Report No DWI0131
DETERIORATION OF ASBESTOS CEMENT WATER MAINS (MSS 9731 SLD)
Final report to the Department of the Environment
The objectives of the investigation are:
- To determine the amount,
size, age and geographical distribution of asbestos cement pressure
pipe conveying potable water in the UK water supply system.
- To estimate the population supplied by water which has been conveyed through asbestos cement mains.
- 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.
- To assess the efficacy
of measures which could be taken to reduce the deterioration of
asbestos cement pipes or prevent further release of fibres.
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.
- 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.
- 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.
- 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.
- 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.
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.
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
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.
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 this report may be available as an Acrobat pdf download under the 'Pre 2000 Reports' heading on the DWI website.