Access the journal article here: https://doi.org/10.1016/j.engfailanal.2024.108762

John, E., Boxall, J., Collins, R., Bowman, E., Susmel, L. (2024) 'Fatigue failure analysis of grey cast iron water pipes accounting for fatigue strength variation', Engineering Failure Analysis, 165, https://doi.org/10.1016/j.engfailanal.2024.108762

Abstract: 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.

Access the journal article here: https://authors.elsevier.com/sd/article/S0142-1123(23)00503-0

John, E., Boxall, J., Collins, R., Bowman, E., Susmel, L. (2024) 'Multiaxial fatigue of water pipe grey cast iron', International Journal of Fatigue, 178, https://doi.org/10.1016/j.ijfatigue.2023.108002

Abstract: 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.

Access the conference paper here: https://fatigue2024.com/conference-information-for-attendees/ 

John, E., Boxall, J.B., Collins, R., Bowman, E., Sumel, L. (2024) ‘Experimental validation of a model for predicting the Bending fatigue strength of corroded grey cast iron water pipes’ Proceedings of the 9th Engineering Integrity Society International Conference on Durability & Fatigue (Fatigue 2024), Vol. 2, 19-21 June 2024, Cambridge (UK).

Abstract: Leakage of drinking water caused by mechanical failures of old, buried, Grey Cast Iron (GCI) water pipes is a serious issue for water utilities in the UK and around the world. To enable better-informed pipe health assessments to be made, this work aimed to experimentally validate a method that could be used to assess the damaging effect of corrosion pitting on GCI pipes subject to bending fatigue loading. Fatigue testing of GCI pipes revealed pitting had a small detrimental effect on the pipes’ bending fatigue strength, characterised by Kt = 1.38 for the sharp pit specimens. An effective volume approach coupled with the SWT multiaxial fatigue criterion was found to provide reasonable fatigue life predictions, at the expense of requiring the 3D geometry of the pit to be known. Making predictions simply using the net stresses provided conservative predictions, but only required the pit’s depth.

Access the conference paper here: https://doi.org/10.4995/wdsa-ccwi2022.2022.14005 

John, E., Boxall, J.B., Collins, R., Bowman, E., Sumel, L. (2022) ‘Investigating an alternative to exhumed grey cast iron water pipes for small-scale fatigue tests’ 2nd International Joint Conference on Water Distribution Systems Analysis & Computing and Control in the Water Industry (WDSA/CCWI) 18-22 July 2022, Valencia (Spain), https://doi.org/10.4995/wdsa-ccwi2022.2022.14005

Abstract: Reducing and preventing leakage is a priority for water distribution network managers in many countries, including the UK. Understanding the mechanisms that cause leaks to form, and developing the ability to model these processes, will enable proactive replacement of water pipes before they start to leak. Smaller diameter Grey Cast Iron (GCI) water pipes are understood to experience biaxial, repeating loads, so fatigue cracking may be a cause of leakage for these pipes. To investigate this fatigue cracking mechanism a small-scale biaxial fatigue experiment is under development at The University of Sheffield. A large number of small diameter, un-corroded GCI pipes are needed to serve as specimens for this experiment. Therefore, in this work off-the-shelf BS416-2 DN 50 mm soil pipes are explored as an alternative to using exhumed pipes, which are often corroded and ≥76.2 mm diameter. The graphite microstructure and tensile stress-strain behaviour of a BS416-2 pipe were characterised and compared with literature data for exhumed spun-cast GCI water pipes, and a good agreement was found. This work concluded that BS 416-2 soil pipes can be used to represent spun-cast GCI water pipes in small-scale destructive experiments.