The fracture and fatigue properties of cast irons used for trunk mains in the water industry
In order to assess the remaining life of cast iron assets in the water sector, an understanding of their fracture and fatigue characteristics is necessary. The present work is concerned with the toughness and Paris crack growth behaviour of cast iron materials with a range of micro-structures, taken from trunk mains currently in service. When considered with other data from the literature, the results from the present study enable the range of fatigue crack growth behaviour likely to be seen in service to be quantified. The role of microstructure in fracture and fatigue behaviour is discussed. Calculations of fatigue life based on integration of the Paris law are then carried out and compared with previously published data for samples from cast iron distribution mains. The results from these investigations support the development of asset management tools for use in the water industry.
TRUNK MAINS FAILURES: THE EFFECT OF CORROSION ON RESIDUAL PIPE STRENGTH
Trunk mains are critical components of any water supply network and their failures can have significant consequences. This paper investigates nine (9) cast iron mains recovered from service using a deterministic model to predict the likelihood of failure, denoted by the factor of safety. The investigation is made on the basis of their corrosion defects and material strengths, collected as part of a larger study (where it was shown that corrosion morphology can have a significant effect on the measured residual strength). The integrity of the deterministic model to proactively predict failure is sustained by choosing a lower limit strength value of 40 MPa as the input failure stress, which leads to failure being expected when the corrosion pits are more than 40% of pipe wall thickness.
Relation between Graphitic Corrosion and Strength-degradation of Cast Iron Pipe
The corrosion behavior and the degradation of the gray cast-iron pipes, which had been buried for 22 to 79 years and used for natural water, have been investigated. The rate of the graphitic corrosion of pipes was in the range of 0.167 to 0.25mm/yr. The graphitization reduced the real wall thickness so that the strength of pipe was lowered. Therefore, it is possible to estimate the degradation of tensile strength, crushing load, and fatigue strength of a pipe using the relation between its duration buried and graphitization depth.