Abstract
Grey cast iron water pipe networks have been installed around the world, often 100–180 years ago. Cohorts (which can be defined by age, size, casting technology and geographical location, to specify but a few groups) degrade at different rates due to environmental and in-service issues, which can lead to a significant loss in mechanical performance. Hence, the management of these assets can be extremely problematic in terms of identifying priorities. The current paper considers the causes of such degradation, the consequences for defining accurate and up-to-date condition assessment protocols and hence the type and urgency of rehabilitation strategies. It follows that understanding the integrity/life expectancy of water networks requires non-destructive evaluation (NDE) of large-diameter cast iron trunk mains, with particular reference to the kinds of defects that are likely to be present and the issues that make assessment difficult. From this, recommendations are outlined for asset managers required to specify NDE protocols, based on an understanding of the nature of the material and conditions in the field.
Highlights
Large-diameter trunk mains, with diameters of the order of 12–60 in. (300–1500 mm), are vital components of water networks around the world, conveying large volumes of water over long distances
The current paper considers the causes of such degradation, the consequences for defining accurate and up-to-date condition assessment protocols and the type and urgency of rehabilitation strategies
This review shows the start of non-destructive evaluation (NDE) of cast iron pipes and comprises a literature review and a physical study split between the laboratory and the field
Summary
A plethora of NDE techniques are available to determine the condition of large structures. ■ Passive acoustics are used in water mains to detect leaks but can be employed to listen for mechanical deterioration in a structure, such as the wires breaking inside a prestressed concrete pipe (Travers, 1997) This method can be applied only to situations requiring continual monitoring and not inspection as it can only measure the deterioration since it was installed rather than providing a complete instantaneous picture of condition (Makar and Chagnon, 1999). This may be mitigated through the use of ultrasonic immersion testing: in such systems, a thick layer or column of water is used between the sensor and the pipe wall to couple the ultrasound to the pipe Despite these potential issues, tools using ultrasound have been developed to inspect cast iron trunk mains and it are commonly offered as a method for characterising a pipe’s condition. It is worth noting that it is highly unlikely that a true NDE of a pipe can be carried out, as in most situations, some surface cleaning to facilitate an inspection will be required, and this will inevitably have an impact on the remaining life of the pipe
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