TPT May 2009

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37 May 2009
Technology Update
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the coating is allowed to cool down more
before hitting the first support roll, avoiding
loss in quality.
Secondly, by using a coupling, radial
movement of pipes when the weld hits
the support roll, is reduced. An equally
spread coating application free of air voids
is ensured. Normally this is achieved by
lowering the line speed, but a coupling also
solves the problem and production can run
at full capacity.
Dhatec has developed three main models:
standard coupling, advanced coupling and
premium coupling. The basic demands
for the design were: reducing radial pipe
movements to almost zero; strong, shock-
resistant construction; adjustable for a
wide wall thickness range; bridge thermal
expansion of the pipe in an induction oven
(220°C); small contact surface with the
pipe, to minimise heat loss; room for cooling
water to flow through the pipe; and fast and
easy application or removal.
An important feature is that the coupling is
placed in only one pipe-end. This means
that the coupling has a clamping side and a
centring side. When two pipes run together,
the upcoming pipe-end is automatically
caught and lined up by conical centring
rolls.
The standard coupling has a three‐point
clamping system that consists of two fixed
support feet and one adjustable clamping
foot. The adjustable foot bridges thermal
expansion and ensures strong clamping
inside the pipe. In tests and later experience
the Standard Model performed well with
smaller diameters up to Ø 30" and under
normal circumstances.
The following circumstances demand
better performance of the coupling: large
diameters (higher pipe-weights); thin wall
thicknesses (risk of deformation); oval
pipes; curved pipes; worn out or uneven
support rolls; high velocities of rotation; and
high friction forces between pipes.
To improve performance in these harsher
circumstances, the advanced coupling was
developed. This coupling has a five point
clamping system instead of three, and all
five clamping feet move simultaneously.
This ensures perfect centring, stronger
clamping and less deformation of the pipe.
For an even stronger fixing inside the pipe-
end, the clamping feet can be covered with
a heat isolating material that also increases
the friction factor between the clamping feet
and the pipe surface.
On the centring side of the advanced
coupling, there is a pre-centring ring with
extra rolls that take the first blows when
the pipes are running towards each other.
Because of the extra ring the construction of
the coupling is much stronger and the extra
rolls can handle larger radial movements of
the pipes.
Technically the advanced coupling performs
well, but there is one disadvantage. For
different wall thicknesses the clamping
side can be adjusted very easily, but on
the centring side the rolls need to be
exchanged or re-positioned. This is not only
time consuming, but there is also an extra
risk of human error. The wrong rolls can be
mounted on the coupling, or rolls can be
mounted in the wrong position.
To solve this issue the premium coupling
was developed. This coupling is equipped
with a new clamping system that centres
both the clamping side and the centring
side of the coupling at the same time.
When force is applied on the central
screw, five clamping feet and centring rolls
automatically expand and force themselves
against the inner pipe wall.
The premium coupling can clamp on only
25mm of pipe surface, taking into account
the cutback of an internal flowcoat. The
coupling combines all advantages in one
solution and is the result of experience
with many different coating processes
worldwide.
Dhatec BV – The Netherlands
Fax: +31 497 55 53 99
Email:
Website:
 The standard coupling during coating
 Advanced coupling inside a pipe-end
 Premium coupling with movable centring rolls
 Centring and clamping side of a premium
coupling
Coil end weld planisher
Kent Corporation, USA, has developed a new coil end weld planisher. The new machine
has a fixed upper planisher roll that is hydraulically driven on two linear bearings. The
lower anvil is adjusted up and down by a precision screw and wedge assembly.
A machine mounted dial indicator allows for the anvil to be positioned to the exact
material thickness. This prevents over planishing and eliminates the need to adjust
pressure for each thickness. The planisher will flatten TIG welds back to original metal
thickness so they can easily pass through roll form, tube and progressive die lines. This
also allows for strip processors to sell the weld in their final product.
Kent Corporation – USA
Fax: +1 440 237 5368 • Email: • Website :