Valve how to prevent electrostatic valve leakage to deal with the five ways

Valve how to prevent electrostatic valve leakage to deal with the five ways

Contact valve technical data more people know that in many cases, the valve has anti-static requirements.
1. Generation of static electricity.
Static electricity is a common physical phenomenon. When two different materials rub together, an electrostatic charge is created because of the transfer of electrons. Things that gain electrons are negatively charged, and things that lose electrons are positively charged. This process is called triboelectrification. In theory, as long as the two sides of the friction compared, one side is easy to lose electrons, and the other side is easy to get electrons, two different material objects friction can produce static electricity! Friction between two objects of the same material will not produce static electricity.
2, the application range of antistatic device in the valve.
API 6D-2014, page 23, “5.23 Antistatic Devices” states: “Soft-seal ball valves, plug valves, and gate valves shall have antistatic devices.” API 6D-2014 only stipulates that the soft seal should have anti-static device, but does not require the hard seal to have anti-static device. This is because the soft seal plastic valve seat (PTFE, PPL, NYLON, DEVLON, PEEK, etc.) is easy to produce static electricity when friction with the ball (generally metal), and the metal — metal seal, Because the two groups of materials rubbing against each other are of the same kind, static electricity will not be generated. If someone in the future needs to design a hard seal valve antistatic device, you can say two reasons: 1, hard seal valve will not produce static electricity; 2. API 6D-2014 only stipulates that anti-static devices are required for soft seal valves, not for hard seal valves.
3, the valve why need to design anti-static device.
When the valve is a soft seal, the valve opening and closing parts will produce static electricity when the valve is switched on and off, which is easy to generate sparks. If the medium is flammable and explosive, then electrostatic sparks are likely to make the medium burn or occur. The ANTISTATIC DEVICE will discharge the STATIC electricity from the opening and closing parts of the valve to the nature, which is good to avoid the combustion or occurrence of the electrostatic spark to the medium, and play a protective role in the pipeline.
4, antistatic test.
API 6D-2014, page 23, “5.23 Antistatic Device” states: “If so specified by the Buyer, the test of this device shall be carried out in accordance with Section H.5.” On page 82, “h.5 antistatic test” states: “the resistance between the shutoff and the body, and between the stem/shaft and the body shall be tested with a dc power supply not exceeding 12V. The RESISTANCE MEASUREMENT SHALL BE PERFORMED ON A DRY VALVE PRIOR TO THE PRESSURE TEST, WITH A RESISTANCE NOT EXCEEDING 10 ¦Ø.”
5, antistatic device in the valve application example.
Anti-static principle of floating ball valve. As shown in the figure below.
The ANTISTATIC DEVICE CONSISTS OF a SPRING AND a BALL (hereafter referred to as the “ELECTROSTATIC SPRING SET”). The common floating ball valve consists of two sets of “electrostatic spring sets”, one on the contact surface between the stem and the ball, and the other on the contact surface between the stem and the body, as shown in the figure above. When the valve is in the process of switching, the ball and the seat friction, static electricity. Had clearance, because with stem and ball valve stem when driven in a sphere, the department of the electrostatic spring group in the small sphere will generate beats, the static electricity on the sphere is exported to the valve stem, at the same time, the contact surface of the valve stem and valve body, the electrostatic spring group, because in the same way, the static electricity on the valve stem is exported to the valve body, valve body grounding, electrostatic discharge completely.

Five ways to deal with valve leakage
Leakage of body and bonnet
The reason:
1, cast iron casting quality is not high, the valve body and valve cover body has trachoma, loose organization, slag and other defects;
2, day freezing crack;
3. Poor welding, slag inclusion, unwelded, stress cracks and other defects;
4, cast iron valve is damaged after heavy impact.
Maintenance Methods:
1. Improve the casting quality and conduct strength tests in strict accordance with the provisions before installation;
2, the temperature of 0¡æ and 0¡æ below the valve, should be heat preservation or mixing, stop using the valve should be removed water;
3. The welding seam of the body and valve cover composed by welding should be carried out according to the relevant welding operation rules, and the flaw detection and strength test should be carried out after welding;
4. It is forbidden to push and put heavy objects on the valve. It is not allowed to hit the cast iron and non-metal valve with a hammer.
2
Leakage at packing
Valve leakage, packing accounted for the proportion of large.
The reason:
1, packing choice is wrong, not resistant to medium corrosion, not resistant to the use of high pressure or vacuum valve, high temperature or low temperature;
2, packing installation is wrong, there are small instead of large, screw coil joint is poor, tight and loose and other defects;
3, the packing exceeds the use period, has been aging, loss of elasticity;
4, the stem accuracy is not high, bending, corrosion, wear and other defects;
5, the number of packing rings is insufficient, the gland is not pressed;
6. Gland, bolts, and other parts are damaged, so that the gland can not be pressed tightly;
7, improper operation, excessive force, etc.;
8, gland skew, gland and stem gap is too small or too large, resulting in stem wear, packing damage.
Maintenance Methods:
1. The material and type of packing should be selected according to the working conditions;
2, according to the relevant provisions of the correct installation packing, the pan root should be placed and pressed one by one, the joint should be 30¡æ or 45¡æ;
3, the use of too long, aging, damaged packing should be replaced in time;
4, valve stem bending, wear should be straightened, repair, serious damage should be replaced in time;
5. The packing should be installed according to the prescribed number of turns, the gland should be tightened symmetrically and evenly, and the pressure sleeve should have a pretightening gap of more than 5mm;
6. Damaged gland, bolts and other parts should be repaired or replaced in time;
7, should comply with the operating rules, except the impact of the handwheel, with uniform speed normal force operation;
8. The gland bolt should be tightened evenly and symmetrically. If the gap between the gland and the valve stem is too small, the gap should be appropriately increased. If the gap between gland and stem is too large, it should be replaced.
3
Leakage of the sealing surface
The reason:
1, sealing surface grinding uneven, can not form a close line;
2, the connection between the stem and the closing part at the center of the suspension, is not straight or wear;
3, the valve stem bending or assembly is not correct, so that the closing part is skewed or not in the middle;
4. Improper selection of sealing surface material quality or not selection of valve according to working conditions.
Maintenance Methods:
1. Correctly select the material and type of bouncing gasket according to the working conditions;
2, careful adjustment, smooth operation;
3, should be evenly and symmetrically screw the bolt, if necessary, should use torque wrench, preload should meet the requirements, not too large or small. Flange and thread joints should have a certain preload clearance;
4, the gasket assembly should meet the center, the force is uniform, gasket is not allowed to lap and use double gasket;
5, static sealing surface corrosion, damage processing, processing quality is not high, should be repaired, grinding, coloring inspection, make the static sealing surface meet the relevant requirements;
6. When installing the gasket, attention should be paid to cleaning, sealing surface should be kerosene clear, and the gasket should not fall to the ground.
4
Leakage at seal ring connection
The reason:
1, sealing ring rolling is not strict;
2, sealing ring and body welding, surfacing quality is poor;
3, sealing ring connection thread, screw, pressure ring loose;
4. The sealing ring is connected and corroded.
Maintenance Methods:
1. The leakage in the sealed rolling place should be fixed by injecting adhesive and then rolling;
2. The sealing ring should be repaired according to the welding specification. When the surfacing cannot be repaired, the original surfacing and processing should be carried out;
3. Remove the screws, clean the pressure ring, replace the damaged parts, grind the sealing and connecting seat close surface, and assemble again. The parts with large corrosion damage can be repaired by welding, bonding and other methods;
4. The sealing ring connection surface is corroded, which can be repaired by grinding and bonding, and the sealing ring should be replaced when it cannot be repaired.
5
The closing part falls off and leaks
The reason:
1, poor operation, so that the closing piece is stuck or more than the dead point, the connection is damaged and broken;
2, close the connection is not firm, loose and fall off;
3, the choice of connection material is not right, can not stand the corrosion of the medium and mechanical wear.
Maintenance Methods:
1, correct operation, close the valve can not force too much, open the valve can not exceed the dead point, the valve is fully opened, the handwheel should reverse a little;
2. The connection between the closing part and the valve stem should be firm, and the thread connection should have a backstop part;
3. Fasteners used for connecting the closing parts and the valve stem should withstand the corrosion of the medium, and have certain mechanical strength and wear resistance.