Analysis of Safety Inspection of Pressure Pipe Valves

Abstract: According to the relevant national standards, it is necessary to periodically perform safety inspections of pressure piping valves. This article first described the importance and significance of safety inspections for pressure piping valves, followed by the identification and review of the safety of pressure piping valves, pointed out several problems that were prone to occur, and finally put forward several solutions, hoping to Related studies provide lessons.
Keywords: pressure pipeline valve safety inspection 1. pressure pipeline valve safety inspection According to the "Pipeline Component Manufacturing Licensing Rules", "Pressure Pipeline Original Installation Approval Guidelines" and "Special Equipment Safety Supervision Regulations", as special equipment pressure pipeline valve The mandatory inspections need to be implemented regularly so that problems and hidden dangers in the operation of the equipment can be detected in a timely manner and the occurrence of safety accidents can be effectively avoided. On the one hand, regular inspections can eliminate safety accidents. On the other hand, they can more accurately understand the safety conditions of the equipment, thereby prolonging the service life of equipment and saving costs. Pressure pipelines often have problems in design, manufacture, installation, and management during their use. To prevent pressure pipelines from being damaged due to these problems, they must be inspected, repaired, and reformed on a regular basis, and a review report must be completed in strict accordance with the requirements. .
Second, pressure piping valve safety appraisal and assessment appraisal review Pressure pipe valve safety is mainly on the valve shell inspection, the use of pressure inspection method to check the valve body and valve cover valve housing. This inspection method can identify the tightness of the valve body and the valve cover and the pressure resistance of the entire housing including the connection between them. All valves must be inspected before leaving the factory. Only through the step of shell inspection can the valve be further painted or impermeable coating treatment, but the step of chemical rust prevention without sealing effect can be performed before the shell inspection step. If you want to check the inventory valve, you do not need to remove the existing coating. During the inspection and appraisal process, no external force sufficient to affect the inspection result can be applied to the valve, and the inspection pressure during the inspection process must remain unchanged.
1. The problem of leakage. The so-called leakage refers to the leakage of the media between the stem packing and the valve cover gasket, which is one of the important indicators to measure the quality of the valve. For some media, the requirement for leakage is the most stringent, because these media have a certain degree of flammability or toxicity. Emissions to the atmosphere from external leaks can easily lead to safety accidents, which seriously threaten people's life and health and property safety. In this case, people often use bellows sealing valves or diaphragm valves to avoid the problem of valve leakage. The external leakage identification standards are mainly based on the provisions of the US Environmental Protection Agency, and the leakage cannot exceed 500 ppm.
2. Endoleak problem. For pressure piping valves, the condition of internal leakage is the most important criterion for measuring valve quality. For petrochemical production, most of the media they handle are flammable, explosive, or toxic. When the valve is closed, the internal leakage of the valve is more severe and the valve's risk factor is higher. The identification criteria for internal leakage of the valve are ANSIB16.104, APl598 and JB/T9092. Among them, JB/T9092, which is the “Valve Test and Inspection Standard”, stipulates the valve travel standards as follows: The valve should be subjected to shell pressure before leaving the factory. Test and seal test. Here, the shell pressure test generally selects the water below 52 degrees Celsius or the non-corrosive fluid with a viscosity lower than that of water as the medium, and the test is performed at a temperature of 38 degrees Celsius and 1.5 times the nominal pressure. The seal test is composed of three types: upper seal test, high pressure seal test, and low pressure seal test. The upper seal test is used for valves with seal structure such as gate valve and globe valve. The air or inert gas is mainly used and the nominal pressure is 1.1 times. The high pressure seal test is the same as the upper seal test. Low-pressure sealing tests use air or inert gas at pressures between 0.5 and 0.7 times. The JB/T9092 standard not only stipulates the pressure holding time of the valve sealing test, but also stipulates the leakage inspection method and the allowable leakage. The standard adopts the API 598 standard and has strong standards.
3. Material quality issues. Material quality is also one of the important indicators to identify valve strength quality and service life. In general, most of the valves with DN ≥ 50 belong to the casting valve body. If the casting quality fails to meet the standards, the safety and service life of the valve will be reduced. The material quality appraisal standards are mainly ASTM standards and China's material standards. The requirements of these two standards are generally relatively low. In order to make the material meet the operating conditions in harsh environments, a lot of selective additional inspection items are set for the two standards to be used by the designer under different environmental conditions. The selection and use of additional items are very technical. If they are not properly requested, it will easily lead to increased infrastructure investment.
Third, improve the safety of pressure pipeline valve countermeasures For pressure pipeline valve safety issues, can be improved by the following three countermeasures.
1. Use bellows expansion joints. For petrochemical production plants, some high-temperature and large-diameter pipes cannot absorb natural thermal expansion displacements by means of natural compensation, and some can absorb thermal expansion displacement but the piping system reaction force is higher than the limit of connected equipment. It is possible to use bellows expansion joints to absorb the length extension of the pipe due to thermal expansion. There are mainly two types of corrugated expansion joints, constrained and unconstrained. The thrust of pipeline internal pressure of the constrained bellows expansion joint does not act at the fixed point or limit point, but acts on the position of the metal components. The internal pressure thrust of an unconstrained bellows expansion joint pipe acts on a fixed point or a constraining point, so it is mainly applied to absorb axial displacement and a small amount of angular displacement.
2. Use a filter. Filters refer to the filtration of solid particles in pipes to protect mechanical equipment and other piping equipment. There are many types of filters. Generally, there are two temporary filters and permanent filters. According to the shape of the filter, it can be divided into three-way DC and Y models, three-way side flow, and extended type. In general, the Y filter is mainly applied to the DN100. If the filter area is in large demand, then an extended three-pass filter can be used. The filter commonly used level is 30 mesh, generally according to the requirements of the connected instruments to select the corresponding filter mesh number.
3. Use a flame arrester. Flame arresters are often used in low-pressure combustible gas pipelines. The end of the pipeline is often prone to open flames. If the pressure in the pipeline causes the medium to flow backwards, the open flame can easily be directed to the source of the medium and cause a fire or explosion. At this time, the flame arrester can be installed at the end of the pipeline to prevent the open flame at the end of the pipeline, and the flame arrestor should be selected by the regular manufacturers.
IV. Conclusion In this paper, the safety inspection of pressure pipeline valves was studied, and the key problems related to the safety leakage, internal leakage, and material quality of pressure piping valves were identified and reviewed. Subsequently, the use of bellows expansion joints, the use of filters, and the use of flame arresters to solve countermeasures, hoping to provide a reference for the development of China's pressure pipeline valve industry.
[1] Xu Weipu, Ma Jingyong, Li Wei, Fu Minghai, Zhou Luyun. Research on Type Testing Technology of Pressure Pipe Valves[J].Chemical Equipment Technology.2012(03).
[2] Xiu Xianzhi, Zou Fan, Huang Yikang. Interpretation of API6D Pipeline Valves (23rd Edition) [J]. Valves. 2009 (01).
[3] Li Yu, Xu Weipu, Fu Minghai, Ma Hongbo, Zhou Luyun. Development of Fire Test Equipment for Pipeline Valves [J]. Valves, 2014(02).

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