Page 482 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

Ancillary Sensors
CHAPTER CONTENTS
18
18.1 Nondestructive testing definition and sensors...............................................................................477
18.1.1 Magnetic particle inspection.................................................................................. 478 18.1.2 Alternating current field measurement.................................................................... 479 18.1.3 Ultrasonic flaw detection ...................................................................................... 480
18.2 Metal object detection ................................................................................................................481
18.2.1 Active versus passive ............................................................................................ 481 18.2.2 Activepulseinductance........................................................................................481 18.2.3 Passive inductance............................................................................................... 483 18.2.4 Magnetometers and gradiometers........................................................................... 486
18.3 Flooded Member Detection (FMD).................................................................................................493
18.3.1 Acoustic FMD ...................................................................................................... 494
18.3.2 Radiographic FMD................................................................................................ 494
18.4 Cathodic potential sensors ..........................................................................................................494
18.5 Ultrasonic metal thickness ..........................................................................................................499
In this chapter, further payload sensor technology is examined. These sensors are integrated through the ROV (by attaching to the frame with sensor power coming from the vehicle and telem- etry typically routed through the vehicle tether) and fit into the category of inspection, repair, and maintenance (IRM) sensors.
18.1 Nondestructive testing definition and sensors
Nondestructive testing (NDT), by definition, is a series of techniques whereby materials are tested for structural flaws through direct and/or indirect means such that the procedures do not destroy the test subject. These types of tests include acoustic, electromagnetic field, radiographic, and other active and/or passive physical stimulations in order to verify metal integrity. The objective of this process is to identify and quantify discontinuities in the metal structure for assuring structural integ- rity of the test subject.
Homogeneous metals allow magnetic, sound, and radiographic waves to pass evenly through the medium. Cracks, discontinuities, and other faults in the metal interrupt the flow of these waves,
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© 2014 Robert D Christ and Robert L Wernli. Published by Elsevier Ltd. All rights reserved.
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