Report No DWI0033
INTERIM REPORT - USAGE AND PERFORMANCE OF ASBESTOS CEMENT PRESSURE PIPE
To report the first years work of a DoE contract to:
Asbestos cement (AC) pipes contain approximately 11% by weight of asbestos fibres and are known to deteriorate in certain aggressive environments. To determine the scale of any potential degradation, data on the lengths and age profile of AC in use in the UK water supply system are required. The usage with respect to water quality and population will highlight those areas where deterioration and hence the potential for fibre release is likely to be most critical.
To identify whether asbestos cement pipe represents an acceptable option for mains laying or renewal, data on the engineering performance of AC in different environments are required. This will also enable comparison of its performance with alternative materials.
An understanding of the parameters controlling degradation of asbestos cement pipe is required to enable the potential rate of fibre release to be assessed Examination of various age pipe samples exhumed from a variety of water qualities and environments will enable determination of the mechanism and rate of deterioration of asbestos cement pipe. Such an exercise is planned for part 2 of the contract.
A detailed survey of the Water Industry's records has enabled the length of asbestos cement pipe in use for water supply to be determined. Where available, diameter and age profiles of the system have been collated with an assessment of the population served.
Following a general survey of the Industry's mains laying and burst records, four areas which have used substantial quantities of asbestos cement pipe, and have maintained good records, were selected for a detailed examination of the material's performance. Of the four areas, three have predominantly soft waters which are generally aggressive to asbestos cement. The fourth was chosen as a control, with hard water and clay soils which are generally not aggressive to asbestos cement.
The overall failure rate for the four areas is 0.10 failures/kilometre year (fails/km yr) which broadly compares with previously reported rates of 0.14 fails/km yr for cast iron, and 0.139 fails/km yr for uPVC pipes laid in London.
The failure rate in a non-aggressive environment was found to increase linearly with age for both class B (7.5 bar rated) and class C (10 bar rated) pipe. In soft water aggressive environments, corrosion related failures have been recorded for pipes app roximately 20 years old. The proportion of corrosion related failures increases with age.Copies of this report may be available as an Acrobat pdf download under the 'Pre 2000 Reports' heading on the DWI website.