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F O C U S O N T U B E 2 0 0 6 P A G E 3P A G E 2 F O C U S O N T U B E 2 0 0 6
No matter which method is used for
joining tubular components, whether
for example welding, threaded joints
or pressure-energised couplings,
accurate end preparation is essential.
This applies to tubes and pipes of
both non-metallic and metal
construction, the latter being the
subject of this article.
Preparation, which often constitutes
the final stage of the manufacturing
process, serves not only a cosmetic
purpose, it also produces a finished
product which will be more
acceptable to the buyer. Accurate end
preparation of tube ensures that,
where lengths of tube are to be joined
to each other or to other components,
the squareness of the tube end will
guarantee proper fit-up and correct
alignment on long runs. The many
types of preparation vary according to
the size of the component, wall
thickness and the joining method to
be employed. Most welding
specifications call for a pre-
determined end form which will vary
according to the subsequent welding
method.
Methods of end preparation vary
from the simplest, e.g. a hacksaw and
file, to high-tech, high-volume CNC
production machinery, which can turn
out hundreds of finished tubes or
pipes per hour.
Hacksaw and file
Although inexpensive in terms of
equipment, this process is too slow
and inaccurate to be considered as a
practical method of preparing weld
joints. The high cost of labour also
makes the benefits of this method
dubious.
GrindingGrinding is the most common of the
low-tech methods employed in the
tube and pipe fabrication shops. It is
relatively inexpensive, as the initial
investment in equipment is
considerably less than many of the
alternative types of machinery
currently available. It can be used on
a wide selection of materials and it
will, given sufficient time and a good
operator, create most of the common
weld preps in use at present.
However, grinding is of no value
where there is risk of fire or explosion.
It is also dirty and can be dangerous
because of the risk of inhaling
airborne particles (though
precautions can be taken against this
risk). Grinding is also very noisy and
can contribute to industrial deafness.
Hidden costs can include the
grinding discs, especially if they are
designed for use on exotic materials,
and maintenance. The accuracy of
grinding is not optimal under any
circumstances, and the more
complicated the profile, the harder it
is to achieve. Particles of the grinding
disc can be deposited on the pipe
material, which can result in weld
defects in the subsequent joining
process.
Flame or plasma cuttingSeveral methods exist for creating
end preparations on tube and pipe
using flame or plasma cutting. Many
of them provide acceptable surfaces
for welding under certain
circumstances and depending on the
skill of the operator. The cost of
manual flame/plasma cutting
equipment is not prohibitive, and
these methods can be employed in a
number of on-site situations, both
indoors and out. Mechanised
methods of flame and plasma cutting
High-quality end preparation is essential before orbital welding of tubes. But what
types of equipment and methods are suitable in what circumstances? Using cheaper,
low-tech methods is sometimes acceptable, but often it is counter-productive. When
Dragados Offshore used portable bevellers from Protem to prepare duplex pipes in an
offshore oil & gas project, it brought clear advantages in productivity and quality.
Hand-held milling andnibbling machinesHand-held milling and nibbling
machines vary in size and capacity
from a small electric drill for
lightweight plates about 3mm thick to
free-standing machines that have the
workpiece fed through by hand. Some
of these machines carry a milling
cutter that will remove large amounts
of material very quickly. These leave a
surface finish that is generally
acceptable for most methods of
welding. Other machines use a
system similar to a miniaturised
guillotine that nibbles the material
away to a predetermined shape.
Purpose-built endpreparation machinesDedicated end preparation machinery
can prove invaluable in certain areas.
The first is at the end of a tube or pipe
production line. A customised end
preparation system, matched to the
speed of the line, will give the
manufacturer a product which will
look well finished and be more
acceptable to a customer than a saw
cut end. It also offers the producer
the facility of sending out a product
end-finished to meet the exact
requirements of the customer,
thereby removing the need for further
processing.
The producer can offer the client a
choice of end profiles applicable to
the joining process to be used in
assembly. Similar facilities are
available to the manufacturer of plate
By Nadia Reicher Fournel
Preparing metal tubes for orbital weldingare more accurate than hand-held
torches, although there are still
limitations to be taken into account.
Plasma cutting has the advantage
over flame of being able to work on
more exotic materials such as
stainless steel, but it can be extremely
messy and, on heavy materials, the
cut tends to dissipate as it advances
through the wall, leaving an
inaccurate finish. Both flame and
plasma cutting induce a certain
amount of heat into the material.
Lathe or boring machineEmploying a lathe or boring machine
is an accurate and sometimes fast
method compared to the others
available. It can also produce complex
profiles with a high level of
repeatability. In a lathe, with the
workpiece rotating, there are
limitations as to the size and shape of
the pieces to be prepared. A 12-metre
length of tube spinning at high speed
can be very hard to control. A boring
machine has far fewer limitations, but
there are many disadvantages
common to both machines. Using
these machines for end preparation
ties up the machines and prevents
them from being used for the many
more complex operations of which
they are capable. Handling large or
complicated pipes, possibly with
bends or fittings welded into them,
can be difficult and slow.
Protem internal tube cutting machine for steamgenerators in a French nuclear pow
Protem drilling, facing, threading, boring, coredrilling and stud removal machine
Protem tube cutting and pipe bevelling machine
Nadia Reicher Fournel, CEO Protem GmbH Dettenheim, GermanyA graduate of Mulhouse University, has worked for Protem since 1987 where shestarted out as Business development manager of Protem SA. rising through theranks to General manager of Protem GmbH, and to her current position of CEOProtem GmbH Dettenheim a position she has held since 1991. Her otherresponsibilities include steering conferences on cold cutting techniques; member ofthe German nuclear community; head of project for dismantling a German fastbreeder reactor; head of communication for all major nuclear projects for theProtem Group; management of the German subsidiary of Protem SAS.
F O C U S O N T U B E 2 0 0 6 P A G E 5P A G E 4 F O C U S O N T U B E 2 0 0 6
products, with largely the same
benefits as for tube and pipe. In some
instances, for example where plate is
being rolled into a tubular section,
accurate machining to width is
imperative as this will govern the
diameter of the finished tube.
Machines of this nature are usually
built into production lines, together
with rolling and welding equipment.
For workshop activities, a vast range
of both fixed and portable systems is
available. The choice of using a fixed
system, as opposed to a portable
machine, largely depends on the
volume of ends to be prepared and
the speed at which it is to take place.
If there is a large number of similar-
sized items to be prepared in a
common profile, a fixed system
should be preferred. This can be
installed on a production line and
work in harness with any other
process that the components have to
pass through.
Portable machines also have the
advantage that, if the prepared pipes
are to be assembled on site, the
machinery can be taken to the job
location and the same standards of
accuracy can be achieved as in the
workshop. Machines designed for in-
situ use are usually lightweight in
relation to the dimensions they are
made to work on. They can be
supplied with a variety of drive
systems. There is a wide choice of
methods for attaching the machine to
the work, and several different cutting
methods can be employed.
Equipment for tube and pipe end
preparation can range from a
machine as simple as a grinder
mounted in a jig which clamps the
pipe to faster and more accurate CNC
machines.
On occasions end preparations have
to be created in an environment that
precludes normal methods. This may
be under water or in an irradiated
area, or possibly in a situation where
a human operator cannot be
employed due to inaccessibility or
danger to life. For these applications
remote-control machines are needed.
In situations where it is not permitted
to touch the inside of the tube, for
example with an electrochemically
polished tube, machines employ
special clamping collets to grip the
workpiece, while others use a system
of jaws similar to a chuck. For smaller
sizes the collet system is the optimal
solution. Another subcategory of the
collet method is the chain fixing, the
biggest advantage of which is that it is
practically without limit of diameter.
The principal disadvantage of the
chain method is that it is difficult to
set up and, if care is not taken, the
cutter may wander, resulting in a
spiral instead of a prepped end.
Nearly all the users of such chains
use a mandrel to facilitate self-
centring and self-alignment. Most of
the operators employ also form tools
to create the desired shape on the
pipe end. Many will perform more
than one cutting operation
simultaneously, i.e. a compound
bevel, counter-bore and root face. For
thicker wall applications some
machines use single-point tooling
with articulated tool holders. These
types of machines can also be
adapted to reinstate a damaged
gasket seat on flanges and vessels.
Welding (super) duplex pipesThe advantages of using high-tech
portable tools were made evident
when Dragados Offshore SA was
asked to build an LNG processing
plant on Melkøya Island as part of
Statoil’s Snøhvit project. In the past
the company had prepared large-
diameter hard-alloy pipes (stainless
steel duplex and super duplex, P91,
etc.) using several methods,
including cutting by flame or band
saw, manual bevelling with abrasive
discs or, when high quality was
important, using a lathe. But these
methods proved unproductive,
polluting, low quality and
inconvenient. So Dragados Offshore
asked Kalmia SA and its partner
Protem to propose a method of
machining pipes that avoided all
these problems.
Most of the conduction of this plant
had to be constructed in duplex and
super duplex pipes to handle high
pressures in corrosion weather
conditions. The weld preps were to be
made in different configurations (30°,
37°30” and “J” shape) and in different
sizes, schedules and materials. After
studying the problem, Kalmia and
Protem decided to offer portable
tools for working pipes ranging from
1” to 42” . The toolkit comprised low-
speed bevellers using high-speed
steel tool bits for the lower sizes, and
high-speed bevellers using carbide
inserts for the bigger sizes. Most of
the tools were offered with hydraulic
drives, because the working torque
was more stable compared with other
types of motorisation.
Dragados Offshore accepted the offer
and worked all weld preps in hard
alloy tubes with Protem portable
bevellers. The most important
advantage of this method was a
noticeable increase in productivity.
“Due to the high quality of the weld
preps we were able to carry out a lot
of the welding using newly acquired
orbital welding equipment,” said José
Ramón Damborenea, General Sales
Manager of Kalmia SA.
Capital investmentPortable machine tools and
sophisticated production systems
require a large initial capital
investment. This can be a daunting
prospect, particularly for small
businesses. However, the enhanced
accuracy and repeatability of these
machines can lead to a reduction in
the number of components needing
to be scrapped and a reduction in the
number of weld defects. Accurate end
profiles mean that more advanced
welding processes can be employed.
Many automated welding systems
need very accurate fit-up, and are very
unforgiving if there are inaccuracies
in the weld preparation. If an
estimator can judge more accurately
the time taken to perform end
profiles, the total time allowed for the
operation can be more easily
quantified. This makes it easier to
calculate labour costs and make a
correct price quote. In most cases
therefore it is of considerable benefit
for companies to invest in the most
advanced equipment available to
enhance quality and productivity.
Protem pipe bevelling and tube cutting machine
Protem pipe bevelling machine
Stationary bevelling and cutting machine