Common problems and analysis in the manufacture of pressure vessels

The pressure vessel is a special precision instrument widely used in industrial, agricultural and other production, with a wide variety, complicated process and technology. The safety during use affects the entire industrial or agricultural area. At this stage, there are some problems in the manufacturing process of pressure vessels. This paper briefly describes several common problems and analyzes them.
Since the beginning of the 21st century, with the rapid development of China’s economy and the improvement of science and technology, China’s pressure vessels have greatly improved from design to manufacturing and maintenance, ranking among the best in the world. In the past ten years, China has established and improved the relevant laws, regulations and standard systems for pressure vessels, so that the pressure vessels are standardized from the whole process of design, manufacture and maintenance. The design and manufacturing method of risk-based pressure vessels were proposed and improved. In order to realize the national sustainable development strategy, we began to advocate and implement the green design of pressure vessels, and gradually formed a modern pressure vessel manufacturing model. Although China has realized the independent design and manufacture of pressure vessels in terms of materials, design and manufacturing, there are still some problems and challenges in the manufacture of pressure vessels.

1 Pressure vessel manufacturing features

Pressure vessel is a kind of special equipment used in petrochemical industry, agriculture, national defense and other fields. It is divided into four categories: storage, reaction, heat exchange and separation. Since most of the pressure vessels are used in harsh environments such as high temperature and high pressure, it is necessary to ensure the safety of the design and manufacture of the pressure vessel. The material requirements for the manufacture of pressure vessels are very strict. In actual operation, the manufacture of pressure vessels is very difficult, and it requires the cooperation of various professions. The technology is very complicated. For pressure vessel designers, in addition to the expertise of pressure vessels, they also need to have the expertise of the industry they use, and strictly design pressure vessels in accordance with standards and specifications to ensure their safety.

2 Common problems and analysis in the manufacturing process of pressure vessels

With the continuous development of the pressure vessel manufacturing process, some problems in the manufacturing process are gradually exposed, requiring us to find problems in time, avoid risks, and improve the safety of pressure vessels. These problems include material problems, deformation problems, weld problems, stress corrosion problems, and hydrogen embrittlement problems.

2.1 Material issues

The problems in the manufacturing process of pressure vessels mainly include the problem of material substitution, which is superior to poor and thin, and this situation is not uncommon in the actual production process. The control of material quality is a prerequisite for the safe use of pressure vessels. Strictly control the quality of materials from design, procurement, acceptance, storage, distribution and use. National standards and specifications must be strictly enforced in the selection of materials. When purchasing materials, it must be ensured that the materials produced by the material manufacturer comply with relevant standards and specifications. Materials need to be accepted before entering the site. The first is to verify the qualification of the material supplier. If the main pressure components of the pressure vessel are in modern use, they need to be filed with the original unit; the transplantation of the material mark is an effective means to prevent the mixing and mistaking of materials, and establish a perfect material labeling management. The procedure ensures the traceability of the pressure-bearing components from the process of storage, distribution, cutting and production circulation; secondly, the parameters of the raw materials are inspected and the acceptance is strictly in accordance with relevant standards and specifications. After the material enters the site, the material owner will accept the acceptance number of the material. The management of welding materials must be carried out in accordance with special specifications to avoid potential safety hazards. It is impossible to ensure that the storage of welding materials in the quality production process of pressure vessels must be set up in the secondary storage. When storing, it should be classified according to the area, according to the grades and specifications. The material inspection number should be clearly marked. For special welding materials, special storage should be carried out.

2.2 Deformation problem

The deformation of the pressure vessel seriously affects the rigor and reliability of the use, which in turn affects the safety of the pressure vessel during operation. The manufacturing process and standards must be carefully formulated and strictly adhered to ensure that the quality of the pressure vessel meets the requirements of national regulations and various regulations. The deformation of the pressure vessel during the manufacturing process is mainly caused by the error in the size of the blank, the shape of the mold, and the error in the assembly process. To solve this problem, we must start from these three aspects. The first is to improve the level of blanking, strictly calculate the required materials, and use computer software to assist in the calculation of blanking and management; secondly, strictly control the shape of the mold, fully consider During the molding process of the pressure vessel and after the molding, in addition, during the assembly of the pressure vessel, the positioning fixture is used to prevent deformation of the pressure vessel, and the straightness is detected by the theodolite. In the actual operation process, symmetrical cutting or machining is adopted, and the method of smoothing and correcting after the blank slanting plate is cut to avoid flame cutting deformation; for the unstable deformation, the opening area can be strengthened by the ribs close to the shell, and the resistance welding is performed. When the rear casing is in an overall stable state, the reinforcing plate is removed. Avoid heat treatment deformation, set a fire wall at the flame nozzle of the furnace wall, and if necessary, reinforce the pressure vessel parts that are easy to lose temperature at high temperatures.

2.3 Weld problem

In the manufacturing process of pressure vessels, many components are connected by welding. The arrangement of welds and the quality of welding directly affect the quality of pressure vessels, especially the weld defects and stress concentration. In the welding process, pay attention to the arrangement of the welds, the intersection and overlap of the welds are unavoidable. Therefore, the stress analysis of the pressure vessel is required before the operation, and the auxiliary calculation can be performed by computer software. The key to affecting the quality of welding is the professional level of the operators. Therefore, it is necessary to pay attention to the management of welding staff, review their qualifications and related qualifications, and ensure that they are certified.

2.4 Stress corrosion problems

Stress corrosion cracking is caused by the interaction of stress and corrosive environment. In the actual operation process, stress can not be avoided, and there is no way to get rid of the corrosive environment. Therefore, it is necessary to solve this problem from the material itself. When designing a pressure vessel, it is necessary to fully consider the stress corrosion problem and select a suitable material. In addition, the structure can be treated, heat treated, anti-corrosive, etc., to minimize stress corrosion; the possibility of cracks.

2.5 Hydrogen embrittlement problem

Hydrogen embrittlement is hydrogen dissolved in steel, polymerized into hydrogen molecules, causing stress concentration, exceeding the strength limit of steel, forming fine cracks inside the steel, also known as white spots. Hydrogen embrittlement can only be prevented and cannot be cured. Once hydrogen embrittlement is produced, it cannot be eliminated. The higher the temperature, the deeper the degree of hydrogen embrittlement. The higher the carbon content of steel, the more serious the phenomenon of hydrogen embrittlement. To prevent the occurrence of hydrogen embrittlement, metal elements such as chromium, titanium and vanadium can be added to steel. Corrosion inhibitors can also be added. Electroplating, sand blasting and rust removal can all reduce the occurrence of hydrogen embrittlement to some extent.

3 Non-destructive testing

After the pressure vessel is manufactured, the quality inspection must be carried out before the finished product leaves. At present, the main detection methods used in China are the radiation detection (RT) technology and the UT inspection of the weld. With the innovation and development of non-destructive testing technology, the results of non-destructive testing are more objective, accurate and realistic.

4 Conclusion

There are many problems that need to be paid attention to during the manufacturing process of pressure vessels. There are still some problems in design and testing. From design, manufacture to acceptance, we have a good grasp of each link, strictly in accordance with national standards and various specifications. At the same time, we use computer software to assist in minimizing the quality problems of pressure vessel manufacturing and ensuring the safety of pressure vessels after operation.

Source: China Pressure Vessels Manufacturer – is one of the leading china filtration equipment & sanitary stainless steel pressure vessels manufacturer, with professional factory. We focus on the sanitary pressure vessels, filtration equipment research and development, manufacturing, sales and service since the company been established. Our products is widely used on bio-pharmaceutical, food and beverage, fine chemical industry. 

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