environment. Due to the deformation performance, the load is distributed
to its surroundings and the force acting on the pipe will be diminished.
Within a short time there is a balance in the area around the pipeline and
the deformation comes to a standstill. Plastic pipes react very flexibly to static
loads, while the loads do not concentrate themselves on the pipe, but are diverted
to the surrounding soil. Flexible pipes still work when other rigid pipe
systems already show damages like breaks or cracks.
Even in the case of a deformation the system is still
absolutely resistant against infiltration and exfiltration.
Since the pipes are profiled on the outside, these profiles can protect
the pipes in the soil a bit. There will be almost no axial extensions in the
pipeline. Krah pipes are nearly unaffected by temperature variations.
Pipes made of polyethylene and polypropylene have considerable
advantages to other pipe materials like concrete, steel, ductile etc.
Due to their material the Krah pipes come with a high elongation at
The Krah pipes deform conformly with the movement of the
earth without any breaks or cracks, so that the activity of the pipeline
is not drastically affected. As soon as the overload and earth movement
ends, the pipe will go back to its initial condition and position.
Another advantage is the high flexibility. Even in areas which are
highly affected by earthquakes, our pipes are hardly damaged in
comparison to pipes made of other materials. Despite the flexibility
of the Krah pipes they have a great capacity to carry loads, so that
they are also suitable for road construction.
3 bar, depending on the thickness of the waterway wall (e4,e5).
Equivalent to DIN8074 the hoop stress formula can be used with
minimum (e4,e5) as the minimum wall thickness of the A1 pipe, or
the minimum wall thickness of the waterway for A2 pipes.
e = minimum wall thickness
p = internal pressure
di = internal diameter
σ = permitted strength (MRS/C)
MRS = Minimum Required Strength
C= Safety Factor (for water 1,25)
The standard laying length (L) of the Krah pipes is six meters, because
in this way they are easy to handle, store and transport. In addition
it is possible to continuously produce any length between one
and six meters. The longer a pipe is the fewer joints are necessary
and this is advantageous for the pipe installation. Moreover it
is possible to deliver the pipes already jointed, whereat the installation
time on site can be reduced significantly.
These materials feature the properties mentioned in the table on the right side.
Other material can be used after prior acceptance of the producer and a third
party for quality control. However, the processed material should
have the specifications listed in the table below.
Both profiled and solid wall pipes with wall thicknesses of up to 300mm can be produced. The quality of the pipe is highly dependent on the quality of the waterway wall, therefore all Krah pipes are usually produced with a minimum waterway wall of 4mm.
the pipes shall be designed according to nominal
ring stiffness classes (SN) like SN2 (only for
pipes DN > 500), SN4, SN8 or SN16 (according
to ISO 9969), or other standard stiffness classes
(DIN16961, ASTM F894, NBR 7373 etc) not depending
on the testing method (constant speed
or constant load).
In addition, according to EN13476-3 (9.1), the
manufacturer is also allowed to produce pipes
DN/ID > 500mm in between the SN classes, in
case he is able to prove and underline this decision
with the help of a static calculation.
According to CEN/TS 15223, piping systems of stiffness classes ≥
SN 4 ,designed to be used underground, are sufficiently resistant to
external water pressure.
More stringent requirements with regard to external water pressure
can be checked in diagram 2 as a function of the ring stiffness
of the pipe.