Talk about the "running, leaking, dripping and leaking of equipment!"
一. Preventive measures for valve leakage and steam leakage.
1. All valves must undergo different levels of water pressure test after entering the factory.
2. Valves that need to be disassembled for maintenance must be ground.
3. During the over-repair process, you must carefully check whether the packing is added and the packing gland is tightened.
4. Before installing the valve, check whether there is dust, sand, iron oxide and other debris inside the valve. If there is any above-mentioned debris, it must be cleaned up before installation.
5. All valves must be equipped with corresponding grade gaskets before installation.
6. The fasteners must be tightened when installing the flange door, and the flange bolts must be tightened in symmetric directions when tightening the flange bolts.
7. During the valve installation process, all valves must be installed correctly according to the system and pressure, and random or mixed installation is strictly prohibited. For this reason, all valves must be numbered and recorded according to the system before installation.
二. Precautions against leakage of pulverized coal.
1. All flanges must be installed with sealing materials.
2. The areas prone to powder leakage are the inlet and outlet coal valves of the coal mill, the coal feeder, the manufacturer's flange, and all the parts with flange connections. To this end, we will conduct a comprehensive inspection of all the parts of the manufacturer's equipment that are capable of leaking powder. If there is no additional sealing material, we will conduct a second installation and tighten the fasteners.
3. If there is potential for powder leakage at the welded joint of the pulverized coal pipe, we will take the following measures.
3.1 Before welding, the area of the weld must be polished to give a metallic luster and the groove required for welding must be polished.
3.2 Prior to the counterparty, a gap must be reserved for the counterparty, and it is strictly forbidden to force the counterparty.
3.3 Welding consumables must be used correctly and must be preheated as required when the weather is cold.
三. Preventive measures for oil system leakage and oil running.
1. It is very important to do a good job in oil system leakage and oil running.
2. Systems with fuel storage tanks must be carefully inspected and cleaned before installation.
3. Water pressure test must be carried out for equipment with oil cooler.
4. For the oil piping system, water pressure test and pickling work should also be done.
5. During the installation of the oil pipeline, all flange joints or threaded unions must be equipped with oil-resistant rubber gaskets or oil-resistant asbestos gaskets.
6. Leakage points in the oil system are mainly concentrated on flanges and threaded unions, so bolts must be evenly tightened when installing flanges. Prevent leaks or tightness from happening.
7. In the process of oil filtering, construction workers must always stick to their jobs, and it is strictly forbidden to leave their posts and shift jobs.
8. The oil filter must be stopped when replacing the oil filter paper.
9. When installing the temporary oil filter connecting pipe (high-strength plastic transparent hose), the joint must be bound firmly with lead wire to prevent the oil from jumping off after the oil filter has been running for a long time.
10. Deployment of responsible construction personnel to take care of the work of the oil filter.
11. Before the auxiliary engine oil system starts oil circulation, the engineering department organizes a detailed technical explanation to the personnel responsible for the auxiliary engine oil circulation.
四. To prevent foaming, dripping and leakage of equipment and pipe fittings, there are the following preventive measures:
1. Flange gaskets above 2.5Mpa are all metal wound gaskets.
2. The flange gasket of 1.0Mpa-2.5Mpa adopts asbestos gasket and is painted with black lead powder.
3. The flange gasket of water pipes below 1.0Mpa adopts rubber gasket and is painted with black lead powder.
4. The packing of the water pump adopts PTFE composite packing.
5. The asbestos rope used for the sealing part of the smoke, air and coal pipes is twisted and flatly added to the joint surface at a time. It is strictly forbidden to force it after tightening the screws.
五. The following measures are taken to eliminate the internal leakage of the valve: (For the leakage prevention of the valve, we should take the following measures)
1. For pipeline installation and construction, it is necessary to establish a good quality awareness, consciously clean the oxide scale and the inner wall of the pipeline, leave no debris, and ensure that the inner wall of the pipeline is clean.
2. First of all, ensure that 100% of the valves entering the site must undergo a hydraulic test.
3. Valve grinding should be carried out conscientiously, requiring all valves (except imported valves) to be sent to the grinding team to be disassembled for inspection, grinding and repair, and responsible, consciously recorded and marked for easy traceability. Important valves should be listed in detail for secondary acceptance, to meet the requirements of "stamping, inspection and recording".
4. The boiler's first water inlet and discharge door should be determined in advance. During the hydraulic test, only these valves are allowed to be opened, and other valves are not allowed to be opened at will, so as to protect the valve core.
5. When the pipeline is flushed, it should be opened wide and lightly closed to prevent damage to the door core.
If it leaks, what is the reason?
(1) The contact between the opening and closing parts and the two sealing surfaces of the valve seat;
(2) The matching place of packing, valve stem and stuffing box;
(3) The connection between the valve body and the valve cover
The previous leakage is called internal leakage, which is commonly referred to as lax closure, which will affect the valve's ability to cut off the medium.
The last two leaks are called external leakage, that is, the medium leaks from the inside of the valve to the outside of the valve.
Leakage will cause material loss, pollute the environment, and even cause accidents in severe cases.
In the real place, analyze the internal leakage, the internal leakage is generally:
(1) The internal leakage of the parallel gate valve,The working principle of the parallel gate valve is to rely on the pressure difference of the system to compress the valve core and the sealing surface of the valve seat on the outlet side. When the system pressure is very low, there may be slight internal leakage behind the valve. In case of such internal leakage, it is recommended to continue to observe and check the sealing of the valve when the system inlet pressure reaches the design pressure or normal working pressure. If there is still an excessive leakage, it should be disassembled and the sealing surface of the valve should be ground.
(2) Internal leakage of wedge gate valve Sometimes it is due to the different control methods of the valve. Due to the manufacturer's selection during the design, the corresponding valve stem and valve stem nut are designed for strength. The torque control method is not considered, and the stroke control method is used. If it is forced to close Changing the position stroke control method to torque control may cause damage to the valve stem nut, etc., and at the same time cause the electric head to malfunction when it is turned on, and an open torque fault alarm occurs. In the case of internal leakage of this kind of valve, you can usually close it manually after it is electrically closed and close it tightly. If the internal leakage still exists after manual closing, it means that there is a problem with the valve sealing surface, and it needs to be disassembled and polished.
(3) The internal leakage of the check valve, The seal of the check valve also depends on the pressure difference of the system. When the inlet pressure of the check valve is very low, the outlet pressure will also rise slightly. At this time, various factors should be analyzed to determine the internal leakage. Analyze the structure to determine whether to engage in physical overhaul work.
(4) The internal leakage of the large-diameter butterfly valve, The internal leakage standard of large-diameter butterfly valves is generally very large. When the inlet pressure increases, the outlet pressure will also increase. For this kind of problem, the internal leakage should be judged first, and whether to check or repair according to the internal leakage decision.
(5) Internal leakage of the regulating valve, Due to the different forms of the regulating valve, the standard for internal leakage is different. At the same time, the regulating valve generally uses the stroke control method (not the torque control method), so there is generally an internal leakage phenomenon. The internal leakage of control valves should be treated differently, and control valves with special internal leakage requirements should be considered when designing and manufacturing. There are many such contradictions in XX nuclear power plants, and many valves are forced to be changed to torque control, which is detrimental to the work of the regulating valve.
To be more specific:
(1) The material selection and heat treatment of the valve trim are poor, the hardness is not enough, and it is easy to be damaged by high-speed fluid.
(2) Due to the limitation of the valve structure, the energy (speed) is not effectively consumed when the fluid passes through the valve, and the impact and wear force on the sealing surface is large; excessive speed causes the pressure behind the valve to be too small, lower than the saturation pressure, and cavitation occurs. During the cavitation process, when the bubble bursts, all the energy is concentrated on the rupture point, producing an impact of several thousand Newtons. The pressure of the shock wave is as high as 2×103Mpa, which greatly exceeds the fatigue damage limit of existing metal materials. The extremely hard disc and valve seat will also be damaged in a short time, causing leakage.
(3) The valve works for a long time in a small opening state, the flow rate is too high, the impact force is large, and the internal parts of the valve are easily damaged.
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