Page 169 - Water Loss Control

Modelling W ater Losses 147

Pressure and Pipe Failure
As the pipes deteriorate through age (and possibly corrosion), and other
local and seasonal factors, the failure pressure gradually reduces until
at some point in time, burst frequency starts to increase significantly

Temperature Ground movement Traffic loading Age + corrosion
Failure Combination of factors
rate causes increased
failure rate

Boom !!!

Operating range Pressure

FIGURE 10.5 Combination of adverse factors (including surges) cause increased failure rates
(Source: Ref. 6.).
A reduction in pressure variation and if possible a reduction in zonal pressure will increase
the factor of safety for the zone. A hypothesis as to why mains and/or service connections in
some systems show large % reductions in new break frequency with pressure management,
but in others the % reduction is only small, can be proposed using this concept.
If, before pressure management, there is already a relatively high break frequency
(point 3 in Fig. 10.8), then a relatively small % reduction in pressure may cause a large
% reduction in new break frequency (toward point 2).
But if there is already a relatively low break frequency before pressure management
(point 2 in Fig. 10.8), then any % reduction in pressure (from point 2 to point 1) should
have little effect on new break frequency, but will create a greater factor of safety and
extend the working life of the infrastructure.

Reduce Surges and Variations
The first step in pressure management is to check for the presence of
surges or variations; if they exist, reduce the range and frequency of both

Low temperatures Ground movement Traffic loading Age + corrosion
Failure
rate Step 1: Reduce surges

Pressure
FIGURE 10.6 Reduction of surges and variations limits interaction with adverse factors and
increases factor of safety (Source: Ref. 6.).