Probabilistic physical modelling of corroded cast iron pipes for lifetime prediction

Abstract

Cast iron was the dominant material for buried pipes for water networks prior to the 1970s in Australia and overseas. At present, many water utilities still have a significant amount of ageing cast iron pipes. Cast iron is a brittle material and when large diameter cast iron pipes (diameters above 300mm) further deteriorate, the consequences of failure can be substantial. Focusing on the likelihood of failure to assist risk assessment, this paper examines the performance of large-diameter cast iron pipes using probabilistic analysis, incorporating uncertainties of governing variables. Finite element analysis is first conducted to study the physical mechanism of buried pipes subjected to complex environmental conditions. The deterioration of cast iron pipes due to corrosion is considered on the basis of recent research. The uncertainties of governing variables, such as the physical properties of soil, cast iron, water pressure and corrosion patterns, in pipe failure risk assessment are considered. Using probabilistic physical modelling, the lifetime probability of failure is derived and a time-dependent sensitivity analysis is presented. The results of this probabilistic physical modelling are compared with cohorts of failure data from two Australian water utilities to examine the underlying trends from both physical modelling and statistical analysis.

Robotic pipeline wall thickness evaluation for dense nondestructive testing inspection

“…Where wall loss is present the spread of the reduction is clearly evident and can be identified and measured. Such patches are modelled as ellipsoids (also depicted in Figure d overlaid over the reconstructed map), and their defining parameters can then be incorporated for stress calculation and remaining life prediction of the asset (Ji et al, ).…”

“…Recent research in the space of stress analysis and failure prediction of critical CI water mains has revealed that over and above pit depths, as traditionally provided during condition assessment of a critical asset, there is a need to ascertain the presence and geometries of large corrosion patches in the pipe walls (Ji, Robert, Zhang, Zhang, & Kodikara, ; Kodikara, Valls Miro, & Melchers, ), such as those depicted in Figure d. There exist a wide range of NDT technologies developed for the purpose of material characterisation for CI (Liu & Kleiner, ), yet the provision to build dense 2.5D maps of remaining wall geometries for lined water mains has driven the need to design an internal inspection tool around PEC sensing technology, as a proven technique typically used in the NDT sector for ferromagnetic material thickness estimation (Huang, Xinjun, Zhiyuan, & Kang, ; Huang, Wu, Xu, & Kang, ; Xu, Wu, Li, & Kang, ), resilient to sensor lift‐off.…”

Tensile Fracture Behavior of Corroded Pipelines: Part 2—Numerical Simulation Based on Monte Carlo Method

“…In addition, as an extension of the deterministic analysis method adopted in this series of paper, the probabilistic physical modelling method presented in [29,30] has been proven to be a powerful tool for assessment of the lifetime risk of cast iron pipelines. It provides a new perspective to explore the long-term mechanical behavior and fragility of the pipeline in a statistical way and deserves further attention.…”

Numerical interpretation of pressurized corroded cast iron pipe tests

“…With the proposed FEA approach, water utilities may be able to evaluate the remaining structural capacity of a corroded and aged CI pipe with more confidence. Additionally, the authors have developed an efficient statistically predictive model to approximate numerical solutions [24] and conducted probabilistic analysis based on FEA solutions [25]. Besides, a closed-form stress analysis solution close to numerical calculations of concentrated stresses due to corrosion is also being under developed.…”