POWER May 2023 - 31

OPERATIONS & MAINTENANCE
2. Comparison of ultrasonic testing (UT) and phased array ultrasonic testing (PAUT) techniques.
Courtesy: ASNT
■ Casting Defects. Porosity, blowholes,
inclusions, shrinkage, hot tears,
cracks, cold shuts, unfused chaplets.
■ Rolling defects. Laps, seams, laminations.
■ Forging defects. Laminations, forging
laps, cracks, centre bursts, hot tears.
■ Welding defects. Porosity, non-metallic
inclusions, incomplete fusion, lack
of penetration, cracks.
Items that have flaws exceeding acceptance
criteria are either replaced or
repaired and re-examined. Both UT and
PAUT are used during the manufacturing
and fabrication phase, although UT is the
more common method.
In-Service Flaws. Unlike manufacturing
and fabrication defects, in-service flaws are
created by thermal growth, cyclical movement,
and aggressive fluids in a plant's
piping systems. Fluids may produce intergranular
stress cracks; piping corrosion; cyclical
and thermal cracks; and component,
material, or weld and heat-affected zone
(HAZ) cracks. When plants have outages,
periodic maintenance occurs to evaluate
and address the situation. Ultrasonics
(PAUT/FMC) is the predominant volumetric
NDT method used to assess in-service
flaws. As such, PAUT is displacing RT as
the preferred examination method. Reasons
for this include:
■ In the nuclear industry, PAUT is emerging
as the superior inspection method.
PAUT inspections require a lower time
investment than radiography, which
requires valuable time to set up and
use the equipment.
■ RT requires removing people from the
work area to conduct an inspection.
■ PAUT scanning improves reliability
compared to conventional UT, using
multiple angles to scan larger areas.
■ PAUT offers better access to difficultto-reach
components.
■ Inspectors can use the same PAUT
probe to detect randomly oriented
cracks at different depths.
■ PAUT increases accuracy in detection,
sizing, and location of critical defects,
regardless of their orientation.
Whereas, UT requires the use of mulMay
2023 | POWER
tiple focused beams with the ability of
changing focal depth and sweep angle
to examine flaws.
How UT-PAUT Technology Has Been
Incorporated in Standards and Codes
During the initial construction and manufacturing
of a plant or station, owners,
governmental agencies, and insurance
companies implement their associated
standards that are carried into the inservice
phase. Some important American
National Standards Institute (ANSI)
and American Society of Mechanical
Engineers (ASME) power industry codes
and standards include ANSI B31.1 Power
Piping, ASME Boiler and Pressure Vessel
Code (BPVC) Section I Power Boilers,
ASME BPVC Section VIII (Division 1 and
2) Pressure Vessels, ASME BPVC Section
III Nuclear Construction, and ASME
BPVC Section XI Nuclear In-service.
Standards are created and updated by
industry volunteers, including users, regulators,
and professional society members
(managers, engineers, and technicians).
When the industry observes technological
advancements, volunteers recognize
those improvements and adopt them into
their society standards.
Codes are standards endorsed by a
regulatory agency that are then " Incorporated
by Reference " into laws. Codes are
normally cited in a law or regulation. Since
codes are, therefore, enforceable by law,
they are cited in engineering specifications,
bid packages, and contracts.
The steps occurring when adopting improvements
into standards and codes are
similar across technical societies. Normally,
a " Code Case " is presented to the applicable
standards committee. In the past,
UT-PAUT has been introduced to various
standard committees as Code Cases.
How Industries Qualify UT-PAUT
Inspectors
For NDT inspectors, qualification and
certification is necessary to conduct
proper UT-PAUT evaluations in the power
and process piping industry. The Power
Piping (B31.1) and Process Piping (B31.3)
codes contain sections addressing dewww.powermag.com
sign,
materials, dimensional requirements,
fabrication, assembly, erection,
inspection, examination, and testing. The
inspection section references the ASME
BPVC Section V Nondestructive Testing.
This makes the requirements in the
daughter document contractual.
ASME BPVC Section V Article 1 (with
Mandatory Appendix II) cites the general
requirements for NDT personnel qualifications,
including requirements for UTPAUT
personnel. Also, it incorporates the
American Society for Nondestructive Testing
(ASNT) documents SNT-TC-1A (2016
Edition), as amended by ASME V, Article
4, Mandatory Appendix III; or ANSI/ASNT
CP-189 (2016 Edition), as amended by
ASME V, Article 4, Mandatory Appendix IV.
The U.S. has 92 operating nuclear
power plants. In the nuclear industry, preservice
and in-service nondestructive examinations
are required and must follow
implemented codes. ASME BPVC Section
XI governs plant systems in the reactor
containment, which in many plants
includes a reactor, pressurizer, steam
generators, main steam piping, and reactor
coolant piping. To meet code requirements,
UT-PAUT personnel must abide by
ASNT CP-189, as modified by Appendices
VII and VIII of ASME BPVC Section XI.
Employers who fulfill the base UT
personnel qualification program have to
follow CP-189 and Appendix VII. UT and
PAUT personnel are also required to gain
qualification in the Mandatory Supplements
of Appendix VIII when examining
most containment components. Typically,
personnel obtain these certifications
by qualifying with the Electric Power
Research Institute (EPRI). The other
buildings of a nuclear plant, such as the
primary auxiliary building and turbine
building, are referred to as the balance of
plant (BOP), and for UT and PAUT examinations
governed by ANSI B31.1.
The analog ultrasonic single element
straight beam transducer primarily used
since the 1940s evolved into a computercontrolled
64 - 128 element transducer
that can locate, size, and create real-time
flaw images. The diligent efforts of volunteers
and professional society organizations
to incorporate new and advancing
technology into standards and codes is
essential to the transformation of the industry.
When organizations like the ASNT
adopt new technology into their training
programs to support code requirements,
UT-PAUT personnel are equipped with the
latest inspection knowledge and skills. ■
-A.M. (Marty) Wenzig is an ASNT Fellow
and an ASNT advocacy committee member.
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POWER May 2023

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