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154 C h a p t e r 6 R e c o g n i z i n g t h e F o r m s o f C o r r o s i o n 155
Dual element
transducer
Paint coating
Ultrasonic waves
Internal corroded surface
FIGURE 6.6 Thickness measurements obtained through a paint coating using
a dual UT probe (adapted from [2]).
return to the transducer measured using either signal T or T as
3
2
shown in Fig. 6.7. Ultrasonic testing (UT) digital gauges with 4- to
5-MHz, dual-element transducers are able to inspect carbon steel or
austenitic stainless steel for walls thicker than 1 mm [5]. Dual-
element transducers can focus the ultrasonic beam at a specific depth
range thus enabling optimum sensitivity on corroded, eroded, or
irregular internal riser surfaces (Fig. 6.6). These transducers are
highly sensitive to small pits in their optimum thickness range.
T 1 T 2 T 3
Paint coating
Time
FIGURE 6.7 Thickness testing using longitudinal waves (wave propagation is
actually perpendicular to the surface, but is spread out in the image to show
the source of ultrasonic probing signals) (adapted from [2]).
