Survemahutite rikete põhjuste analüüs ja arutelu ennetusettepanekute üle

The industrialization construction has led to the rapid development of chemical enterprises in China. From a long-term development perspective, chemical enterprises face high safety risks, and once problems arise, they will have a relatively adverse social impact. The failure of production equipment caused by cracks in pressure vessels is a major safety hazard in major chemical enterprises. If not prevented as soon as possible, it will not only affect the normal operation of production equipment but also threaten the safety of residents, causing unnecessary economic losses. Exploring the causes of pressure failure and constructing preventive measures have become the focus of attention for chemical enterprises. This article will take two cases of pressure vessel failure as the research object, analyze the causes of cracks, discuss high-quality prevention measures, and promote the long-term and stable development of chemical enterprises.

Pressure vessels are common special equipment under pressure and serve as the foundation for ensuring industrial production’s normal and stable operation. They are widely used in chemical reactions, material separation and storage, and heat exchange. From a theoretical perspective, the properties of pressure vessels are relatively unique. Strict management is required to establish good application conditions regardless of the type of pressure vessel. Otherwise, there may be chemical or physical explosions. High-level production, management, and subsequent maintenance of pressure vessels can effectively reduce the risk of accidents and demonstrate a country’s production level and progressiveness technology. With the rapid development of various fields in China and the wider application range of pressure vessels, new requirements have been put forward for the safe use of pressure vessels. Enterprise businesses must regularly monitor pressure vessels, strictly comply with the relevant regulations in the “Safety Technology Supervision Regulations for Fixed Pressure Vessels, ” minimize safety risks, and achieve maximum economic practicality.

1. Overview of two inspection cases

1.1 Regular inspection status of multifunctional extraction tanks

This study was conducted in January 2020 with a multifunctional extraction tank located in an industrial park in the province. Before testing, the testing personnel should have a deep understanding of the regional characteristics and relevant testing standards; During the inspection, it was found that the written information of this multifunctional extraction tank showed a designed service life of 8 years. However, the investigation found that the extraction tank was first applied in 2008, and its usage seriously exceeded the estimated service life. Through inspection of its appearance, it was found that there were many fine cracks at the cutting cover position; To further understand the damage situation, technicians began using penetration testing to complete relevant inspections and found that there were fine lines of continuous fracture in the entire circle at the weld seam on the outer wall of the lower cover. The relevant parameters are shown in Table 1.

Table.1 Relevant parameters of multifunctional extraction tank

Name Parameter
Container Category Class I
Inspection Category Regular Inspection
Service Life  8 Years
Application Time Jan-08
Running State  In Use
Design Pressure/Mpa Atmospheric Pressure (Inner)/Jacket (0.33)
Operating Pressure/Mpa Atmospheric Pressure (Inner)/Jacket (0.33)
Design Temperature/° C 100 (Inner)/146 (Jacket)
Operating Temperature/° C 95 (Inner)/143 (Jacket)
Nature Of Work Liquid Medicine (Internal)/Saturated Steam (Jacket)

1.2 Regular inspection status of the reaction kettle

In March 2020, a periodic inspection was conducted on the reaktsioonikannu of a glass manufacturing plant in the same province. In verifying relevant written materials, it was found that the reactor was first used in March 2009, and the expected service life should have been mentioned in the relevant documents. A detailed inspection of its appearance revealed no obvious abnormalities or damage. However, after magnetic particle testing, it was found that there were obvious fine cracks at the root of the equipment meshing teeth and kettle cover meshing teeth, with the longest being up to 72mm. The relevant parameters are shown in Table 2.

Table.2 Relevant parameters of the reaction kettle

Name Parameter
Container Category Class Ii
Inspection Category Regular Inspection
Service Life  Unknown
Application Time Mar-09
Running State  In Use
Design Pressure/Mpa One Point Six
Operating Pressure/Mpa 1.5
Design Temperature/° C One Hundred And Sixty
Operating Temperature/° C 160
Nature Of Work Air

2. Analysis of the causes of pressure vessel failure in two cases

2.1 Causes of cracks in multifunctional extraction tanks

To understand the reasons for the failure of the pressure vessel, technical personnel actively organized data and conducted detailed inspections of the equipment. Upon verification, it was found that this multifunctional extraction tank is mainly used for preserving medicinal liquids. Still, these medicinal liquids have complex structures and involve various substance types and chemical elements, commonly including hydrogen ions and free hydrogen ions. In actual use, it is necessary to repeatedly, repeatedly, and frequently open and close the extraction tank door cover. Affected by many factors, such as temperature, pressure, and air impurities, the upper mouth of pressure vessels is prone to corrosion. Long-term exposure to corrosion can easily cause macroscopic corrosion of the discharge cover, with a large number and complex overall structure. Due to the weak fusion line of the weld seam on the outer surface of the cutting cover during the welding process, cracks are prone to occur, leading to deviations in the microstructure and properties of this position, ultimately leading to the formation of crack defects. In addition, researchers also found that this multifunctional extraction tank has exceeded the estimated service life at the time of design, indicating that its overall material and structure will undergo significant deterioration or deterioration.

2.2 Causes of cracking in the reactor

Through on-site inspection, it was found that this reactor belongs to a quick-opening pressure vessel and was first used in March 2009. Due to various factors such as enterprise scale and investment, this reactor has been operating at full capacity for a long time. When manufacturing equipment, the meshing teeth of the kettle flange are mainly applied to plasma cutting technology, and at the same time, repair welding arc transition is achieved at the root of the teeth. The inspection results show that the crack defects are mainly concentrated in the repair welding position, which belongs to the area with relatively poor-quality meshing teeth. By polishing the cracks on the on-site reaction kettle, it was found that a large number of pores, debris, and other small defects appeared in the repair welding area. These defects, to some extent, concentrated local stress, and over time, it would induce the generation of fine cracks, which are the main factor causing the cracks. This indicates that safety hazards have already emerged during the equipment manufacturing stage. To ensure meticulous investigation, technical personnel further inspected the structure of the flange meshing teeth of the kettle body and found the following characteristics. There is a discontinuity around the meshing teeth, and under the influence of complex stress conditions, the meshing teeth not only bear axial shear force but also generate bending moment. Normally, the root of the meshing teeth of a quick-opening pressure vessel will bear cyclic loads, which to some extent, leads to an increase in the force on the meshing teeth and a significant increase in complexity. Affected by the pressure increase and decrease during the production process, the meshing teeth of the reaction kettle will undergo significant damage under alternating stress, resulting in an increase in the fatigue of the meshing teeth and the generation of cracks.

3. Suggestions for preventing pressure vessel failure

The failure of pressure vessels caused by cracks has become a key safety hazard in the chemical industry. It affects the safe and stable operation of the device and threatens the health and safety of workers and surrounding residents, resulting in unnecessary economic losses and other issues. This requires enterprises and relevant testing institutions to increase the importance of design, production, manufacturing, and inspection processes. Summarizing two cases, it was found that the main causes of pressure vessel failure were initial defects in the pressure vessel, including non-compliance with relevant standards during the manufacturing process, defects in the production and processing process, high internal stress, and design defects. As for the causes of cracks in multifunctional extraction tanks, users must strictly follow relevant standards during the opening process to ensure standardized operation. At the same time, technical personnel should regularly visit the site to conduct safety hazard investigations, fully understand the actual application status, do a good job in daily maintenance and upkeep, carefully review product documents, regularly and regularly verify the product’s service life, strictly follow relevant standards for risk investigation, and try not to use equipment beyond its service life as much as possible. Suppose the equipment replacement will affect normal operation. In that case, it is necessary to organize relevant technical personnel to conduct a complete and comprehensive risk assessment of the equipment to ensure its stable operation.

As for the reaction kettle, it is required that the production and manufacturing enterprises strictly control the production process and ensure quality control. Manufacturing enterprises should strictly follow regulations and standards such as “Pressure Vessels” and “Nondestructive Testing of Pressure Equipment” for management and testing. Based on actual production characteristics, appropriate processing techniques, and welding techniques should be selected to improve the cutting accuracy of meshing teeth as much as possible, ensure that the meshing teeth comply with relevant specifications, and ensure the quality of forming. When repairing welding at the root of meshing gear, qualified welders shall be selected for welding to ensure the progressiveness of welding technology. At the same time, welding shall be carried out strictly with relevant assessment standards to ensure that the welding quality meets relevant standards. After welding, the technical personnel should conduct a complete and comprehensive heat treatment and non-destructive inspection and attach importance to the supervision and inspection process during manufacturing. After the product leaves the factory, relevant quality inspection agencies must conduct a complete and detailed inspection of the meshing teeth to ensure that the product meets the marketing and usage standards. When using such products, chemical enterprises must develop a complete, detailed, and comprehensive production and usage system based on actual usage scenarios and characteristics to ensure stable pressure boosting and depressurization as much as possible and to avoid excessive alternating stress on the meshing teeth, causing the reactor to be overloaded for a long time, accelerating the formation of cracks in the reactor, and causing serious damage. In the actual use process, the user unit should actively implement the main responsibility of use management, reasonably divide the responsibilities of each link, increase the investigation of pressure vessel cracks and defects, promptly identify potential safety hazards, report any problems immediately, and complete on-site rectification. In addition, enterprises should strengthen crack detection to prevent key projects and objects in their daily inspections. In non-destructive testing, innovative technologies such as ultrasonic phased array and array eddy current can be attempted to be integrated to improve detection accuracy and maximize crack detection.

By analyzing the above two cases, the following protective measures can be summarized:

  • (1) Strengthen the installation and monitoring of pressure vessels. The installation process, as the foundation for the safe operation of pressure vessels, requires technical personnel to focus on controlling it to avoid problems such as lack of professional qualifications and lax installation by the installation team and to prevent potential safety hazards from being reserved; Increasing the inspection intensity during the installation process helps to eliminate potential installation hazards of pressure vessels and ensure their long-term stable operation. Hire a third-party testing agency to inspect the pressure vessels during and after installation, laying a solid foundation for subsequent normal and stable work.
  • (2) Regularly organize technical personnel to conduct scientific testing and maintenance of pressure vessels. The technical personnel of the pressure vessel user unit should regularly inspect the usage of the pressure vessel, fully record the special equipment whose safety inspection certificate is about to expire, and provide relevant explanations and regular inspection requirements to the relevant testing agency one month in advance. The inspection unit should combine written instructions, organize and plan on-site investigations, and prepare for the container inspection. After the inspection is completed, a complete inspection report should be issued for the reference of the user unit. The user unit must perform targeted rectification work with the paper report. If there are any questions, they should promptly contact and confirm with the inspection unit. The inspection unit will issue a “Special Equipment Inspection Opinion Notice” for pressure equipment with significant safety hazards, which comprehensively explains the rectification suggestions. After the user unit completes the changes individually, they should contact the inspection agency again and conduct a secondary inspection until the pressure vessel inspection meets the relevant standards.
  • (3) Conduct self-inspection and screening of pressure equipment. Self-inspection and screening are necessary guarantees to ensure the safe operation of pressure vessels. Only through regular maintenance can we understand the problems existing in pressure vessels. In principle, it is required that the unit using the pressure vessel should conduct 2-3 inspections of the equipment every month. If there are special circumstances, it should be ensured that the inspection is conducted at least once a month, and the inspection results should be recorded. Before conducting self-inspection, technical personnel should scientifically plan based on usage and characteristics, clarify key inspection items and inspection standards, screen safety accessories, electrostatic grounding, and corrosion conditions of pressure vessels one by one, ensure orderly operation, improve operational reliability, timely detect defects in inspection, and ensure safe and stable operation of pressure vessels.
  • (4) Increase the training of technical personnel. Usually, non-standard or incorrect operation by technical personnel can cause pressure vessel failure to a certain extent, leading to a rapid increase in internal stress and explosion risk. This threatens the life and health of technical personnel, causes unnecessary economic losses, and has a relatively adverse social impact, and affects the reputation of enterprises. This is enough to demonstrate the importance of conducting vocational skills training. Require pressure vessel users to conduct regular training on the operational skills of technical personnel based on the actual working characteristics to enhance their self-protection awareness; Technical personnel is required to hold a certificate to work, strictly follow relevant regulations to complete operations, and minimize human factors.
  • (5) Develop operating procedures and emergency plans based on relevant standards. The unit using pressure vessels should develop complete and detailed safety operation procedures based on the application status of the enterprise, including process indicators during operation, job operation methods, and key inspection items and locations. Based on long-term work experience and actual inspection results, comprehensively consider the potential safety risks during its use and build targeted emergency plans, including possible abnormal phenomena and existing safety hazards. Enterprises should regularly carry out safety drills according to relevant standards, cultivate employees’ self-protection ability, improve the abnormal analysis and judgment ability of operators and management personnel, ensure that they can quickly enter the state when problems occur, identify potential safety hazards, and minimize losses after pressure vessel failure as much as possible.

4. Conclusion

In summary, by analyzing and reflecting on the causes of cracks in the two pressure vessels mentioned above, we aim to gain a deeper understanding of the current application status and existing problems of pressure vessels. We require manufacturing, user, and testing units to closely connect, continuously increase attention, and strengthen daily management. To solve and prevent the failure of pressure vessels caused by cracks, the following three aspects of work should be strengthened: firstly, the manufacturing unit must possess noble professional ethics, ensure the selection of construction materials, welding processes, and other aspects during the container manufacturing stage, attach great importance to the inspection before and after welding, strengthen the non-destructive inspection and self-inspection process after heat treatment, and strictly follow relevant technical standards and procedures to complete all work. Secondly, the user unit should implement the main responsibility of maintenance and daily maintenance, establish dedicated personnel for management, and ensure that problems occur and are resolved as soon as possible. Afterward, strengthen the management of the installation process, focusing on whether the container body is complete, especially for quick opening pressure vessels and pressure vessels that exceed the design’s expected lifespan. Finally, strengthen the regular inspection efforts to ensure that the equipment is in a stable operating state, comprehensively inspect pressure vessels that exceed the design’s expected lifespan, and quick opening pressure vessels that are inspected for the first time to prevent fatigue cracks from occurring when this equipment operates under overload. Actively adopt advanced detection instruments and technologies to improve sensitivity and achieve maximum crack detection. Only by deeply analyzing the causes of pressure vessel failure and constructing preventive measures can the overall stability of its operation be improved and the development of chemical enterprises be promoted.

Author: Zhou Xiaodong

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