JPS64889B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the invention of a multi-layered bellows, which can withstand large internal pressures and reduce power transmission losses as a bellows used in connections of cryogenic cable piping for transmitting large amounts of power. It is intended to provide bellows.

The use of cryogenic cables has long been used as a power transmission method that enables large-capacity power transmission, and uses a phenomenon in which electrical resistance decreases by cooling power transmission cables with a refrigerant such as liquid nitrogen. As shown in Fig. 1, the structure is such that a spacer 3 is provided on an inner pipe 1 provided with a heat insulating layer 2, and an outer pipe 4 is attached to the inner pipe, a bellows 5 is provided on the inner pipe, and a A bellows 6 is also attached, and a connecting tube 7 is provided between the outer tubes 4, 4 thus formed to connect them. That is, such an inner tube 1
When a refrigerant is introduced into the cable and a current is passed through the power transmission cable 8, eddy current loss occurs in the stainless steel pipe that houses the cable, and the loss is large, approximately three times the resistance of the cable itself. It has been experimentally known that the resistance reached by the eddy current occurs as an eddy current. Therefore, in order to reduce such eddy current loss, we lined the inner stainless steel tube with an aluminum tube with a lower electrical resistivity.
Alternatively, by using an aluminum tube wrapped with FRP as the inner tube, it is possible to significantly reduce eddy current loss. (Tokugan Sho 57-219211, Tokugan Sho
57-223076) In addition, the thicker the aluminum tube is, the more effective it is in reducing eddy current loss, and the experimental results are summarized in Figure 2. m/3 phase), but by inserting an inner tube made of aluminum with a thickness of 10 mm, this can be reduced to 1.3 (μΩ/m/3 phase).

On the other hand, when refrigerant is put into pipes at room temperature, the pipes undergo heat contraction, so it is necessary to absorb the heat shrinkage, so in addition to using bellows 5 as described above, aluminum-lined pipes are used to reduce eddy current. In some cases, it is necessary to use aluminum bellows to absorb the heat shrinkage of the piping. The reason for this is, firstly, to reduce the eddy current in the bellows portion, and secondly, it is technically impossible to weld bellows made of other metals to aluminum in the straight pipe portion. However, as mentioned above, even though eddy currents can be reduced as aluminum becomes thicker, there is a problem in that it becomes impossible to form bellows if the plate is too thick, and bellows are made by layering thin aluminum plates. There is another method, but if the entire pipe is made of aluminum, there is a problem that the bellows becomes weaker than other pipe parts when a force such as internal pressure is applied.

The present invention was devised after repeated studies in view of the above-mentioned circumstances, and is capable of being connected to a straight pipe body lined with aluminum to reduce eddy current, and capable of withstanding the same pressure as a straight pipe. As can be seen, aluminum has a higher elastic modulus than aluminum,
We propose a multilayer bellows tube made of a material that has a large yield point and does not substantially exhibit material embrittlement even in a low temperature range, and its specific configuration is as shown in FIG.

That is, this is a multilayer bellows in which the innermost layer 11 is made of aluminum, and the outer layer is made of metal 12, which has higher strength than aluminum. In other words, in this configuration, eddy current loss is reduced by placing aluminum on the inside, and strength is maintained by the metal on the outside. now,
Find the required thickness when the same internal pressure and displacement are applied to a single-layer bellows made of only aluminum and a two-layer bellows with an inner layer of aluminum and an outer layer of stainless steel (however, the strength of the two-layer bellows is that of stainless steel). ) and as follows.

In other words, the stress generated in the bellows when internal pressure and heat absorption act is S = 1.5EtΔ/h ^0.5 W ^1.5 N + pW ² /2t ² ... () where, S: Stress generated due to internal pressure and deformation E: Elastic modulus t: Bellows thickness W: Height of bellows peak h: Pitch of bellows peak N: Number of bellows peaks p: Internal pressure Δ: Amount of expansion and contraction (=α・Δt・l) α: Coefficient of linear expansion Δt: Temperature difference l: Unit length of pipe (excluding bellows) When the above equation () is expanded and rearranged in terms of t, it is as follows.

t ³ −2S・h ^0.5・W ^1.5 N/3E・Δt ² +p・W ^3.5・h ^0.5 N
/3E・Δ= 0...() As an example, consider the case where a maximum internal pressure of 45Kg/ ^cm2 acts on a 200A inner pipe, and calculate the h, W, and
Let N be h = 25 mm, W = 30 mm, and N = 5, respectively, and Δt
= 200°C, l = 10 m, and when applied to the above equation (), it becomes t ³ −43.6S/E・Δt ² +2006/E・Δ=0 ().

In this equation (), the value of E・Δ is large (for example, in a single-layer bellows made of aluminum, E・Δ
= 1.8×10 ⁷ ), therefore, the rightmost term can be considered zero, so t ³ −46.3S/E・Δt ² =0 …() t ² (t−46.3S/E・Δ)=0 …( ') From this equation ('), since t≠0, the following equation is obtained.

t=46.3S/E・Δ…() Assuming Δ=α・Δt・l, when a single layer aluminum bellows and a multilayer bellows made of aluminum + stainless steel are cooled under the same conditions and internal pressure is applied, the required plate thickness ratio is It is as follows (the subscripts Al indicates aluminum and SUS indicates stainless steel).

t _sus ／t _Al ＝S _sus ／E _sus・Δ _sus・E _Al・Δ _Al ／S _Al ＝S _sus ／S _Al・E _Al ／E _sus・α _Al ／α _sus …() Therefore, the stress generated here If S is assumed to be equal to the tensile strength of the material and entered into the above equation (), S _Al = 16 (Kg/mm ² ), S _sus = 53 (Kg/mm ² ) α _Al = 2.35×10 ^-5 (/℃ ), α _sus = 1.5×10 ^-5 (/℃) E _Al = 7×10 ³ (Kg/mm ² ), E _sus = 1.9×10 ⁴ (Kg/mm ² ), and t _sus /t _Al = 0.17 becomes.

In other words, when the same internal pressure and deformation are applied to a multilayer stainless steel bellows lined with aluminum and a single layer aluminum bellows, the thickness of the SUS of the multilayer bellows is approximately 17% of the thickness of the single layer aluminum bellows. It will be strong enough to withstand.

Furthermore, as an example, if the outer layer of a bellows is made of stainless steel and the inner layer is made of aluminum with a thickness of 5 mm to reduce eddy current, the plate thickness is determined for 200A. First, the inner layer of aluminum is 2.5 mm thick due to the manufacturing plate thickness limit. The bellows is made of two layers of mm, and in this case, since the plate thickness does not change even if there are two layers, the effect of reducing eddy current loss does not change. However, the bellows is subject to repeated stress, so the number of repetitions of rupture is
If Nf is 7000, stress S and number of rupture cycles Nf
There is a design formula between Nf=(1.6×10 ⁶ /S) ^3.5 ...().

Assuming the internal pressure is 4.5Kg/cm ² , other values are W = 30mm, h = 25mm N = 5, l = 10m Δt = 200℃, E = 1.93×10 ⁴ Kg/mm ² α = 1.5×10 ^-5 (/ ℃), then it is determined as follows using the above equation ().

t=43.6S/E・Δ=1.7×10 ^-1 (in)=4.3 (mm) Therefore, as shown in Figure 4, the inside of the outer layer 12 consisting of three layers of 1.5 mm stainless steel bellows (4.5 mm in total) It is clear that a multilayer bellows consisting of two layers 11, 11 of aluminum with a thickness of 2.5 mm may be used.

An example of the connection between the aluminum-lined multilayer bellows and the aluminum-lined cryogenic cable piping is shown in FIG.

That is, the straight pipe portion is made of fiber-reinforced resin pipe lined with aluminum, the multilayer bellows is made of stainless steel material 12 on the outer surface of the aluminum lining 11, and the end of the stainless steel portion of the multilayer bellows is made of stainless steel sleeve of the same thickness. The material 13 is welded 15. In other words, when there are two or more layers of stainless steel in the multilayer bellows due to welding 15, the same amount of expansion and contraction in the axial direction acts on each layer of stainless steel.

Further, the aluminum portion 11 of the bellows and the aluminum portion of the straight pipe are connected on-site by fillet welding 16 via a sleeve 14 made of aluminum, which serves to maintain the airtightness of the inner pipe. The connection between the fiber-reinforced resin layer of the straight pipe and the bellows part is made by laminating the fiber-reinforced resin on-site using the hand lay-up method, which makes it possible to transmit the heat shrinkage of the straight pipe to the bellows through the fiber-reinforced resin. , it becomes possible for the fiber-reinforced resin to receive the internal pressure that acts on the joint part.

With the above-mentioned joint construction method, the aluminum sleeve is fillet welded to maintain airtightness, and fiber-reinforced resin is laminated to transmit the heat contraction of the straight pipe section to the bellows side, while also increasing the strength of the joint against internal pressure. It has a protective effect. The innermost layer of the multilayer bellows is aluminum, but the outer layer is made of a material other than SUS that can be used at extremely low temperatures (for example, a material that does not have a transition region), has a higher elastic modulus than aluminum, and has a lower yield point. Any material may be used as long as it is made of a large material.

According to the present invention as described above, the inner layer is made of aluminum as a bellows used for cryogenic cable piping in order to transmit a large amount of power, and the outer layer of the aluminum member is made of stainless steel or other material having a higher elastic modulus and yield point than other aluminum. By laminating materials that are large in size and hardly exhibit embrittlement even in low temperature ranges, the parts are relatively thin and have good expansion and contraction properties, and can withstand large internal pressures, while effectively reducing power loss. This invention has great industrial effects.

[Brief explanation of drawings]

The drawings show the technical contents of the present invention, and Fig. 1 is a cross-sectional explanatory diagram showing the configuration of cryogenic cable power transmission piping, and Fig. 2 summarizes eddy current loss in various types of piping. Figure 3 is an explanatory diagram showing an outline of the bellows according to the present invention;
The figure is a partial cross-sectional view of a specific example.
The figure is a sectional view showing a mode in which the bellows according to the present invention is connected to a straight pipe which is an aluminum-lined fiber-reinforced resin pipe. In these drawings, 1 is an inner pipe, 2 is a heat insulating layer, 3 is a spacer, 4 is an outer pipe, 5 and 6 are bellows, 7 is a connecting pipe, 8 is a power transmission cable, 11 is an aluminum inner layer, 12 is an outer layer, Reference numeral 13 indicates a stainless steel material, 14 indicates an aluminum sleeve, and 15 and 16 each indicate welding.

Claims (1)

[Claims] 1 A bellows for connecting cryogenic cable piping, the inner layer of which is made of aluminum, and the outer layer of the aluminum material has a higher elastic modulus and yield point than stainless steel or other aluminum, and exhibits embrittlement even in low temperature ranges. A multilayer bellows characterized by laminating members made of different materials.