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Ultrasonic Contact Shoe Rotary Heads
A History of Development |
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Prior to the 1960’s most of the
full body ultrasonic tube testing systems for tubes above 4½" OD relied on
the technique of either rotating or spiralling the product under test. This
type of approach was, and still is limited in the testing speeds that could
be achieved and even with multiple banks of transducers, the testing speeds
could not match the production requirements of the typical tube mills. For
this reason together with the aim of simplifying tube handling in a tube
production/flow line the then Department of Research and Technical
Development (DR/&TD) of the Stewarts and Lloyds company based at Corby in
the UK embarked on the development of ultrasonic rotating heads.
For the smaller diameter tubes rotating heads were already
beginning to emerge from other commercial N.D.T. companies; these heads used
conventional bearings and water chambers and were generally |
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RP 6 |
restricted to
diameters less than 100mm. The first larger diameter heads developed by the
DR&TD
Corby used hydrodynamic bearings and carried water jet
transducers; heads to test diameters up to 6⅝" O.D. were produced and
installed in various plants within the Stewart and Lloyds group, later to
become British Steel Tubes Division. These initial designs under the trade
name of Heliscan were also supplied to various companies around the world,
under licence by the Davey Instruments Company.
This type of rotary head with its water jet non-contact probe
system proved highly successful for welded and cold drawn tube type of
product, although testing speeds were relatively slow. For seamless pipe
however, it soon became apparent that out of straightness conditions
particularly at the pipe ends meant that a more sophisticated probe
mechanism would be required |
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; the solution was to develop a probe block/shoe
containing an increased number of transducers which actually rides on the
surface of the tube and follows the pipe bends during testing.
Increasing numbers of transducers together with the requirement to test
the larger diameters in the OCTG range and the increase in weight due to the
more complex probe assembly mechanisms meant that a bearing with a higher
load carrying capability would be required. |
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This ultimately led to
the development of the world’s first hydrostatic bearing to be used for a
rotary device and by 1970 rotating heads using this type of bearing began to
be produced by the then Research Centre of the British Steel Corporations
Tube Division based at Corby. The major benefits which were realised
when using hydrostatic bearings for ultrasonic rotating heads were (i) high
load carrying capabilities (ii) virtually no bearing wear since there is no
metal to metal contact between the static and rotating parts and (iii) water
is used for both bearing and the ultrasonic coupling medium, which avoids
the need for seals and simplifies the mechanical design.
The first hydrostatic bearing head to be produced was known as the RP18 with
the capability to test pipe diameters in the range 4½" to 18" O.D.
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RP 18 |
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