Report No DWI0131

Dec l988

The objectives of the investigation are:

1. To determine the amount, size, age and geographical distribution of asbestos cement pressure pipe conveying potable water in the UK water supply system.
2. To estimate the population supplied by water which has been conveyed through asbestos cement mains.
3. To determine the rates of deterioration of asbestos cement pipe occurring in UK waters and the potential for release of asbestos fibres into the water supply.
4. To assess the efficacy of measures which could be taken to reduce the deterioration of asbestos cement pipes or prevent further release of fibres.

The recent interest in asbestos in the environment has resulted in questions being raised over the suitability of asbestos cement pipes for conveying potable water. A recent study commissioned by the Department of the Environment has concluded that asbestos cement pipes may contribute to the numbers of asbestos fibres in the conveyed water in the distribution system, and suggests that the aggressiveness of the water and the length and age of the pipes are contributory factors.

1. Asbestos cement usage

• Asbestos cement (AC) pipes account for approximately 11% (37,000kms) of the total length of mains in the United Kingdom water supply system.
• Approximately 22% of the population (12 million people) receive water which has passed through asbestos cement pipes.

2. Deterioration

• Low pH, low alkalinity waters are aggressive to asbestos cement pipes.
• Of the asbestos cement pipe laid approximately half is in locations where the conveyed water may be aggressive.
• The most reliable method of assessing the depth of degradation incurred was by elemental analysis through sections of the pipe. Phenolphthalein staining showed a very good correlation with elemental analysis. None of the other techniques assessed proved suitable.

3. Failures/Degradation rate

• In areas of aggressive conveyed and groundwaters corrosion related failures have been reported from pipes less than 20 years old.
• In less aggressive environments the failure rate of asbestos cement pipes has been seen to increase linearly with age.
• Prediction of rates of attack are very difficult in the UK as most of the pipes are bitumen coated, and the pipe degradation is thus very localised around defects in the coating.
• The maximum internal degradation observed was 8mm in a period of 40 years.

4. Protection

• Both epoxy resin and cement mortar can be successfully applied to the inside of new and degraded pipes to provide enhanced protection, or to renovate the pipes.
• Cement mortar lining may only be a temporary solution to internal degradation as the mortar itself deteriorates by the same mechanisms as asbestos cement.
• Epoxy resin lining prevented any further degradation of the inside of the pipe.
• Acceleration factors of approximately 10 have been achieved in the accelerated corrosion rig when compared to the most severe degradation observed in service.
• Rates of deterioration of asbestos cement can be reduced by chemically treating the conveyed water to increase its buffering capacity. However chemical treatment cannot prevent release of fibres from pipes which are already degraded.

Water utility records have been examined to determine the amount of asbestos cement pipe in use in the UK water supply system. The data has been analysed to identify the size, age and geographical distribution of AC pipes. An assessment of the population served has been made. Failure data from four selected areas were analysed and show a failure rate below the national average for all pipe materials. Various trends have been identified in the failures from each of the areas, and possible reasons for these trends have been proposed.

Examination of pipes exhumed from a wide variety of environments showed attack to be non uniform due to the presence of a bitumen coating. Because of this non-uniform attack no simple model could be determined to explain the deterioration, although reasonably good correlations could be made for low pH, low alkalinity waters. It is thus not possible to accurately predict potential rates of release of fibres into the water supply.

Cement mortar and epoxy resin protective linings were successfully applied to asbestos cement pipes in various conditions of degradation. Accelerated corrosion tests were developed to determine the efficacy of these protective linings. The tests provided an acceleration of approximately 10 compared to the most severe degradation observed from exhumed pipe samples, thus 12 months exposure to the accelerated tests approximates to a 10 year service exposure.

Short term tests examining the effect of modifications to the chemical characteristics of the water were undertaken to assess whether protection could be afforded by treatment of the conveyed waters.

Copies of the Report are available from FWR, price £35.00 less 20% to FWR Members