Bellows type expansion joint

Abstract

To provide a bellows type expandable pipe joint capable of exhibiting good anticorrosion against high corrosive fluid while preventing excessive cost increase.SOLUTION: A bellows type expandable pipe joint having a bellows shape comprises an inner layer that comes into contact with fluid flowing inside a pipe, and an outer layer that is provided on the inner layer in an overlapped manner. A pitting corrosion index expressed by formula: [Cr+3.3Mo+16N] is 35 or more for a material constituting the inner layer, and 26 or less for a material constituting the outer layer.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an expansion pipe joint used in a piping path for guiding a fluid such as a liquid or a gas, and more particularly to a bellows-type expansion pipe joint having a bellows shape. [Background technology]

[0002] From everyday lifelines to cutting-edge energy fields and space development, countless pipelines are spread throughout various production facilities. In these pipelines, expansion joints with a bellows shape absorb the repeated displacement and bending deformation acting on the pipes with the bellows part, reducing the load and preventing damage to the pipes.

[0003] Bellows-shaped expansion joints are disclosed, for example, in Japanese Patent Laid-Open Publication No. 2-195096 (Patent Document 1) and Japanese Utility Model Publication No. 2-39103 (Patent Document 2).

[0004] Austenitic stainless steel (e.g., SUS304, SUS316L) generally has good corrosion resistance and workability, and is reasonably cost-effective, so it is used as the material for bellows-type expansion joints from the standpoint of economy and workability. The use of stainless steel bellows-type joints ensures that they can flexibly deform and maintain water permeability even in the event of an earthquake, land subsidence, etc.

[0005] The expansion joint disclosed in Patent Document 1 is made up of a single layer, whereas the expansion joint disclosed in Patent Document 2 is made up of multiple layers.

[0006] Patent Document 2 describes an expansion joint to be installed in a piping system in which a fluid is present inside the piping, characterized in that it is configured such that a boundary maintaining layer made of a highly ductile metal is used as the inner layer, and a shape maintaining layer made of a high-strength metal is used as the outer layer. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2-195096 [Patent Document 2] Publication number 2-39103 Summary of the Invention [Problem to be solved by the invention]

[0008] A wide variety of fluids flow through pipe joints, including highly corrosive liquids, gases, and powders. Expansion joints are also used in applications where liquids containing microorganisms flow.

[0009] Austenitic stainless steel is known as a material that exhibits good corrosion resistance, and is therefore effectively used for pipes that guide highly corrosive fluids.

[0010] The inventors of the present application have found that, although a straight pipe without irregularities exhibits good corrosion resistance against highly corrosive liquids if made of general-purpose austenitic stainless steel such as SUS304 or SUS316L, a bellows-type expansion joint having a bellows shape is prone to corrosion on the inner surface of the bellows-shaped part. That is, in an expansion joint having a bellows shape, liquid remains in the bellows part even when no highly corrosive liquid is flowing, and this part repeatedly dries and wets, and the inventors have recognized the problem that the corrosion resistance of the general-purpose austenitic stainless steels (SUS304, SUS316L, etc.) that have been used conventionally is insufficient.

[0011] The first step of this invention is to recognize the problem particular to such bellows-type expansion joints, namely, the problem that corrosion progresses due to highly corrosive liquid remaining in the bellows portion.

[0012] In recent years, major steel manufacturers have begun to sell highly corrosion-resistant steels such as duplex stainless steels (SUS329J4L, etc.) and super stainless steels (SUS312L, etc.). However, their prices are several times higher than those of general-purpose stainless steels (SUS304, SUS316L, etc.), and so their use in thick-walled bellows-type expansion joints with increased pressure resistance results in high costs.

[0013] The invention described in Patent Document 2 proposes an expansion joint with an inner boundary maintaining layer made of a highly ductile metal and an outer shape maintaining layer made of a high strength metal in order to improve both the boundary maintaining performance and shape maintaining performance of piping bellows and achieve a large amount of expansion and contraction and a high number of repetitions (long life). This publication does not recognize the problem of corrosion resistance that is unique to bellows-type expansion joints.

[0014] An object of the present invention is to provide a bellows type expansion joint that exhibits good corrosion resistance against highly corrosive fluids while preventing an excessive increase in cost. [Means for solving the problem]

[0015] The present invention relates to a bellows-type expansion joint having a bellows shape, which comprises an inner layer that contacts the fluid flowing inside the pipe, and an outer layer that overlaps the inner layer. The characteristic of the invention is that, in terms of the pitting corrosion index represented by "Cr+3.3Mo+16N", the material that constitutes the inner layer has a pitting corrosion index of 35 or more, and the material that constitutes the outer layer has a pitting corrosion index of 26 or less.

[0016] In one embodiment, the material constituting the inner layer is stainless steel containing, by weight, 19 to 26% Cr, 2.50 to 7% Mo, and 0.08 to 0.30% N, and the material constituting the outer layer is stainless steel containing, by weight, 16 to 20% Cr, 3% or less Mo, and 0.07% or less N. Preferably, the stainless steel constituting the inner layer and the stainless steel constituting the outer layer are austenitic stainless steel.

[0017] In another embodiment, the stainless steel constituting the inner layer is a duplex stainless steel having ferritic and austenitic phases, and the stainless steel constituting the outer layer is an austenitic stainless steel.

[0018] For example, the stainless steel constituting the inner layer is SUS312L or SUS329J4L according to the JIS standard, and the stainless steel constituting the outer layer is SUS304, SUS304L, SUS316 or SUS316L according to the JIS standard.

[0019] The expansion joint has a diameter of, for example, 50 to 3600 mm, and the inner layer has a thickness (T1) of, for example, 0.3 to 3.0 mm. In this case, the ratio (T2 / T1) of the outer layer thickness (T2) to the inner layer thickness (T1) is preferably 1 to 5.

[0020] A bellows type expansion joint according to another embodiment includes a second outer layer overlapping the outer layer, the second outer layer being made of a material having a pitting corrosion index of 35 or more.

[0021] In a bellows type expansion joint according to still another embodiment, the material constituting the inner layer is a nickel alloy containing Ni as a main component. The nickel alloy contains, for example, by weight, 14 to 17% Cr, 14.5 to 17.5% Mo, and 0.07% or less N. Such a nickel alloy is, for example, NW0276 of the JIS standard.

[0022] When the material constituting the inner layer is a nickel alloy containing Ni as a main component, the material constituting the outer layer is, for example, stainless steel. Effect of the Invention

[0023] In the bellows-type expansion joint according to the present invention having the above-mentioned configuration, the inner layer that is in direct contact with the passing fluid is made of a highly corrosion-resistant material with a pitting index of 35 or more, and the outer layer that overlaps this inner layer is made of a general-purpose material with a pitting index of 26 or less. Therefore, an excessive increase in costs is prevented, while good corrosion resistance against highly corrosive fluids is exhibited. [Brief description of the drawings]

[0024] [Figure 1] Photographs showing the procedure for an experiment evaluating the corrosion resistance of a straight pipe and a bellows pipe. [Diagram 2] 1 is a photograph showing the occurrence of rust on a straight pipe. [Diagram 3] 1 is a photograph showing the state of rust formation on a bellows tube. [Figure 4] Photographs showing the procedure for an experiment evaluating the corrosion resistance of SUS304 and SUS312L bellows pipes. [Diagram 5] This is a photograph showing the state of rust formation on a SUS312L bellows pipe. [Figure 6] Photographs showing the state of rust on a SUS304 bellows tube. [Figure 7] This is a photograph showing the occurrence of stains on the bellows tube of NW0276. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Conventional bellows-type expansion joints having a bellows shape typically have a single-layer structure made of general-purpose austenitic stainless steel such as SUS304, SUS316L, etc. This general-purpose austenitic stainless steel is known as a material that exhibits good corrosion resistance, and also has high ductility and good formability, so it is commonly used as a material for pipe joints that guide highly corrosive fluids.

[0026] The inventors of the present application began to suspect that, although a straight pipe without irregularities exhibits good corrosion resistance against highly corrosive liquids if the material is a general-purpose austenitic stainless steel such as SUS304 or SUS316L, in the case of an expansion joint having a bellows shape, liquid remains in the bellows portion even when no highly corrosive liquid is flowing, and this portion repeatedly dries and gets wet, so that even higher corrosion resistance would be required.

[0027] First, an experiment was conducted to evaluate the corrosion resistance of a straight pipe made of general-purpose austenitic stainless steel and a bellows pipe made of general-purpose austenitic stainless steel and having a bellows shape, against highly corrosive liquids.

[0028] [Corrosion resistance evaluation experiment for straight pipes and bellows pipes]

[0029] 1) Test sample The material of both the straight pipe and the bellows pipe was SUS304, a general-purpose austenitic stainless steel.

[0030] The dimensions of the straight pipe and bellows pipe are as follows: Straight pipe: nominal diameter 100A, length 220mm, plate thickness 0.6mm, number of layers 1 Bellows pipe: nominal diameter 100A, length 220mm, plate thickness 0.6mm, number of layers 1 Bellows part: Height 20 mm, pitch 30 mm, number of threads 5

[0031] 2) Equipment and tools used Hot plate: Economy hot plate made by AS ONE Co., Ltd., product number 1-9385-22 Enamel container: Noda Horo Co., Ltd., product number TK-58

[0032] 3) Fluid used Marine Art Super Formula (artificial seawater for testing and research) manufactured by Tomita Pharmaceutical Co., Ltd.

[0033] 4) Ingredients of the artificial seawater used and the amount per 1L when dissolved Sodium chloride: 22.1g Magnesium chloride: 9.9g Calcium chloride: 1.5g Anhydrous sodium sulfate: 3.9g Potassium chloride: 0.61g Sodium bicarbonate: 0.19g Potassium bromide: 96mg Borax: 78mg Anhydrous strontium chloride: 13mg Sodium fluoride: 3mg Lithium chloride: 1mg Potassium iodide: 81μg Manganese chloride: 0.6μg Cobalt chloride: 2μg Aluminum chloride: 8μg Ferric chloride: 5μg Sodium tungstate: 2μg Ammonium molybdate: 18μg

[0034] 5) Immersion conditions Room temperature: 20℃ Water temperature: 50℃ Water amount: 2000ml Artificial seawater amount: 76g Concentration of artificial seawater: (76 / 2076) x 100 = 3.66% Soaking time: 15 minutes Exposure time: 30 minutes

[0035] 6) Test procedure A photograph showing the test procedure is shown in Figure 1. The specific procedure is as follows:

[0036] A) Place an enamel container on each hot plate and pour the solution of artificial seawater into the container.

[0037] a) When the water temperature reaches 50°C, place the test sample in the enamel container with the solution and leave it for 15 minutes.

[0038] c) Remove the test sample and leave it for 30 minutes.

[0039] d) The above b) and c) constitute one cycle, and the rusting state was observed. Before the next cycle, the evaporated water was added back in, and the concentration in the enamel container was adjusted to the initial state before moving on to the next cycle.

[0040] 7) Test results The state of rust on the straight pipe is shown in Figure 2, and the state of rust on the bellows pipe is shown in Figure 3.

[0041] Regarding the occurrence of rust, the surface of the material was observed from a distance of 30 cm, and the number of spots that could be judged to be rust was compared.

[0042] As shown in Figure 2, in the case of a straight pipe, there was no rust after one cycle, but after two cycles visible rust of less than 1 mm appeared, and after 10 cycles rust of less than 1 mm appeared in several places. After 25 cycles, stains were observed, and after 50 cycles the stains became darker. After 75 cycles, some of the stains began to discolor.

[0043] As shown in Figure 3, in the case of the bellows tube, after one cycle, several visible spots of rust measuring less than 1 mm appeared, and after 10 cycles several spots of rust measuring more than 1 mm appeared. After 25 cycles, a large amount of rust appeared in the bellows-shaped part (boundary surface), after 50 cycles the number of rust spots increased, and after 75 cycles the number of rust spots increased further.

[0044] 8) Evaluation It was found that rust occurs more significantly in bellows pipes than in straight pipes when the material is SUS304, a general-purpose austenitic stainless steel. From this result, it was recognized that it is necessary to use a material with higher corrosion resistance, rather than general-purpose austenitic stainless steel such as SUS304, for the material constituting the inner surface of bellows pipes that may come into contact with highly corrosive fluids.

[0045] The components of typical general-purpose austenitic stainless steels, SUS304, SUS304L, SUS316 and SUS316L, are shown in the table below.

[0046] [Table 1]

[0047] The pitting corrosion index, expressed by the following formula, is an index that indicates the pitting corrosion resistance of stainless steel. Pitting corrosion index=Cr+3.3Mo+16N

[0048] In the case of SUS304 and SUS304L, the pitting corrosion index is approximately 20 when calculated assuming Cr content of 19%, Mo content of 0.2% (as an unavoidable impurity), and N content of 0.02% (as an unavoidable impurity).

[0049] In the case of SUS316 and SUS316L, the pitting corrosion index is approximately 25.6, calculated assuming Cr content of 17%, Mo content of 2.5%, and N content of 0.02% (as unavoidable impurities).

[0050] Considering the results of this study, it is recognized that general-purpose austenitic stainless steels with a pitting corrosion index of 26 or less are not the best materials for forming the inner surface of a bellows tube that passes highly corrosive fluids.

[0051] [Corrosion resistance evaluation experiment of SUS304 and SUS312L bellows pipes]

[0052] 1) Test sample As a test sample of the present invention, a bellows pipe made of SUS312L, an austenitic stainless steel, was used, and as a test sample of a comparative example, a bellows pipe made of SUS304, a general-purpose austenitic stainless steel, was used.

[0053] The dimensions of the bellows tube are as follows: Bellows pipe: nominal diameter 100A, length 220mm, plate thickness 0.6mm, number of layers 1 Bellows part: Height 20 mm, pitch 30 mm, number of threads 5

[0054] 2) Equipment and tools used Hot plate: Economy hot plate made by AS ONE Co., Ltd., product number 1-9385-22 Enamel container: Noda Horo Co., Ltd., product number TK-58

[0055] 3) Fluid used Marine Art Super Formula (artificial seawater for testing and research) manufactured by Tomita Pharmaceutical Co., Ltd. The ingredients and amounts are the same as previously described.

[0056] 4) Immersion conditions Room temperature: 20℃ Water temperature: 50℃ Water amount: 2000ml Artificial seawater amount: 76g Concentration of artificial seawater: (76 / 2076) x 100 = 3.66% Soaking time: 15 minutes Exposure time: 30 minutes

[0057] 5) Test procedure A photograph showing the test procedure is shown in Figure 4. The specific procedure is as follows:

[0058] A) Place an enamel container on each hot plate and pour the solution of artificial seawater into the container.

[0059] a) When the water temperature reaches 50°C, place the test sample in the enamel container with the solution and leave it for 15 minutes.

[0060] c) Remove the test sample and leave it for 30 minutes.

[0061] d) The above b) and c) constitute one cycle, and the rusting state was observed. Before the next cycle, the evaporated water was added back in, and the concentration in the enamel container was adjusted to the initial state before moving on to the next cycle.

[0062] 6) Test results The occurrence of rust on a bellows tube made of SUS312L is shown in Fig. 5, and the occurrence of rust on a bellows tube made of SUS304 is shown in Fig. 6. The occurrence of rust was evaluated by observing the surface of the material from a distance of 30 cm, and comparing the number of spots that could be determined to be rust.

[0063] As shown in Figure 5, in the case of a bellows pipe made of SUS312L, there was no rust after one cycle, visible rust of less than 1mm appeared after two cycles, and rust of less than 1mm appeared in several places after 10 cycles. Rust of less than 1mm appeared in several places after 25 cycles, and stains began to appear on the boundary surface of the bellows shape after 50 cycles. Then, after 75 cycles, some of the stains discolored (rusted).

[0064] As shown in Figure 6, in the case of the bellows pipe made of SUS304, after one cycle, visible rust of about 1 mm or less appeared in several places, and after 10 cycles, rust of about 1 mm or more appeared in several places. After 25 cycles, a large amount of rust appeared in the bellows-shaped part (boundary surface), and blue rust was also observed. After 50 cycles, the area of ​​rust increased, and after 75 cycles, the area of ​​rust increased further.

[0065] 7) Evaluation It was clearly observed that bellows pipes made of SUS312L rusted less than those made of SUS304, a general-purpose austenitic stainless steel. From this result, it was recognized that SUS312L, which has higher corrosion resistance, is more suitable than general-purpose austenitic stainless steels such as SUS304 as the material for the inner surface of bellows pipes that may come into contact with highly corrosive fluids.

[0066] The components of SUS312L are shown in the table below.

[0067] [Table 2]

[0068] In the case of SUS312L, the pitting corrosion index is approximately 43 when calculated assuming Cr content of 20%, Mo content of 6%, and N content of 0.2%.

[0069] The pitting corrosion index of SUS304 is approximately 20.

[0070] Considering the results of this study, it can be seen that a material with a higher pitting corrosion index (e.g., 35 or higher) is more suitable as a material for forming the inner surface of a bellows tube that passes highly corrosive fluids, rather than general-purpose austenitic stainless steels with a pitting corrosion index of 26 or lower.

[0071] [Materials with high pitting index]

[0072] The pitting corrosion index of the austenitic stainless steel SUS312L is approximately 43, making it suitable as a material for forming the inner surface of a bellows pipe that passes through highly corrosive liquids.

[0073] The composition of SUS329J4L, a duplex stainless steel having ferritic and austenitic systems, is shown in the table below.

[0074] [Table 3]

[0075] In the case of SUS329J4L, if the Cr content is 25%, Mo content is 3%, and N content is 0.19%, the pitting corrosion index is approximately 38. This pitting corrosion index value is more than 10 higher than the pitting corrosion index of 26 for general-purpose austenitic stainless steels, making it suitable as a material for forming the inner surface of a bellows pipe that passes highly corrosive liquids.

[0076] In the case of stainless steel, if the pitting corrosion index is 35 or more, which is about 10 higher than the 26 of general-purpose austenitic stainless steel, it is recognized as suitable as a material for forming the inner surface of a bellows tube that passes highly corrosive liquids.

[0077] Materials other than stainless steel may be used as the material for forming the inner surface of a bellows tube, through which highly corrosive liquids pass, as long as they are alloys that exhibit high corrosion resistance. For example, nickel alloys exhibit high corrosion resistance and can be used as the material for forming the inner surface of a bellows tube. This will be described in detail later.

[0078] [Multi-layered bellows tube]

[0079] High corrosion resistance materials with a pitting corrosion index of 35 or more, typically high corrosion resistance stainless steel, generally have a high market price, so manufacturing a bellows type expansion joint with this high corrosion resistance material would be very expensive. In order to suppress the increase in cost, it is considered to form a coating made of a high corrosion resistance material on the inner wall surface of the bellows type expansion joint that directly contacts the highly corrosive fluid. However, if a corrosion resistance coating is formed on the bellows-shaped part by plating or the like, there is a possibility that the thickness of the coating will vary and parts with poor corrosion resistance will appear partially. In addition, there is a possibility that the corrosion resistance coating will peel off due to deformation of the bellows.

[0080] Instead of a corrosion-resistant coating, it is possible to use a multi-layered bellows pipe that has an inner pipe (inner layer) of a certain thickness made of a highly corrosion-resistant material and an outer pipe (outer layer) of a certain thickness that overlaps the inner pipe. In this case, in order to suppress an increase in cost, the outer layer is made of a material with a low market cost.

[0081] However, since loads such as bending stress are repeatedly applied to the bellows tube, it must be avoided that the strength of the multi-layered bellows tube becomes inferior to that of a single-layered bellows tube. The inventors of the present application investigated the life span of a single-layered bellows tube and a multi-layered bellows tube when repeatedly loaded under the same conditions.

[0082] Specifically, the calculated lifespan was calculated using the bellows strength calculation formula II described in JIS B2352.

[0083] The conditions for the calculation are as follows:

[0084] [Table 4]

[0085] Applying the above conditions, the following results were obtained:

[0086] Multilayer structure (0.8mm x 3 layers): 15968 times Single layer structure (2.4mm x 1 layer): 706 times The above lifespans were calculated using the following formula:

[0087] First, the symbols required for strength calculation are shown in the table below.

[0088] [Table 5]

[0089] [In the case of a three-layer structure] First, the total mountain displacement e is calculated.

[0090]

number

[0091] Next, the stress Sp is calculated.

[0092]

number

[0093] Next, the stress Sd is calculated.

[0094]

number

[0095] Next, the number of lifespans Nc is calculated.

[0096]

number

[0097] [Single-layer structure] First, the total mountain displacement e is calculated.

[0098]

number

[0099] Next, the stress Sp is calculated.

[0100]

number

[0101] Next, the stress Sd is calculated.

[0102]

number

[0103] Next, the number of lifespans Nc is calculated.

[0104]

number

[0105] From the above results, it can be seen that, with all conditions other than the number of layers kept the same, the three-layer bellows pipe has a lifespan 22.6 times longer than the single-layer bellows pipe. Therefore, in terms of resistance to repeated loads, the multi-layer bellows pipe is found to be superior to the single-layer bellows pipe.

[0106] [Inner and outer layer materials]

[0107] Materials for the bellows tube having inner and outer layers are discussed below.

[0108] (1) Both the inner and outer layers are austenitic stainless steel Austenitic stainless steel has high ductility and good formability. It also has better weldability than ferritic stainless steel and martensitic stainless steel. Considering these points, it is desirable to construct the inner and outer layers from austenitic stainless steel. For the inner layer that comes into direct contact with highly corrosive fluids, it is desirable to use a highly corrosion-resistant stainless steel with a pitting corrosion index of 35 or more, and for the outer layer that overlaps the inner layer, it is desirable to use a general-purpose stainless steel with a pitting corrosion index of 26 or less.

[0109] For example, the following combination of materials is preferred:

[0110] Inner layer: SUS312L Outer layer: SUS304, SUS304L, SUS316 or SUS316L

[0111] The components of the above materials are as shown in Tables 1 and 2. The pitting corrosion index values ​​are as follows: SUS312L:43 SUS304, SUS304L:20 SUS316, SUS316L: 25.6

[0112] Focusing on the amounts of Cr, Mo, and N, which have a significant effect on corrosion resistance, the amounts fall roughly within the following ranges for the above materials.

[0113] In the case of the inner layer (SUS312L), the specifications are as follows. Cr:19~21% by mass Mo: 6~7% by mass N:0.16~0.25% by mass

[0114] For the outer layer (SUS304, SUS304L, SUS316 or SUS316L), the following applies: Cr:16~20% by mass Mo: 3% by mass or less N: 0.07% by mass or less (as an unavoidable impurity)

[0115] (2) The inner layer is duplex stainless steel and the outer layer is austenitic stainless steel SUS329J4L, a duplex stainless steel with both ferritic and austenitic systems, also exhibits good corrosion resistance. The chemical composition of SUS329J4L is shown in Table 3, and its pitting index is 38.

[0116] SUS329J4L contains 24-26% Cr, 2.5-3.5% Mo, and 0.08-0.30% N, and has a pitting corrosion index of 35 or more, so it exhibits good corrosion resistance and is therefore suitable as a material for forming the inner layer of a bellows pipe.

[0117] The preferred material combinations are as follows:

[0118] Inner layer: SUS329J4L Outer layer: SUS304, SUS304L, SUS316, SUS316L

[0119] (3) Cr, Mo and N contents of stainless steel Considering the contents of (1) and (2) above, the Cr content, Mo content and N content of the highly corrosion-resistant stainless steel constituting the inner layer are as follows:

[0120] Cr: 19~26% Mo: 2.5-7.0% N: 0.08~0.3%

[0121] The Cr, Mo and N contents of the general-purpose stainless steel constituting the outer layer are as follows:

[0122] Cr: 16~20% Mo: 3% or less N: 0.07% or less

[0123] The amount of N in general-purpose stainless steels is an unavoidable impurity, but is thought to be less than the amount of N in highly corrosion-resistant stainless steels, and so is set at 0.07% or less.

[0124] The preferred material combinations are as follows:

[0125] [Inner and outer layer thickness]

[0126] The diameter of the bellows type expansion joint that the present inventors intend to use is in the range of 50 to 3600 mm. When a multi-layered bellows pipe having an inner layer and an outer layer is subjected to a force greater than the design limit and cracks occur, it is believed that the layer with the greater plate thickness will crack first. Since it is the inner layer that comes into contact with highly corrosive liquid, it is desirable to prevent the inner layer from cracking before the outer layer.

[0127] From the above viewpoints, it is desirable to set the ratio (T2 / T1) of the thickness of the outer layer (T2) to the thickness of the inner layer (T1) in the range of 1 to 5. From the viewpoint of cost, it is also preferable to set the thickness of the expensive inner layer to 1 / 2 or less of the total thickness of the inner and outer layers.

[0128] In order for the inner layer to maintain high corrosion resistance for a long period of time, it is desirable for the thickness of the inner layer to be 0.3 mm or more and 3 mm or less. From the viewpoint of the seam welding ability of thin plates, it is also desirable for the thickness to be 0.3 mm or more.

[0129] From the viewpoint of formability, the upper limit of the total thickness of the inner and outer layers is preferably set to 6.0 mm.

[0130] [Bellows pipe with 3 or more layers]

[0131] If the external atmosphere of the bellows-type expansion joint is, for example, an environment accompanied by salt damage, in addition to constructing the inner layer from a highly corrosion-resistant material, a second outer layer may be placed on the outer layer and this second outer layer may be constructed from a highly corrosion-resistant material.

[0132] The material combinations in the above embodiment are, for example, as follows.

[0133] Inner layer: SUS312L or SUS329J4L Outer layer: SUS304, SUS304L, SUS316 or SUS316L Second outer layer: SUS312L or SUS329J4L

[0134] [Inner layer made of nickel alloy]

[0135] Nickel alloys that exhibit high corrosion resistance can be used as the material for the inner layer of a multi-layered bellows tube. The inventors of the present application compared the corrosion resistance of a bellows tube made of a nickel alloy that corresponds to JIS standard NW0276 with that of a bellows tube made of stainless steel (SUS312L, SUS304).

[0136] The corrosion resistance evaluation experiment for SUS312L is shown in Figure 5, and the corrosion resistance evaluation experiment for SUS304 is shown in Figure 6. As mentioned above, comparing the two, SUS312L, which has higher corrosion resistance, is more suitable than general-purpose austenitic stainless steels such as SUS304 as the material for the inner surface of a bellows pipe that may come into contact with highly corrosion-resistant fluids.

[0137] Bellows type expansion joints are sometimes installed in places with severer temperatures and corrosive environments. For example, in the case of bellows type expansion joints used in salt production equipment, even highly corrosion-resistant stainless steels such as SUS312L may not be able to withstand the severe corrosive conditions. For bellows type expansion joints intended to be installed in such severe corrosive environments, it is preferable to use an inner layer made of a nickel alloy.

[0138] The inventors of the present application conducted an experiment to evaluate the corrosion resistance of a bellows pipe made of a nickel alloy that meets JIS standard NW0276.

[0139] The components of NW0276 are shown in Table 6 below.

[0140] [Table 6]

[0141] In calculating the pitting corrosion index of the above nickel alloy, the Cr content was set to 15.5%, the Mo content to 16%, and the N content to 0.02%, which is the amount contained as an unavoidable impurity. As a result, the pitting corrosion index is Cr + 3.3Mo + 16N = 68.62.

[0142] The conditions for the corrosion resistance evaluation experiment of the above nickel alloys were the same as those for the experiments on SUS312L and SUS304 in Figures 5 and 6, so a repeated explanation will not be given here.

[0143] Figure 7 shows the occurrence of stains on a bellows tube made of nickel alloy (NW0276).

[0144] As shown in Figure 7, in the case of the bellows tube made of NW0276, no stains were observed after one cycle, stains of about 1 mm or less appeared in several places after two cycles, and stains were observed on the boundary surface of the bellows-shaped part after 10 cycles. After that, no increase in stains was observed after 25 cycles, 50 cycles, or 75 cycles, and there was no discoloration of the stains even after 75 cycles.

[0145] When comparing the rust occurrence on the SUS304 bellows pipe shown in Figure 6 and the rust occurrence on the SUS312L bellows pipe shown in Figure 5, it can be seen that the NW0276 bellows pipe shown in Figure 7 exhibits higher corrosion resistance.

[0146] In this experiment, the nickel alloy used was a material that corresponds to the JIS standard NW0276, but it is believed that any nickel alloy that contains Ni as its main component and also contains 14 to 17 mass% Cr, 14.5 to 17.5 mass% Mo, and 0.07 mass% or less N will exhibit similar corrosion resistance.

[0147] In a multi-layer expansion joint used in a more severe corrosive environment, it is preferable that the inner layer is made of the above nickel alloy and the outer layer is made of a general-purpose stainless steel. If a second outer layer is provided to cover the outer layer, the second outer layer may be made of the above nickel alloy.

[0148] In the above description, specific embodiments have been used as examples, but the scope of the present invention is not limited to the embodiments, and various modifications and changes are possible within the scope of the present invention or within an equivalent scope. [Industrial Applicability]

[0149] The present invention can be advantageously used in a bellows type expansion joint for guiding highly corrosive fluids.

Claims

1. An expansion joint having a bellows shape for use in a piping path for guiding a liquid, an inner layer in contact with the liquid flowing through the tube; an outer layer overlying the inner layer; The material constituting the inner layer is a stainless steel containing, by weight, 19 to 21% Cr, 6 to 7% Mo, and 0.16 to 0.25% N, A bellows type expansion joint, wherein the material constituting the outer layer is a stainless steel containing, by weight, 16 to 20% Cr, 3% or less Mo, and 0.07% or less N.

2. An expansion joint having a bellows shape for use in a piping path for guiding a liquid, an inner layer in contact with the liquid flowing through the tube; an outer layer overlying the inner layer; The material constituting the inner layer is a duplex stainless steel containing, by weight, 24 to 26% Cr, 2.5 to 3.5% Mo, and 0.08 to 0.30% N; A bellows type expansion joint, wherein the material constituting the outer layer is a stainless steel containing, by weight, 16 to 20% Cr, 3% or less Mo, and 0.07% or less N.

3. The stainless steel constituting the inner layer is SUS312L according to the JIS standard, 2. The bellows type expansion joint according to claim 1, wherein the stainless steel constituting the outer layer is SUS304, SUS304L, SUS316 or SUS316L according to JIS standard.

4. The stainless steel constituting the inner layer is SUS329J4L according to the JIS standard, 3. The bellows type expansion joint according to claim 2, wherein the stainless steel constituting the outer layer is SUS304, SUS304L, SUS316 or SUS316L according to JIS standard.

5. The diameter of the expansion joint is 50 to 3600 mm, The plate thickness (T1) of the inner layer is 0.3 to 3.0 mm, 5. The bellows type expansion joint according to claim 1, wherein a ratio (T2 / T1) of a plate thickness (T2) of the outer layer to a plate thickness (T1) of the inner layer is 1 to 5.

6. a second outer layer overlying the outer layer; 5. The bellows type expansion joint according to claim 3, wherein a material constituting the second outer layer is SUS312L or SUS329J4L according to JIS standard.

7. An expansion joint having a bellows shape for use in a piping path for guiding a liquid, an inner layer in contact with the liquid flowing through the tube; an outer layer overlying the inner layer; The material constituting the inner layer is a nickel alloy containing, by weight, 14 to 17% Cr, 14.5 to 17.5% Mo, and 0.07% or less N; A bellows type expansion joint, wherein the material constituting the outer layer is a stainless steel containing, by weight, 16 to 20% Cr, 3% or less Mo, and 0.07% or less N.

8. 8. The bellows type expansion joint according to claim 7, wherein the nickel alloy is JIS NW0276.

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