Page 559 - Corrosion Engineering Principles and Practice

522 C h a p t e r 1 2 C o r r o s i o n a s a R i s k 523

the standard MFL tool but its induced magnetic field is in a
transverse or perpendicular direction. This tool also has
limitations, for example, cracks must have sufficient width,
or gap, to be detected, and the severity of the crack is not
determined.
3. Elastic wave tools operate by sending ultrasounds in two
directions along the pipeline to locate and size longitudinally
oriented crack and manufacturing defects.
4. Electromagnetic acoustic tools are particularly adapted to the
detection of cracks in dry gas pipelines. This tool generates
ultrasonic signals without requiring liquid couplant to
transfer the ultrasound into the steel. These tools are new to
the pipeline inspection industry, so their effectiveness has not
yet been determined.

Geometry Tools
Geometry tools gather information about the physical shape, or
geometry, of a pipeline. Geometry tools are primarily used to find
“outside force damage,” or dents, in the pipeline. However, they can
also detect and locate mainline valves, or fittings. As with all ILI tools,
geometry tools have limitations on their use and in the usefulness of
the results obtained.

1. Caliper tools use a set of mechanical fingers or arms that ride
against the internal surface of the pipe or use electromagnetic
methods to detect dents or deformations.
2. Pipe deformation tools operate on the same principle of
caliper tools with the addition of gyroscopes to provide the
o’clock position of the dent or deformation in the pipe. This
tool can also provide pipe bend information.
3. Mapping tools can be used in conjunction with other ILI tools
to provide GPS correlated mapping of the pipeline and other
physical details, for example, valves.

References
1. Dawson J, Bruce K, John DG. Corrosion risk assessment and safety manage-
ment for offshore processing facilities. Offshore Technology Report 1999/064.
Norwich, U.K.: Health and Safety Executive, 2001.
2. Moreland PJ, Hines JG. Corrosion Monitoring: Select the right system.
Hydrocarbon Processing, 1978; 57: 251-255.
3. Horvath RJ. The role of the corrosion engineer in the development and applica-
tion of risk-based inspection for plant equipment. Materials Performance, 1998;
37: 70–5.
4. Wyatt LM, Bagley DS, Moore MA, Baxter DC. An Atlas of Corrosion and Related
Failures. St. Louis, Mo.: Materials Technology Institute, 1987.
5. Sachs NW. Understanding the multiple roots of machinery failures. Reliability
Magazine 2002; 8: 18–21.