Page 76 - Reliability and Maintainability of In service Pipelines

Pipeline Inspection and Maintenance 65

Figure 2.7 Example of an intelligent pigging device.
A three-phase automated pipe condition assessment is normally considered
while using an intelligent pigging device, including defect detection, defect inter-
rogation, and defect classification.
The first phase of the process (defect detection) involves the use of a robot
which moves at a relatively normal speed to detect defects along the pipeline. If a
potential defect is identified, the robot stops and records higher quality visual
images and data to determine either it is a real defect or just a false alarm. After
this step, the robot will continue to move forward and look for more defects.
The second phase (defect interrogation) involves the robot stopping completely
once a defect is determined, and performing an examination of the area where it
was detected. Here, the robot will discriminate each defect specifically among sev-
eral types such as cracks, fractures, roots, corrosion, or lining failure.
The third phase (defect classification) involves classifying the defects either dur-
ing the inspection or online after the entire inspection process has been completed
using several classification techniques which the system has been programmed with.
For example, if a crack was identified in the second phase, it could be identified as a
horizontal or spiral crack in the third and final phase of the inspection. The final
classification also determines the severity of the defect and whether it needs imme-
diate attention, further monitoring or it is safe to ignore it at the current time.

2.3.4 MAGNETIC FLUX LEAKAGE TECHNIQUE

Magnetic flux leakage (MFL) detection technique is one of the common methods
of pipeline inspection in oil and natural gas industry. It is a nondestructive testing
technique which uses magnetic sensitive sensors to detect the magnetic leakage
field of defects on both the internal and external surfaces of pipelines. It provides
very high and accurate resolution pictures of the interior walls of pipelines where
defects and other anomalies can be identified and assessed.