JPH0318475A - Method for welding peripheral joint of duplex tube - Google Patents

Abstract

PURPOSE:To perform welding with high working efficiency at the inexpensive welding material cost by forming gaps between outer tube and inner tube of tube end parts of duplex tube abutting outer tubes and inner tubes on each other respectively and welding the outer tubes and the inner tubes from the tube exterior side and the tube interior side separately respectively. CONSTITUTION:The gap 4 is formed between the outer tube 2 and the inner tube 3 of the tube end part of the duplex tube 1 and the gap 4' is formed between the outer tube 2' and the inner tube 3' of the tube end part of the duplex tube 1' and the outer tubes 2 and 2', and the inner tubes 3 and 3' are abutted on each other and welded together separately respectively. The outer tubes 2 and 2', and the inner tubes 3 and 3' are welded from the exterior side and the interior side, respectively and at this time, the care is taken so that weld zones are not brought into contact and fused with each other. By this method, working efficiency is improved and the working material cost can be reduced.

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 pipes and piping in the chemical industry, and the fields of use are expanding more and more recently.

Double pipes include clad pipes in which metal materials of different compositions are joined together, and pipes in which inner and outer pipes are fitted together using heat expansion methods, etc. Both are composite pipes that have the characteristics of both the inner and outer materials. It is effective as a special material. 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 for the conventional circumferential joint welding method for double pipes, for example, when the outer pipe is made of carbon steel and the inner pipe is made of corrosion-resistant materials such as austenitic stainless steel and Inconel high alloy, welding is performed as shown in Figure 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.

[Problem to be solved by the invention]

In the conventional circumferential joint welding method for double pipes, welding using only corrosion-resistant welding materials has a lower welding speed and lower construction efficiency than carbon steel pipes, and the cost of welding materials is high. When the outer tube is made of a high-strength material, a problem arises in that the joint strength is insufficient. In addition, although the method of welding the intermediate layer with pure iron or nickel can improve the joint strength, there is a risk that a hardened part will be formed in the intermediate layer or the next layer due to the dilution of components from the corrosion-resistant material layer, resulting in cracking. is large. Furthermore, 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 outer pipe. It is inefficient in cases such as laying construction. Furthermore, in the above method, the welded part of the inner tube and its vicinity undergoes multiple thermal cycles due to multilayer welding, resulting in the problem of deterioration of corrosion resistance due to oxidation of the surface of the part, and in order to prevent this, it is necessary to Time-consuming back shield construction was required.

The object of the present invention is to perform circumferential joint welding between double pipes with high work efficiency at low welding material costs, and to maintain the high strength and high corrosion resistance characteristics inherent to double pipes in the welded part. The first purpose. 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.

[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 materials with different components,
A gap is formed between the outer tube and the inner tube at the tube ends of both double tubes, and the outer tubes and the inner tubes are butted against each other, so that the outer tube is on the outer surface of the tube {! ! ! t, a circumferential joint welding method for double pipes, characterized in that the inner pipes are individually welded from the inside surface of the pipe.

(2) When circumferentially welding double pipes composed of an outer pipe and an inner pipe made of metal materials with different components,
A gap is formed between the outer tube and the inner tube at the tube ends of both double tubes, and a gap is also provided between the butted outer tubes, and after the inner tubes are first butted and welded, the outer tubes are welded together. A circumferential joint welding method for double pipes, characterized in that the gap is bridged with an insert member made of the same material as the outer pipes, and the outer pipes are welded together from the outer surfaces of the pipes.

(3) When circumferentially welding double pipes made up of an outer pipe and an inner pipe made of metal materials with different components,
A gap is formed between the outer tube and the inner tube at the tube ends of both double tubes, and a gap is provided between the butted outer tubes, and the inner tubes are first butted and welded, and then the welded A circumferential joint welding method for double pipes, characterized in that the outer circumference of the inner pipe is covered with a non-fusible spacer and the outer pipe is welded from the outer surface of the pipe.

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 steel, high-alloy steel, stainless steel, super alloy, titanium, titanium alloy, copper alloy, and other combinations. Materials are designed to have characteristics such as corrosion resistance, abrasion resistance, and strength, depending on the properties of the pipes and liquids, operating conditions, installation of double pipes, piping conditions, etc.

In the method of claim (1), as shown in the axial cross-sectional view of FIG.
A gap 4' is formed between the outer tube 2' and the inner tube 3' at the tube end of the double tube 1', and the outer tubes 2 and 2' are connected to each other, and the inner tubes 3 and 3' are connected to each other. Butt them together and weld each one separately. This can be done by forming the gaps 4, 4' or cutting with a cutting tool. The outer tube 2.2' is welded from the outside side, and the inner tube 3.2' is welded from the outside side.
3' are welded from the inner side, but at this time, be careful not to let the welded parts come into contact with each other and fuse together. If necessary, it is also possible to insert a copper ribbon or the like into the gap 4.4' to prevent contact fusion. In addition, Figure 1 shows the process of circumferential joint welding of double pipe 1 and double pipe 1' in axial cross section. The upper side of each figure is the outer surface, the lower side is the inner surface, and 5 is the inner surface. 6 shows the first M welding part of the outer pipe, and 7 shows the whole outer pipe welding part.

The method of claim (2), as shown in FIG. Provide a gap between the inner tubes 3.3 and 3.
’ After butt welding the outer tube 2 as shown in (C).
, 2' is bridged with an insert member 8 made of the same material as the outer tube, and the outer tubes 2, 2' are connected as shown in (d) to (e).
’ are welded together. The inner tubes 3, 3' can be welded from the outside or the inside, and the outer tubes 2.2' can be welded from the outside. As for the method of welding the inner tubes 3, 3' from the outer surface side, the inner tubes 3, 3' are welded from the outer surface side as shown in FIG.
3' are abutted against each other, a welding torch and a welding wire are placed between the outer tube 2 and the outer tube 2' from the outer surface side, and Uranami welding is performed by using the gap to aim at the abutting portion of the inner tube. Inner tube 3
．． In order to weld the outer tubes 2 and 2' together after welding the outer tubes 2 and 2' together, attach the ring-shaped insert member 8 cut in half from the outside and attach the outer tubes 2 and 2' together as shown in (C). This is done by means such as filling in the gaps. The insert member 8 is made of the same type of material as the outer tube, and the contact surface with the outer tube 2.2' is melted to have a good uranami bead without poor penetration, and the first layer of the outer tube is welded. It is preferable to form part 6.6'. At this time, be careful not to melt the inner tubes 3, 3'. If necessary, it is also possible to insert a copper ribbon or the like into the gap 4.4' to prevent contact fusion. After welding the insert member 8, the inside of the groove of the outer tubes 2, 2' is welded using a welding material of the same type of material. Note that if the strength of the outer tube is not so important, an insert member 8 made of a material different from that of the outer tube may be used.

The method of claim (3), as shown in FIG. 3(a), forms gaps 4.4' at the pipe ends of the double pipes 1, 1' in the same manner as the method of claim (2). , and a gap is provided between the outer tubes 2.2', and the inner tubes 2.2' and 3.3' are butt welded as shown in (b). After that, as shown in (C), the outer circumference of the inner tube is covered with a non-fusible spacer 9, and the outer tubes 2 and 2' are welded and connected from above, and the inside of the groove is connected to the outer tube in the same system as the outer tube. Welding using welding materials made of materials. Welding between inner tubes can be performed from the outside or inside, and welding between outer tubes can be performed from the outside. In order to weld the inner tube from the outer surface side, it may be performed in the same manner as in the method of claim (2). In order to cover the outer periphery of the inner tube with the spacer 9, a ring-shaped piece cut in half is used, and the spacer 9 is attached from the outer side as shown in FIG. 3(C). A non-fusible material is used as the spacer 9, which assists in the welding of the outer tubes 2, 2' in a bead shape and at the same time prevents the inner tubes 3, 3' from melting.

In claims (1) to (3), the groove shape including the gap 4.4' or the protrusion. The fitting conditions (root gap) and the shapes and dimensions of the insert member 8 and spacer 9 are appropriately set to the optimum values according to the welding method to be applied. Furthermore, in claims (1) to (3), the butt welding of the outer tubes 2, 2' and the inner tubes 3, 3' can be carried out without using welding material if necessary.

According to the method of claim (1), the outer tube 2.2' and the inner tube 3,
Since a gap 4.4' is defined between r, welding of the inner tube and first N welding of the outer tube can be performed without contact and fusion with the facing outer and inner tube sides, respectively, and both welds can be welded. The power of parts 5 and 6 will not be 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, the inner tubes 3, 3'
Sufficient corrosion resistance can be ensured by single N welding using corrosion-resistant welding materials, and sufficient joint strength can be obtained by welding the outer tubes 2 and 2' with high efficiency welding using high-strength welding materials. . In addition, with this method, the area near the welded part of the inner pipe does not undergo multiple thermal cycles due to welding of the outer pipe, so it is simple to install a back shield to prevent oxidation on the surface of the part when laying pipes. construction efficiency can be greatly improved. Furthermore, even in the case of a double pipe made of materials with significantly different melting points, such as the inner pipe made of titanium and the outer pipe made of carbon steel, the joint can be easily constructed by welding the outer pipe and inner pipe individually. can be done. Note that gaps 4 and 4' are provided so that the outer tube or the welded part of the outer tube is not melted when the inner tube is welded.
It is sufficient that the size does not melt the inner tube or the welded portion of the inner tube when the outer tube is welded, and is set appropriately depending on the wall thickness of the tube, the welding method, etc.

According to the method of claim (2), in addition to the effect of the method of claim (1), both the inner tube and the outer tube can be welded from the outside surface side, so even in the case of small diameter tubes for which internal welding is difficult. It has the advantage of being easy to construct. Furthermore, when the inner tube is welded from the inner surface side, the shape of the Uranami bead can be visually inspected from the outer surface side using the gap between the outer tube parts. The dimensions of the gap 4.4' may be approximately the same as in claim (1).

According to the method of claim (3), due to the gap 4.4' and the spacer 9, the inner pipe welded part 5 and the outer pipe first layer welded part 6 can be welded without contacting each other and fusing together during welding, and both welds can be welded together. Part 5
, 6 are not diluted. Therefore, the same effects as in claim (1) can be obtained. Furthermore, since both the inner tube and the outer tube can be welded from the outside surface side, claim (2)
The same effects can also be obtained. The dimensions of the gap 4.4' may be approximately the same as in claim (1).

〔Example〕

Outer diameter 5. 5 incL 14.0 mm thick X60 seamless steel tube with a thickness of 3. We conducted construction experiments using various circumferential joint welding methods using double pipes in which inner pipes made of 0- Incoloy 825 TIG welded pipes were fitted using a heat expansion method, and we evaluated the workability, soundness of welded parts, Joint strength, corrosion resistance, construction efficiency, welding material cost, and other aspects were compared and examined. The results are shown in Table 1.

In Table 1, the corrosion resistance of the joint weld is AST? 'IG
A pitting corrosion test was conducted using -48A, and those with good pitting corrosion resistance were marked with a circle, and those with very good pitting corrosion resistance were marked with an ◎ mark.

The strength of the welded joint is determined by the tensile test results of the welded joint of the outer pipe.
All fractured at the base material, and the tensile strength was API standard (X60
) was satisfied, so it was marked O. Welding material costs were evaluated as ○ (inexpensive), △, and × (expensive) in this example.

The Inconel 625 used as the filler material has better corrosion resistance than the Incoloy 825 used in the inner tube, and yield strength of X60 or higher than that of the outer tube. 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 This is because the method of the present invention is not affected by dilution, whereas it is easily diluted. Regarding the efficiency of joint welding, in the example of the present invention, the inner blue part welding is completed in one layer, so the efficiency is very high. This is extremely effective in pipeline construction, etc., where a large number of welds need to be performed in succession. Overall time for joint welding construction efficiency (
Inventive Example 1, when the inner and outer tubes are welded at the same time, Inventive Examples 2.3 and Conventional Example 4.5, when the inner tube is welded and then the outer tube is welded, and the conventional example 6
is the time when the first layer of the outer tube is first welded, and then the inner and outer tubes are simultaneously welded. Invention examples 1 and 2
．． 3 and Conventional Examples 5 and 6 use carbon steel wire capable of achieving a high welding rate as the filler material for outer tube welding, so the overall arc time is shorter than that of Conventional Example 4. Inventive example 1 welded the inner and outer tubes simultaneously, so construction could be completed in the shortest time, and in conventional example 5, Y309 Mo was used for part of the outer tube weld.
Since wire was used, it took a long time. Regarding the strength of the joint welds, in all cases a strength equivalent to that of the X60 base metal of the outer tube was obtained, but in Conventional Example 4, this was the limit. In the method of the present invention, the composition of the filler material for the outer tube portion can be designed according to the required strength, so that a strength equivalent to, for example, X70 or X80 can be obtained.

According to the method of the present invention, it is possible to obtain the high strength and excellent corrosion resistance characteristic of a double pipe in the welded portion, and also to significantly improve work efficiency and reduce the cost of welding materials.

Moreover, it is possible to construct a joint for a double pipe made of a combination of materials with greatly different melting points, such as a titanium double pipe.

〔Effect of the invention〕

According to the method of the present invention, a double pipe in which the outer pipe and the inner pipe are made of metal materials with different compositions, for example, corrosion-resistant double pipes in which the inner pipe is made of a corrosion-resistant material and the outer pipe is made of a high-strength material, can be circumferentially welded together. In doing so, work efficiency is significantly improved and welding material costs can be reduced. Moreover, the original characteristics of the double pipe are maintained even at the welded part. Therefore, it will greatly contribute to improving the construction of double pipes, for which the 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 the industrial value will increase. It is enormous.

Further, according to the method of the present invention, it is possible to construct a joint for a double pipe made of a combination of materials having greatly different melting points, so the field of application, such as titanium double pipe, is greatly expanded.

[Brief explanation of drawings]

Figures 1 to 3 are axial cross-sectional views of double pipes to be circumferentially welded by the method of the present invention, and Figures 4 to 6 are diagrams showing conventional circumferential joint welding methods for double pipes. . 1. 1': Double pipe, 2.2': Outer pipe, 3, 31
, Inner pipe, 4.4': Gap, 5: Inner pipe welded part, 6: Outer pipe first N welded part, 7: Entire outer pipe welded part, 8: Insert member,
9: Spacer

Claims (3)

[Claims] (1) When circumferentially welding double pipes made up of an outer pipe and an inner pipe made of metal materials with different components,
A gap is formed between the outer tube and the inner tube at the tube ends of both double tubes, and the outer tubes and the inner tubes are butted against each other, and the outer tube is separated from the outer surface of the tube, and the inner tube is separated from the inner surface of the tube. A circumferential joint welding method for double pipes, which is characterized by welding to the circumference of a double pipe. (2) When circumferentially welding double pipes composed of an outer pipe and an inner pipe made of metal materials with different components,
A gap is formed between the outer tube and the inner tube at the tube ends of both double tubes, and a gap is also provided between the butted outer tubes, and after the inner tubes are first butted and welded, the outer tubes are welded together. A circumferential joint welding method for double pipes, characterized in that the gap is bridged with an insert member made of the same material as the outer pipes, and the outer pipes are welded together from the outer surfaces of the pipes. (3) When circumferentially welding double pipes made up of an outer pipe and an inner pipe made of metal materials with different components,
A gap is formed between the outer tube and the inner tube at the tube ends of both double tubes, and a gap is provided between the butted outer tubes, and the inner tubes are first butted and welded, and then the welded A circumferential joint welding method for double pipes, characterized in that the outer circumference of the inner pipe is covered with a non-fusible spacer and the outer pipe is welded from the outer surface of the pipe.