JPH0252155B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The disclosed technology belongs to the field of pipe end treatment technology for corrosion-resistant double-pipe unit pipes used for corrosion-resistant fluid piping such as oil country tubular goods.

Therefore, the present invention provides a unit pipe in which the outer tube is made of carbon steel and the inner tube is made of stainless steel, one of which is corrosion resistant and the other is non-corrosion resistant, before being joined with a joint,
For unit double pipes in which the inner and outer tubes are firmly fitted at the general part and not completely metallurgically connected at the tube ends, a corrosion-resistant metal such as stainless steel is welded in a ring shape to the tube ends. This invention relates to a double pipe structure of a certain end pretreatment welding unit, and in particular, a non-corrosion resistant pipe is cut thin at the end of the pipe, and a corrosion resistant metal is formed in a ring shape with the wall thickness being thinned at the pipe end and tensile force is applied in the width direction. The ends of both tubes were welded together metallurgically, and then the tube ends were machined so that the inner surfaces were flush with each other and compressive residual stress was applied to at least the outer tube. This invention relates to a double pipe structure of an end pretreatment welding unit.

<Prior art> As is well known, in order to provide pressure resistance, heat resistance, corrosion resistance, abrasion resistance, etc. to the pipe bodies of corrosive fluid piping such as oil country tubular goods and nuclear power plant piping, for example, the outer pipe is made of carbon. A double-walled pipe is used in which the inner pipe is made of stainless steel and the two pipes are joined in a predetermined manner to form a single layer.

For on-site piping, for example, as shown in FIG. etc., to connect them.

Of course, in addition to welded joints, coupling joints and flange joints may also be used.

By the way, the length of the unit double pipe 3 is limited due to the conditions of the equipment at the time of manufacture and restrictions on transportation to the site. Due to the length of time, as shown in FIG.
There is a risk that corrosion 7 may enter the area.

Generally, at the pipe end 5, the inner and outer pipes 1 and 2 are not firmly connected metallurgically due to, for example, forming the joint processing surface 8 at the equipment stage in the factory. Corrosion progresses at the interface 6 during transportation and sea transportation.

<Problems to be Solved by the Invention> To deal with this, measures such as fitting a cap or the like to the tube end 5 have been attempted, but the effectiveness varies in degree and it has not been possible to completely prevent corrosion. The drawback was that there was no.

At the tube end 5 of the unit tube, as described above, since the inner and outer tubes 1 and 2 are not completely metallurgically connected and integrated, a so-called notch effect appears. Furthermore, due to competing complex conditions such as the difference in thermal stress during welding and bonding with the weld metal, cracks 9 form in the welded part 4 from the boundary 6 between the inner and outer pipes 1 and 2, as shown in FIG. There were also problems that occurred.

On the other hand, there are, for example, the inventions disclosed in Japanese Patent Publication No. 44-5289 and the inventions disclosed in Japanese Patent Application Laid-open No. 54-78340, but these publicly known inventions are related to welding techniques for joints of multiple unit double pipes. Techniques for dealing with corrosion intrusion into the inner and outer pipes at the end of the pipe before the joint is formed, i.e. during the period from the manufacturing of unit double pipes of a set length at the factory to the installation on site. isn't it.

<Objective of the Invention> The object of the present invention is to solve problems such as corrosion intrusion at the end of the corrosion-resistant unit double pipe based on the above-mentioned prior art, and to A ring-shaped metal is pre-welded to at least the corrosion-resistant pipe side of the section, the metal joint surface on the non-corrosion-resistant pipe side is also cut to reduce the wall thickness, the corrosion-resistant metal side is made thicker, and both pipes are metallurgically joined together. In addition, it is an object of the present invention to provide a double pipe structure with an excellent end pretreatment welding unit that prevents corrosion intrusion, crack generation, etc., and is useful in the field of piping technology in various industries.

<Means/effects for solving the problem> In order to solve the above problem, the structure of the present invention, which is based on the scope of the above-mentioned claims, is as follows:
At the junction of the inner and outer tubes at the end of the unit corrosion-resistant double tube, the end of the non-corrosion-resistant tube is cut to make it thinner, and a ring-shaped ring is attached to the cut portion while applying a tensile force to the non-corrosion-resistant tube. The two pipes are metallurgically joined by overlay welding of corrosion-resistant metal, and then machined to make the pipe ends flush with each other in preparation for the subsequent joint processing, reducing the tensile force against the non-corrosion-resistant pipe. Since the ends of both pipes are metallurgically joined together by pre-treatment welding, corrosion is prevented at the boundary between the ends of both pipes before the on-site joint is connected. Technical measures have been taken to prevent penetration, cracks during welding, and stress corrosion due to compressive residual stress.

<Example> Next, an example of the present invention will be described below based on FIGS. 4 and 5. In addition, the first
Components having the same features as those shown in FIGS. 2 and 3 will be described using the same reference numerals.

A unit corrosion-resistant double tube 3 of a predetermined length is made by layering an outer tube 1 made of carbon steel and an inner tube 2 made of stainless steel, for example, by the heat expansion method, which is an earlier invention of the applicant. The inner tube 2
At the end of the tube, as shown in FIG. 4, the set length is made shorter than the outer tube 1 to form a stepped portion 10.

After manufacturing the raw tube of the unit double tube 3 in this manner, the tube end of the outer tube 1 is pulled in the axial direction by appropriate means to apply tensile stress to the outer tube 1, as shown in FIG. As shown in FIG. 4, the inner surface of the outer tube 1 is also machined by machining the tip of the stepped portion 10 shown in FIG. As shown in FIG. 5, the stainless steel build-up weld 11 is pre-welded in a ring shape to form a bonding surface and provide a metallurgical bond by more securely sealing the interface 6 between the two pipes 1 and 2. The tube end of the inner tube 2 and the inner surface (boundary surface) of the tube end of the outer tube 1 are integrally metallurgically connected by making the wall thicker.

Therefore, after pretreatment welding, the interface between the inner and outer tubes 1 and 2 is reliably joined and sealed by the thick ring-shaped overlay welding 11 at the end of the unit tube 3, and the outer tube 1 When the tensile force is released, a compressive residual stress can also be generated in the outer tube 1, the inner tube 2, especially the tube ends thereof, which prevents stress corrosion cracking.

In this case, overlay welding 11 of corrosion-resistant metal to the end of the corrosion-resistant tube 2 is metallurgically compatible with the corrosion-resistant tube 2, and compressive residual stress is easily imparted to the outer tube 1, and the amount of overlay is small. This is because there are various merits such as being easy to use.

In addition, applying thick overlay welding 11 to the outer tube 1 at the tube end basically has the same metallurgical incomplete bonding problem as described above, but the unit tube 3 is If this is done after manufacturing, it can be done under advantageous conditions such as fully equipped equipment and sufficient management, so there is no risk of the above-mentioned cracks, etc., and the unit is Misalignment during butt welding between tubes can also be prevented, and the outer tube of a non-corrosion resistant tube can be prevented from melting.

Finally, in the factory, the inner surface of the overlay weld 11 of the pre-treatment welding is machined to a specified level with the inner surface of the inner tube 2, in preparation for joint connection on site, by appropriate mechanical cutting, etc. Form a grooved surface for butt welding on the end.

In this state, even if the pipe is stored in a predetermined location in the factory, piled up in the open, or transported by sea in preparation for on-site joint connection, corrosion will not invade through the boundary surface 6 of the pipe end 5. can definitely be prevented.

When connecting the joints at the factory, if the on-site butt weld joint is performed, both pipes 1 and 2 are metallurgically connected and integrated by the overlay welding 11 of pre-treatment welding, so the inner pipe There is no misalignment between the two joints, the notch effect as shown in FIG. 3 does not occur, and the occurrence of cracks and the like is prevented.

It goes without saying that the embodiments of the present invention are not limited to the above-mentioned embodiments. For example, a ring-shaped corrosion-resistant metal is formed separately in advance and attached to the tube end of a unit tube by electron beam welding, friction welding, etc. Pretreatment welding may also be performed.

<Effects of the Invention> As described above, according to the present invention, at least the pipe end of the corrosion-resistant pipe has a stepped portion with respect to the non-corrosion-resistant pipe in the pipe end of the unit double pipe in which one of the inner and outer pipes is a corrosion-resistant pipe. The non-corrosion-resistant pipe, which has a machined surface to reduce the wall thickness, is pre-welded in a ring shape with corrosion-resistant metal under tension, and then machined in preparation for on-site joint connection. By processing the tube ends flush, the inner and outer tubes of the tube ends of the unit double tube are metallurgically reliably joined together, and therefore, after the tube is manufactured at the factory, it is not piled up in the open. There is no risk of corrosion occurring and penetrating the tube interface at the end of the unit tube during sea transportation.

In addition, the wall thickness of the end of the non-corrosion-resistant pipe is made thinner, and the built-up part of the corrosion-resistant metal is made thicker, which prevents mistakes when joining the unit pipes together, and prevents the non-corrosion-resistant pipe side from melting. You can.

Furthermore, by pre-welding a corrosion-resistant metal to the corrosion-resistant tube side, the amount of corrosion-resistant metal that is compatible with the corrosion-resistant tube can be reduced, leading to weight reduction, resource conservation, and cost reduction. .

Also, when unit pipes are connected via welded joints, no notch effect occurs, and therefore,
An excellent effect is achieved in that defects such as cracks do not occur in the welded portion.

In addition, by applying tensile stress to the non-corrosion-resistant tube before pre-welding to the tube end, the tensile force is released after machining, so at least compressive residual stress is imparted to the non-corrosion-resistant tube and the stress is reduced during operation. An excellent effect is achieved in that stress corrosion cracking does not occur.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a common double pipe joint welded, Figure 2
3 is a sectional view of a crack in the welded joint, and FIGS. 4 and 5 are process sectional views of an embodiment of the present invention. 1... Outer tube, 2... Inner tube, 6, 6'... Boundary (surface), 5... Tube end, 11... Pretreatment welding (corrosion resistant metal), 3... Double tube.

Claims (1)

[Claims] 1 In a unit double pipe structure in which one of the inner and outer pipes of the unit pipe before being joined to the joint is a corrosion-resistant pipe and pretreatment welding is performed on the pipe end at the boundary between the inner and outer pipes, the inner and outer pipes are A joining surface is cut to reduce the wall thickness at the end of the non-corrosion resistant pipe, and while a tensile force is applied to the non-corrosion resistant pipe, at least the corrosion resistant pipe side is pre-welded in a ring shape with a corrosion resistant metal. The front end is integrally connected to a non-corrosion resistant pipe, the corrosion resistant metal is mechanically jointed and formed flush with the corrosion resistant pipe, and a compressive residual stress is applied at least to the non-corrosion resistant pipe side. Processing welding unit double pipe structure.