Accident Prevention and Handling of Floating Roof Tanks

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Prevention and Handling of Oil Tank Accidents I. Oil Spills The main causes of oil spill accidents are measurement errors or prolonged operation of the oil pumps, which results in the oil level in the tank exceeding the safe limit; as a result, the oil spills out through foam generators, breather valves, etc. In the case of internal floating roof tanks, oil can spill out through the ventilation holes in the tank wall. When the floating roof reaches its upper limit, continuing to operate the oil pumps can lead to a sinking accident. In the event of an oil spill, the operation of the oil pumps must be stopped immediately. It is necessary to check whether the ditches, wells, and valves in the oil tank area are properly closed. No operations that could generate sparks should take place at the accident site, and the emergency hotline should be called right away. II. Accidents of sinking of internal floating roof tanks 1. Causes of sinking accidents of internal floating roofs (1) Deformation of the floating roof: During long-term and frequent operation, the floating roof is subject to corrosion by the oil, changes in oil temperature, deformation of the tank body, and issues related to the condition of the floating roof’s attachments; these factors cause the floating roof to gradually deform, resulting in an uneven surface. During operation after deformation, the floating disc tilts due to different buoyant forces acting on various parts of it; moreover, the pulleys of the oil level guiding tube attached to the floating disc get stuck, causing the tilt of the floating disc’s movement to increase gradually. When the buoyancy acting on the floating disc is not sufficient to overcome its upward resistance, it eventually leads to oil leaking from the sealing ring and the automatic breather valve holes onto the floating disc, causing the vessel to sink. When the floating disk seal ring detaches or is crushed locally, there is a greater likelihood of oil entering the floating disk, which can more easily lead to the sinking of the disk. 2. The floating pad supports become loose and lose their supporting function; the supports on the floating pad of an internal floating roof tank are evenly distributed across the bottom of the floating pad. During the up and down movement of the floating tray, improper installation of the pillar pins or their slipping can cause the tray pillars to fall to the bottom of the tank. When the floating tray is operating at a lower position, the lack of pillar support leads to uneven stress on the tray, resulting in deformation; in severe cases, part or all of the tray may collapse, causing it to sink. 3. Improper maintenance and management: The guide wheels of the internal floating disk need to be lubricated regularly. It is also necessary to keep an eye on the automatic breathing valve of the floating disk, the surface of the floating disk, its sealing rings, as well as the anti-corrosion condition of the inner surface of the oil tank. Any issues detected must be addressed promptly; otherwise, improper operation can very likely lead to accidents involving the sinking of the floating disk. Additionally, if the oil inlet speed is too high and the oil contains a large amount of gas, it will cause uneven forces on the floating disc, leading to shaking and subsequent sinking of the disc. Precautionary measures 1: Operational precautions. The actual oil level stored in an internal floating roof tank must not exceed the safe oil level of the tank. When filling an empty tank with oil, the initial flow speed of the oil should not exceed 1 m/s; once the oil submerges the inlet and outlet pipes, the flow speed should not be greater than 4.5 m/s. When discharging oil, the amount of oil remaining in the floating roof tank should not be below the level at which the floating disk moves up and down. Otherwise, if the flow speed of the oil is too high during the next filling process, uneven forces on the floating disk due to gas effects may cause it to tilt, get stuck, and sink. 2. Regular inspections: For internal floating roof tanks, the seal mechanism of the floating roof, the condition of the guide wheels, the unevenness of the floating roof surface, and the stability of the floating roof should be inspected on a monthly basis. In case of any abnormalities, measures should be taken promptly. It is essential to establish strict and reliable safety measures during these inspections. III. Oil tank collapse accidents: Local collapse of metal oil tanks usually occurs at the top or upper ring plates of the tank, and it is difficult to repair. During the oil storage process, the positive and negative pressures inside the tank are regulated by breather valves. The deflation of the oil tank is caused by an excessive vacuum level within it; such incidents usually occur when oil is discharged too quickly, and occasionally they happen after thunderstorms in summer. 1. Principle of oil tank collapse: During the process of oil discharge from a tank, if the volume of oil released per unit time is greater than the amount of air that enters the tank through the breather valve, the vacuum level inside the tank increases. The larger this difference, the higher the vacuum level inside the tank. When the vacuum level exceeds the negative pressure at which the tank is designed to operate, it can easily lead to the collapse of the tank, and even cause accidents. 2. Reasons for oil tank deflation: The root cause of oil tank deflation accidents lies in the breather valve; the valve disc of the breather valve gets stuck, it freezes or is blocked by snow in winter, the inlet and outlet of the breather valve become blocked, the flame arrester is blocked, or there is excessive resistance to gas flow ； Additionally, excessive fluctuations in the oil discharge flow rate, a mismatch with the breathing capacity of the breather valve, and insufficient air intake are also the main reasons for the oil tank collapsing. 3. Measures to prevent oil tank collapse: Strengthening the inspection and maintenance of breather valves to ensure their safety and keep them in good working condition is the main measure to prevent oil tank collapse. A regular monthly inspection routine should be established; in cases of heavy snowfall, any blockages should be removed immediately. Controlling the flow rate of operations can also help prevent oil tank collapse