Causes and consequences of changes in the values of hydraulic characteristics of metal water supply and sanitation networks during their operation
- Authors: Prodous O.A.1, Shlychkov D.I.2, Yakubchik P.P.3
-
Affiliations:
- INKO-Engineering LLC
- Moscow State University of Civil Engineering
- St. Petersburg State University of Railways of Emperor Alecsandr I
- Issue: Vol 13, No 3 (2023)
- Pages: 42-49
- Section: WATER SUPPLY, SEWERAGE, CONSTRUCTION SYSTEMS FOR PROTECTION OF WATER RESOURCES
- URL: https://journals.eco-vector.com/2542-0151/article/view/611060
- DOI: https://doi.org/10.17673/Vestnik.2023.03.06
- ID: 611060
Cite item
Abstract
Purpose: It consists in carrying out a comparative analysis of the values of the characteristics of the hydraulic potential of metal pipelines used in assessing the energy consumption of pumping units installed on pipelines with different thickness of the layer of internal deposits.
Methods: The reasons for changing the values of hydraulic characteristics of metal pipelines during their operation are developed in tabular form. A concrete example shows the change in the values of the characteristics of the hydraulic potential of pipes with different thickness of the layer of internal deposits included in the calculated dependence for determining the actual energy consumption of pumping units.
Results: It is proposed to develop for the entire range of manufactured steel pipes and pipes made of gray cast iron, a scale of maximum permissible values of the thickness of the layer of internal deposits, according to which a decision should be made to continue or stop the operation of pipe wires.
Conclusion: To recommend, based on the hydraulic calculation of the characteristics of the hydraulic potential of pipes for the given example, minimizing the use of steel and cast iron pipes made of gray cast iron in projects of water supply and drainage networks. When operating metal pipelines, take into account the dynamics of changes in the energy consumption of pumping units with different thickness of the layer of internal deposits.
Full Text
Introduction
During their operation life cycle, water supply networks made of metal pipes (gray cast iron), as well as drainage networks made of any type of material, are subject to the formation of a layer of internal deposits on the pipe walls under certain conditions, which change the values of the characteristics of the hydraulic potential of the pipes (V, din, i) [1–6].
Figure 1 presents fragments of deposits on the inner surfaces of metal water supply and wastewater networks.
Fig. 1. Fragments of internal deposits on the walls of metal pipes. a,b – Pressure drainage networks; c,d – gravity drainage networks
A layer of internal deposits on the walls of pipes causes consequences that change the values of the characteristics of the hydraulic potential of pipes and affect the duration of use of worn-out networks and the energy consumption of pumping units for pressure networks and collectors [1, 2].
Table 2 lists the causes and consequences of changes in the hydraulic characteristics of water supply and wastewater pipelines with internal deposits.
Fig. 2. Causes and consequences of changes in the hydraulic characteristics of water supply and wastewater pipelines
Methods
Using a specific example (Fig. 1), we perform a hydraulic calculation and show changes in the values of the characteristics of the hydraulic potential of a pressure drainage collector made of cast iron pipes with a diameter dn of 0.404 m.
Problem
A pressure cast iron collector with a diameter dn of 0.404 m (GOST 9583-75) and a wall thickness Sp of 12.5 mm (0.0125 m) pumps wastewater flow q of 140 l/s (0.14 m3/s). The thickness of the layer of internal deposits σ is 25 mm (0.025 m).
We calculate and compare the values of the actual characteristics of the hydraulic potential of pipes , , and and new cast iron pipes with a diameter of 0.429 m. Here, we present the change in the energy consumption of the pumping unit for the given conditions of the problem.
Solution
- Accounting for the actual internal diameter, we calculate the average flow velocity Vn for new cast iron pipes and pipes with a deposit layer thickness σ of 25 mm as follows:
m/s;
m;
m;
m/s.
- The values of the hydraulic slope are calculated for new cast iron pipes dn and for pipes with a layer of deposits σ of 0.025 m. The calculation was made using the following equations [7, 8]:
, m/m;
m/m;
m/m.
The changes in the actual values of the hydraulic characteristics of cast iron pipes din of 0.404 m with different thicknesses of the layer of internal deposits of 0 ÷ 30 mm (0 ÷ 0.03 m) are given in Table 1.
Table 1
Deposited layer thickness σ (m) | Actual average velocity Va (m/s) | Actual internal diameter of pipes with deposits (m) | Actual specific pressure loss 1000 ia | Pipeline hydraulic efficiency coefficient |
0 | 1.24 | 0.379 | 5.81 | 1.0 |
0.005 | 1.31 | 0.369 | 6.71 | 0.87 |
0.01 | 1.38 | 0.359 | 7.72 | 0.76 |
0.018 | 1.52 | 0.343 | 9.94 | 0.58 |
0.02 | 0.55 | 0.339 | 10.49 | 0.56 |
0.03 | 2.47 | 0.319 | 28.83 | 0.14 |
According to the authors, the operating efficiency of pressure and nonpressure water supply and wastewater pipelines (K*eff) should be assessed using the value of the dimensionless coefficient of the hydraulic efficiency of pipelines, which is the ratio of the energy consumption of pumping equipment installed in the new pipeline to the value of energy consumption in the pipeline with the actual thickness of the deposit layer – or the ratio of the product of the values of the characteristics of the hydraulic potential of new pipes ( , , and ) to the product of the values of the same characteristics for pipes with a specific thickness of the deposit layer σa on their inner surface [9]:
, (1)
where is the rated value of the energy consumption of the pumping unit in the new pipeline (kW/h); is the actual value of energy consumption of a pumping unit operating in a pipeline with a deposit layer thickness σa (kW/h); , , and are the values of the calculated (certified) characteristics of the hydraulic potential of new pipes at the time of putting the pipeline into operation; and , , and are the values of the actual characteristics of the hydraulic potential of worn pipes with deposits at the time of assessment.
The limiting value of the layer thickness of internal deposits σ in Table 1 is presented in bold.
The analysis of the values of hydraulic characteristics presented in Table 1 revealed the following.
For the conditions of the given example, the values of the actual internal diameter of a pipe with internal deposits of different thicknesses decreased from a din of 0.400 m (pipe without deposits) to a of 0.319 m (pipe with a layer of deposits σ = 0.03 m, i.e., by 15.83% or 1.19 times). This resulted in an increase in the flow speed from V = 1.24 m/s (in a new cast iron pipe) to Va = 2.47 m/s (in a pipe with a deposited layer of σ = 0.03 m), that is, by 49.8% or 1.99 times.
Under these conditions, in comparison with a new pipe, the values of the actual pressure loss due to resistance along the length (hydraulic slope) ia increased in the range ip = 0.00581 m/m ≤ ia ≤ 0.02883 m, that is, by 51.29% (pipe with a layer of deposits σ = 0.03 m) or by 4.96 times.
According to Table 1, a graph of the dependence = f(σ) is plotted in Figure 3, confirming that the smaller the value of the actual internal diameter in pipes with a deposited layer σ, the greater the value of the hydraulic slope ia and the greater the value of the actual flow velocity Va. This was also confirmed by the values of the hydraulic efficiency coefficient of the pipeline Keff, which, for the given example, characterized the influence of the layer thickness of internal deposits σ on the values of the pipeline hydraulic characteristics.
Fig. 3. Dependency graph ia = f(σ)
For the given example, we determined the limit value of σ, above which further operation of the pipeline is unacceptable—0.018 m (Table 1). That is, at σa of 0.018 m, the pipeline must be decommissioned.
An expert assessment by specialists involved in the operation of water supply networks made of metal pipes recommends the following:
The decrease in the actual internal diameter of steel and cast iron pipes (made of gray cast iron) with internal deposits should not exceed 5% of the nominal internal diameter of the pipes; that is,
For the example given, this corresponds to
m.
Therefore, for the given example, the limiting value of the actual thickness of the deposit layer σa should not exceed the value
= 0.379 − 0.360 = 0.018 m (1.8 mm).
This is indicated in bold in Table 1.
In this case, the limiting value of the pipeline hydraulic efficiency coefficient Keff is as follows:
This proves that with a value Keff of 0.58, further operation of the pressure manifold with a diameter dn of 0.404 m is unacceptable.
For the conditions of the problem considered, we calculated the actual energy consumption of pumping equipment installed on a pressure manifold with a diameter dn of 0.404 m and an internal deposit layer thickness σa of 0.03 m (30 mm).
The methodology for calculating the energy consumption values of pumping and power equipment has been presented in previous studies [2, 9].
The value of for the conditions of the given example was calculated using the following equation [9, 10]:
, kW/h, (2)
where is the value of energy consumption of pumping equipment in the new (p) and worn-out (a) pipelines at the time of assessment (kW/h); , , and are the values of the characteristics of the hydraulic potential of new (р) and worn-out (a) pipes with a deposited layer thickness σ; and η is the pumping unit efficiency. For the calculations, the value η was taken as 0.7.
Table 2 presents the energy consumption values of the pumping units installed in a new pipeline and in a pipeline with different thicknesses of the layer of internal deposits σф.
TABLE 2. Energy consumption of pumping units
Actual inner diameter of pipes (m) | Actual thickness of the internal layer of deposits σa (m) | Actual energy consumption of pumping units (kW/h) |
0.379 | 0 | 11.94 |
0.369 | 0.005 | 13.81 |
0.359 | 0.010 | 15.84 |
0.343 | 0.018 | 20.51 |
0.339 | 0.020 | 21.56 |
0.319 | 0.030 | 83.62 |
The graph presented in Figure 4 for the given example confirms the change in energy consumption of the pumping units and shows that the greater the thickness of the deposit layer σ, the greater the energy consumption of the pumping units (Table 2). With a value of 0.018 m, the actual value of the energy consumption of the pumping units installed in a pipeline with a diameter of 0.404 m increased sharply. This means that during the operation of pressure collectors made of cast iron pipes, the actual values of the layer thickness of internal deposits σф must be controlled.
Fig. 4. Dependency graph Nф дв = f(σф)
Conclusion
The analysis of the graphs presented in Figs. 3 and 4 enables us to draw the following conclusions:
- For the entire range of steel and cast iron pipes (from gray cast iron) produced following GOST, a scale of limit values of the permissible thickness of the layer of internal deposits σ must be developed to regulate the further operation of pipelines.
- The use of steel and gray cast iron pipes when developing projects for water supply and wastewater networks should be minimized by law.
- A method for monitoring the actual layer thickness of internal values σa during the operation of pipelines made of metal pipes should be developed.
- Based on the thickness of the deposited layer σ, a legislative method should be developed to justify the need for hydrodynamic (mechanical) cleaning of pressure water supply and drainage networks from metal pipes.
- When selecting pumping units for metal water supply and sewerage networks, the dynamics of changes in the energy consumption of pumping units operating in pipelines with different thicknesses of the layer of internal deposits σф should be considered.
About the authors
Oleg A. Prodous
INKO-Engineering LLC
Author for correspondence.
Email: pro@enco.su
doctor of engineering science, professor, ceo
Russian Federation, 190005, St. Petersburg, Moskovsky pr., 37/1, lit. Ah, pom. 1-NDmitry I. Shlychkov
Moscow State University of Civil Engineering
Email: ShlyichkovDI@mgsu.ru
phd in engineering science, associate professor of the water supply and wastewater chair, deputy director of the institute of engineering and environmental construction and mechanization
Russian Federation, 129337, Moscow, Yaroslavl sh., 26, ULB, office 322gPetr P. Yakubchik
St. Petersburg State University of Railways of Emperor Alecsandr I
Email: P.Jakub@mail.ru
phd in engineering science, professor of the water supply and drainage and hydraulics chair
Russian Federation, 105187, St. Petersburg,Moskovsky pr., 9References
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