JPH03207575A - Circumferential welding method for double pipes - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to line pipes for transporting oil or natural gas containing corrosive substances, or when double pipes are used for piping in the chemical industry. This relates to a circumferential joint welding method between double pipes.

[Conventional technology]

Corrosion-resistant double pipes, which reduce the amount of expensive corrosion-resistant alloys used and have increased strength, are used for line vibrators and piping in the chemical industry, and the field of use has recently expanded considerably.

Single-walled pipes include clad pipes in which metal materials of different components are joined together, and pipes in which inner and outer pipes are fitted together using a heat expansion method, etc., and both are made of composite characteristics that have the characteristics of both the inner and outer materials. The effect is demonstrated as follows. However, when installing or piping double pipes, it is necessary to weld circumferential joints between the double pipes, which have a limited length, and conventionally this welding has had problems.

As a conventional circumferential joint welding method for a double pipe, for example, when the outer pipe is made of carbon steel and the inner pipe is made of a corrosion-resistant material such as austenitic stainless steel or Inconel high alloy, welding is performed as shown in Fig. 4. , a method in which the entire thickness of the pipe is joint welded using an expensive corrosion-resistant welding material, or after welding only the inner pipe part using a corrosion-resistant welding material as shown in Figure 5,
A method of welding pure iron or nickel to form an intermediate layer, and then welding to the final layer using carbon steel welding material,
Furthermore, as shown in Fig. 6, there is a known method in which the outer tube is first welded from the outer surface of the tube using a carbon steel welding material, and then the inner tube is welded from the inner surface of the tube using a corrosion-resistant welding material. ing. Furthermore, in the case of a double pipe made of materials with significantly different melting points, such as titanium for the inner pipe and carbon steel for the outer pipe, it is difficult to fusion weld these dissimilar metals, and there are currently no effective joining methods. It has not been done.

[Problems to be Solved by the Invention] In the conventional circumferential joint welding method for double pipes, the method of welding using only corrosion-resistant materials generally has poor workability with the welding rod in coated arc welding, and the GTAW method ( Since the welding speed is low in TIG welding), the construction efficiency is lower than in the case of carbon steel pipes. Furthermore, when the welding material cost 1- is high and the outer tube is made of a high-strength material, there is a problem that the joint strength is insufficient.

The method of welding the intermediate layer with pure iron or nickel improves joint strength, but due to the dilution of components from the corrosion-resistant material layer, a hardened part is formed in the intermediate layer or the next layer, and there is a high risk of cracking. .

In the method of welding using corrosion-resistant material from the inner surface of the pipe, it is necessary to weld two or three layers of corrosion-resistant material to ensure corrosion resistance due to the dilution of the components from the carbon steel of the outer pipe. It is inefficient in cases such as laying construction. Furthermore, in the above method, the inner surface of the joint weld and its vicinity undergoes multiple thermal cycles due to multilayer welding, resulting in deterioration of corrosion resistance due to oxidation of the surface of the weld. Time hank shield construction was required.

In addition, in the case of double-walled pipes, it is not easy to perform uranami welding using corrosion-resistant materials such as Inco, and in order to avoid some dilution due to the fusion of the inner and outer pipe materials, it is necessary to match the grooves on-site. is particularly important, and requires strict management of offsets and gaps, which poses a problem of inefficiency.

Furthermore, in non-destructive inspection of joint welds using X-rays or the like, it is not easy to determine whether the detected defect is in the weld on the inner tube side or the outer tube side.

The present invention provides I'? between double tubes. In il joint welding,
The primary objective is to perform welding with high work efficiency at low cost for welding materials, and to maintain the high strength and high corrosion resistance characteristics inherent in the double pipe at the welded part. A second object of the present invention is to provide a method for joining double pipes in which materials having significantly different melting points are combined, such as titanium for the inner pipe and carbon steel for the outer pipe. The third objective is to provide a double pipe with high matching performance that facilitates groove alignment during on-site joint welding. Finally, the fourth object is to make it possible to easily identify the defect position of a joint weld. [Means and actions for solving the problem] The gist of the present invention is as follows.

(1) When circumferentially welding double pipes made up of an outer pipe and an inner pipe made of metal abrasives with different compositions, the end of one double pipe is removed with the inner pipe removed and the outer pipe A gap is formed between the tube and the inner tube, and the tube end of the other double tube removes the outer tube and forms a gap between the outer tube and the inner tube, and then the outer tubes are separated from each other and the inner tube. A circumferential joint welding method for double pipes, which is characterized by butting the pipes together and welding them individually.

(2) When circumferentially welding double pipes in which an outer pipe and an inner pipe made of metal materials with different components are fitted together, the inner pipe at the end of one double pipe is removed, and the inner pipe at the end of the other double pipe is welded together. The double pipe is made by removing the outer pipe at the end of the pipe to expose the inner pipe, compressing the exposed inner pipe to reduce its diameter, and forming a gap between the outer pipe end and the inner pipe. A double pipe characterized in that the inner pipe of the reduced diameter portion is inserted into the inner pipe of the one double pipe, the outer pipes of both double pipes are butted together, and the outer pipes and the inner pipes are welded to each other. Circumference joint welding method for pipes.

The double pipes to which the present invention is applied include so-called clad pipes in which an outer pipe and an inner pipe are joined together, and double pipes in which an outer pipe and an inner pipe are fitted together by a heat expansion method or the like. Fitting by the thermal expansion method is performed, for example, by inserting an inner tube into an outer tube that has been heated and expanded, and cooling the outer tube while applying water pressure to the inner tube. The metal materials for the outer and inner tubes include carbon steel, low alloy mesh, high alloy steel, stainless steel, super alloy, and titanium. There are various combinations of titanium alloys, copper alloys, etc., and depending on the atmosphere inside and outside the pipe, the properties of the gas or liquid being transported, operating conditions, double pipe installation or piping conditions, etc., corrosion resistance and wear resistance can be improved. The material is designed to have properties such as strength.

The double pipe to which claim (1) is directed is a so-called cratted pipe in which an outer pipe and an inner pipe are joined.

The method of claim ( ) will be explained with reference to FIG. Figure 1 (
As shown in a), the double pipe 1 is composed of an outer pipe 2 and an inner pipe 3, which are made of metal abrasives with different components. It consists of an inner tube 3'.

As shown in FIG. 1(b), one double-walled tube 1 has an inner tube 3 at the tube end removed, and a gap 4 is formed between the outer tube 2 and the inner tube 3, and the other double-walled tube 1 is In the tube 1', the outer tube 2' at the tube end is removed and a gap 4' is formed between the outer tube 2' and the inner tube 3'. After beveling the outer tube and inner tube, both double tubes 1. (2) The outer tube 2.2' and the inner tube 3.3' are butted together as shown in Figure 1 (C) and welded together.

The outer tube and inner tube at the tube ends can be removed as shown in FIG. 1(b) and the gaps 4 and 4' can be formed by cutting with a cutting tool or the like. The outer tubes 2 and 2' are welded from the outside, and the inner tubes 3 and 3' are welded from the inside. At this time, care must be taken to ensure that the welded parts do not come into contact with each other and fuse together. If necessary, insert a refractory ribbon etc. into the gap 4.4',
It is also possible to prevent contact fusion. In addition, Fig. 1 (C)
shows an axial cross section after circumferentially welding the double pipe 1 and the double pipe 1', the upper side of the figure is the outer surface, the lower side is the inner surface, 5 is the welded part of the inner pipe, 6 is the first layer welded part of the outer pipe, 7 shows the laminated welded part of the outer tube.

In the method of claim (1), when the target is a clad pipe and the gaps 4 and 4' are formed by cutting with a cutting tool as shown in FIG. 1(b), ,■
There is a method of removing both the inner tube and the outer tube, but in either case, the boundary portion between the inner tube and the outer tube is removed so that it does not remain at the part 5.6 to be welded in FIG. 1(C).

The double tube to which claim (2) is directed is a double tube in which an outer tube and an inner tube are fitted together by a thermal expansion method or the like.

The method of claim (2) will be explained with reference to FIG. First, as shown in Fig. 2(a), the inner tube 3 at the end of one double tube 1 is removed, and the outer tube 2' at the end of the other double tube 1' is removed. The exposed inner tube 3' is compressed to reduce its diameter as shown in FIG. 2(b), and a gap 4' is formed between the outer tube 2' and the inner tube 3' at the tube ends. Then, as shown in Fig. 2 (C), insert the inner tube 3' of the double tube 1' with the reduced diameter into the inner tube 3 of the double tube 1, and then insert the inner tube 3' of the double tube 1' into the inner tube 3 of the double tube 1, The tubes 2.2' are butted against each other, and the outer tubes 2, 2' and the inner tubes 3.3' are welded, respectively. To remove the outer tube and inner tube at the tube ends as shown in FIG. 2(a), height cutting or the like can be performed. The diameter of the exposed inner tube 3' can be reduced using a hydraulic swaging machine or the like. The outer tube ±2.3' is welded from the outside, and the inner tube ±3.3' is welded from the inside. At this time, the inner tube must be welded in the same way so as not to melt the inner tube when welding the outer tube. Be careful not to melt the outer tube during welding. If necessary, it is also possible to insert a non-fusible ribbon or the like into the gap 4' to prevent contact fusion of the inner tube 3'.

According to the method of claim (1), since the welded part 5 of the inner pipe and the first layer welded part 6 of the outer pipe are separated in the axial direction of the double pipe, they can be welded without coming into contact with each other. , inner tube welding part 5
Since gaps are formed between the outer tube and the outer tube and between the outer tube first layer welded portion 6 and the inner tube, they are not fused by welding, and the components in both welded portions 5.6 are not diluted. Therefore, for example, in the case of a double tube in which the inner tube is made of a thin-walled corrosion-resistant material and the outer tube is made of a thick-walled, high-strength material, sufficient corrosion resistance can be ensured by welding the inner tube 33' in just one pass, and the outer tube 33' can be welded in just one pass. ,2
For the welding of 10, sufficient joint strength can be ensured by conventional high-efficiency lamination welding using carbon steel welding materials. Furthermore, according to this method, even in the case of a double pipe made of a combination of materials with significantly different melting points, such as the inner pipe made of titanium and the outer pipe made of carbon steel, the outer pipe and inner pipe can be welded separately. This makes it possible to construct joints. Furthermore, in this method, due to the insulation effect of the gap, the inner tube section is not directly subjected to multiple thermal cycles due to welding of the outer tube section, so when constructing pipes, etc., Ar Hank shield construction using gas or the like can be simplified, construction costs can be significantly improved, and when the inner pipe is a Cr-containing steel pipe, there is little deterioration in corrosion resistance due to thermal effects. Further, since the inner tube welded portion 5 and the outer tube welded portion 6.7 are located apart in the axial direction, it is easy to detect the position of defects by non-destructive inspection such as X-rays after welding.

The gap 4.4' may be of a size that does not allow the inner tube weld 5 to come into contact with the outer tube and the outer tube first layer weld 6 to not come into contact with the inner tube, and may vary depending on the wall thickness of the tube, welding method, etc. It can be set as appropriate. For example, when the GTAW method is employed as the welding method, the thickness t11 of the gaps 4, 4' should be 1 mm or more, and if this is the thickness, there will be no effect on properties such as corrosion resistance and strength.

According to the method of claim (2), in addition to the effect of the method of claim (1), as shown in FIG.
Since the inner tube 3' of the double tube f is inserted inside, the groove alignment work during circumferential joint welding becomes extremely easy, and at the same time, the accuracy of the butt alignment is improved. At this time, the outer surface of the inner tube 3'
It is preferable to reduce the diameter of the inner tube 3' so that it rubs against the inner surface of the tube. Furthermore, according to this method, there is no need to precisely cut the inner tube and outer tube material, and the gap can be formed by extremely simple swaging, and the strength of the joint is not impaired by cutting the base material. When welding the outer tube by hand, as shown in Fig. 3, a step is provided at the end of the inner tube 3 so that the tip of the inner tube 3' is in contact with the inner tube 3', and the outer tube is welded between the outer tubes 2 and 2'. A predetermined root gap 8 can be provided.

[Example] Outer diameter 5.5 inches, thickness 1 4. 0 mm AP
I standard, 5LX We carried out construction experiments using the method, and evaluated the workability, soundness of joint welds, joint strength, corrosion resistance, construction efficiency,
Welding material costs and other factors were compared and examined. The result is the first
Shown in the table. The soundness of the welded joint is determined by performing PT tests and RT tests during and after welding, then microscopically inspecting the cross section of the welded joint, and performing front, back, and side bending tests on the joint. Comparisons were made based on the presence or absence of defects such as cracks. As a result, it was confirmed that in Conventional Example 5, due to component dilution from the first layer of Inconel 625, a hardened portion was formed in the intermediate layer or the first layer of carbon steel, and cracks occurred. The corrosion resistance of the welded joint was determined by a pitting test according to ASTM G-48A, and those with good pitting corrosion resistance were marked with a circle, and those with very good pitting corrosion resistance were marked with a mark of ◎.

The strength of the welded joint is determined by the tensile test results of the welded joint of the outer pipe.
All of them broke at the base material and the tensile strength satisfied the API standard, so they were marked O. The welding material cost was a relative evaluation within this example, where ◯ was cheap, × was 13 expensive, and △ was in between. Note that the Inconel 625 used as the filler material has a higher corrosion resistance than the Incoloy 825 in the inner tube.
The outer tube has a yield strength of X60 or higher. The reason for the difference in the corrosion resistance of the welded joints is that in the conventional example, the outer tube was strongly affected by heat during welding, and oxide scale was likely to grow on the surface of the uranami bead, and that the cracking of the uranami bead was Whereas it is easy to be diluted, the method of the present invention is not affected by these effects. This is because there is no J. Groove alignment was performed in Invention Examples 2 and 3
We confirmed that by using the pipe insertion method as shown in the figure, it is possible to set butts with little offset in a short time without making any fine adjustments.

Furthermore, when adopting the SMAW method as the welding method for the outer tube part, the groove shape as shown in Example 3 of the present invention (Fig. 3) can be used to manage the root gap, which requires precision and a long time. It was confirmed that this can be omitted. Regarding the joint welding arc time, in the example of the present invention, the inner blue part welding is completed in one layer, so efficiency is very high. This is extremely effective in pipeline construction, etc., where a large number of welds must be performed in succession.

The overall joint welding arc time (minutes) for the example of the present invention is 4.5 minutes for the conventional example when the inner and outer tubes are welded at the same time.
In conventional example 6, when the inner tube is welded and then the outer tube is welded, the first layer of the outer tube is first welded, and then the inner and outer tubes are welded at the same time. In the example of the present invention and the conventional example 56, a carbon steel filler metal capable of obtaining a high welding rate was used as the filler metal for outer tube welding, so the overall arc time was shorter than that of the conventional example 4. In the example of the present invention, the inner and outer tubes were welded at the same time, so construction could be completed in the shortest time, whereas in the conventional example 5, stainless steel filler material (JIS standard Y3 0 9Mo) was used for a part of the outer tube welding. Therefore, it takes a long time. Regarding the strength of the joint welded part, in Conventional Example 4, there is a limit to the strength due to the characteristics of the filler material Inconel 625, whereas in the case of the present invention, the filler material in the outer tube part is adjusted according to the required strength. Since it can be designed to a certain extent, for example, X7
It is possible to obtain a joint strength equivalent to 0 or X80. In addition, in non-destructive inspection such as X-rays after welding15, in the case of the present invention, since the inner tube weld and the outer tube weld are separated in the axial direction, it is easier to detect defect positions than with conventional methods. be.

As described above, according to the present invention, it is possible to obtain the high strength and excellent corrosion resistance characteristic of a double pipe in the welded part, and also to significantly improve work efficiency and reduce the cost of welding materials. Furthermore, it is possible to construct a joint for a double pipe made of materials with significantly different melting points, such as a titanium double pipe.

1 6 [Effects of the Invention] According to the present invention, a double pipe in which the outer pipe and the inner pipe are made of metal materials with different components, for example, a corrosion-resistant double pipe in which the inner pipe is made of a corrosion-resistant material and the outer pipe is made of a high-strength material. When pipes are circumferentially welded together, construction efficiency and cost are significantly improved, and the original characteristics of the double pipe are maintained in the welded part. Furthermore, according to the method of claim (2), the groove alignment work becomes easier and the accuracy of the alignment improves. Therefore, it will greatly contribute to improving the construction of double-pipe joints, for which demand is expected to increase in the future, for line pipes that transport oil and natural gas containing corrosive substances, and for various chemical industries, etc., and will have industrial value. is enormous. Furthermore, according to the present invention, it is possible to construct a joint for a double pipe that combines materials with significantly different melting points.
For example, the field of application of titanium double tubes will be greatly expanded.

[Brief explanation of drawings]

1 to 3 are diagrams for explaining the present invention. 4 to 6 are diagrams showing a conventional joint welding method for double pipes. l8 1.1'...double tube, 2.2'...outer tube, 3,3'
... Inner pipe, 4.4'... Gap, 5... Inner pipe welded part, 6... Outer pipe first layer welded part, 7... Outer pipe laminated welded part. 19

Claims (2)

[Claims] (1) When circumferentially welding double pipes made up of an outer pipe and an inner pipe made of metal materials with different components, the pipe end of one double pipe is removed by removing the inner pipe and and the inner tube, and the tube end of the other double tube removes the outer tube and forms a gap between the outer tube and the inner tube, and then the outer tubes and the inner tubes A circumferential joint welding method for double pipes, which is characterized by butting together and welding each part. (2) When circumferentially welding double pipes in which an outer pipe and an inner pipe made of metal materials with different components are fitted together, the inner pipe at the end of one double pipe is removed, and the inner pipe at the end of the other double pipe is welded together. The double pipe is made by removing the outer pipe at the end of the pipe to expose the inner pipe, compressing the exposed inner pipe to reduce its diameter, and forming a gap between the outer pipe end and the inner pipe. A double pipe characterized in that the inner pipe of the reduced diameter portion is inserted into the inner pipe of the one double pipe, the outer pipes of both double pipes are butted together, and the outer pipes and the inner pipes are welded to each other. Circumference joint welding method for pipes.