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co extrusion sliderthumbnailCo-extrusion

If requested all pipes can be manufactured either with a bright,
inspection friendly or an electro-conductive inner surface made by
the co-extrusion process. The co-extrusion provides an inspection-
friendly, bright inner surface and at the same time a long term UV-resistant
outer surface (for example for the storage of pipes outside
for a long time).
co extrusion content variety of tubes

diameter sliderthumbnailDiameter

Krah pipes can be produced steplessly at intervals of 100mm with
internal diameters (ID) ranging from DN/ID 300mm to DN/ID 4000mm. The nominal
diameters (DN) coincident with the internal diameter (ID) of the
pipe, because in case of any change in the design of the pipe the
wall thickness can be increased or reduced while the internal diameter
remains the same.

diameter content pipe diagram


flexibility deformation resistance sliderthumbnailFlexibility/Deformation

Elastic pipes can react to changes in their

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.

Deformation resistance

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.

flexibility content deformation resistance
flexibility content deformation resistance 2

hydraulics sliderthumbnailHydraulics

Due to the smooth anti-adhesive inner pipe surface the inner
diameter and hydraulic properties of Krah pipes will remain
constant regardless of the wall thickness or the profiles .
The nominal diameter (e.g. DN/ID 500) corresponds to
the respective inner diameter according to DIN 16961.
Compared to other pipe materials like concrete smaller
diameters can be used, which means that costs for material
and installation can be reduced significantly.
hydraulics content material chart
click to enlarge

internal pressure sliderthumbnailInternal pressure

The Krah pipe system can withstand low working pressure up to

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.

internal pressure content

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)

length sliderthumbnail Length

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.

lifetime sliderthumbnailLifetime

The lifetime of the complete Krah pipe system for gravity and low
pressure application is 100 years. Basically every component is designed
for a 50 year full and constant load case.
In the upper shown diagram you can see that the stability of the
pipes are designed for a usage of 100 years (a), including a calculated
safety margin. A stability (b) is reached - with constant load,
in our case due to the usage of polyolefins we have an additional
safety. As soon as the load is released the time is starting again, and
you have the extra safety again.

lifetime content diagramclick to enlarge


material sliderthumbnailMaterial

Polyethylene (PE80 and PE100) and polypropylene are thermoplastics
with excellent properties for the application with water and sewer,
as well as for the fabrication of containers for liquids and solid
materials. The environmentally friendly plastics polyethylene and polypropylene
are resistant against many chemicals and are very suitable for conveying
and storing various liquids.
Krah pipes can be made from the following thermoplastic materials:
  • High density polyethylene (PE80 and PE100)
  • Polyethylene with CaCo3
  • PP high stiff (PPB-HM)
  • Polypropylene-random (PP-R)
  • Polypropylene-homo (PP-H)
  • Polypropylene-none-flammable (PP-S)

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.

pipe materials content
click to enlarge

minimum wall thicknesses sliderthumbnail Wall thicknesses

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.

minimum content wall thicknesses profile aclick to enlarge

minimum content wall thicknesses profile bclick to enlarge


minimum wall thicknesses content minimum required thicknessclick to enlarge

standards sliderthumbnailStandards

The Krah pipe system is designed to meet the requirements
of present applicable international norms and standards.
The Krah Pipes GmbH & Co. KG is member of the major standardization
committees to guarantee that the pipes are corresponding
to the standards, but also that the standards are corresponding
to the pipes.
The Krah pipe corresponds to the following international
standards content table
click to enlarge

stiffness sliderthumbailStiffness

According to different norms and standards,

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.

stiffness content table
click to enlarge