Report No DWI0033

May 1985

To report the first years work of a DoE contract to:

1. determine the length, size range and age distribution of asbestos cement pipe in use in the UK supply system for potable water.
2. assess the geographical distribution of asbestos cement pipe relative to conveyed water quality.
3. estimate the number of consumers receiving water which has been conveyed through asbestos cement.
4. determine the structural performance of asbestos cement pressure pipe for comparison with cast iron and uPVC.
5. identify environmental and service parameters which influence the failure frequency.

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.

III CONCLUSIONS

1. >Asbestos cement pipes form approximately 11% by length of the UK supply system for potable water with approximately 22% of the population receiving water which has, at some stage, been conveyed through AC. A more detailed breakdown was not undertaken for the purposes of this report.
2. Approximately 18,500 kms of AC pipe have been laid in areas where a significant proportion of the conveyed water is potentially aggressive.
3. A majority of the asbestos cement pipe was laid during the 1950's and 1960's. With the introduction of plastic pipes, use of AC for the small diameters has declined. However an increasing proportion of the AC pipe laid over recent years has been for large diameter mains where its materials and laying costs compare favourably with alternative pipe materials.
4. The general failure rate of AC pipework is similar to that of both cast iron and uPVC. Therefore it can be considered as an alternative to each of these materials.
5. In the control area studied where the environments are not aggressive to AC the failure rate of AC increases linearly with age. The cause of this upward trend is unknown and may be affected by the external environment or changes in the materials properties. The overall failure rate however, remains below the National average.
6. In aggressive environments, corrosion related failures have been reported after as little as 20 years service. Much AC is now 20 to 30 years old, which is the age when corrosion related failures are first seen Based on the examination of failure records, it can therefore be anticipated that the number of corrosion related failures will increase over the next decade. The degradation of AC will be examined in part 2 of the current contract.
7. No conclusion can be drawn on the effects of water quality on internal degradation of the pipes as the failure records do not include such data. These effects will be studied in the second phase of the contract.
8. No comment can be made on the efficacy of bitumen seal coats as the presence or absence of such coatings was not generally recorded.

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 'Find Completed Research' heading on the DWI website.