JPH0132393B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The disclosed technology belongs to the technical field of corrosion-resistant structures of threaded joints for corrosion-resistant double pipes such as oil country tubular goods.

Accordingly, the present invention provides a structure in which at least the inner tube for the flow of a corrosive fluid is made of a corrosion-resistant material such as stainless steel, and the unit tube of the corrosion-resistant double tube is connected via a threaded joint, and the tube end of the threaded portion is made of a corrosion-resistant material. This invention relates to a joint structure in which a single-layer corrosion-resistant short pipe is metallurgically joined from the threaded surface of the pipe end to the inner surface, and the thread is machined. This invention relates to a corrosion-resistant double pipe joint structure.

As is well known, corrosion-resistant double-walled pipes such as oil country tubular goods for transporting corrosive fluids are widely used, such as cladding made by layering a stainless steel inner pipe over a pressure- and heat-resistant carbon steel outer pipe to provide corrosion resistance. It is used.

Therefore, the unit pipe length of this kind of corrosion-resistant double pipe is determined by the standard due to the size conditions from the manufacturing equipment, transportation restrictions to the site, etc. Therefore, when installing the pipe on site, the unit pipe length is set using a joint. It is designed to be connected long.

Various types are used for this joint, but
Threaded joints are widely used because of their advantages such as ease of disconnection and good sealing performance.

However, in order to provide the same corrosion resistance as that of the general pipe part, it is necessary to perform corrosion-resistant processing on the pipe end part at the connecting part such as the pipe end thread part and the coupling thread part.

For example, as shown in Fig. 1, the pipe end 4 of a corrosion-resistant double pipe 3 in which a stainless steel inner pipe 2 is clad on a carbon steel outer pipe 1 is removed by mechanical cutting of the outer pipe 1 as shown in Fig. 2. 5, as shown in Fig. 3, stainless steel overlay welding 6 is applied to the stepped portion 5 of the inner pipe 2 and outer pipe 1 for a set length, and finally, as shown in Fig. 4, by machining. A threaded portion 7 was formed.

However, this type of technology has the disadvantage that it requires a large number of man-hours and is cumbersome.

The purpose of this invention is to solve the technical problem of the corrosion-resistant pipe end of the corrosion-resistant double pipe threaded joint based on the above-mentioned prior art, to ensure good sealing performance, sufficient corrosion resistance, and easy manufacturing. It is an object of the present invention to provide an excellent corrosion-resistant double pipe joint structure that is easy to use and is useful for piping applications in various industries.

The structure of the present invention in accordance with the above-mentioned object is to form a single-layer short pipe made of a corrosion-resistant material with a predetermined length on the pipe end of a pre-made corrosion-resistant double-walled pipe with a threaded part formed in advance, and metallurgically integrally form the pipe. Alternatively, after integration, the threaded portions are machined and the unit corrosion-resistant double pipes are connected by threading to ensure sealing performance at the threaded portions, guarantee corrosion resistance, and prevent stress corrosion cracking in the portions. The gist is that the technical measures taken to achieve this goal were taken.

Next, one embodiment of the present invention will be described below based on FIG. The same parts as those shown in FIGS. 1 to 4 will be described using the same reference numerals.

In the embodiment shown in FIG. 5, the corrosion-resistant double pipe 3' of the unit pipe has a carbon steel outer pipe 1 and a stainless steel inner pipe 2.
At the tube end 4, a short stainless steel tube 8' of a set length is integrally friction welded from the front side to the inside surface in a single layer with a male thread 7 engraved in advance.
0 and coupled metallurgically through coupling 9
The entire area is undercovered.

Therefore, the short pipe 8 in this embodiment has a sufficiently longer axial length than the overlay shown in FIG. Also, there is no tensile residual stress.

In the above configuration, the unit corrosion-resistant double pipe 3',
3' are fastened and connected by the coupling ring 9 and operated in the illustrated state, the pipe end is a single-layer corrosion-resistant pipe, so even if there is a leak of the corrosive fluid flowing through the fastening seal part, it exhibits a sufficient corrosion-resistant function. However, as mentioned above, there is no tensile residual stress, so stress corrosion cracking does not occur.

Of course, sealability is fully guaranteed.

It goes without saying that the embodiments of the present invention are not limited to the above-mentioned embodiments; for example, various embodiments can be adopted, such as being able to be used not only as a coupling joint but also as a box joint.

Furthermore, in addition to double pipes, triple pipes and quadruple pipes can be used as corrosion-resistant double pipes, and fitting pipes other than clad pipes are of course also applicable.

As described above, according to the present invention, a single-layer corrosion-resistant material short tube is metallurgically installed at each end of the threaded joint of a multi-functional corrosion-resistant double pipe from the external threaded portion to the internal surface through which the corrosive fluid flows. Because the tube ends are integrally connected and the threaded parts are machined, there is no complicated welding at the tube ends, so there is no material change.
Corrosion resistance and physical properties do not deteriorate, and no tensile stress is generated, so an excellent effect is achieved in that stress corrosion cracking does not occur.

Further, since the corrosion-resistant material is provided in a single layer, excellent effects such as improved reliability due to uniformity of sealing performance and constant accuracy of the joint portion are produced.

Furthermore, there are fewer manufacturing steps, which increases precision, makes management easier, and reduces costs.

Furthermore, single-layer short tubes with metallurgically bonded tube ends have a degree of freedom in design regarding their length, and have the advantage of being flexible in designing designs that improve the sealing performance and corrosion resistance of the joint.

[Brief explanation of drawings]

Figures 1, 2, 3, and 4 are partial cross-sectional views explaining the process of forming a pipe end joint of a corrosion-resistant double pipe based on the prior art;
The figure is a partial sectional view of one embodiment of the invention. 2...Inner pipe, 3'...Double pipe, 7...Threaded part,
8,8'...Short tube.

Claims (1)

[Claims] 1. In a corrosion-resistant double pipe joint structure in which the threaded end of a joint of a double pipe whose inner pipe is made of a corrosion-resistant material is integrally joined with a corrosion-resistant material, the end of the threaded part of the double pipe is A corrosion-resistant double pipe joint structure characterized by a single-layer corrosion-resistant material short pipe metallurgically joined and machined from the inner surface to the outer surface.