Investigations on Thickness of Deposits in PVC Pipes

Transcription

1 International Journal of Sustainable Civil Engineering (IJSCE) 3(1) Jan-June 2011; pp Research Science Press Investigations on Thickness of Deposits in PVC Pipes B.J.S. VARAPRASAD Associate Professor, Civil Engineering Department, G.pulla Reddy Engineering College, Kurnool, India, G.K. VISHWANADH Professor of Civil Engineering, J. N. T. University, Hyderabad, India, Abstract: The various dissolved particles like salts, present in flowing water, generally tend to deposit on the inner walls of the pipe. In the case of domestically used PVC pipes of small diameters, the thickness of deposition on the inner walls of the pipe varies considerably with water quality parameter such as hardness, flow characteristics such as water pressure and velocity and also the usage(age) of the pipe. A series of laboratory experiments was carried out to observe the thickness of deposit formation against hardness of water, water pressure/velocity and age of the pipe. The observations for the thickness of deposits were made against each parameter separately by keeping the constant values of other two parameters. From the experimental investigations, it was concluded that the deposit formation (thickness) increases with increase in hardness of water and age of the pipe, whereas it decreases with increase in water pressure/velocity. The thickness of deposit formation in all the cases shows a linear variation. Further a multiple linear regression equation was established for the thickness of deposition in terms of three variable parameters. A comparison is also made between experimental and field observations. The experimental results are in good agreement with the field data. 1. INTRODUCTION The use of plastic pipes has increased tremendously in the recent past for water supply and distribution systems both in domestic and irrigation front. This helped in replacing the conventional pipes and proved to be helpful to overcome most of the difficulties being felt by water supply engineers. Such replacements have also proved to be economical both in installation as well as long range operations. Practical observations in the case of domestic pipes reviewed the presence of certain deposits on the inner walls of the pipes over a period of usage. This problem increases when the fluid of appreciable hardness flows for a considerable period of time. This phenomenon will render the PVC pipes less useful when the hardness or salinity of the water flowing in the pipes is high. Though, considerable amount of research work is reported regarding the friction factor studies, the causes for the deposit formation have not been reported in literature. In this context it becomes necessary to investigate the reasons for this deposit formation and the thickness of deposits. It has been observed practically that when water, especially ground water, flows in a PVC pipe, the salts and various dissolved particles present in water, generally tend to deposit on the

2 26 / INTERNATIONAL JOURNAL OF SUSTAINABLE CIVIL ENGINEERING (IJSCE) inner walls of the pipe. Such deposits may strengthen over a period of time, thus hindering the flow as well as friction factor and eventually even close the pipe completely. Thus in the case of PVC pipes, it is observed that as the usage increases, the diameter of the pipe is getting reduced because of the deposits that are taking place along the inner walls of the pipes. In the coastal regions, where the water is saline in nature, the deposits have occupied the entire area of cross section of the pipe because of which the entire pipe system had to be replaced. (V.V. Nageswara Rao, 2004). PVC and Iron pipe materials differentially impacted manganese deposition with in a drinking water distribution system that experiences black water problems. Water samples obtained from PVC pipes showed higher total Mn concentrations and more black color than that obtained from iron pipes. The PVC pipes contained a thin surface scale consisting of white and brown layers of different chemical composition; the brown layer was in contact with the water and contained 6% manganese by weight. Mn composed a greater percentage by weight of the PVC scale than the iron pipe scale; the PVC scale was easily dislodged by flowing water. (Cerrato JM., et al. 2006). It has been studied that, the effect of stagnation time, pipe age, pipe material and water quality parameters such as ph, Alkalinity and chloride to sulfate mass ratio on lead and iron release from different types of water pipes used in Egypt. The different types of pipe materials used are polyvinyl Chloride (PVC), Polypropylene (PP) and Galvanized iron (GI). It is found that lead and iron release increased then this release decreased with time. In general, GI pipes showed to be the most effected by water quality parameters tested and the highest iron release. PVC pipes are the most lead releasing pipes while PP pipes are the least releasing. (Lasheen MR., 2008). The present study is aimed to investigate the thickness of deposition against each factor influencing it separately and establishing a combined equation for the thickness of deposition in terms of all the parameters. 2. SCOPE AND OBJECTIVES The deposit formation is the major problem in the case of domestically used PVC pipes. Hence it becomes necessary to investigate the reasons for the deposit formation. The probable reasons are assumed to be the hardness of water, velocity or pressure of flowing water and also the usage (age) of the pipe. If these reasons are investigated and modeled, the criterion for avoiding the formation of these deposits can be suggested. The specific objectives of the present study are 1. Observing the effect of hardness of water, velocity/pressure of flowing water and age of the pipe separately on the deposit formation. 2. Establishing the relationships between the thickness of deposition and all the factors influencing the formation of deposits.

3 INVESTIGATIONS ON THICKNESS OF DEPOSITS IN PVC PIPES / Establishing the combined equation for the thickness of deposition in terms of variable parameters. 4. Comparing the experimental results with the field data. To achieve the objective no. 1, the experiments have been conducted and the data obtained from the experiments has been analyzed to get the remaining objectives. 3. METHODOLOGY Experiments have been carried out in the Fluid Mechanics and Hydraulic Machinery Laboratory of Civil Engineering Department, G. Pulla Reddy Engineering College, Kurnool by fabricating and installing the experimental setup. The experimental setup consists of PVC pipe under study, 3 meters long placed horizontally at 1. 5 meters height from the ground level. It consists of Two MS tanks of dimensions m one of which is attached with Half HP motor which pumps the water through the PVC pipe steadily, without any fluctuations. Water has been re-circulated from one tank to the other through the bottom pipe. A pressure gauge is fixed at the beginning of the pipe under study to monitor the pressure in the pipe. The Experimental Setup was assembled using PVC Pipe, Electrical Motor, Tanks, Pressure Gauge and Valves as shown in the Figure i. Figure i: Experimental Setup (Not to Scale)

4 28 / INTERNATIONAL JOURNAL OF SUSTAINABLE CIVIL ENGINEERING (IJSCE) The details of pipe characteristics used in the experimental setup are as follows: Type of PVC pipe used Colour of the pipe Internal diameter of the pipe External diameter of the pipe Initial thickness of the pipe : NANDI make : Blue : 25.40mm : 32.00mm : 3.30mm The details of flow characteristics are as follows: Total quantity of water used in experiments : 1000 lit (1 cu-m) Range of hardness of water : 300 mg/lit to 1200 mg/lit as CaCO 3 Range of water pressure : 0.2 kg/cm 2 to 2.0 kg/cm 2 Range of age of the pipe Type of flow : 6 months to 60 months : Turbulent 4. CALCULATION OF THICKNESS OF DEPOSITION From the experimental observations the thickness of deposition formed is calculated by considering the weight of the pipe per unit length with respect to initial thickness of the pipe. (B.J.S. Varaprasad et.al, 2010). The thickness of deposition is given by t = [(W o /W i ) 1]t i where t = thickness of deposition in mm t i = initial thickness of the pipe in mm W i = initial weight of the pipe per unit length in gms/cm W o = observed weight of the pipe per unit length in gms/cm 5. OBSERVATIONS The investigations were made for the thickness of deposition against the hardness of water, pressure/velocity of flowing water and the age of the pipe from the experimental observations. There are 3 sets of observations, one for each parameter. Observation 1: Study of thickness of deposition against hardness of water. The hardness of water due to the presence of salts is the major factor influencing the deposit formation. Hence the observations were made for deposit formation by increasing the hardness of water artificially. The hardness of water has been increased artificially by adding some dissolved salts such as Calcium Chloride (CaCl 2 ), Magnesium Chloride (MgCl 2 ) and Magnesium Sulphate (MgSO 4 ).

5 INVESTIGATIONS ON THICKNESS OF DEPOSITS IN PVC PIPES / 29 In this case the thickness of deposition was measured against the hardness of water ranging from 300mg/lit to 1200mg/lit. The other two parameters viz., water pressure (1.0 kg/ cm 2 ) and age of the pipe (6 months) were kept constant. The thickness of deposition has been increased linearly with increase in the hardness of water. The observations were tabulated in Table (1). The variation of thickness of deposition against hardness of water is shown in Figure (1). The linear equation for the thickness of deposition, y(in mm) in terms of hardness of water, x(in mg/lit) is given by y = 0.001x (1) Table 1 Observations for Thickness of Deposition with Hardness of Water (Age of the pipe and water pressure as constant) Age of the pipe = 6 Months; Water pressure = 1.0kg/cm 2 Si.No Hardness of water(mg/lit) Thickness(mm) Figure 1: Variation of Thickness of Deposition Against Hardness of Water Observation 2: Study of thickness of deposition against water pressure/velocity. The thickness of deposition decreases linearly with increase in pressure/velocity of flowing water. Hence the observations were made for deposit formation by varying the water pressure.

6 30 / INTERNATIONAL JOURNAL OF SUSTAINABLE CIVIL ENGINEERING (IJSCE) In this case the thickness of deposition was measured against the water pressure ranging from 2.0 kg/cm 2 to 0.2kg/cm 2. The other two parameters viz., hardness of water (1000 mg/ lit) and age of the pipe (6 months) were kept constant. The observations were tabulated in Table (2). The variation of thickness of deposition against water pressure is shown in Figure (2). The linear equation for thickness of deposition, y(in mm) in terms of water pressure, x(in kg/cm 2 ) is given by y = x (2) Table 2 Observations for Thickness of Deposition with Water Pressure (Age of the Pipe and Hardness of Water as Constant) Age of the Pipe = 6 Months; Hardness of Water = 1000mg/lit Si.No Water pressure (kg/cm 2 ) Thickness(mm) Figure 2: Variation of Thickness of Deposition Against Water Pressure Observation 3: Study of thickness of deposition against age of the pipe. The thickness of deposition increases linearly as the period of usage (age) of the pipe for the constant values of hardness and pressure. Hence the observations were made for deposit formation by increasing the usage of the pipe.

7 INVESTIGATIONS ON THICKNESS OF DEPOSITS IN PVC PIPES / 31 In this case the thickness of deposition was measured against the age of the pipe ranging from 6 months to 60 months. The other two parameters viz., hardness of water (1000 mg/lit) and water pressure (1.0 kg/cm 2 ) were kept constant. The observations were tabulated in Table (3). The variation of thickness of deposition against the age of the pipe is shown in Figure (3). The linear equation for thickness of deposition, y(in mm) in terms of age of the pipe x(in months) is given by y = x (3) Table 3 Variation of Thickness of Deposition with Age of the Pipe (Hardness of water and water pressure as constant) Hardness of water = 1000mg/lit; Water pressure = 1.0kg/cm 2 Si.No Age of the pipe (Months) Thickness (mm) Figure 3: Variation of Thickness of Deposition Against Age of the Pipe

8 6. COMBINED EQUATION 32 / INTERNATIONAL JOURNAL OF SUSTAINABLE CIVIL ENGINEERING (IJSCE) From the experimental observations for the thickness of the deposition against each parameter, by using multiple linear regression analysis, a combined equation was established in terms of three variable parameters. The combined equation is given by where y = thickness of deposition in mm. y = x x x x 1 = hardness of water in mg/lit as CaCO 3 x 2 = water pressure in kg/cm 2 x 3 = age of the pipe in months 7. COLLECTION OF FIELD DATA To compare the experimental results with the field observations, the samples of domestically used PVC pipes were collected from different locations of Kurnool city. A total no. of 8 pipe samples were collected from the existing pipe networks and the thickness of deposit formation was measured for each pipe. The data regarding hardness of water in the locations, where the pipe samples collected is obtained from the O/o Deputy Director, A.P. Ground Water Department, Kurnool. The field observations were tabulated in Table (4). By using the combined equation, the thickness of deposition was calculated for all the pipes from the field data. While calculating the thickness, the pressure values for all the samples are assumed as 1.0kg/cm 2 (constant). The calculated values are tabulated in Table (5). These calculated values of thickness are compared with the actual (measured) values. The comparison of experimental results with the field observations is mentioned in Table (5). Table 4 Field Observations Si.No. Location Hardness of Diameter of the Age of the Thickness of water (mg/lit) pipe (mm) pipe (years) deposition (mm) 1 Muzafar Nagar Chenchu Nagar Kallur Village Santhosh Nagar State Guest House Prakash Nagar C-Camp Joharapuram

9 INVESTIGATIONS ON THICKNESS OF DEPOSITS IN PVC PIPES / 33 Table 5 Comparison of Experimental Results with the Field Observations Si.No. Location Hardness of Age of the Thickness of water (mg/lit) pipe (years) deposition (mm) Calculated Observed 1 Muzafar Nagar Chenchu Nagar Kallur Village Santhosh Nagar State Guest House Prakash Nagar C-Camp Joharapuram RESULTS AND CONCLUSIONS 1. In the case of domestically used PVC pipes, the rate of increase of thickness of deposits is directly proportional to the hardness of water and the age of the pipe and inversely proportional to the water pressure. 2. For every 100mg/lit increase of water hardness, the thickness of deposits increases by 0.104mm over a constant time period and water pressure. 3. For every 6 months period of usage, the increase in the thickness of deposits is 0.818mm at constant pressure and hardness. 4. At every 0.1kg/cm 2 decrease in water pressure with constant hardness of water over a period of 6 months, the thickness of deposits increases by 0.102mm. 5. From the multiple linear regression equation, for the given values of pressure and hardness of flowing water at any stage of usage the thickness of deposition (in mm) can be determined. 6. The experimental results are in good agreement with the field data. References [1] V.V. Nageswara Rao and G.K. Vishwanath, Variation of Hydraulic Loss Coefficient in PVC Pipes, Conference on Hydraulics and Water Resources, HYDRO 2004, pp [2] Cerrato JM., et al. Effect of PVC and Iron Materials on Mn(II) Deposition in Drinking Water Distribution Systems, Journal of Water Resources, 2006 Aug, 40(14): [3] Lasheen MR., et al., Factors Influencing Lead and Iron Release from Some Egyptian Drinking Water Pipes, Journal of Hazard Mater, 2008 March 20. [4] B.J.S.Varaprasad., et al. Deposit Formation in Domestically used PVC Pipes: A Scientific Study, Journal of Indian Water Works Association, Jan-Mar 2010, XXXXII, No.1, pp &