Pipelines for the transport of various liquids are an integral part of units and installations in which work processes related to various fields of application are carried out. When choosing pipes and piping configuration, the cost of both the pipes themselves and the pipeline fittings is of great importance. The final cost of pumping the medium through the pipeline is largely determined by the size of the pipes (diameter and length). The calculation of these values is carried out using specially developed formulas specific to certain types of operation.
A pipe is a hollow cylinder made of metal, wood or other material used to transport liquid, gaseous and granular media. The transported medium can be water, natural gas, steam, oil products, etc. Pipes are used everywhere, from various industries to domestic applications.
A variety of materials can be used to make pipes, such as steel, cast iron, copper, cement, plastics such as ABS, PVC, chlorinated PVC, polybutene, polyethylene, etc.
The main dimensional indicators of a pipe are its diameter (outer, inner, etc.) and wall thickness, which are measured in millimeters or inches. Also used is such a value as a nominal diameter or nominal bore - the nominal value of the inner diameter of the pipe, also measured in millimeters (indicated by Du) or inches (indicated by DN). The nominal diameters are standardized and are the main criterion for the selection of pipes and fittings.
Correspondence of nominal bore values in mm and inches:
A pipe with a circular cross section is preferred over other geometric sections for a number of reasons:
- The circle has a minimum ratio of perimeter to area, and when applied to a pipe, this means that with equal throughput, the material consumption of round pipes will be minimal compared to pipes of a different shape. This also implies the minimum possible costs for insulation and protective coating;
- A circular cross section is most advantageous for the movement of a liquid or gaseous medium from a hydrodynamic point of view. Also, due to the minimum possible internal area of the pipe per unit of its length, friction between the conveyed medium and the pipe is minimized.
- The round shape is the most resistant to internal and external pressures;
- The process of manufacturing round pipes is quite simple and easy to implement.
Pipes can vary greatly in diameter and configuration depending on the purpose and application. Thus, main pipelines for moving water or oil products can reach almost half a meter in diameter with a fairly simple configuration, and heating coils, which are also pipes, have a complex shape with many turns with a small diameter.
It is impossible to imagine any industry without a network of pipelines. The calculation of any such network includes the selection of pipe material, drawing up a specification, which lists data on the thickness, pipe size, route, etc. Raw materials, intermediate products and/or finished products pass through the production stages, moving between different apparatuses and installations, which are connected by pipelines and fittings. Proper calculation, selection and installation of the piping system is necessary for the reliable implementation of the entire process, ensuring the safe transfer of media, as well as for sealing the system and preventing leakage of the pumped substance into the atmosphere.
There is no single formula and rule that can be used to select pipeline for every possible application and working environment. In each individual area of application of pipelines, there are a number of factors that need to be taken into account and can have a significant impact on the requirements for the pipeline. So, for example, when dealing with sludge, a large pipeline will not only increase the cost of the installation, but also create operational difficulties.
Typically, pipes are selected after optimizing material and operating costs. The larger the diameter of the pipeline, i.e. the higher the initial investment, the lower the pressure drop will be and, accordingly, the lower the operating costs. Conversely, the small size of the pipeline will reduce the primary costs for the pipes themselves and pipe fittings, but an increase in speed will entail an increase in losses, which will lead to the need to spend additional energy on pumping the medium. Speed limits fixed for different applications are based on optimum design conditions. The size of pipelines is calculated using these standards, taking into account the areas of application.
Pipeline design
When designing pipelines, the following main design parameters are taken as a basis:
- required performance;
- entry point and exit point of the pipeline;
- medium composition, including viscosity and specific gravity;
- topographic conditions of the pipeline route;
- maximum allowable working pressure;
- hydraulic calculation;
- pipeline diameter, wall thickness, tensile yield strength of the wall material;
- number of pumping stations, distance between them and power consumption.
Pipeline reliability
Reliability in piping design is ensured by adherence to proper design standards. Also, personnel training is a key factor in ensuring the long service life of the pipeline and its tightness and reliability. Continuous or periodic monitoring of pipeline operation can be carried out by monitoring, accounting, control, regulation and automation systems, personal control devices in production, and safety devices.
Additional pipeline coating
A corrosion resistant coating is applied to the outside of most pipes to prevent the damaging effects of corrosion from the outside environment. In the case of pumping corrosive media, a protective coating can also be applied to the inner surface of the pipes. Before commissioning, all new pipes intended for the transport of hazardous liquids are tested for defects and leaks.
Basic provisions for calculating the flow in the pipeline
The nature of the flow of the medium in the pipeline and when flowing around obstacles can differ greatly from liquid to liquid. One of the important indicators is the viscosity of the medium, characterized by such a parameter as the viscosity coefficient. The Irish engineer-physicist Osborne Reynolds conducted a series of experiments in 1880, according to the results of which he managed to derive a dimensionless quantity characterizing the nature of the flow of a viscous fluid, called the Reynolds criterion and denoted by Re.
Re = (v L ρ)/μ
Where:
ρ is the density of the liquid;
v is the flow rate;
L is the characteristic length of the flow element;
μ - dynamic coefficient of viscosity.
That is, the Reynolds criterion characterizes the ratio of the forces of inertia to the forces of viscous friction in the fluid flow. A change in the value of this criterion reflects a change in the ratio of these types of forces, which, in turn, affects the nature of the fluid flow. In this regard, it is customary to distinguish three flow regimes depending on the value of the Reynolds criterion. At Re<2300 наблюдается так называемый ламинарный поток, при котором жидкость движется тонкими слоями, почти не смешивающимися друг с другом, при этом наблюдается постепенное увеличение скорости потока по направлению от стенок трубы к ее центру. Дальнейшее увеличение числа Рейнольдса приводит к дестабилизации такой структуры потока, и значениям 2300
| Velocity profile in the stream | ||
|---|---|---|
| laminar flow | transitional regime | turbulent regime |
 |
 |
|
| The nature of the flow | ||
| laminar flow | transitional regime | turbulent regime |
 |
 |
 |
The Reynolds criterion is a similarity criterion for the flow of a viscous fluid. That is, with its help, it is possible to simulate a real process in a reduced size, convenient for studying. This is extremely important, since it is often extremely difficult, and sometimes even impossible, to study the nature of fluid flows in real apparatuses due to their large size.
Pipeline calculation. Calculation of pipeline diameter
If the pipeline is not thermally insulated, that is, heat exchange between the transported and the environment is possible, then the nature of the flow in it can change even at a constant speed (flow rate). This is possible if the pumped medium has a sufficiently high temperature at the inlet and flows in a turbulent regime. Along the length of the pipe, the temperature of the transported medium will drop due to heat losses to the environment, which may lead to a change in the flow regime to laminar or transitional. The temperature at which the mode change occurs is called the critical temperature. The value of the viscosity of a liquid directly depends on the temperature, therefore, for such cases, such a parameter as the critical viscosity is used, which corresponds to the point of change in the flow regime at the critical value of the Reynolds criterion:
v cr = (v D)/Re cr = (4 Q)/(π D Re cr)
Where:
ν kr - critical kinematic viscosity;
Re cr - critical value of the Reynolds criterion;
D - pipe diameter;
v is the flow rate;
Q - expense.
Another important factor is the friction that occurs between the pipe walls and the moving stream. In this case, the coefficient of friction largely depends on the roughness of the pipe walls. The relationship between the coefficient of friction, the Reynolds criterion and the roughness is established by the Moody diagram, which allows you to determine one of the parameters, knowing the other two.
The Colebrook-White formula is also used to calculate the coefficient of friction for turbulent flow. Based on this formula, it is possible to plot graphs by which the coefficient of friction is established.
(√λ ) -1 = -2 log(2.51/(Re √λ ) + k/(3.71 d))
Where:
k - pipe roughness coefficient;
λ is the coefficient of friction.
There are also other formulas for the approximate calculation of friction losses during the pressure flow of liquid in pipes. One of the most frequently used equations in this case is the Darcy-Weisbach equation. It is based on empirical data and is mainly used in system modeling. Friction loss is a function of the fluid velocity and the resistance of the pipe to fluid movement, expressed in terms of the pipe wall roughness value.
∆H = λ L/d v²/(2 g)
Where:
ΔH - head loss;
λ - coefficient of friction;
L is the length of the pipe section;
d - pipe diameter;
v is the flow rate;
g is the free fall acceleration.
Pressure loss due to friction for water is calculated using the Hazen-Williams formula.
∆H = 11.23 L 1/C 1.85 Q 1.85 /D 4.87
Where:
ΔH - head loss;
L is the length of the pipe section;
C is the Haizen-Williams roughness coefficient;
Q - consumption;
D - pipe diameter.
Pressure
The working pressure of the pipeline is the highest excess pressure that provides the specified mode of operation of the pipeline. The decision on the size of the pipeline and the number of pumping stations is usually made based on the working pressure of the pipes, pumping capacity and costs. The maximum and minimum pressure of the pipeline, as well as the properties of the working medium, determine the distance between the pumping stations and the required power.
Nominal pressure PN - nominal value corresponding to the maximum pressure of the working medium at 20 ° C, at which continuous operation of the pipeline with given dimensions is possible.
As the temperature increases, the load capacity of the pipe decreases, as does the allowable overpressure as a result. The pe,zul value indicates the maximum pressure (g) in the piping system as the operating temperature increases.
Permissible overpressure schedule:
Calculation of the pressure drop in the pipeline
The calculation of the pressure drop in the pipeline is carried out according to the formula:
∆p = λ L/d ρ/2 v²
Where:
Δp - pressure drop in the pipe section;
L is the length of the pipe section;
λ - coefficient of friction;
d - pipe diameter;
ρ is the density of the pumped medium;
v is the flow rate.
Transportable media
Most often, pipes are used to transport water, but they can also be used to move sludge, slurries, steam, etc. In the oil industry, pipelines are used to pump a wide range of hydrocarbons and their mixtures, which differ greatly in chemical and physical properties. Crude oil can be transported over longer distances from onshore fields or offshore oil rigs to terminals, waypoints and refineries.
Pipelines also transmit:
- refined petroleum products such as gasoline, aviation fuel, kerosene, diesel fuel, fuel oil, etc.;
- petrochemical raw materials: benzene, styrene, propylene, etc.;
- aromatic hydrocarbons: xylene, toluene, cumene, etc.;
- liquefied petroleum fuels such as liquefied natural gas, liquefied petroleum gas, propane (gases at standard temperature and pressure but liquefied by pressure);
- carbon dioxide, liquid ammonia (transported as liquids under pressure);
- bitumen and viscous fuels are too viscous to be transported through pipelines, so distillate fractions of oil are used to dilute these raw materials and result in a mixture that can be transported through a pipeline;
- hydrogen (for short distances).
The quality of the transported medium
The physical properties and parameters of the transported media largely determine the design and operating parameters of the pipeline. Specific gravity, compressibility, temperature, viscosity, pour point and vapor pressure are the main media parameters to consider.
The specific gravity of a liquid is its weight per unit volume. Many gases are transported through pipelines under increased pressure, and when a certain pressure is reached, some gases may even undergo liquefaction. Therefore, the degree of compression of the medium is a critical parameter for the design of pipelines and the determination of throughput capacity.
Temperature has an indirect and direct effect on pipeline performance. This is expressed in the fact that the liquid increases in volume after an increase in temperature, provided that the pressure remains constant. Lowering the temperature can also have an impact on both performance and overall system efficiency. Usually, when the temperature of a liquid is lowered, it is accompanied by an increase in its viscosity, which creates additional frictional resistance on the inner wall of the pipe, requiring more energy to pump the same amount of liquid. Very viscous media are sensitive to temperature fluctuations. Viscosity is the resistance of a medium to flow and is measured in centistokes cSt. Viscosity determines not only the choice of pump, but also the distance between pumping stations.
As soon as the temperature of the medium drops below the pour point, the operation of the pipeline becomes impossible, and several options are taken to resume its operation:
- heating the medium or insulating pipes to maintain the operating temperature of the medium above its pour point;
- change in the chemical composition of the medium before it enters the pipeline;
- dilution of the conveyed medium with water.
Types of main pipes
Main pipes are made welded or seamless. Seamless steel pipes are made without longitudinal welds by steel sections with heat treatment to achieve the desired size and properties. Welded pipe is manufactured using several manufacturing processes. These two types differ from each other in the number of longitudinal seams in the pipe and the type of welding equipment used. Steel welded pipe is the most commonly used type in petrochemical applications.
Each pipe section is welded together to form a pipeline. Also, in main pipelines, depending on the application, pipes made of fiberglass, various plastics, asbestos cement, etc. are used.
To connect straight sections of pipes, as well as to transition between pipeline sections of different diameters, specially made connecting elements (elbows, bends, gates) are used.
| elbow 90° | elbow 90° | transition branch | branching |
 |
 |
 |
|
| elbow 180° | elbow 30° | adapter | tip |
 |
 |
 |
For the installation of individual parts of pipelines and fittings, special connections are used.
| welded | flanged | threaded | coupling |
 |
 |
 |
 |
Thermal expansion of the pipeline
When the pipeline is under pressure, its entire inner surface is subjected to a uniformly distributed load, which causes longitudinal internal forces in the pipe and additional loads on the end supports. Temperature fluctuations also affect the pipeline, causing changes in the dimensions of the pipes. Forces in a fixed pipeline during temperature fluctuations can exceed the permissible value and lead to excessive stress, which is dangerous for the strength of the pipeline both in the pipe material and in flanged connections. Fluctuations in the temperature of the pumped medium also create a temperature stress in the pipeline, which can be transferred to valves, pumping stations, etc. This can lead to depressurization of pipeline joints, failure of valves or other elements.
Calculation of pipeline dimensions with temperature changes
The calculation of the change in the linear dimensions of the pipeline with a change in temperature is carried out according to the formula:
∆L = a L ∆t
a - coefficient of thermal elongation, mm/(m°C) (see table below);
L - pipeline length (distance between fixed supports), m;
Δt - difference between max. and min. temperature of the pumped medium, °C.
Table of linear expansion of pipes from various materials
The numbers given are averages for the listed materials and for the calculation of pipelines from other materials, the data from this table should not be taken as a basis. When calculating the pipeline, it is recommended to use the coefficient of linear elongation indicated by the pipe manufacturer in the accompanying technical specification or data sheet.
Thermal elongation of pipelines is eliminated both by using special expansion sections of the pipeline, and by using compensators, which may consist of elastic or moving parts.
Compensation sections consist of elastic straight parts of the pipeline, located perpendicular to each other and fastened with bends. With thermal elongation, the increase in one part is compensated by the deformation of the bending of the other part on the plane or the deformation of bending and torsion in space. If the pipeline itself compensates for thermal expansion, then this is called self-compensation.
Compensation also occurs due to elastic bends. Part of the elongation is compensated by the elasticity of the bends, the other part is eliminated due to the elastic properties of the material of the section behind the bend. Compensators are installed where it is not possible to use compensating sections or when the self-compensation of the pipeline is insufficient.
According to the design and principle of operation, compensators are of four types: U-shaped, lens, wavy, stuffing box. In practice, flat expansion joints with an L-, Z- or U-shape are often used. In the case of spatial compensators, they are usually 2 flat mutually perpendicular sections and have one common shoulder. Elastic expansion joints are made from pipes or elastic disks, or bellows.
Determination of the optimal size of the pipeline diameter
The optimal diameter of the pipeline can be found on the basis of technical and economic calculations. The dimensions of the pipeline, including the dimensions and functionality of the various components, as well as the conditions under which the pipeline must operate, determine the transport capacity of the system. Larger pipes are suitable for higher mass flow, provided the other components in the system are properly selected and sized for these conditions. Usually, the longer the length of the main pipe between pumping stations, the greater the pressure drop in the pipeline is required. In addition, a change in the physical characteristics of the pumped medium (viscosity, etc.) can also have a great influence on the pressure in the line.
Optimum Size - The smallest suitable pipe size for a particular application that is cost effective over the lifetime of the system.
Formula for calculating pipe performance:
Q = (π d²)/4 v
Q is the flow rate of the pumped liquid;
d - pipeline diameter;
v is the flow rate.
In practice, to calculate the optimal diameter of the pipeline, the values of the optimal speeds of the pumped medium are used, taken from reference materials compiled on the basis of experimental data:
| Pumped medium | Range of optimum speeds in the pipeline, m/s | |
|---|---|---|
| Liquids | Gravity movement: | |
| Viscous liquids | 0,1 - 0,5 | |
| Low viscosity liquids | 0,5 - 1 | |
| Pumping: | ||
| suction side | 0,8 - 2 | |
| Discharge side | 1,5 - 3 | |
| gases | Natural traction | 2 - 4 |
| Small pressure | 4 - 15 | |
| Big pressure | 15 - 25 | |
| Couples | superheated steam | 30 - 50 |
| Saturated pressurized steam: | ||
| More than 105 Pa | 15 - 25 | |
| (1 - 0.5) 105 Pa | 20 - 40 | |
| (0.5 - 0.2) 105 Pa | 40 - 60 | |
| (0.2 - 0.05) 105 Pa | 60 - 75 | |
From here we get the formula for calculating the optimal pipe diameter:
d o = √((4 Q) / (π v o ))
Q - given flow rate of the pumped liquid;
d - the optimal diameter of the pipeline;
v is the optimal flow rate.
At high flow rates, pipes of a smaller diameter are usually used, which means lower costs for the purchase of pipeline, its maintenance and installation work (denoted by K 1). With an increase in speed, there is an increase in pressure losses due to friction and in local resistances, which leads to an increase in the cost of pumping liquid (we denote K 2).
For pipelines of large diameters, the costs K 1 will be higher, and the costs during operation K 2 will be lower. If we add the values of K 1 and K 2 , we get the total minimum cost K and the optimal diameter of the pipeline. Costs K 1 and K 2 in this case are given in the same time period.
Calculation (formula) of capital costs for the pipeline
K 1 = (m C M K M)/n
m is the mass of the pipeline, t;
C M - cost of 1 ton, rub/t;
K M - coefficient that increases the cost of installation work, for example 1.8;
n - service life, years.
The indicated operating costs associated with energy consumption:
K 2 \u003d 24 N n days C E rub / year
N - power, kW;
n DN - number of working days per year;
C E - costs per kWh of energy, rub/kW*h.
Formulas for determining the size of the pipeline
An example of general formulas for determining the size of pipes without taking into account possible additional factors such as erosion, suspended solids, etc.:
| Name | The equation | Possible restrictions |
|---|---|---|
| The flow of liquid and gas under pressure | ||
| Friction head loss Darcy-Weisbach |
d = 12 [(0.0311 f L Q 2)/(h f)] 0.2 |
Q - volume flow, gal/min; d is the inner diameter of the pipe; hf - friction head loss; L is the length of the pipeline, feet; f is the coefficient of friction; V is the flow rate. |
| Equation for total fluid flow | d = 0.64 √(Q/V) |
Q - volume flow, gpm |
| Pump suction line size to limit frictional head loss | d = √(0.0744 Q) |
Q - volume flow, gpm |
| Total gas flow equation | d = 0.29 √((Q T)/(P V)) |
Q - volume flow, ft³/min T - temperature, K P - pressure psi (abs); V - speed |
| Gravity flow | ||
| Manning Equation for Calculating Pipe Diameter for Maximum Flow | d=0.375 |
Q - volume flow; n - roughness coefficient; S - bias. |
| The Froude number is the ratio of the force of inertia and the force of gravity | Fr = V / √[(d/12) g] |
g - free fall acceleration; v - flow velocity; L - pipe length or diameter. |
| Steam and evaporation | ||
| Steam pipe diameter equation | d = 1.75 √[(W v_g x) / V] |
W - mass flow; Vg - specific volume of saturated steam; x - steam quality; V - speed. |
Optimal flow rate for various piping systems
The optimal pipe size is selected from the condition of minimum costs for pumping the medium through the pipeline and the cost of pipes. However, speed limits must also be taken into account. Sometimes, the size of the pipeline line must meet the requirements of the process. Just as often, the size of the pipeline is related to the pressure drop. In preliminary design calculations, where pressure losses are not taken into account, the size of the process pipeline is determined by the allowable speed.
If there are changes in the direction of flow in the pipeline, then this leads to a significant increase in local pressures on the surface perpendicular to the direction of flow. This kind of increase is a function of fluid velocity, density, and initial pressure. Because velocity is inversely proportional to diameter, high velocity fluids require special attention when sizing and configuring pipelines. The optimum pipe size, for example for sulfuric acid, limits the velocity of the medium to a value that prevents wall erosion in the pipe bends, thus preventing damage to the pipe structure.
Fluid flow by gravity
Calculating the size of the pipeline in the case of a flow moving by gravity is quite complicated. The nature of the movement with this form of flow in the pipe can be single-phase (full pipe) and two-phase (partial filling). A two-phase flow is formed when both liquid and gas are present in the pipe.
Depending on the ratio of liquid and gas, as well as their velocities, the two-phase flow regime can vary from bubbly to dispersed.
| bubble flow (horizontal) | projectile flow (horizontal) | wave flow | dispersed flow |
 |
 |
 |
 |
The driving force for the liquid when moving by gravity is provided by the difference in the heights of the start and end points, and the prerequisite is the location of the start point above the end point. In other words, the height difference determines the difference in the potential energy of the liquid in these positions. This parameter is also taken into account when selecting a pipeline. In addition, the magnitude of the driving force is affected by the pressures at the start and end points. An increase in the pressure drop entails an increase in the fluid flow rate, which in turn allows the selection of a pipeline of a smaller diameter, and vice versa.
In the event that the end point is connected to a pressurized system, such as a distillation column, the equivalent pressure must be subtracted from the height difference present to estimate the actual effective differential pressure generated. Also, if the starting point of the pipeline will be under vacuum, then its effect on the total differential pressure must also be taken into account when choosing a pipeline. The final selection of pipes is made using differential pressure, taking into account all of the above factors, and not based only on the difference in heights of the start and end points.
hot liquid flow
In process plants, various problems are usually encountered when working with hot or boiling media. The main reason is the evaporation of part of the hot liquid flow, that is, the phase transformation of the liquid into vapor inside the pipeline or equipment. A typical example is the cavitation phenomenon of a centrifugal pump, accompanied by point boiling of a liquid, followed by the formation of vapor bubbles (steam cavitation) or the release of dissolved gases into bubbles (gas cavitation).
Larger piping is preferred due to the reduced flow rate compared to smaller diameter piping at constant flow, resulting in a higher NPSH at the pump suction line. Points of sudden change in flow direction or reduction in pipeline size can also cause cavitation due to pressure loss. The resulting gas-vapor mixture creates an obstacle to the passage of the flow and can cause damage to the pipeline, which makes the phenomenon of cavitation extremely undesirable during the operation of the pipeline.
Bypass pipeline for equipment/instruments
Equipment and devices, especially those that can create significant pressure drops, that is, heat exchangers, control valves, etc., are equipped with bypass pipelines (to be able not to interrupt the process even during maintenance work). Such pipelines usually have 2 shut-off valves installed in line with the installation and a flow control valve in parallel to this installation.
During normal operation, the fluid flow passing through the main components of the apparatus experiences an additional pressure drop. In accordance with this, the discharge pressure for it, created by the connected equipment, such as a centrifugal pump, is calculated. The pump is selected based on the total pressure drop across the installation. During movement through the bypass pipeline, this additional pressure drop is absent, while the operating pump pumps the flow of the same force, according to its operating characteristics. To avoid differences in flow characteristics between the machine and the bypass, it is recommended to use a smaller bypass with a control valve to create a pressure equivalent to the main installation.
Sampling line
Usually a small amount of fluid is sampled for analysis to determine its composition. Sampling can be carried out at any stage of the process to determine the composition of a raw material, an intermediate product, a finished product, or simply a transported substance such as wastewater, heat transfer fluid, etc. The size of the section of pipeline on which sampling takes place usually depends on the type of fluid being analyzed and the location of the sampling point.
For example, for gases under elevated pressure, small pipelines with valves are sufficient to take the required number of samples. Increasing the diameter of the sampling line will reduce the proportion of media sampled for analysis, but such sampling becomes more difficult to control. At the same time, a small sampling line is not well suited for the analysis of various suspensions in which solid particles can clog the flow path. Thus, the size of the sampling line for the analysis of suspensions is highly dependent on the size of the solid particles and the characteristics of the medium. Similar conclusions apply to viscous liquids.
Sampling line sizing typically considers:
- characteristics of the liquid intended for selection;
- loss of the working environment during selection;
- safety requirements during selection;
- ease of operation;
- selection point location.
coolant circulation
For pipelines with circulating coolant, high velocities are preferred. This is mainly due to the fact that the cooling liquid in the cooling tower is exposed to sunlight, which creates the conditions for the formation of an algae-containing layer. Part of this algae-containing volume enters the circulating coolant. At low flow rates, algae begin to grow in the pipeline and after a while create difficulties for the circulation of the coolant or its passage to the heat exchanger. In this case, a high circulation rate is recommended to avoid the formation of algae blockages in the pipeline. Typically, the use of high circulation coolant is found in the chemical industry, which requires large pipelines and lengths to provide power to various heat exchangers.
Tank overflow
Tanks are equipped with overflow pipes for the following reasons:
- avoidance of fluid loss (excess fluid enters another reservoir, rather than pouring out of the original reservoir);
- preventing leakage of unwanted liquids outside the tank;
- maintaining the liquid level in the tanks.
In all the above cases, the overflow pipes are designed for the maximum allowable flow of liquid entering the tank, regardless of the flow rate of the liquid leaving. Other piping principles are similar to gravity piping, i.e. according to the available vertical height between the start and end points of the overflow piping.
The highest point of the overflow pipe, which is also its starting point, is at the connection to the tank (tank overflow pipe) usually near the very top, and the lowest end point can be near the drain chute close to the ground. However, the overflow line can also end at a higher elevation. In this case, the available differential head will be lower.
Sludge flow
In the case of mining, ore is usually mined in hard to reach areas. In such places, as a rule, there is no rail or road connection. For such situations, hydraulic transportation of media with solid particles is considered the most appropriate, including in the case of the location of mining plants at a sufficient distance. Slurry pipelines are used in various industrial areas to convey crushed solids along with liquids. Such pipelines have proven to be the most cost-effective compared to other methods of transporting solid media in large volumes. In addition, their advantages include sufficient safety due to the lack of several types of transportation and environmental friendliness.
Suspensions and mixtures of suspended solids in liquids are stored in a state of periodic mixing to maintain uniformity. Otherwise, a separation process occurs, in which suspended particles, depending on their physical properties, float to the surface of the liquid or settle to the bottom. Agitation is provided by equipment such as a stirred tank, while in pipelines, this is achieved by maintaining turbulent flow conditions.
Reducing the flow rate when transporting particles suspended in a liquid is not desirable, since the process of phase separation may begin in the flow. This can lead to blockage of the pipeline and a change in the concentration of the transported solids in the stream. Intense mixing in the flow volume is promoted by the turbulent flow regime.
On the other hand, an excessive reduction in the size of the pipeline also often leads to blockage. Therefore, the choice of pipeline size is an important and responsible step that requires preliminary analysis and calculations. Each case must be considered individually as different slurries behave differently at different fluid velocities.
Pipeline repair
During the operation of the pipeline, various kinds of leaks may occur in it, requiring immediate elimination in order to maintain the system's performance. Repair of the main pipeline can be carried out in several ways. This can be as much as replacing an entire pipe segment or a small section that has a leak, or patching an existing pipe. But before choosing any method of repair, it is necessary to conduct a thorough study of the cause of the leak. In some cases, it may be necessary not only to repair, but to change the route of the pipe to prevent its re-damage.
The first stage of repair work is to determine the location of the pipe section requiring intervention. Further, depending on the type of pipeline, a list of the necessary equipment and measures necessary to eliminate the leak is determined, and the necessary documents and permits are collected if the pipe section to be repaired is located on the territory of another owner. Since most pipes are located underground, it may be necessary to extract part of the pipe. Next, the coating of the pipeline is checked for general condition, after which part of the coating is removed for repair work directly with the pipe. After repair, various verification activities can be carried out: ultrasonic testing, color flaw detection, magnetic particle flaw detection, etc.
While some repairs require the pipeline to be shut down completely, often only a temporary shutdown is sufficient to isolate the repaired area or prepare a bypass. However, in most cases, repair work is carried out with a complete shutdown of the pipeline. Isolation of a section of the pipeline can be carried out using plugs or shut-off valves. Next, install the necessary equipment and carry out direct repairs. Repair work is carried out on the damaged area, freed from the medium and without pressure. At the end of the repair, the plugs are opened and the integrity of the pipeline is restored.
→ Water disposal systems
Hydraulic calculation of gravity pipelines
The calculation of gravity pipelines consists in determining their diameter (or the dimensions of the collector, if it is not round), the slope and the parameters of their operation - filling and speed. Usually, the flow rate is preliminarily determined, which is the starting point for the calculation. The calculation of pipelines is not only a hydraulic task. The results obtained must satisfy the technological and economic requirements, which will be discussed below.
In order to simplify the hydraulic calculations of drainage networks, the movement of water in them is conventionally assumed to be steady and uniform. Regarding the calculation of gravity pipelines, there are two points of view.
According to formula (2.7), the coefficient A (hence, the coefficient C) depends not only on the relative roughness, but also on the Reynolds number. This formula is valid for all three regions of the turbulent regime of fluid motion: regions of smooth, completely rough friction and the transition region between them. Studies have shown that pipelines of drainage networks operate in the area of quite rough friction. For possible design conditions, calculations using formulas (2.1) - (2.3) and (2.6) - (2.7) give practically the same results.
It is known that the maximum water flow in pipes is observed when filling h / d = 0.95. Therefore, it is not advisable to accept a content greater than this value. However, it is recommended to take calculated fillings even less than this value for the following two reasons. Firstly, when determining the estimated costs, fluctuations in costs within the hour of the day, when the maximum flow can be observed, are not taken into account. And this fluctuation can be both smaller and larger. Secondly, due to the uneven movement of water, the filling in the pipeline in some places may be greater than the calculated one. In order to avoid flooding of pipelines under design conditions, it is recommended that the filling in the pipelines of the domestic drainage network be no more than 0.8.
In the pipelines of rain networks (drains) of complete separate drainage systems, as well as in all-alloy pipelines and all-alloy collectors of semi-separate drainage systems, under design conditions, the filling is recommended to be taken equal to 1, i.e., full. This is explained by the fact that the design conditions in these pipelines are observed very rarely - 1 time in 0.25-10 years. Thus, for a significant part of the time, these pipelines will also operate at partial filling.
The undissolved impurities contained in wastewater can precipitate, reduce the cross section of pipelines and cause their complete clogging. It is most difficult to transport mineral impurities with a high density by the flow of water. Transportation of undissolved impurities by the flow is a consequence of its turbulence. At certain low velocities, suspended solids settle to the bottom and form a dense sediment layer. When a certain speed is reached, the sediment begins to move, forming a layer of sediment in the form of continuous ridges that move in the direction of the flow, but at a slower speed (Fig. 2.4). The speed corresponding to the beginning of sediment movement is called scouring. With a further increase in speed and reaching a certain value, the entire sediment is weighed by a turbulent flow, and the pipeline is self-cleaning. The speed corresponding to this moment is called self-cleaning. The concept of critical speed is also known. This speed corresponds to the beginning of the sedimentation of impurities (when the speed decreases) or complete self-purification (when the speed increases). Wastewater flow in drainage networks varies over a wide range from a certain minimum to a known maximum, which is taken as calculated. It is not possible to ensure the possibility of transporting all impurities by flow at any flow rate, including the minimum one, since in this case it would be necessary to lay pipelines with large slopes, and this would lead to their significant deepening. Currently, the calculation of pipelines is carried out on the condition of maintaining the pipes in a clean state at the maximum design flow rate. Thus, at minimum flow rates, deposits are allowed in the pipelines, but when the design flow rate is reached, the pipelines must be self-cleaning. Therefore, the concept of self-cleaning speed is widely used in the calculation. This is the minimum speed that must be provided in the drainage networks at the calculated flow rate.
Rice. 2.4. Scheme of continuous movement of sediments in the drainage network
Professors N. F. Fedorov and A. M. Kurganov, the minimum speed that must be observed in pipelines from self-cleaning conditions is called non-silting.
Formula (2.11) takes into account the size of the sand that may be contained in wastewater. The change in sand size may be due to the type of wastewater (domestic, rainwater, industrial), the perfection of driveway pavements, the peculiarities of their content, etc.
The self-cleaning velocity also depends on the roughness coefficient n, since an important source of flow turbulence is the roughness of the channel. If there is sediment in the form of ridges in the pipelines, then the coefficient u ~ 0.025. If the pipeline is clean, then l ~ 0.014. According to formula (2.11), the self-cleaning rate in the first case is less than in the second. The first case determines the conditions for self-purification, and the second determines the critical conditions (conditions that exclude the precipitation of suspended solids). Formula (2.11) allows you to determine both the self-cleaning speed and the critical one. They are different because the roughness of the channels is different. But the turbulence conditions in the two cases described are practically the same.
Sand and other mineral impurities contained in wastewater are abrasive materials that abrade the walls of pipelines as a result of liquid transportation. In this case, the intensity of abrasion is proportional to the speed of the flow moving in the pipe. Therefore, based on many years of experience in the operation of drainage networks, the maximum allowable speeds are set equal to 4 m / s for non-metallic pipes and 8 m / s for metal pipes.
The calculation of pipelines according to formulas (2.1) - (2.4) or others is extremely complicated. Methods for solving various problems in the calculation of pipelines are described in special literature.
When designing drainage networks, it is required to perform calculations for a large number of individual sections of pipelines with different design conditions. Their calculation is carried out by applying certain simplifying techniques, in which the developed tables, graphs, nomograms, various generalized parameters, etc. are used.
Currently, various tables are used to calculate gravity pipelines, which include the tables of A. A. Lukinykh-1 and N. A. Lukinykh (Tables for the hydraulic calculation of sewer networks and siphons according to the formula of academician N. N. Pavlovsky. - M .: Stroyizdat, 1987) and N. F. Fedorova and L. E. Volkova (Hydraulic calculation of sewer networks. -L .: Stroyizdat, 1968). The first ones are compiled according to formulas (2.1) - (2.4), the second - according to formulas (2.6) and (2.7).
The values of wastewater flow rate d and the speed of their movement v in pipes d=2Q0 mm
In table. 2.4 is a brief excerpt from the first tables for a pipeline with a diameter of 200 mm. The tables contain flow and velocity values for various fillings from 0.05 to 1.0 for all pipe diameters and slopes possible in engineering practice.
When designing drainage networks, the flow rate is preliminarily determined. The slope of the pipeline is taken taking into account the slope of the earth's surface and guided by economic considerations (minimum earthworks and construction costs). The calculation of pipelines according to the tables described is reduced to the selection of the diameter of the pipeline, which ensures the passage of flow during filling, corresponding to the self-cleaning speed.
This calculation is very simple and convenient. However, it requires large tables, which are published in separate books. They should be "at hand" for every designer. At the same time, the published tables do not cover all possible diameters and slopes of pipelines and their operation parameters in engineering practice.
Similarly, the calculation is carried out according to graphs and nomograms. It requires hard work. In engineering practice, they are used less frequently.
Determination of the diameters of gravity pipelines
Water from the head is transported through two gravity lines. The diameter of gravity lines should be such that the speed of water movement along them is not less than the speed of water movement in the river in order to minimize the deposition of silt. To do this, in the flood with increased turbidity, we pass the entire flow through one gravity line, with a speed of Vsurf = 1.31 m/s.
The diameter of the gravity pipeline is determined by the formula:
ds.tr. \u003d v (4 * Qp / pV) \u003d?? 4 * 0.4 / 3.14 * 1.31? \u003d 0.62m
we accept steel pipes with a diameter of ds.tr \u003d 700 mm, with a speed of V \u003d 0567 m / s, according to the Shevelev table, in low water, the entire flow rate of 0.22 m³ / s will be passed through two gravity lines, with a speed of V \u003d 0.283 m / s, along SNIP.
The pressure loss during the movement of water in gravity lines is determined by the formula:
??=і*?+?(g*VI)/2g+?р, where
i - hydraulic slope or pressure loss per unit length of the pipeline (determined according to the Shevelev table),
Estimated length of gravity pipeline, m,
g - resistance coefficient, taken depending on the local obstacle (determined according to the reference book of Kurganov A.N. and Fedorov N.F. "Handbook on hydraulic calculations of VC systems").
For the case of shutting down one line for repair or flushing.
For the case of two lines.
As a result of calculating the pressure loss, we determine the water level marks of the well. Let's use the following values:
For a narrowing transition - w=0.25
For two welded bends with an angle of 45º - w \u003d 0.45
For a tee in the forward direction of the pipe - w = 0.1
For valve - w=50
To exit the pipe (spout) into the water intake chamber - f = 1
Therefore - ?zh=51.8
Thus, we consider the pressure loss when water moves along one gravity line:
By length i*?
So the pressure loss along the length will be equal to:
0.00061 *120m=0.0732
Head loss through gratings? p = 0.1 and the amount? is:
H=0.0732*51.8*(0.8І/2*9.81) +0.1=0.227
We found the head loss during the movement of the entire water flow along one gravity line.
We determine the loss of water pressure when passing the flow through two gravity lines.
2) By length i*?
According to Shevelev's tables for a flow rate of 800 m3/h.
For this expense, we determine according to the Shevelev table:
d=700 mm, therefore, i=0.00061 (1000 i=0.61), with a speed V=0.567m/s.
By expense:
According to this flow rate, which we pass through two steel pipes with a diameter of 700 mm according to the Shevelev table 1000 i = 0.178, therefore, i = 0.000178 at a speed V = 0.286 m / s, then the loss in length:
??= i*?=0.00061 *120m=0.0732
Amount? W = 51.8
H=51.8*0.4І/2*9.81+0.0732+0.1=0.596
We get the pressure loss in two gravity pipelines.
Automation of a syrup preparation plant
The diameter of the pipelines can be determined by the product flow rate: D =, m, (5) where Qp - product flow rate, m3/s; W is the speed of the product (liquid), m/s; D - internal diameter of the pipeline, m...
Analysis of the results of gas-hydrodynamic studies of wells connected to GTP-14 of the Orenburg oil and gas condensate field
To find the optimal diameter of an oil pipeline in accordance with Table 3 for a throughput of 4.5 million tons/year, we select three competing diameters through which a given volume of oil can be pumped: D1 = 377 mm, D2 = 426 mm, D3 = 529 mm .. .
Hydraulic drive of the manipulator
To do this, let's set the fluid flow rates: in the pressure pipeline - 3.8 m/s; in the drain pipeline - 1.5 m / s; in the suction pipeline - 1 m/s. , m where, is the value of the fluid flow through the pipe, [m3/s]; - fluid flow rate, [m/s]...
Hydraulic calculation of the volumetric hydraulic drive of the circular saw feed mechanism
The inner diameter of the pipeline is determined by the formula, where Q is the highest flow rate in the calculated section of the hydraulic line, m3/s; V - allowable fluid velocity, m/s. For the pressure line: accept dn-r = 16 mm For the executive line...
Hydraulic cylinder with one-sided rod
We accept the speeds in the lines: for the suction pipeline = 1.6 m/s; for drain pipeline =2 m/s; for pressure pipeline = 3.2 m/s (at p<6,3 МПа). Зная расход Q (расход жидкости во всасывающей, напорной и сливной линиях)...
Evaporator design
We determine the diameter of the fitting for the inlet of the raw solution. Determine the nozzle diameter d1, m d1 = where V is the volumetric flow rate of the raw solution, m/s; w is the speed of the wet solution, w = 1 m/s. d1 = V = where G0 is the amount of initial solution...
Pumping unit
The given technological scheme contains tanks located at different elevations...
Determination of design parameters of evaporator units
Let's accept the following values of speeds of movement of streams: · speed of the movement of the heating couple vgp=20 m/s; Condensate speed wk=0...
Construction project of a 4 MW boiler house
Where Gset is the consumption of network water, kg / s; v - specific volume of water, v = 0.001m3/kg; Vv - the speed of water in the pipeline, we take 1 m / s · The diameter of the network water pipeline We accept a pipe with a standard diameter of 200 mm. Direct water pipeline diameter...
Industrial boiler room with steam boilers
The main pipelines in a steam heat generating plant include saturated steam pipelines within the boiler room and feed water pipelines. The diameter of pipelines is calculated by the formula: , m (1.36) where...
Calculation of the hydraulic drive for the LT-154 tractor
The pipeline diameter is determined by the formula: where QC is the flow rate in the hydraulic system, m3/s; VZh is the speed of fluid movement in the pipeline, m/s; In accordance with the recommendations, we accept the fluid flow rates: - for the suction hydraulic line VВ=0.5...2m/s...
Calculation of the hydraulic drive of rotary motion
To connect the elements of a hydraulic system, pipelines are used, the inner diameter of which is determined by the diameter of the connecting thread of hydraulic devices or a conditional approach, i.e. ...
Calculation and design of a water intake structure from a surface source of water supply (river)
2=2Dr - at least two socket diameters; Dr = 1.3 - 2 d - suction pipe; Dp =1.5*0.6=0.9m, ?2=2Dp=2*0.9=1.8; ?1=0.8D - not less than 0.5 m; ?1=0.8*(0.9)=0.72 All parameters are considered as recommended minimum. Suction pipe diameter...
Functional diagram of automation
The diameter of the pipelines can be determined by the product flow rate: D =, m, (5) automation is a technological controlled parameter where Qp is the product flow rate, m3/s; W is the speed of the product (liquid), m/s; D - internal diameter of the pipeline, m...
Trench chain excavator ETC-250
We calculate the diameters of pipelines from the condition of ensuring permissible operating speeds: - suction - drain - discharge According to the calculated diameters, we select the closest standardized diameter of steel ...
The diameter of gravity pipes is determined at UNV by the flow rate during normal operation of the water intake and by the speed of water movement 0.7 ... 2.0 m / s (Table 14). The number of gravity water conduits must be at least two. When laying gravity water conduits by lowering under water, steel pipes with reinforced insulation are used.
Water conduits are buried under the bottom of the river by at least 0.8-1.5 m on navigable ones to protect them from being washed away by the river flow, abrasion by sand, damage by anchors of ships and rafts. Conduits should not have sharp turns, narrowing, expansion. They can be laid horizontally, with a straight and reverse slope.
Pipe diameter:
where Q R- estimated consumption of one section, equal to 0.8 m 3 /With;
V calc- Estimated speed.
We accept according to the range of pipes d fact=800 mm.
Actual speed:
In fact, the velocity in gravity pipes must meet two conditions:
A) must be greater than the critical, i.e., the speed at which silting of pipes does not occur, transported by sediments:
V f >V kr,
where: - amount of sediment, kg/m 3 ;
w is the weighted average hydraulic fineness, m/s;
d - diameter of the conduit, m;
u is the rate of precipitation of suspended particles in the flow, m/s;
g - free fall acceleration, m/s 2 .
Find the speed in the pipeline in emergency mode:
Condition V f >V kr is performed, because 1.6>1.406.
b) should be greater than the rate of capture in the pipe of sediments with a size of D, m
Wastewater in the sewer network must move at such a speed that no solid contents are deposited on the route. Otherwise, over time, it will inevitably lead to siltation of transportation elements - pipelines or trays.
But there is also an upper limit to the flow rate. Solid particles in water moving at high speed increase the mechanical abrasion of the surface of the collectors.
Estimated speeds
The maximum design speed is the maximum flow rate of wastewater in channels and pipes, at which mechanical damage is not applied to the collector material.
Minimum design velocity (critical) - the lowest flow velocity required to prevent silting of pipes and collectors.
The average speed of wastewater is the ratio of the flow rate Q of wastewater in the line to the value of its free cross section ω:
v = Q/ω m/sec.
The flow velocities in different places of the cross section of the flow are in fact not the same. The closer to the middle (core) of the flow, the larger they are than near the bottom and walls. Bottom and near-wall velocities are minimal. It is impossible to calculate the sewer network for bottom and near-wall velocities due to the high complexity of such calculations. Therefore, the basic value from which the design is based is the transport capacity of the flow. It is determined through the estimated flow velocity. The main criterion for determining this speed is to ensure self-cleaning of collectors and pipes.
For gravity lines, the correct speed is ensured by the correct slope. Where slope is not possible, use sewer pumps appropriate power.
Design speed - this is the speed of wastewater flow at the calculated (maximum) flow rates and, accordingly, filling. The calculated speeds should be between its maximum permissible values in the channel - maximum and minimum.
For the maximum design speed of movement of wastewater according to the norms, it should be taken for
- metal pipes - no more than 8 m / s;
- non-metallic (reinforced concrete, concrete, asbestos-cement, ceramic and others) - up to 4 m / s.
The magnitude of the calculated self-cleaning channels and pipes of the velocities of the movement of effluents is influenced by such parameters as the hydraulic radius or the degree of filling and the size of suspended solids present in the wastewater.
The minimum design flow rate in pipelines of untreated domestic and storm sewage at the calculated filling value is indicated in the relevant SNiP.
If the filling of the pipes of the sewer network is not calculated, then the rate of their self-cleaning vn (the index "n" means "non-silting") is calculated according to the formula proposed by Professor N. F. Fedorov:
- R is the hydraulic radius in m;
- n is the exponent of the root (3.5 + 0.5R).
The lowest design speed in trays and pipes for clarified or biologically treated wastewater can be taken equal to 0.4 m / s.
In siphons with diameters up to 800 mm, the value of 1 m/s is taken as the lower limit of design velocities for non-clarified wastewater. For diameters greater than 80 cm, vн is also determined by the Fedorov formula.
Wastewater should approach the siphon at a speed not higher than the calculated speed in the siphon itself. In this case, it is necessary to observe the minimum values \u200b\u200bthat were indicated above or calculated using the Fedorov formula.
In order for the collectors to self-clean, the velocity along the flow path must be constantly increased. The required speed values are set by the slopes of the pipelines. The minimum values of slopes for any sewerage systems with their calculated filling of pipes with diameters:
- 150 mm - 0.007;
- 200 mm - 0.005;
- 1250 mm and above - 0.0005.
The load of the initial sections of the sewerage network with pipelines of 200 mm or less almost never reaches the calculated one. Therefore, the speed in them is not calculated, and they are called non-calculated.
For sewer pipelines with a diameter greater than 200 mm, the required minimum slopes must be calculated taking into account the provision of a flow rate that guarantees self-cleaning of the collector. Quite satisfactory results are given for this by the simplest empirical formula:
Here the pipe diameter d is taken in mm.
