The design of pressure vessel is a complex and systematic work, and there are relatively many influencing factors, so it is easy to have some problems in the design process. In order to ensure the quality of pressure vessel, designers should carefully analyze the causes of these problems and take corresponding countermeasures to solve them. Only by ensuring the design quality of pressure vessels can we really manufacture excellent equipment with qualified quality.
Pressure vessels have an important impact on the development of petrochemical field and are the key carrier to bear oil pressure. Therefore, pressure vessels need to have good safety and their relevant design work is relatively strict. Because the purposes of pressure vessels are different, there are great differences in the relevant energy quality of vessels, and designers need to combine the pressure of vessels, Optimize the design scheme.
Characteristics of pressure vessels
The so-called pressure vessel specifically refers to the closed equipment that contains liquid or gas and can bear a certain pressure. The more common pressure vessels include reflection vessel, storage and transportation vessel, separation vessel and so on. No matter what type of pressure vessel basically has the following characteristics: first, the professionalism of product design is strengthened. The design of pressure vessel is different from the design of general mechanical products. When using various software for product design, designers are required to master computer technology and relevant knowledge of chemical equipment, so that the designed products can meet the use requirements more; Second, the diversity of manufacturing processes. Due to the wide application range of pressure vessels, they are used in many industries, such as pharmacy, diet, chemical industry, smelting, petroleum, etc., which leads to a wide variety of pressure vessels. Even in the same type of products, sometimes there are some differences in products due to special reasons or customer needs, and the product structure is different, Cause the diversity of manufacturing processes; Third, the product is comprehensive. In the process of design and manufacturing, pressure vessel products need to involve machining technology, metallurgical technology, nondestructive testing technology, safety protection technology, anti-corrosion technology, etc. it is a product involving many disciplines, which leads to the fact that the product must be completed jointly by multi-party cooperation in the process of design and manufacturing to ensure product quality.
Important role of pressure vessel design
If there are various problems in the design process of pressure vessels, it will endanger the personal safety of relevant construction personnel during the operation of pressure vessels. Therefore, comprehensive consideration needs to be taken in the design process, so as to further improve the design and manufacturing quality of pressure vessels. For example, the installation convenience, pressure bearing capacity, stress state of pressure vessel and material selection principle of pressure vessel. Relevant designers of pressure vessels need to have good professional quality, solid knowledge and theoretical foundation and professional practice training. The design of pressure vessels brings certain challenges to relevant designers, because the overall quality of pressure vessels is related to safety production, so it is necessary to be meticulous, detailed and meticulous. Because various problems will inevitably appear in the design of pressure vessels, designers need to have good flexible response ability, and persevere in learning to improve their design ability. In the design process of pressure vessel. The following three problems need to be paid attention to: the first is safety. Because various chemical materials are dangerous, if they are not operated properly, there will be irreparable consequences. The second is the application life of the container, which will involve various chemical raw materials and corrode the container in the process of use, and then the container will become thinner and reduce the application life of the container. The third is the convenience of container transportation. Select practical, convenient and high-quality materials to make pressure vessels.
Design requirements for pressure vessels
As far as petrochemical enterprises are concerned, due to the complexity of their production process, if any equipment fails, it will affect the product quality to a certain extent, and in serious cases, it will cause shutdown. As one of the more important equipment in the product production of petrochemical enterprises, the design of pressure vessel should meet the following requirements: first, it should ensure that the process production can be completed. The pressure used in the production of petroleum and chemical products shall be easy to bear the temperature, pressure and structure required in the whole production process; Second, it should have high operation safety and reliability. In the production process of chemical products, the main raw materials used usually have strong toxicity and corrosivity, and are very easy to cause fire accidents, and even explosion in serious cases. When the pressure vessel is running, a certain amount of energy is often stored in the vessel. Once the vessel itself is damaged, this part of energy will be released in a very short moment, and its destructive power is quite large. In addition, the production process of chemical products emphasizes continuity. If the pressure vessel fails, it is likely to endanger the safety of other devices, resulting in chain damage. Therefore, when designing the pressure vessel, it is required not only to ensure that each pressure bearing part in the vessel has high stability, stiffness and strength, but also to meet the requirements of safe and reliable operation under different working conditions; Third; Predetermined service life. Corrosion is one of the most important factors leading to the shortening of the service life of pressure vessels, especially the pressure vessels used in petrochemical production are more vulnerable to the corrosion of raw materials. Once the vessels are corroded, the inner wall will become thinner. When the corrosion is serious, it may cause internal corrosion. In order to ensure the service life of pressure vessels, additional corrosion allowance must be fully considered in the design. For pressure vessels that need to contain highly corrosive raw materials, materials with strong corrosion resistance shall be selected in the design, or corresponding anti-corrosion measures shall be taken to achieve the required service life of the vessel; Fourth, it shall be convenient for manufacturing, inspection, installation, operation and maintenance. In the process of container design, the ultimate purpose of putting forward the above requirements is to ensure the safety of products. This is because the container with simple structure is easy to manufacture and flaw detection, and its quality can be guaranteed accordingly. Even if there are some problems exceeding the standard in the manufacturing process, it can be found and removed in time.
Common problems and solutions in pressure vessel design
Cost of pressure vessel
In the design process of pressure vessels, cost has always been one of the main problems perplexing designers. The main factors affecting the cost of pressure vessels are structural size and materials. Because some industries have high requirements for the use of containers, although selecting materials with lower prices can reduce the cost, it may not meet the use needs of customers, which brings great difficulty to the container design. The author believes that the following countermeasures can be taken to solve this problem: first, on the premise of meeting the use of pressure vessels, if different shell sizes are selected, different equipment quality can be obtained. Selecting an optimal combination of different shell sizes can minimize the quality of vessels, so as to reduce the cost; Secondly, when the design temperature of the pressure vessel is lower than – 20 ℃ and under the condition of low temperature and low pressure, it is not necessary to design according to the provisions of the low temperature pressure vessel, so it is not necessary to select the low temperature steel with high price, and the equipment cost will naturally be reduced.
Flange design issues
Flange is an important part of pressure vessel, and the standard of pressure vessel flange is also specified in detail. However, in the actual design, we often encounter such problems, that is, the equipment pressure and diameter exceed the standard range of the flange. At this time, it is necessary to redesign the structural size of the flange and calculate the strength requirements it should meet, that is, the design of the non-standard flange. At this time, the problem appears. After the software calculation, although the strength of the flange meets the design requirements, it is found that the flange is unreasonable during the actual production and installation, and some can not even meet the normal use requirements. To solve this problem, the following countermeasures can be taken: first, the size of non-standard flange should be designed according to the provisions of relevant national standards. In the actual design, it should ensure that the wrench has enough operating space; Secondly, since the bolts of high pressure vessels are generally much larger than those of ordinary pressure vessels, when their diameter is greater than 64mm, the space of the hydraulic tensioner shall be determined according to the relevant standards in Hg/T 21573-95 to ensure that the bolts can be tightened; Thirdly, the calculation of corrosion allowance should be fully considered in the design; Fourth, because the allowable stress of carbon steel and alloy steel components is lower than that of plates of the same material, the thickness of the small end of the flange shall be 2-3mm thicker than that of the head and cylinder plate at the connection position.
Corrosion problems in pressure vessel design
Corrosion is a complex problem in the design process of pressure vessels. Most of the damage of pressure vessels is caused by medium corrosion, so the anti-corrosion measures of vessels have become a problem that must be paid attention to in the design process. However, in order to reduce the manufacturing cost of the container, some designers choose some materials with poor anti-corrosion performance for design, which leads to poor anti-corrosion performance of the container itself. After running for a period of time, some equipment will have problems under the corrosion of the medium, affecting the normal use of the equipment. The following countermeasures can be taken to solve this problem: first, the technical requirements and process conditions of the equipment in production and operation should be fully understood in the design, and the container anti-corrosion design should be carried out on this basis; Secondly, structures that are easy to cause corrosion damage such as stress corrosion, galvanic corrosion and erosion corrosion should be avoided; Third, dead corners should be avoided in the design to prevent precipitation corrosion; Fourth, the residual liquid discharge design shall be carried out at the bottom of the container to prevent the corrosion of the container caused by liquid residue.
The quality of materials determines the application performance of pressure vessels. Therefore, in the design of pressure vessels, it is necessary to select reasonable materials and select various high-quality materials to manufacture pressure vessels. In the design work, the most suitable materials should also be selected in full combination with the on-site process conditions and the actual needs in the application of pressure vessels. It can be seen that the materials selected in the process of making pressure vessels are mainly selected according to the actual application requirements of pressure vessels, and relevant designers need to fully combine the application performance of different materials. For example, the materials used for making pressure vessels are thick as a whole, and the relevant designers do not carry out strict check and calculation, but only roughly estimate. They simply believe that with the increase of material thickness, the allowable stress of pressure vessels will increase, resulting in the problem of strain brittle fracture on the surface of pressure vessels.
From the perspective of application life, all products have their unique application life, especially the pressure vessel, which usually has a long application life. However, if the application life of the pressure vessel is short, it will cause a waste of production cost. In the process of R & D, relevant technicians need to consider the impact of different materials on the application time of vessels, so as to select materials with good durability and durability to make pressure vessels. In the welding process of pressure vessel manufacturing, it is easy to produce the problem of temperature difference between the welded joint and other parts, resulting in the problem of welding thermal stress. At the same time, there are changes in the structural stress of steel materials, which have a great impact on the pressure vessel under the simultaneous action of the two stresses.
Countermeasures for pressure vessel design and manufacturing
Specific measures for prolonging the service life of equipment
In the process of designing and manufacturing pressure vessels, relevant designers need to implement them in strict accordance with specific standards and specifications, and make reasonable design in combination with the application period of pressure vessels, in which external factors play an important role, such as air temperature and humidity. In addition, they also need to consider the corrosion rate of materials under relevant working environment, So as to reserve corresponding corrosion allowance for materials and ensure the stable and safe operation of the container within its service life. In practical application, pressure vessels also need regular inspection by relevant maintenance personnel, so as to effectively prevent various accidents.
Welding treatment of pressure vessels
In the welding process of pressure vessel manufacturing, it is necessary to minimize the occurrence of welding gap under the condition of ensuring its basic performance. When dealing with various high-strength steel materials, preheating before welding needs to be carried out in advance, so as to ensure that the welding position can maintain the same level as the temperature of other parts and effectively reduce the internal stress. In addition, in the design process of pressure vessels, various operations need to be carried out in accordance with relevant regulations. The external load applied to the pressure vessels needs to exceed the external load received by the pressure vessels under the operating state, so as to ensure that the pressure vessels will not have various accidents due to the external load under the operating state. With the development of the times, computer technology is gradually integrated into mechanical manufacturing, which further simplifies various manual operation links, reduces the delivery time of products, improves the construction quality, effectively optimizes the traditional mechanical manufacturing and avoids the errors in manual manufacturing. Mechanical design, manufacturing and automation belong to a perfect system. Relevant operators only need to input commands into the system to realize automatic operation and optimize the whole manufacturing process.
To sum up, in the process of designing and manufacturing pressure vessels, it is necessary to strictly follow the relevant requirements of quality standards, strictly control the vessel manufacturing process, select high-quality materials, analyze from the welding process level, meet the standard welding requirements, strengthen the supervision of manufacturing process, and strictly check the quality of finished products, Only in this way can we meet the basic design and manufacturing requirements and improve product quality.
Source: China Flange Manufacturer – Yaang Pipe Industry (www.steeljrv.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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