Hydraulic operating modes of distributed gas pipelines must be taken from the conditions of creation (at Δ P max.adm.) a system that ensures the stability of the operation of all hydraulic fracturing units and burners within the permissible limits of gas pressure.

Calculation of gas pipelines comes down to determining the required diameters and checking the specified pressure drops. In practical calculations of gas networks, nomograms constructed in coordinates and calculated flow rates are widely used Q r.h., for standard diameters.

The nomogram is based on a formula for the entire region of the turbulent regime.

Where k e And d in cm

The calculation procedure can be as follows:

1. The initial pressure is determined by the operating mode of the gas distribution system or hydraulic fracturing unit, and the final pressure is determined by the passport characteristics of consumer gas appliances.

2. Select the most distant points of branched gas pipelines and determine the total length l vol. them in selected main areas. Each direction is calculated separately.

3. In gas supply systems, the rule is a constant pressure drop per unit length of the gas pipeline. Local resistance in the gas pipeline is taken into account by increasing the total design length by 5-10%, (km).

4. Determine the estimated gas costs for each section of the gas pipeline Qp. i..

5. By size A avg And Qp. i. According to the nomogram, the diameters of the sections are selected, rounding them up according to GOST, i.e. towards lower pressure drops in the area.

6. For the selected standard diameters according to GOST, find the actual values A d, then clarify R k according to the formula

7. Pressures are determined starting from the beginning of the gas pipeline, because the initial pressure of the hydraulic fracturing system or hydraulic fracturing is known. If the pressure R c.d. significantly more than the specified value (more than 10%), then the diameters of the final sections are reduced

main direction.

8. After determining the pressure in this main direction, a hydraulic calculation of gas pipeline branches is carried out using the same method, starting from the second point. In this case, the pressure at the sampling point is taken as the initial pressure.

Problem 9.2.2. Carry out a hydraulic calculation of a branched high-pressure network, “tree” type, using two options: a, b (Fig. 9.4).

A) Q 6= 700 m 3 /h; R 6= 0.3 MPa;

Q 7= 900 m 3 /h; R 7= 0.33 MPa;

Q 4= 1200 m 3 /h; R 4= 0.4 MPa;

Q 2= 1700 m 3 /h; R 2= 0.5 MPa;

R GRS= 1 MPa;

l GRS-1= 4 km; l 1-2= 7 km;

l 1-3= 6 km; l 3-4= 8 km;

l 3-5= 10 km; l 5-6= 3 km; l 5-7= 7 km;

b) Q 8= 1500 m 3 /h; R 8= 0.3 MPa; Q 10= 2000 m 3 /h; R 10= 0.4 MPa; Q 13

2100 m 3 /h; R 13= 0.45 MPa; Q 14= 2300 m 3 /h; R 14= 0.6 MPa; R GRS= 0.8 MPa; l GRS-11= =5km; l 11-12=7 km; l 12-14 =l 12-13=8 km; l 11-9=20 km; l 9-8=4 km; l 9-10=6 km;

Rice. 9.5. Nomogram of high and medium pressure gas pipelines.

9.2.3. Calculation of high and medium pressure gas pipelines

Example 9.2.1. Determine the gas flow in a gas pipeline 5 km long, 500 mm in diameter. The excess pressure at the beginning and end of the gas pipeline is respectively equal to p 1=3∙10 5 N/m 3 and p 2=1∙10 5 N/m 3. Gas constant 500 (N∙m)/(kg∙K). Gas temperature 5 o C. Hydraulic resistance coefficient λ =0.02. Gas density is 0.7 kg/m3.

Solution

Absolute temperature gas

T= 273+5=278 K.

The coefficient of deviation of the value of real gases from the value of ideal gases is taken equal to unity ( z=1).

The mass flow will be equal to

Volumetric gas flow

Hourly gas consumption

Example 9.2.2. Determine the pressure drop in a horizontal gas pipeline 10 km long, 300 mm in diameter, with a gas flow of 500,000 m 3 /day. Gas density 0.7 kg/m3, gas constant R=500 (N∙m)/(kg∙K). Hydraulic resistance coefficient λ =0.015. Coefficient Z=1. The gas temperature in the gas pipeline is 7 o C. The absolute pressure at the end of the gas pipeline is p 2=6∙10 5 Pa.

Solution

Let us express the second mass flow of gas in terms of volumetric

Determine the square pressure difference

Pressure drop

Example 9.2.3.z= 500 m, T= 280 K, p 2=5∙10 5 Pa (absolute pressure), R=500 (N∙m)/(kg∙K). The gas pipeline has been stopped ( M 0=0).

Solution

Determine the value of the coefficient b

Example 9.2.4. Determine the pressure of the gas column in an inclined gas pipeline if Δ z= 280 m, absolute pressure at the starting point of the gas pipeline p 2=3∙10 5 Pa, R=490 (N∙m)/(kg∙K), T=280 K. The gas pipeline is stopped ( M=0).

Solution

Determining the coefficient b

Determining the pressure of the gas column

or r 1 -r 2 is 2% of the pressure at the beginning of the gas pipeline r 1 .

Example 9.2.5. Determine the mass and volume flow rate of methane gas in a gas pipeline 10 km long, with an internal diameter of 0.3 m. The positive difference in gas pipeline elevations is 500 m. The excess pressure at the beginning of the gas pipeline is p 1 = 15 kgf/cm 2, at the end of the gas pipeline r 2 =14 kgf/cm2. Gas temperature 5 o C, density ρ =0.7 kg/m 3, gas constant R=500(N∙m)/(kg∙K).

Solution

Determining the coefficient b

Referred pressure and temperature

According to the graphs, we set the compressibility coefficient to 0.95.

To facilitate calculations based on formulas (VI. 19) - (VI.22), tables and nomograms have been developed. From them, with sufficient accuracy for practical purposes, they determine: based on a given flow rate and pressure loss, the required diameter of the gas pipeline; according to the given diameter and losses - throughput gas pipeline; for a given diameter and flow rate - pressure loss; according to known local resistances - equivalent lengths. Each table and nomogram is compiled for gas with a certain density and viscosity and separately for low or medium and high pressure. To calculate gas pipelines low pressure most often they use tables, the structure of which is well illustrated in Table. VI.2. The range of pipes in them is characterized by the outer diameter d„, wall thickness s and inner diameter d. Each diameter corresponds to specific pressure loss D r and equivalent length Z 3KB, depending on a certain gas flow V. Nomograms (Fig. VI.3 - VI.7) are the graphic equivalent of the data given in the tables.

Table VI.2

Pressure loss Ar and equivalent lengths in for natural gas (p = 0.73 kg/m 3, v = 14.3 * 10 "* m 2 / sec, steel water and gas pipes according to GOST 3262-62)

d H X« (d), mm
21.3X2.8 (15,7)	26.8X2.8 (21,2)	33.5X3.2 (27,1)	42.3X3.2 (35,9)	48.0X3.5 (41,0)

Note. The numerator shows the pressure loss, kgf/m* per 1 u, the denominator is the invivalent length, and.

A- natural woof, p - 0.73 kg/m*, v = 14.3‘Yu - * m*/sec; b - propane gas, p?= 2 Kf/m *, v "= 3.7* 10~* m"/sec.

Example 17. Through a pipe (GOST 3262-62) dH X s= 26.8 X 2.8 mm long I = 12 m natural gas of low pressure with p = 0.73 kg/m 9 is supplied in quantity V= 4 m 3 / h. A plug valve is installed on the gas pipeline and two 90° bent elbows are installed. Determine pressure loss in the gas pipeline.

Solution. G1o table VJ.2 we find that at flow V= 4 m 9 /h specific friction losses Ar - 0.703 kg/m2 per 1 m, and the equivalent length? Ek p = = 0.52 m. According to pas data. 108 we find the coefficients of local resistance: For a plug valve = 2.0 and for a bent elbow 90°? 2 = 0.3. Calculated length of the gas pipeline according to formula (VI.29) / calculated = 12 + (2.0 + 2-0.3) X 0.52 = = 13.5 m. Required total pressure loss Dr sum - 13.5-0.703 = = 9.52 kg/m2.

Example 18. Along a low-pressure steel gas distribution pipeline assembled from pipes dH X s= 114 X 4 mm, long I = 250 m natural gas is supplied with p = 0.73 kg/m 9 in quantity V- 200 m 3 /h. The geodetic elevation of the end gas pipeline is 18 m higher than the initial one. Determine the pressure loss in the gas pipeline.

Solution. According to the nomogram in Fig. VI.3 we find that at a flow rate V = = 200 m 3 / h, the specific pressure loss due to friction in the gas pipeline d H Xs = 114 X X 4 mm A r - 0.35 kg/m2 per 1 m. To take into account pressure losses in local resistances, we increase the actual length of the gas pipeline by 10%, T.V. I race Ch = 1.1 1fact = 1.1 * 250 = 275 m. Total pressure loss due to friction and local resistance Lr SuI = 0.35-275 = 96 kg/m 2.

The transported gas is lighter than air, therefore hydrostatic pressure is created in the gas pipeline. According to formula (VI.24) Ar g ~ 18 (1,293 - 0,73)

*=“10 kg/m2. Then the required pressure loss in the gas pipeline is Ap* aKX = 96 - - 10 = 86 kgf/cm 2.

Example 19. Through a low-pressure steel gas pipeline d H X s = = 21.3-2.8 mm and length I = 10 m propane is supplied in quantity V== 1.2’m 8 /h. A plug valve is installed on the gas pipeline and there is one 90° bent elbow. Determine pressure loss in the gas pipeline.

Solution. According to the nomogram in Fig. VI.4 we find that at gas flow

V= 1.2 m 3 /h specific friction losses Ar= 0.75 kg/m2 per 1 m. According to the nomogram in Fig. VI.5, b for these conditions, the equivalent length of the gas pipeline /ekp = 0.41 m. According to the data on p. 108 local resistance coefficients: for a plug valve?, = 2.0, for a bent bend 90 s ? 2 = 0.3.

The estimated length of the gas pipeline according to formula (VI.29) 1 raS h = 10 + 0.41 (2.0 + + 0.3) = 10.94 11 m. The required total pressure loss Dr sum = 11 X

X 0.75 = 8.25 kg/m2.

Example 20. Through a steel gas pipeline Dy= 200 mm, 1600 m long, natural gas with a density p = 0.73 kg/m 3 is supplied in an amount of 5000 m 8 /h. Determine the excess pressure at the end of the gas pipeline, if at the beginning of the gas pipeline it is equal to 2.5 kgf/cm 2.

Solution. According to the nomogram in Fig. VI.7 we find that with gas consumption

V- 5000 m 3 /h for gas pipeline Dy= 200 mm (p - pl)IL= 1.17. Hence the absolute pressure at the end of the gas pipeline

kgf/cm2. Excessive pressure at the end of the gas pipeline p,-= 2.22 kgf/cm 8,

For safe and trouble-free operation of the gas supply, it must be designed and calculated. It is important to perfectly select pipes for mains of all types of pressure, ensuring a stable supply of gas to the devices.

To ensure that the selection of pipes, fittings and equipment is as accurate as possible, a hydraulic calculation of the pipeline is performed. How to make it? Admit it, you are not too knowledgeable about this issue, let's figure it out.

We offer you to familiarize yourself with carefully selected and thoroughly processed information about options for producing hydraulic calculations for gas pipeline systems. Using the data we present will ensure that the devices are supplied with blue fuel with the required pressure parameters. Carefully verified data is based on the regulations of regulatory documentation.

The article describes in great detail the principles and schemes for performing calculations. An example of performing calculations is given. Graphic applications and video instructions are used as a useful informative addition.

Any hydraulic calculation performed is a determination of the parameters of the future gas pipeline. This procedure is mandatory, as well as one of the most important stages of preparation for construction. Whether the gas pipeline will function optimally depends on the correctness of the calculation.

When performing each hydraulic calculation, the following is determined:

necessary, which will ensure efficient and stable transportation of the required amount of gas;
Will the pressure loss be acceptable when moving the required volume of blue fuel in pipes of a given diameter?

Pressure losses occur due to the fact that there is hydraulic resistance in any gas pipeline. If calculated incorrectly, it can lead to consumers not having enough gas for normal operation in all modes or at times of maximum consumption.

This table is the result of a hydraulic calculation carried out taking into account the given values. To perform calculations, you will need to enter specific indicators in the columns.

Beginning of the section	End of the section	Estimated flow m³/h	Gas pipeline length	Inner diameter, cm	Initial pressure, Pa	Final pressure, Pa	Pressure drop, Pa
1	2	31,34	120	9,74	2000,00	1979,33	20,67
2	3	31,34	150	9,74	1979,33	1953,48	25,84
3	4	31,34	180	7,96	1953,48	1872,52	80,96
4	5	29,46	90	7,96	1872,52	1836,2	36,32
5	6	19,68	120	8,2	1836,2	1815,45	20,75
6	7	5,8	100	8,2	1815,45	1813,95	1,5

4	8	9,14	140	5	1872,52	1806,38	66,14

6	9	4,13	70	5	1815,45	1809,83	5,62

Such an operation is a state-standardized procedure that is performed in accordance with the formulas and requirements set out in SP 42-101–2003.

The developer is required to carry out the calculations. The data is taken as a basis technical specifications pipelines, which can be obtained from your city gas.

Gas pipelines requiring calculations

The state requires that hydraulic calculations be performed for all types of pipelines related to the gas supply system. Since the processes that occur when gas moves are always the same.

These gas pipelines include the following types:

low pressure;
medium, high pressure.

The first ones are intended for transporting fuel to residential facilities, all kinds public buildings, household businesses. Moreover, in private apartment buildings, in cottages, gas pressure should not exceed 3 kPa; in household enterprises (non-industrial) this figure is higher and reaches 5 kPa.

The second type of pipelines is intended to supply networks of all kinds, low and medium pressure through gas control points, as well as supplying gas to individual consumers.

These can be industrial, agricultural, various public utility enterprises, and even free-standing or attached to industrial buildings. But in the last two cases there will be significant pressure restrictions.

Experts conditionally divide the types of gas pipelines listed above into the following categories:

intra-house, in-shop, that is, transporting blue fuel inside a building and delivering it to individual units and devices;
subscriber branches, used to supply gas from some distribution network to all existing consumers;
distribution, used to supply gas to certain areas, for example, cities, their individual areas, industrial enterprises. Their configuration varies and depends on the layout features. The pressure inside the network can be any specified - low, medium, high.

In addition, hydraulic calculations are performed for gas networks with different numbers of pressure stages, of which there are many varieties.

Thus, to meet the needs, two-stage networks can be used, operating with gas transported at low, high pressure or low, medium pressure. Three-stage and various multi-stage networks have also found application. That is, everything depends only on the availability of consumers.

Despite the wide variety of gas pipeline options, the hydraulic calculations are similar in any case. Since structural elements from similar materials are used for manufacturing, and the same processes occur inside the pipes.

Hydraulic resistance and its role

As mentioned above, the basis for the calculation is the presence of hydraulic resistance in each gas pipeline.

It affects the entire pipeline structure, as well as its individual parts, assemblies - tees, places of significant reduction in pipe diameter, shut-off valves, and various valves. This leads to a loss of pressure in the transported gas.

Hydraulic resistance is always the sum of:

linear resistance, that is, acting along the entire length of the structure;
local resistances acting at each component part of the structure where the gas transportation speed changes.

The listed parameters constantly and significantly influence the performance characteristics of each gas pipeline. Therefore, as a result of incorrect calculations, additional and significant financial losses will occur due to the fact that the project will have to be redone.

Rules for performing calculations

It was stated above that the procedure for any hydraulic calculation is regulated by the profile Code of Rules with the number 42-101–2003.

The document indicates that the main way to perform the calculation is to use a computer for this purpose with special programs that allow you to calculate the planned pressure loss between sections of the future gas pipeline or the required pipe diameter.

Any hydraulic calculation is performed after creating a calculation diagram that includes the main indicators. Moreover, the user enters known data into the appropriate columns

If there are no such programs or a person believes that their use is inappropriate, then other methods permitted by the Code of Rules can be used.

Which include:

calculation using the formulas given in the SP is the most complex method of calculation;
calculation using so-called nomograms is a simpler option than using formulas, because you don’t have to make any calculations, because the necessary data is indicated in a special table and given in the Code of Rules, and you just need to select them.

Any of the calculation methods leads to the same results. Therefore, the newly built gas pipeline will be able to ensure timely, uninterrupted supply of the planned amount of fuel even during the hours of its maximum use.

PC computing option

Performing calculus using a computer is the least labor-intensive - all that is required of a person is to insert the required data into the appropriate columns.

Therefore, hydraulic calculations are done in a few minutes, and this operation does not require a large amount of knowledge, which is necessary when using formulas.

To perform it correctly, it is necessary to take the following data from the technical specifications:

gas density;
coefficient of kinetic viscosity;
gas temperature in your region.

The necessary technical conditions are obtained from the city gas department of the locality in which the gas pipeline will be built. Actually, the design of any pipeline begins with the receipt of this document, because it contains all the basic requirements for its design.

Each pipe has a roughness, which leads to linear resistance, which affects the process of gas movement. Moreover, this figure is significantly higher for steel products than for plastic ones.

Today, the necessary information can only be obtained for steel and polyethylene pipes. As a result, design and hydraulic calculations can only be carried out taking into account their characteristics, which is required by the relevant Code of Practice. The document also contains the data necessary for the calculation.

The roughness coefficient is always equal to the following values:

for all polyethylene pipes, regardless of whether they are new or not, - 0.007 cm;
for already used steel products - 0.1 cm;
for new ones steel structures- 0.01 cm.

For any other types of pipes this indicator is not indicated in the Code of Practice. Therefore, they should not be used for the construction of a new gas pipeline, since Gorgaz specialists may require adjustments to be made. And these are again additional costs.

Calculation of flow in a limited area

If the gas pipeline consists of separate sections, then the calculation of the total flow rate for each of them will have to be performed separately. But this is not difficult, since the calculations will require already known numbers.

Defining data using the program

Knowing the initial indicators, having access to the simultaneity table and technical data sheets of stoves and boilers, you can begin the calculation.

To do this, perform the following steps (the example is given for a low-pressure intra-house gas pipeline):

The number of boilers is multiplied by the productivity of each of them.
The resulting value is multiplied by the simultaneity coefficient specified using a special table for this type of consumer.
The number of stoves intended for cooking is multiplied by the productivity of each of them.
The value obtained after the previous operation is multiplied by the simultaneity coefficient taken from a special table.
The resulting amounts for boilers and stoves are summed up.

Similar manipulations are carried out for all sections of the gas pipeline. The obtained data is entered into the appropriate columns of the program with which the calculations are performed. The electronics does everything else itself.

Calculation using formulas

This type of hydraulic calculation is similar to that described above, that is, the same data will be required, but the procedure will be lengthy. Since everything will have to be done manually, in addition, the designer will need to carry out a number of intermediate operations in order to use the obtained values for the final calculation.

You will also have to devote quite a lot of time to understand many concepts and issues that a person does not encounter when using a special program. The validity of the above can be verified by familiarizing yourself with the formulas to be used.

Calculation using formulas is complex and therefore not accessible to everyone. The picture shows formulas for calculating the pressure drop in the high, medium and low pressure network and the coefficient of hydraulic friction

In the application of formulas, as in the case of hydraulic calculations using a special program, there are features for low, medium and, of course, gas pipelines. And it’s worth remembering, since a mistake is always fraught with significant financial costs.

Calculations using nomograms

Any special nomogram is a table that shows a number of values, by studying which you can obtain the desired indicators without performing calculations. In the case of hydraulic calculations, the diameter of the pipe and the thickness of its walls.

Nomograms for calculation are in a simple way receiving necessary information. It is enough to refer to the lines that meet the specified network characteristics

There are separate nomograms for polyethylene and steel products. When calculating them, standard data were used, for example, the roughness of the internal walls. Therefore, you don’t have to worry about the correctness of the information.

Calculation example

An example of performing hydraulic calculations using a program for low-pressure gas pipelines is given. In the proposed table, all the data that the designer must enter independently is highlighted in yellow.

These are listed in the paragraph on computer hydraulic calculations above. These are gas temperature, kinetic viscosity coefficient, and density.

In this case, calculations are carried out for boilers and stoves; therefore, it is necessary to specify the exact number of burners, which can be 2 or 4. Accuracy is important, because the program will automatically select the simultaneity coefficient.

In the picture, the columns in which the indicators must be entered by the designer himself are highlighted in yellow. Below is the formula for calculating the flow rate on the site

It is worth paying attention to the numbering of sections - they are not invented independently, but are taken from a previously drawn up diagram, where similar numbers are indicated.

Next, the actual length of the gas pipeline and the so-called calculated length, which is longer, are written down. This happens because in all areas where there is local resistance, it is necessary to increase the length by 5-10%. This is done in order to prevent insufficient gas pressure among consumers. The program performs the calculations independently.

Total consumption in cubic meters, for which a separate column is provided, is calculated in advance at each site. If the building is multi-apartment, then you need to indicate the number of housing, starting from the maximum value, as can be seen in the corresponding column.

IN mandatory All elements of the gas pipeline, during the passage of which pressure is lost, are entered into the table. The example shows a thermal shut-off valve, a shut-off valve and a meter. The value of the loss in each case was taken from the product passport.

The internal diameter of the pipe is indicated according to technical specifications, if Gorgaz has any requirements, or from a previously drawn up diagram. In this case, in most areas it is prescribed in the size of 5 cm, because most of the gas pipeline runs along the facade, and the local city gas requires that the diameter be no less.

If you even superficially familiarize yourself with the given example of performing a hydraulic calculation, it is easy to notice that, in addition to the values entered by a person, there is large number others. This is all the result of the program, since after entering the numbers in the specific columns highlighted in yellow, the calculation work is completed for the person.

That is, the calculation itself occurs quite quickly, after which the received data can be sent for approval to the city gas department of your city.

Conclusions and useful video on the topic

This video makes it possible to understand where hydraulic calculations begin and where designers get the necessary data:

The following video shows an example of one type of computer calculation:

To perform a hydraulic calculation using a computer, as the profile Code of Rules allows, it is enough to spend a little time familiarizing yourself with the program and collecting the necessary data.

But all this has no practical significance, since drawing up a project is a much more voluminous procedure and includes many other issues. In view of this, most citizens will have to seek help from specialists.

Do you have any questions, find any shortcomings, or can you add valuable information to our material? Leave your comments, ask questions, share your experience in the block below.

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DESIGN AND CONSTRUCTION OF GAS PIPELINES FROM POLYETHYLENE PIPES WITH A DIAMETER OF UP TO 300 MM - SP 42-101-96 (2020) Current in 2018

HYDRAULIC CALCULATION OF GAS PIPELINES

1. Hydraulic calculations of gas pipelines should be performed, as a rule, on electronic computers using the optimal distribution of calculated pressure losses between sections of the network.

If it is impossible or impractical to perform calculations on an electronic computer (lack of an appropriate program, certain small sections of gas pipelines, etc.), hydraulic calculations can be performed using the formulas given below or nomograms compiled using these formulas.

2. The calculated pressure losses in high and medium pressure gas pipelines should be taken within the pressure limits accepted for the gas pipeline.

The calculated pressure loss in low-pressure gas distribution pipelines should be taken to be no more than 180 daPa (mm water column), incl. in street and intra-block gas pipelines - 120, in yard and internal gas pipelines - 60 daPa (mm water column).

3. The values of the calculated gas pressure loss when designing gas pipelines of all pressures for industrial, agricultural and municipal enterprises are taken depending on the gas pressure at the connection point, taking into account technical characteristics accepted for installation, gas burners, automatic safety devices and automatic control of the technological regime of thermal units.

4. Hydraulic calculations of medium and high pressure gas pipelines throughout the entire area of turbulent gas movement should be made according to the formula:

where: P_1 - maximum gas pressure at the beginning of the gas pipeline, MPa;

P_2 - the same, at the end of the gas pipeline, MPa;

l is the estimated length of a gas pipeline of constant diameter, m;

d_i - internal diameter of the gas pipeline, cm;

theta - coefficient of kinematic viscosity of gas at a temperature of 0°C and a pressure of 0.10132 MPa, m2/s;

Q - gas consumption under normal conditions (at a temperature of 0°C and a pressure of 0.10132 MPa), m3/h;

n - equivalent absolute roughness inner surface pipe walls, taken for polyethylene pipes equal to 0.002 cm;

po - gas density at a temperature of 0°C and a pressure of 0.10132 MPa, kg/m3.

5. Pressure drop in local resistances (tees, shut-off valves etc.) can be taken into account by increasing the estimated length of gas pipelines by 5-10%.

6. When performing hydraulic calculations of gas pipelines using the formulas given in this section, as well as using various methods and programs for electronic computers compiled on the basis of these formulas, the diameter of the gas pipeline should first be determined using the formula:

(2)

where: t - gas temperature, °C;

P_m - average gas pressure (absolute) at the design section of the gas pipeline, MPa;

V - gas speed m/s (accepted as 7 m/s for low pressure gas pipelines, 15 m/s for medium pressure and 25 m/s for high pressure gas pipelines);

d_i, Q - the designations are the same as in formula (1).

The obtained value of the gas pipeline diameter should be taken as the initial value when performing hydraulic calculations of gas pipelines.

7. To simplify calculations for determining pressure losses in polyethylene gas pipelines of medium and high pressure, it is recommended to use the one shown in Fig. 1 nomogram developed by the VNIPIGazdobycha and GiproNIIGaz institutes for pipes with a diameter from 63 to 226 mm inclusive.

Calculation example. It is required to design a gas pipeline with a length of 4500 m, a maximum flow rate of 1500 m3/h and a pressure at the connection point of 0.6 MPa.

Using formula (2), we first find the diameter of the gas pipeline. It will be:

We accept the nearest larger diameter according to the nomogram; it is 110 mm (di=90 mm). Then, using the nomogram (Fig. 1), we determine the pressure loss. To do this, draw a straight line through the point of a given flow rate on the Q scale and the point of the resulting diameter on the d_i scale until it intersects with the I axis. The resulting point on the I axis is connected to a point of a given length on the l axis and the straight line continues until it intersects with the axis. Since the l scale determines the length of the gas pipeline from 10 to 100 m, for the example under consideration we reduce the length of the gas pipeline by 100 times (from 9500 to 95 m) and the corresponding increase in the resulting pressure drop is also 100 times. In our example, the value 106 will be:

0.55 100 = 55 kgf/cm2

We determine the value of P_2 using the formula:

A negative result means that pipes with a diameter of 110 mm will not provide transport of a given flow rate of 1500 m3/h.

We repeat the calculation for the next larger diameter, i.e. 160 mm. In this case, P2 will be:

= 5.3 kgf/cm2 = 0.53 MPa

Received positive result means that the project requires laying a pipe with a diameter of 160 mm.

Rice. 1. Nomogram for determining pressure loss in polyethylene gas pipelines of medium and high pressure

8. The pressure drop in low-pressure gas pipelines should be determined using the formula:

(3)

where: N - pressure drop, Pa;

n, d, theta, Q, rho, l - the designations are the same as in formula (1).

Note: for aggregated calculations, the second term indicated in brackets in formula (3) can be neglected.

9. When calculating low-pressure gas pipelines, the hydrostatic head Hg, mm water column, should be taken into account, determined by the formula:

where: h is the difference in absolute elevations of the initial and final sections of the gas pipeline, m;

po_a - air density, kg/m3, at a temperature of 0°C and a pressure of 0.10132 MPa;

ro_o - the designation is the same as in formula (1).

10. Hydraulic calculations of ring gas pipeline networks should be performed by linking gas pressures at the nodal points of the calculation rings with maximum use of the permissible gas pressure loss. The discrepancy between pressure losses in the ring is allowed up to 10%.

When performing hydraulic calculations of overhead and internal gas pipelines, taking into account the degree of noise created by the movement of gas, gas movement speeds should be taken within 7 m/s for low-pressure gas pipelines, 15 m/s for medium-pressure gas pipelines, 26 m/s for gas pipelines high pressure.

11. Considering the complexity and labor intensity of calculating the diameters of low-pressure gas pipelines, especially ring networks, it is recommended to carry out this calculation on a computer or using known nomograms to determine pressure losses in low-pressure gas pipelines. A nomogram for determining pressure losses in low-pressure gas pipelines for natural gas with rho = 0.73 kg/m3 and theta = 14.3 106 m2/s is shown in Fig. 2.

Due to the fact that the indicated nomograms were compiled for the calculation of steel gas pipelines, the obtained diameter values, due to the lower coefficient, the roughness of polyethylene pipes, should be reduced by 5-10%.

Rice. 2. Nomogram for determining pressure losses in low-pressure steel gas pipelines

APPENDIX 11
(informative)