1) The document discusses the differences between long range ultrasonic testing (LRUT) and medium range ultrasonic testing (MRUT) for inspecting pipelines. LRUT uses lower frequencies to inspect over longer distances, while MRUT uses higher frequencies to inspect shorter distances but with higher sensitivity. 2) It describes a new technique using MRUT with shear horizontal guided waves for circumferential scanning to inspect inaccessible areas like under pipe supports. This provides better detection and resolution than LRUT within close proximity to defects. 3) The new technique uses a magnetostrictive strip adhered around the pipe that is scanned by a single transducer scanner to perform circumferential inspections and complement LRUT for inspecting shorter

1. A new wave of EMAT
inspection
Borja Lopez and Frank Weinmeister, Innerspec Technologies, USA, highlights the
differences between long range and medium range ultrasonic testing.
E
lectro magnetic acoustic transducer (EMAT) is an
ultrasonic testing (UT) technique that generates sound
in the part that is under inspection instead of the
transducer. As illustrated in Figure 1, EMAT generates
ultrasonic waves in a test object using electromagnetic
induction with two interacting magnetic fields. A relatively
high frequency field is generated by electrical coils interacting
with a low frequency or static field that is created by magnets.
This interaction creates a Lorentz force in a manner that is
similar to an electric motor. The disturbance is transferred
to the lattice of the material, producing an elastic wave. In
a reciprocal process, the interaction of elastic waves in the
presence of a magnetic field induces currents in the receiving
EMAT coil circuit.
Since the sound is generated in the part inspected as
opposed to the transducer, EMAT is a non-contact technique,
which gives the inspection method significant advantages for
in-service applications over more conventional piezoelectric
UT inspection techniques.
The two most common methods used for in-service
inspections with guided waves are long range UT (LRUT)
and medium range UT (MRUT). This article will discuss the
applications and techniques deployed when using guided
waves along with a MRUT system.
1

2. In-service inspection methods and equipment
LRUT is used almost exclusively for pipeline inspection in
reflection mode to cover long distances (tens of meters) from
a fixed ring of sensors. It normally works with low frequencies
(sub-100kHz) and typical detection capabilities are 10% of
the cross-sectional wall loss. Meanwhile, MRUT can be used
in both attenuation and reflection mode to cover shorter
distances (0.1 - 5 m). Sensors are mounted onto scanners in
order to inspect long stretches of pipe. It typically works with
frequencies ranging from 100kHz to 1MHz, and can detect
small pits (with approximately 10 times more sensitivity than
LRUT).
The MRUT uses high frequency guided waves with a typical
inspection range of between 4 in. (0.1 m) and 16 ft (5 m) to
detect corrosion, cracks and discontinuities on exposed oil
pipelines. The system uses high power EMAT technology to
perform 100% scanning at speeds of up to 150 mm/s on pipe
diameters of between 2 in. (50 mm) and 46 in. (1168 mm) with
wall thickness of 0.5 in. (13 mm) or less. The inspection can be
performed on rough and corroded surfaces and on pipelines
that are covered with thin wraps and/or coatings (<3 mm).
The equipment used for the inspection can be configured
with a handheld instrument and scanner for smaller, easy
to access jobs or a high speed portable system with an
automated crawler for fast scanning and climbing on pipes
horizontally and vertically. The handheld instruments are
designed to be used with permanent magnet sensors, while
the high speed system can be used with permanent or pulsed
magnet sensors for superior signal-to-noise. Both equipment
options are suitable for axial and circumferential scanning
techniques.
The equipment includes sensors and software
configurations that excite guided wave modes for different
thicknesses and environmental conditions. With the use of
higher frequencies and a shorter range, the MRUT technique
detects isolated pitting and wall loss with enhanced resolution
of up to t0 times better than LRUT systems with minimal or
no dead zone.
In-service applications
For inspection of in-service pipelines, the MRUT technique
using Shear horizontal (SH) and lamb guided waves is an
effective choice for rapid screening and detection of cracks,
pits and corrosion. The applications include:
)) Inspection under supports – these are one of the most
problematic areas for corrosion. The abovementioned
MRUT method works for both pipelines that are welded or
standing on supports.
)) Air-to-soil interfaces – using non-leaking guided waves, the
MRUT technique can be used for inspection of the first 1 -
2 m of an inaccessible structure (buried or hidden).
)) On free-standing pipelines, the MRUT technique detects
smooth corrosion, pitting and cracks with minimum
insulation (less than 3 mm).
Detecting defects and corrosion under pipe
supports
Both corrosion and cracking are ever-present problems for
every industry that relies on pipelines to transport liquid and
gas products. There are already several techniques and much
equipment available on the market for non-destructive testing
of pipelines. The most effective inspection methods are tend
to be ones that have been designed to align with specific
needs, access restrictions and environmental conditions.
Over the last few years, EMAT has become more
prominent due to its ability to provide fast scanning
capabilities when detecting corrosion, cracks and other
defects using medium-range guided waves on exposed
pipelines.
Recent developments in the sensors and techniques used
for MRUT have enhanced the technique’s capabilities to
reliably inspect inaccessible areas, such as corrosion under
supports and pipes with heavy coatings.
Axial and circumferential scanning with MRUT
LRUT uses encircling rings to generate guided waves that can
detect moderate defects over long distances on relatively
clean pipes. One of the main disadvantages of this technique
is that it has an uninspected dead zone of 1 - 2 m in front of
the transducer. This deems LRUT an inappropriate method
for small distances and where valves, connections and other
features are present.
EMAT-generated MRUT lamb waves have been used for
axial scanning using attenuation techniques for several years.
This technique permits fast scanning of exposed pipe with
effective detection results. However, its use in circumferential
Figure 2. Circumferential scanning using attenuation vs. axial
scanning using reflection.
Figure 1. A UT technology comparison.
2 World Pipelines / MARCH 2017

3. scanning (reflection mode) when inspecting inaccessible areas
is limited by the use of lamb guided waves, which can leak
into coatings or supports and restrict MRUT’s practical use in
the field.
In response to these limitations, a new patent-pending
scanner and technique developed by Innerspec Technologies,
in co-operation with GuidedWave, has introduced the ability
to use SH guided waves for MRUT circumferential scanning.
SH waves provide several benefits for defect and corrosion
detection in pipelines. Being less dispersive than Lamb waves,
SH waves allow for clearer signal interpretation. They are
more consistent through materials, while also being less
susceptible to mode conversion. Higher frequency ranges can
be used with SH waves, which provides improved axial and
lateral resolution. Moreover, SH waves have minimum out-of-
plane motion and can travel greater distances with minimum
attenuation on coated pipes and on full pipes.
In addition to these advantages of using SH waves,
Innerspec’s single transducer scanner has a dead zone of 10 - 15
cm. This permits inspection in very close proximity to the area
of interest. By inspecting closer to the defects, the detection
and resolution are 10 times more effective than with LRUT.
The equipment required for Innerspec’s technique includes:
)) PowerBox H; a high power EMAT instrument.
)) MRUT software for circumferential scanning.
)) A scanner with a built-in coil and encoder for outside
diameters of over 4 in.
)) A magnetostrictive strip material.
)) A magnetiser.
This technique uses a thin magnetostrictive material
that is adhered around the circumference of the pipe, either
temporarily or permanently. The strip is then magnetised
and the scanner is moved along the strip and around the
pipe. Magnetic wheels facilitate scanning on ferromagnetic
pipes, although the technique is valid for any type of pipeline
material, including plastic.
The inspection data can be recorded and saved for
analysis and reporting once the job has been completed. If the
magnetostrictive tape is permanently applied, it only needs to
be magnetised again before performing the inspection. Thus,
multiple locations can be inspected quickly on a scheduled
basis.
Innerspec’s method can complement LRUT by providing
greater detection and resolution on both shorter lengths of
pipe and on restricted access areas, where the deployment of
LRUT rings is not feasible.
Conclusion
With the addition of an SH circumferential scanner, the range
of applications that EMAT can be used for has increased. Thus,
EMAT can be used for axial scanning on exposed pipe, along
with circumferential scanning for inspection under support
and other inaccessible areas.
With the ability to be used to complement other
techniques or as a standalone application, the MRUT SH
circumferential scanner offers a new EMAT solution for an
inspector’s toolbox.
Figure 3. A MRUT circumferential scanner.
MARCH 2017 / World Pipelines 3