JPS60130465A - Welding method - Google Patents

Abstract

PURPOSE:To form a welded joint having high material quality and particularly creep strength of the weld zone by subjecting the part near the weld zone to force cooling during welding thereby controlling the growth of the columnar crystal in the solidifying process of the molten pool of the weld metal in a desired direction. CONSTITUTION:Partitions 1, 1 are provided on both sides of the weld zone W of steel pipes P1, P2 to be welded and cooling water C is supplied through water feed pipes 2, 2 to the surface of the pipes P1, P2 from the outside of the partitions 1, 1 to control the growth of the columnar crystal in the solidifying stage of the molten pool of the weld metal along the approximately the axial center direction of the pipe bodies P1, P2 in the stage of directing a welding torch T to the weld zone W of the pipes P1, P2 and welding said weld zone in the circumferential direction while forming the molten pool of the weld metal. The welded joint having high creep strength is thus formed and the improvement in the service life of the member of a high-temp. and high pressure device is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a welding method, and more particularly, the present invention relates to a welding method. This improves the material quality of the parts, especially the creep strength.

Heat-resistant cast steel pipes made by centrifugal casting are usually used as pipe bodies constituting rifoma tubes and the like in right-hand chemical plants. Since this tube body is used under high temperature and high internal pressure, voids occur inward in the tube wall due to the creep phenomenon during use, which develop into fissures, which further grow into cracks, and finally. It becomes unusable.

Generally, the crystal structure of a cast product is roughly divided into columnar crystals and granular crystals, and the damage caused by the creep phenomenon develops from the inner surface along the columnar crystals. As a countermeasure to this problem, a centrifugally cast tube with a granular crystal structure on its inner surface is used. but,
In a product made by welding several centrifugally cast tubes, such as a re-former tube, the welded metal part (5) extends from the inner surface to the outer surface of the tube wall in the thickness direction, as shown in Figure 5. Because of the columnar crystal structure that has grown in this area, the creep damage is likely to be concentrated in that area, and axial stress due to thermal stress is added to this, causing circumferential cracking, which can shorten the service life of the re-former tube. This is a major factor contributing to the shrinkage.

The present invention solves the above problems.

In the welding method of the present invention, in view of the fact that the material properties of the weld zone are closely related to the form of the columnar crystal structure of the weld metal, especially the growth direction of the columnar crystals, the welding method of the present invention includes forced cooling near the weld zone during welding. The growth of columnar crystals during the solidification process of the weld metal molten pool is controlled in a desired direction.

The method of the present invention will be explained below.

According to the method of the present invention, a weld metal molten pool is formed at the welded part of a material to be welded such as a steel pipe using a welding heat source, while the vicinity of the welded part is forcibly cooled with cooling water, and the molten pool is formed by heat conduction. It has a cooling effect. FIGS. 1 to 8 each show a specific example of the implementation procedure of the present invention in butt welding of steel pipes.

(PI, P2) is the steel pipe to be welded, (T) is the butt weld (
The welding torch 5) is directed into the groove, and the welding torch σ) moves at an appropriate speed and forms a welded joint in the circumferential direction while forming a weld metal molten pool within the groove.

To cool the molten pool during this welding process, as shown in Figure 1, screen members (1, 1) are provided on both sides of the welded area to prevent cooling water from entering the welded area, and the steel pipes outside the This can be done by supplying cooling water (C) toward the surface from the water supply pipes (2, 2).

In addition, as shown in Fig. 2, the casing (3) with an open bottom is
A seal (4) to prevent water leakage is applied to the periphery of the opening, installed near both sides of the welded part (W), and connected to the water supply and drainage pipes (5, 6) attached to the housing (3) inside the housing (S). ).) The housing (3) may be moved along the welding area following the movement of the welding torch, and if necessary, the housing (3) may be moved along the welding area. 3) is delayed from the welding torch, and after the required molten pool is generated by heat supply from the welding torch, the casing (3) is moved forward to bring it close to both left and right sides of the generated molten pool. Good too.

In addition, as shown in Fig. 8, leakage prevention gaskets (8) are applied to both edges of the opening of the arcuate gutter member (7) having a U-shaped cross section that opens inward, and the gaskets (8) are placed around the circumferential surface of the steel pipe. It is also possible to install the cooling water on both sides near the welding part so as to circulate the cooling water through water supply and drainage pipes (9, 10) connected to the gutter member (7).

In order to ensure weld quality, cooling the weld zone with cooling water does not interfere with sufficient fusion of the weld metal and base metal, floating separation of non-metallic inclusions in the molten pool, and release of contained gas.
It goes without saying that the cooling process should be controlled so as not to cause problems such as the occurrence of cracks due to thermal stress during the cooling process, but as long as such conditions are met, it is desirable that the cooling of the molten pool be as strong as possible.

FIG. 4 shows an example of the macrostructure of a cross-section of a welded part obtained by butt welding of steel pipes under the above cooling conditions. The weld formed by the normal welding method exhibits a columnar crystal structure that grows in the wall thickness direction (diameter direction) within the pipe wall, as shown in Figure 5 above. Due to the cooling effect, it can be seen that it has a columnar crystal structure that grows along the axis of the zotube.

A welded part with such a crystal structure has excellent mechanical properties, and guarantees high temperature creep strength superior to conventional materials, as shown in the examples below.

Note that there are no particular restrictions on other welding conditions in the present invention, and the welding methods include gas welding, arc welding (submerged arc welding, TIG welding, MIG welding, etc.), and other welding methods in which the joint is formed while forming a weld metal molten pool. Various welding methods may be used to form the .

Next, examples of the present invention will be described.

Example As shown in Figure 8, annular gutter members were installed on both sides of the welded part to go around the steel pipe surface, and while cooling water was flowing at a flow rate of 1.5 t/min, centrifugally cast pipes were butt welded under the following conditions. I did it. As a control, butt welding was performed using the normal welding method without forced cooling (the welding, welding materials, welding conditions, etc. were the same).

A test piece was taken and prepared in the axial direction from each of the obtained welds, and a creep rupture test was performed, and the results shown in Table 1 were obtained. Incidentally, the crystal structure of the welded part according to the present invention is as shown in FIG. 4, and the crystal structure in the conventional welding method is the same as that in FIG. 5.

[l] Material to be welded (1) Steel pipe material: ASTM HK40 (2) Steel pipe size: diameter 125, wall thickness 12 (3) Groove shape: U shape, IV-) Spacing 0 tan, Groove angle 2
0゜[2] Welding conditions (1) Welding method: TIG welding (2) Welding current/voltage 2 100-20OA, 15-5V Table 1 As is clear from the above test results, the examples of the present invention were used at the same temperature and stress. It can be seen that the rupture time at the bottom was improved compared to that of the comparative example, and the creep strength was excellent.

As described above, according to the method of the present invention, it is possible to form a welded joint with high creep strength, and it is possible to improve the service life of high-temperature/high-pressure equipment members, such as a rifoma tube.

The present invention is applicable not only to butt welding of steel pipes, but also to butt welding of steel plates, fillet welding, etc., and the temperature gradient and solidification rate of the weld metal molten pool are reduced by forced cooling from the vicinity of the weld. It is also possible to improve the tensile strength and other mechanical properties by controlling the amount appropriately to form a desired columnar crystal structure.

[Brief explanation of the drawing]

Figures 1 to 8 are perspective views showing specific examples of the implementation procedure of the present invention in butt welding of steel pipes, Figure 4 is a photograph (Xl) substituted for a drawing showing the structure of a cross section of a welded part according to the present invention,
FIG. 5 is a photograph substituted for a drawing showing the structure of a cross-section of a welded part by a conventional method. 1: Screen member, 2: Water supply pipe, 8; Housing, 5,6°9.1
0: Water supply and drainage pipe, 8: Annular gutter member. Agent Patent Attorney Arata Miyazaki Department Figure 1

Claims (2)

[Claims] (1) A welding method characterized by controlling the growth direction of columnar crystals during the solidification process of the weld metal molten pool by applying forced cooling near the weld zone. (2) In butt welding of steel pipes, by cooling the weld metal pool while cooling the weld metal pool with water near both sides of the weld, the pipe body forms a columnar crystal structure that grows along the zo-axis direction. The welding method according to item ci) above.