JPS61165091A - Expansion pipe joint - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a bellows having a multilayer structure, and particularly to a bellows-type expansion pipe joint suitable for absorbing a large amount of expansion and contraction.

[Background of the invention]

In piping of various high-temperature plants such as nuclear reactors and chemical equipment, the piping expands or contracts thermally due to changes in the ambient temperature or changes in the temperature of the fluid flowing inside the pipe. Therefore, unless measures are taken to absorb the dimensional changes caused by this, excessive stress may be generated in the piping, a large load may be applied to the equipment, and the equipment and piping may be damaged. In order to avoid such problems, bent pipes or bellows-type expansion pipe joints are often used. Among these, piping routing using bent pipes requires a certain amount of space, and is not practical in large-scale plants where space is limited and economic consideration is required.

For bellows type expansion joints, axial displacement of piping.

In addition to straight pipe type expansion joints, hinge type expansion joints, and universal type expansion joints, they are applicable to axis-perpendicular displacement, angular displacement, and compound displacement. These include the displacement conditions above, as well as the piping shape and operating conditions.

The shape of the pipe is determined by the cycle life, load limits of piping and equipment, and the support structure used.

Further, bellows type expansion joints include single-layer bellows type expansion joints and multilayer bellows type expansion joints with two or more layers.

Multilayer bellows type expansion joints are used to reduce the stress generated on the bellows surface. The stress σ generated on the surface of the bellows is proportional to the plate thickness t of the bellows, and σctt...
1). Therefore, the thickness of the bellows is tingled,
By increasing the number of calendars, the desired spring constant can be obtained and stress can be reduced. Furthermore, by providing a plurality of layers, it is possible to prevent the occurrence of penetrating cracks in the entire bellows. This is because damage to each layer can be detected from pressure changes in the gaps between the layers.

For forming the bellows 8 as described above, a hydropressure forming method is used as shown in FIG. A two-split molding die 7 is installed on the outside, and hydraulic pressure is introduced into the bellows blank tube 6 in the direction of arrow A to increase the hydraulic pressure inside the blank tube to a predetermined pressure, and the bellows blank tube 6 is moved by pressure. Make it swell. At this time, in order to withstand the hoop stress of the internal pressure, the part where the mold 7 is placed is bulged out, and at the same time, the bellows material tube 6 in between is compressed in the axial direction (in the direction of arrow B) and the bellows is Raw pipe 6
The portion that will become the bulging peak 4 is buckled and further formed into a bellows shape. In the above-mentioned hydroforming method, the troughs 3 of the bellows 8 are guided by the molding die 7 and have an accurate radius of curvature, but the peaks 4 are expanded only by the hydraulic pressure, so the radius of curvature ρ is It is considered that the valley portion 3 is not precise and the radius of curvature at the tip of the peak portion 4 is small.

The above-described hydroforming method is applied not only to single-layer bellows but also to multi-layer bellows having two or more layers. In the multi-layered bellows made in this way, the layers are in close contact with each other, and when the bellows expands and contracts, the layers may slide and cause wear.

Here, in order to analytically investigate the contact between the two-layer bellows, the third
Elastic analysis was performed using the model shown in the figure using the finite annealing method. The bellows shape is a large diameter bellows with an inner diameter of about 1000φ. As shown in FIG. 3, one layer of the bellows 8 consisting of an outer bellows 1 and an inner bellows 2 was divided into 20 elements and analyzed using an isoparametric axisymmetric shell element (ELEMENT A15).

The material constant used in the analysis is Young's modulus E = 1.98XIQ'
Kg/m”, Poisson’s ratio ν=Q, 25(i, specific weight r
= 7.97 Displacement is also allowed.In this analysis, it is assumed that there is no mutual interference between the two layers.

An example of the analysis results is shown in Fig. 4. The condition is 0 per half white.
The tensile displacement is 5 ram. The horizontal axis represents the node number corresponding to FIG. 3, and the vertical axis represents the meridional stress σm on the outer surface of the outer bellows 1. In this case, the maximum stress occurs at the top of the valley. Next, when examining the contact state of the two-layered bellows, as shown in FIG. 4, the two-layered bellows are in contact across the troughs 3 and peaks 4. Although the analysis was performed assuming that there was no interference between the two layers in the initial state, it can be seen that the peaks 4 and valleys 3 are likely to come into contact with each other due to tensile displacement. On the other hand, it has been analytically confirmed that the peak portions 4 and the valley portions 3 do not come into contact with each other during compressive displacement, but are likely to come into contact with the parallel portions 5.

As described above, when the multilayer bellows 8 expands and contracts, each part contacts and slides, and the sliding surfaces of each layer are likely to be worn out by the surface pressure generated at that time. Particularly, thinning due to wear in the valley portion 3 where the maximum stress occurs reduces the life of the Ciperose, which causes stress concentration. Furthermore, since the bellows tube 6 shown in FIG. 2 is manufactured by welding a flat plate into a cylindrical shape, build-up remains at the welded portion. Normally, the plate thickness t of the welded part is the nominal plate thickness t
Using t, =l, Q 5 t ~1.20 t
Therefore, it is thicker than other parts of the board. Therefore, stress concentration due to wear when the bellows 8 expands and contracts is likely to occur particularly at the peaks 4 and troughs 3 that are in contact with the weld.

In order to eliminate the above-mentioned problems, there is a multilayer bellows in which gaps are provided at equal intervals between each layer of the bellows 8, as shown in FIG. The method for manufacturing such bellows 8 is as follows. A bellows material is obtained by sequentially stacking cylinders each having an inner diameter approximately equal to the outer diameter of the innermost cylinder on the outside of the innermost cylinder. A high temperature pressure fluid is applied to the material to form it in a short time. The molded bellows material 6 is taken out from the mold and cooled to room temperature. Since the molding time of the bellows material 6 is short, each cylinder is molded with a temperature difference, resulting in different amounts of shrinkage up to room temperature, and minute voids are created between the bellows 80 layers at room temperature.

In the manner described above, a multilayer bellows 8 having voids between each layer can be manufactured. However, this molding method uses the heat conduction of the material, so it is difficult to obtain a uniform temperature distribution. Particularly during molding, since adjacent bellows are brought into close contact due to internal pressure, it is difficult to create a temperature difference between each layer. Therefore, this method seems to be unsuitable as a multilayer bellows manufacturing method that reliably provides a structure that prevents contact wear.

[Purpose of the invention]

An object of the present invention is to provide a mourning bellows that eliminates contact that occurs during expansion and contraction in the troughs where the maximum strain occurs in a multilayered bellows, thereby preventing shortening of life due to wear.

[Summary of the invention]

The present invention achieves this by using a material having greater rigidity as the bellows material on the inner layer side than the bellows material on the outer layer side.
This prevents a decrease in life by eliminating the contact that occurs during expansion and contraction in the troughs, which are the areas where the maximum strain occurs.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 1(a) and 1(b). FIG. 1 shows a two-layer bellows, which is a type of multilayer bellows. Here, it is assumed that the outer and inner layers of the bellows 8 have the same thickness, and the Young's modulus E+ of the outer bellows 1 is smaller than the Young's modulus Ex of the inner bellows 2.

When the two-layer bellows as described above expands and contracts, the radial displacement δ of each bellows can be determined by the following equation.

δ＝几r” [r+ (g/2−t) a ]/EI
(2) where R is the axial reaction force, r is the radius of curvature of the bellows, a is the parallel length, E is Young's modulus, and I is the moment of inertia of area.

Here, using the two-layer bellows model described in Figure 3,
Reaction force R = 0.17 regarding the outer layer bellows at the tensile displacement per unit length in the circumferential direction obtained from the experimental results of ooc.
8 (Kff/mm), average radius r of peak portion 4 = 11.
75 (ms+), Et = 16200 (Kgf
/Simple 2), plate thickness t = 1.5 am, I = 0.
283 (recommended), ! = 35 (m), δ
=0.171(,,). Here, assuming that the center point of the parallel portion 5 is not displaced, the amount of radial displacement δ of the valley portion 3
Due to symmetry,
Et I......(8) becomes.

When the above formula is applied to the valley portion 3 of the inner bellows 2, δ'=0.
It will be displaced outward by 086m. Next, reaction force R1 parallel part a, moment of inertia of area) I are equal, radius re (<r
), when applied to the valley part 3 of the inner layer bellows 2 with Young's modulus FJx, the radial displacement δ" at that time is δ""Rr6 (to + (π/ 2 1 )
)/2Et I・・・・・・・・・(4) Here, E snow=17000(Kf
/m”) t to = 11.75←Seaweed) then δ”=0.081 (a+) ・・・・・・・・・
...(5). As described above, when a tensile displacement is applied to the two-layer bellows 8, the valley portion 3 is displaced outward, but the displacement amount δI of the outer layer bellows 1 is larger than the displacement amount δ'' of the inner layer bellows 2, and the two layers are mutually displaced. They do not come into contact.Furthermore, when a compressive displacement is applied, the contact occurs not at the troughs but at the parallel portions, so wear of the troughs where the maximum stress occurs is not a problem.

The above embodiments describe two-layer bellows, which is relatively commonly used among multi-layer bellows. Similarly, for the multilayer bellows having three or more layers, by sequentially using materials with lower rigidity from the inner layer side to the outer side, wear due to mutual interference in the troughs can be prevented.

In this way, contact between the multi-layered bellows is avoided due to the difference in rigidity, so even if the multi-layered bellows is manufactured by the hydroforming method, shortening of life due to contact sliding wear is reduced.

〔Effect of the invention〕

According to the present invention, by using a material for the inner layer side bellows that has greater rigidity than the outer layer side bellows material, contact that occurs during expansion and contraction in the troughs where the maximum strain occurs can be eliminated, and the life span of the bellows can be increased. It has the effect of preventing the decline.

[Brief explanation of drawings]

FIG. 1(a) is an overall view of the multilayer bellows according to the present invention, FIG. 1(b) is an enlarged sectional view of the arrow C in FIG. 3 is an analytical model diagram of a two-layer bellows, FIG. 4 is a stress distribution diagram showing the analysis results of the model shown in FIG. 3, and FIG. 5 is a structural sectional view of a conventional example of a two-layer bellows. 1... Outer layer bellows, 2... Inner layer bellows, 3...
- Bellows trough, 4... Bellows peak, 5... Bellows parallel part, 6... Bellows blank tube, 7... Molding mold, 8... Multilayer bellows.

Claims (1)

[Claims] 1. An expansion pipe joint characterized in that a multilayer bellows consisting of two or more layers of bellows having peaks and valleys is provided with a bellows on the outer layer side than on the inner layer side, and a bellows whose material has a smaller longitudinal elastic modulus.