Installation, inspection, and maintenance of storage tank vent valves

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Installation, Inspection, and Maintenance of Tank Vent Valves I. Which tanks require vent valves? 1. Article 6.2.19 of the \"Code for Fire Protection Design of Petrochemical Enterprises\" GB 50160-2008 (2018 edition): Fixed-roof tanks storing Class A B and Class B liquids shall be equipped with flame arresters and vent valves ； Storage tanks for Class A B and Class C liquids that use nitrogen or other gases for gas sealing should also be equipped with emergency pressure relief devices. 2. Article 5.4.15 of the “Code for Fire Protection Design of Buildings” GB 50016—2014 (2018 edition): For boilers and diesel generators installed within buildings, their fuel supply pipelines shall comply with the following requirements: 1 Automatic and manual shut-off valves shall be installed on the pipelines both before they enter the building and inside the equipment room ； 2 The tanks in the oil storage room shall be sealed, and ventilation pipes leading to the outside should be installed; these ventilation pipes shall be equipped with breather valves fitted with flame arresters. Facilities to prevent the spillage of oil should be provided at the bottom of the tanks ； 3 The installation of gas supply pipelines shall comply with the provisions of the current **standard, the «Code for Design of Urban Gas Systems» GB 50028. 3. Article 6.4.4 of the «Code for Design of Oil Depots» (GB 50074-2014): Breather valves shall be installed at the vents leading to the atmosphere of the following storage tanks: 1 Fixed-roof storage tanks and above-ground horizontal storage tanks used for storing Class A B and Class B liquids ； 2 Horizontal earth-covered oil tanks for storing Class A and B liquids ； 3 Tanks equipped with a nitrogen sealing protection system. Section 6.4.5 The exhaust pressure of the breathing valve shall be lower than the design positive pressure of the storage tank, while the intake pressure of the breathing valve shall be higher than the design negative pressure of the storage tank. When the ambient temperature around the breather valve may be less than or equal to 0°C, an all-weather breather valve should be selected. 4. Article 6.4.4 of the «Code for Fire Protection Design of Oil and Gas Engineering Projects» (GB 50183-2004) stipulates that breather valves, flame arresters, and hydraulic safety valves shall be installed on the tops of oil tanks and sewage sedimentation tanks. The requirement to install breather valves, hydraulic safety valves, and flame arresters on the tops of oil waste tanks and sewage sedimentation tanks is aimed at preventing the tanks from rupturing due to overpressure or a vacuum, which could lead to the leakage of the substances contained within them. It also prevents external sources of fire from igniting the medium inside the tank. Each vent valve and hydraulic safety valve shall be equipped with a flame arrester, and their performance shall meet the requirements of \"Vent Valves for Oil Storage Tanks\" SY/T 0511, \"Hydraulic Safety Valves for Oil Storage Tanks\" SY/T 0525.1, and \"Flame Arresters for Oil Storage Tanks\" SY/T 0512, respectively. II. Requirements for the inspection and maintenance of breather valves: 1. According to 8.6.1 of \"Integrity Management of Atmospheric Pressure Storage Tanks\" (GB/T37327-2019), breather valves used in atmospheric pressure storage tanks must be inspected at least once a year. 8.6.2 Before inspection, the following documents should be reviewed: a) the product model and operating pressure rating of the breathing valve; b) the date of manufacture, product certificate, date of installation, and completion acceptance documents; c) records of online inspections during the operational period; d) previous regular inspection reports. 8.6.3 Before the inspection, the inspection items and acceptance criteria shall be clarified and approved by the user unit, which shall then carry out the necessary preparatory work as required. 8.6.4 The inspection items for breather valves include visual inspection, opening pressure test, air flow rate test, and leakage test. 8.6.5 The vent valve shall show no abnormal rust, leakage, or blockage by debris. 8.6.6 Operation of the breather valve: The pressure, ventilation volume, and leakage rate shall meet the design requirements. 2. \"Guidelines for the Identification and Rectification of Safety Risks and Hazards in Hazardous Chemical Enterprises\", Emergency [2019] No. 78: (IV) Management of Static Equipment – Enterprises shall install safety accessories such as tank vent valves (hydraulic safety valves), flame arresters, foam generators, level gauges, and vent pipes in accordance with relevant standards, and conduct regular inspections or tests, while keeping records of these inspections and maintenance activities. 3. The “Notice on Carrying Out Safety Risk Assessments for Large Oil and Gas Storage Facilities” requires that enterprises install safety accessories such as tank vent valves (hydraulic safety valves), flame arresters, foam generators, level gauges, and vent pipes in accordance with relevant standards, and that they conduct regular inspections or tests while keeping records of these inspections and maintenance activities. 4. Guidelines for Safety Risk Assessment of Oil and Gas Storage Enterprises (Trial) 4.3 Equipment Safety Risk Assessment 4.3.1 Key Assessment Items 1) Assess whether the selection of storage tanks meets the requirements related to the hazards of the stored materials. 2) Has effective safety and reliability assessment been conducted for the tank type adopted for the first time in the country? 3) Evaluate the compliance, effectiveness, and operational status of the safety accessories related to storage tanks (such as safety valves, rupture disks, vent valves, flame arresters, nitrogen seals, etc.). 5. 《Notice of the General Administration of Work Safety on Further Strengthening the Safety Management of Chemical Tank Areas》 (An Jian Zong Guan San [2014] No. 68) (IV) Strengthen the management of equipment and facilities in chemical tank areas. The equipment and facilities in the chemical tank area should be regularly inspected and tested to ensure that tanks, pipelines, valves, pumps, and other equipment are in good condition. Strengthen the monitoring of corrosion in chemical storage tanks, conduct regular tank inspections, and address any corrosion-induced thinning promptly. Ensure that the safety accessories of the storage tank, as well as the lightning protection, anti-static measures, flood prevention facilities, and fire suppression systems are in good condition ； For storage tanks equipped with nitrogen protection systems, it is necessary to ensure that the nitrogen sealing system is in good working condition. 6. Article 7.4.1.1 of \"SY 5225-2005 _ Technical Regulations for Safe Production in Fire and Explosion Prevention during Oil and Gas Drilling, Development, Storage, and Transportation\": The installation of breather valves, flame arresters, and hydraulic safety valves in oil storage tanks shall be carried out in accordance with SY/T 0511, SY/T 0512, and SY/T 0525.1 respectively. The safety valve should be inspected and calibrated at least once a year by a qualified testing institution. Article 7.4.1.2: Flame arresters shall be installed at the bases of breathing valves and hydraulic safety valves. Breathing valves and hydraulic safety valves shall be inspected at least twice a month during winter, and calibrated once a year. The flame arrester should be inspected at least once per quarter. The breather valve is flexible and easy to use. The oil level of the hydraulic safety valve is within the specified range, and the oil quality is satisfactory. The flame arrestor’s flame-retardant layer is in good condition, with no sludge blockage. III. Recommendations for the maintenance of breathing valves: 1. The common faults of breathing valves include air leakage, jamming, sticking, blockage, freezing, as well as the valves remaining open under pressure or vacuum conditions. (1) Air leakage: It is generally caused by rust, hard objects scratching the contact surface between the valve and the valve disc, deformation of the valve disc or seat, and an inclined valve disc guide rod. (2) Jamming: This usually occurs when the breathing valve is not installed properly or when the oil tank deforms, causing the valve disc guide rod to become misaligned or the valve rod to rust; as a result, the valve seat cannot move up and down along the guide rod to its proper position, thereby jamming the valve disc at a certain point on the guide rod. (3) Adhesion: This occurs as oil vapors, moisture, and dust and other contaminants deposited on the valve disc, valve seat, and guide rods undergo chemical and physical changes; over time, this leads to the adhesion of the valve disc to the valve seat or the guide rods. (4) Blockage: This is mainly caused by the long-term lack of maintenance of mechanical breathing valves, which leads to the accumulation of dust, rust, and other debris inside the valve or the breathing tube. It can also be caused by bees or birds building nests at the opening of the breathing valve, resulting in its blockage. (5) Freeze of the breather valve: This occurs due to changes in temperature, causing moisture in the air to condense on parts such as the valve body, valve disc, valve seat, and guide rod of the breather valve, eventually leading to freezing and making it difficult to open the valve. 2. Contents of regular inspections: (1) Check for phenomena such as constant opening, air leakage, jamming, sticking, blockage, freezing, and rusting ； (2) Check whether the sealing gasket is leaking; if so, it should be replaced ； (3) Check whether the valve disc can rotate freely and whether there is any sticking issue ； (4) Check whether the sealing mesh of the valve body is frozen or blocked, and whether there is dust or dirt attached to the mesh ； (5) To check whether metal components such as the valve disc, valve seat, guide rod, and air guide spring are rusted or contaminated, kerosene can be used for cleaning. (6) When loading and unloading materials from the storage tank, check whether the breathing valve is operating properly. 3. The breathing valve should be calibrated regularly once a year, and the calibration method shall follow SY/T 0511.1-2010 \"Attachments for Oil Storage Tanks – Part 1: Breathing Valves\".