Thread Content
I. Detection of the gas phase above the secondary seal of external floating roof tanks 1. Detection location: For external floating roof tanks with a capacity of less than 100,000 m3, four points are selected evenly distributed on the floating deck; for tanks with a capacity of 100,000 m3 or more, eight points are selected evenly distributed on the floating deck. The detection is carried out within a range of 200 mm from the secondary seal. 2. Detection method: Gas chromatographic analysis can be carried out using portable gas alarm devices, or samples can be collected manually for analysis in the laboratory. Regardless of the method used, the sampling hose must be an anti-static hose or other anti-static measures must be taken to ensure safe sampling. 3. Testing items and standards: The concentration of combustible gases in the gas space above the floating roof of external floating roof storage tanks should be less than 25% of the lower explosive limit of the medium. II. Gas phase analysis between the primary and secondary seals of external floating roof tanks 1. Sampling locations: For external floating roof tanks with a capacity of less than 100,000 m³, four points are selected evenly distributed on the floating deck; for tanks with a capacity of 100,000 m³ or more, eight points are chosen in a uniform manner on the floating deck. The rain shield is slowly removed to create enough space for gas phase testing, and the sampling point is inserted into the secondary seal at a depth of more than 200 mm. After the inspection is complete, the rain shield should be slowly returned to its original position to avoid any risk of it hitting the tank wall. External floating roof tanks should be equipped with primary and secondary sealed sampling ports to facilitate sampling operations. 2. Detection method: Gas chromatographic analysis can be carried out using portable gas alarm devices, or samples can be collected manually for analysis in the laboratory. Regardless of the method used, the sampling hose must be an anti-static hose or other anti-static measures must be taken to ensure safe sampling. III. Testing items and standards: The concentration of combustible gases in the gas space between the primary and secondary seals of the floating roof of external floating roof storage tanks should be less than 25% of the lower explosive limit. Requirement: This parameter can be adjusted appropriately based on the actual sealing condition of the floating disk, as well as the actual monitoring data from different seasons and different types of oils, but it should not exceed 50% of the lower explosive limit of the stored medium. IV. Requirements for Testing Management 1. Manual gas-phase testing operations shall comply with GB13348 \"Code for Static Electricity Safety of Liquid Petroleum Products\" as well as the relevant provisions outlined in the gas-phase testing operation guidelines provided by the sampling unit, and the following precautions must be taken: a) Operators should wear anti-static work clothes and anti-static shoes. b) Do not put on or take off clothes, hats, or similar items at the sampling site. c) Human body static electricity discharge devices should be installed at the entrance to the ladder leading to the oil tank and at the sampling port; human body static electricity must be discharged before and after ascending to the tank and sampling. d) When conducting artificial gas phase testing, anti-static measures should be taken for the sampling equipment, and the metal components of the sampling tools must be properly grounded. If the anti-static sampling hose is kept in constant contact with the sampling port, ensuring that it is at the same potential as the tank, which is then grounded. e) As soon as the operator reaches the platform or descends the floating ladder of an external floating roof tank, they must turn on the alarm and head toward the detection port; if the alarm goes off before reaching the detection port, they must evacuate the site immediately. During sampling, do not pull or release abruptly; the lifting speed must not exceed 0.5 m/s, and the lowering speed must not exceed 1 m/s. f) Manual sampling is not permitted during the transfer of oil in storage tanks. When floating roof tanks are used to store light oils, gas phase testing must be carried out only after the tank has been left stationary for 1 hour. g) The sampling process should avoid severe weather conditions that pose a safety risk, such as thunderstorms. h) Manual testing should be performed twice, and the maximum value should be taken. 2. The department should maintain records related to gas phase testing, documenting the values obtained from manual gas phase tests for future reference. The gas phase inspection of storage tanks should be carried out every 3 months, while tanks holding lightly contaminated oil should be inspected on a monthly basis. For external floating roof tanks with mechanical seal sealing, the gas phase is inspected once a month. During the thunderstorm season, floating roof tanks should have their internal and external concentrations of flammable gases in the secondary sealing system checked twice a month. If the inspection of the primary and secondary sealing areas of an external floating roof tank is successful, it is not necessary to repeat the inspection of the area above the secondary seal. 3. When the gas-phase concentration exceeds the limit, the cause should be identified promptly. When the vapor concentration of the primary and secondary seals in an external floating roof tank exceeds the specified limits, it is necessary to immediately check whether the primary seal is intact; if damage to the primary seal is detected, shutdown for maintenance should be arranged promptly. Name Explosive limit 25﹪ 50﹪ Crude oil 1.1-6.4 0.27 0.55