Grey Cast Iron Pipes Research Articles

Identifying key pipe attributes and locations to best determine chlorine decay coefficients within a water distribution system

Abstract Water distribution system (WDS) characteristics can impact drinking water quality. Kinetic reaction coefficients of residual disinfectant associated with bulk water (kb) and pipe wall (kw) during water distribution can lead to water quality degradation. Determining these coefficients can be expensive and time-consuming. The main objective of this study is to determine the most relevant pipe characteristics and locations to best determine chlorine decay coefficients in a WDS. This article aims to evaluate various scenarios of kb and kw values and compare them to measured data in a full-scale WDS. The most accurate scenario is also compared with the lowest-cost scenario to identify the most effective information needed to determine these coefficients, in terms of location within the WDS and pipe characteristics (age, diameter, and material). Results showed that the scenario with the highest kw and kb values corresponds best to the field-measured data. Moreover, determining specific kinetic coefficients was shown to be more accurate for gray cast iron pipes, pipes installed in a period before 1960, and vulnerable zones for residual chlorine decay.

Repair Welding of Broken Gray Cast Iron Pipes Instead of Applying Lock-Stitching Method

Repair Welding of Broken Gray Cast Iron Pipes Instead of Applying Lock-Stitching Method

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.

Предотвращение вторичного загрязнения питьевой воды в металлических сетях водоснабжения

Introduction. The requirements of current regulatory documents guarantee the quality of drinking water leaving water treatment facilities (WTF). Hence, the water, coming into water supply networks, made of steel and cast iron pipes, made of gray-cast iron, is transported to consumers. Its quality must meet the standards of GOST R (Russian National Standard) 51232-98 “Drinking water” and SanPiN (Sanitary Regulations and Norms) 1.2.3685-21 “Hygienic standards and requirements to ensure the safety and (or) harmlessness of habitat factors for people”. The aim of the study is to analyze methods of preventing secondary pollution of drinking water in water supply networks, made of metal, and to identify the most effective and practically grounded method. Materials and methods. The concepts of electrochemical corrosion and microbiological corrosion of the inner surface of pipes were used to perform the analysis. Three methods of preventing the formation of a layer of deposits on the inner surface of steel and gray cast-iron pipes are used in the practice of water treatment and disinfection of drinking water: the method of using strong oxidants, such as chlorine and sodium hypochlorite, for the disinfection of drinking water; the method of increasing the pH level of drinking water; the method of using chemicals to ensure the formation of a microscopic film on the surface of layers of deposits to “slow down” electrochemical and microbiological corrosion processes on the inner surface of pipes. Results. The authors have identified a method for preventing the secondary pollution of drinking water, time-tested by the twelve years of practical use by the operator of WTF and drinking water supply and distribution networks made of metal. Conclusions. The effectiveness of the method of preventing the secondary pollution of drinking water through the use of new generation reagents, made of polyhexamethyleneguanidine hydrochloride, has been proven in practice.

Case Studies in Graphitic Corrosion of Cast Iron Pipe

Throughout many parts of the world, cast iron pipe has been and continues to be used for utility piping (water and sewage) and gaseous media piping. Gray cast iron is known to have a limited life in service but is often left in place beyond its reasonable service life. Therefore, end of life is then left to be defined as a rupture or a crack and a subsequent leak, often at an unpleasant time with unpleasant results. The controlling mechanism involved is time dependent and known as graphitic corrosion. This paper provides a review of the phenomenon of graphitic corrosion in the form of key characteristics. Several references are cited that further explore the mechanism involved and corrosion prevention/mitigation. Two case studies are presented that explore graphitic corrosion in gray cast iron pipe from a failure analysis point-of-view. Both case studies feature conditions that further aid in the interpretation of graphitic corrosion and an appreciation for when and how this phenomenon occurs.

Surface Representation of Pulsed Eddy Current Sensor Signals for Improved Ferromagnetic Material Thickness Quantification

Pulsed eddy current (PEC) sensing is a nondestructive testing and evaluation technique widely used for detecting and quantification of flaws and properties of metallic test pieces. In recent years, the use of the technique for the assessment of ferromagnetic materials, specifically, for the purpose of thickness quantification of ferromagnetic plates, or wall-like structures, has risen. The detector coil-based PEC sensor architecture has been the most commonly used sensor architecture for the purpose. Recent works have demonstrated the effectiveness of the detector coil voltage decay rate for this purpose. The decay rate signal feature has been used to construct a linear functional relationship between thickness and the feature value. This functional relationship has eventually been used for thickness estimation. However, this method has proven to come with a limitation of accuracy in thickness estimates. Therefore, we present in this article a method for surface representation of PEC sensor signals. In this method, the thickness varies as a surface-like function in 3D, relying on two signal feature values provided as independent variables. We demonstrate how the surface representation yields a 2% improvement in accuracy (with respect to correlation coefficient) in previous results (i.e., thickness estimates) through a case-study of quantifying wall thickness of a gray cast iron pipe. Such an improvement in accuracy has significant cost-saving implications in the field of structural health monitoring, especially in managing critical pipes in sectors such as water and energy. Cost savings result by enabling infrastructure managers to optimize rehabilitation and thereby provide improved services.

Method for Determining the Probability of a Lack of Water Supply to Consumers

The water distribution subsystem is the most failing subsystem included in the water supply system. One of the main consequences of water supply failures is the lack of water supply to consumers, which is always very onerous. The paper presents a method of determining the conditional probability that a break in the supply of water to consumers of a certain duration will be caused by a specific type of failure. The result of the work was to identify water supply network failures that result in the longest water supply suspension time. The method was presented on a real water supply system. In order to reduce the incidence of long-term interruptions in water supply, water supply companies should mainly continue replacing gray cast iron pipes with thermoplastic materials. Actions taken to increase the safety of drinking water supply meet the current standards for the safety of drinking water, developed by the World Health Organization and the European Union.

송수관 유동 및 피로해석

In theory, the maximum allowable working pressure of cast iron, with flange specification PN10 and pressure rating KS B1501, is 1.0 ㎫. However, in reality, the maximum allowable pressure can be 1.3 ㎫ if the strength of the materials used and the stability of the bolted joints are considered. The stability of the flange part of a cast iron pipe was confirmed using function test analysis SPS-KWWA-D111. Next, a D900 (denotes pipe diameter) water pipe was modeled based on the combination of a steel pipe and gray cast iron pipe. Subsequently, the streamline, flow velocity, and pressure distribution, when the valve opened and closed based on the general pipe flow rate and discharge pressure, were calculated. Finally, fatigue analysis was performed using the pressure data for the pipeline, to confirm stability.

An Analysis of the Potential Impact of Climate Change on the Structural Reliability of Drinking Water Pipes in Cold Climate Regions

The climate is changing worldwide. For the northern hemisphere there are distinct challenges related to climate change. It is expected that temperature on a general basis will increase within the next 100 years, and that the increase will be most severe during winter months. The literature shows a correlation between temperature and failures. This correlation is most evident for smaller grey cast iron pipes, and for pipes which is constructed in trenches vulnerable to frost heave. A comprehensive amount of failure data (over 25,000 failures) has been gathered from Norwegian cities in order to quantify the correlation between temperatures and failure rates. The analysis supports the findings in the literature, by establishing a statistical significant correlation, which states that failure rates increase with falling temperatures. At the same time, the expected increase in future temperatures has been used to analyze the impact on failure rates within 2070. The results show that the increasing temperatures will have a positive effect on failure rates. It can be expected that failure rates will be reduced by 2.7% to 7.2% within 2070, depending on the climate scenario.

Wpływ wybranych czynników na intensywność uszkodzeń przewodów podsystemu dystrybucji wody, zlokalizowanych na terenie oddziaływania wstrząsów pochodzenia górniczego

The article presents the influence of the selected factors, including mining tremors, described by the parameter PGVHmax on the failure rate of the water distribution pipelines. In created multiple regression models, the following independent variables were used: diameter and material from which the pipes were made, operation time without failure, the age of pipes, the value of pressure and PGVHmax. The values of PGVHmax in places with damaged water pipelines were determined by constructed the seismic wave propagation models. The analysis was carried out for a random sample of all water pipelines and extracted from this sample new groups: steel and gray cast iron pipes, their diameters, diameters and materials, and their construction time.

Effect of Residual Chlorine Concentration on Water Pipe Corrosion

1. Introduction Water pipe corrosion corrodes the iron by the oxidation reduction reaction, and the corrosion rate is accelerated by the oxidizing agent used as disinfectant in the tap water. The major oxidizing agent in tap water are ozone and chlorine. pH, alkalinity and residual chlorine concentration are factors of internal corrosion. We are replacing the ductile cast iron pipe with inner coating and stainless steel pipe. However, it is still used in many cases, such as gray cast iron pipes and galvanized steel pipes without internal coatings in Korea. Chlorine is a very strong oxidant for all metals and organics, and the reaction between chlorine and iron is as follows. HOCl + 2Fe2+ + 5H2O → 2Fe(OH)3↓ + Cl- + 5H+ Recently, as the problem with sinkholes has arisen on the a buried road as water pipes, sewage pipes, etc, interest in corrosion has been growing. The purpose of this study is to evaluate the effect of residual chlorine on the corrosion factor by analyzing the water quality and to evaluate the necessity of the proper residual chlorine on in the water purification plant. 2. Experimental Method In order to evaluate the corrosion of residual chlorine concentration of tap water, we were carried out Tafel experiment and water quality analysis. The corrosion rate was measured by a Tafel experiment using an electrochemical corrosion measurement system (PAR VMP-3). For tap water in Seoul, corrosion evaluation was performed according to alkalinity and hardness, residual chlorine concentraion. 3. Summary of results The tap water quality of Seoul was as follows that residual chlorine is 0.4 mg/L, and alkalinity is 50 mg/L as CaCO3, with a pH of 7.3. The results of experiments on the rate of corrosion of Carbon Steel specimens to residual chlorine in seoul tap water, can be seen in Fig. 1. As a result of the Tafel experiment according to the initial residual chlorine concentration under the same conditions (same LI index), The corrosion rate was 0.01 mmpy at 0 mg/L of residual chlorine and 0.074mmpy at 0.8mg/L of residual chlorine, corrosion rate for residual chlorine in carbon steel specimens was more than 7 times. It was confirmed that the higher the concentration of residual chlorine, the faster the corrosion rate was increased. The corrosivity of tap water in Korea is evaluated by the LI index, but residual chlorine has a large effect on corrosion, so it is required to add residual chlorine for the tap water corrosion evaluation. It is reducing the concentration of residual chlorine for reduce the chlorine odor of tap water in the distribution water system in Korea. But, residual chlorine guideline for corrosion reduction is necessary in Korea. Figure 1

Effect of flushing on the detachment of biofilms attached to the walls of metal pipes in water distribution systems

Biofilm detachment caused by flushing can result in secondary contamination in drinking water distribution systems (DWDSs). To evaluate the impact of flushing on biofilm detachment, actual water supply pipes including ductile cast iron pipes (DCIPs), gray cast iron pipes (GCIPs), and stainless steel compound pipes (SSCPs) were used in this study. Real-time quantitative polymerase chain reaction and 454 pyrosequencing were used to quantify bacteria and analyse microbial community composition, respectively. The results showed that the pipe material greatly influences the resistance of a biofilm to flushing. Biofilms attached to DCIPs were able to resist quite strong flushing, while those attached to GCIPs and SSCPs were sensitive to flushing. Both flush-resistant and flush-sensitive bacteria were present in all the biofilms, but their frequency differed among the different metal pipes. Thus, the resistance to flushing of bacteria is related not only to the nature of the bacteria, but also to the pipe material. Although flushing can remove some of the biofilm and may be a good way to clean the DWDS, the shear stress needed to remove the biofilm differs among different pipe types. The results of this study provide technical support for the management and operation of DWDS.

Bacterial community radial-spatial distribution in biofilms along pipe wall in chlorinated drinking water distribution system of East China.

Biofilms in the pipe wall may lead to water quality deterioration and biological instability in drinking water distribution systems (DWDSs). In this study, bacterial community radial-spatial distribution in biofilms along the pipe wall in a chlorinated DWDS of East China was investigated. Three pipes of large diameter (300, 600, and 600mm) were sampled in this DWDS, including a ductile cast iron pipe (DCIP) with pipe age of 11years and two gray cast iron pipes (GCIP) with pipe ages of 17 and 19years, and biofilms in the upper, middle, and lower parts of each pipe wall were collected. Real-time quantitative polymerase chain reaction (qPCR) and culture-based method were used to quantify bacteria. 454 pyrosequencing was used for bacterial community analysis. The results showed that the biofilm density and total solid (TS) and volatile solid (VS) contents increased gradually from the top to the bottom along the pipe wall. Microorganisms were concentrated in the upper and lower parts of the pipe wall, together accounting for more than 80% of the total biomass in the biofilms. The bacterial communities in biofilms were significantly different in different areas of the pipe wall and had no strong interaction. Compared with the upper and lower parts of the pipe wall, the bacterial community in the middle of the pipe wall was distributed evenly and had the highest diversity. The 16S rRNA genes of various possible pathogens, including Escherichia coli, Staphylococcus epidermidis, Pseudomonas aeruginosa, and Salmonella enterica, were detected in the biofilms, and the abundances of these possible pathogens were highest in the middle of the pipe wall among three areas. The detachment of the biofilms is the main reason for the deterioration of the water quality in DWDSs. The results of this study suggest that the biofilms in the middle of the pipe wall have highly potential risk for drinking water safety, which provides new ideas for the study of the microbial ecology in DWDS.

The spatial distribution of pollutants in pipe-scale of large-diameter pipelines in a drinking water distribution system

In large-diameter drinking water pipelines, spatial differences in hydraulic and physiochemical conditions may also result in spatial variations in pipe corrosion, biofilm growth and pollutant accumulation. In this article, the spatial distributions of various metals and organic contaminants in two 19-year-old grey cast iron pipes which had an internal diameter of 600mm (DN600), were investigated and analyzed by Atomic Absorption Spectrometry, Gas Chromatography–Mass Spectrometry, Energy Dispersive Spectrometer, X-ray Diffraction, etc. The spatial distribution of heavy metals varied significantly across the pipe section, and iron, manganese, lead, copper, and chromium were highest in concentration in the upper portion pipe-scales. However, the highest aluminum and zinc content was detected in the lower portion pipe-scales. Apart from some common types of hydrocarbons formed by microbial metabolites, there were also some microalgae metabolites and exogenous contaminants accumulated in pipe-scale, which also exhibited high diversity between different spatial locations. The spatial distributions of the physical and chemical properties of pipe-scale and contaminants were quite different in large-diameter pipes. The finding put forward higher requirements on the research method about drinking water distribution system chemical safety. And the scientific community need understand trend and dynamics of drinking water pipe systems better.

Characteristics of pipe-scale in the pipes of an urban drinking water distribution system in eastern China

Pipes that carry drinking water have gradually aged. Events occurring with increasing frequency, such as substandard water quality in residential taps, red water, and black water, reveal the deterioration of the chemical stability of a drinking water distribution system (DWDS). Pipes in the DWDS serving City S, located in eastern China, were sampled to analyze the concentration and distribution of pollutants in pipe-scale of pipes of different materials, ages and diameters, and the factors (such as materials, age, and diameter) influencing the accumulation of pollutants were also investigated. The quantity of pipe-scale in the most commonly used gray cast iron pipe and ductile cast iron pipe (DN150) was 151.5–195.0 g·m−1 and 7.1–29.4 g·m−1, respectively. The concentration of heavy metals in pipe-scale was positively correlated with the quantity of pipe-scale (R2 = 0.874); the sequence of concentration of metals was Fe > Al > Mn, Zn > Pb, Cu > Cr, Cd. Galvanized steel pipe, with the highest degree of corrosion, had the highest concentration of heavy metals in pipe-scale. The morphology and composition of pipe-scale were substantially influenced by pipe material and age. For example, in the oldest galvanized steel pipe-scale, there was not only a large number of iron compounds but also some zinc composite oxides. In addition to hydrocarbons produced by microbial metabolism, there were microalgae metabolites and exogenous contaminants such as polycyclic aromatic hydrocarbons (PAHs). The concentrations of microbial metabolites increased with increasing service time.

Pyrosequencing analysis of bacterial communities in biofilms from different pipe materials in a city drinking water distribution system of East China.

Biofilms in drinking water distribution systems (DWDSs) could cause several types of problems, such as the deterioration of water quality, corrosion of pipe walls, and potential proliferation of opportunistic pathogens. In this study, ten biofilm samples from different pipe materials, including ductile cast iron pipe (DCIP), gray cast iron pipe (GCIP), galvanized steel pipe (GSP), stainless steel clad pipe (SSCP), and polyvinyl chloride (PVC), were collected from an actual DWDS to investigate the effect of pipe material on bacterial community. Real-time quantitative polymerase chain reaction (qPCR) and culture-based method were used to quantify bacteria. 454 pyrosequencing was used for bacterial community analysis. The results showed that the numbers of total bacteria and culturable heterotrophic bacteria from iron pipes were higher than that in PVC, while the numbers of Shigella and vibrios were low in biofilms from iron pipes. Bacterial community analysis showed that Hyphomicrobium or Desulfovibrio were the predominant microorganism in iron pipes, whereas Sphingomonas or Pseudomonas were dominant in other types of pipe. This study revealed differences in bacterial communities in biofilms among different pipe materials, and the results were useful for pipeline material selection in DWDSs.

Investigating in-service failures of water pipes from a multiaxial notch fatigue point of view: A conceptual study

Many mechanisms and processes can cause deterioration and ultimately failure of water distribution pipes during in-service operation, amongst these is damage caused by metal fatigue. This paper summarises an attempt at formalising a novel methodology suitable for estimating the number of years taken for a through thickness fatigue crack to form in this complex scenario. The devised method is based on the so-called modified Wöhler curve method and can be applied to estimate fatigue damage of water pipes independently from the degree of multiaxiality and non-proportionality of the load history. The computational approach of the proposed fatigue life estimation technique makes full use of an incremental procedure: fatigue damage is evaluated year by year by assuming that all variable involved in the process can change over time. The detrimental effect of corrosion pits is directly accounted for by treating them as conventional notches whose size increases with time. Finally, by taking as reference information the number of years for a blowout hole to form, the proposed approach is used to show how the lifetime of grey cast iron pipes can be remarkably shortened by fatigue.

Water hammer effects on a gray cast iron water network after adding pumps

A numerical model was developed to simulate the propagation of pressure waves in water gray cast iron pipe systems in the presence of pumps. The pressure waves are caused by the water hammer phenomenon due to fast valve maneuvers in the pipe network. The mathematical formulation of the present model is based on a system of two partial differential equations of hyperbolic type. This system was solved by the method of characteristics. The constructed numeric algorithm permits to follow the propagation of pressure waves. It provides the damping of the water hammer waves in the network taking into account the effect of reflection and refraction phenomena to the passage of junctions, bifurcations and change of conducts characteristics. The numerical algorithm sustains the maximum pressure values and; therefore, FEM ABAQUS simulation of gray cast iron pipes with a superficial defect gives the maximum stresses in the different network pipes. The severity of a corrosion crater defect was estimated by calculating the safety factor for the stress distribution at the tip of defects. It allows the acquisition of the applied notch intensity factor. To study the effects of the geometry defects, semi-elliptical defects are deemed to exist up to half the thickness of the pipe wall. To obtain the value of the safety factor, the results were fed into the assessment procedure for the structural integrity (SINTAP) which offers a Failure Assessment Diagram (FAD). Conventionally, it is considered that the risk of failure occurs if the safety factor is less than two. The study allows concluding that the entire network, studied after the addition of pumps, does not work in the security field and, therefore, requires the installation of control and protection systems against sudden pressure variations.

Developing a Sealing Material: Effect of Epoxy Modification on Specific Physical and Mechanical Properties.

To develop a matched sealing material for socket rehabilitation of grey cast iron pipes, an epoxy resin is modified by the addition of different components to improve the flexibility. Three different modifications are made by adding ethylene-propylene diene monomer (EPDM) rubber powder, reactive liquid polymer (ATBN) and epoxidized modifier. In this paper the effect of the modification method as well as the influence of absorption of water on the mechanical and physical properties are analyzed in terms of: tensile strength, modulus of elasticity, adhesion performance, pressure resistance, glass transition temperature and water content. A comparison with neat epoxy shows for all materials that the modulus of elasticity and strength decrease. Unlike other tested modification methods, the modification with rubber powder did not enhance the flexibility. All materials absorb water and a plasticization effect arises with further changes of mechanical and physical properties. The application of the sealant on the grey cast iron leads to a reduction of the strain at break (in comparison to the common tensile test of the pure materials) and has to be evaluated. The main requirement of pressure resistance up to 1 MPa was tested on two chosen materials. Both materials fulfill this requirement.

Development of a sealing material and robot for automatic socket rehabilitation of grey cast iron pipes in drinking water supply systems

The project DeWaLoP, led by Vienna Water, aims to develop a robot that is able to apply a sealing system to repair the joint sockets of pressure operating water pipes measuring about 1 m in diameter. To do this, a modification of the sealing material for inner surface application will be developed and a complex robot system will be designed to perform various tasks, such as inspecting, cleaning and restoring. Seven commercial sealing materials with a broad spectrum of mechanical and physical properties were tested. For this purpose, a series of tests was carried out to measure tensile strength, bending and adhesion; in addition, dynamic mechanical analyses, differential scanning calorimetry and thermogravimetric analyses were also conducted. A change in the mechanical and physical properties of these materials after water exposure could be observed. Furthermore, the surface preparation and remaining contaminants, e.g. rust, can affect the adhesion properties of the sealant. The plan is to develop a formulation of a matched material based on the results of these tests and the existing knowledge about the behaviour of sealing materials. The proposed in-pipe robot consists of three main subsystems: a control station, a mobile robot (similar to a vehicle) and a maintenance unit with a redevelopment system. An operator controls the movement of the cable-tethered robot system remotely from outside the construction side.