Cast Iron Water Research Articles

Fatigue failure analysis of grey cast iron water pipes accounting for fatigue strength variation

Fatigue cracking is thought to be a critical failure mode for Grey Cast Iron (GCI) water pipes; however, this failure mechanism is poorly understood. Using a novel approach to sourcing GCI pipe material for testing, the variation in fatigue strength between pipes from the same batch was experimentally quantified. These results were used to assess the impact of fatigue strength variation on a hypothetical but realistic GCI water pipe years-to-failure scenario. Full-pipe sections were used during fatigue testing and the observed failure mode gave physical meaning to the years-to-fatigue-failure predictions for the first time. The accumulation of fatigue damage was predicted to represent a terminal and very small part of a GCI pipe’s life, so the loads applied to a GCI pipe early in its life are likely to have a limited impact on its remaining life and so do not need to be included in predictive modelling. For the scenario considered here, the predicted variation in lifetime was an 8.6-year range about an average of 59.4 years. GCI pipes in the UK are all > 50 years old, so this is a significant variation for asset and investment planners to account for as these pipes approach the end of their lives.

Pressure-induced fatigue failures in cast iron water supply pipes

Cast iron pipes have been extensively utilised in water supply networks worldwide. Many of these pipes are either at the onset or within their wear-out phase, during which failure rates rapidly increase, and the pipes should be repaired or replaced. However, the replacement and rehabilitation of these pipes might require extensive resources and time. Therefore, it is essential to investigate the effects of operational practices that might reduce failure rates for ageing cast iron pipes. In this paper, we investigate the conditions under which water pressure fluctuations may impact and accelerate fatigue failures in cast iron pipes. We carried out a systematic review of the mechanical properties of cast iron pipes and conducted sensitivity analyses to estimate fatigue crack propagation using fracture mechanics. Our investigation suggests that cast iron pipes which are affected by reduced wall thickness due to corrosion may experience a significant decrease in their operational life when subjected to water pressure fluctuations. Moreover, this negative influence of pressure fluctuations is exacerbated with an increase in the mean operating pressure. As an example, a 150 mm pipe featuring a corrosion patch of about 7 mm depth could extend its remaining fatigue life by over fourfold through a minor reduction of both mean pressure and pressure fluctuations of approximately 10 mH2O each. The manuscript further explores various pressure reduction combinations and trends, demonstrating the beneficial effects of reducing both mean pressure and pressure fluctuations. Consequently, the presented analysis suggests that water operators should proactively manage (reduce) the magnitude of both pressure components to extend the operating life of ageing cast iron pipes.

Multiaxial fatigue of water pipe grey cast iron

Grey Cast Iron (GCI) water pipes are subjected to multiaxial, cyclic stresses caused by combinations of loads such as internal water pressure and road vehicle weight. However, the multiaxial fatigue performance of this material has not previously been characterised. To address this gap more than 45 fatigue tests, including some under non-proportional tension-torsion loading, were completed using a GCI material very similar to water pipe GCI. Of the four multiaxial fatigue criteria tested, the Smith-Watson-Topper (SWT) criterion provided the best predictions by a narrow margin, supporting the idea that a tensile cracking mode dominates the fatigue life of GCI.

Time-Dependent Reliability Analysis of Fracture Failure of Corroded Cast Iron Water Pipes and Bayesian Updating for Lifetime Prediction

Affected by the underground soil environment, buried cast iron pipelines are subject to corrosion during their long-term service, resulting in damage accumulation to the pipe wall and the eventual fracture failure of pipes. This paper aims to propose a probabilistic method to quantitively assess the time-dependent reliability of fracture failure of corroded cast iron pipes. A Gamma-based corrosion process of the pipe wall is derived according to the reported corrosion models. The first-order reliability method and the Monte Carlo simulation are used to cross-validate and conduct the time-dependent reliability analysis based on the fracture failure criterion. Furthermore, uncertain physical parameters of the pipes are updated by the Bayesian Markov Chain Monte Carlo (MCMC) algorithm based on the regional historical data of failed pipes, and lifetime predictions of buried cast iron pipelines are then obtained. A worked example is provided to illustrate the application of the proposed method. It is found that the Gamma process can well simulate the corrosion process hence can be employed to calculate the probability of pipe fracture failure. Sensitivity analysis reveals that the pipe internal water pressure, the fracture toughness, and the geometry of corrosion pits are the most influential parameters to the probability of fracture failure. It is also found that the predicted lifetime of corroded cast iron pipes in the worked example decreases from 110 to 85 years after the Bayesian updating.

Structural safety evaluation of decrepit gray cast iron water valves for the control of water supply

Structural safety evaluation of decrepit gray cast iron water valves for the control of water supply

Active Air-borne noise suppression for pipe break early warning in smart water networks

Acoustic alarm systems using IoT (internet of things) smart sensors (e.g. accelerometers) for leak detection in water networks are rapidly gaining popularity. One of the issues for such systems is the false alarms which often occur as a result of signal contamination by environmental noise, especially by air-borne noise resulting in additional vibration. This research proposes a dual-sensor concept for active air-borne noise suppression in accelerometer signals that are excited by both fluid-borne noise (including the leak signal) and air-borne environmental noise. In the proposed arrangement, a microphone adjacent to the measurement station is used to measure the air-borne noise simultaneously to the accelerometer mounted to the pipe. Three methods have been applied in this paper: 1) using the non-coherent output power (NCOP) between the accelerometer and microphone signals; 2) using a Wiener filter; and 3) using adaptive least mean square (LMS) filters together with adaptive infinite impulse response (IIR) filters. Field tests have been carried out on a cast iron water main embedded in a water distribution system. A speaker was used to generate air-borne noise around the measurement station and to excite unwanted vibrations in the pipe. The results show that all three methods can effectively suppress air-borne noise from the accelerometer signals mounted to the pipe. A noise reduction of 30 dB can be achieved using the NCOP in the frequency domain or using the Wiener filter in the time domain. The adaptive filters are relatively less effective and the effectiveness reduces with the increase in bandwidth of the air-borne noise. However, the adaptive filters have the potential to be applied online for real-time processing.

Leaching of chromium and lead from the cement mortar lining into the flowing drinking water shortly after pipeline rehabilitation

Internal cement lining protection is used for both new and renovation of old cast iron water pipes. However, under unfavorable conditions, contaminants may be released from the cement lining into the drinking water shortly after the rehabilitation of old or installation of new water pipes. This paper proposes a mathematical model for the leaching of heavy metals from the inner cement lining of the pipe into the flowing water, taking sorption into account. Previously, mathematical models described in the literature for the leaching of contaminants from a cement coating into water only addressed static conditions or did not consider sorption. Experimental verification of the mathematical model under dynamic conditions showed very good agreement between calculated and measured results and confirmed the necessity of taking into account the sorption phenomenon. It also demonstrated the need for periodic water changes during laboratory experiments to describe the release of contaminants from the cement coating into the flowing water. Based on the results of laboratory experiments and the developed mathematical model, the concentrations of heavy metals at the ends of different lengths of drinking water supply pipeline sections after their eventual rehabilitation by cementation were calculated. Maximum lead concentrations at the end of 30, 23 and 13-km cemented sections of the pipeline were 2.0; 1.5 and 1.0 mg/m 3 , respectively. In contrast, chromium concentrations were 2.5; 1.6 and 0.9 mg/m 3 , respectively. Although all of these values are below the drinking limits, they can reach them if there is another additional source of contaminants or if the water stagnates periodically. The developed methodology and mathematical model allow to select the maximum length of the water main section that can be renovated or replaced at one time without significant impact on drinking water quality. • Modeling the leaching of heavy metals from an internal cement coating into flowing drinking water. • Significant effect of concentration gradient at the water-cement interface on metal leaching intensity. • Slight increase in heavy metal concentrations in drinking water flowing through newly cement-lined pipeline.

Time-Dependent Reliability Analysis of Buried Water Distribution Network: Combined Finite-Element and Probabilistic Approach

Corrosion deterioration is the predominant factor for a large number of cast iron (CI) water main breaks. The reliability of CI pipelines decreases overtime as corrosion growth on pipe walls significantly reduces the strength of pipeline materials. To predict the reliability of water pipelines accurately, this study used a finite-element analysis (FEA) approach to determine the maximum pipeline stress at various stages of the pipeline’s life. A series of FEAs was performed to consider uncertainties in parameters associated with stress analysis. The circumferential stress was found to be the most critical stress for pipelines. Time-variant circumferential stress was obtained by accounting for the time-dependent corrosion pit growth on the pipeline wall. The time-variant failure probability of pipelines was determined by comparing the circumferential stress and the tensile failure strength of the pipeline at the burst limit state. The FEA model developed in this study was validated with the results obtained from previous studies. Monte Carlo simulation was performed to generate the fragility curves in a probabilistic manner. This study also compared the fragility curves obtained utilizing FEA and conventional equations (elastic ring theory and the Spangler formula). The results showed that analytical equations are too conservative and provide a higher failure probability of pipeline. A sensitivity analysis was performed to identify the relative importance of parameters contributing to the pipeline’s performance. Additionally, the reliability of the water distribution network (WDN) was calculated based on the minimum cut set (MCS) and graph decomposition methods. The results showed that the two methods provide similar outcomes, however, MCS provides a greater safety margin. The proposed approach was illustrated for an example WDN.

Use of optical fibers to investigate the performance of pressure pipe liners spanning across a ring fracture

Cured in place pipe liners have been used in the rehabilitation of cast iron water pipes for over twenty years. Previous research has established that the liner’s performance may be controlled by local strain concentrations that develop where the liner spans across a ring fracture in a pipe subjected to differential ground movement. This paper reports on the application of distributed strain sensing using optical fibers to quantify the longitudinal strain distribution along the inside surface of a polymer composite liner. It was confirmed that the location of maximum opening in the fracture is the critical location where the liner could experience failure. The measurements quantify how debonding (due to slip and separation between the liner and the host pipe) decreases the maximum strain in a liner and how the extent of debonding is impacted by internal pressure and the alignment of the two pipe segments across the fracture. At rotation angles of approximately 0.3°, longitudinal strains of up to 17,000 microstrain were observed in a liner subjected to internal pressure of 600 kPa. Findings from this investigation confirm that the behavior of CIPP liners installed in pressure pipes containing pre-existing ring fractures, and subsequently subjected to angular movements, should be considered in design standards.

Response of a polymer liner passing across a pressure pipeline joint opening under axial ground movements

A closed form solution is developed to quantify the stresses that develop in polymer liners installed within pressure pipes, where the liner spans across a joint or ring fracture in the ‘host’ pipeline that is subjected to axial extension as a result of ground movements. The solution considers the zones of slip between liner and host pipe on either side of the joint that is opening. The expression derived indicates that maximum axial liner stress is proportional to the square root of the product of the gap that opens across the joint, liner modulus, internal fluid pressure, coefficient of friction between liner and host pipe, and inverse of liner thickness. Calculations are presented for a typical liner installed within a cast iron water pipe, though research is needed to quantify liner-host pipe friction. Comparisons to finite element calculations demonstrated that the new solution characterises the liner as having higher stiffness than numerical analysis using thick shell elements. Initially the two solutions match, but the new closed form solution becomes more conservative with increasing gap size. FEA was then used to show that temporary reductions in water pressure decrease axial liner stresses significantly.

Hydraulic and Technological Investigations of a Phenomenon Responsible for Increase of Major Head Losses in Exploited Cast-Iron Water Supply Pipes

The paper presents results of investigations of influence of major head losses on exploitation properties of water supply pipes after 30-year exploitation. The tested materials were cast-iron pipes with the internal diameter of 150 mm. A flowability drop coefficient ηt with average value of 0.45 was determined. Using the measured values of pressure difference Δp determined the absolute roughness of internal walls of the pipes after 30-year exploitation, which was referred to the new pipelines. The absolute roughness for the exploited pipes was equal to k = 27.6 mm, whereas for the new ones it was significantly lower and equal to k = 0.9 mm. Additionally, an analysis of the chemical and mineral composition of sediments gathered in the investigated pipelines was also performed. The top layer of the sediments was dominated by the compounds of a character of the iron hydroxide: goethite (α-FeOOH) and lepidocrocite (γ-FeOOH), whereas the internal layer was supplemented by the gypsum and sulfur, which was proven by the investigations performed with the use of scanning electron microscope (SEM). The sediment gathered within the pipes is the main reason of ca. 30-fold increase of the absolute roughness, which resulted in the flowability drop of the exploited water supply pipes.

Terrain wetness indices derived from LiDAR to inform soil moisture and corrosion potential for underground infrastructure

The external corrosion of cast iron water supply pipes has been associated with the availability of free moisture at the pipe wall. This is difficult to observe or measure for extensive pipe networks such as in major cities. A proxy is soil surface moisture content. This may be estimated using terrain wetness indices with highly accurate elevation data derived from airborne Light Detection and Ranging (LiDAR). Such information was obtained for several pipelines and compared with data from 6 cm deep soil moisture Theta Probe measurements along 12 pipeline transects. Additionally, all soil moisture data (in volumetric water content, %) were combined and separated by thresholds of transect means into low (<20%), medium (20%–35%) and high (>35%). Good correlations were obtained (R values 0.49–0.93, all with p value < 0.05). Higher R values were found for wetter conditions (above ~20%). The wetness indices were also found to relate to pipe-wall maximum pitting corrosion rates (mm/yr) when soil classifications were taken into account, with separate trends for clay, silty clay, sandy clay and sand. Some outliers were detected. These were all associated with pipes for which there is evidence of poor workmanship or quality during installation. In total, 25 catchments from inner city to coastal and lakeside suburbs as well as semi-rural regions were assessed. Results show the potential for terrain indices to indicate relative soil wetness in urban areas and thus potential for pipe failure. This is the first study of its kind. This also may assist water authorities to improve life prediction, management and replacement schedules for water supply pipelines and other underground assets.

Pipes could release toxic chromium into tap water

A new study shows that the carcinogen hexavalent chromium can slip into drinking water when commonly used chlorine disinfectants corrode cast-iron water distribution pipes ( Environ. Sci. Technol. 2020, DOI: 10.1021/acs.est.0c03922 ). Until now, most scientists thought that chromium found in drinking water originated from natural sources or industrial pollution. Haizhou Liu and his team at the University of California, Riverside, found another possible source by scraping some of the crusty scale out of two sections of cast-iron pipes from US drinking water systems. Cast iron is widely used in these pipes and contains significant amounts of Cr(0) in the alloy to help prevent corrosion. The scientists incubated the scale samples in a solution of hypochlorous acid, the oxidizing sanitizer commonly used to treat drinking water. The disinfectant-treated scales rapidly cranked out Cr(VI), whereas scales in water with no disinfectant produced none of the toxic metal species. Also, when exposed

Distributed Strain Sensing to Study a Composite Liner for Cast Iron Water Pipe Rehabilitation

Abstract The use of cured-in-place pipe lining systems for the rehabilitation of cast iron water pressure pipe has grown significantly in the past 20 years. With limited information on the performance of these lining systems in service, strain measurements are needed to evaluate theoretical findings about three-dimensional strength limits. The application of distributed optical fiber sensing to study the properties of a polymer composite liner was investigated in this research. Polyimide optical fibers were installed into flat liner coupons fabricated in the laboratory, and the specimens were subsequently tested in uniaxial tension and four-point bending. Using optical frequency domain reflectometry, Rayleigh backscatter was monitored from preinstalled optical fiber sensors and strains of up to 4,000 με were obtained. Comparisons between experimental optical fiber measurements and results obtained from conventional strain measurement techniques (i.e., extensometer and crosshead displacement) showed a strong correlation with an average difference of 3 % in four-point bending and 6 % in tension. However, the orientation and diameter of the composite fiber reinforcements were observed to affect distributed sensing performance.

A model of stress concentration factors for external corrosion patches on large-diameter underground cast iron pipes

ABSTRACT Field evidence revealed that buried cast iron water pipes can deteriorate through large localized corrosion patches with lengths greater than 1 m, formed by a cluster of small pits. This study investigated the effect of large corrosion patches on the performance of large-diameter cast iron pipes. Although large corrosion patches are highly irregular in nature, they were idealized as semi-ellipsoids. To validate the approximation of corrosion patch geometries with semi-ellipsoids, comparison of finite element models of scanned corroded pipe geometries with the approximated semi-ellipsoidal patches on the same pipes were conducted. Following this validation, parametric studies were performed, which covered a wide range of the pipe and patch dimensions. Based on the finite element analysis, an equation for stress concentration factors was derived and is presented in this paper. This development will significantly assist the pipe engineers and asset managers in the condition assessment of corroded cast iron pipelines.

Experimental Investigation into the Effects of Cast-Iron Pipe Corrosion on GPR Detection Performance in Clay Soils

Cast iron water distribution pipes are used widely in the UK and worldwide. Corrosion of these cast iron pipes often occurs due to an electrochemical process where the pipe is buried directly in a chemically aggressive ground (as is the case for some clays). The electrochemical process changes the pH environment and releases iron ions into the clay. This can cause chemical alteration of the clay minerals and corrosion products, such as iron oxide, hydroxide, and aqueous salts, to form in the soil. These chemical interactions are complex and time dependent, and can potentially result in pipe failure, and thus the conditions under which they occur need to be understood. Ground penetrating radar (GPR) has been proposed for routinely detecting, assessing, and monitoring buried cast iron pipes, and thus it is important to know how these chemical changes affect the electromagnetic properties of soil. A bespoke set of laboratory experiments was devised to simulate and accelerate cast iron corrosion (using electrokinetics) and ion migration processes in two types of clay, namely Kaolin clay and Oxford clay. Tests were conducted for periods of up to 3 months using both inert electrodes and a cast iron disc as the anode. The changes in the geotechnical properties (undrained shear strength, moisture content, and Atterberg limits), the geophysical properties (permittivity), and the geochemical properties (iron content, pH, and conductivity) were monitored. The results indicated that the Oxford clay was much more aggressive in terms of the corrosion activity compared to the Kaolin clay. The laboratory results were used in GPR simulations in relation to the detection of a buried cast iron pipe. The results showed that the chemically induced changes to the Kaolin clay did not materially affect the performance of GPR to detect the cast iron pipe, whereas for a pipe buried in Oxford clay the (greatly accelerated) chemically-induced changes were sufficiently advanced after approximately 7–8 weeks to cause the GPR to be unable to detect the corroded pipe.

Field evaluation of in-service buried pipeline using robust instrumentation

In-depth field instrumentation was undertaken on a section of a large diameter (660 mm) cast iron water pipe in Sydney, Australia to monitor the performance of a field pipeline under internal and external loads. This paper elaborates the instrumentation details and procedures adopted to capture various infield data to support the condition assessment of buried ageing pipelines under operational conditions including internal water pressure and external traffic loads. The adopted instrumentation realistically captured pipe strain, pipe joint displacement and rotation, soil pressure, temperature and moisture content. The results are discussed to evaluate the efficiency of the instrumentation for real-time monitoring which facilitates the understanding of the behaviour of a field pipeline. The pipe strains measured under various traffic conditions provide useful estimations for the evaluation of the condition of ageing pipelines. Fairly uniform strains were detected under internal water pressure loadings which showed a considerably larger impact on pipe performance than that due to other influential factors. The soil vertical and lateral pressures measured at various locations around the pipe revealed the relative magnitudes of ground stresses, facilitating new designs and the failure assessment of in-service buried pipelines. Soil moisture and temperature data showed variations directly related to atmospheric conditions. The robust field instrumentation adopted in this study is useful for the accurate monitoring of in-service pipes which may be highly vulnerable to catastrophic failure due to ageing-induced corrosion and severe operational loads.

On Image Fusion of Ground Surface Vibration for Mapping and Locating Underground Pipeline Leakage: An Experimental Investigation.

This paper is concerned with imaging techniques for mapping and locating underground pipeline leakage. Ground surface vibrations induced by the propagating axisymmetric wave can be measured by an array of acoustic/vibration sensors, with the extraction of magnitude information used to determine the position of leak source. A method of connected graph traversal is incorporated into the vibroacoustic technique to obtain the spatial image with better accuracy compared to the conventional magnitude contour plot. Measurements are made on a dedicated cast iron water pipe by an array of seven triaxial geophones. The spectral characteristics of the propagation of leak noise signals from underground water pipes to the ground surface are reported. Furthermore, it is demonstrated that suspicious leakage areas can be readily identified by extracting and fusing the feature patterns at low frequencies where leak noise dominates. The results agree well with the real leakage position in the underground pipeline.

Framework for Analyzing Cast Iron Water Main Fractures due to Moisture-Induced Soil Expansion

AbstractCast iron pipe break rates in North American water distribution systems have increased significantly in the last six years (a 43% increase with respect to 2012). Of the numerous mechanisms ...

Material properties for fracture mechanics based strength assessment of cast iron water mains

Municipal water distribution systems in Canada and other countries include a large number of cast iron pipes that were installed almost 50 years ago. For structural integrity assessment of these pipes, the fracture mechanics approach is found to be more effective than the conventional continuum mechanics-based approach. This paper presents the mechanical properties for fracture mechanics-based strength assessment of water mains determined through testing of cast iron pipes exhumed from two cities in Canada. Microstructure analysis is conducted to understand the materials’ inherent properties. Uniaxial tensile tests are conducted to determine the stress–strain relations. The influence of the rate of loading on stress–strain behaviour and loading-unloading responses are investigated. A simplified single-edge notch beam test is used to obtain the fracture toughness. Probabilistic distributions of the parameters are provided to account for the uncertainty and variabilities observed in the test results.