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High Integrity In-Line Ultrasonic Inspection of
Large Diameter Electric Welded Pipe |
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Introduction
Several ultrasonic testing systems have been installed in an
Electric Weld mill in the United Kingdom, specialising in large diameter
pipes, for both
in-house quality control and customer acceptance purposes.
These systems were originally to provide the pipe mill with
modern ultrasonic testing facilities to meet the ever increasing demand for
quality assurance of large diameter electric welded pipe in the gas, oil and
associated industries. Automatic ultrasonic inspection has been almost
universally adopted at various strategic locations within the process route
to ensure product integrity, strongly influenced by stringent customer
acceptance criteria, coupled with excellent test performance and reliability
necessary for a high volume, modern welded pipe mill. |
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Description of Test Systems
The automatic ultrasonic test systems at the mill are sited at three
separate locations within the process route. Each of the three test systems
incorporate a weld line tracking facility which relies on the detection of a
white line edge by means of a line scan video camera. Both the camera and
ultrasonic probe assemblies are mounted on a common rotating ring and a weld
seam tracking accuracy of ± 2mm is readily achieved. All pipes produced are
automatically marked with a narrow white line which is accurately reference
to the weld line centre and is applied just prior to the actual welding
point.
The first test system in the process route is located immediately after
welding and includes an ultrasonic shear wave weld seam inspection. |
Combined ultrasonic weld test system
with automatic weld tracking |
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The ultrasonic shear wave probes are
similar to those used on the sizing mill exit and are as described in the
following paragraph.The weld trim profile monitoring system uses a laser
viewing system located on the I.D. trimmer
bar and has been recently developed by the plant engineers. These two
systems therefore provide a rapid feedback to the welding mill operator on
the weld and bead trimming quality.
Further downstream a second system is located at the exit of the sizing
mill and comprises of a composite weld seam/weld edge inspection unit. This
system provides a high sensitivity weld seam integrity check together with
an ultrasonic probe system for the detection of laminar imperfections
immediately adjacent to and on either side of the weld line. |
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The weld seam inspection equipment
at this location consists of two pairs of specially developed 45° shear wave
probes. The probes have been designed to enable reliable detection of very
short imperfections whilst still maintaining a tolerance of probe to weld
position of ± 6mm. An additional feature of the probe design also ensures
that, in addition to detection surface breaking imperfections, totally
enclosed imperfections are also detected. The electronic equipment
associated with the shear wave probes provides for twin trigger levels on
each channel and allows for enhanced sensitivity to be used for those
imperfections (purely radial in nature) giving rise to similar reflected
signal amplitudes from both sides of the weld. The weld edge inspection
unit, when required, utilises four compression wave probes, providing an
inspection for laminations over a 25mm wide band either side of the weld
seam. This composite inspection system provides a means of segregating
acceptable and suspect pipes prior to further pipe finishing operations.
Subsequent to pipe-end bevelling and hydrostatic testing, pipes pass to
the third location, which is a sophisticated automatic ultrasonic testing
acceptance facility comprising of a final weld seam inspection unit
immediately followed by a full body rotary probe examination. The weld seam
inspection unit, similar to that on the sizing mill incorporates automatic
weld line tracking, 45° probe angle inspection and twin sensitivity levels.
The probe mechanics are designed such that self-application of the probes,
together with automatic pipe speed control permit testing very close to the
pipe ends, i.e. less than 25mm at the nose end and less than 12mm at tail
end. During calibration adjustment of the probes circumferential position
relative to the calibration notch is controlled remotely from inside the
operator’s cabin; in addition the longitudinal position of the probes can be
altered by up to 50mm to allow signal optimisation from the calibration
holes or notches. The rotary probe unit RP20 provides full body inspection
for the detection of laminar imperfections, longitudinal imperfections and
thickness measurement. The rotary probe unit can test pipes in the diameter
range 114mm – 508mm at rotational speeds up to 450rpm. Normally four probe
assemblies are used, each carrying one compression wave and two shear wave
probes. The design of the self applying probe assemblies, which utilise
contact wear shoes, allow for the testing of pipes which can be positionally
offset by ± 10mm. The electronic equipment associated with the two test
systems produces automatic test result graphic displays and pass/fail data
which can be used for process/quality control purposes and customer
documentation if required. In addition the results of the test are
automatically stored and transferred to a ‘Hand Probe’ confirmation site to
facilitate operator assessment of detected imperfections.
Additional pipe-end testing facilities using MPI and/or ultrasonic
methods are available further downstream in the finishing line.
Consistent with the high level of quality assurance throughout the plant,
the ultrasonic systems described represent a total inspection capability to
ensure the integrity of large diameter welded pipe used in many critical
applications as required by the current needs of the gas, oil and associated
industries.
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Author |
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C. James
C.Phys., M.Inst. P., M.Inst.NDT |
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