Lead: Regulating valve is an indispensable part of petrochemical refining unit, the use of regulating valve type and quantity, large number of chemical production medium is corrosive, toxic or flammable and explosive, when regulating the valve leakage, It will not only cause serious waste of raw materials, energy and products, but also cause serious environmental impact and even cause serious accidents. Therefore, today's instrument control Jun told everyone to talk about the leakage of the regulation valve in the petrochemical production process.
First, adjust the valve leakage analysis
Under normal circumstances, there are generally two ways to regulate the leakage of the valve, that is, external leakage and internal leakage. The author in detail in the following content on the regulation of external leakage and internal leaks for specific analysis.
01 regulating valve leakage reasons
Valve body leakage reasons: the valve body is usually cast, easy to form trachoma and other casting defects, the body of the trachoma will lead to the leakage of media, the leakage are generally manifested as leakage, flow is smaller, through the hydraulic test Can be found.
Leakage stem causes: regulating valve stem due to improper design and material selection will cause the stem in a certain position is stuck, so that the valve can not be closed or closed lax, resulting in medium leakage.
Leakage of the valve body at the valve causes: We often say that the valve body connection parts of the seal, the valve body and the actual is the connection and sealing between the valve cover. Normally, the sealing method adopted between the valve body and the bonnet is the flange connection seal; however, when the nominal diameter of the adjustment valve is relatively small, the thread connection sealing method is required. In both types of sealing, if the type of gasket is not reasonable, the quality of the material, the material size does not meet the sealing requirements, as well as the flange sealing surface processing quality is poor, the tightness of the screw connection and bolt fastening Insufficient degree and other reasons can cause leakage of oil and gas connections at the valve body.
02 to adjust the cause of valve leakage
Regulating the valve internal leakage is due to the regulation valve is not closed due to the fact that such cases generally occur in the seat sealing surface. Investigate the specific reasons for the internal leakage of the regulating valve are: regulating valve structure design and valve manufacturing, construction process there are some problems, such as valve structure in the production of a certain size, there is a certain error, and the error exceeds the production Process allowable range, resulting in regulating valve seal is not tight conditions, resulting in the device medium flow of small continuous leakage phenomenon.
In addition to the valve design and manufacturing process there are errors and problems, the cause of the valve leakage caused by valve seat sealing surface deformation, valve sealing lax, resulting in the oil refining equipment leakage problems occur. This valve seat sealing surface deformation caused by the media leakage problems, the leakage of the form of mostly leakage. In addition, if the medium contained in the refinery contains a small amount of solid impurities, the same can also cause the regulator valve is not closed, leading to leakage of regulating valve, which due to the medium containing solid impurities caused by leakage problems, its leakage The same form of leakage, but the discharge of traffic may be a small flow, it may be a large flow.
Second, to prevent the regulation of valve leakage countermeasures
01 Optimization of valve design selection
Regulating valve leakage control and prevention of the principle is mainly to take a series of effective measures to regulate the degree of leakage of the valve to minimize and minimize to achieve the purpose of extending the excellent life. The regulation of the valve to reduce and reduce the amount of media leakage, refining equipment, the extension of the life of the medium, the media to improve the rate of use, to a large extent, depends on the selection of regulating valve design is reasonable, the valve quality of the product quality , The valve installation and construction of superb level and the correct choice of the valve seal form. Simply put, you want to regulate the valve to solve the problem of leakage and control, then we must first consider the design and regulation of regulating valve optimization.
The optimization of valve design selection involves the choice of regulating valve form, the design and manufacture of regulating valve itself, the selection of regulating valve material and many other issues. Select the form of regulating valve, from the requirements of process conditions and design specifications and other aspects of the need to fully optimize the consideration. Regulating the use of the valve, the media temperature, pressure, flow rate, pressure drop and the corrosive nature of the media, etc., have a direct impact on the selection of regulating valve, but also according to the medium temperature and corrosive, choose to manufacture materials used to regulate the valve . According to the construction and practical experience, in addition to meeting the requirements of the relevant process, the design of regulating valve should also take full account of the specific circumstances, to make it as much as possible with the operating conditions to meet the maximum use requirements.
02 stuffing box leakage countermeasures
The traditional soft packing seal is based on the axial pressure of the packing gland so as to achieve a certain radial contact stress between the valve stem and the packing as well as between the packing and the packing box side wall to achieve the sealing. Therefore, the gland axial force must be quite large, resulting in friction between the filler and the stem increased torque, increased wear, soft seal packing wear fast, and therefore often have to tighten the gland bolts or replace the filler, to ensure Better sealing effect.
The use of suitable packing seal and packing seal combination can improve the reliability of regulating valve and prolong the service life. Such as the combination of flexible graphite ring packing, sealing than the use of flexible graphite ring packing effect. At present, there is a lot of cases where a single flexible graphite ring packing is used in China. In other countries, the use of a combination of flexible graphite ring packing has started to prevail and good results have been achieved.
03 Elimination of leakage at body connection
Sealing of the connection part of the valve body belongs to the static seal in terms of its sealing property, and it should meet the following requirements: it can adapt to the drastic changes of temperature and pressure; it can be disassembled without damaging the sealing element; the structure is simple and compact; the consumption of metal is small; Not sensitive to vibration and shock load; can meet the requirements of various working media.
The connecting parts of the valve body are usually sealed with the birch groove type or concave-convex type flat gasket. In recent years, "O" ring seals have also been widely used. Zen groove flat gasket seal is the installation of flat gasket in the closed groove, this structure in the sealing surface, can produce a high pressure seal, usually far beyond the yield limit gasket material, thus ensuring the Reliable sealing. The pressure is greater than or equal to 4.0MPa in the high pressure regulating valve. The disadvantage of this type of seal structure is that the gasket is difficult to remove from the seal groove when the regulator valve is disassembled, and if it is removed rigidly, the gasket tends to be damaged.
Uneven flat gasket seal, the flat gasket is mounted on the sealing surface of the concave and convex flanges, compared with the campanula flat gasket seal structure, has the following advantages: Remove the regulator valve, the gasket is easy to remove; due to Sealing groove is ladder-shaped, so the processing performance is better.
Flat gasket material, according to process parameters and fluid properties, optional aluminum, copper, 1Cr18Ni9Ti and rubber asbestos board. Fluoroplastics are also commonly used gasketing sealants, but because of their cold flow properties, poor design of the seal structure can result in undesirable consequences.
"O" ring, the structure is simple, easy to manufacture, as long as the sealing structure design is reasonable, the assembly can produce sufficient radial compression deformation, can not be axially loaded to achieve the seal, therefore, as a flange Connection seal, can reduce the size of the flange structure, thereby reducing the weight of regulating valve.
04 stem leakage measures
Valve stem is an important component of the valve, it is mainly used for transmission, valve switching and regulation. Because the valve stem in the valve opening and closing process as a moving part, the role of force and the role of the seal, it must have a certain strength and toughness to meet the requirements of opening and closing the valve and assist the valve to play its regulatory role . In general, we will use some of the choice of stem material can withstand the corrosion of media, fillers and other substances, and better process performance of the material. And in order to further improve the stem of the friction, corrosion resistance, the staff will be on the surface of the stem for enhanced treatment to prevent the valve stem by the impact of media and corrosion, so that the valve stem leakage problems can be effectively controlled.
to sum up
Want to completely solve the leakage of regulating valve in the refining unit, the first measure is to optimize the selection of the design of regulating valve, and secondly, the sub-item control valve components in the various parts of the leak, the only way to effectively solve and control Regulate the leakage of the valve to prevent media leakage, to achieve the purpose of improving media utilization.
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