought into close contact with the upper surface of the thin steel plate so as to cover the tip part, and the lower groove part is fully automatically TIed.
A method for welding thin steel plates, characterized by welding in an upward position by G welding.