Preventive Measures For Valve Leakage And Steam Leakage

- Aug 21, 2019-

With more   than 30 years of casting history, Wenzhou Longzhu Industrial Co., Ltd. has a   large number of experienced casting engineers and technicians. We can produce   castings of various sizes, shapes and materials according to the drawings   provided by customers, especially in the field of valve castings. Cooperate   with Fortune 500 companies for many years.





Material selection:

GS-C251.0619,WCB.WCC,LCB,LCC,LC3,4C,4D,WC6,C5,C12, C12A,CA15CF3,CF8(-196’C),CF3M,CF8M,CF8C,CD4MCu,CK3MC   uN,ZG200-400,ZG230-450,ZG270-500,2G40Cr1,ZG20CrM0.2G15C   r1Mo1V,ZG35Cr1MO.ZG16CrMOG(1Cr5Mo),ZG1Cr13,ZGOCr18Ni9 Ti.5A.KmTB   Cr26.4A




Resin sand casting, etc.

1.All valves must be tested at different levels after entering the factory.

2. Valves that need to be disassembled and repaired must be ground.

3. In the course of overhaul, it is necessary to check carefully whether there are additional roots and whether the roots and caps are tightened.

4. Valves must be inspected for dust, sand, iron oxide and other impurities before installation. If any of the above debris must be cleaned up before installation.

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

6. When installing flange doors, fasteners must be tightened, and flange bolts must be tightened in a symmetrical direction in turn.

7. In the process of valve installation, all valves must be installed correctly according to the system and pressure. No random or mixed assembly is allowed. For this reason, all valves must be numbered and recorded according to the system before installation.

stainless steel Check valve

Preventive measures for pulverized coal leakage

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, factory flanges, and all flanged joints. To this end, we will conduct a comprehensive inspection of all the parts of the equipment that are willing to leak powder. Without sealing materials, we will carry out a second installation and tighten the fasteners.

3. We will take some measures to solve the problem of powder leakage at the weld of pulverized coal pipe.

3.1 Before the weld, the weld area must be polished with metallic luster and the groove needed for welding must be polished carefully.

3.2 Gap must be reserved before counterpart and forcible counterpart must be strictly prohibited.

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

Preventive measures for oil system leakage and run-off

1. It is very important to do a good job in oil system leakage and oil running.

2. The system with oil tank must be carefully checked and cleaned before installation.

3. Hydraulic test must be carried out for equipment with oil cooler.

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

5. During the installation of oil pipelines, all flanged joints or loose joints with threads must be equipped with oil-resistant rubber pads or asbestos pads.

6. The leakage points of oil system are mainly concentrated on flanges and threaded joints, so bolts must be tightened evenly when installing flanges. Prevent tightness or tightness from happening.

7. In the process of oil filtering, the construction personnel must always stick to their work posts and strictly prohibit leaving or leaving their posts.

8. It is necessary to stop the oil filter when replacing the oil filter paper.

9. When installing the temporary connection pipe of oil filter (high-strength plastic transparent hose), it is necessary to tie the joint firmly with lead wire to prevent oil skipping after long operation of the oil filter.

10. Dispatch the construction personnel with strong sense of responsibility to take care of the work of the oil filter.

11. Before the start of the oil cycle in the auxiliary oil system, the Engineering Department organizes a detailed technical presentation for the personnel responsible for the oil cycle.

 Butterfly valve

To eliminate foaming, bubbling, dripping and leakage on the joint surface of equipment and fittings, the following preventive measures are taken:

1.Flange gaskets above 1 and 2.5 Mpa are all made of metal winding gaskets.

2.1.0Mpa-2.5Mpa flange gasket, asbestos gasket, and black lead powder.

3. The flange gasket of 1.0 Mpa water pipeline is covered with rubber pad and painted with black lead powder.

4. The base of the pumps are all made of Teflon fiber composite packing

5. The asbestos rope used in the sealing part of the flue gas and air coal pipeline is twisted and added to the joint surface smoothly at one time. It is strictly forbidden to tighten the screw and add it forcefully. Fifth, there are the following measures to eliminate valve leakage: (For valve leakage, we should do the following measures)

1. Pipeline installation and construction, we must establish a good quality awareness, consciously clean iron oxide scale and pipeline wall, leaving no debris, to ensure that the pipeline wall is clean.

2. First of all, ensure that the valve entering the site must be 100% hydraulic test.

3. Valve grinding should be carried out conscientiously, requiring all valves (except imported valves) to be sent to the grinding class for examination, grinding and repair, and fulfilling their responsibilities, consciously recording and marking, so as to facilitate traceability. Important valves should be listed in detail for secondary acceptance, so as to meet the requirements of "stamping, inspecting and recording".

4. Boiler's first water gate and discharge valve should be determined in advance. Only these valves are allowed to be opened during hydraulic test, and other valves should not be opened at will, so as to protect the valve core.

5. Pipeline flushing should be opened and lightly closed to prevent spool damage.

If it fails, reasons?

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

(2) Matching of packing with valve stem and packing box;

(3) Connection between body and cover

The former leakage is called internal leakage, which is commonly referred to as lax closure, and it will affect the ability of the valve to cut off the medium. Leakage at the last two places is called leakage, i.e. medium leaks from inside to outside of the valve. Leakage can cause material loss, pollution of the environment, and serious accidents.

In practice, analysis of internal leakage, internal leakage is generally:

Valves have an allowable internal leakage standard according to their caliber, system pressure difference and system medium. In a strict sense, there is no real "0" leakage valve. In general, small-caliber globe valves are easy to achieve invisible leakage (not zero leakage), while large-caliber gate valves are difficult to achieve invisible leakage. When encountering the internal leakage of the valve, we should first try to understand the specific internal leakage, consult the allowable leakage standard of the valve, and make a comprehensive analysis of the factors such as the working environment of the system when the internal leakage occurs, so as to correctly judge the internal leakage of the valve.

(1) Internal leakage of parallel gate valves.

The working principle of parallel gate valve is to press the valve core and seat sealing surface on the outlet side by the pressure difference of the system. Under very low pressure of the system, there may be a slight internal leakage after the valve. In case of such leakage, it is suggested that we continue to observe it.

When the system inlet pressure reaches the design pressure or normal working pressure, check the sealing of the valve. If there is leakage beyond the standard, it should be disintegrated and the sealing surface of the valve should be grinded.

(2) Internal leakage of wedge gate valve.

Sometimes it is because of the different control modes of the valves. Because the manufacturer chooses the type when designing, the corresponding stem and stem nut are the strength design without considering the moment control mode, but the stroke control mode is used. If the stroke control mode of the closed position is forcibly changed to the moment control mode, it may lead to the valve stem. Nut damage and so on, at the same time lead to motor head failure at the start, open moment fault alarm. When encountering the internal leakage problem of this kind of valve, it is usually possible to close it manually after the electric closure. If there is still an internal leakage phenomenon after the manual closure, it indicates that there is a problem with the sealing surface of the valve. At this time, it needs to be disintegrated and grinded.

(3) Internal leakage of 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 rise slightly. At this time, various factors should be analyzed to judge the internal leakage and decide whether to take part in the repair work according to the analysis structure.

(4) Internal leakage of large diameter disc valve.

The internal leakage standard of large-caliber disc valves is generally very large. When the inlet pressure rises, the outlet pressure will also rise. To solve this problem, the internal leakage should be judged first, and the maintenance decision should be made according to the internal leakage.

(5) Internal leakage of control valve.

Because of the different forms of control valves, the standards of internal leakage are also different. At the same time, the control valves generally use the way of stroke control (not the way of moment control), so there are generally internal leakage phenomena. The internal leakage of the control valve should be treated differently, and the control valve with special internal leakage requirements should be considered in design and manufacture. There are many such contradictions in XX nuclear power plant, many valves have to be changed into moment control, which is not conducive to the work of control valves.

More specifically:

(1) The material selection and heat treatment of the inner parts of the valve are poor, the hardness is not enough, and they are easy to be washed out by high-speed fluid.

(2) Due to the limitation of valve structure, the energy (velocity) of the fluid passing through the valve is not effectively consumed, and the impact wear force on the sealing surface is large; the excessive speed causes the pressure behind the valve to be too small, which is lower than the saturation pressure, resulting in cavitation. During the process of cavitation, all the energy of the bubble bursting concentrates on the breaking point and generates thousands of Newtons. The impact force, the shock wave pressure as high as 2 x 103 Mpa, greatly exceeds the fatigue damage limit of existing metal materials. Hard discs and seats can also be damaged and leaked in a very short time.

(3) The valve operates for a long time in a small opening state, with high flow rate, high impact force and easy damage to the inner parts of the valve.