Corrosion Of Cast Iron Pipes Research Articles

Reliability based failure assessment of deteriorated cast iron pipes lined with polymeric liners

Defects may appear or further develop in cast iron pipes lined with polymeric liners in the form of surface corrosion pits/patches, through-wall holes, gaps, longitudinal cracks, circumferential cracks and/or failed joints etc. This paper examines the performance of deteriorated cast iron pipes lined with polymeric liners using probabilistic analysis. The deterioration of lined cast iron pipes includes corrosion of cast iron pipes together with creep and creep rupture of polymeric liners. Various potential failure modes of lined pipes and the uncertainties of key physical parameters, including geometries, deterioration models and material properties of the pipe and liner, dimensions of the defects in the pipe and loading conditions etc., in probabilistic failure assessment of lined pipes are considered. The probability of failure of each lined pipe is calculated over its lifetime and a sensitivity analysis is also conducted to identify the most influential parameters on the failure probability of the lined pipe. It is found that the coefficients for the rupture strength and the creep retention factors of the liners are most influential on the probability of failure of the lined pipes.

Coupled Effect of Soil’s Acidity and Saturation on Pitting Corrosion of Buried Cast Iron

Abstract This paper presents the results produced from long-term tests designed to investigate the key factors affecting the external corrosion of cast iron pipes buried in clayey soil. The coupled effect of varying acidity (pH) and saturation (moisture content) of soil on the corrosion of cast iron buried in soil, including pitting corrosion, is thoroughly examined. Based on the observations and analysis of the test results, it is found that the coupled effect of high acidity (2.5 pH) and high saturation (80 %) of soil could create an accelerating environment for corrosion in the short term. In addition, the coupled effect of low acidity (5 pH) and high saturation (80 %) of soil could lead to a high corrosion rate for cast iron buried in the soil in the longer term. An empirical model for predicting pitting corrosion was also developed. The findings of this paper can have widespread applications, including corrosion protection and the development of models for the prediction of the remaining safe life of pipelines buried in corrosive soils.

Development of long-term localised corrosion of cast iron pipes in backfill soils based on time of wetness

ABSTRACT Parameters characterising the properties of soils used as backfill in immediate contact with cast iron pipes exhumed from a variety of soils after up to 129 years exposure are used together with average annual precipitation to estimate the average time of wetness. This is shown to correlate closely with pipe wall corrosion penetration. The possibility of microbiologically influenced corrosion is dismissed owing to lack of critical nutrients. The presence of chlorides in some soils most likely arises from pipe wall corrosion penetration and subsequent leakage of chlorinated drinking water. The predictions from the derived model are compared with an independent set of 16 pipe-wall corrosion penetration observations for pipes with up to 98 years exposures and found to agree well. The potential influences of soil temperature, physical damage and poor quality backfill are discussed.

Models for Prediction of Long-Term Corrosion of Cast Iron Water Mains

Corrosion of cast iron pipes buried in wet soils has long been associated with severe localized effects often attributed to microbiological influences and also with the chemical and physical properties of the soils. Despite more than 70 y of research effort, correlations have remained poor. Recently, the reasons for this have been elucidated, as reviewed briefly herein. Also, interpretation of data from actual cast iron pipes buried in a variety of soils for up to 129 y shows that two critical factors governing depth of local corrosion penetration are the type of soil and the compaction of that soil around the pipe. The latter influences the size of wet air-voids in the soil at the pipe surface. These cause differential aeration and associated severe localized corrosion. The other critical factor is the time of wetness of the soil/metal interface. This is related both to atmospheric precipitation (e.g., rain) and to soil permeability as governed by compaction. Microbiological corrosion has no influence unless essential nutrients continue to be available. These new views on an old subject permit the development of corrosion penetration models for longer-term corrosion.

Probabilistic failure investigation of small diameter cast iron pipelines for water distribution

At present, a significant proportion of Australia’s ageing water infrastructure is composed of cast-iron pipes. The corrosion of cast-iron pipes is the main triggering factor for Australia’s water industry. It has been found that the failure mode of small diameter water mains (<300 mm external diameters) from Yarra Valley Water is mainly the longitudinal failure (hoop-stressed) instead of broken back failure, which is unexpected. Therefore, the purpose of this paper is to examine the failure mechanism of longitudinal failure of small diameter cast-iron pipes. The observational failure database provided by Yarra Valley Water show limited data availability. This has stimulated the focus of this paper: to examine the corrosion mechanism by utilising probabilistic inverse analysis for unknown physical parameters. Focusing on the likelihood of failure, this paper investigates the performance of small diameter cast-iron pipes by using statistical analysis based on the observational failure lifetime data within pipe cohorts. Background studies on the deterioration of cast-iron pipes due to corrosion are made to help set up the probabilistic physical modelling (PPM). Using the updated corrosion parameters, the lifetime probabilities of failure and the hazard rate of the cast iron model are derived from PPM. Last, it is found that the modelling results agree reasonably well with prediction curves of statistical data, indicating that the proposed method for pipe lifetime prediction is promising.

Effects of disinfection efficiency on microbial communities and corrosion processes in drinking water distribution systems simulated with actual running conditions

The effects of disinfection efficiency on microbial communities and the corrosion of cast iron pipes in drinking water distribution systems (DWDSs) were studied. Two annular reactors (ARs) that simulated actual running conditions with UV/Cl2 disinfection and chlorination alone were used. High chlorine consumption and corrosion rate were found in the AR with UV/Cl2. According to functional genes and pyrosequencing tests, a high percentage of iron recycling bacteria was detected within the biofilm of the AR with Cl2 at early running stage, whereas siderophore-producing bacteria were dominant in the biofilm of the AR with UV/Cl2. At the early running stage, the sequential use of UV light and an initial high chlorine dosage suppressed the biomass and iron-recycling bacteria in both bulk water and biofilms, thereby forming less protective scales against further corrosion, which enhanced chlorine consumption. Non-metric multidimensional scaling analysis showed that the bacterial communities in the ARs shaped from within rather than being imported by influents. These results indicate that the initial high disinfection efficiency within the distribution system had not contributed to the accumulation of iron-recycling bacteria at the early running stages. This study offer certain implications for controlling corrosion and water quality in DWDSs.

Empirical models for long-term localised corrosion of cast iron pipes buried in soils

ABSTRACTEmpirical models are proposed for the progression of maximum depth of localised corrosion of cast iron pipes, based on data for pipes buried in 67 different backfill clay and sandy soils for up to 129 years. Early corrosion increases with increased inhomogeneity of the backfill soil and with greater availability of free water at the soil–pipe wall interface. Longer term corrosion is correlated with free water availability and occurs at a much slower rate. In most cases, the free water is fresh, oxygenated rainwater, known to be corrosive, but may also include some groundwater. Statistical uncertainty in pit depth is estimated and factors are proposed to allow for different annual rates of precipitation.

Corrosion Evaluation of Buried Cast Iron Pipes Exposed to Fire Water System for 30 years

The corrosion evaluation of buried cast iron pipe of fire hydrant system in a nuclear power station exposed to raw water for 30 years was carried out. The samples from cast iron pipe section were characterised by inductively coupled plasma atomic emission spectroscopy, optical microscopy, scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction and laser Raman spectroscopy. Metallographic examination revealed typical flake graphite microstructure with uniform distribution, randomly oriented graphite structure, rosette grouping, for pipes of different diameters. The presence of microbes in water side of the pipes and in contact with soil was seen. SEM examination revealed loose spherical deposits, rust layers comprising of iron oxide, silica and spherical nodules covered with network structures. EDS analysis of rust layers revealed the presence of Si, Ca, S and P apart from Fe and O. XRD analysis revealed that the rust on the surfaces comprised of SiO2 and Fe2O3. The results of the study indicated that the external corrosion of cast iron pipes was due to sand and gravel type of soil in contact with pipes. EDS elemental X-ray maps revealed regions rich in Si indicating localised graphitic corrosion. Detailed corrosion characterisation studies revealed that despite signatures of graphitic corrosion, microbes and rust formation, there was no substantial reduction in the pipe thickness, and hence, the service life of buried cast iron pipes can be further extended.

Sewer Water Effect on the Corrosion of Cast Iron before and after Treatment

This study aimed to compare and evaluate the effects of sewer water treated by bio-filter reactors using agriculture waste and that untreated on the corrosion of cast iron pipes. The bio-filter reactor used in this study composed of two types of agriculture wastes which are a two layer of both grape stalks and rice husk. Also, the sewer water quality parameters were tested and calculated before and after treatment. The corrosion rate was tested chemically by using the weight loss technique and it was found that the rate in case of iron immersed in sewer water before treatment was higher than that immersed in treated one.

Electrochemical corrosion of cast iron pipes in reclaimed water containing disinfectant

The corrosion characteristics of cast iron pipes in reclaimed water containing 1, 2, and 4 mg/L NaClO and ClO were investigated using potentiodynamic polarization curves (PPCs) and electrochemical impedance spectra (EISs). Scanning electron microscopy (SEM) was also used to evaluate the morphology of the corrosion scales. The results showed that NaClO and ClO utilization changed the electron-transfer pathway and corrosion-product characteristics significantly. In reclaimed water containing NaClO at 1, 2, and 4 mg/L HClO could take precedence over dissolved oxygen (DO) to react with Fe and enhance the corrosion process at 4 days. However, the consumption of NaClO caused a shortage of HClO reacting with iron and induced the re-passivation of previously eroded areas at 30 days in the 1 mg/L NaClO experiments. Furthermore, high concentrations of NaClO (2 and 4 mg/L) also enhanced the corrosion process at 30 days. In the 1, 2, and 4 mg/L ClO experiments, the ClO molecule could take precedence over DO to react with the Fe and formed iron chlorides, enhancing the uniform corrosion throughout the whole experiment. Additionally, iron oxides or iron hydroxides usually showed a compact, needle-like structure in the control experiments, while flocculated iron chlorides were the main components in the disinfection experiments. Moreover, the acidification caused by H accumulation initiated distinct localized corrosion after 4 days of immersion in the 2 and 4 mg/L ClO experiments, earlier than that in NaClO experiments (30 days). Thus, from a corrosion control perspective alone, NaClO is a better disinfection choice than ClO.

Corrosion Prevention of Cast Iron Industrial Water Pipes: A Preliminary Comparative Study of Hexamine and Aniline Inhibitors

Using cast iron pipes in various industrial and water systems is experiencing a majorproblem of corrosion occurrence. Hence the operation and maintenance of these pipesbecome costly and infeasible. Corrosion inhibitors have a great role in decreasing pipescorrosion rate. In this study, the inhibition effect by applying two inhibitors ofhexamethylenetetramine (hexamine) and aniline on cast iron pipes was studied.Experimental measurements of the corrosion behavior of cast iron pipes was thoroughlyexamined in three aqueous salt solutions of 2% NaCl, 2% Na 2 SO 4 and 2% CaCO 3 . Thecorrosion inhibition efficiency of the cast iron pipes by aniline or hexamine in the threeaqueous salt aqueous solutions was investigated at constant temperature and for differenttime intervals. Corrosion rates of the pipes were determined using weight loss technique.It has been found that, for the corrosion of cast iron pipes, a satisfactory inhibitionefficiency is observed for a concentration close to 150 ppm hexamine and 150 ppmaniline over the whole aqueous salt solutions tested in the work. The results showed thatat the same inhibitor concentration and temperature, aniline exhibits higher inhibitioncorrosion efficiency on cast iron pipes than the efficiency achieved by hexamine.

Impacts of water quality on the corrosion of cast iron pipes for water distribution and proposed source water switch strategy

Switch of source water may induce “red water” episodes. This study investigated the impacts of water quality on iron release, dissolved oxygen consumption (ΔDO), corrosion scale evolution and bacterial community succession in cast iron pipes used for drinking water distribution at pilot scale, and proposed a source water switch strategy accordingly. Three sets of old cast iron pipe section (named BP, SP and GP) were excavated on site and assembled in a test base, which had historically transported blended water, surface water and groundwater, respectively. Results indicate that an increasing Cl− or SO42− concentration accelerated iron release, but alkalinity and calcium hardness exhibited an opposite tendency. Disinfectant shift from free chlorine to monochloramine slightly inhibited iron release, while the impact of peroxymonosulfate depended on the source water historically transported in the test pipes. The ΔDO was highly consistent with iron release in all three pipe systems. The mass ratio of magnetite to goethite in the corrosion scales of SP was higher than those of BP and GP and kept almost unchanged over the whole operation period. Siderite and calcite formation confirmed that an increasing alkalinity and hardness inhibited iron release. Iron-reducing bacteria decreased in the BP but increased in the SP and GP; meanwhile, sulfur-oxidizing, sulfate-reducing and iron oxidizing bacteria increased in all three pipe systems. To avoid the occurrence of “red water”, a source water switch strategy was proposed based on the difference between local and foreign water qualities.

Effects of Iron Bacteria on Cast Iron Pipe Corrosion and Water Quality in Water Distribution Systems

Effects of Iron Bacteria on Cast Iron Pipe Corrosion and Water Quality in Water Distribution Systems

Framework for Forensic Investigation of Associations between Operational States and Pipe Failures in Water Distribution Systems

AbstractWater distribution systems throughout the world are deteriorating in part due to corrosion of cast iron pipes. Developing a deeper understanding of the operational association with failure may lead to operational improvements extending asset life. Operations engineers can be expected to develop credible theories of pipe failure based on their experience dealing with failures in the field. However, these failure theories can be more rigorously tested by a systemwide investigation of a large number of pipe failures. A forensic framework was developed to investigate how system operations are associated with large-diameter trunk-main failures. The framework utilizes a pipe failure database and historical supervisory control and data acquisition (SCADA) data to analyze trunk-main failures. Using the framework, about 141 large-diameter (≥300 mm) trunk-main failures were investigated in the Lake Zone in Newcastle, Australia. A predominant system failure mode called pump off peak (POP) was identified tha...

Characterization of the bacterial communities and iron corrosion scales in drinking groundwater distribution systems with chlorine/chloramine

The effect of chlorine and chloramine disinfection on bacterial communities and the corrosion of cast iron pipes was studied in drinking water distribution systems (DWDSs) transporting groundwater. α-FeOOH was the main corrosion product for both systems. However, loose corrosion products were formed in DWDSs with chlorine, whereas dense crystallized particles were formed in DWDSs with chloramine. Based on the functional genes and pyrosequencing assay results, both DWDSs had different compositions of corrosion-related bacteria in the bulk water and biofilms. The percentage of total denitrifying gene copy numbers in the 16S rRNA and the bacterial diversities were much higher at 220 d within the bulk water and biofilm in DWDSs disinfected with chloramine compared with those disinfected with chlorine. Most of the NO3−–N in the raw water was biologically denitrified through chlorine DWDSs in the experimental period, whereas the same phenomena occurred only when denitrifying bacteria were increased in the effluent due to the role of autotrophic microbial nitrification in chloramine DWDSs. Furthermore, nitrate-dependent Fe(II) oxidation occurred to a greater extent, leading to denser corrosion scales in DWDSs with chloramine compared with those disinfected with chlorine.

Effects of microbial redox cycling of iron on cast iron pipe corrosion in drinking water distribution systems

Bacterial characteristics in corrosion products and their effect on the formation of dense corrosion scales on cast iron coupons were studied in drinking water, with sterile water acting as a reference. The corrosion process and corrosion scales were characterized by electrochemical and physico-chemical measurements. The results indicated that the corrosion was more rapidly inhibited and iron release was lower due to formation of more dense protective corrosion scales in drinking water than in sterile water. The microbial community and denitrifying functional genes were analyzed by pyrosequencing and quantitative polymerase chain reactions (qPCR), respectively. Principal component analysis (PCA) showed that the bacteria in corrosion products played an important role in the corrosion process in drinking water. Nitrate-reducing bacteria (NRB) Acidovorax and Hydrogenophaga enhanced iron corrosion before 6 days. After 20 days, the dominant bacteria became NRB Dechloromonas (40.08%) with the protective corrosion layer formation. The Dechloromonas exhibited the stronger corrosion inhibition by inducing the redox cycling of iron, to enhance the precipitation of iron oxides and formation of Fe3O4. Subsequently, other minor bacteria appeared in the corrosion scales, including iron-respiring bacteria and Rhizobium which captured iron by the produced siderophores, having a weaker corrosion-inhibition effect. Therefore, the microbially-driven redox cycling of iron with associated microbial capture of iron caused more compact corrosion scales formation and lower iron release.

Characterization of biofilm and corrosion of cast iron pipes in drinking water distribution system with UV/Cl2 disinfection

The effect of UV/Cl2 disinfection on the biofilm and corrosion of cast iron pipes in drinking water distribution system were studied using annular reactors (ARs). Passivation occurred more rapidly in the AR with UV/Cl2 than in the one with Cl2 alone, decreasing iron release for higher corrosivity of water. Based on functional gene, pyrosequencing assays and principal component analysis, UV disinfection not only reduced the required initial chlorine dose, but also enhanced denitrifying functional bacteria advantage in the biofilm of corrosion scales. The nitrate-reducing bacteria (NRB) Dechloromonas exhibited the greatest corrosion inhibition by inducing the redox cycling of iron to enhance the precipitation of iron oxides and formation of Fe3O4 in the AR with UV/Cl2, while the rhizobia Bradyrhizobium and Rhizobium, and the NRB Sphingomonas, Brucella producing siderophores had weaker corrosion-inhibition effect by capturing iron in the AR with Cl2. These results indicated that the microbial redox cycling of iron was possibly responsible for higher corrosion inhibition and lower effect of water Larson–Skold Index (LI) changes on corrosion. This finding could be applied toward the control of water quality in drinking water distribution systems.

External and Internal Corrosion of Large-Diameter Cast Iron Mains

Deterioration in cast iron mains manifests itself in the form of corrosion. External corrosion is typically found to occur in pipes buried in corrosive soils while internal corrosion is dependent on water chemistry and flow characteristics. In the literature, corrosion of cast iron pipes (external and internal) is typically characterized by corrosion pit depth even though corroded area and corroded pit volume as well as pit location may enhance this characterization. Knowledge of these corrosion pit properties permits the assessment of its structural integrity. Typically, internal and external corrosion pits and corroded areas are observed to occur in many irregular shapes and sizes, which make their characterization a challenge. This paper describes extreme value statistical models that can be used to estimate external and internal corrosion pit depths in cast iron pipes using indirect properties or parameters. The goal of these corrosion models is to be able to predict corrosion pit depth based on available data with an acceptable degree of confidence. The external corrosion model is calibrated using external corrosion data collected by Thames Water Utilities Ltd (TWUL) and subsequently validated with data obtained from the inspection of four cast iron pipe lengths. The internal corrosion model was calibrated using internal corrosion data but sufficient appropriate data was not available for its validation.

Effects of disinfectant and biofilm on the corrosion of cast iron pipes in a reclaimed water distribution system

The effects of disinfection and biofilm on the corrosion of cast iron pipe in a model reclaimed water distribution system were studied using annular reactors (ARs). The corrosion scales formed under different conditions were characterized by X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), and scanning electron microscopy (SEM), while the bacterial characteristics of biofilm on the surface were determined using several molecular methods. The corrosion scales from the ARs with chlorine included predominantly α-FeOOH and Fe 2O 3, while CaPO 3(OH)·2H 2O and α-FeOOH were the predominant phases after chloramines replaced chlorine. Studies of the consumption of chlorine and iron release indicated that the formation of dense oxide layers and biofilm inhibited iron corrosion, causing stable lower chlorine decay. It was verified that iron-oxidizing bacteria (IOB) such as Sediminibacterium sp., and iron-reducing bacteria (IRB) such as Shewanella sp., synergistically interacted with the corrosion product to prevent further corrosion. For the ARs without disinfection, α-FeOOH was the predominant phase at the primary stage, while CaCO 3 and α-FeOOH were predominant with increasing time. The mixed corrosion-inducing bacteria, including the IRB Shewanella sp., the IOB Sediminibacterium sp., and the sulfur-oxidizing bacteria (SOB) Limnobacter thioxidans strain, promoted iron corrosion by synergistic interactions in the primary period, while anaerobic IRB became the predominant corrosion bacteria, preventing further corrosion via the formation of protective layers.

Experimental Investigation on Corrosion of Cast Iron Pipes

It is well known that corrosion is the predominant mechanism for the deterioration of cast iron pipes, leading to the reduction of pipe capacity and ultimate collapse of the pipes. In order to assess the remaining service life of corroded cast iron pipes, it is imperative to understand the mechanisms of corrosion over a long term and to develop models for pipe deterioration. Although many studies have been carried out to determine the corrosion behavior of cast iron, little research has been undertaken to understand how cast iron pipes behave over a longer time scale than hours, days, or weeks. The present paper intends to fill the gap regarding the long-term corrosion behaviour of cast iron pipes in the absence of historical data. In this paper, a comprehensive experimental program is presented in which the corrosion behaviour of three exservice pipes was thoroughly examined in three simulated service environments. It has been found in the paper that localised corrosion is the primary form of corrosion of cast iron water pipes. It has also been found that the microstructure of cast irons is a key factor that affects the corrosion behaviour of cast iron pipes. The paper concludes that long-term tests on corrosion behaviour of cast iron pipes can help develop models for corrosion-induced deterioration of the pipes for use in predicting the remaining service life of the pipes.