JP5184122B2 - Ferritic stainless steel flexible tube - Google Patents

Description

  The present invention relates to a ferritic stainless steel flexible tube.

For example, an air conditioner is a heat exchanger through a refrigerant, and a copper pipe having excellent heat conductivity is used for its pipe. Since the copper pipe is excellent not only in heat conductivity but also in workability, it is also used in connection pipes for indoor and outdoor units that do not involve heat conductivity. When installing an air conditioner indoor / outdoor unit, it is necessary to manually bend or return the piping according to the installation location. Furthermore, the pipe connection part is flared by 45 ° according to the shape of the connection joint, and flared to expand the flared tip outer diameter by about 40% compared to the outer diameter of the raw pipe. Connected by tightening with a predetermined torque with a flare nut. In other words, it is necessary for the worker to be able to bend using a tool or the like at the construction site, or to be workable so that flare processing can be performed.
However, due to recent soaring copper materials, it is necessary to examine the application of materials other than copper. For example, connection pipes using aluminum tubes that are excellent in workability like copper have been found. However, in the case of an aluminum pipe, copper pipes are welded to both ends for connection, and there is a problem that it takes labor and cost for processing.
Stainless steel, on the other hand, is used for various types of indoor and outdoor water supply, hot water supply, and gas piping due to its excellent corrosion resistance. The flexible pipe which gave is used (for example, patent document 1). This flexible tube can be bent to some extent like a copper or aluminum tube. These stainless steel flexible tubes are made of austenitic stainless steel such as SUS304, 304L, 316, 316L.
When these austenitic stainless steel flexible pipes are applied to air conditioner indoor / outdoor connection pipes, austenitic stainless steel is expensive because of its high Ni content, and stress corrosion cracking may occur depending on the environment in which it is used. There is a drawback that there is a possibility of doing. Furthermore, although austenitic stainless steel has excellent workability, it is harder than copper and aluminum, and because it is harder to work, the manufactured flexible pipe must be manually installed at the construction site. There are problems that it is difficult to repeatedly bend back and flaring the tube end using a tool.
In addition, water supply, hot water supply, and gas pipes that use flexible pipes made of austenitic stainless steel are connected via rubber packing and O-rings (for example, Patent Document 2). Application to high-pressure applications is difficult, and it has been difficult to apply flexible pipes using austenitic stainless steel to current copper pipes.
Compared to austenitic stainless steel, flexible pipes made of ferritic stainless steel that are less expensive and less work-hardening have been studied in automobile exhaust systems (for example, Patent Document 3), but have different purposes and necessary characteristics. The bending workability during construction and the flare workability of the connecting part have not been studied.
JP 2006-177529 A JP-A-9-242949 JP-A-11-159616

  The present invention has been made in view of the above circumstances, and is a ferritic stainless steel flexible pipe that is economically superior and has excellent bending workability during construction and flare workability of a pipe end that is a connection part. Objective.

  In order to achieve the above object, the present inventors have examined the bending workability and the flare workability of the tube end portion of flexible pipes using various ferritic stainless steels. As a result, the knowledge that the bending workability and flare workability of flexible pipes can be improved by a specific combination of the thickness of the material plate and the average rankford value (average r value) that is an index of workability. To the present invention.

That is, the ferritic stainless steel flexible tube of the present invention is a ferritic stainless steel flexible tube in which peaks and troughs are alternately arranged to form a corrugated flexible portion, A ferrite stainless steel plate having a thickness of 0.2 to 0.5 mm and an average r value of 1.2 or more is used as a raw material, and the corrugated shape of the flexible portion is a ratio of a trough outer diameter and a crest outer diameter. A crest that is a ratio of a trough outer diameter / crest outer diameter of 0.70 to 0.90, and a crest outer diameter and an outer diameter of a raw pipe before forming a flexible portion. The outer diameter / outer tube outer diameter is 0.9 to 1.2, and the pitch / outer tube outer diameter, which is the ratio of the pitch formed by the top of the peak and the bottom of the valley, to the outer diameter of the outer tube is 0. .13 to 0.30.
The ferritic stainless steel is C: 0.02 mass% or less, N: 0.02 mass% or less, Si: 1.0 mass% or less, Mn: 1.0 mass% or less, P: 0.05 mass% Hereinafter, S: 0.03% by mass or less, Cr: 16 to 23% by mass, further containing at least one selected from the group consisting of Ti and Nb 0.1 to 0.6% by mass, The balance is preferably composed of Fe and inevitable impurities, and further Mg: 0.0050 mass% or less, Ni: 0.6 mass% or less, Cu: 0.6 mass% or less, Mo: 2.0 mass% or less It is more preferable to contain at least one selected from the group consisting of: Al: 0.05% by mass or less; Ca: 0.0050% by mass or less; B: 0.0050% by mass or less; V: 0.2 Less than mass%, REM: 0.10 mass% or less It is further preferred to contain one or more members selected from the group.
The flexible pipe made of ferritic stainless steel according to the present invention preferably has a base pipe part in which the flexible part is not formed, and the plurality of base pipe parts and the plurality of flexible parts are alternately formed. The entire length may be wound in a coil shape, or flared portions may be provided at both ends or one end.

  According to the flexible pipe made of ferritic stainless steel of the present invention, it is possible to provide an inexpensive flexible pipe that is excellent in bending workability during construction and flare workability at the end of the pipe.

The ferritic stainless steel flexible tube of the present invention is made of a ferritic stainless steel plate having a plate thickness of 0.2 to 0.5 mm and an average r value of 1.2 or more.
An example of the flexible tube will be described with reference to FIG. FIG. 1 is a side view of a ferritic stainless steel flexible tube (hereinafter sometimes simply referred to as a flexible tube) 10 according to an embodiment of the present invention.
As shown in FIG. 1, the flexible tube 10 includes a flare processing portion 14 provided at both ends, a raw tube portion 12, and a flexible portion 20. The flexible portion 20 is formed with a corrugated shape by alternately arranging independent crest portions 22 and trough portions 24 along the circumferential direction of the peripheral surface of the flexible tube 10. The flare nut 30 is inserted into the flexible tube 10 so as to be rotatable and slidable.

  The flare nut 30 is used to connect the pipes by tightening with a predetermined torque, and is generally inserted into the flexible pipe before flare processing.

The waveform shape of the flexible portion 20 is not particularly limited, and the shape of the top portion of the peak portion 22 and the bottom portion of the valley portion 24 may form a curved surface, or may form an acute convex portion. .
The waveform shape of the flexible portion 20 will be described in detail with reference to FIG. FIG. 2 is a cross-sectional view of the flexible tube 10. The size of the corrugated shape of the flexible portion 20 is not particularly limited, but the ratio (dv / dm) of the valley outer diameter dv (mm) to the mountain outer diameter dm (mm) is 0.70 to 0.90. The ratio (dm / d) of the part outer diameter dm to the raw pipe outer diameter d (mm) is 0.9 to 1.2, and the pitch Dw (mm) from the top of the peak 22 to the bottom of the valley 24 It is preferable that the ratio (Dw / d) to the outer diameter d (mm) of the raw tube is in the range of 0.10 to 0.30.
If the trough outer diameter dv / crest outer diameter dm is smaller than 0.70, the wave height becomes too large, and the productivity may be lowered. On the other hand, if it exceeds 0.90, the height of the wave becomes too small, and the bending workability as a flexible pipe may be lowered.
When the ridge outer diameter dm / element tube outer diameter d is smaller than 0.9, the manufacturability is lowered and the resistance when gas or liquid flows in the pipe is increased, and when it exceeds 1.2, the manufacturability is lowered. There is a fear.
If the pitch Dw / outer pipe outer diameter d is smaller than 0.10, the manufacturability is lowered, and if it exceeds 0.30, the bending workability may be lowered.

The “element tube” generally refers to a tube manufactured from a steel strip or steel plate by electric resistance welding or arc welding. In the present invention, the tube includes a drawn tube and indicates a portion where the flexible portion 20 is not provided. .
The location of the raw tube portion 12 is not particularly limited, and may be arranged on both sides or one side of the flexible portion 20, and a plurality of raw tube portions 12 and a plurality of flexible portions 20 are alternately arranged. Also good.
In addition, the outer diameter d of the raw pipe is not particularly specified. For example, in air conditioner connection piping, two types are generally used: 6.35 mm on the liquid side and 9.52 mm on the gas side. Pipes that exceed the limit may be used. For this reason, it is preferable that the raw tube outer diameter d is appropriately determined in the range of 6 to 30 mm.

The flare workability of the flare processed portion 14 is preferably such that the tube expansion rate (%) represented by the following formula (1) can be 40% or more.
Tube expansion ratio (%) = flared portion outer diameter dt (mm) ÷ element tube outer diameter d (mm) × 100 (1)

  The thickness of the ferritic stainless steel plate that is the material of the flexible tube 10 is 0.2 to 0.5 mm. If the plate thickness is less than 0.2 mm, the bending workability will be good, but the strength as a flexible tube will decrease, and it will not be possible to process to a predetermined tube expansion rate at the time of flare processing, and cracks will occur at the flare processing tip This is because there is a fear. In addition, if the thickness is 0.2 mm or more, it is relatively easy to obtain in the market. On the other hand, when the thickness exceeds 0.5 mm, the bending workability at the construction site is remarkably deteriorated, and it is difficult to flare to a predetermined tube expansion ratio in the flare processing at the construction site.

The ferritic stainless steel plate used as the material of the flexible tube 10 has an average r value of 1.2 or more.
Here, the Rankford value (r value) indicates the ratio of reduction in the plate width and thickness of the tensile test piece as defined in JIS Z2254, and the higher the r value, the better the workability. . And the average r value, when the r value in the rolling direction _{r 0,} perpendicular to the rolling direction of the r value _{r 90,} the r value in the rolling direction of 45 ° was _{r 45,} represented by the following (2) formula r It is a weighted average value.
Average r value = (r ₀ + r ₉₀ + 2r ₄₅ ) / 4 (2)
This is because if the average r value is less than 1.2, sufficient flare workability cannot be obtained.

The composition of the ferritic stainless steel is not particularly limited, but a composition for ensuring bending workability and flare workability at the tube end can be selected. The composition of the ferritic stainless steel will be described in detail below.
Ferritic stainless steel is C: 0.02 mass% or less, N: 0.02 mass% or less, Si: 1.0 mass% or less, Mn: 1.0 mass% or less, P: 0.05 mass% or less , S: 0.03% by mass or less, Cr: 16-23% by mass, further containing at least one selected from the group consisting of Ti and Nb, 0.1-0.6% by mass, the balance being It preferably consists of Fe and inevitable impurities.

  Carbon (C): The content of C in the ferritic stainless steel is not particularly limited, but is preferably 0.02% by mass or less. If the C content exceeds 0.02 mass%, workability and corrosion resistance deteriorate. Moreover, it is because the amount of Ti and Nb necessary for fixing them increases. On the other hand, in order to make the C content less than 0.001% by mass, the refining cost increases. Therefore, the lower limit value of C is preferably 0.001% by mass.

  Nitrogen (N): The content of N in the ferritic stainless steel is not particularly limited, but is preferably 0.02% by mass or less. If the N content exceeds 0.02% by mass, workability and corrosion resistance deteriorate. Moreover, it is because the amount of Ti and Nb necessary for fixing them increases. On the other hand, in order to make the N content less than 0.001% by mass, the refining cost increases. Therefore, the lower limit value of N is preferably 0.001% by mass.

  Silicon (Si): The content of Si in the ferritic stainless steel is not particularly limited, but is preferably 1.0% by mass or less. Si is an element used as a deoxidizing element, but when it exceeds 1.0% by mass, workability is remarkably lowered. On the other hand, refining costs increase to make the Si content less than 0.01% by mass. Therefore, the lower limit of Si is preferably 0.01% by mass.

  Manganese (Mn): The content of Mn in the ferritic stainless steel is not particularly limited, but is preferably 1.0% by mass or less. In order to reduce workability and corrosion resistance, the upper limit is preferably 1.0% by mass. On the other hand, in order to make the Mn content less than 0.01% by mass, the refining cost increases. Therefore, the lower limit value of Mn is preferably set to 0.01% by mass which is inevitably mixed.

  Phosphorus (P): The content of P in the ferritic stainless steel is not particularly limited, but is preferably 0.05% by mass or less. This is because if it exceeds 0.05% by mass, the workability is lowered due to solid solution strengthening, and the corrosion resistance and manufacturability may be lowered. On the other hand, the lower limit of P is preferably 0.01% by mass from the viewpoint of preventing an increase in steelmaking cost due to selection of raw materials.

  Sulfur (S): The content of S in the ferritic stainless steel is not particularly limited, but is preferably 0.03% by mass or less. This is because if it exceeds 0.03 mass%, corrosion resistance may be deteriorated by inclusions or the like. On the other hand, the lower limit of S is preferably 0.0005% by mass in consideration of steelmaking costs.

  Chromium (Cr): Cr is an element necessary for ensuring corrosion resistance, which is a basic characteristic of stainless steel. The Cr content in the ferritic stainless steel is not particularly limited, but is preferably 16 to 23% by mass. If it is 16% by mass or more, sufficient corrosion resistance can be obtained in an environment where the flexible tube is used, and if it exceeds 23% by mass, workability is reduced, product cost is increased, and manufacturability is deteriorated. This is because there is a fear.

  Titanium (Ti), niobium (Nb): Ti and Nb are elements that combine with C and N to form precipitates and reduce the solid solution C and N in the steel to improve workability. Moreover, it is an element which improves corrosion resistance, especially the corrosion resistance of a welded part. The ferritic stainless steel preferably contains 0.1 to 0.6% by mass of at least one selected from the group consisting of Ti and Nb. If the amount is less than 0.1% by mass, sufficient workability may not be improved, and if it exceeds 0.6% by mass, the workability may be reduced, and Ti may cause flaws due to inclusions. is there.

The ferritic stainless steel is further selected from the group consisting of Mg: 0.0050 mass% or less, Ni: 0.6 mass% or less, Cu: 0.6 mass% or less, and Mo: 2.0 mass% or less. It is preferable to contain seeds or more.
Magnesium (Mg): Mg in ferritic stainless steel forms Mg oxide together with Al in molten steel and acts as a deoxidizer and also acts as a crystallization nucleus of TiN. TiN becomes a solidification nucleus of the ferrite phase in the solidification process, and by facilitating crystallization of TiN, the ferrite phase can be finely formed during solidification. By refining the solidified structure, surface defects caused by coarse solidified structures such as ridging and roping of products can be prevented and workability can be improved. Aggressive formation in the molten steel of Mg oxide, which serves as a crystallization nucleus of TiN, appears stably from 0.0001% by mass. Therefore, to obtain these effects, the lower limit is preferably made 0.0001% by mass. However, if it exceeds 0.0050% by mass, the weldability deteriorates, so the upper limit is preferably made 0.0050% by mass.

  Nickel (Ni): Ni in ferritic stainless steel is an element effective for improving corrosion resistance. The Ni content is not particularly limited, but the upper limit is preferably 0.6% by mass from the viewpoint of workability and cost, and the lower limit is preferably 0.01% by mass with which a stable effect can be obtained.

  Copper (Cu): Cu in ferritic stainless steel is an element effective for improving corrosion resistance. The Cu content is not particularly limited, but the upper limit is preferably 0.6% by mass from the viewpoint of workability and cost, and the lower limit is preferably 0.01% by mass with which a stable effect can be obtained.

  Molybdenum (Mo): Mo in ferritic stainless steel is an element that improves the corrosion resistance of stainless steel. The content of Mo is not particularly limited, but the upper limit is preferably 2.0% by mass from the viewpoint of workability and cost, and the lower limit is preferably 0.01% by mass with which a stable effect can be obtained.

Ferritic stainless steel is further Al: 0.05 mass% or less, Ca: 0.0050 mass% or less, B: 0.0050 mass% or less, V: 0.2 mass% or less, REM: 0.10 mass It is preferable to contain 1 or more types selected from the group consisting of% or less.
Aluminum (Al): Al in ferritic stainless steel is an effective element as a deoxidizing element, and when added, 0.005% by mass or more is preferable. Since excessive addition deteriorates workability, toughness, and weldability, the upper limit is preferably 0.05% by mass.

  Calcium (Ca): Ca in the ferritic stainless steel is an element that improves the hot workability of the steel, and when added, 0.0005% by mass or more is preferable because a stable effect can be obtained. On the contrary, excessive addition lowers hot workability, so the upper limit is preferably 0.0050% by mass.

  Boron (B): B in ferritic stainless steel is an element that improves secondary workability, and addition to Ti-added steel is effective. Since Ti-added steel fixes C with Ti, the strength of the grain boundaries decreases, and intergranular cracking is likely to occur during secondary processing. When adding, it is preferable to set it as 0.0003 mass% or more which the effect expresses stably. However, since excessive addition causes a decrease in elongation, the upper limit is preferably 0.0050% by mass.

  Vanadium (V): V in ferritic stainless steel is an element that suppresses Cr carbonitride that degrades corrosion resistance and the like. When added, the effect is stable and 0.01% by mass or more. Is preferred. However, excessive addition causes a problem of wrinkling during hot rolling, so the upper limit is preferably 0.2% by mass.

  REM: REM in ferritic stainless steel is an element that improves the hot workability of steel, and when added, it is preferably 0.005% by mass or more so that a stable effect can be obtained. On the contrary, excessive addition reduces hot workability, so the upper limit of the content is preferably 0.10% by mass. Here, REM is the total content of lanthanoid rare earth elements such as La and Ce.

  The manufacturing method of the flexible tube 10 is not particularly limited. For example, a ferritic stainless steel sheet having a plate thickness of 0.2 to 0.5 mm and an average r value of 1.2 or more is obtained as a welded pipe or a drawn pipe using an existing method, and the raw pipe is shaped like a blade. There is a method of forming a waveform shape by pressing the mold. Moreover, for example, a method of forming a corrugated shape of the ferritic stainless steel plate with a concavo-convex roll and welding the corrugated steel plate while winding it into a tube can be exemplified.

  According to the present invention, by using a ferritic stainless steel plate having a plate thickness of 0.2 to 0.5 mm and an average r value of 1.2 or more, it is inexpensive and excellent in bending workability and flare workability. A flexible tube made of ferritic stainless steel can be obtained. In particular, due to the improvement in flare workability, the tube expansion rate can be made 40% or more as with copper piping. Thereby, similarly to copper piping, the connection using a flare nut becomes easy and a flexible pipe can be applied to a high-pressure use.

According to the present invention, the corrugated shape of the flexible portion is determined as follows: trough outer diameter dv / crest outer diameter dm: 0.70 to 0.90, crest outer diameter dm / element tube outer diameter d: 0.9 to 1. 0.2, pitch Dw / element tube outer diameter d: 0.10 to 0.30, the bending workability can be further improved.
The flexible pipe made of ferritic stainless steel according to the present invention can facilitate flaring by having a raw pipe portion. In particular, by making a long flexible tube in which a plurality of flexible portions and a plurality of raw tube portions are alternately arranged, any arbitrary tube portion is cut according to the length required at the construction site, A flexible tube having an element tube at the end can be obtained.

  In FIG. 1, the flexible portion of the flexible tube is such that independent crests and troughs are arranged at a constant pitch (one pitch type), but the crests and troughs spiral on the peripheral surface portion. It may be formed in a shape. Moreover, when actually using as piping, the length of about 4-5 m is required as connection piping in a normal household air conditioner, and if it is piping of buildings etc., it will often exceed 10 m. In consideration of the ease of transportation and the like in this situation, it is preferable to have a coil shape (pipe-in-coil) in which the entire length is wound in a coil shape like the flexible tube 40 shown in FIG. In FIG. 3, the flexible portion and the tube portion are wound up at the same position. However, it is possible to change the length of the flexible portion and the tube portion or by changing the coil diameter to be wound. The positions of the flexible part and the raw pipe part may be shifted.

  In FIG. 1, the flared portion is provided at the end of the flexible tube. However, the raw tube portion may be the end of the flexible tube without providing the flared portion. May be the end. Further, the flared portion, the raw tube portion or the flexible portion may be provided at both ends of the flexible tube, or only at one end.

  As described above, the present invention can provide a ferritic stainless steel flexible pipe excellent in repeated bendability and flare workability during construction, such as an air conditioner connection pipe, instead of expensive copper. Industrial value is great.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, it is not limited to an Example.
(Examples 1-12, Comparative Examples 1-3)
A steel plate having a composition shown in Table 1 and the balance being Fe was used, and an 8 mmφ TIG welded tube was manufactured with the plate thickness shown in Table 2. Using the TIG welded pipe, according to the description in Table 2, a long flexible pipe having a total length of 4 m in which a plurality of corrugated parts having a length of 170 mm and a plurality of raw pipe parts having a length of 30 mm are alternately arranged is manufactured and transported. The entire length was wound in a coil shape to obtain a flexible pipe pipe-in-coil having a coil diameter of about 1 m. About this flexible tube pipe-in-coil, by cutting the raw tube portion sandwiched between the corrugated portions, cut out a flexible tube having a corrugated flexible portion at the center and a raw tube portion at both ends, Bending workability and flare workability were evaluated. The evaluation results are shown in Table 2.

(Bending workability)
<Test method>
Bending workability is repeated by using a tube bender (outer diameter: 8mmφ, bending R: 17.5mm), bending 180 °, and then returning to the state before bending using a vise and pliers. The sample was bent back and visually observed.
<Evaluation criteria>
According to the test method described above, the test was repeated three times, and returned without bending, and no damage such as cracks or cracks was accepted.

(Flare workability)
<Test method>
For the flare workability, flare processing was performed with a flare tube expansion rate of 40% using a commercially available flare tool, and the flare processed portion was visually observed.
<Evaluation criteria>
The flare-processed part was judged as acceptable if it had no damage such as cracks and cracks.

As shown in Table 2, Examples 1 to 12 in which the plate thickness was 0.2 to 0.5 mm, which is the range of the present invention, were able to be bent back three times. On the other hand, Comparative Example 1 in which the plate thickness is outside the scope of the present invention can be bent with a tube bender, but it is difficult to return to the shape of the base, and cracking occurred during the second bending. From this, it was found that it is difficult to apply to applications such as air conditioner indoor / outdoor connection pipes that are manually bent.
About flare workability, it turned out that Examples 1-12 whose board thickness and average r value are the scope of the present invention can perform flare processing with a tube expansion rate of 40%. However, Comparative Example 1 in which the plate thickness is out of the range of the present invention could not perform 40% flare processing. Further, Comparative Examples 2 and 3 in which the average r value was outside the range of the present invention were found to be difficult to apply to air conditioner connection pipes and the like because cracks occurred at the flared tip.

(Examples 13 to 15, Reference Examples 16 and 17 )
The waveform shape and bending workability were evaluated. Steel A shown in Table 1 was used as a stainless steel plate having a plate thickness of 0.3 mm and an average r value of 1.7. Using the stainless steel plate, various corrugated flexible tubes shown in Table 3 were produced by the same processing method as in Example 1. About the bending workability of the created flexible pipe, it tested by the test method similar to the above, the number of times of bending return just before a crack and a crack generate | occur | produce was measured, and the result is shown in Table 3.

In Examples 13 to 15 and Reference Examples 16 and 17 , dm / d, which is the ratio of the ridge outer diameter / element tube outer diameter, is 0.90 to 1.20 within the range of the present invention.
As shown in Table 3, in any of Examples 13 to 15 and Reference Examples 16 and 17 , bending back was performed three times or more. Of these, dv / dm, which is the ratio of the valley outer diameter to the mountain outer diameter, is 0.70 to 0.90 within the scope of the present invention, and the pitch Dw between the top of the peak and the bottom of the valley Examples 13 to 15 in which the ratio (Dw / d) between the outer diameter d and the outer diameter d of the raw tube is 0.10 to 0.30 within the scope of the present invention can be returned 7 times or more, and the bending workability is improved. Was planned.

It is a side view of the flexible pipe made from ferritic stainless steel of an embodiment of the present invention. It is sectional drawing of the flexible pipe made from ferritic stainless steel of embodiment of this invention. It is a perspective view of the flexible pipe made from ferritic stainless steel wound up in the shape of a coil of an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Flexible pipe made of ferritic stainless steel 12 Element pipe part 14 Flare processing part 20 Flexible part 22 Mountain part 24 Valley part 40 Flexible pipe wound up in coil shape dm Mountain part outer diameter dv Valley part outer diameter d Elementary pipe Outer diameter Dw Pitch composed of the top of the mountain and the bottom of the valley

Claims (8)

A flexible pipe made of ferritic stainless steel in which peaks and valleys are alternately arranged to form a corrugated flexible part, and has a plate thickness of 0.2 to 0.5 mm and an average Rankford value Is made of ferritic stainless steel sheet having a thickness of 1.2 or more,
The corrugated shape of the flexible portion has a trough outer diameter / crest outer diameter that is a ratio of a trough outer diameter to a crest outer diameter of 0.70 to 0.90, and a crest outer diameter and a flexible portion. Is the ratio of the outer diameter of the raw tube to the outer diameter of the raw tube before forming the outer diameter of the crest / outer pipe is 0.9 to 1.2, and the top of the crest and the bottom of the trough A flexible pipe made of ferritic stainless steel, wherein the pitch / element pipe outer diameter, which is the ratio of the pitch consisting of: and the outer diameter of the element tube, is 0.13 to 0.30.   The ferritic stainless steel is C: 0.02 mass% or less, N: 0.02 mass% or less, Si: 1.0 mass% or less, Mn: 1.0 mass% or less, P: 0.05 mass% Hereinafter, S: 0.03% by mass or less, Cr: 16 to 23% by mass, further containing at least one selected from the group consisting of Ti and Nb 0.1 to 0.6% by mass, 2. The flexible pipe made of ferritic stainless steel according to claim 1, wherein the balance is made of Fe and inevitable impurities.   Furthermore, Mg: 0.0050 mass% or less, Ni: 0.6 mass% or less, Cu: 0.6 mass% or less, Mo: One or more selected from the group consisting of 2.0 mass% or less The flexible pipe made of ferritic stainless steel according to claim 2.   Furthermore, from the group consisting of Al: 0.05 mass% or less, Ca: 0.0050 mass% or less, B: 0.0050 mass% or less, V: 0.2 mass% or less, REM: 0.10 mass% or less. The flexible pipe made of ferritic stainless steel according to claim 2 or 3, characterized by containing one or more selected.   The flexible pipe made of ferritic stainless steel according to any one of claims 1 to 4, wherein the flexible pipe has a base pipe part in which the flexible part is not formed.   The flexible pipe made of ferritic stainless steel according to claim 5, wherein the plurality of elementary pipe parts and the plurality of flexible parts are alternately formed.   The flexible pipe made of ferritic stainless steel according to any one of claims 1 to 6, wherein the entire length is a coiled shape.   The flexible pipe made of ferritic stainless steel according to any one of claims 1 to 7, wherein a flared portion is provided at both ends or one end.

Images