POWER December 2014 - 19

4. Ready for action. This image, taken
at a refinery in Rome, Italy, shows the scanning
force microscope, mounted on a pipe,
ready to test the low-alloy steel component.
Courtesy: ETD Consulting
P92 Inspection and Life Assessment. " This
portable tool (Figure 4) was specifically
developed in an attempt to detect early
stage nano-level creep cavitation in P91
and P92 in-service components (Figure 5).
Notoriously, damage can go undetected by
traditional means (such as replication, or
standard ultrasonic testing) in these components
until 70% to 80% of their useful
life has expired, and failure can occur by
fast fracture without much warning.
The SFM also gives three-dimensional
5. Finding flaws. The image shown here
was produced using the scanning force microscope
and shows nano-level cavitation damage
in a P91 pipe at a coal-fired power plant in
the Philippines. Courtesy: ETD Consulting
images (Figure 6) and can thus calculate
and plot cavity volume, which is a better
measure of the component damage. SFM
has now been used on two sets of P91
creep-tested specimens (tested at 600C
and 625C) where tests were interrupted at
20%, 40%, 60%, and 80% of life, and the
cavity volume measured using the SFM was
compared to the life fraction consumed. It
has also been used successfully on steam
valves at an EDF-owned power plant in
France, on P91 in-service steam pipes in
power plants in the Philippines and Malaysia,
and on 1CrMo rotors in Poland.
In Phase 2 of the above-mentioned indus6.
Deep trouble. The three-dimensional
image generated by the scanning force microscope
shows the depth of a cavity in a P91
pipe. Courtesy: ETD Consulting
try-sponsored project, P91 and P92 welded
pipes are being tested in Germany at 600C
(P91) and 625C (P92) for test durations of
up to 10,000 hours, both under creep and
creep-fatigue conditions. These tests are being
stopped at intervals of 2,000 hours, and
SFM-together with other nondestructive examination
inspection and monitoring tools,
some equally innovative-is being used to
relate the creep cavity damage observed with
the remaining life of these pipes.
Several problems are faced at high-temtime,
depending upon the measured strength
level and the operating conditions (temperature
and stress). In these situations, ETD recommends
that the component be monitored
closely until it is eventually replaced.
Although the work described above
is for a power plant under construction,
" boat sampling " is equally useful for assessing
the integrity and safe remaining
life of critical components in operating
power and process plants for all types of
metallic/alloy materials.
Nano-Level Creep Detection
ETD and one of its European industry partners
developed another new tool, known
as the scanning force microscope (SFM), as
part of the now-completed Phase 1 of another
joint industry project named " P91/
December 2014 | POWER
perature plants containing P91 components
worldwide. Aberrant or abnormal P91 material
and welds are frequently found to have
been caused by improper heat treatment,
which was not carried out with the critical
accuracy required for this generation of
martensitic steels. Although new tools can
help to inspect and quality check some of
the aberrant material components, some
others, such as those with wrong root runs,
may be difficult to identify, thus leaving
the risk unknown and unmanaged.
Even components that can be identified
to be at risk are creating issues for plant
owners and integrity assessors in view of
the unknown long-term rupture strength
of the aberrant steels. This emphasizes the
need for the generation and interpretation
of data to help evaluate the safe operating
life of plant components. ■
-Dr. Ahmed Shibli (ashibli@etd
-consulting.com) is managing director and
Dr. David Robertson is lead metallurgist
for ETD Consulting.
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POWER December 2014

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