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[Key words] pressure pipeline valve; fault; solution strategy CLC number: TP259 Document code: A Article ID:1009-914X(2018)38-0313-01
1. Valve common faults 1.1 Leakage between valve body or bonnet The main causes of such faults include the following: (1) Poor welding, that is, slag inclusion, incomplete welding or presence in the welding process of valve body and bonnet Insufficient welding cracks; (2) quality problems in the cast material, resulting in defects such as blisters and slag inclusions in the valve body and bonnet; (3) valve body and bonnet gasket failure; (4) flange preload Insufficient force or installation problems.
1.2 Filler leakage failure (1) The selected filler material has weak corrosion resistance or expired use, which makes the valve susceptible to media erosion and cannot withstand the high pressure, high temperature or low temperature generated during valve use. (2) During the installation process, the filler has defects such as small generation, poor spiral coiled joint, tightness and looseness; (3) the accuracy of the valve stem is relatively low, and it is prone to bending, abrasion or corrosion; (4) If the number of packing rings is insufficient, the gland is not pressed, or the relevant parts are damaged, the leakage of the gland may not be tight, or the gap between the gland and the valve stem is too small or too large due to the gland being skewed. The stem is worn and the packing is damaged; (5) Improper operation during installation or actual work.
1.3 Internal seal failure failure (1) Natural cause: internal seal failure failure due to the internal seal component meeting or exceeding its service life; (2) Other reasons: the sealing surface grinding effect is not good; The internal sealing surface is damaged; the material is not properly selected, it can not withstand the corrosion of the medium; the foreign matter is stuck on the sealing surface; the operation is wrong.
2. Precautions for valve failure The valve is an important mechanical device in the pipeline. The pressure, flow and flow direction of the medium in the control equipment and pipeline are controlled by the opening, closing and adjustment of the valve. Usually, the valve is required to be opened to reduce the water loss of the pipe section. Once required, the valve should be able to close quickly and reliably cut. Due to the opening and closing torque, the large diameter valve is equipped with a variable speed transmission box. For the use of such components, it should be noted that the gearbox is often easily immersed in water when installed outdoors, so the cabinet should have sealing measures. Otherwise, the water leaks from the packing, so it is easy to string into the box. If the maintenance and maintenance of these large valves are neglected in daily management, the valve failure will seriously restrict the smooth operation of the chemical equipment. Therefore, the daily operation management must start from four aspects to maintain the valve.
2.1 Management of valve technical data Establish a valve technical file. These include the factory instructions for the valve; the inspection certificate after the valve is purchased; the valve assembly and position card; the valve inspection record. For faulty valve replacement or valve addition and update, the valve card should be updated in time to establish a dynamic management mode for the valve.
2.2 Valve operation management The quality requirement of valve operation management is that the valve should be closed tightly or basically tightly; the valve shaft seal packing does not leak; the valve is light and easy to open and close.
2.3 Valve well management The valve well management includes the valve well masonry to meet the design requirements; the manhole cover is non-destructive, and the pavement is well connected; the hole of the operating valve is accurate; there is no debris and sewage in the well; the valve surface has no rust spots. Usually, the valve well should be patrolled regularly to establish a patrol record. Because the valve well is a closed space, it is easy to lack oxygen, resulting in an increase in carbon dioxide content. Operators or maintenance personnel must carry out oxygen content analysis before downhole operation, and take mandatory ventilation measures for valve wells with unqualified oxygen content. Otherwise, rushing into a relatively closed space is likely to endanger the safety of the operator. In the inspection, if the manhole cover is lost, damaged and the valve is faulty, corresponding measures should be taken and dealt with in time.
2.4 The new technology of steel valve testing uses new technology to detect steel valves in order to better detect the degree of steel valve damage and at the same time realize real-time monitoring of steel valves. When the steel valve is put into use, when the temperature change and pressure change occur, when it exceeds the normal value, it needs to be adjusted in time and the filler type is replaced. When the size of the packing is difficult to meet the correct requirements, the interface is cut out to a 45 degree break, then installed in a circle and gradually pressed. When the filler is contaminated, you can choose to add the lubricant for easy operation. When the stem is deformed and corroded, it can be simply repaired, and then the specific solution should be replaced if necessary.
2.5 Standardization of valve operation In the process flow chart, all valves need to be numbered, and then the sequence of the switch operation is gradually advanced according to the labeling of the process. In addition, valve management for key parts needs to eliminate the phenomenon of random operation, and put the daily identification and maintenance work in place. According to relevant regulations, the valve is identified and updated. During the development of these tasks, leaking valves need to be processed and replaced in time to ensure the safety of the pipeline. Of course, the division of labor system is a positive factor in ensuring the quality of work, which will allow the damaged valves to be regularly maintained and updated.
3. Valve leakage problems and handling Under the normal working pressure of the equipment, leakage occurs above the allowable degree at the sealing surface of the valve disc and the valve seat. The leakage of the safety valve will not only cause media loss. In addition, the continuous leakage of the medium will also damage the hard sealing material. However, the sealing surface of the commonly used safety valve is made of metal material to metal material. Although it is intended to be smooth and smooth, it should be done under the condition of medium pressure. It is also very difficult to never miss. Therefore, for a safety valve whose working medium is steam, if the leak is not visible to the naked eye at the specified pressure value, the sealing performance is considered to be acceptable. There are three main reasons for the leakage of the valve:
(1) The dirt impurities fall on the sealing surface, and the sealing surface is padded, causing a gap between the valve core and the valve seat, so that the valve leaks. The way to eliminate this kind of failure is to remove the dirt and impurities that fall to the sealing surface. Generally, when the boiler is ready to be shut down, the safety door running test is first carried out. If it is found that the leak is stopped, the disassembly and repair are carried out. The safety door leak was found during the running test after the furnace. It is estimated that this is caused by the situation. After the running for 20 minutes, the rudder can be run once again to flush the sealing surface.
(2) Damage to the sealing surface. The main reasons for the damage of the sealing surface are as follows: First, the sealing surface material is poor. For example, in the main safety door of No. 3-9 furnace, due to years of maintenance, the sealing surface of the main safety valve spool and the valve seat has been generally studied very low, so that the hardness of the sealing surface is also greatly reduced, thereby causing a decrease in sealing performance, eliminating this The best way to do this is to turn the original sealing surface down and then re-surge the welding according to the drawings to improve the surface hardness of the sealing surface. Note that the processing quality must be guaranteed during the processing. For example, cracks such as cracks and trachoma on the sealing surface must be turned and reworked. Newly processed spool seats must meet the drawing requirements. At present, the effect of the valve sealing surface of YST103 universal steel electrode surfacing welding is better. Second, the quality of the inspection is poor, and the valve seat is not up to the quality standard. The method to eliminate the failure is to repair the sealing surface by grinding or turning after grinding according to the degree of damage.
(3) Due to improper assembly or improper size of the parts. During the assembly process, the valve seat is not completely aligned or the joint surface is transparent, or the sealing surface of the valve seat is too wide to seal. The elimination method is to check the size and uniformity of the matching clearance around the valve core, to ensure that the top hole of the valve core and the sealing surface are the same degree, and it is not allowed to lift the valve core to check the gap of each part; the width of the sealing surface is appropriately reduced according to the drawings to achieve effective sealing. .
In conclusion, the management of the valve requires an analysis of the fault department of the valve and its causes, and then considers and seeks a more effective solution strategy. In order to achieve such work goals, management companies need to regularly organize employees to participate in training and learning activities, and put the testing work in place, in order to improve the work ability of relevant staff, maximize the risk of safety hazards, and ensure the tank The valve can be in a good working condition.
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[2] Sun Zhimin. Application of Computational Fluid Dynamics in Fault Analysis and Structural Improvement of Control Valves [J]. Modernization, 2016, 36(06): 176-178.
[3] Liu Shaowei, Gao Bingbing. Failure Analysis and Treatment of Pneumatic High Pressure Ball Valve[J]. Equipment Management and Maintenance, 2016(S1): 41-43.
[4] Guo Haikuan, Cai Qi, Zhao Xinwen, Zhang Yongfa. Time-varying research on failure probability of nuclear-grade valves[J].Nuclear Power Engineering, 2016,37(02):111-115.
Brief Discussion on Pressure Pipe Valve Failure and Solution
[Abstract] Valve equipment plays an important role in the daily operation and operation of pipelines. Through the analysis of various types of safety accidents occurring in the pipeline, the understanding of the quality, shape design and daily operation of the valve will be deepened, and the cause of the accident and the elimination method can be well explored. When the valve fails, it will directly lead to oil leakage and oil running. Therefore, the safe use of valve equipment is a key step to ensure the safety of the pipeline.