Page 201 - Pipeline Pigging Technology

Pipeline Pigging Technology

Pig run Reported Total Field-verified % verified
investigated corrosion

1st report 241 189 122 65
2nd report 178 123 69 56
Total 419 312 191

The unverifiable reported anomalies were the result of laminar inclusions,
other magnetic variations and false reports.

Table 1. Magnetic-flux corrosion pig field verification results.

Magnetic flux Ultrasonic
verified calls where a pipe anomaly was found 93% 97%
verified calls where corrosion was found 61% 73%
verified calls that required repair 7% 29%
Table 2. Comparison of field results of pig technologies.

oil or product lines can use either type, but ultrasonic pigs are usually
limited to use in liquid lines because of the need for a couplant.

ultrasonic pigs, because of their higher level of accuracy, have distinct
advantages in areas where pipelines have limited accessibility, such
as deep burial areas, river crossings or high-density population areas.

ultrasonic technology has the capability of measuring isolated patch or
pit corrosion to depths of 10% of pipe wall, whereas at the present
time magnetic flux is more suited to detection of general corrosion
to depths of 20% to 30% of pipe wall in 48-in diameter pipe due to
performance of sensing units and experience and capability of the
personnel grading the data.

magnetic-flux pigs may not be able to detect corrosion in the area
adjacent to the girth weld and longitudinal seams due to sensor lift-
off. If these heat-affected zones are of specific concern, the ultra-
sonic pig will produce data up to the weld.

Both corrosion technologies have some blind areas: that is, areas which,
because of limitations in the technology, are not able to produce valid data.

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