JPS58218391A - Circumferential welding method of joint of steel pipes - Google Patents

Abstract

PURPOSE:To form a circumferentially welded joint part having an excellent fatigue characteristic, by welding short pipes of a specific shape respectively to the end faces of a pair of steel pipes to be circumferentially welded to each other then welding the short pipes to each other. CONSTITUTION:Two short pipes 2 are inserted between a pair of steel pipes 1a, 1b to be circumferentially welded to each other. The wall thickness t1 in the parts of the pipes 2 facing the pipes 1a, 1b is made the same as the wall thickness t2 of the pipes 1a, 1b, and the wall thickness T1 in the other end part is made about 1.5-2 times of the thickness t2 of the pipes 1a, 1b; in addition, projection parts 12 are formed. The end parts of the pipes 1a, 1b and the pipes 2 are first subjected respectively to both-side welding to form circumferentially welded joint parts 3, whereafter the reinforcement of weld is chipped off. The pipes 2 are then butted to each other and are subjected to one-side welding from the outside to form circumferentially welded joint parts 4. The stress to be generated in the parts 4 is thus reduced and the fatigue strength is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for circumferential welding of steel pipes, and more specifically, in circumferential welding of line pipes used for transporting pressurized fluids such as petroleum and scum, the present invention relates to a method for circumferential welding of steel pipes. This method provides superior welded joints.

In pipeline construction work, circumferential welding is performed to join the pipes, but due to the structure, this circumferential welding requires internal welding, which is often difficult to do in the first stage, and it is usually joined from the outside by single-sided circumferential welding. Enter with awn. Therefore, stress concentration areas remain in the inner welded part (Uranami) K due to welding defects such as poor fusion and undercuts, and irregularities in the square shape of the reinforcement.

Under these circumstances, is it possible to use high-strength steel pipes as currently available? Designed to be used and operated under high stress 8f'1. Moreover, in pipelines that are subject to frequent internal pressure fluctuations, the circumferential weld is the most vulnerable part to force failure.

For this reason, there is a circumferential weld joint K having such a stress concentration area, and stress concentration f
Reducing this will help improve the pipeline's fatigue strength!
be.

The purpose of the present invention is to solve the above-mentioned drawbacks, and specifically, it proposes a circumferential joint welding method that eliminates the fatigue failure that occurs in the circumferential welded joints of ordinary hard pipes (1.1111). provide・In other words, the method of the present invention provides a method in which between a pair of steel pipes to be welded to be circumferentially welded to each other, the outer diameter and inner diameter of one end are substantially equal to the wall thickness or the other end of the steel pipes to be welded. The wall thickness of the end is j smaller than the wall thickness of the steel pipe to be welded, and there are main parts 2 at both ends.
A pair of short pipes t1 having a straight pipe part on g mmu and a protrusion protruding from the other end, so that these protrusions face each other,
The method of the present invention will be described in detail below, which is characterized in that the first layer is formed by melting each step, and the second layer is sequentially welded by a conventional method.

1. The Ministry of Invention et al. made a pressure vessel-like test specimen by fully welding the head plates on both ends of a steel pipe, and conducted an internal pressure fatigue test by repeatedly applying internal pressure to this test specimen. For this reason, it is necessary to avoid damage from the circumferential welded joint at the seam (circumferential welded joint). Yo, eh.Ka3
Yo, Kayu:: That's it.

The first factor is a front view of a steel pipe circumferentially welded by the method of the present invention, Fig. 2 is a detailed cross-sectional view If1 of the welded joint part, and Fig. 3 is an enlarged cross-section of the welded part of the steel pipe and smoke pipe. FIG. 4 is a sectional view of the welded joint shown in FIG. 2 after welding. In FIGS. 1 and 2, the bone canal with which the canal has been eroded is cut to a predetermined size, and a pair of #canals 1a and 1a are cut.
.

] Insert two short pipes 2f between b. One end of each short pipe 2, one end, one m pipe] a, ] b The outer diameter, inner diameter, and wall thickness of the K opposing threaded portion are the same as each steel pipe 1a.

1b, and the wall thickness at the other end is a steel pipe]
The wall thickness is thicker than 8% lb, and the short pipe is connected to the circumferential weld part n7. In addition, the material of the short pipe 2 is preferably a crack arrester material, and the strength is determined by taking into account internal pressure fluctuations.
, shi, # The strength of the pipe a or tfflb is equal to or higher than the strength of the pipe a or tfflb. For example, the thickness of the vfIIA pipe side, tl, is the curve at the circumferential weld joint 3, and the stress generation vr
- To prevent this, the thickness should be at2, which is the same as the 18% lb steel pipe. Kon
, N at the other end of the smoke tube 2 is also the thickness of the Tlijm tube'! t
The circumferential weld part 4 is thicker than 2, preferably 1.5 to 2 times, and has a stress concentration part t;
, circumferential weld between two and two layers 4. The stress at low I
kg.

Moreover, the bending in the inner circumferential bi part 3.4 helps to prevent the generation of stress.
The white pipe parts 5a and 5b are formed on the simple river, and the medium heat part 64 is formed.
At C, the thickness of L is also changed by the curvature of the excessive taper 1 due to the thickness tl and the embedding Tlz. Also, in each short pipe 2, the other end, the Opposite end VC
12 are drawn out, and 12 protrusions are formed at once in the bath as described later.

Next, Vpvcrts of fcrh, ti, circle i
=+h Three joints are formed, and then the circumference #1 joint 4 is formed at'L. That is, the circumferential weld joint 3 is formed by double dlJb welding (full penetration welding), and the stress concentration parts of the welding excess 8a, 8b are sufficiently removed using a grinder I or cutting pad, and the final finish is The surface is equivalent to the level of the circumferential surface.

In this case, since the length δ of the flue pipe is short, the welding peak can be easily removed from the inside and outside, and therefore, the stress concentration rate is small on the inside and outside surfaces of the circumferential weld joint 3. αt
t i, o. Ryoukorai 1a, 1ll
c phantom viper W2 keson.

After fL welding, the circumferential weld joint 4 is formed by welding the short pipes 2 together. Me, outside aj
+ to 4% -r for single-sided melting. In addition, if one side welds a small amount, A wave 9 will exist on the inner surface of the tube, and if the back wave shape or outflow condition is bad, this kIS & U reaction will occur, which is not good. In the present invention, by making the thickness of the short pipe of the circumferential welded joint 4 thicker than the plate thickness t1 of the TI welded steel pipe, it is possible to reduce the occurrence of chipping at the long joint with ψ on the circumference. can do. Furthermore, is it possible to weld the first layer uniformly on one side using the method of the present invention? Improvement'f by J&
By controlling the corrugation well and reducing the stress concentration in the pipe, it is possible to reduce the fatigue strength of the internal pressure at the circumferential welded joint where the weld joint is in tension.

-f-7) Inside each short pipe 2 [fi111IIVc
[Protrusions] 2 are formed under the protrusions. To form the first layer, each of the 12 protrusions is melted by using a tungsten electrode, for example, and adjusting the shielding gas (argon), electric current, and slow electrode transfer tube.・Join and form 10 welding excess welds for the first layer.

The second layer of moonlight will be done in the usual way. When the first layer is completely formed and welded in this manner, the stress concentration rate due to the back welding welding can be as low as 29 in any case. '! 'fc, Circumferential Weld Joint Circumferential Weld Joint Surface 4 Stress Concentration Pipe 2 The stress applied to this part due to internal pressure is controlled to be The same effect can be achieved with steel pipes 117r and 117l, which are steel pipes with less than three circumferential welded joints, by making the stress sufficiently lower than that applied to the circumferential welding joint s3.

, “=, :.

Next, put it in the dice IM column and be kind.

1. As shown in FIG.
? It was inserted between the copper pipes 1a and 1b, and both sides of the steel pipe [a% 1b] and the length of the short pipe 2 were welded to complete penetration welding. At this time, welding reinforcements 8a and 8b of the circumferential welding joint part 3
t;r was sufficiently removed to completely eliminate stress concentration due to the extra buildup; in particular, the final finishing direction was the same as the circumferential direction, and the finishing roughness was also set to 100μ under the hook.

Next, welded both ends of the steel pipe ia% lb, processing is performed on both ends of the integrated short pipe to form a groove l] and a straight pipe part 5b. At this time, the groove shape is very similar to a V-groove, and the second As shown in the figure, the tube is processed to have a protrusion 12' in the axial direction around the inner circumference of the tube.

Next, the melt if# of the first layer is tungsten 1! The opposing protrusions 12f were fused and welded to give a good welded build-up shape 9.10f, and the stress concentration ratio was controlled to a total of 1.5 to 2. (After 7-r, the second layer was welded by the usual method. 1.Protrusion 12 was attached without using a short pipe for υ■, and 911■ and °■ for 1) were welded using a short tube. I used a tube, but
The protrusion 912 was not attached to the former, and the latter had a diameter of f'L, and the final welding was carried out using the IktBL welding method on one side at room temperature.

Attach end plates A%B to both ends of the steel pipe welded to the traces on the J-cono as shown in Figure 1. Welding 4 was carried out in the same manner as in the case of circumferential welding and circumferential welding joint formation, and an internal pressure fatigue test was carried out.

The reason why the end plate was used is that the situation where the steel pipes are connected in a welding field can cause problems.
□ As a result of this test, in the test rows ■ and ■, there was no fracture at all from the circumferential welded joint 4, which had fatigue fractured in the conventional example, and at the same time, it was confirmed that the circumferential welded joint 3 did not undergo fatigue fracture either. did. According to the method of the present invention, the fatigue life (as shown in Table 1) is 3 to 5 times longer than the conventional method. In comparison, a short pipe was not inserted in Comparison B, but the entire inner and outer surfaces of the circumferential welded joint 3 were cut. Process to remove welding excess? In order to reduce the number of pipes that already have a short pipe shape 1, the technique used to manufacture the pipes is used.

Ru.

[Brief explanation of the drawing]

JiBl, the figure is a top view of a steel pipe circumferentially welded by the method of the present invention, Fig. 2 is a detailed sectional view of the welded joint part, and Fig. 3
The figure is a cross-sectional view of a welded part between a steel pipe and a short pipe, and the m4 figure is a cross-sectional view when the welded joint shown in FIG. 2 is welded. Code 1a, Jb...Steel pipe 2...Short pipe 3...Circumferential joint welded part 4...Circumferential joint welded part 5a15...・・・Straight pipe part 6a, 6□ force...Tapered part ga, g6...Welding excess part 9...Back i'-fill 1O...・・Single side first layer welding excess □1-:, Fl nose □2-------*
ssA%B・・・・・・End plate

Claims (1)

[Claims] ]) The end surfaces of a pair of S-tubes to be welded to be welded to each other are formed into grooves so that protrusions or protrusions protrude toward the inner periphery in the tube axis direction, and these protrusions are melted to form a first weld. A method of circumferential welding of steel pipes, which is characterized by forming layers and sequentially welding the second layer by a conventional method. 2) Between a pair of pipes to be welded to be circumferentially welded to each other, the outer diameter, circular diameter, and wall thickness of one end are substantially equal to those of the steel pipes to be welded. The wall thickness is thicker than the wall thickness of the pipe to be welded, and both ends are made of 20 feldspar.
Insert the valve and melt it with one end of the short pipe! ＃Cast pipes are circumferentially welded, and after removing the weld excess on the inner dead surface by cutting or polishing, the thick-walled short pipe is welded on one side.Characteristics and method of circumferential welding of steel pipes . 3) Between a pair of steel pipes to be welded to be circumferentially welded to each other, the outer diameter, inner diameter, and wall thickness of one end are substantially equal to those of the pipe to be welded, or the wall thickness of the other end is substantially equal to the thickness of the pipe to be welded. A pair of short pipes t1, which are thicker than the steel pipes and have straight pipe parts at both ends with a length of 20111 m, and a protrusion protrudes from the other end.
Since these protrusions face each other, one end of the short pipe and the welded pipe are inserted. d Weld and cut the welding excess on the inner and outer surfaces! 'fct;rω) After removing by friction, each of the protrusions is completely melted to form the first layer, and after the second mth μ, welding is carried out in a conventional manner or in a sequential manner.1. Circumference of the steel pipe characterized by: Welded joint method.