I. Precautionary measures on water and vapor leakage of valves.
1. All valves must be subjected to different levels of hydrostatic test after entering the factory.
2. It is necessary to disassemble the overhaul of the valve must be ground.
3. In the process of overhaul must carefully check whether there is no added packing, packing gland is tightened.
4. The valve must be checked before installation to see if there is dust, sand, iron oxide and other debris inside the valve. If there is any of the above debris must be cleaned up before installation.
5. All valves must be installed before the installation of the appropriate level of gaskets.
6. In the installation of the flange door must be tightened fasteners, in the tightening of the flange bolts must be symmetrical direction for sequential tightening.
7. In the process of valve installation, all valves must be installed correctly according to the system, pressure, is strictly prohibited indiscriminate installation, mixed installation. For this reason, all valves must be numbered according to the system before installation, and make a good record.
Second, on the coal leakage precautions.
1. All flanges must be installed with sealing materials.
2. The areas prone to powder leakage are the coal mill’s inlet and outlet coal valves, the coal feeder, the manufacturer’s flange, and all parts with flange connections. For this reason, we will carry out a comprehensive inspection of all the parts of the manufacturer’s equipment that are susceptible to powder leakage, and if no sealing materials are installed, we will install them for the second time and tighten the fasteners.
3. We will take the following measures for the phenomenon of powder leakage in the welded mouth of coal powder pipe.
3.1 Before welding, we must carefully polish the welded area with metallic luster and grind out the bevel required for welding.
3.2 Before the alignment must be reserved for the alignment gap, it is strictly prohibited to force the alignment.
3.3 Welding consumables must be used correctly, and must be preheated according to the requirements in cold weather.
Third, on the oil system leakage, run oil and other preventive measures.
1. Do a good job of the oil system leakage, running oil and other work is very important.
2. The system with oil storage tank must be carefully checked and cleaned up before installation.
3. The equipment with oil cooler must be hydrostatically tested.
4. For the oil pipeline system should also do hydraulic test and pickling work.
5. In the process of oil pipeline installation, all flange interfaces or live fittings with wire fasteners must be equipped with oil-resistant rubber gaskets or oil-resistant asbestos gaskets.
6. Leakage points of the oil system are mainly concentrated in the flange and the live joint with thread, so the bolts must be tightened evenly when installing the flange. Prevent leakage or not tighten the situation.
7. In the oil filtration process, the construction personnel must always adhere to the workstation, is strictly prohibited off duty and string of posts.
8. In the replacement of the oil filter paper must be shut down the oil filter.
9. When installing the temporary connecting pipe of oil filtering (high-strength plastic transparent hose), the joints must be firmly tied with lead wire to prevent bouncing off and running oil phenomenon after running the oil filter for a long time.
10. Deploy responsible construction personnel to supervise the work of the oil filter.
11 in the auxiliary oil system before the start of the oil cycle, organized by the Ministry of Engineering specifically responsible for the auxiliary oil cycle of the personnel to carry out a detailed technical briefing.
Fourth, to put an end to equipment and pipe fittings combined surface bubbles, bubbling, dripping, leakage, the following preventive measures:
1, 2.5Mpa above the flange gasket, are used in metal winding gasket.
2、1.0Mpa-2.5Mpa flange gasket, the use of asbestos gasket, and painted black lead powder.
3、Flange sealing gaskets for water pipes below 1.0Mpa are made of rubber gasket and coated with black lead powder.
4, pump packing are used PTFE composite packing. 5, smoke, wind and coal pipeline sealing parts, the asbestos rope used once twisted, flat to join the bonding surface, it is strictly prohibited to tighten the screws and then force to join.
V. Eliminate valve leakage has the following measures:
(For the valve leakage prevention we should do the following measures)
1. Pipeline installation and construction, must establish a good sense of quality, consciously clean up the iron oxide and pipeline walls, do not leave debris, to ensure that the pipeline walls are clean.
2. First of all, ensure that the valves entering the site must be 100% hydrostatic test.
3. Valve grinding should be carried out seriously, requiring all valves (except for imported valves) to be sent to the grinding class disintegration inspection and grinding overhaul, and the implementation of the responsibility to consciously make good records and marking, easy to trace. Important valves should be listed in detail for the second level of acceptance, to achieve the requirements of “stamping, stamping, records.
4. The first boiler water door and discharge door to be determined in advance, in the hydrostatic test process is only allowed to open these valves, other valves shall not be opened at will, so as to protect the valve core.
5. Pipe flushing should be opened wide, gently closed to prevent damage to the valve core.
If the leakage, the reason is?
(1) the contact between the opening and closing parts and the two sealing surfaces of the valve seat;
(2) Packing and valve stem and packing box at the mating;
(3) the valve body and valve cover connections
One of the first leakage is called internal leakage, which is often referred to as the shut-off is not tight, it will affect the valve’s ability to cut off the medium. After the two leaks are called leakage, that is, the medium from the valve leakage to the valve. Leakage will cause material loss, pollution of the environment, and in serious cases will cause accidents. Down to earth, the analysis of internal leakage, internal leakage in general: the valve according to its different calibers, different system differential pressure, and the system medium is not the same, there is a permissible internal leakage standards. In a strict sense, the real ‘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 to achieve invisible leakage is very difficult. When encountering the phenomenon of internal leakage of the valve, you should first try to understand the specific amount of internal leakage, check the allowable leakage standard of the valve, the internal leakage occurs when the system’s operating environment and other factors for a comprehensive analysis, in order to correctly determine the internal leakage of the valve.
(1) Parallel gate valve internal leakage. The working principle of the parallel gate valve is to rely on the differential pressure of the system to press the sealing surfaces of the spool and seat on the outlet side, in the case of very low system pressure, there may be a slight internal leakage phenomenon at the back of the valve. Encountering such internal leakage phenomenon, 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 excessive leakage, the valve should be disassembled and the sealing surface should be ground.
(2) Internal leakage of wedge gate valve. Sometimes it is due to differences in the control of the valve, due to manufacturers in the design of the selection, the corresponding valve stem and stem nut, etc. is the strength of the design did not take into account the way of torque control, and the use of the way of travel control, if forced to close the position of the way of travel control to change into the way of torque control, it may result in damage to the valve gate stem nut and so on, and at the same time lead to the failure of the motorized head in the opening of the open torque failure Alarm. Encountered this valve internal leakage problems, usually can be closed manually after the motorized shutdown again, shut down can be, if the manual shutdown still exists after the phenomenon of internal leakage, it shows that the valve sealing surface has a problem, this time the need to disassemble grinding processing.
(3) check valve leakage. Check valve sealing is also dependent on the differential pressure of the system, when the inlet pressure of the check valve is very low, the outlet pressure will also have a slight increase in the phenomenon, which should be analyzed to determine the amount of internal leakage of a variety of factors, according to the analysis of the structure of the decision on whether to take over the medical repair work.
(4) The internal leakage of large diameter disc valve. Large-diameter disc valve leakage standards are generally very large, when the inlet pressure increases, the outlet pressure will also have the phenomenon of increasing this problem should first determine the amount of internal leakage, according to the amount of internal leakage to carry out the decision of whether to overhaul.
(5) internal leakage of the control valve. Due to the different forms of control valves, the standard of internal leakage is not the same, at the same time, control valves are generally used in the way of stroke control, (not the way of torque control), so there is generally an internal leakage phenomenon. The problem of internal leakage of control valves should be treated differently, and control valves with special internal leakage requirements should be considered when designing and manufacturing. xx nuclear power plant there are many such contradictions, there are many valves that have no choice but to be changed to torque control, which is detrimental to the work of the control valve.
Be more specific:
(1) The material selection and heat treatment of the inner parts of the valve is poor, not hard enough, easy to be washed out by the high-speed fluid.
(2) Due to the limitations of the valve structure, the fluid through the valve when the energy (velocity) is not effectively consumed, the impact of the sealing surface wear force is large; speed is too large resulting in too small a pressure after the valve is lower than the saturation pressure, resulting in vapor corrosion, cavitation process when the bubble rupture of all the energy is concentrated in the point of rupture, resulting in a few thousand Newtons of impact, the pressure of the shock wave is as high as 2 × 103Mpa, which is greatly exceeded by the existing Fatigue damage limit of metal materials. Extremely hard valve and valve seat will also be destroyed in a very short time, leakage.
(3) valve for a long time in the small opening state, the flow rate is too high, the impact force is large, the valve is easy to damage the internal parts.