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In many cases, it is more practical
to move the transducer assembly along the weld seam with the pipe stationary
(weld at TDC), either with the operator/electronics on the traversing
carriage. The latter has the advantage that the operator is in close
attendance during the test to monitor weld seam tracking and carry-out
confirmation checks on auto indications as they occur etc, etc.
The choice of which system, moving pipe or moving test head, to adopt is
highly dependant on the particular circumstances within the pipe mill, the
degree of automation of the ultrasonic equipment, the degree of operator
involvement in the test etc., etc, and the cost to implement.
Ultrasonic Transducer Configurations
There are a number of different ultrasonic transducer configurations
possible in SAW pipe weld seam testing, the most common being the X, K and
IX configurations (see figure 1). The X configuration is the most common but
is not popular with many of the oil majors and others, as it suffers from a
number of technical limitations. Most of the major pipe makers, e.g. use the
K, modified K or IX configurations. These configurations use separate
longitudinal and transverse imperfection seeking transducer pairs, as
opposed to the X system which uses the same transducers for both
longitudinal and transverse detection.
The choice of whether to use the K or IX configuration is dependant on
the maximum pipe thickness to be tested, and to some extent on the
prevalence of particular imperfections in a specific process route. The
simple K – configuration is suitable for pipe thicknesses up to circa 18mm,
while the modified K increases the longitudinal detection up to about 26mm
thickness, and the IX configuration full detection up to 26mm thick pipe.
Pipe/Weld Geometry
The pipe shape and weld seam geometry are critically important to a
satisfactory ultrasonic test when using automatic/semi-automatic equipment
(incorporating fixed transducers). UOE pipe mills provide a high degree of
pipe shape and weld geometry control, whereas other SAW pipe processes may
have limitations in this area. The following pipe shape/weld geometry
conditions can cause limitations to a satisfactory ultrasonic test of the
weld seam:
(a) Apple/Pear Shape (including ‘flats’ close to the weld)
(b) Scale on the parent pipe external surface close to the weld
(c) Weld spatter on the external pipe surface
(d) Poor weld shape, both inside and outside welds
(e) Edge misalignment
(f) Weld misalignment
(g) Flat/peaked welds
(h) Presence of edge laminations/inclusion clusters in plate
(i) et al
It cannot be stressed too highly that good pipe shape and weld seam
geometry is essential to a satisfactory ultrasonic test of the weld seam.
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