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Oil tank

Large containers with regular shape for storing oil products

This entry is made by Compilation and application of scientific encyclopedia entries of "Science Popularization China" to examine.

Storage tank , short for Oil tank perhaps Storage tank It is a large and regular shape used for storing oil products container According to different construction materials, it can be divided into metal oil tank and non-metal oil tank. Most metal oil tanks are steel oil tanks oil depot A class commonly used in; Non metal oil tanks, also known as "soil oil tanks", have been phased out since the 1990s due to poor safety hazards. [1]

A container for storing crude oil or other petroleum products. It is used in refineries, oil fields, oil depots and other industries. The oil tank farm consists of several oil tanks. Each oil tank farm generally stores one oil product.

Chinese name: Oil tank
Foreign name: oil tank
Applicable industries: Refinery , oil field, oil depot

Interpretation: Storage crude oil Or other petroleum products
Abbreviation: Oil tank or storage tank
Classification: Metal and non-metallic oil tanks

catalog

brief introduction

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Storage crude oil Or other petroleum products. Used in refineries oil field , oil depots and other industries.

classification

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By material

Oil tank

1. Divided into steel reinforced concrete And masonry. Steel oil tanks are vertical (including vault type and floating roof cylindrical), spherical shell type (spherical) and horizontal (cylindrical). The vertical dome roof oil tank is composed of spherical crown tank roof and vertical cylindrical tank wall. It is mainly used to store non-volatile oil products, such as diesel oil And similar oil products. The most commonly used volume is 1000 - 10000 m ³.

Floating roof oil tank It is composed of a floating roof floating on the surface of the medium and a vertical cylindrical tank wall. The floating roof rises and falls with the increase or decrease of the storage of medium in the tank. There is an annular sealing device between the outer edge of the floating roof and the tank wall, and the medium in the tank is always Inner floating roof Direct coverage to reduce medium volatilization. It is mainly used for storing volatile oil products, such as gasoline and similar oil products. The volume of floating roof oil tanks is generally large. The floating roof is divided into single disc floating roof, double disc floating roof and float floating roof.

Horizontal oil tank It is composed of end caps and horizontal round or oval tank walls, and is usually used in production links or gas stations. The volume of horizontal oil tank is generally less than 100m ³;.

By structure

2. According to the structure, it mainly includes crude oil storage tank, fuel oil storage tank, lubricating oil tank, animal and vegetable oil storage tank, etc.

Avoid foundation shear failure. According to the nature of the oil stored, it can be divided into heavy oil tank and light oil tank. At the same time, pay attention to the change of surface soil around the tank, which can be divided into ground, semi underground and underground types according to the burial depth. To prevent the tank body from settling too fast, if the steel oil tank is buried underground or semi underground, a retaining wall must be set to bear the earth pressure.

The oil tank farm consists of several oil tanks. Each oil tank farm generally stores one oil product. The oil tank farm shall be equipped with fire-fighting, lightning protection and anti-static facilities. Fire dike shall also be built in the aboveground oil tank farm. Settlement observation shall be carried out continuously.

Steel oil tank

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Main types

① Vertical cylindrical dome roof steel oil tank. The capacity is generally below 10000 cubic meters. The wall plate is connected by sleeve (fillet weld). The inverted installation method is commonly used during construction (starting from the tank top, install the tank wall layer by layer from top to bottom, and use the fan to supply air to raise the tank body). Compared with the forward installation method (starting from the bottom ring plate of the tank wall and installing the tank wall layer by layer from bottom to top), aerial work is reduced.

② Vertical cylindrical floating roof steel oil tank. A double disk floating roof or a single disk floating roof that can float up and down is provided. The double disk floating roof can reduce the influence of thermal radiation, so the evaporation loss of oil products is small. However, when the capacity is large (more than 10000 m3), in order to reduce the cost, the single deck floating roof is generally used. Reasonable sealing device shall be selected for such oil tank, which requires good sealing effect and convenient installation and maintenance. The wall plate is connected by butt welding, and the normal installation method is commonly used in construction.

③ Vertical cylindrical inner floating roof steel oil tank. It has both dome roof and inner floating roof. The inner floating roof floats on the liquid surface inside the dome roof oil tank and can float up and down. It not only has the characteristics of floating roof oil tank, but also can ensure the cleanliness of oil products.

④ Spherical steel oil tank. It can withstand the working pressure of 0.45~3 MPa, and the capacity is generally 50~2000m3). It is commonly used for storage Liquefied petroleum gas 。

⑤ Horizontal steel oil tank. The capacity is generally below 50 m3. It can store gasoline and volatile petroleum products.

Calculation principle

① Vertical cylindrical steel oil tank. Tank wall thickness t, in mm, shall meet the following formula: H Is the vertical distance from the bottom edge of a circle of tank wall plate to the top of the tank wall (to the lower edge of the overflow port when there is an overflow port), in meters; D Is the internal diameter of the oil tank, in meters; [ σ ]Is the allowable stress of tank wall steel plate at design temperature, unit: kg/mm2; γ is the volume weight of liquid storage, unit: t/m3, and hiss is the weld joint coefficient, taken as 0.9; C0 is the allowable negative deviation of steel plate thickness, in mm; C is the corrosion allowance, in mm. The wind ring and tank wall stiffening ring on the floating roof tank wall shall be determined by calculation. The stability of the vault shall be checked first, that is, the design external pressure of the vault shall be less than the allowable critical pressure of the vault. When building oil tanks in earthquake fortification areas, the tank walls must be checked for earthquake resistance. When the volume is more than 50000 m3, if the floating roof steel tank is used, the steel plate at the lower part of the tank wall is more than 40 mm thick, which is not easy to roll into a circular arc, and the floating roof reinforced concrete tank can be used instead.

② Spherical steel oil tank. The thickness of the spherical shell, the stability of the strut, the size of the base plate, the pull rod and its connection, and the connection part between the strut and the spherical shell shall be calculated. The steel oil tank foundation vertical oil tank shall be set on the asphalt sand insulation layer to prevent the corrosion of the oil tank bottom plate. If the oil temperature is greater than 80 ° C, the upper part of the insulation layer shall be provided with an additional insulation layer. The lower part is vibrated sand or gravel Mixed materials Cushion, with slope protection or ring wall around. Reinforced concrete ring wall foundation can be used when it is soft foundation or in seismic area or when the land is limited. Reinforced concrete independent foundation or ring foundation can be used under the pillar of spherical oil tank. Pier wall foundation shall be adopted for horizontal oil tank, and the position and height of tank body shall be able to make oil flow automatically. Although the foundation of the steel oil tank is allowed to have large uniform settlement, the foundation should be raised in advance to offset the settlement value. The uneven settlement of the foundation shall be prevented to avoid damage to the oil tank.

quality testing

The destruction of steel oil tanks can be divided into two categories:

① Welding residual stress Brittle failure;

② Foundation and foundation damage.

Therefore, the construction quality of steel oil tanks must be strictly inspected. During welding, reasonable welding sequence shall be adopted, welding deformation shall be controlled, and leakage test and flaw detection shall be conducted. The floating ship warehouse with floating roof shall be Air tightness test Vacuum leakage test shall be adopted for the welds of floating roof single panel and bottom plate of the ship's cabin.

Other oil tanks

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Reinforced concrete oil tank

It is often made into a cylindrical structure. The tank body is composed of top cover, wall plate and bottom plate. It is generally used to store heavy oil products. This type of oil tank has the advantages of steel saving, good durability, low maintenance cost and low oil consumption, but it has more construction procedures and longer cycle. Semi underground or underground reinforced concrete oil tanks also have the advantages of good fire resistance, small tank spacing, small temperature difference of wall panels, etc. When the oil tank capacity is large, prestressed concrete oil tanks are often used to apply circumferential prestress. The methods are as follows:

① Electrothermal tensioning method;

② Jack tensioning method;

③ The steel wire is continuously wound and tensioned along the wall height with a wire winder (referred to as wire winding prestress).

The cylindrical oil tank built by wire wrapping prestress method is characterized by uniform tensile stress, small prestress loss and convenient operation. The tank bottom plate is poured on site; The top cover and wall plate can be cast on site, prefabricated in factory and assembled on site. After the circumferential prestress is applied to the tank wall, under the external load, the residual compressive stress in the circumferential direction should still be about 0.3 MPa. The operating negative pressure of 500 Pa shall be considered in the top cover load, and the operating pressure of 2000 Pa shall be considered for the wall plate load. For reinforced concrete oil tank, in order to reduce the wall height and increase the capacity, the bottom plate can be made into an inverted cone. Due to the strong permeability of oil products, the best concrete gradation is generally used to improve the anti-seepage capacity of tank walls. Non metallic oil tanks can also be made into rectangles, often called oil pools, which are mostly semi underground or underground. The reinforced concrete oil pool has certain economic effect only when its capacity is greater than 5000m3.

Masonry oil tank and oil pool

The general capacity is below 2000m3. When the wall height increases, the seepage pressure also increases and is easy to leak, so the wall height is mostly controlled below 6m. The impermeability of masonry is poor. During construction, masonry is required to be dense, mortar is full, and effective impermeability measures are taken inside the tank, such as Ferrocement Mortar plastering layer or anti-seepage coating, etc. China has adopted wire wrapped prestressing method to increase capacity and improve crack resistance. For oil tanks and oil pools constructed of reinforced concrete and masonry, the structural requirements and calculation principles are shown in the pool. The non-metallic oil tank and oil pool are sensitive to the settlement of the foundation, so the foundation treatment must be carried out for the weak or uneven soil foundation.

accessory equipment

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In order to facilitate the transportation of oil products, heaters are installed in the tanks for storing heavy oil and crude oil, and thermal insulation measures are also taken outside the tank walls above the ground. According to the requirements of production, maintenance and safety, the oil tank is equipped with: ① oil measuring hole (also used as sampling hole); ② The tanks for storing gasoline, kerosene, light diesel oil, crude oil and aromatics need to be equipped with breather valves; ③ The tanks storing heavy oil products such as fuel oil, raw oil, heavy diesel oil and wax oil shall be equipped with ventilation holes; ④ Manhole, light hole and cleaning hole (the latter is only set in the heavy oil tank).

Inspection observation

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After the completion of the oil tank, water filling inspection must be carried out. The main purposes are: to inspect the reliability of the tank structure; Check for leakage (including welds of steel oil tanks and cracks of non-metallic oil tanks); Preload the foundation. For soft foundation, the water filling rate shall be strictly controlled to prevent the tank body from settling too fast. At the same time, attention shall be paid to the change of surface soil around the tank body to avoid foundation shear failure. The settlement observation shall be carried out continuously for a period of time from the foundation construction to the production of the oil tank.

For floating roof oil tanks, floating roof lifting test is also required. During water filling and drainage, the stability of floating roof lifting, sealing, flexibility of guide part and leakage of central drainage pipe shall be checked.

Cleaning operation

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Generally speaking, oil tank cleaning shall be carried out under the following conditions^[1] : Before the new oil tank is filled with oil; When changing different types of oil and the original oil storage has an impact on the newly changed oil; When open flame welding or paint removal is required for oil tank; Clean the tank when the oil is loaded for a long time and the tank is dirty. As the purpose of each tank washing is different, the specific requirements for tank washing are also different. If the oil is changed, clean it; When welding oil tanks, the removal of oil vapor is very strict, so it needs to be treated differently.

Anticorrosive coating

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1. For inner wall Electrostatic conductive coating

According to GB13348-92 Safety Code for Static Electricity of Liquid Petroleum Products and GB15599-95 Safety Code for Lightning of Petroleum and Petroleum Facilities, the internal wall of crude oil tank is required to use electrostatic conductive coating, GB6950-2001 Technical Indexes of Static Conductive Coatings for Oil Tanks requires that the surface resistivity of static conductive coatings for oil tanks should be 10 Ω<ps<10 Ω according to the standard GB/T16906-1997 Measurement of Resistivity of Static Conductive Coatings for Oil Tanks.

The electrostatic conductive coatings used for coating the inner wall of the oil storage tank are classified according to the conductive medium, including the following:

Conductive medium	Metal powder	Conductive carbon black and graphite powder	Conductive composite mica powder (metal oxide coating treatment)
Performance characteristics	1. The color is limited by the color of metal powder. 2. The conductive property of the coating film is reduced because the metal powder is easy to oxidize, while the inert metal is expensive. 3. If the metal powder with the electrode potential higher than that of steel is used as the conductive medium, when it is in direct contact with the steel substrate, electrochemical corrosion will be formed to accelerate the corrosion of steel as the anode. 4. Metal powder (such as zinc powder) with potential lower than steel is used as conductive medium, which has cathodic protection and rust prevention effect on steel.	1. The color is limited and can only be made into dark paint. 2. Because its electrode potential is higher than that of steel, when it directly contacts with steel, it will form electrochemical corrosion, which will accelerate the corrosion of steel as anode. 3. Due to its high oil absorption, when the requirements for conductivity are high, the amount is large, the paint film is loose, shielding and permeability are reduced, causing corrosion under the film and poor rust resistance.	1. Light color, can be made into a variety of colors (gray, red, yellow, green, blue and other limited colors) of electrostatic conductive paint. 2. The film has good compactness and is superior to the electrostatic conductive coating made of conductive carbon black and graphite powder. 3. The electrostatic conductivity is durable and effective. 4. The price is expensive.
Our corresponding products	ZIES213 inorganic zinc rich primer ZIEP212 epoxy zinc rich primer	EPSP393-1 black epoxy oil resistant anti-static anti-corrosion coating EPSP394-1 black epoxy phenolic oil tank coating PU414-1 black polyurethane oil resistant and anti-static coating	EPSP393-2 light color epoxy oil resistant anti-static anti-corrosion coating EPSP394-2 light color epoxy phenolic oil tank coating PU414-2 light color polyurethane oil resistant and anti-static coating EPSP409 solvent-free epoxy anti-static oil tank paint

2. For outer wall Anticorrosive coating

Considering that most crude oil tanks are in the marine atmospheric environment with strong corrosivity at the seaside, and the tank has a long service life, the coating should have a long anti-corrosion life, so it is advisable to select the primer with good rust resistance, the intermediate paint with good shielding performance, and the topcoat with good light and color retention, good weather resistance, and easy coating and maintenance.

The performance characteristics of common coatings for the outer wall of storage tank are as follows:

position	category	Paint variety	Main performance characteristics
Aboveground part	Primer	Epoxy zinc rich primer Or inorganic zinc rich primer	The paint film contains a large amount of zinc powder, which has excellent rust resistance, cathodic protection, excellent oil resistance, fast drying, and good compatibility. It is often used as a primer in long-term heavy-duty anti-corrosion systems.
Midcoat	Epoxy micaceous iron midcoat	The paint film contains a large amount of scaly mica iron oxide, forming a "fish scale" overlapping structure and a "labyrinth" effect, which has excellent shielding and impermeability, effectively preventing corrosion of the substrate due to immersion of corrosive media. It has good adhesion to zinc rich primer and good compatibility with finish paint.
Topcoat	Aliphatic polyurethane topcoat	Excellent light and color retention performance, anti pulverization, no yellowing, good decoration, excellent oil and solvent resistance, and good coating ability, with unlimited coating time.
Underground part	Primer	Epoxy zinc rich primer Or inorganic zinc rich primer	Same as the above ground part
Topcoat	Epoxy asphalt high build paint (summer or winter)	The paint film has excellent water resistance and rust resistance, good oil resistance and chemical resistance, good adhesion, impact resistance, abrasion resistance, and good cathodic protection resistance. The winter type can be used between - 15 and 10 degrees.

Heating technology

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Oil tank local fast heater

Oil tanks play a very important role in the process of oil and gas storage and transportation. In oil and gas storage, oil tanks are mostly used for oil storage. When oil products are needed, they are exported from the oil tank. In the process of oil output, it is inevitable to encounter such a problem. The oil becomes viscous due to low temperature, which reduces the fluidity of the oil, leading to the oil can not be smoothly output from the tank. How to solve such a problem? It is reported that the new type of oil tank local rapid heating technology has solved this problem well.

working principle:

1. Set“ Vortex hot film heat exchanger ”Extending radially into the bottom of the tank along the tank, the heat medium (steam) goes through the tube side, the oil flows from the tube to tube in the shell side, and the oil suction port of the shell is directly connected with the medium in the tank.

2. A temperature control valve is set at the steam inlet of the heat exchanger to control the steam inlet of the heat exchanger through the temperature detection of the oil outlet by the temperature sensing probe, so as to ensure the constant oil temperature.

The heat exchanger adopts high-efficiency heat exchange element eddy current hot film tube to keep the oil flowing reasonably between the tubes. The thermal efficiency is 3-5 times that of the ordinary heat exchanger. Its enhanced heat transfer mechanism is: when the oil fluid flows on the internal and external surfaces, it is designed as turbulent flow, which produces strong shock and scouring effects. The flow direction is constantly changing, so that the high-temperature oil fluid close to the pipe wall surface is constantly replaced, The heat insulation layer is thinned and even destroyed, the heat transfer on the metal surface is accelerated, and the micro eddy current of the fluid is strengthened, so that the internal heat diffusion of the oil fluid is strengthened. The fluid close to the pipe wall surface will not produce local high temperature overheating, so the oil can be properly and fully heated without the possibility of coking and decomposition. It can transfer heat well without great resistance.

Heating characteristics:

1. Fast heating speed, high heat transfer efficiency, not easy to scale.

2. It can heat the oil quantitatively as much as needed.

3. The oil will not have local high temperature and carbonization, ensuring the oil quality and heat transfer efficiency of the heater.

4. The temperature of the oil outlet in the oil tank is the highest, ensuring the fluidity of the poured oil.

5. It avoids repeatedly heating the oil in the tank, ensures the oil color and reduces the cost of oil treatment.

6. Long service life, corrosion resistance, high temperature resistance, high pressure resistance and anti scaling function greatly improve the overall performance of the heat exchanger.

7. Advanced process structure design ensures smooth flow of oil products and good“ Bottom pumping ”Role.

8. Automatic control can be realized, and the steam feed can be controlled according to the inlet and outlet temperature of oil products and the flow of oil.

9. Compact structure, easy installation and maintenance, will not affect the safety of the tank due to the installation of the heater. Compared with U-tube heat exchanger, under the condition of the same heat exchange area, the overall dimension of vortex heat film heat exchanger is only about half of the overall dimension of U-tube heat exchanger.

10. Compared with electric heating, it is safer, more gentle and has less impact on oil quality.

It is reported that this new oil tank heating technology has obtained a number of national patents and has been applied in many oil and gas storage and transportation units of PetroChina.

Comparison between new heating technology and traditional tubular oil tank heating:

Heating mode	Heat medium	Oil output	Temperature rise	heating time	Condensate temperature	Steam consumption
Tubular heat exchanger	0.8Mpa saturated steam	60T/t	30℃-60℃	14 hours and 30 minutes	100℃	14.6t
Oil tank local fast heater	0.8Mpa saturated steam	60T/t	30℃-60℃	1 hour and 30 minutes	55℃	1.96 tons

Note: The data is from the actual measurement comparison table of Sinopec lubricating oil

Composition

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The most commonly used vertical steel structure cylindrical For example, oil tanks mainly include oil tank foundation, bottom plate, wall plate, top plate and Oil tank accessories form.

Oil tank foundation [edit]

The oil tank foundation is the carrier of the oil tank shell itself and the weight of the stored oil, and transfers it to soil The general laying sequence is from bottom to top, including plain soil layer, lime soil layer, sand cushion and asphalt Anti corrosion coating. The required bearing capacity of the foundation shall not be less than 10 tons per square meter groundwater At least 30 cm apart is required. The reasonable arrangement of the soil layer of the foundation makes the foundation have a certain elasticity, which can cope with the foundation settlement after the oil tank is stored. When building in the soft soil area, the foundation periphery can reinforced concrete Ring beam to prevent the sand cushion around the tank bottom from being squeezed out when the foundation sinks.

Base plate [edit]

The bottom plate itself is not affected by power , storage tank and material pressure It is directly acting on the oil tank foundation through the bottom plate, but because the lower layer of the bottom plate is in contact with the foundation, it is easy to be eroded by the deposited materials and the water in the foundation soil, so even if it is not stressed, 4-6 mm thick steel plates are used, and 8 mm thick steel plates are used for those with a volume of more than 50000 cubic meters. Around the tank stress The situation is complicated, so thickening is adopted, generally 2-4mm.

Tank wall [edit]

The tank wall is the main load-bearing part of the tank. The higher the liquid level, the greater the pressure of the bottom layer (p=ρ gh). Therefore, the thickness of the tank wall steel plate is the lower thickness and the upper thickness. The thickness of the steel plate referred to in the general specification is the thickness of the thinnest part at the upper end. According to the size of the tank, from 4mm to 32mm, the steel plate of the tank is welding The upper and lower layers are arranged in interactive, sleeve, butt and hybrid ways. The interactive rivet connection is not convenient for construction and seldom used. The sleeve type is to extend the upper ring plate into the lower part. The circumferential welds of the ring plate are overlapped, and the diameter of the tank ring is smaller as it goes up. The sleeve type is most commonly used because of its convenient construction and good welding quality. Butt joint construction requires high requirements, and the upper and lower layers are of the same size, which is mainly used for Floating roof oil storage tank 。 As the name implies, hybrid mode refers to the method of combining several connection modes, which is no longer used.

Tank roof [edit]

See: Floating roof oil storage tank

The tank with vault as the roof of the tank is called "vault tank". The vault is a fixed roof. The vault is required to withstand large internal pressure (from 2kPa to 10kPa). The thickness of the steel plate is generally 4-6 mm. The advantage of arch crown is that it is small in cost and simple in construction, but has large evaporation loss. The other kind of top cover is "floating roof", that is, the top cover rises and falls with the rise and fall of the liquid level. This kind of top cover can greatly reduce the Oil evaporation loss However, the construction technology is strong and the cost is high.

Attachment [Edit]

In order to ensure the safe use of the tank, the tank is also equipped with the following accessories, manholes: manholes are an opening above the tank bottom plate for personnel to enter and exit during installation, maintenance and cleaning; Light hole: installed on the tank roof for lighting and ventilation during cleaning; Oil measuring hole: device used for measuring at the tank top; Safety valve Safety protection device ； Breather valve, used for oil products Breathing due to temperature difference Safety device for protecting oil tank; Ladders and railings, devices for workers to go up and down the oil tank, etc^[2] 。

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