Assessment of hydraulic efficiency and duration of residual service life of metal water supply pipelines

. Substantiation of the necessity to develop projects of reconstruction of non-wood metal water supply pipelines, which have been in operation for a long time, including in the far north regions. Development of methodology of estimation of hydraulic efficiency and duration of residual service life of metal pipes depending on the thickness of the actual layer of deposits on their inner walls. Methods. It is proposed to estimate the period of residual use of steel and gray cast iron pipes by the value of the coefficient of efficiency of their operation. Outcomes. The study allows us to determine the values of the coefficient of efficiency of the use of the pipeline, assembled from steel and gray cast iron pipes, characterizing the residual duration and hydraulic efficiency of its operation. We obtained a formula for determining the coefficient of hydraulic efficiency of metal water supply pipelines, which is the ratio of values of actual characteristics of the hydraulic potential of non-metal pipes at the moment of evaluation to the values of these characteristics for steel and gray cast iron pipes. Practical Relevance. The developed methodology is recommended for use in determining the possibility of extending the period of further use of worn metal water supply pipelines, as well as for predicting the duration of their residual operating life.


Introduction
The peculiarity of water supply pipelines made of steel and gray cast iron, including in the conditions of the far north, is the possibility of their inner surface being covered with deposits in the process of long-term operation. The thickness of the formation of a layer of deposits on the inner walls of steel and gray cast iron pipes depends on the physical and chemical composition of the transported water, the mode of its pressure on the pipes, and the age of the pipeline. It has been established that the lower the flow rate, the greater the thickness of the layer of deposits. [1,2] The authors have found that the thickness of the actual layer of deposits on the inner walls of the pipes affects the values of the characteristics of the hydraulic potential of the water supply pipeline. In this case, the values of actual inner diameter change-d vn f , the actual speed of a stream of liquid -V f and actual losses of head-on resistance along the length-i f [4,5].
Therefore, the use of the reference book "Tables for hydraulic calculation of water pipes" by F. A. Shevelev for hydraulic calculation of pipelines made of non-wood metal pipes of steel and gray cast iron leads to an error in the calculation of actual head losses along the length, which may reach more than 80% [6,7].
The calculation error of the head loss values along the length of the pipeline, in turn, leads to errors in the selection of pumping equipment used to transport water to the consumer, and therefore to an overestimation of the cost of 1 m 3 of water [8,9].
While operating of water supply pipelines made of metal pipes and predicting the period of their residual use, it is necessary to monitor the values of the actual thickness of the layer of internal deposits Δ f , which changes during the life cycle of "Operation" [10].
Therefore, substantiation of the necessity of developing projects of reconstruction of metal water supply pipelines must be made based on analysis of values, values of coefficients of efficiency of steel and gray cast iron pipes Kef, which expert evaluation is used to determine the actual values of characteristics of the hydraulic potential of pipes and justification of the need to develop projects of reconstruction of pipelines.

Outcomes
An efficient pipeline made of metal pipes is the pipeline that has the minimum values of the actual head losses on the resistance about the length of hf. Actual losses hf depend on the actual hydraulic slope and the length of the pipeline. Losses of head-on resistance along the length significantly influence the value of energy consumption of pumping equipment, i.e. the value of actual characteristics of the hydraulic potential of pipelines. The hydraulic potential of metal water supply pipelines is characterized by the following parameters: d vn f -actual inner diameter of the pipes, m; V f -actual average flow velocity, m/s; i f -actual hydraulic slope, the value of which determines the actual friction loss along the length of the pipeline, m/m.
The head losses along the length of the pipeline h f in water pipes are determined by the formula: Where it is the actual hydraulic slope, which determines the head loss per unit length of the water pipeline; l is the length of the water pipe. Taking into account local head losses in fittings and fittings, which amount to 5-10% of the loss along the length, the total head loss is determined by the formula: The value of the actual hydraulic slope for non-metal (steel and cast-iron) pipelines operating in the quadratic region at Vf ³ 1,2 m/s is recommended to determine the formula of F.A. Shevelev [7,11]: Where Vf -design actual flow velocity, m/s, depending on the value of the actual inner diameter of the pipes d vn f taking into account the thickness of the layer of internal deposits on their walls Δ f .
For non-wooden steel and cast-iron water supply pipelines operating in the transition region at Vf<1.2 m/s F.A. Shevelev recommended the following formula [7]: The aggregate values of the characteristics of the hydraulic potential of non-wood metal pipes the coefficient of efficiency of water supply pipeline use Kef, characterizing the residual duration and hydraulic efficiency of its use, is determined: d vn f , V f , i f by the coefficient of efficiency of the use of the water supply pipeline K ef , which characterizes the residual duration and hydraulic efficiency of its use: Where: N dv f -the value of the actual energy consumption of pumping equipment at the time of the assessment, kWT; Where i f , d vn f , V f -values of the actual characteristics of the potential of unwound pipes at the time of the assessment; i p , d vn p -values of the design (passport) characteristics of the hydraulic potential of new pipes at the time the pipeline is put into operation; η-pump efficiency. For calculations, we take the value η=0,7. The value of the actual inner diameter d vn f , taking into account the thickness of the layer of internal deposits on the pipe walls, is determined by the formula: Where d n -outer diameter of the pipe, m; S p -standard wall thickness of the pipe, m; Δ f -actual thickness of the internal sediment layer, m. Actual (average) speed of liquid flow V f m/s is determined by the formula: Where q-given flow rate, m 3 /s Taking into account the value of the actual inner diameter d vn f ,and the actual speed of the fluid flow V f formulas (3) and (4) take a form: Based on the values of the coefficient of hydraulic efficiency Kef, an expert assessment of the duration of the remaining use of the metal water pipeline is made and the order of replacement of pipes that have reached the limit state is set.
Four zones of variation of Kef values, which characterize the efficiency of the use of unworn metal pipelines, have been established: The first zone: 0.95 ≥ Kef ≤ 1-the zone of effective use of the pipeline with the minimum values of the actual hydraulic slope if.
The pipeline is subject to further use. The second zone: 0,90≥Kef ≤ 0,95-the zone of energy-consuming use of the pipeline, characterized by increased values of the value of the actual hydraulic slope if. Further use of the pipeline is energy-consuming. Development of the project of pipeline reconstruction is required.
The third zone: Kef≤0,90-zone of inexpedient use of the pipeline with unacceptable values of the actual hydraulic slope if. Further use of the pipeline is inexpedient. It is necessary to reconstruct the pipeline and replace it with a new one with substantiation of pipe material choice [13,14].
The fourth zone: Kef ≫1-zone of unacceptable use of the pipeline. Decommissioning of the pipeline and re-laying not new is required [15].

Conclusions
Grounding upon numerous studies, the authors proposed a methodology for assessing the hydraulic efficiency of metal water pipelines. The dependence of the period of residual use of metal pipes on the thickness of the actual layer of internal deposits is shown. The method of hydraulic prognostication of the period of remaining used of metal pipelines made of steel and grey cast iron comes to a stage-by-stage evaluation of values of characteristics of the hydraulic potential of pipes if, d vn f and Vf, which are included in the calculated dependence for determining the value of Kef To substantiate the necessity of developing renovation projects for metallic pipelines made of steel and gray cast iron, it is necessary to estimate the duration of their residual use based on hydraulic forecasting methodology, which provides: account the actual thickness of the layer of internal sediments measured by the instrument f; -Calculation of the values of design characteristics of the hydraulic potential for new pipes i p , d vn f , V f taking into account the values f.
-Calculation of actual characteristics of the hydraulic potential of the operating metal pipeline-if, d vn f , Vf -Expert prediction of the duration of the residual use of metal water supply pipelines by the value of the coefficient of efficiency of use Kef.