Basic knowledge of storage tanks

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I. Purpose of storage tanks: Steel sealed containers used for storing liquids or gases are known as steel storage tanks. Steel storage tank systems represent essential and important infrastructure in industries such as petroleum, chemicals, grain and oil, food processing, firefighting, transportation, metallurgy, and national defense. Our economic life relies heavily on these small steel storage tanks, which play an irreplaceable role in the development of the national economy. Steel storage tanks are specialized devices used for storing various liquid (or gas) raw materials and finished products. For many enterprises, production cannot proceed without such tanks; in particular, **the storage of strategic materials relies on storage tanks of different capacities and types. In our country, oil storage facilities are mainly composed of above-ground tanks, many of which have metal structures; therefore, this website will focus on providing basic information regarding the dome-type tanks, internal floating roof tanks, and horizontal tanks that are widely used in China. II. Classification of storage tanks: Due to the differences in the media stored, there are various types of storage tanks. Classification by location: They can be categorized into above-ground tanks, underground tanks, semi-underground tanks, offshore tanks, subsea tanks, etc. Classified by oil type: they can be divided into crude oil storage tanks, fuel oil storage tanks, lubricating oil tanks, edible oil tanks, fire water tanks, etc. Classified by purpose: they can be divided into production oil tanks, storage oil tanks, etc. Classified by form: They can be divided into vertical storage tanks, horizontal storage tanks, etc. Classified by structure: they can be divided into fixed-roof storage tanks, floating-roof storage tanks, spherical storage tanks, etc. Classified by size: Tanks with a capacity of over 100 m3 are considered large storage tanks, and they are mostly vertical tanks ； Storage tanks with a capacity of 100 m³ or less are considered small storage tanks, and they are usually horizontal in design. III. Standards for storage tanks: Common standards for storage tanks: 1. American Petroleum Institute standard API650 ； 2. British Standard BS2654 ； 3. Japanese Standard JISB8501 ； 4. German standard DIN4119 ； 5. Petroleum industry standard SYJ1016-82 ； 6. Petrochemical industry standard SH3046-92. IV. Materials for storage tanks: The materials required for tank construction are divided into tank body materials and materials for auxiliary facilities. Tank materials can be classified as low-strength steel or high-strength steel based on their tensile yield strength (бs) or tensile ultimate strength (бb); high-strength steel is commonly used in storage tanks with a capacity of over 5,000 m3 ； The auxiliary facilities (including wind-resistant ring beams, joints, spiral staircases, guardrails, etc.) are made of ordinary carbon structural steel with lower strength, while other components and accessories are made of different materials depending on their intended use. Commonly used domestic steel grades for manufacturing tanks include 20, 20R, 16Mn, 16MnR, and the Q235 series. V. Structure of storage tanks: At present, the types of storage tanks that are most widely used in China, and for which the manufacturing and installation techniques are the most mature, are dome-shaped storage tanks, floating roof storage tanks, and horizontal storage tanks. (1) Structure of domed storage tanks. A domed storage tank is a steel container whose roof is spherical in shape and whose body is cylindrical. Dome storage tanks are simple to manufacture and inexpensive, which is why they are widely used in many industries both domestically and internationally. The most common capacity range is 1000–10,000 m³; currently, the maximum capacity of dome storage tanks used in China has reached 30,000 m³. Bottom of the tank: The bottom of the tank is assembled from steel plates; the steel plate in the middle of the bottom is a medium-width plate, while the steel plates around it are edge plates. The edge plate can be either a strip-shaped plate or an arc-shaped plate. Generally, when the inner diameter of the tank is < 16.5 m, strip-shaped edge plates are preferred; when the inner diameter is ≥ 16.5 m, arc-shaped edge plates are preferred. Tank wall: The tank wall is formed by butt-welding multiple rings of steel plates; it can be either sleeved or straight-type. The circumferential welds of the sleeve-type tank wall plates are lap welded, while the longitudinal welds are butt welded. This form is commonly used for vaulted storage tanks; its advantage is that it facilitates the alignment of the various wall panels, and construction using the inverted method is relatively safe. The circumferential welds of the straight-type tank wall panels are butted. The advantage is that the diameter of the tank wall remains constant from top to bottom, making it particularly suitable for internal floating roof tanks; however, it requires high precision during assembly and installation, and the process is rather complex. Tank roof: The tank roof is spherical in shape, formed by welding multiple fan-shaped plates together. On the inner side of the roof, flat steel bars are used as reinforcing ribs. Overlapping welds are employed between the individual fan-shaped plates. The entire tank roof is welded to the angle iron ring at the upper part of the tank wall (also known as the locking ring). (II) Structure of floating roof tanks A floating roof tank consists of a floating roof that floats on the surface of the medium, along with vertical cylindrical tank walls. The floating roof rises and falls as the volume of the medium inside the tank increases or decreases. An annular sealing device is present between the outer edge of the floating roof and the tank wall, ensuring that the medium inside the tank is always directly covered by the inner floating roof, thereby reducing vaporization of the medium. Bottom of the tank: Floating roof tanks generally have a large volume, and their bottom plates are equipped with arc-shaped edge plates. Tank wall: A straight-type tank wall is used; the butt welds should be polished smoothly to ensure a smooth inner surface. The upper part of the floating roof tank is open; to increase the stiffness of the wall panels, wind-resistant ring beams and reinforcement rings must be installed at the top of the tank walls, depending on the wind load in the area. Floating roof: Floating roofs are divided into single-disc floating roofs, double-disc floating roofs, and float-type floating roofs, among other types. Single-disc floating roof: It consists of several separate compartments forming a circular floating structure, with a single-disc roof on the inner side of this circle. Multiple annular steel rings are provided at the bottom of the single-disc top plate for reinforcement. Its advantages are low cost and easy maintenance. Double-disc floating roof: It consists of an upper disc plate, a lower disc plate, and deck edge plates, and is divided into several separate annular compartments by radial and circumferential partitions. Its advantages are high buoyancy and excellent drainage performance. (III) Structure of internal floating roof storage tanks: Internal floating roof storage tanks are created by adding a floating roof inside an arch-shaped roof storage tank. The floating roof installed inside helps to reduce the loss of vaporized material, while the external arch-shaped roof prevents rainwater, snow, dust, and other contaminants from entering the tank, thus ensuring that the material stored inside remains clean. Such storage tanks are primarily used to store light oils, such as gasoline and aviation kerosene. Internal floating roof storage tanks feature straight tank walls, with the wall panels welded together at their joints; the vault is constructed in accordance with the requirements for vault-type storage tanks. Currently, there are two types of internal floating roofs used in China: one is a steel floating roof identical to that used in floating-roof storage tanks ； Another type is an aluminum alloy floating roof that is assembled in place. (IV) Structure of horizontal storage tanks: The volume of horizontal storage tanks is generally less than 100 m3, and they are typically used in production facilities or gas stations. The circumferential welds of horizontal storage tanks use lap welding, while the longitudinal welds use butt welding. The ring plates are arranged interactively in an odd number so that the diameters of the end caps are identical. The end caps of horizontal storage tanks are divided into flat end caps and disc-shaped end caps; horizontal storage tanks with flat end caps can withstand an internal pressure of 40 kPa, while those with disc-shaped end caps can withstand an internal pressure of 0.2 MPa. Underground horizontal storage tanks must be equipped with reinforcing rings, which are fabricated from angle steel. VI. Technical Specifications of Storage Tanks – Technical specifications for the series of vertical storage tanks with steel vault tops. Volume (m³): Nominal volume: 100, 300, 400, 500, 700, 1000, 2000, 3000, 5000, 10000; Design volume: 110, 330, 440, 550, 770, 1100, 2200, 3300, 5500, 10700. Tank dimensions (mm): D1: 5172, 7750, 8288, 8983, 10263, 11580, 15781, 18992, 23760, 31852; D2: 5252, 7830, 8368, 9063, 10343, 11680, 15881, 19092, 23880, 31402; H: 5300, 7070, 8240, 8810, 9140, 10580, 11370, 11760, 12530, 14070; H1: 5870, 7920, 9148, 9194, 10533, 11847, 13110, 13857, 15143, 17504. Note 1: D1 refers to the inner diameter of the tank ； D 2 represents the diameter of the tank bottom ； H represents the height of the tank wall ； H 1 represents the total height of the storage tank. Note 2: The data in this chart is for reference only; quotes and construction shall be based on the requirements specified in the drawings. Technical specifications for internal floating roof tank series
Volume (m³) | Nominal volume
100 300 400 500 700 1000 2000 3000 5000 10000
Design volume 114 325 430 533 750 1152 2255 3457 5275 10755

Tank dimensions (mm)
D1 14700 6500 7500 8200 9200 11000 14500 17000 21000 30000
H 7050 10300 10300 10660 11840 12690 14270 15850 15850 15850
h 408 713 822 893 1007 1199 1500 1863 2300 3284
H1 7462 11017 11126 11563 12852 13894 15866 17710 18156 19142

Note: D1 refers to the inner diameter of the tank ； H represents the height of the tank wall ； H 1 represents the total height of the storage tank ； h represents the height of the vault. Note 2: The data in this chart is for reference only; quotes and construction shall be based on the requirements specified in the drawings. Technical specifications for horizontal storage tanks with flat end caps: Nominal capacity in m³: 8, 15, 30, 40, 50, 60; Actual capacity in m³: 8.5, 15.6, 31, 39, 53, 60. Diameter in m: 1.9, 2.2, 2.2, 2.2, 2.55, 2.55; Length in m: 3.0, 4.09, 8.19, 10.34, 10.34, 11.77. Wall thickness in mm: 4, 4, 4, 4, 4, 4. End cap thickness in mm: 4, 5, 5, 5, 5, 5. VII. Foundation of the storage tank: (I) Types of storage tank foundations: There are typically three types of foundations – slope-type foundations, ring-wall type foundations, and outer ring-wall type foundations. (II) Basic bearing capacity: Requirements for the bearing capacity of tank foundations. Nominal capacity (m³): 100, 200, 300, 400, 500, 700, 1000, 2000, 3000, 5000, 10000. Bearing capacity of the foundation (t/m²): 8, 8, 8, 10, 10, 10, 10, 13, 13, 16, 18. (III) Selection of tank foundation types: When the underlying soil can meet the requirements regarding bearing capacity and settlement, and there are no constraints on the site, it is advisable to use a slope-type or outer ring wall-type foundation ； When the bearing capacity of the native soil layer does not meet the design requirements, but the settlement amount is within the allowable limits, a ring wall foundation or an outer ring wall foundation can be used ； When the foundation soil is soft soil, it is advisable to treat the foundation before adopting an external ring wall foundation ； When space is limited, a ring wall foundation can be used. (IV) Construction of storage tank foundation: Earthwork excavation: Compaction of the foundation pit ； Reinforced concrete and masonry work: (omitted) ； Earth backfilling: mechanical compaction, with the backfill layer being greater than 500 mm thick ； Sand cushion: Medium and coarse sand is used, with a laying thickness of 200–250 mm; it is compacted by sprinkling water and using a flat vibrator ； Asphalt sand cushion: Medium and coarse sand, along with No. 60 road petroleum asphalt, are heated to produce asphalt sand, which is then laid in layers and sections in a even manner; its thickness ranges from 80 to 100 mm. The surface of the storage tank foundation has a slope of 15 to 35‰ from the center outward ； Slope protection construction: Slope protection construction is carried out after the hydrostatic test of the storage tank; the width of the slope protection is 800–1,000 mm. The gap between the slope protection and the tank bottom plate is filled with asphalt mastic. During the design and construction of tank foundations, please refer carefully to SH/T3083-1997 \"Technical Specifications for Foundation Treatment of Steel Storage Tanks in Petrochemical Industries\" and SH3086-1995 \"Design Specifications for Foundations of Steel Storage Tanks in Petrochemical Industries\". VIII. Fabrication and Installation of Storage Tanks The construction process of storage tanks consists of two parts: prefabrication of semi-finished products and on-site assembly and installation. Prefabrication of semi-finished products: Components such as the tank bottom, tank walls, and tank top all need to be prefabricated (the specific methods for prefabrication are not detailed here). On-site alignment and installation methods: They are generally divided into the inverted construction method, the normal construction method, and special construction methods. IX. Storage tank accessories – Ladder (or straight ladder): equipped with a rest platform, 650 mm wide, rotating counterclockwise. Anti-slip steps are provided on the top of the tank. Guardrail: height of 800~1000mm. Overpass: Used for connecting tank rooms, with a width of 650 mm. Manholes: There are three common specifications: DN500, DN600, and DN750. Light-transmitting hole: Common specification: DN500. Cleaning or drain holes: Drain holes are used for light oil, while cleaning holes are used for heavy oil. There are three models: DN50, DN80, and DN100. Oil measurement port: Common specification: DN150. Drain pipe and automatic water cut-off device: Inlet and outlet connection pipes: Table of accessories for vault-type storage tanks. Nominal volume (m³): Oil measurement hole, light-transmitting hole, manhole, waste/discharge hole or cleaning hole, suction valve or vent hole. Drain pipe: ≤2000 – 1, 1, 1, 1; these are standard products, and the model is selected based on the maximum inlet and outlet flow rates. 1–3000–5000: 1, 2, 2, 1, 1; 10000: 1, 3, 3, 2, 1; 20000–30000: 1, 3, 4, 3, 2; ≥50000: 1, 3, 4, 3, 2