Page 73 - Reliability and Maintainability of In service Pipelines

62 Reliability and Maintainability of In-Service Pipelines

2.3.2 LASER SCANNING

Another inspection method which is similar to the CCTV, is the laser scanning
(Fig. 2.6). CCTV produces high quality imaging however, the laser scanning pro-
vides even greater detailed pictures, which is greatly beneficial and improves the
effectiveness of successfully identifying defects in pipeline networks. Laser scan-
ning is able to demonstrate segmentation and classification of some common
defects within pipes such as cracks, joints, and holes. This technology is not
widely used among the industry due to its high inspection costs, time taken to
complete an evaluation of pipes, and other implementation limitations.
Laser scanning together with supportive software quickly spread out across
pipeline inspection techniques in 2000. Duran et al. (2007) describe in their study
how the CCTV camera device can be mounted with a laser-based profiler and an
optical diffuser and is supported by a defect classification algorithm. The algo-
rithm was based on the image intensity values quantification of the projected
rings viewed by the camera where intelligent image processing and Artificial neu-
ral network (ANN) techniques were adopted. This approach enables the building
up of a signature database for a number of defect types for future automatic iden-
tification. Conventional laser scanning techniques have an incorrigible error in
measurements which is equal to the diameter of the laser spot, usually around
4 mm. An advantage of the method proposed by Duran et al. (2007) over other
existing methods is that laser size has no implication on result accuracy and even
a small imperfection can be measured; as such, the results were reported to have
an accuracy of 1 mm. Additionally, the proposed method has no significant
requirement to have the laser ring pointing directly in the pipe center and does
not require an extra smooth motion.

Figure 2.6 Laser scanner for pipe inspection.