JPS63165028A - Manufacture of corrosion resistant double pipe - Google Patents

Abstract

PURPOSE:To obtain the corrosion resistant double pipe having no rupture caused on the way of the expansion of an inner pipe nor variation in the thickness by respectively specifying the material of an outer pipe and inner pipe, inserting the inner pipe into the outer pipe and expanding the inner pipe with its pressurization by heating it at a specific temp. CONSTITUTION:A carbon steel, low alloy steel or an austenite stainless steel is selected as the material for an outer pipe 1 and on the other hand the outer pipe 1, inner pipe 2 are respectively prepared by selecting the Ti, Zr and these alloy steels excellent in a corrosion resistance and having smaller thermal expansion coefft. than that of the material of the outer pipe 1 as the material for the inner pipe 2. A clad pipe is then made by inserting the inner pipe 2 into the outer pipe 1, heated at 350-800 deg.C, the inner pipe 2 is expanded with its pressurization simultaneously and a corrosion resistant double pipe is obtd. by compactly fixing the inner pipe 2 and outer pipe 1 by cooling them thereafter.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a method for manufacturing a corrosion-resistant double-walled pipe, and in particular, an outer pipe made of an inexpensive material and a double-walled pipe that has excellent corrosion resistance against seawater, chemicals, etc. The present invention relates to a method of manufacturing a corrosion-resistant double pipe with an inner pipe made of expensive material.

<Prior Art> Pipes are required to have various properties depending on their use, so they are manufactured using materials that satisfy these properties. In recent years, due to the development of industry, especially the development of the chemical industry and related technologies, the characteristics required of pipes have become more diverse and severe, and in order to satisfy all of the required characteristics with one type of pipe material, it is extremely difficult. Currently, expensive materials have to be used.

On the other hand, in order to suppress the increase in tube costs due to the use of the above-mentioned expensive materials, various methods have been proposed for manufacturing multilayer tubes, each of which is a composite of multiple materials with different characteristics. JP-A No. 58-112612 discloses a method of manufacturing a double tube by inserting an inner tube inside to form a stacked tube, heating the stacked tube, and simultaneously expanding the inner tube by pressurizing the inner tube with gas. has been disclosed. The invention disclosed in JP-A-58-112612 selects a material with a smaller thermal expansion coefficient than that of the outer tube as the material for the inner tube, heats the stacked tubes, and simultaneously pressurizes and expands the inner tube with gas. The present invention relates to a method of joining an inner tube and an outer tube by cooling the tube.

The present invention is an improvement on the invention disclosed in JP-A No. 58-112612, in which the inner tube is made of expensive Ti, Zr, and alloys thereof, which have excellent corrosion resistance against seawater and chemicals, and the outer tube is made of inexpensive Ti, Zr, and alloys thereof. The present invention relates to a method for manufacturing double-walled pipes that are inexpensive and have excellent corrosion resistance using carbon steel, low-alloy steel, and austenitic stainless steel.

<Problems to be solved by the invention> Ti, Zr, or an alloy thereof with excellent corrosion resistance is selected for the inner tube of the double tube, and carbon steel, low alloy steel, or an alloy thereof is selected for the outer tube.
Alternatively, when austenitic stainless steel is selected and a corrosion-resistant double pipe is manufactured using the method of the prior invention, in order to smoothly insert the inner pipe into the outer pipe, 2% of the inner pipe diameter is required, taking into account the bending of the pipe. A gap larger than this is required. Therefore, when the inner tube is expanded and brought into close contact with the inside of the outer tube, the inner tube is subjected to an elongation strain of 2% or more in the radial direction. Here, if the heating temperature of the stacked tubes is inappropriate, the inner tube may be locally stressed in the direction of combined stress in both the radial and axial directions (close to 45 degrees to the tube axis) during tube expansion. The problem is that the reduced wall thickness often occurs and breaks, and even if the pipe does not break, the reduced wall thickness causes variations in the wall thickness of the inner tube, making it difficult to meet the dimensional tolerances of the standard. was there.

The present invention has been made in order to solve the problems of the prior invention and to provide a method for manufacturing a double-walled pipe without breakage or wall thickness variation that occurs during expansion of the inner pipe.

Means for Solving Problems〉 In order to manufacture a double-walled pipe so as to prevent breakage during pipe expansion, the inventors developed inner pipe materials using small test pieces of Ti and Z.
After examining the high-temperature tensile properties of R and conducting double-pipe manufacturing experiments based on the results, we found that in hot tensile tests using small test pieces of Ti and Zr, the decrease in wall thickness was small, and the width direction contracted significantly and broke. temperature range i.e. 350~8
It was discovered that by heating the stacked tubes to 00°C and then expanding the inner tube under pressure with gas, it was possible to manufacture a double-layered tube without breaking the inner tube or changing the wall thickness.
The present invention was made based on this knowledge.

The present invention provides a method for manufacturing a double tube in which an inner tube is inserted inside an outer tube and the outer tube and the inner tube are overlapped and connected, and the outer tube is made of carbon steel, low alloy steel, or austenitic stainless steel. Steel was selected as the material for the inner tube, while Ti and Z, which have excellent corrosion resistance and have a smaller coefficient of thermal expansion than the tube material, were selected.
r and their alloy steels are selected to produce an outer tube and an inner tube, respectively, and then the inner tube is inserted into the outer tube to form a laminated tube, and the laminated tubes are heated to 350 to 800°C. This is a method of manufacturing a corrosion-resistant double-walled pipe in which the inner pipe is simultaneously pressurized and expanded, and then cooled to tightly bond the inner pipe and outer pipe.

Function> The gist of the present invention is that carbon steel, low alloy steel,
Alternatively, select austenitic stainless steel, select Ti or Zr, which has a smaller coefficient of thermal expansion than the material of the outer tube, as the material for the inner tube, and insert the inner tube into the outer tube to form an overlapped tube. In the manufacturing process of double-layered tubes, in which the inner tube is heated, the inner tube is expanded by pressurizing it with gas, and then the inner tube and outer tube are tightly bonded by cooling, the stacked tubes are heated at 350 to 800℃. It's about doing.

Here, the material of the outer tube is carbon steel, low alloy steel, or austenitic stainless steel because the method of the present invention manufactures a double tube by utilizing the difference in the coefficient of thermal expansion between the outer tube and the inner tube. This is because it is necessary to select a material with a relatively large coefficient of thermal expansion for the outer tube material, and also takes into consideration the hardness required for the tube and low cost.

Ti or Zr was selected as the material for the inner tube because it was necessary to select a material with a smaller coefficient of thermal expansion than the material for the outer tube, and it also had excellent corrosion resistance against seawater, fJl chemicals, and acids. This is because

Insert the inner tube into the outer tube and heat the large stacked tubes to 35
As shown in Figure 1, the range of 0 to 800°C is
In the tensile test in this temperature range, both Zr and Zr showed a large reduction in width of the test piece, and as shown in Figure 1, only when double-walled pipes were manufactured in this temperature range did inner pipe breakage or wall thickness increase. This is because no fluctuation occurs.

Here, FIG. 2 shows a Ti tube with an outer diameter of 581 and a wall thickness of 1.5 nm, which should be the inner tube of the double tube, and a Ti tube with an outer diameter of 58 mm and a wall thickness of 1 and 0.
A test piece with a width of 15 mm and a length of 120 mm was prepared from an AS Zr tube and tensile fractured at a strain rate of 30 fat seconds using a high-temperature, high-speed tensile tester (L~W)/W. ×100
(%) (L: 15 times, W: width after rupture) is plotted against the test temperature.

Figure 1 shows the outer tube as C: 0.22% by weight (hereinafter referred to as %),
Si: 0.31%, Mn! 0.52%, C
A low-alloy seamless steel tube with an outer diameter of 73.0 m, a wall thickness of 6.351, and a length of 6000 + n containing r: 1.02% and Mo: 0.60% was selected, and the inner pipe had an outer diameter of 58.0 m.
m, wall thickness 1.5 mm, length 6000 mm - TIG welded Ti
Pipe or outer diameter 5B, 0I11゜wall thickness 1.01 fat, length 6
000 TIG welded Zr tube was selected, and using the manufacturing equipment schematically shown in Fig. 3, the heating temperature was changed using an induction heating coil from one end of the stacked tubes, and while band heating was performed, this coil was heated to the other end. The minimum wall thickness of the inner tube in the longitudinal direction center part 20 (1 m-) of the double tube and the stacked tube heating temperature when the inner tube is manufactured by moving it to the tube end and simultaneously pressurizing the inner tube with gas and expanding the tube. This shows the relationship between

<Example> Next, examples of the present invention will be described.

The quality of tightness between the inner tube and the outer tube as determined by cross-sectional optical microscope observation when manufactured using the outer tube material, inner tube material, heating temperature of the stacked tubes, and internal pressure of the inner tube as shown in Table 1. and the maximum and minimum values of the inner tube wall thickness in the range of 20 on length at the central portion in the longitudinal direction, and the same first values for the case where the heating temperature of the stacked tubes is within the range of the present invention and the case where it is outside the range of the present invention.
Shown in the table.

In addition, all the pressurization of the inner tube in Table 1 was performed using an Ar gas cylinder. A double tube with good tightness was obtained.

<Effects of the Invention> The present invention is a material with excellent corrosion resistance against seawater, chloride solutions, alkalis, organic chemicals, nitric acid, hydrochloric acid, sulfuric acid, etc.
The present invention provides a corrosion-resistant double pipe made of an inexpensive Ti or Zr thin-walled pipe and a carbon steel, low alloy steel, or austenitic stainless steel pipe instead of an expensive Ti or Zr single pipe, and has great industrial value.

[Brief explanation of the drawing]

Figure 1 is a characteristic diagram showing the relationship between the test temperature and the width reduction ratio of the test piece in a high-temperature, high-speed tensile test of inner tube material, and Figure 2 is a characteristic diagram showing the relationship between the heating temperature of the stacked tube and the inner diameter during double tube manufacturing. FIG. 3, a characteristic diagram showing the relationship with the minimum wall thickness of the pipe, is a schematic diagram of a double pipe manufacturing apparatus. DESCRIPTION OF SYMBOLS 1...Outer pipe, 2...Inner pipe, 3...Seal camp, 4...Induction heating coil, 5...Gas feed pipe, 6...Inner pipe pressure regulating valve Patent applicant Kawasaki Steel Corporation Fig. 2 Test temperature (°C) Fig. 1-m-outer tube 2-m-inner tube 3----/-le cap 4-m-induction heating coil 5-m-gas supply Pipe 6-11 Inner pipe pressure regulating valve

Claims (1)

[Claims] In the method of manufacturing a double tube, in which the inner tube is inserted inside the outer tube and the outer tube and inner tube are overlapped and joined together, carbon steel, low alloy steel, or austenitic stainless steel is selected as the material for the outer tube. On the other hand, as the material for the inner tube, Ti, Zr, and their alloy steels, which are excellent in corrosion resistance and have a smaller coefficient of thermal expansion than the material for the outer tube, are selected to manufacture the outer tube and the inner tube, respectively, and then the inner tube is placed inside the outer tube. It is characterized by inserting the tubes into stacked tubes, heating the stacked tubes to 350 to 800°C, simultaneously pressurizing the inner tubes to expand them, and then cooling them to tightly adhere the inner tubes and the outer tubes. A method for manufacturing corrosion-resistant double pipes.