Talk about “running and leaking” of valves

One, the valve leakage, steam leakage prevention measures.  

1. All valves must be subjected to hydraulic test of different grades after entering the factory.  

2. It is necessary to disassemble and repair the valve must be ground.  

3. During the overrepair, check whether the coiling is added and the coiling gland is tightened.  

4 valve before installation must check whether there is dust, sand, iron oxide and other debris inside the valve.  If the above sundries must be cleaned up before installation.  

5. All valves must be fitted with gaskets of the corresponding grade before installation.  

6. Tighten the fasteners when installing the flange doors, and tighten the flange bolts in the symmetrical direction.  

7. In the process of valve installation, all valves must be installed correctly according to the system and pressure, and random and mixed installation are strictly prohibited.  For this purpose, all valves must be numbered and recorded according to the system before installation.  

Two, on the prevention of coal leakage measures.  

1. All flanges must be installed with sealing materials.  

2. The areas prone to powder leakage are the import and export coal valves of coal mills, coal feeders, flanges of manufacturers, and all parts connected with flanges.  Therefore, we will carry out a comprehensive inspection on the parts of all manufacturers’ equipment that may leak powder. If there is no sealing material, we will carry out secondary reinstallation and tighten the fasteners.  

3. The phenomenon of powder leakage may occur in the welding joint of pulverized coal pipe, we will take the following measures.  

3.1 Before welding joint, the welding joint area must be carefully polished to a metallic luster and polished to the welding groove required.  

3.2 The matching gap must be reserved before the matching, and it is strictly prohibited to force the matching.  

3.3 Welding materials must be used correctly, and must be preheated as required in cold weather.  

Three, oil system leakage, oil running and other preventive measures.  

1. It is very important to do well the leakage and oil running of the oil system.  

2. Check and clean the system with oil storage tank carefully before installation.  

3. Hydraulic test must be carried out on the equipment with oil coolers.  

4. Hydraulic test and pickling work should also be done for the oil pipeline system.  

5. In the installation process of oil pipeline, all flange joints or live joints with silk buckle must be fitted with oil-resistant rubber pad or oil-resistant asbestos pad.  

6. The leakage point of the oil system is mainly concentrated on the flange and the threaded live joint, so the bolts must be tightened evenly when installing the flange.  Prevent leakage or loose tightness.  

7. In the process of oil filtration, the construction personnel must always stick to their posts, and it is strictly forbidden to take off or cross posts.  

8. The oil filter must be stopped before replacing the oil filter paper.  

9. When installing the temporary oil filter connection pipe (high-strength transparent plastic hose), the joint must be firmly bound with lead wire to prevent the phenomenon of escaping oil after the oil filter has been running for a long time.  

10. Deploy responsible construction personnel to take care of the work of the oil filter.  

11. Before the auxiliary oil system starts the oil cycle, the engineering department organizes the personnel responsible for the auxiliary oil cycle to make a detailed technical disclosure.  

Iv. Prevent bubbles, bubbling, dripping and leakage in the combination of equipment and pipe fittings. There are the following prevention measures:   

1. Metal winding gaskets are used for flange gaskets above 2.5mpa.  

2, 1.0Mpa-2.5mpa flange gaskets, asbestos gaskets, and coated with black lead powder.  

3, below 1.0mpa water pipe flange sealing pad with rubber pad, and coated with black lead powder.  

4, water pump coil are made of PTFE fiber composite coil.  

5. For the sealing part of smoke and wind coal pipelines, the asbestos rope is twisted and added to the joint surface at a time. It is strictly forbidden to tighten the screws after strong joining.  

Five, eliminate the valve leakage has the following measures :( for the valve leakage we should do the following measures)  

1. Good quality awareness must be set up for pipeline installation and construction, and the oxide sheet and the inner wall of the pipeline must be cleaned consciously, leaving no sundries and ensuring the inner wall of the pipeline is clean.  

2. First, ensure that 100% of the valves entering the site must be hydrostatic test.  

3. Valve grinding should be carried out seriously. All valves (except imported valves) should be sent to the grinding team for disintegration inspection, grinding and maintenance, and the realization of responsibility, consciously record and identify, easy to trace back.  Important valves should list the details for secondary acceptance, so as to meet the requirements of “stamping, checking and recording”.  

4. The boiler first water inlet door and discharge door should be determined in advance. Only these valves are allowed to open during the hydrostatic test, and other valves are not allowed to open at will, so as to protect the valve core.  

5. When the pipeline is flushed, turn it on and off gently to prevent damage to the spool.  

If it’s leaking, what’s the reason?  

(1) the contact between the opening and closing parts and the sealing surface of the valve seat;  

(2) packing and stem and packing box matching;  

(3) the connection between the valve body and the valve cover  

One of the former leakage is called internal leakage, which is usually said to be lax, it will affect the ability of the valve to cut off the medium.  The latter two leakage is called external leakage, that is, media leakage from the valve to the valve outside. Leakage will cause material loss, pollution of the environment, serious will also cause accidents.  

Fall in the real place, analysis of internal leakage, internal leakage is generally:  

Valves have an allowable internal leakage standard according to their caliber, system differential pressure, and system media.  In a strict sense, a true ’0′ leakage valve does not exist.  In general, small diameter globe valves are easy to achieve invisible leakage (not zero leakage), while large diameter gate valves are difficult to achieve invisible leakage.  In the event of internal leakage of the valve, first of all, we should try to understand the specific internal leakage, refer to the valve leakage standards, internal leakage occurs when the system working environment and other factors for comprehensive analysis, in order to correctly judge the internal leakage of the valve.  

(1) The internal leakage problem of parallel gate valve.  

The working principle of parallel gate valve is to rely on the differential pressure of the system to the outlet side of the spool and seat sealing surface pressure, in the case of very low system pressure, there may be a slight internal leakage phenomenon after the valve.  In the event of such internal leakage, it is recommended to continue to observe and check the sealing of the valve when the inlet pressure of the system reaches the design pressure or the normal working pressure. If there is excessive leakage, it should be disintegrated and ground the sealing surface of the valve.  

(2) internal leakage of wedge valve.  

Sometimes it is because of the different valve control mode, because the manufacturer when the design selection, the corresponding stem and stem nut is the strength of the design did not consider torque control mode, and using the stroke control mode, if forced to travel in the closed position control mode to torque control, may cause damage to the valve stem nut, etc.  At the same time, it leads to the failure of the electric head when it is opened and the opening torque fault alarm.  In the case of internal leakage of this valve, it is usually manually closed after the electric closure, and then closed. If there is still internal leakage after the manual closure, it indicates that the sealing surface of the valve has a problem, and then it needs to be disintegrated and ground.  

(3) internal leakage of check valve.  

Check valve sealing is also dependent on the pressure difference of the system, when the inlet pressure of the check valve is very low, the outlet pressure will also have a slight rise, then should be analyzed by a variety of factors, determine the internal leakage, according to the analysis of the structure to decide whether to take the physical repair work.  

(4) Internal leakage of large diameter disc valve.  

The standard of internal leakage of large diameter disc valve is generally very large. When the inlet pressure increases, the outlet pressure will also increase. For this problem, the internal leakage should be judged first, and the decision of whether to repair or not should be made according to the internal leakage.  

(5) the internal leakage of the regulating valve.  

Because the form of the regulating valve is different, the standard of internal leakage is not the same, at the same time, the regulating valve is generally used in the way of stroke control, (not using torque control), so there are generally internal leakage phenomenon.  The internal leakage problem of the regulating valve should be treated differently, and the regulating valve with special internal leakage requirements should be considered in the design and manufacture.  There are many such contradictions in XX Nuclear Power Plant. Many valves are forced to be changed into torque control, which is detrimental to the work of the regulating valve.  

To be more specific:  

(1) Poor material selection and heat treatment of valve inner parts, insufficient hardness, easy to be damaged by high-speed fluid.  

(2) Due to the valve structure limit, fluid through the valve energy (speed) has no effective consumption, impact wear force on the sealing surface;  Excessive speed leads to too small pressure behind the valve, which is lower than the saturation pressure, resulting in cavitation. In the cavitation process, all the energy when the bubble bursts is concentrated on the rupture point, resulting in thousands of Newtons of impact force, and the pressure of shock wave is as high as 2×103Mpa, which greatly exceeds the fatigue failure limit of existing metal materials.  Extremely hard discs and seats can also be damaged and leak in a very short time.  

(3)The valve works in a small opening state for a long time, the flow rate is too high, the impact force is large, and the internal parts of the valve are easily damaged.


Post time: Dec-20-2021