CT scans as a reference for determining the condition of AC and PVC

Drinking water companies plan to replace AC pipes in the coming decades. In order to determine which pipes need replacing first, it is important to have information about the level of degradation and how it affects the strength of the pipes. Research is therefore needed into ways of measuring degradation and using the measurement results as a basis for conclusions about pipe status. In this project we use a detailed technique (CT scans) to help validate, interpret and improve the determination of pipe status in the field.

More accurate measurements of the wall thickness of AC pipes

Recent studies of the strength of AC pipes have shown that CT scans provide a more detailed picture of degradation than the non-destructive techniques currently available such as radar and ultrasound. It proved difficult to determine the level of degradation correctly with the conventional approach. The research involved removing AC pipes from the mains and subjecting them to failure testing to determine the material properties. In parallel with these tests, CT scans were made of the same pipes, both before and after failure. Results were then compared with the conventional techniques. This project provides answers to a number of questions on the basis of the results so that water companies will be better placed in the future to determine the actual condition of AC pipes.

Research phases

In this study, we run through the following phases and approaches:

  1. Determination of the level of suitability of a recently developed UltraSonic sensor (US) for determining the actual wall thickness of AC pipes.
  2. Recalculation of the failure stress and modulus of elasticity resulting from the strength testing based on the results of the CT scans.
  3. Derivation of the degradation profile on the fractured surface of a failed pipe from CT scans and comparison with the degradation of the rest of the pipe. This provides a better picture of the requirements for the detailing of wall thickness measurements and shows the importance of non-homogeneous degradation (current state models for AC assume homogeneous degradation).
  4. The drafting of a protocol for the use of CT scans in AC exit assessments, including a feasibility assessment. The high level of detail afforded by CT makes it not only valuable in terms of validating other techniques but also as an exit assessment for situations where this extra detail is desirable.
  5. Extension of the research to PVC pipes in order to analyse whether CT scans can provide information for those pipes that is just as valuable as for AC pipes.
    Even better decisions for pipe replacement

The results of this project will improve the capacity of water companies to assess the added value of potential measuring techniques and to make decisions about which pipes should be replaced on the basis of the actual wall thickness of AC pipes.