Abstract: The differences between the integral intermediate flange structure and split flange structure of the large diameter electric gate valve are analyzed, and advantages of the integral intermediate flange structure concerning anti seismic performance of the valve and characteristics of reducing costs and increasing efficiency are explained in this article.
1. Overview
Nuclear power valves are important safety equipment in nuclear power plants. They must be able to withstand the use and seismic loads during the service life of the nuclear power plant. For example, China's the third generation nuclear power CAP1400 stipulates that some valves with seismic requirements should be able to withstand 6g seismic acceleration in 3 directions, and the natural frequency should be greater than 33HZ. The electric high-pressure gate valve with large diameters has a great movement stroke and a large opening and closing torque, resulting in a good valve height, a heavy electric actuator and a high longitudinal center of gravity, which is not conducive to ensuring anti seismic performance of the valve. The advantages of the integral intermediate flange structure concerning anti seismic performance of the valve and features of cost reducing and efficiency increasing are introduced.
2. Optimized design of intermediate flange structure
Traditional electric gate valves with large diameters for nuclear power plants (Figure 1) adopt split flange structure. The valve body and bonnet, the bonnet and bracket are both connected by two sets of studs, which have an advantage of more convenient on-site maintenance. The disadvantage is that heights of valves will be great. Moreover, because of limitation of the stud arrangement position and operating space, the connecting flange of the bonnet and bracket is significantly smaller than that of the valve body and bonnet, resulting in sectional areas, moment of inertia, flexural modulus and torsion modulus and other parameters of dangerous sections of the bracket and stud connecting the bonnet and bracket are all small, which is not conducive to the guarantee anti seismic performance of valves. Therefore, the traditional split flange structure needs to be optimized to make the large diameter electric high-pressure gate valve have good anti seismic performance.
Figure 1 The split type electric high-pressure gate valve with large diameters
2.1 Analysis of factors affecting the anti seismic performance of gate valves
According to the analysis of the structural characteristics of nuclear equipment, there are three main key factors to improve the anti seismic performance of the gate valve.
(1) Combine and optimize the dangerous section.
(2) Reduce the center of gravity, dead-weight and height of the partitioning and whole valve.
(3) Increase the cross-sectional area, moment of inertia, flexural modulus and torsional modulus of the dangerous section.
2.2 Research goals
Take a CAP1400 electric high-pressure gate valve with DN250 as an example. Its basic parameters are as follows:
Design pressure: 172MPa
Design temperature: 350℃
Security level: SC-1
Earthquake resistance category: Ⅰ
Active: Yes
In order to make the gate valve have good anti seismic performance, it is designed as a large diameter electric gate valve with integral intermediate flange structure (Figure 2).
Figure 2 Integral electric high-pressure gate valves with large diameters
A comparison of the two structures of electric gate valves with large diameter (Figure 3). The main feature of integral intermediate flange structure is that the valve body, bonnet and bracket are connected by a set of studs, while two sets of studs are required for split flange structure to connect the valve body to bonnets and bonnets to brackets.
Figure 3 A comparison of the two structures
3. Seismic analysis before and after structural optimization
3.1 Combining and optimizing dangerous sections
The split flange structure (Figure 4) usually has 7 dangerous sections, namely 1-1 the valve body neck section, 2-2 the bonnet neck section, 3-3 the valve body and bonnet connecting to the stud section, 4-4 the bracket root section, 5-5 the bracket and valve bonnet connecting to the stud section, 6-6 the bracket and driving device connecting to the stud section and 7-7 the valve body corner section. The integral intermediate flange structure (Figure 5) simplifies the valve structure. The cross section of the stud connecting to the bracket and bonnet and the cross section of the stud connecting to the valve body and bonnet are designed to be consistent. The center circle of the stud is enlarged to make the cross section have relatively large cross-sectional areas, moment of inertia, flexural modulus and torsion modulus, etc., so that integral intermediate flange structure can combine and optimize the dangerous section of the stud connecting to the bonnet and bracket.
Figure 4 Dangerous sections of split flange gate valves
Figure 5 Dangerous sections of integral intermediate flange gate valves
See the Figure 6 for integral intermediate flange structure of the bonnet. Combined with Figure 5, it can be seen that the bonnet neck structure has been removed, that is, the bonnet neck section is no longer a dangerous section, thereby optimizing the dangerous section of the valve.
Figure 6 Integral intermediate flange structure bonnets
1. Overview
Nuclear power valves are important safety equipment in nuclear power plants. They must be able to withstand the use and seismic loads during the service life of the nuclear power plant. For example, China's the third generation nuclear power CAP1400 stipulates that some valves with seismic requirements should be able to withstand 6g seismic acceleration in 3 directions, and the natural frequency should be greater than 33HZ. The electric high-pressure gate valve with large diameters has a great movement stroke and a large opening and closing torque, resulting in a good valve height, a heavy electric actuator and a high longitudinal center of gravity, which is not conducive to ensuring anti seismic performance of the valve. The advantages of the integral intermediate flange structure concerning anti seismic performance of the valve and features of cost reducing and efficiency increasing are introduced.
2. Optimized design of intermediate flange structure
Traditional electric gate valves with large diameters for nuclear power plants (Figure 1) adopt split flange structure. The valve body and bonnet, the bonnet and bracket are both connected by two sets of studs, which have an advantage of more convenient on-site maintenance. The disadvantage is that heights of valves will be great. Moreover, because of limitation of the stud arrangement position and operating space, the connecting flange of the bonnet and bracket is significantly smaller than that of the valve body and bonnet, resulting in sectional areas, moment of inertia, flexural modulus and torsion modulus and other parameters of dangerous sections of the bracket and stud connecting the bonnet and bracket are all small, which is not conducive to the guarantee anti seismic performance of valves. Therefore, the traditional split flange structure needs to be optimized to make the large diameter electric high-pressure gate valve have good anti seismic performance.
Figure 1 The split type electric high-pressure gate valve with large diameters
2.1 Analysis of factors affecting the anti seismic performance of gate valves
According to the analysis of the structural characteristics of nuclear equipment, there are three main key factors to improve the anti seismic performance of the gate valve.
(1) Combine and optimize the dangerous section.
(2) Reduce the center of gravity, dead-weight and height of the partitioning and whole valve.
(3) Increase the cross-sectional area, moment of inertia, flexural modulus and torsional modulus of the dangerous section.
2.2 Research goals
Take a CAP1400 electric high-pressure gate valve with DN250 as an example. Its basic parameters are as follows:
Design pressure: 172MPa
Design temperature: 350℃
Security level: SC-1
Earthquake resistance category: Ⅰ
Active: Yes
In order to make the gate valve have good anti seismic performance, it is designed as a large diameter electric gate valve with integral intermediate flange structure (Figure 2).
Figure 2 Integral electric high-pressure gate valves with large diameters
A comparison of the two structures of electric gate valves with large diameter (Figure 3). The main feature of integral intermediate flange structure is that the valve body, bonnet and bracket are connected by a set of studs, while two sets of studs are required for split flange structure to connect the valve body to bonnets and bonnets to brackets.
Figure 3 A comparison of the two structures
3. Seismic analysis before and after structural optimization
3.1 Combining and optimizing dangerous sections
The split flange structure (Figure 4) usually has 7 dangerous sections, namely 1-1 the valve body neck section, 2-2 the bonnet neck section, 3-3 the valve body and bonnet connecting to the stud section, 4-4 the bracket root section, 5-5 the bracket and valve bonnet connecting to the stud section, 6-6 the bracket and driving device connecting to the stud section and 7-7 the valve body corner section. The integral intermediate flange structure (Figure 5) simplifies the valve structure. The cross section of the stud connecting to the bracket and bonnet and the cross section of the stud connecting to the valve body and bonnet are designed to be consistent. The center circle of the stud is enlarged to make the cross section have relatively large cross-sectional areas, moment of inertia, flexural modulus and torsion modulus, etc., so that integral intermediate flange structure can combine and optimize the dangerous section of the stud connecting to the bonnet and bracket.
Figure 4 Dangerous sections of split flange gate valves
Figure 5 Dangerous sections of integral intermediate flange gate valves
See the Figure 6 for integral intermediate flange structure of the bonnet. Combined with Figure 5, it can be seen that the bonnet neck structure has been removed, that is, the bonnet neck section is no longer a dangerous section, thereby optimizing the dangerous section of the valve.
Figure 6 Integral intermediate flange structure bonnets
Next: Optimized Intermediate Flange Structure of Nuclear Grade Large Diameter Gate Valves (Part Two)
Previous: Notes for Quick Installation of Ball Valves
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