Reasons and countermeasures of fire prevention in regulating valve in chemical industry

Abstract: In the chemical control system with high risk of fire, the control valve acts as the terminal executive device of the regulating system and receives the control signal to adjust the chemical process. Its motion sensitivity is directly related to the quality of the regulation system. This article describes the analysis of the valve leakage valve leakage, leakage valve body interface, the main control valve after the action of the impulse valve does not move, the main control valve recoil after the impulse valve back seat back too long and the seat back pressure regulator valve low , Frequency hopping and flutter and other common causes of fire safety failures, and put forward countermeasures for the cause of the malfunction. Key words: control valve failure reasons countermeasures Preface In the fire risk higher chemical control system, the control valve as a regulatory system of the terminal implementation of the device is widely used in a variety of pressure vessels and piping systems, to accept control signals to chemical processes When the pressure in the pressurized system exceeds the specified value, it can automatically open excess flammable or flammable media to the atmosphere to ensure the safe operation of pressure vessels and piping systems to prevent the occurrence of a fire accident, And when the system pressure back to the working pressure or slightly lower than the working pressure can automatically shut down. Regulating valve work is directly related to the reliability of production equipment and personal fire safety and production. Control valve common fire safety fault analysis and solutions Valve leakage Under the normal working pressure of the device, the valve flap and valve seat sealing surface occurred more than allowable degree of leakage, the valve leakage will not only lead to loss of media. In addition, the continuous leakage of media will make the hard sealing material is damaged, but the sealing surface of the commonly used control valve is a metal material on the metal material, although strive to be smooth and smooth, but in the case of media pressure To the absolute leak is also very difficult. Therefore, the valve is flammable or flammable or medium, at the specified pressure value, if the use of professional testing tools test, such as to the extent permitted by the standard, can be considered sealing performance is acceptable. Common causes of valve leakage mainly in the following three conditions: First, debris falls on the sealing surface, the sealing surface padding, resulting in a gap between the valve core and the valve seat, so the valve leakage. To eliminate this failure is to remove debris falling to the sealing surface, usually in the pressure vessel to prepare the size of the repair, the first to do pressure vessel safety gate running test and found that leakage, the pressure vessel to stop working and the valve overhaul, Wash the sealing surface. Second, sealing surface damage. Seal surface damage caused by the following main reasons: First, poor sealing surface material. Due to years of use, valve core and seat sealing surface has generally been studied very low, so that the sealing surface hardness is greatly reduced, resulting in reduced sealing performance, the best way to eliminate this phenomenon is the original sealing surface turning Go down, and then re-welding the drawings required processing to improve the sealing surface hardness. Note that in the processing must ensure the quality of processing, such as the sealing surface cracks, trachoma and other defects must be machined back after processing. Newly processed valve seat must meet the drawing requirements. Second, the poor quality of maintenance, valve seat grinding can not meet the quality standards, the way to eliminate this failure is based on the degree of injury using grinding or turning grinding method to repair the sealing surface or reinstall the new control valve. Third, another cause of leakage caused by the control valve is due to improper assembly or parts size is not appropriate. In the assembly process, the valve seat is not fully aligned or the surface with light transmission phenomenon, or the valve seat sealing surface is too wide, which is not conducive to sealing. Elimination method is to check the spool around the size and uniformity of the gap to ensure that the valve core tip hole and the sealing surface with a positive, check the Ministry of the gap does not allow lift valve, according to the drawing requirements to reduce the width of the sealing surface to achieve effective sealing . Fourth, spool, seat deformation leak. Valve core, seat leakage is mainly due to the production process of valve casting or forging defects can lead to enhanced corrosion. The corrosive medium through the erosion of the fluid medium can also cause the regulator valve leakage. Corrosion mainly exists in the form of erosion or cavitation. When the corrosive medium passes through the regulating valve, erosion and impact on the valve core and the valve seat material will occur, causing the valve core and the valve seat to become oval or other shapes as The passage of time, leading to spool, seat is not complete, there is clearance, the strict control of leakage. The key to the solution to the valve spool, valve seat and other material selection off, quality control. Select corrosion-resistant materials, pitting, trachoma and other defects of products resolutely removed. If the valve core, seat deformation is not serious, can be fine sandpaper grinding, eliminate traces, improve seal finish, to improve the sealing performance. If the damage is serious, the new valve should be replaced. Leakage of the valve body surface? Leakage of the valve body surface refers to the phenomenon of leakage at the joint surface between the upper and lower valve body. The main causes of such leakage are as follows: First, the bolt force on the joint surface is not enough or tight Partial, resulting in poor sealing surface. Elimination method is to adjust the bolt tightness, the tight bolt must be diagonally tight manner, it is best to measure the tightness around the gap, the bolt tight so far, and the junction of the gap around Consistent. Second, the valve body with the tooth surface seal does not meet the standards. For example, the radial seal groove slightly grooved, poor parallelism, tip too sharp or over-the-slope and other defects can cause seal failure. So that the valve body surface leakage. In the maintenance of good spare parts quality, the use of standard toothed gaskets can avoid this phenomenon. Third, the flatness of the valve body with poor or hard padded impurities caused by seal failure. The valve body due to the flatness of the joint surface caused by poor bonding surface leakage, the elimination of the valve is to disintegrate the valve to re-ground the joint until the quality standards. As a result of impurities caused by gasket failure seal in the valve assembly carefully clean the surface to avoid impurities fall into. The main control valve after the action of the impulse regulating valve does not act The impulse regulating valve does not act after the main regulating valve is actuated. The main control valve refused to move on the equipment is very harmful, is a major equipment fire hazard, seriously affecting the safe operation of equipment, once the pressure in the pipeline and medium pressure exceeds the rated value, the main control valve No action, the device over-voltage operation can easily cause equipment damage and major fire accidents. Main control valve refused to move mainly with the following three factors: First, the valve moving parts have jamming phenomenon. This may be due to improper assembly, dirt and impurities mixed or parts corrosion; poor surface finish of the piston chamber, surface damage, there are defects such as groove marks caused by defects. Second, the main control valve piston chamber leak large. Piston chamber caused by a large amount of air leakage and the valve itself is not air tightness and piston ring does not meet the size requirements or excessive wear and tear of the piston ring seal does not meet the requirements. The way to eliminate this defect is to deal with the inner surface of the piston chamber, replace the qualified piston and piston ring, and set off the small throttle opening in the throttle safety device system with throttle, and increase the pressure into the main control valve piston chamber Into the amount of steam, where conditions permit, you can also increase the stroke of the impulse regulator valve to increase the intake into the main control valve piston chamber method to promote the main regulator valve action. Third, the main control valve and impulse valve matching properly, impulse valve steam flow is too small. The nominal diameter of the impulse regulating valve is too small, resulting in insufficient amount of steam flowing into the piston chamber of the main regulating valve, insufficient force to push the piston downward, causing the main regulating valve spool not to move. This phenomenon occurs in the main regulator valve type impulse valve has a replacement, due to poor consideration caused. Impulse valve back seat after the main control valve delay back seat too long This failure occurs mainly in the following two aspects: On the one hand, the main control valve piston chamber leakage size, although the impulse valve back seat , But there is still pressure in the pipeline and the steam in the piston chamber is still high, pushing the piston downward force is still large, resulting in the main control valve back slowly. The way to eliminate this kind of failure is mainly solved by opening the large throttle opening and increasing the throttle diameter. The large opening of the throttle valve and the increase of the throttle aperture allow the medium left in the pulse tube to be drained rapidly , Thus reducing the pressure inside the piston, so that the role of the piston on the downward movement of the thrust quickly decreased, the valve core in the medium upward thrust and the main control valve spring pull back quickly under its own seat. On the other hand the reason is that the friction between the moving parts of the main regulating valve and the fixed parts is too large and the main regulating valve can be slung back slowly. The solution to this problem is to match the clearance between the moving part of the main regulating valve and the fixed part Control standard range. Regulating valve back seat pressure is low? Regulating valve back seat pressure is too low will cause a large number of media out of time emissions, to the production, the equipment constitutes a fire hazard. Analysis of the reasons are mainly caused by the following factors: First, the spring pulse control valve on the media excretion, this form of the impulse valve is opened, the media continue to discharge, promote the main regulating valve action. On the one hand, the pressure before the pressure regulating valve due to the main regulating valve medium discharge is insufficient and continue to rise, continue to flow to the impulse regulating valve to maintain the impulse regulating valve action. On the other hand, because the flow of the medium of the impulse regulating valve flows to the piston chamber of the main regulating valve through the gap between the valve core and the guide sleeve, the medium flushes out the sealing surface of the impulse regulating valve to form a dynamic pressure zone around it, High, so to achieve the momentum adjustment valve to continue to discharge ,, the greater part of the core part of the kinetic energy pressure zone pressure, the greater the upward thrust on the valve spool, the more impulse regulating valve is less easy to back seat, this time to eliminate this Fault method is to throttle small, so that out of the flow control valve to reduce the flow of media, reducing the pressure in the kinetic energy pressure area, so that the impulse valve back seat. Second, the spool and the guide sleeve with the gap is not appropriate, with the gap is small, the impulse adjustment valve Kai seat, instant throttle in this area to form a higher kinetic energy pressure zone, the valve lift, delay back seat time When the container is lowered to a lower level, the pressure in the kinetic energy pressure zone is reduced and the impulse valve returns to seat. Way to eliminate this failure is to carefully check the size of each part of the valve plug and the guide sleeve, with the gap is too small, reducing the diameter of the valve disc sealing surface straight valve cap or increase the radial clearance between the valve disc and the guide sleeve , To increase the flow area of ​​the site, so that the local pressure rise to form a high kinetic energy pressure zone. Third, the friction of various sports parts, some parts have jam, the solution is to carefully check the various moving parts, maintenance standards in strict accordance with the repair of the various components, the various components with the clearance adjustment to the standard range, eliminating jam as possibility. Regulating valve frequency jump Frequency jump refers to the control valve back seat, to be slightly elevated pressure, the control valve will open again and again several times, this phenomenon is called the control valve "jump." Regulating valve mechanical properties require regulating valve in the entire process reaches the required opening height, the card is not allowed to block, tremor and frequency hopping phenomenon. Occurrence of frequency regulation valve seal is extremely unfavorable, easily lead to the sealing surface of the leak. Analysis of the main reasons for the back pressure valve seat and the high, back seat pressure is high, the container less excess media emissions, the control valve has been back to the seat, and when the operator improper adjustment, the pressure in the container will be very fast Rise, it also caused the action of regulating valve to solve the frequency control valve can be opened by opening the throttle opening method to be eliminated. When the throttle valve is opened, the steam source leading to the main control valve piston chamber is reduced, the force pushing the piston downward is smaller, and the main control valve is less likely to operate, thereby avoiding the continuous starting of the main control valve. Damping valve regulating valve in the discharge process of jitter phenomenon, called the control valve of the flutter, flutter phenomenon can easily lead to metal fatigue, so that the mechanical properties of the control valve, causing a serious fire hazard , The main cause of flutter has the following two aspects: On the one hand the improper use of the valve, the use of the valve discharge capacity is too large (relative to the amount of emissions must be), the elimination method should be selected valves rated displacement As close to the equipment as necessary emissions. On the other hand is due to the inlet pipe diameter is too small, smaller than the inlet diameter of the valve, or inlet pipe resistance is too large, the elimination of the valve is installed, the inlet pipe diameter not less than the inlet diameter of the valve or reduce the import pipe resistance. Excessive discharge pipe resistance, resulting in excessive discharge when the North pressure is also a factor that causes the valve flutter can be reduced by reducing the resistance of the discharge pipe to be resolved. Conclusion Through the analysis of the cause of the malfunction of the regulating valve, proper treatment and improvement measures will greatly improve the utilization rate of the regulating valve, reduce the failure rate of the instrument, and improve the production efficiency and economic benefit of the process technology