Durability of Clay Pipes

Roman-pipe

Clay pipes have been in use since ancient Roman times

Clay pipes are extremely durable, as has been proven over periods of hundreds and even thousands of years in service.

Clay pipes have long been the preferred option in a broad range of aggressive conditions and can carry all effluents acceptable to sewage treatment plants. They are unaffected by the presences of hydrogen sulphide in the pipeline and sulphates in the ground. At temperatures found in public sewers in the UK they are resistant to damage from effluents and groundwater over the PH range 2-12.

Although clay pipes are rigid and do not distort under load, modern clay systems ensure a rigid pipeline with flexible joints capable of compensating for settlement after laying. Pipes and couplings are temperature resistant and will not distort, soften or embrittle even when subject to temperatures well above those experienced in normal service. Special seals are available to meet the challenges of abnormally aggressive environments.

As a result of the ability of clay drainage to withstand these aggressive conditions, it is eminently suitable to use on reclaimed industrial or commercial development sites. Clayware has excellent resistance to abrasion and is unaffected by pipe cleaning operations, particularly rodding and high pressure jetting and therefore for all of the above reasons, for design and ‘lifetime’ costing purposes, a clay drainage system can be considered to have unlimited life.

It is essential for the designer and owner to understand the long term life implications of pipe material selection and this selection process is more complicated than in the past. New materials are developed or used in new ways to make pipes. Different resins or classifications of cell structure must be understood and specified to achieve expected performance. In some cases, materials can be coatings or relatively thin layers that rely on adherence to the main pipe body to reach expected performance.

The references below are provided to give basis to the material selection process as related to life expectancy; comments are derived from a wide range of research papers- details available on request.

 Sewer Pipe
Material

 Strength
of Pipe
Material at
50 years

 Initial Internal
Corrosion
resistance

 Initial
External
Corrosion
resistance

 Design
Basis

 Typical Seal
Pressure
Rating

 Longevity,
Greater than
100 years
 GRP, glass
fibers, sand,
polyester		  50% of
initial, loss
of cross
linking
naturally
occurs –
accelerated
by stress and
corrosion
elements.
Water
damage		  Good, 1 pH – 10
pH (based upon
1.15 yr.
extrapolation at
22ᴼ C.);
deteriorates with
temperature
increase		  Good, 1 pH –
10 pH (based
upon 1.15 yr.
extrapolation
at 22ᴼ C.);
deteriorates
with
temperature
increase		  Flexible  >2bar  Poor,
extrapolated
from 50%
strength
deterioration at
50 years,
corrosion
acceleration
with stress and
molecule
linking failures
with age
 GRP, glass
fibers, sand,
polyester,
vinyl ester
interior
coating		  50% of
initial, loss
of cross
linking
naturally
occurs –
accelerated
by stress and
corrosion
elements		  Very good, 1 pH
– 10 pH (based
upon 1.15 yr.
extrapolation at
22ᴼ C.);
deteriorates with
temperature
increase		  Very Good, 1
pH – 10 pH
(based upon
1.15 yr.
extrapolation
at 22ᴼ C.);
deteriorates
with
temperature
increase		  Flexible  >2bar  Poor,
extrapolated
from 50%
strength
deterioration at
50 years,
corrosion
acceleration
with stress and
molecule
linking failures
with age
 HDPE, high
density
polyethylene		  70% to 80%
loss of
strength		  Very good, but
subject to
deterioration in
chemicals or
high temperature		  Very good, but
subject to
deterioration
in
contaminated
soils including
benzene or
high
temperature		  Flexible  Fused or
push joints
varying
pressure
ratings		  Poor,
extrapolated
from 70% to
80% strength
deterioration at
50 years;
corrosion
acceleration
from stress and
molecule
linking failure
with age
 PVC,
polyvinyl
chloride		  65% to 80%
loss of
strength		  Very good, but
subject to
deterioration in
chemicals or
high
temperature		  Very good, but
subject to
deterioration
in
contaminated
soils including
benzene or
high
temperature		  Flexible  >1bar  Poor,
extrapolated
from 65% to
80% strength
deterioration at
50 years;
corrosion
acceleration
from stress and
molecule
linking failure
with age
 Polymer
Concrete,
graded sand
and gravel,
polyester		  50% of
initial, loss
of cross
linking
naturally
occurs –
accelerated
by stress
and
corrosion
elements		  Good, 1 pH – 10
pH (based upon
1.15 yr.
extrapolation at
22ᴼC.); deteriorates
with temperature
increase		  Good, 1 pH –
10 pH (based
upon 1.15 yr.
extrapolation
at 22 ᴼ C.);
deteriorates
with
temperature
increase		  Rigid  >2bar  Poor,
extrapolated
from 50%
strength
deterioration
at 50 years;
corrosion
acceleration
with stress
and molecule
linking
failures with
age
 Reinforced
Concrete,
sand,
aggregates and
cement		  100%, less
corrosion
of concrete
& rebar		  Poor, in corrosive
conditions		  Poor, in
corrosive
conditions		  Rigid  >1bar  Poor, in
applications
with internal
or external
corrosion
environment
 Reinforced
Concrete
with Plastic
Liner,
concrete,
sand,
aggregates
and cement
with a cast
plastic liner		  100%, less
corrosion of
concrete &
rebar		  Moderate, liners
have shown short
and moderate life
<50 years		  Poor, in
corrosive
conditions		  Rigid  >1bar  Poor, in
applications
with internal
or external
corrosion
environment
 Steel, when
used as carrier
pipe		  100% where
there are
no
corrosion
effects		  Very poor  Very poor  Flexible  Welded  Poor, if
corrosion
possible.
Good, if no
corrosion
present
 Vitrified
Clay, high
temperature
fired
structural
ceramic		  100%  Excellent, pH 0 to
pH 14		  Excellent, pH
0 to pH 14		  Rigid  >> 2bar
10 psi,
>17 psi
depending upon
manufacturer
and joint type		  Excellent,
demonstrated
long life