Page 354 - Pipeline Pigging Technology

Corroston surveys with the 'UltraScan' pig

CORROSION SURVEYS WITH THE

ULTRASCAN PIG

CORROSION INSPECTION of long-distance pipelines is increasingly car-
ried out by electronic surveying robots, so-called intelligent pigs. These
devices locate dents, cracks, and corrosion damage by utilizing modern
electronic NDT technology. A 2nd-generation corrosion-detecting pig is
described in this paper, a device whose development has only been made
possible due to recent advances in microprocessor technology.

BASIC PRINCIPLES

The idea of using electronic-surveying pigs for checking the condition of
a pipeline is not new. During the early 1970s, a generation of research tools
was developed by a number of companies which employed the magnetic
stray flux method to locate corrosion in pipelines.
The disadvantages of the stray flux technology applied by these first-
generation tools was their inability to measure both wall thickness and the
depth of corrosion directly. These tools only reacted to a local metal loss in
the pipe's wall; the error margin was quite wide. They were able to indicate
the location of corrosion, but did not accurately measure its depth. Another
disadvantage of this method was that other inhomogeneites in the pipe wall
are indicated as defects, even though they are not always relevant to safety
considerations.
For the new second-generation pig, the task was defined to measure the
pipeline's residual wall thickness directly. The method of measuring wall
thickness with ultrasonics was selected, because it is both a very accurate
technique and has proved itself in many years of industrial use. The pig was
developed by Pipetronix GmbH in co-operation with the Nuclear Research
Centre in Karlsruhe.-
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