Static electricity of oil
1. The generation of static electricity
In the process of oil delivery, transportation, and filling, the friction between oil molecules and between oil and other substances will generate static electricity, and its voltage will increase with the increase of friction. If it is not removed in time, When the voltage increases to a certain level, it will flash over between the two charged bodies (ie, electrostatic discharge), causing the oil to explode and catch fire.
The higher the electrostatic voltage, the easier it is to discharge. The level of voltage or the amount of electrostatic charge is mainly related to the following factors:
1. The faster the oil flow rate. The more severe the friction, the higher the electrostatic voltage generated.
2. The drier the air, the less likely it is for static electricity to dissipate from the air, and the easier it is for the voltage to rise.
3. The greater the distance between the oil pipe outlet and the oil surface, the more violent the friction between the oil product and the air, the more severe the agitation and impact of the oil flow on the oil surface, the higher the voltage.
4. The rougher the inner wall of the pipeline, the more elbow valves that flow through, and the higher the electrostatic voltage generated. When the oil product contains water in the transportation, the voltage generated by it is several to several tens of times higher than that without water.
5. Non-metal pipes, such as canvas, rubber, asbestos, cement, plastic pipes, are more likely to generate static electricity than metal pipes.
6. The denser the oil filter screen is installed on the pipeline, the higher the electrostatic voltage generated. The electrostatic voltage generated by the silk felt filter is higher.
7. When the atmospheric temperature is high (22~40℃) and the relative humidity of the air is 13%~24%, it is easy to generate static electricity.
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8. Under the same conditions, light fuel oil is easier to generate static electricity than lubricating oil.
2. Methods to prevent electrostatic discharge
1. All oil tanks, pipelines, and loading and unloading equipment used to store and transfer oil must have a good grounding device to introduce static electricity into the ground in time, and check the technical status of the electrostatic grounding device and test the grounding resistance frequently. The grounding resistance of the oil tank in the oil depot should not be greater than 10Ω, and the grounding resistance of other equipment should not be greater than 100Ω (including static electricity and safety grounding). The grounding electrode of the vertical oil tank is calculated according to the circumference of the oil tank, one group every 18m, and the grounding electrode of the horizontal oil tank is not less than two groups.
2. When filling oil into oil tanks, tank cars, and railway tank cars, the oil pipeline must be inserted below the oil level or close to the bottom of the tank to reduce the impact of the oil product and the friction between the air.
3. In the season when the air is particularly dry and the temperature is high, special attention should be paid to the inspection of the grounding equipment, and the oil filling speed should be appropriately slowed down. If necessary, water can be watered around the work site and the static conductive grounding electrode.
4. Electrostatic discharge accidents are prone to occur at the beginning of oil delivery and oil filling and three-quarters to the end of oil filling to the container. At this time, the flow rate should be controlled within 1m/s.
5. When the ship is loaded with oil, the outlet of the refueling pipeline should be kept in metal contact with the oil inlet of the tanker.
6. It is strictly forbidden to pour light fuel oil into plastic barrels in the oil depot, and it is prohibited to use plastic containers to invert the light fuel oil in the area that affects the safety of the oil depot.
7. All personnel who board the oil tank and engage in fuel oil filling operations are not allowed to wear chemical fiber clothing (except for the certified anti-static overalls). Before boarding the tank, the personnel on the tank should hold the unpainted tank escalator for a while to dissipate the static electricity of the human body.
Three, the setting of the grounding device
1. Grounding wire
The grounding wire must have good conductivity, appropriate cross-sectional area and sufficient strength.
The grounding wires of oil tanks, pipelines, and loading and unloading equipment often use flat steel with a thickness of not less than 4mm and a cross-sectional area of not less than 48mm2; for tank cars and tankers, copper or aluminum wires with a diameter of not less than 6mm can be used; rubber pipes generally use a diameter of 3 ~4mm stranded copper wire.
2. Grounding electrode
The grounding electrode should use a steel pipe with a diameter of 50mm, a length of 2.5m, and a pipe wall thickness of not less than 3mm. Remove the rust and dirt on the surface of the pipe (do not use anti-corrosion treatment). Dig a hole with a depth of about 0.5m and drive the grounding electrode vertically. In the bottom of the pit. The grounding electrode should be buried in places with high humidity and high groundwater level as much as possible. All contacts between the grounding electrode and the grounding wire should be bolted or snapped to ensure good contact.