A table explains which storage tanks require high liquid level alarms, high-high liquid level alarms and interlocks, low liquid level alarms, and low-low liquid level alarms and interlocks

The basis for the information in the table above is as follows: ♢ According to Article 6.2.23 of the \"Code for Fire Protection Design of Petrochemical Enterprises\" GB50160-2008 (2018 edition), storage tanks for flammable liquids shall be equipped with level gauges and high-level alarms; where necessary, automatic interlock systems to shut off the feeding facilities can also be installed； An automatic dehydrator should also be installed. 6.3.10 Liquid ammonia storage tanks shall be equipped with level gauges, pressure gauges, and safety valves ； Low-temperature liquid ammonia storage tanks should also be equipped with temperature indicators. 6.3.11 Liquefied hydrocarbon storage tanks shall be equipped with level gauges, thermometers, pressure gauges, safety valves, as well as high-level alarms and automatic interlock shutdown mechanisms for extremely high levels to cut off feeding. Fullly frozen liquefied hydrocarbon storage tanks should also be equipped with vacuum relief facilities and high/low temperature monitoring, and should be connected to an automatic control system. ♢\"Code for Design of Oil Storage Tanks\" GB50074-2014, 6.3 Horizontal oil tanks buried in soil; 6.3.7 Horizontal oil tanks shall be equipped with a level monitoring system that includes a high liquid level alarm function. The liquid level monitoring system for single-layer oil tanks should also have a leakage detection function. 15.1 Automatic control systems and instruments 15.1.1 Storage tanks with a capacity greater than 100 m³ shall be equipped with remote liquid level measurement instruments, and shall comply with the following requirements: 1 The continuous liquid level measurement signals shall be transmitted to the automatic control system in either analog form or via communication methods. 2 High and low liquid level alarms should be installed in the automatic control system. 3 The set level for the high liquid level alarm in storage tanks shall comply with the relevant provisions of the current industry standard \"Design Code for Tank Areas in Petrochemical Storage and Transportation Systems\" SH/T 3007. 4 The set level for the low liquid level alarm in storage tanks should be such that cavitation does not occur in the pumps. For external floating roof and internal floating roof storage tanks, the set level for the low liquid level alarm (measured from the bottom of the tank) should be at least 0.2m higher than the height at which the floating roof touches the bottom of the tank. 15.1.2 The following storage tanks shall be equipped with high liquid level alarms and interlocks; the high liquid level alarm shall be capable of simultaneously interlocking to close the control valve of the tank’s inlet pipeline: Storage tanks for Class A B and Class B liquids with a turnover rate of more than 6 times per year and a capacity of 10,000 m³ or more ； Class A B and Class B liquid storage tanks with a turnover rate of 6 times or less over 2 years, and a capacity of more than 20,000 m³ ； 3 Storage tanks for liquids of toxicity levels I and II. 15.1.3 External floating roof tanks and internal floating roof tanks with a capacity of 50,000 m³ or more shall be equipped with a low-low liquid level alarm. The set height for the low-low liquid level alarm (measured from the bottom of the tank) should not be lower than the height at which the floating roof touches the bottom; the low-low liquid level alarm should also be capable of triggering the pump to stop simultaneously. 15.1.4 The level measurement instruments used for high and low high/low level alarm signals in storage tanks shall be separate continuous level measuring instruments or level switches, and alarms and interlocks shall be provided in the automatic control system. ♢\"Safety Management Specifications for Atmospheric Pressure Storage Tank Areas of Flammable Liquids in Chemical Enterprises\" AQ 3063-2025: 6.1.8 The switch valves installed on the inlet and outlet pipelines for liquid materials in storage tanks must meet the following requirements: a) For tank groups that constitute level 1 or level 2 major hazard sources, remote-controlled switch valves should be installed on the inlet and outlet pipelines for the liquid materials in those tanks ； b) For the highly toxic liquid storage tanks in tank groups that constitute primary or secondary major hazard sources, switch valves controlled remotely by the Safety Instrumented System (SIS) should be installed on the inlet and outlet pipelines of these tanks. The remotely controlled switch valves on the inlet pipelines shall be interlocked with the high liquid level sensors of the tanks, and manual actuators (such as handwheels) should be provided; such manual actuators must have measures in place to prevent accidental operation. 6.1.10 The designed low-low liquid level for external floating roof tanks and internal floating roof tanks shall be no lower than the height at which the floating roof touches the bottom, and a low-low liquid level alarm shall be provided. 6.6.4 For newly built storage tanks for extremely hazardous and highly hazardous liquids, the level measurement instruments shall be installed as 2 sets of continuous level measuring instruments together with 1 high-high level switch, or as 3 sets of continuous level measuring instruments. ♢\"Technical Specifications for Safety Monitoring of Major Hazard Sources of Hazardous Chemicals\" GB17681—2024 6.3.2 Monitoring requirements for atmospheric and low-pressure tank areas 6.3.2.1 Tanks shall be equipped with at least 2 sets of continuous level detection instruments, or 1 set of continuous level detection instrument and 2 level switches. 6.3.2.2 The system shall be equipped with high liquid level alarms, low liquid level alarms, very high liquid level alarms, and very low liquid level alarms, and shall comply with the following provisions. a) The alarm set value shall comply with the relevant provisions of SH/T3007 ； The low-low liquid level alarm setpoints for external floating roof tanks and internal floating roof tanks should not be lower than the height at which the floating disk touches the bottom. b) The high liquid level alarm should interlock to close the remotely controlled on/off valve on the storage tank inlet pipeline, and measures should be taken to prevent pressure buildup in the feed pump ； The low liquid level alarm should interlock to shut off discharging. 6.3.3 Monitoring requirements for pressure storage tank areas 6.3.3.1 Pressure storage tanks shall be equipped with at least 2 sets of continuous level detection instruments and 1 high-high level switch, or with 3 sets of continuous level detection instruments. The continuous level monitoring instrument should provide local indication of the liquid level, alarms for high and low levels, as well as alarms for extremely high and extremely low levels. The alarm for extremely high level should trigger the interlock to close the emergency shut-off valve on the feed pipeline to the storage tank, and measures should be taken to prevent pressure buildup in the feed pump ； The low liquid level alarm should interlock to shut off discharging. 6.3.4 Monitoring requirements for the fully refrigerated storage tank area 6.3.4.1 The installation of liquid level detection instruments in the storage tanks and the control of liquid levels shall comply with the following provisions. a) At least 3 sets of level detection instruments shall be installed, of which at least 2 sets shall be continuous level detection instruments, used for level measurement as well as for high and low level alarms, high-high level alarms and interlocks, and low-low level alarms and interlocks. ♢\"Code for Safety Management of Liquefied Hydrocarbon Storage Areas\" AQ3059-2023: 6.6.2 For newly installed liquefied pressure storage tanks, the level measurement instruments shall be configured as 2 sets of continuous level measuring instruments along with 1 high-high level switch, or as 3 sets of continuous level measuring instruments. Liquefied hydrocarbon pressure storage tanks should be equipped with high liquid level alarms, low liquid level alarms, high-high liquid level alarms, and low-low liquid level alarms. The high-high liquid level alarm should trigger the interlocked shutdown of the tank’s feed emergency shut-off valve. 6.1.8 When butadiene material is stored in pressure tanks, in addition to meeting the requirements mentioned above, the following requirements must also be satisfied: a) The tanks should have their oxygen content, polymer content, and inhibitor content checked regularly to prevent polymer aggregation ； b) Control the oxygen content in the gas phase within the storage system; it should not exceed 0.2% for polymer-grade material and 0.3% for industrial-grade material ； c) Pipelines should minimize dead zones such as drain legs and dead ends ； d) When the storage period is less than two weeks, the storage tank should be equipped with a water spray cooling system, or a refrigeration cycle system along with a polymerization inhibitor addition system ； When the storage period is more than two weeks, the storage tank should be equipped with a refrigeration cycle system and a polymerization inhibitor addition system ； e) Burst discs and pressure instruments should be installed in front of the safety valves of storage tanks and pipelines; continuous nitrogen purging should be applied to the outlet pipeline of the safety valves of storage tanks, or nitrogen purging should be triggered via an interlock system when the pressure in the storage tank rises too high ； f) The storage coefficient of the tank should be less than or equal to 0.9, and measures such as high liquid level alarms and automatic interlock shutdown of feeding should be in place. ♢\"Safety Management Standards for Fine Chemical Enterprises\" AQ3062—2025 7.4.1.5 The filling facilities for flammable, toxic, and highly corrosive liquids involved in construction projects shall be equipped with functions such as automatic flow control and high liquid level interlock. 7.4.2.4 Hazardous chemical metering tanks and surge tanks shall be equipped with high and low level alarms, as well as overflow pipes, or interlock measures to stop feedstock supply when the high level alarm is triggered. 7.4.2.5 Flammable liquid storage tanks and storage tanks for liquids with acute toxicity in Category 1 or Category 2 shall be equipped with high-level and very high-level alarms; the values for these alarms shall be interlocked with the feed valve. The tanks shall have two sets of remote transmission level measurement instruments, at least one of which shall have continuous measurement capability. ♢\"Code for Design of Tank Areas in Petrochemical Storage and Transportation Systems\" SH/T 3007—2014: 5.4.1 Storage tanks with a capacity greater than 100 m³ shall be equipped with remote liquid level measurement instruments. 5.4.2 High and low liquid level alarms shall be provided in the automatic control system, and the following requirements shall be met: a) The set point for the high liquid level alarm in the storage tank shall not be higher than the designed maximum liquid level of the tank ； b) The set level for the low liquid level alarm in the storage tank should not be lower than the designed low liquid level for storage in that tank. 5.4.3 Storage tanks for liquids of toxicity grades I and II, storage tanks for Class A B and Class B flammable liquids with a capacity of 3000 m³ or more, and storage tanks for other liquids with a capacity of 10000 m³ or more shall be equipped with high-high liquid level alarms and interlocks; the high-high liquid level alarm shall trigger the interlock to close the control valve of the tank’s inlet pipeline. 5.4.4 The raw material storage tanks of the unit should be equipped with a low-low liquid level alarm, and this alarm should be linked to shut down the pump. 6.3.2 A set of remote transmission instruments and a set of local indication instruments shall be provided for the liquid level measurement of pressure storage tanks; glass plate level gauges shall not be used as local indication instruments. 6.3.3 Level measurement remote transmitters shall be equipped with high and low level alarms. The set level for the high liquid level alarm should be the designed maximum liquid level of the storage tank ； The set level for the low liquid level alarm should ensure that the pump will not experience cavitation within 10 to 15 minutes from the onset of the alarm. 6.3.4 The pressure storage tank shall be equipped with a separate set of level measurement instruments or level switches dedicated to high-level liquid level alarm and interlocked shutdown of the tank’s feed pipe valves. The set level for the high liquid level alarm should not be higher than the level at which the liquid volume reaches 90% of the tank’s calculated capacity.

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