[introduction] pressure vessel design rationality not only affects the cost of production and the container, also affect the safe use of containers, of great significance. This paper analyzes the common problems in the design of the pressure vessel, and discusses the optimization design of the pressure vessel.
With the development of economy, the use of pressure vessels becomes more and more frequent. The design of pressure vessel is to meet the safety and economy of the basic requirements, which requires us in pressure vessel design to choose reasonable and scientific design methods, parameters and materials etc.. A qualified pressure vessel, not only need to have the normal use of performance, the use of security is also very important. The design of the pressure vessel usually includes its structure, rigidity, strength and seal design. This paper discusses the problems in the design of pressure vessels, and analyzes the measures to optimize the design.
First, the design principles and requirements of the pressure vessel
Generally speaking, the design steps of the pressure vessel is mainly based on the requirements of the customer's use, grasp the conditions of the use of the container, and then determine the design parameters. Then the container structure analysis, material selection and selection of reasonable standards and norms, calculation and stress analysis are also required in order to determine the strength of the container, the component size and material, the last is drawing drawings, design calculations and other technical documents. A pressure vessel, in the use of inputs, are to go through the design, manufacture, safety, inspection, operation and maintenance, and many other aspects of the work, design is one of the important links.
Pressure vessel is widely used in various industries including chemical industry, petroleum, scientific research, energy industry and other industries. In the use of pressure vessel, especially in petroleum and chemical industry, higher requirements for the design, which is mainly due to the use of pressure vessels in these industries will involve the use of safety, so that the design and production process are more complex, quality standard of excellent equipment, will ensure safety and function in the play in the use of the. The main content of the design of the pressure vessel is the technology design of the main equipment and the design of the auxiliary equipment selection, calculation and check of the equipment and the manufacture and construction of the tank as well as the welding method. Therefore, the pressure vessel in the design, the need to meet the following requirements:
1, to meet the technical requirements
Pressure vessel pressure, temperature and process required to produce such as thickness, diameter and volume requirements of the specifications and the opening hole and the sealing ring like structure, these requirements in its application in petroleum industry and chemical industry is necessary to meet the requirements.
2, the protection of life
Due to the effect of corrosion erosion, material benefit by external conditions as well as the container itself occurred aging and so on, the service life of pressure vessel has a certain period, so in order to ensure that the installation of the material does not leak, pressure vessel use is good, designers usually at design time for pressure vessels to be taken the factor of safety measures, in order to cope with the effects of the above factors to shorten the service life of the pressure vessel caused by the.
3, to ensure that the use of security
Usually, stored in a pressure vessel material has certain toxic or corrosive, easily lead to the occurrence of fire, some even lead to explosion and other accidents, these materials in the process of pressure vessel in its internal storage will accumulate a certain capacity, once the container itself is damaged, the energy will be instantly release, greatly destroy and destructive force, so it is necessary to ensure the safe use of.
4, to have a better use of convenience
Easy to use should be the need to run through the whole process, acceptance, installation and use and maintenance of the process. To meet this requirement, it is necessary to reduce the risk coefficient of pressure vessel, and effectively improve the safety of the container. A simple structural design, not only bring convenience to the processing and inspection, but also to ensure the quality of the equipment, which will to a certain extent to use business days after the maintenance convenience, reduce cost, bring economic benefits to the enterprise.
Two. Analysis of common problems in design of pressure vessel
1, economic
The material used in pressure vessel is not only the need to take into account the equipment design pressure and temperature, the material welding performance and characteristics of the medium and the hot and cold processing performance and the structure of the container, also need to take into account the economic and rational. The overall cost of the pressure vessel is usually determined by the material and the overall quality of the equipment. In the total quality of the equipment inside, in which the quality of the housing occupies a large proportion, especially those content and relatively large containers, the quality of its shell almost occupy the quality of equipment 80%-90%. Therefore, in the premise of ensuring the use of containers, in the choice of materials, it should choose those prices are relatively low material to reduce manufacturing costs. In addition, it should choose reasonable structure size, which can reduce the quality of the container shell, so as to reduce the cost of equipment, and ultimately make the equipment to build the economy and reasonable.
2, material allowable stress jump
For a higher pressure vessel, its head is usually relatively thick, the formation of the head will have a certain amount of thinning. When the cylinder is in hot forming, there is a certain amount of thinning. Some designers when calculating this type of design for cylinder head, and does not take into account the reduction, but joined the attenuated amount formed at the time of manufacture, this will result in increased thickness, thereby reducing the allowable stress, the thickness of the lack of design, so the design people need to pay attention to plate materials, the allowable stress of gear jumping problems at design time.
3, non-standard flange design
According to the standard of "pressure vessel flange", which is mainly applicable to the nominal pressure of ≤ 6.4MPA, the nominal diameter of ≤ 800mm; "steel pipe flanges, gaskets and fasteners" specified in the standard for large diameter flange used in nominal pressure 16MPA, nominal diameter ≤ 2000mm & le. However, in the actual process, often encounter vessel diameter and design pressure serious beyond the above limits, when this situation requires the design of the structure of the flange size should be calculated to meet the strength requirements.
Three, pressure vesselDesign optimization
The use of new technologies, new materials, and new technologies has made the pressure vessels at the same time also facing challenges. Customer requirements increase, the design ideas and methods of the original is relatively backward, in order to solve this problem better, should be appropriate to reduce the stress calculation is too strict and reasonable increase the allowable values of stress, so that the safety of the equipment to be greatly improved. To do a good job of pressure vessel design optimization, can proceed from the following aspects:
1, the selection of good materials
The use of pressure vessel materials not only have to bear the pressure and temperature tolerance is very good, also need to have good welding performance, reasonable structure and sealing performance, on the basis of standard conditions, to optimize its economy and safety, and do not blindly design tradeoffs, and cause the device to the the cost increase.
2, the distinction between treatment
In the design of the pressure vessel, the need to make a distinction between treatment. For different stresses, the failure of the performance will be different. Even the same stress, due to the different distribution of the failure will result in different performance. There are a lot of load pressure vessels, such as the use of the pressure vessel internal and external pressure, the self weight, and the temperature difference between the outside container and container parts caused by the weight of the load variety, but the load generated in the container on the stress only into three types: one is the initial stress, the second is two times of stress and peak stress. Some of these three kinds of stress exist at the same time, and sometimes exist, so we have to deal with the actual situation.
3, priority strength properties
If the customer is relatively high, the pressure bearing capacity and large volume requirements, the entire container wall thickness, in this case will not be able to use the traditional Q245R carbon steel materials, it will increase the wall thickness, but the equipment should meet the intensity requirement, selection of low alloy steel. If the customer requirements of the pressure is not high, shell thickness is not thick, you can choose the general carbon steel. The condition for this difference is that the thickness of the wall thickness is 8mm.
4, the design should pay attention to the details
Heat treatment is generally used in cold forming or pressure vessel temperature molding, in our design, we need to consider the scheduling process of the equipment of the theme of the cylinder body, but it will ignore the container for the heat treatment process and take over the head and other accessories of the arrangement. This will lead to equipment design of the short board, but also reduces the container using life, improve the use of dangerous equipment, bring hidden dangers to the day after the use of equipment. So, in the design of the container, you need to pay attention to the design details