What is induction bending?
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Like many engineering ideas, this technique owes its' success to it's
simplicity and effectiveness. It operates on the principle of heating
material by the eddy current effect of an induced electrical current,
a technique which, of course, has been in use for many years. The tube
to be bent is passed through an induction coil, where a narrow band of
the tube is raised to forging temperature. The remainder is kept cool
by a system of air and water cooling coils. The pipe is attached to a
pivoted radial arm which is set to describe the required centre line radius
of the pipe. The pipe is pushed through the induction heating coil by
a hydraulic cylinder, while the radial arm rotates it to the desired radius.
A quick adjustment to the pivot point will change the bend radius accurately
to within a 1/16 " (1.5mm) of centre line radius. It is a simple matter
to produce a series of multiple bends from one single random (6m) or double
random (12m) straight section. Due to the inherent design of the machinery there
are no restrictions on the length of pipe which can be loaded into the
machine. The narrow heat band eliminates pipe wrinkling, and no internal
mandrels or formers are required, since the cold pipe on either side of
the heated zone provides adequate support. Because of the high speed and
efficiency of induction heating, temperatures can be controlled very accurately
(+ or - 30 degrees C ). Neither the outside wall or inside wall of the
pipe develops scaling during bending; previous rusted or scaled tubes,
spiral welded, seam welded and butt welds, can be bent as efficiently
as seamless pipe. Variation in wall thicknesses of the materials present
no problems, but simply necessitates different feed rates and power to
the inductor coil.
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What are the advantages of Gregson Induction Bending machines?
Compare the induction bending process with traditional processes. A number
of positive attributes soon become apparent.
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Induction bending does not require any sand filling or internal mandrels.
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As the inductor coil does not contact the pipe during bending the surface
quality of the pipe is irrelevant.
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The bend radius is infinitely variable from 2D centre line radius to
infinity.
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Wall thickness can vary from Schedule 5 up to 2.5" thick, no alternations
to the machine's tooling are required.
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The quality of the bends with respect to surface finish are equal to
that of cold bending, and better than fire bending, and in the case of
ovality and wall thinning , are superior.
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Multiple and compound bends can be produced from a single length of straight
tube without the need for butt welding.
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The bending times are considerably less than in fire bending or weld
fabrication, making the process cost effective.
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As the process eliminates the need for welded or mechanical joints between
bends, the integrity of the finished pipework is higher than in any other
process.
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Using induction bending enables a system to be designed utilising optimum
bend construction, leading to long term energy savings in operating the
system.
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The machine has other advantages in that it can process a wide range
of materials (see materials list). Furthermore, with minimum tooling cost,
the machine can be adapted to process structural shapes, angles, channels,
beams etc.
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What is the benefit to my business?
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Improvement in overall plant construction time.
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Eliminating the need for forward order of forged elbows at an early stage
of design which inevitably leads to shortages and surplus by the time
the design has been fully developed.
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Bend radius can be altered at a moments notice when problems are discovered
at the erection stage.
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Acceleration of fabrication time by eliminating cutting, rounding-up,
match boring , fitting , heat treating and welding of forged fittings.
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Dispensing with the time and expense of radiographic or ultrasonic examination
of pipework.
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Reducing inspection authorities time engaged in checking welded joints.
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Response time for repair and maintenance work reduced. A pipe can be
bent and in place within 24 hours of material availability.
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Improved quality control with respect to ovality, wall thinning and surface
finish.
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How does it compare with other available techniques?
Fire Bending
While this process can produce almost any bend radius required in a wide variety
of wall thicknesses, it is a slow, time consuming procedure, and hence costly
in man-hours and energy consumption. The finished bend cannot be guaranteed
for wall thinning, as ovality and wrinkling must be beaten out. The residual
scale and sand left behind after bending, requires a cleaning process to render
the pipe ready for service.
Machine Cold Bending
The process is fast and lower in cost. It possesses a fairly good control of
ovality and wall thinning and there is little or no contamination of the material.
The disadvantages however, are that only a few standard radii are available,
usually 3 or 5-D and normally only standard wall thicknesses. Tooling will not
accept wide variations in outside diameter, wall thickness or seams. So, while
the process is inexpensive, it is also relatively inflexible. A further major
disadvantage with this method is that it requires considerable straight clamping
lengths between bends, which prevents the use of tight pipework geometry.
Welded Elbow Fabrication
The main advantages with this process are that forged bends can be welded on
the job-site without the need for a well- equipped workshop. While welding on
site may appear to be an advantage, there are several major disadvantages, which
are , to list a few
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Higher cost of forged elbow weld fabrication ( labour costs)
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Management and control of on site labour force
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Unreliable weather conditions
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Poor conditions for exercising good quality control
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Less versatility in piping system design
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Long lead time in ordering forged elbows
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Higher costs associated with NDT requirements ( on site X-ray of butt
welds)
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More pipe end preparation required
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More activity in documentation and record keeping.
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Higher utility costs on site
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The advantages are that ovality and wall thinning of the forged elbow can
be closely controlled. However, match boring of the elbow is essential to obtain
good quality welds. The main disadvantage of this system is that bend radii
available on the market are very restricted and are normally tight radii such
as 1.5-D, which inevitably produces high pressure drops in the system. The labour
costs of butt welding are high, and consequently, the finished pipework costs
are usually equal to fire bending costs. Where high integral pipework is required,
subject to heavy stress levels or where containment of dangerous media is involved,
the radiography and post heat treatment further escalates the cost. ( more welds
= greater cost and increased risk) Finally where forged elbows are required
in non standard wall thickness, the delivery delays are usually substantial.