Today, oil production is one of the most profitable industries. However, a large amount of raw materials requires more storage tanks. Today, a vertical cylindrical tank is the most convenient and economical option.
Low pressure tanks
It is worth mentioning that there are two types of cylindrical tanks for storing oil. They differ in their design. In other words, they can be vertical or horizontal. Let's consider in more detail.
Vertical cylindrical tanks can be low-pressure, high-pressure, with spatial bottoms (most often used as sedimentation tanks), with floating roofs and pontoons.
Horizontal tanks can be low or high pressure. And also they are divided into underground and ground.
If we talk about the vertical type of the tank with low pressure, then it is immediately worth noting that the overpressure inside the tank is almost equal to atmospheric. It follows that the tank body must be designed with the expectation that hydrostatic pressure will affect it. This factor will cause a tensile force, which will be equal to the weight of the liquid column over its considered section.
In order for a vertical cylindrical tank to withstand a wind load of 30 Pa or more, it must be equipped with special stiffening rings. The storage tank cover is tapered with a slope of 1:20. Due to the fact that it is rather difficult to make and install a roof of a conical shape, since the structure of its supporting structure includes trusses, girders, radial beams and communications, another method was invented. It consists in assembling the roof from large-sized shields that are assembled in factories.
General design and parameters
The frame of a steel vertical cylindrical tank is presented in the form of shields that are assembled from rolling I-beams, as well as channels. By welding, a 2.5 mm thick sheet deck is also attached to these elements. In the middle of the tank there is a head of the central rack, which is a support for the shields. The bottom of such tanks is most often welded, which is located on a sand cushion, and is also installed at an angle. It goes from the center of the tank to its periphery. The numerical value of this slope is 2%. Why is this needed? The presence of a slope is necessary so that there is the possibility of runoff, as well as the removal of produced water.
The actual volume of the vertical cylindrical tank can be determined based on its inner diameter of the lower PBC belt (vertical steel tank). But that is not all. Also, to determine the volume, you need to know the height of the tank body, which is calculated starting from the bottom and ending with the pickaxe of the upper binding corner.
In order to ensure the correct as well as completely safe operation of the vertical cylindrical tank, it must have a certain number of structural elements. These include structural details such as the top skylight, metering sunroof, foam generator, ventilation pipe, manhole, lift pipe, water drain, crackers, fire fuses and breathing valves.
First structural elements
The following should be considered in more detail the structural elements of the tank. The upper skylight in the tank with petroleum products is necessary in order to ventilate the tank, while repairs or stripping are underway. Its second function is the raising of the clapper-cap, as well as the hinged pipes. This is necessary if a break in the working belt occurs.
The second element is a metering hatch, which is designed to measure the level of oil products, as well as to take a sample of raw materials from the tank. It is worth adding that the selection for research can be carried out not only through this metering hatch, but also through special selective systems that can be installed in an additional order.
Another important design detail is the steam generator, which is necessary in order to extinguish possible fires using high-pressure airborne mechanical foam. The safety manual for vertical steel cylindrical tanks prescribes the installation of a foam generator in the upper zone of the tank. At this point, a blowing agent supply must be equipped. The substance thus obtained, after passing through the chamber, will enter the reservoir.
Another structural element is the ventilation pipe, which is located at the highest point of the tank. It is important to note here that its cross section must be tightened with copper wire, which will prevent sparks from entering the tank.
Minor elements of PBC
The rules for the construction of vertical cylindrical steel tanks require the presence of several more structural elements.
The manhole must be located in the first belt of the tank, at a height of approximately 700 mm. The purpose of this element is to provide workers access to the inside of the tank in order to carry out repair work. It is also used when cleaning the bottom of dirt. In addition, the same hole is used to ventilate the tank in the event that hot work is carried out. For this reason, the location of the manhole must be strictly diametrical and opposite with respect to the light. It is important to add that the minimum diameter of this hole is 500 mm.
The rules for the construction of vertical cylindrical tanks imply a compartment such as a lifting pipe. The place of installation of this part is on the receiving pipe of the tank. The purpose of this compartment is the storage, heating and sedimentation of combustible petroleum products. In addition, this pipe is used to select raw materials from the upper layers, in which it is the most heated and the cleanest.
Since the level of location of this pipe is higher than the level of oil products in the tank, this eliminates the possibility of leakage during selection. In order to lift the element, a special winch is used. Lowering the object is carried out under its own weight. However, when lifting, some rules must be observed. This is very important, since at an angle of inclination with a horizontal plane of 70-75 degrees, the pipe will enter into such a friction angle that it will not allow it to return to its original position under the action of only its own weight.
Device for draining water
The device of a vertical cylindrical tank implies the presence of an element responsible for the discharge of water. This is a required item.
A device for draining water is installed in the first zone of the tank with oil products. The main purpose of this element is to periodically lower the produced liquid from the tank. After all, it has the property of accumulating at the bottom of the tank, standing out from the watered oil.
During storage of petroleum products, commercial liquid may accumulate in the tank, which must be periodically removed from the tank. In order to ensure the execution of this operation, drain valves and siphon taps are used. The design of the valve is quite simple. It consists of a housing that is welded to the bottom of the tank, there is also a drain plug, a lead screw and a plate with a gasket.
The principle of operation is also quite simple. While the screw begins to rotate, the poppet rises or falls on the valve seat. Ascent or descent is provided due to the direction of rotation of the screw. In order to carry out the discharge of produced water, it is necessary to rid the drain hole of the cork.
If it is necessary to drain a large amount of liquid from a vertical cylindrical tank for large volume petroleum products, then a siphon valve is used. The diameter of this device can be either 80 mm or 100 mm. Installation of these holes is carried out in the vertical walls of the tank.
The siphon tap is a horizontal pipe. It passes through the stuffing box located in the tank wall. This part also has a handle that allows you to set three positions. The lower position of the handle - indicates the discharge of water, the horizontal position of the handle is inoperative, and the installation in the upper position means flushing the tap with a clean product. This is to avoid problems such as freezing in winter.
Clapper device
Previously, the BCH of cylindrical steel vertical tanks was used as the main document. BCH - departmental building codes. However, at present this document has been replaced by the more modern GOST 31385. According to these rules, the object must have such an element as a clapperboard.
This part of the tank is designed to prevent the leakage of raw materials from the tank, in the event that the pipelines, as well as the expansion joints, were damaged. There are other features. There are times when the tank has two pickup pipes. In such situations, it is allowed to install an uncontrolled clapper on the discharge pipe. In order to ensure the opening of this element, it is provided with a bypass. It controls the pressure before and after the cracker.
If we are talking about vertical cylindrical tanks with pontoons or floating roofs, then installation of a clapper with control is necessary. This element is embedded in the dispensing pipe.
There are also elements with a lateral control option. Such parts are a rotary valve located inside the tank that can be controlled. The purpose of this element is that it can be used to disconnect the tank from the acceptance line in the event that damage is detected, the pipeline is being repaired or valves are being repaired. The difference between a cracker and a conventional check valve is that it does not create such a drawback as constant hydraulic resistance. This is achieved due to the fact that the shutter is removed from the flow zone.
Fire fuse and breathing valve
The fire fuse is designed to prevent sparks or fire from entering the tank through the breathing valves. For this reason, they are located clearly below these elements. The principle of operation of this device is quite simple and it is based on the fact that a spark or fire cannot penetrate inside the tank due to the fact that the hole cross section is quite small, and good heat dissipation is also provided.
Due to the fact that the ambient temperature changes all the time, the content of air and liquid inside the tank also changes. It is very important. Indeed, under the influence of certain temperatures, air can be released from the liquid, or, conversely, air will dissolve in the liquid. All these changes can lead to the fact that either a vacuum or increased overpressure can form inside the tank. It was precisely to regulate the amount of air inside the tank that breathing valves were developed, with the help of which they either let air in or out. This procedure is called "small breath".
There is also a "big breath." This process takes place if large changes in the volume of liquid occur. They are most often caused by the flow of raw materials into the reservoir or by its withdrawal from there. It is important to note that it is impossible to connect containers with the atmosphere itself, using an open pipe for this. This is impractical due to the fact that too much evaporation of raw materials (gasoline, kerosene) is possible.
Vertical steel cylindrical tanks GOST 31385
This document has many points that prescribe everything related to the operation or assembly of the PBC. For example, the scope of its application.
Such GOST regulates all the requirements that relate to the design, manufacture, installation, as well as testing of RCS with a nominal volume of 100 to 12 thousand m 3 . There are several conditions for the operation of containers, which are also covered by this document:
- Tanks with a ground location.
- The action applies to those tanks that store raw materials with a density of not more than 1600 kg / m 3 .
- In this case, the maximum permissible operating temperature of the tank is not higher than 160 ° C and not less than -65 ° C.
- Tank installation can only be carried out in an area characterized by a seismicity of not more than 9 points on the MSK-64 scale.
GOST of vertical cylindrical steel tanks also establishes some terms with their specific concept.
A floating roof is a structure that is used to prevent the evaporation of raw materials from the tank. This type of roof is used for those tanks that do not have a fixed roof. This device floats on the surface of the stored raw materials and covers the entire area of the oil product, which prevents its evaporation.
It is worth adding that other types of tanks have a pontoon. By its design, this is the same floating roof that covers raw materials from evaporation over the entire cross-sectional area of the tank, but with the difference that it is available for those tanks that are equipped with a fixed roof.
Safety Guide for Vertical Cylindrical Steel Tanks
The safety manual applies to those tanks that are operated according to the following principles:
- the raw material tank is located on the ground;
- the density of the goods stored inside the container is not more than 1.1 t / m 3 ;
- maximum working temperature of the tank body is not more than 100 ° C;
- minimum working temperature indicator not lower than -60 ;
- maximum internal overpressure is not higher than 2 kPa.
Safety Manual for Vertical Cylindrical Tanks No. 780 also establishes that these tanks relate to the increased level of responsibility of structures. The separation of these tanks is carried out into 4 groups according to such a feature as the nominal volume of the tank.
- The first category of hazard includes those tanks whose volume is not more than 50,000 m 3 .
- The second category is reservoirs with a volume of 20,000 to 50,000 m 3 inclusive. Also in this category are those tanks with petroleum products that are characterized by a volume of 10,000 to 50,000 m 3 inclusive, and at the same time are located on the banks of rivers or large bodies of water, or in the city.
- the third category includes tanks from 1000 m 3 and not less than 20 000 m 3 .
- The last, fourth category is tanks with a volume of less than 1000 m 3 .
The safety manual for vertical cylindrical tanks also prescribes that the hazard class of each tank made must be set directly by the customer in the tank design task. According to this document, it is also not recommended to make and assemble walls for any type of structures whose volume exceeds 10 thousand m 3 from such material as rolled panels.
Installation of tanks in accordance with GOST
Installation of steel vertical cylindrical tanks should be in accordance with the rules of GOST.
One of them says that the area of the construction site should be fully equipped in accordance with the construction master plan. Also, this area should be equipped with platforms for work and platforms for the transportation of hoisting and transport mechanisms. In addition, there should be a place on the territory for the storage of building materials, temporary roads for transport, all important premises, including utilities, as well as means to extinguish possible fires.
It is important to note that during the installation of vertical cylindrical tanks, it is forbidden to impact on any welded steel structure, the yield strength of which is not more than 390 MPa and at an ambient temperature lower than - 25 ° C.
In addition, before proceeding with the installation of the tank itself, all work should be done to equip the base for the tank and the foundation.
What is worth considering?Acceptance of the erected base and foundation for the tank is carried out by the customer in the presence of a representative of the construction company that was involved in the construction of the facility. The fact of a successful procedure must be certified by an appropriate act. It is important to note that when assembling the bottom of the tank itself, it is important not to damage the existing base and foundation, as well as to protect the waterproofing layers from damage or loads from various kinds of installation works.