Page 297 - Water Loss Control

266 Cha pte r S i x tee n

Pinhole
Pinhole leaks are small circular failures in a pipeline usually caused by corrosion or
stress by stones after poor backfill procedure during installation. Steel pipe installed in
a corrosive environment without proper corrosion protection is particularly susceptible
to the development of pinhole leaks, which can develop very quickly—as short as sev-
eral months time in extremely corrosive environments. Pipelines should always be
placed in a layer of sand as a minimum protective measure, but often more robust pro-
tections are needed, particularly if steel pipe is being specified for the pipeline material.
The quality of leak noise varies depending on the pressure, pipe material, and backfill
but is usually distinct and of high audible frequency.

Seepage
Most commonly found on deteriorated asbestos cement (AC) pipes where the pipe wall
becomes semiporous and water escapes slowly. These types of leaks are extremely dif-
ficult to locate as leak noise is minimal. They are therefore normally classified as unde-
tectable background leakage. Losses caused by seepage can be minimized by use of
pressure reduction and/or infrastructure replacement.

Leakage on Packing Glands of Pumps or Valves
Caused by deterioration over time and usually occurs when a valve is used after a long
period of inactivity. These are relatively easy to detect visually at pumps or by a valve
chamber that is full of clear potable water and a good audible noise detectable by direct
sounding at the valve spindle. Newer types of valves have a more resilient gland and/or
no packing at all, effectively reducing the occurrence of such a common leak problem.

Pipe Joint Leaks
These are common points of leakage, particularly on older cast iron and AC pipes where
the caulking or joint gasket deteriorates over time. Many older couplings are not corro-
sion protected and therefore deteriorate long before the pipe itself. When ground move-
ment occurs, pipe joints bear most of the strain, often resulting in leakage and, eventually,
a fracture.
Welded joints on steel pipes are actually stronger than the pipe itself but are seldom
corrosion protected after jointing and therefore a vulnerable point of corrosive attack.
Joint leakage is reasonably easy to detect on metallic pipes as these pipes usually create
a clear leak noise. However, they can be difficult to locate on AC and plastic pipes due
to leak noise attenuation that occurs on these materials.

Leaking Service Connection Pipe
Service connection pipe leaks are the most common type of leak that occurs in water
distribution systems. From the ferrule connecting the service connection to the water
main, to the customer water meter there is often more than one change of pipe size
and/or material, which necessitates joints which frequently are a weak point in the con-
nection pipeline. Service connections are also often laid very shallowly; very close to
the road surface. They are therefore vulnerable to weakening by movement caused by
traffic load. The ferrule connection is a susceptible point of leakage due to corrosion
combined with frequent fluctuation in pressure. Service connection leaks are usually
easy to detect, as there is normally access to the pipe via a curb stop or meter to enable
close direct sounding for leak noises.