Measures to reduce stress concentration in the process of pressure vessel design and manufacturing

Measures to reduce stress concentration in the process of pressure vessel design and manufacturing

Pressure vessel is the key equipment in China’s petrochemical industry and industrial pharmaceutical industry. Because of its good storage function, it plays a positive role in promoting the production of pressure vessel. Therefore, safety, stability and other performance indicators are the key factors in the design and manufacturing process of pressure vessels, which have attracted extensive attention of designers and enterprises. Based on the characteristics of pressure vessels, the problem of stress concentration in the process of pressure vessel design and manufacturing is analyzed. Based on the existing process design technology, the process structure and design method are improved, and further effective measures to reduce stress concentration are put forward.

Preface

With the continuous development and maturity of China’s industrial design and manufacturing technology level, the existing pressure vessel design and manufacturing process gradually highlights its own deficiencies in process methods and structural design. Among them, stress concentration has always been the main technical problem of pressure vessels in the manufacturing process. On the basis of the existing structural design and process methods, a relatively mature pressure vessel design and manufacturing system is gradually established to overcome the technical problems of stress concentration and further improve the safety and stability of pressure vessels.

Pressure vessel characteristics and design and manufacturing development status analysis

Pressure vessel characteristics

Pressure vessels have good sealing and safety, in the actual industrial production process can withstand greater pressure, and can effectively isolate environmental pollution, for the production of raw materials and material storage to provide a relatively airtight environment. Therefore, pressure vessels are widely used in oil production and industrial production enterprises. Compared with other containers, pressure vessels have absolute advantages in terms of safety, professionalism and structural stability.

• (1) Safety. Usually, industrial and petroleum enterprises for the pressure vessel in the safety performance requirements are relatively high, because the pressure vessel stored in the material is generally more dangerous, if the safety performance is poor, in the process of long-term use of the vessel material leakage, easy to cause an explosion, will cause a huge security accident for the enterprise, affecting the normal production and operation of the enterprise management. Therefore, safety is the most basic quality requirements of the pressure vessel, once the pressure vessel safety performance is poor, will cause serious economic losses to the enterprise.
• (2) Professionalism. For different enterprises, pressure vessels in the storage of supplies are not the same, but basically are highly corrosive chemicals, so the pressure vessel is required to have a high degree of professionalism and good corrosion resistance, at the same time, the pressure vessel to have a good seal, which is also the most basic professional requirements for pressure vessels. Part of the pressure vessel will store some toxic substances, if the sealing performance is poor, there may be toxic gas leakage, affecting the personal safety of staff, at the same time, harmful substances spill will give the enterprise’s production laid a huge security risks.
• (3) Structural stability. Pressure vessel in the production and manufacturing process, due to the technical process and the different production conditions, there are different degrees of influence on its structural stability and other aspects. Therefore, the pressure vessel in the production process, should take reasonable technology, do a good job of the indicators of control, try to avoid the process technology and the corresponding parameters are not standard and lead to pressure vessel stress concentration and other problems, serious container explosion and other safety accidents. Therefore, the pressure vessel in the design of the structure, need for different environments, different storage materials to improve the relevant performance indicators.

Analysis of the current situation of pressure vessel design and manufacturing development

In order to better improve the structure of pressure vessels and the stability of performance, to meet the future development requirements of pressure vessels, China has formed a relatively mature manufacturing system and standards in the design and manufacture of pressure vessels. In the actual work to further improve the relevant technology, effectively solve the stress concentration and other practical problems.
At present, China’s pressure vessel manufacturing process has been relatively mature, whether it is the acceptance of raw materials, or process methods in cutting, welding, and the subsequent process of forming the detection technology, etc., can be manufactured to meet the production needs of different enterprises pressure vessels. At the same time, in the modern pressure vessel design and manufacturing system, the structural design and the improvement of process methods, etc., have further improved the quality and safety performance of the pressure vessel, constantly meet the needs of different production enterprises on the pressure vessel in terms of performance indicators, quality and safety, etc., to promote the good development of China’s pressure vessel design and manufacturing industry.

Pressure vessel stress concentration problems and causes

In the design and manufacturing process of pressure vessels, the technical level of the process design, structural design and the operation process is not standardized, it is easy to produce stress concentration and other technical problems on the surface and inside of the pressure vessel, at the same time, according to the production status of China’s industrial manufacturing industry, the problem of stress concentration has become a more typical technical problem. Therefore, the main content of the stress concentration problem and the causes of the problem are summarized and analyzed to facilitate the effective solution of the stress concentration problem in the actual design and manufacturing process.

Stress concentration problem

Stress concentration mainly refers to the phenomenon of localized increase in stress where the object undergoes a rapid change in shape, at the same time, if the stress is too large, it will also lead to fatigue fracture of the object, and can also make the parts made of brittle materials to static load fracture. So generally in the design and manufacturing process of cutting or welding of pressure vessels, due to the unreasonable operation process, operation points of non-standard, will lead to sharp changes in the shape of the pressure vessel, thus appearing stress concentration and other problems. Stress concentration problem for the pressure vessel is mainly concentrated in the stability and safety and other aspects of the harm. Stress concentration leads to local cracks or performance degradation in the pressure vessel, while causing fatigue of the pressure vessel, whether it is safety, sealing or stability, the design of the pressure vessel and manufacturing effects have caused a certain impact. More serious stress concentration problems, there will be a vessel explosion and other situations, seriously affecting the safe production and stable operation of enterprises.

The main reason for the stress concentration problem

In the design and manufacturing process of pressure vessels, in order to further optimize the product structure design and process design methods, to effectively solve the problem of stress concentration, the need to summarize and reflect on the causes of the problem, and to find effective ways and means to reduce stress concentration, in order to have a greater breakthrough and guarantee the performance of pressure vessels.

• (1) Structural design. The unreasonable structural design is a key factor in the stress concentration problem of pressure vessels. For the pressure vessel, the most important design is the design of the vessel head, scientific and reasonable head design is an important factor to improve the sealing of the pressure vessel. In the actual process and manufacturing process, rotary shell and formed head are usually used. If flat cap head is adopted in structural design, it will significantly reduce the stress distribution of pressure vessel, both in terms of stress, manufacturing and material consumption, which will reduce the performance index of pressure vessel and thus the problem of stress concentration.
• (2) Manufacturing aspect. To further adapt to different industrial production environment, the pressure vessel in the process design will increase the design and requirements of the angles, but the angles make the pressure vessel in the shape of a sharp change, it is very easy to stress concentration phenomenon. Therefore, for this situation, need to further take reasonable technology and technology, the pressure vessel corners for rigorous treatment, improve the production of pressure vessels manufacturing effect, and then enhance the sealing of the pressure vessel, to avoid the problem of stress concentration due to the increase in the design of the corners.
• (3) Operation process. Stress concentration problems will generally be concentrated in the cutting or welding processes, in the manufacturing process, if the operating process errors or not in accordance with the standard requirements for cutting, welding, in the welding point or cutting point will also produce stress concentration problems, and some brittle materials, stress concentration will lead to large cracks on the surface of the object, which may cause greater safety accidents.

Effective way to reduce stress concentration

As we all know, in the design and manufacturing process of the pressure vessel, the stress concentration problem will have a huge impact on the performance of the pressure vessel. At the same time, in the process of pressure vessel application, generally will store some strong corrosive raw materials supplies, once the stress concentration, will cause the pressure vessel explosion and other major safety accidents. Therefore, it is necessary to reduce the problem of stress concentration and reduce the harm of stress concentration on pressure vessel by adjusting various process methods and improving process technology level.

Reasonable choice of head type to improve the sealing of pressure vessel

From the analysis of structural design, choose the suitable head type for pressure vessel to further improve the sealing and safety performance of pressure vessel. In the actual manufacturing of pressure vessel, the head type is generally divided into hemispherical, butterfly and flat head types. At the same time, the pressure vessel can further reduce the occurrence of stress concentration from the perspective of structural design by choosing the appropriate type of head. Therefore, in the actual structural design process of pressure vessel, the sealing of pressure vessel is improved by using rotary shell and formed head. From the analysis of material consumption, elliptical head can be selected for the pressure vessel. Normally, pressure vessels generally do not adopt rectangular cross-sectional vessels as well as flat-capped heads to ensure that the safety performance and stable performance of pressure vessels are not affected by heads.

Reduce stiffness difference and stress concentration problem

In the production and manufacturing process of pressure vessel, the stress concentration problem can be further reduced by effectively reducing the stiffness difference in the process method to reduce the edge stress and improve the safety and stability of the pressure vessel.
First of all, in the process design of pressure vessel, try to reduce the stiffness difference between 2 connections, through the reasonable control of the stiffness difference, reduce the pressure in the vessel, try to avoid the free deformation imbalance of the pressure vessel, and then reduce the probability of stress concentration problem. The discontinuous stress generated at the edge of the connection of the pressure vessel is also called edge stress, and the appearance of edge stress will have a certain impact on the sealing of the pressure vessel. Therefore, the difference in stiffness of the 2 continuous parts should be adjusted by uniform loading, so that the stress in the pressure vessel is in a relatively discontinuous state, thus reducing the stress concentration phenomenon generated by the edge stress and improving the safety and stability of the pressure vessel.
Secondly, in the process design of the pressure vessel, you can also continue to optimize the design of the structure around the pressure vessel, to make local adjustments and optimize the process, and constantly strengthen the local performance indicators. At the same time, also improve the welding quality by improving the level of welding technology at the edge of the pressure vessel to avoid poor welding quality leading to local stress concentration problems. This is also an important method to effectively reduce stress concentration in the design and manufacturing process of pressure vessels.
Finally, in the technical process of the pressure vessel, should further improve the conditions and quality of welding. A circular groove can be placed above the flat cover of the pressure vessel, and the circular groove is set to further reduce the stiffness difference of the connection, thus ensuring uniform distribution of stress at the edge of the pressure vessel. At the same time, after the completion of the welding process, the welding of the pressure vessel is carefully checked, such as abnormalities, need to make timely adjustments and treatment to avoid affecting the use of pressure vessels performance.

Increase the radius of the rounded corners to reduce the stress concentration generated by the angles

For the design and manufacture of pressure vessels, you can use circular arc transition or special curve transition optimized by the shape of the discontinuous position to reduce the stress concentration and other problems, and then improve the performance of the pressure vessel. This way is the pressure vessel in the manufacturing process based on the improvement and innovation, the technical principle of this process is: through the transition of the radius of the corner of the arc to adjust, so that the sharp corners show rounded state, and then reduce the pressure vessel in the corners of the stress concentration problem.

• (1) For the location of the pressure vessel at the receiver, its internal discontinuity of the local structure due to the sharp contact points, which in turn causes the stress concentration problem, the general thickness of the pressure vessel can be used as the radius for the transition to really solve the stress concentration problem.
• (2) Improve the continuity of welding. In the process of welding to the pressure vessel, pay attention to the main points of the welding operation, by designing the pad on the support, rather than welding directly to the shell, can ensure the smoothness of the welding operation, and avoid problems such as stress concentration.
• (3) In the pressure vessel mechanical processing and other aspects of the scratch, arc pit and other problems, timely repair and grinding to ensure the flatness of the pressure vessel surface, improve the use of the pressure vessel performance.

To sum up, the internal and external surfaces of the pressure vessel or the interface end are polished into rounded corners by increasing the radius of the rounded corners and reducing the angles generated at the interface, thus avoiding the problem of stress concentration.

Optimize the welding process and strictly control the residual height of the weld

In the process of manufacturing process of pressure vessel, welding process is the most important kind of process. At the same time, in the process of carrying out the process of pressure vessels, optimize the design of the welding process, strict control of weld residual height is also an effective measure and method to avoid the phenomenon of stress concentration.
On the one hand, by improving the welding process and its technical methods, it can effectively improve the performance index of the pressure vessel at the welding and avoid stress concentration problems. In the welding of pressure vessels, try to avoid spot welding welding, because spot welding is very easy to produce cracks and cracks, cracks at the stress concentration problem will seriously affect the structural stability of the pressure vessel, therefore, should be further improved by improving the level of welding technology to improve all aspects of pressure vessel performance.
On the other hand, the welding should strictly control the value of the residual height of the weld, through the reasonable control of the performance indicators and parameters in the welding process, can better improve the structural performance of the pressure vessel and the quality of the pressure vessel. At the same time, try to control the height of the weld within a reasonable range of standards, give full play to its role in the insulation or slow cooling of the entire weld, but also to further reduce the welding stress. However, if the standard control of the residual height of the weld is missing in the welding process, it will make the pressure vessel appear stress concentration phenomenon.
In summary, in the manufacturing process of pressure vessels affect the structure and quality of pressure vessels of many factors, but from the process point of view, further improve the welding process to ensure the rationality of the pressure vessel structure, the introduction of advanced technical means, strict control of the weld residual height, to a certain extent, can limit the generation of stress concentration.

Conclusion

Pressure vessel is an important storage vessel in the production process of China’s industrial pharmaceutical industry and petroleum industry, and the substances stored in the pressure vessel are highly corrosive and high hazard coefficient of production of raw materials, so in the design and manufacturing process of pressure vessels, to fully consider the impact of stress concentration on the vessel, to further clarify the causes of stress concentration, and then targeted by optimizing the structural design, and Improve the process method to avoid the occurrence of stress concentration problems. In the process of pressure vessel design and manufacturing, the causes of stress concentration problems are analyzed and the methods of reducing stress concentration are analyzed. With the continuous improvement of industrial design technology and manufacturing level in China in the future, we will continue to overcome the technical problems in the design and manufacturing process of pressure vessels based on the existing process methods and structural design, and further improve the stability of pressure vessels in terms of structure and safety in terms of process.

Author: Yang Lixia

Source: China Pressure Vessels Manufacturer – www.secmachinery.com

www.secmachinery.com 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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