JPS6358679B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a welding method for welding thin-walled stainless steel pipes to a tapered joint made of thin-walled stainless steel and a thin-walled stainless steel pipe.

Conventionally, as a method for joining thin-walled stainless steel pipes together by circumferential welding, (1) As shown in the cross-sectional view of Fig. 4, the tube end of thin-walled stainless steel pipe a and the thin-walled stainless steel pipe or joint a' are Butt the ends of the tubes together, and use the welding torch B of a TIG welder to connect the butted parts from the outside to the thin-walled stainless steel tube a and the thin-walled stainless steel tube or fitting.
A method of butt welding and joining a′.

(2) As shown in the cross-sectional view of Figure 5, insert the tip of the thin-walled stainless steel pipe a into the insertion type joint c, and connect it to the thin-walled stainless steel pipe a with the tab of the insertion type joint c. A method of welding joint c.

Two methods are used:

However, these methods have the following drawbacks.

When joining by butt welding as shown in FIG. 4, a high degree of skill is required to perform sound back welding by butt welding thin-walled stainless steel pipe a and thin-walled stainless steel pipe or joint a'.

It is necessary to tighten the groove precision of the butt joint.

In particular, it is difficult to butt joints during on-site construction.

In addition, when welding joints using insertion type joint c as shown in Fig. 5, since the welded part is at the edge of insertion type joint c, it is difficult to connect the inner peripheral surface of insertion type joint c with A gap d exists between the thin walled stainless steel pipe a and the outer circumferential surface of the tip thereof, which causes crevice corrosion and significantly impairs the corrosion resistance of the stainless steel.

The present invention solves the above-mentioned drawbacks by using a tapered joint made of thin-walled stainless steel, inserting the tip of a thin-walled stainless steel pipe into the tapered joint, and connecting the end of the thin-walled stainless steel pipe with the end of the thin-walled stainless steel pipe. Welding of thin-walled stainless steel pipes allows easy and reliable welding of thin-walled stainless steel pipes by circumferential welding from the outer circumferential surface of the tapered joint around the contact line with the tapered part of the tapered joint. It provides legality.

More specifically, the present invention provides a tapered joint made of thin-walled stainless steel whose end is expanded to match the outer diameter tolerance of the thin-walled stainless steel pipe to form a predetermined tapered portion on the inner peripheral surface. Insert the end of the stainless steel pipe, and perform circumferential welding from the outer peripheral surface of the tapered joint centering on the contact line where the pipe end of the thin-walled stainless steel pipe and the tapered part of the tapered joint came into contact. The present invention relates to a method of welding and joining thin-walled stainless steel pipes, which is characterized by joining a thin-walled stainless steel pipe and a tapered joint by welding.

Hereinafter, a method for welding and joining thin-walled stainless steel pipes according to the present invention will be explained in detail with reference to the drawings.

Fig. 1 is a cross-sectional view of a joint showing an embodiment of welding a thin-walled stainless steel pipe and a tapered joint by the method of the present invention, and Fig. 2 shows the joint, steel pipe, and welding shown in Fig. 1 before welding. FIG. 3 is an enlarged cross-sectional view of main parts showing the positional relationship of the torches, and FIG. 3 is a cross-sectional view showing the state after welding of FIG. 2.

In the drawing, 1 is a thin-walled stainless steel pipe to be welded and joined, and 2 is a tapered joint made of thin-walled stainless steel whose end is expanded and into which the tip of the thin-walled stainless steel pipe 1 is inserted. The tapered joint 2 may be formed by expanding the end of the other thin-walled stainless steel pipe 1 to be joined and providing a tapered part.

Although the slope and length of the tapered part of the tapered joint 2 are not particularly limited in the method of the present invention, the thin-walled stainless steel pipe 1 is inserted so that the end of the thin-walled stainless steel pipe 1 is always in contact with the tapered part. A pipe having a predetermined slope and length that matches the outer diameter tolerance of the steel pipe 1 is used.

3 is a circular contact line where the end of the thin-walled stainless steel pipe 1 inserted into the tapered joint 2 contacts the tapered part of the tapered joint 2, and 4 is a circular contact line where the center of the electrode is connected to the end of the thin-walled stainless steel pipe 1. Welding in which the thin-walled stainless steel pipe 1 and the tapered joint 2 are joined by circumferential welding from the outer peripheral surface of the tapered joint 2, located directly above the contact line 3 where the tapered part of the joint 2 is in contact. It's a torch. 5 is a welded metal deposited on the joint after welding, and 6 is a back bead formed on the inner surface of the joint after welding.

In the method of the present invention, a tapered portion having a predetermined slope according to the outer diameter tolerance of the thin-walled stainless steel pipe 1 is connected so that the pipe end of the thin-walled stainless steel pipe 1 to be joined comes into contact with the tapered portion of the tapered joint 2. At the end of the tapered joint 2 provided in the length, a second
As shown in the figure, after inserting the tip of the thin-walled stainless steel pipe 1 and bringing the pipe end into contact with the tapered part of the tapered joint 2, the pipe end of the thin-walled stainless steel pipe 1 and the tapered part of the tapered joint 2 are connected. The thin-walled stainless steel pipe 1 and the tapered joint 2 are welded from the outer peripheral surface of the tapered joint 2 using a welding torch 4 as shown in FIG. This is a method of joining. Furthermore, if necessary, the tapered joint 2 is connected around the contact line 3 where the pipe end of the other thin-walled stainless steel pipe 1 and the tapered part of the other end of the tapered joint 2 are in contact.
If the thin-walled stainless steel pipe 1 and the tapered joint 2 are joined by welding from the outer peripheral surface in the same manner as above,
The thin stainless steel pipes 1 can be welded together via the tapered joint 2.

In this way, the method of the present invention can easily and reliably weld the tapered joint 2 and the thin-walled stainless steel pipe 1. In this case, it is possible to weld the tapered joint 2 and the thin-walled stainless steel pipe 1. To determine from the outside the position of the contact line 3 where the and the tapered part of the tapered joint 2 contact, from the outside, before inserting the thin-walled stainless steel pipe 1 into the tapered joint 2, Mark a position at an arbitrary length from the pipe end, and when inserting the thin-walled stainless steel pipe 1 into the tapered joint 2, mark the position corresponding to the length from the mark to the pipe end on the contact line 3. The location can be easily determined from the outside.

In this way, the method of the present invention can be applied to thin-walled stainless steel pipes.
and the tapered joint 2 can be easily and reliably welded together, and there is no difficulty in welding the joints with the joints butted together as in the conventional method. Since the tapered part and the pipe end of the thin-walled stainless steel pipe 1 are on the contact line 3 where they are in contact, a sound joint can be obtained because no gap is formed in the pipe through which the fluid passes, which is harmful to corrosion resistance. It is possible.

Next, the method of the present invention will be further specifically explained with reference to Examples.

Example 1 A tapered joint 2 is formed from a stainless steel pipe with a nominal diameter of 20Su specified by JIS G3448 (stainless steel pipe for general piping), the slope of the taper part is 8/100, and the length of the taper part is approximately 14 mm. At both ends,
Insert thin-walled stainless steel pipes 1 and 1 with a nominal diameter of 20Su, which are also specified by JIS G3448, into the first
It was assembled as shown in the figure. At this time, a score line is placed in advance at a distance of 50 mm from the tube end of the thin-walled stainless steel pipes 1, 1.
While pressing sufficiently onto the tapered joint 2, weld at a position 50 mm from the score line pre-marked on the thin-walled stainless steel pipes 1, 1 using the welding torch 4 of the TIG welding machine at a welding current of 40 Amp and a speed of 12 cm/min. Circumferential welding was performed from the outer peripheral surface of the tapered joint 2 to join the tapered joint 2 and the thin stainless steel pipes 1, 1.

After welding and joining, we conducted a water leakage test at the joint under a water pressure of 20 kg/cm ² and found that there was no water leakage at all.
Furthermore, when the joint was divided into two vertically and the cut surface was inspected under a microscope at 100x magnification, it was confirmed that the weld had penetrated sufficiently and that a sound welded joint had been achieved. .

Example 2 It is formed from a stainless steel pipe with a nominal diameter of 40Su specified by JIS G3448, and the slope of the tapered part is 8/100.
Both ends of the tapered joint 2, which has a tapered part length of approximately 17 mm, have a nominal diameter that is also specified by JIS G3448.
40Su thin-walled stainless steel pipes 1 and 1 were inserted and assembled as shown in Figure 1 in the same manner as in Example 1.
TIG welding was performed in the same manner as in Example 1 at a welding current of 50 Amp and a speed of 15 cm/min to weld and join the tapered joint 2 and the thin-walled stainless steel pipes 1, 1.

After welding and joining, we conducted a water leakage test at the joint under a water pressure of 20Kg/ ^cm2 , and no water leakage was observed.
Furthermore, when the joint was divided into two in the vertical direction and the cut surface was inspected under a microscope at 100x magnification, it was confirmed that the weld had penetrated sufficiently and that a sound welded joint had been made. .

As described in detail above, the welding method for thin-walled stainless steel pipes according to the present invention is to weld and join the tapered joint 2 made of thin-walled stainless steel and the thin-walled stainless steel pipe 1, which is similar to the conventional butt welding method. (1) The work can be easily performed without having to worry about matching the tube ends, and does not require a high degree of skill.

(2) There is no need to perform tack welding, reducing work time and making work more efficient.

(3) There is no root gap that occurs at the butt part, and there is little risk of burn-through during welding.

It has excellent advantages such as, unlike when welding joints using conventional insertion type joints, there is no gap inside the joint, and it is possible to perform sound welding joints with excellent corrosion resistance. The method of the present invention can be applied to any welding of thin-walled stainless steel pipes other than those in the examples, and can also be used especially when it is difficult to butt the ends of the pipes during on-site processing. The work can be easily accomplished by inserting the tip of the thin-walled stainless steel pipe 1 into the tapered joint 2, and its industrial value is great.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of a joint showing an embodiment of welding a thin-walled stainless steel pipe and a tapered joint by the method of the present invention, and Fig. 2 shows the joint, steel pipe, and welding shown in Fig. 1 before welding. Fig. 3 is a sectional view showing the state after welding of Fig. 2, Fig. 4 is a sectional view showing the state of conventional butt welding, and Fig. 5 is a sectional view of the conventional welding. FIG. 3 is a cross-sectional view showing a state in which the insertion type joint is used for welding and joining. 1...Thin-walled stainless steel pipe, 2...Tapered joint, 3...Contact line, 4...Welding torch, 5...
...Welded metal, 6...Back bead, a...Thin-walled stainless steel pipe, a'...Thin-walled stainless steel pipe or fitting, b...Welding torch, c...Pass-in type fitting, d
……gap.

Claims (1)

[Claims] 1 Thin-walled stainless steel pipe 1 is attached to the tapered part of a tapered joint 2 made of thin-walled stainless steel whose end is expanded to match the outer diameter tolerance of the thin-walled stainless steel pipe 1 and a predetermined tapered part is formed on the inner peripheral surface.
Insert the end of the thin-walled stainless steel pipe 1 and perform circumferential welding from the outer peripheral surface of the tapered joint 2 around the contact line 3 where the pipe end of the thin-walled stainless steel pipe 1 and the tapered part of the tapered joint 2 are in contact. A method for welding and joining thin-walled stainless steel pipes, characterized in that a thin-walled stainless steel pipe 1 and a tapered joint 2 are welded together.