JPH061115B2 - Structure to prevent excessive displacement of gimbal type bellows joint - Google Patents

Description

TECHNICAL FIELD The present invention relates to an excessive displacement prevention structure for a gimbal type bellows joint in a piping system of a nuclear power plant.

[Prior Art and Its Problems] Pipes used in a nuclear power plant, for example, a pipe system used in a primary cooling system of a fast breeder reactor (hereinafter abbreviated as FBR) transports high temperature sodium up to about 500 ° C. Therefore, stainless steel, nickel alloy steel or the like having high strength at high temperature is used as the material for the piping system. Furthermore, since the outer surface is covered with a heat insulating material in order to reduce the amount of heat dissipated, the material temperature of the pipe is almost 500
Reaching ℃. Therefore, thermal expansion of the pipe leads to an increase in thermal stress, and the allowable stress value of the material also decreases, so that there is a risk of damaging the piping system. Therefore, complicated piping was carried out to reduce the thermal stress, but as a result, the plant construction cost increased.

In order to improve such an increase in plant construction cost, it is required to provide an expansion-contraction joint at a predetermined position of the piping system to absorb thermal expansion and to make the piping system compact. However, in a nuclear power plant such as FBR, it is necessary to form a boundary against internal fluid leakage. Therefore, a bellows joint capable of complete sealing is generally used as the expansion-contraction joint. Furthermore, in a nuclear power plant, leakage of the primary fluid will seriously impair the safety of the plant. For example, since liquid metal sodium is used as the coolant in the FBR, if the bellows were damaged and an accidental outflow of sodium occurred, not only would radioactive materials be released into the atmosphere, but oxygen in the air would also be released. It is expected that a violent oxidation reaction will occur, which will cause a large fire. Therefore, the bellows joint has various safety mechanisms.
One of them is a restraint mechanism such as a stopper or guide for the purpose of preventing excessive displacement, which is one of the main causes of axial displacement type bellows damage. Since the load displacement angle is uniquely determined by the balance in the piping system during rated operation, the bellows joint does not require a stopper or restraint mechanism like the axial displacement type bellows joint. No restraint mechanism such as a stopper for preventing excessive displacement was used for the bellows joint.

However, depending on the operating conditions, it is expected that excessive displacement exceeding the design value will concentrate on one joint due to abnormal heating of the piping system or unexpected load. It has been desired to develop an effective restraint mechanism to avoid damage.

[Object of the Invention] The present invention has been made in view of the above technical problems, and provides an over-displacement prevention structure effective for preventing an excessive load on a bellows and avoiding a risk of damage to the bellows. The purpose is to do.

[Means for Solving the Problems] An over-displacement preventing structure of the present invention for solving the above problems is such that one shaft and a fixing ring are arranged so that the axial center of the pin passes through the center of the bellows joint. Connected rotatably by a pair of opposed two pins provided so that the other shell and the fixing ring can be rotated by a pair of opposed two pins at a position rotated by 90 ° with respect to the axis of the two pins. In the connected gimbal type bellows joint, an excessive displacement prevention jig is provided on the fixing ring of the pin mounting part so as to be parallel to the center line of the bellows joint, and the excessive displacement prevention jig is formed as a spring structure. However, it is characterized in that a stopper is attached on the shells facing each other.

[Embodiment] An embodiment of the present invention will be described in detail with reference to FIGS. FIG. 1 is a schematic perspective view of a gimbal type bellows joint,
FIG. 2 is a sectional view showing a part thereof, and FIG. 3 is a sectional view of an excessive displacement prevention structure portion. In the figure, 1 is a boundary bellows, 2 is a backup bellows arranged concentrically outside the boundary bellows 1, and both ends of these bellows 1 and 2 are fixed to shells 7 and 7'through skirts 3. Has been done. Reference numerals 4 and 4'are sleeves for reducing the pressure loss of the fluid flow and smoothing the flow. Reference numeral 5 is a fixing ring which rotatably connects the shells 7 and 7'through the pins 6 and 6'in the central portion.
The shell 7 and the fixing ring 5 are formed by the two opposing pins 6.
And are rotatably connected about the axes of the two pins 6. On the other hand, the shell 7'and the fixed ring 5 are also rotatably connected about the axes of the two pins 6 '. That is, two independent shells 7 through a common fixing ring 5.
And 7'are connected by two opposite sets of pins 6, 6 '. Reference numeral 9 denotes a jig for preventing excessive displacement, which is fixed to the mounting portion of the pin 6 of the fixing ring 5. This excessive displacement prevention jig 9 is fixed at an extension position parallel to the axis of the bellows joint of the pin 6, and a stopper 10 is attached to the shell 7'to face this.

The distance between the stopper 10 and the excessive displacement prevention jig 9 can be adjusted, that is, it can be adjusted by moving the excessive displacement prevention jig 9 forward and backward. It is possible to select. Further, the excessive displacement prevention jig 9 employs a spring structure composed of a displacement stop fitting 9a and a spring 9b as shown in FIG. This excessive displacement prevention jig 9 has a distance δ between the free displacement portion δ, the displacement stop fitting 9a and the stopper 10.
_L and _L are maintained at predetermined values. As the spring structure, it is possible to adopt a flat spring structure shown in FIG. or,
Similarly, an excessive displacement prevention jig 9'is fixed to the mounting portion of the pin 6'of the fixing ring 5 (see FIG. 1), and a stopper 10 'is mounted to the shell 7'to face it.

Next, the operation of this embodiment configured as described above will be described. The bellows joint is installed at a predetermined position in the piping system,
The external force generated by the thermal expansion of the piping system during operation is absorbed by the angular displacement that rotates about the pin 6, and the generation of thermal stress in the piping system is suppressed. That is, a form in which the angular displacement rotating about the shaft center of the pin 6 and the angular displacement rotating about the shaft center of the pin 6'at a position rotated 90 ° with the shaft center of the pin 6 are combined. Since it is rotated by, it can be angularly displaced in all directions by 360 ° around the center point of the bellows joint, and all external force generated by thermal expansion of the pipe can be absorbed. Moreover, the excessive displacement prevention jig 9 and the stopper 10 are attached in parallel with the axis of the pin 6, and
Since another excessive displacement prevention jig 9'and a stopper 10 'are installed in a position parallel to the axis of the pin 6'which is provided at an angle of 90 ° with the axis of the Excessive displacement in all directions can be prevented in exactly the same way as.

Further, the excessive displacement prevention jig 9 includes a displacement stopping metal member 9a and a spring 9b.
Since a spring absorption method consisting of and is adopted, even if a displacement exceeding a certain deformation absorbed by the bellows is applied,
As shown in FIG. 5, the allowable displacement is received by the spring structure, and the displacement applied to the bellows is reduced by the reaction force of the spring (δ
_L− δ) and a free displacement portion (δ) that does not restrain displacement are absorbed separately. Therefore, the displacement spring characteristics of the bellows joint as a whole can be changed from the conventional linear type to the multi-linear type, and the stress of both the bellows and the pipe can be reduced. That is, the spring constant of the bellows is K
_Bellows , spring structure and bellows composite spring constant Ks,
If the spring constant of the bellows joint as a whole is K, the relationship is in the region where the displacement is δ or more. Therefore, by arbitrarily selecting Ks, the spring constant of the bellows joint can be maintained at a predetermined value in the range of K _Bellows <K, and the load on the displacement δ _L −δ part that places an excessive load on the bellows itself. Can be reduced by the reaction force of the spring.

For this reason, the spring structure is balanced so as to absorb the thermal deformation of the entire piping system by distributing it to the deflection of the bellows and the piping itself by arbitrarily selecting the clearance δ and the spring constant Ks at which the bellows can freely deform. Design became possible.

Therefore, it is possible to prevent excessive displacement from being concentrated in one bellows joint of the piping system, and to average the displacements generated in each bellows joint, thus extending the life of the bellows joint. It was

[Effects of the Invention] As described in detail above, the over-displacement prevention structure according to the present invention is a gimbal-type bellows joint in which an over-displacement prevention jig is provided on the fixing ring of the pin mounting portion and the shell facing the pin. Since it is configured so that and the stopper are provided so as to be parallel to the center line of the bellows joint, it is possible to prevent excessive displacement that is concentrated in the bellows joint in the piping system and occurs in each bellows joint. Displacements to be averaged,
The life of the bellows joint has been extended, and it has become possible to maintain the integrity of the piping system of the nuclear power plant for a long period of time.

[Brief description of drawings]

FIG. 1 is a perspective view of a gimbal type bellows joint provided with an excessive displacement prevention structure according to the present invention, and FIG.
FIG. 3 is a sectional view of an essential part of an excessive displacement prevention jig, FIG. 4 is a sectional view of an essential part of another embodiment of the excessive displacement prevention jig, and FIG. 5 is a reaction force-displacement relationship diagram of the embodiment. Is. 1 ... Boundary bellows 2 ... Back-up bellows 3 ... Skirt 4, 4 '... Sleeve 5 ... Fixing ring 6, 6' ... Pin 7,7 '... Shell 9,9' ... Excessive displacement prevention jig 10, 10 ' …stopper

Claims (1)

[Claims] Claim: What is claimed is: 1. One shell and a fixing ring are rotatably connected to each other by a pair of two opposing pins provided so that the axis of the pin passes through the center of a bellows joint, and the other shell and the fixing ring are In a gimbal type bellows joint that is rotatably connected by another pair of two opposing pins at a position rotated 90 ° with the axis of the two pins, parallel to the center line of the bellows joint on the fixing ring of the pin mounting part. To prevent this, an excessive displacement prevention jig is provided, and a stopper is attached on the shell facing the excessive displacement prevention jig, and the excessive displacement prevention jig is formed by a displacement stop metal fitting and a spring. A structure for preventing excessive displacement of a gimbal type bellows joint, characterized in that the displacement is divided into a free displacement portion and a spring displacement portion.