Technology News
70
N
ovember
2014
X-ray technology ensures
quality during production of
composite pipes
2,189 MILLION metres of multi-layer
composite pipes were manufactured
worldwide by over 150 manufacturers
in 2013. Combined, these pipes would
circle the earth 53 times, or have a length
of almost three times the distance from
the earth to the moon and back. Ten
years ago, the worldwide production
volume was about 690 million metres.
According to a study of KWD Global Pipe
2013 (Pipe & Multi Layer Pipe Market
– Today and Trends. Dipl Ing Jutta Hix.
KWD Global Pipe, 2013), the trend for
the coming years is pointing up. At the
same time, quality requirements for
products are increasing.
Before the establishment of multi-
layer composite pipes at the beginning
of the 1980s, lead pipes were used
for installation in the building services
sector. Due to the toxicity resulting from
the potential chemical compounds from
lead, the production of lead pipes was
decreasing. Since 1970, these pipes
have not been used for drinking water
and have been replaced by copper pipes.
The use of copper pipes is also declining.
The advantages of multi-layer composite
pipes are obvious: they are non-
corrosive, more flexible and more cost
effective. Today, multi-layer composite
pipes are being used worldwide and
produced in more and more countries.
In 2013 for instance, the number of
aluminium multi-layer pipes produced in
Asia grew to 55 per cent – in comparison
to 48 per cent in 2010. In addition to
this growth, the end-users’ demand for
quality for the manufactured products is
also increasing. Manufacturers of multi-
layer composite pipes are striving to
further increase product quality in order
to stay competitive in the market. At the
same time, production costs have to
decrease. Measuring techniques with
X-ray technology make both possible.
Multi-layer composite pipes are
used, for instance, in building services
for drinking water, heating and cooling
installations, under the floor and in walls.
Common diameters that can be reached
are from 14mm, over 16mm up to 63mm.
Speciality pipes can have diameters up
to 110mm. These are being used for
water supply applications.
A multi-layer composite pipe is made
of up to five layers: a PE inner pipe, an
adhesive layer, an aluminium tape (butt
welded or lap welded), another adhesive
layer and a PE outer pipe. By means of
online quality control during production,
pipe specifications can be precisely
fulfilled. Wall thicknesses can be 2 to
10mm, depending on the manufacturer
and application. Pipes which conform
to a certain specification are especially
required for easy processing, for instance
for the connection of the pipes by fittings.
The quality control, moreover, saves
on plastic material and ensures cost
reduction at the same time.
Common available technologies
for quality control for composite pipe
extrusion lines are ultrasonics, the
diameter differential measuring principle
or gravimetrics. These technologies are
suitable for classic control of product
parameters, but are limited due to
their function and dependence on
environmental influences. Ultrasound
techniques require a coupling medium
(water or gel) for recording of measuring
values. Furthermore, the speed of
sound is dependent on the material
and temperature, so a change of the
product or production variables could
distort the measuring values. In order to
measure the wall thickness as precisely
as possible, different variables have to
be taken into account, such as the water
and material temperature, line speed and
water quality.
The diameter differential measuring
principle is based on the comparison of
measuring values, which are measured
before and after the extruder, and is for
that reason only applicable for the outer
layer. Although, this approach gives
information about the wall thickness, the
concentricity cannot be determined with
this technique. Thus, it is impossible for
the manufacturer to optimise production
in regards to quality and material
reduction.
During quality control by means of
gravimetrics, the amount of material
that is fed into an extruder is controlled.
This technique again only takes the wall
thickness into consideration, and not the
eccentricity of the pipe.
The precise measurement of all
product parameters without any
dependency on environmental and
material influences can be ensured by
using X-ray technology.
Since the early 1990s Sikora has
been offering X-ray technologies for the
continuous quality control of stranded
X-ray technology for quality control in composite pipe production
