Mitsubishi Heavy Industries Technical Review Vol. 55 No. 2 (June 2018)
1Development of Remote Monitoring System forOperating Power Plants Using Thin-film UT Sensors

YUKO YAMAMOTO*1

KAZUUMI KONDO*2TADASHI KIMURA*1

SEIICHI KAWANAMI*3

YUMA ITAHASHI*4

TAKESHI KODAIRA*4

Mitsubishi Heavy Industries, Ltd. (MHI) has developed an ultrasonic pulsar receiver with aradio communication function that allows wireless transmission of measurement data obtained byan ultrasonic sensor such as a thin-film UT sensor to a remote location. The ultrasonic pulsar
receiver, in combination with a thin-film UT sensor, is installed in piping, etc., thereby realizing
continuous remote monitoring of the high-temperature piping during operation. The developed
ultrasonic pulsar receiver is driven by dry cells so that it can be used in locations where there is nopower supply and is miniaturized to palm size so that it can be installed anywhere. This report
describes the technical specifications of the developed ultrasonic pulsar receiver and thedevelopment of the application of the remote monitoring system in combination with the thin-film
UT sensor.

|1. Introduction
In power plants, pipe wall thinning due to corrosion during system operation is a well-known
issue, and it is important to monitor the state of pipe wall thinning in order to increase theefficiency of replacement plans for maintaining the soundness of facilities. Under present
circumstances, fixed-point measurements of pipe wall thickness are carried out regularly at many
plants in accordance with guidelines and standards. In some cases, in addition to the measurementof pipe wall thickness, the measurement of the water level in a horizontal pipe is conducted
regularly to detect air pockets in pipes in the system. In such regular measurements, it is difficult tofind any significant wall thinning or air pockets immediately by just a single measurement, and it isnecessary to increase the frequency of regular measurements in order to detect any abnormalities
before pipe wall thinning or air pockets adversely affect facilities. But the pipe temperature is highduring system operation, and it is difficult to conduct continuous measurements using a general UT(Ultrasonic Testing) sensor. For measurement during operation halts when the pipe temperaturebecomes normal, the included work such as the installation and removal of heat insulation materials
and temporary scaffolding are required at each measurement, and the increase in the frequency ofmeasurement results in an increase in inspection cost. In order to solve these problems, amonitoring system2 was developed, in which a thin-film UT sensor1 which can be continuously
used at high temperature and an ultrasonic pulsar receiver with a radio communication function arecombined. In this report, the outline of the monitoring system, the features of the thin-film UT
sensor and the ultrasonic pulsar receiver with a radio communication function, as well as thedevelopment of the application of the monitoring system, are described.

|2. Outline of the monitoring system
The configuration of the developed monitoring system is shown in Figure 1. This monitoring
system is comprised of the thin-film UT sensor, the ultrasonic pulsar receiver with a radiocommunication function (hereinafter referred to as the pulsar receiver), a PC for the collection of
*1
*2
*3
*4

Electricity & Applied physics Research Departmen, Research & Innovation Center
Chief Staff Manager, CIS Department, ICT Solution Headquarters
Manager, Electricity & Applied physics Research Departmen, Research & Innovation Center
Quality Assurance Department, Nuclear Energy Systems Division, Power Systems

Mitsubishi Heavy Industries Technical Review Vol. 55 No. 2 (June 2018)
2data and a PC for monitoring. Since the thin-film UT sensor is thin and flexible and can becontinuously used in a high-temperature environment, it is used in a state of being permanently
installed inside of a heat insulating material even during system operation. The heat-resistant cabledrawn out from the thin-film UT sensor through the inside of the heat insulating material isconnected to the pulsar receiver installed in the vicinity of the pipe, etc., to be measured. Using thispulsar receiver, UT data can be obtained from multiple sensors at a specified frequency. It is
assumed that this monitoring system is used by the two methods described below (Figure 2), andthe data acquisition mode can be selected according to the operating conditions such as the use or
non-use of radio communication and PC installation location.

Figure 1 Configuration of the monitoring system

Figure 2(A)Operation modes of the monitoring system

Continuous monitoring mode
The UT data acquired by the thin-film UT sensor is wirelessly transferred to a dataacquisition PC which is setup in a building. On the data collecting PC, the UT data may bechecked or analyzed, but access from the monitoring PC connected by LAN line, etc., to thedata acquisition PC enables remote checking or analysis of the UT data. It is assumed that themonitoring PC is setup at a distant location such as outside of the building, and thisconfiguration realizes continuous remote monitoring.
(B) Patrol mode
When the monitoring system is used in an environment where radio communication
cannot be used because it may affect existing equipment, etc., the UT data acquired by thethin-film UT sensor is recorded in the memory of the pulsar receiver in advance, and the dataacquisition PC that is carried on regular field patrols, etc., is directly connected to the pulsar
receiver to collect the UT data recorded in the memory. The collected UT data can be checked
or analyzed on the data acquisition PC or the monitoring PC in the same way as in continuous
monitoring mode. Although real-time monitoring cannot be conducted in patrol mode, included
work such as heat insulating material work is not required and UT data during system operation
can be the obtained. Therefore, the frequency of measurement can be increased while reducing
costs.

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With one data acquisition PC, multiple pulsar receivers can be set and data from several
pulsar receivers can be collected, which allows the monitoring of a plurality of sections to bemeasured in a building. In addition, UT data collection parameters such as gain and frequency
during continuous measurement can be changed on the data acquisition PC without direct operationof the pulsar receiver, and even in the case where it is difficult to access a measuring site,
continuous monitoring can be realized.

|3. Features of the thin-film UT sensor
The outline of the thin-film UT sensor has already been reported(1), and this report describes
the latest state of the continuous heating test which has been continuously implemented for theverification of durability. In the simulation of the measurement of the wall thickness of a pipe
which reaches high temperature, the heating test has been conducted with a specimen of thethin-film UT sensor installed on a test body pipe. An electric furnace is used for heating to keep thetemperature constant, and the UT data of wall thickness measurement is obtained regularly fromthe outside of the electric furnace. In this test, the wall thickness of the test body pipe is not
reduced, and it has been continuously observed that a constant wall thickness value is exhibited andthere is no substantial change in signal sensibility or fluctuation of the waveform.
Using the thin-film UT sensor with the material of the piezoelectric element changed
according to the test temperature, continuous heating tests have been conducted at constanttemperatures of 200°C, 300°C and 450°C. The cumulative number of days when heating has been
conducted since the start of the heating and the results of the measurement of the pipe wall
thickness are given in Figure 3. At the right of the graph, one example of signal waveform duringcontinuous heating is shown. As can be seen in Figure 3, the signal waveform showing that thepipe wall thickness can be stably measured at the time when 1500 days – the longest duration – haselapsed at the temperature of 300°C was obtained, and a constant wall thickness value has beenacquired except for variations due to temporary changes in measurement conditions. During thistest, there were temperature drops due to several power failures, but no effect of these temperaturechanges on the signal was observed. This continuous heating test will be continued to accumulate
the actual continuous heating data.

Figure 3

Result of continuous heating tests for the thin-film UT sensor

Based on the results of the in-house tests described above, the thin-film UT sensor has been
installed in power plant facilities under operation for trial operation with actual units, and thesignals have been regularly acquired. For the thin-film UT sensor installed in a steam system pipe
(thickness: about 6 mm, system temperature: about 150°C) at a nuclear power plant, the signal

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waveform showing that the pipe wall thickness can be stably measured was obtained after about
800 days of system operation, and for the thin-film UT sensor installed in an exhaust heat recovery
boiler pipe (thickness: about 5 mm, surface temperature: about 170°C) at a thermal power plant, thesignal waveform was obtained after about 300 days of system operation. We will continuously
conduct these measurements, and based on the results of the trials with actual units, not only will
the performance and the durability of the sensor itself be validated, but the installation performancein the field, etc., will also be improved.

|4. Characteristics of the ultrasonic pulsar receiver
Assuming that the developed pulsar receiver is installed in the environment of a plantbuilding where it is planned to be installed or is additionally installed in an existing facility, it wasdesigned with the following concepts:(a) The power supply is driven by a battery and data is wirelessly transmitted so that it can beinstalled in locations where existing infrastructural facilities such as power sources are
not available.
(b) A multi-channel type, by which multiple UT sensors can be connected at the same time,is adopted so that one pulsar receiver can monitor several portions.
(c) It is designed for low power consumption so that the replacement of the battery isminimized during long-term use.
(d) Data can be temporarily recorded in the pulsar receiver main unit so that it can be used in
an environment where radio communication is not available.
(e) The enclosure is miniaturized so that it can be installed in narrow spaces around pipe
support structures.
The appearance of the pulsar receiver developed that satisfies the above concepts isillustrated in Figure 4 and the specifications are provided in Table 1. At some plant sites where thepulsar receiver has been introduced, EMC (Electro Magnetic Compatibility) performance isrequired. Therefore, for operation in the actual environment, additional installation of a filter,ferrite beads, etc., and the strengthening of grounding were implemented as EMC measures in thedesign of the substrate. After the development, the EMC test for this pulsar receiver was conducted
at a specialized agency with ISO/IEC17025 laboratory accreditation, and it was confirmed that thispulsar receiver satisfies the EMC requirements defined by CISPR-11 (the international standards
referred to in Japan and the EU) and FCC Part 18 (U.S. standards).
Table 1 Specifications of the developed pulsar receiver
Item
Number of channels
Power supply
Battery life
Communications systemwith PC
Dimensions of the mainunit

Specifications
8 channels
Four AA alkaline batteries
1 yearIn the case of measurement once a day for
8ch, 2000 samples
Wireless or wired
100×150×75mm

Figure 4 Appearance of thedeveloped pulsar receiver|5. Development of application of the monitoring system
The combination of the thin-film UT sensor and the pulsar receiver allows the realization ofvarious kinds of UT monitoring. Some examples are descried below.
(1) Wall thickness monitoring (Figure 5)
As a measure for reducing pipe wall thinning due to flow-accelerated corrosion, waterquality and operating conditions have been improved. The thin-film UT sensor is installed inlocations where significant wall thinning is observed to obtain data at high frequency using thepulsar receiver, thereby enabling an understanding of changes in the wall thinning state in real

Mitsubishi Heavy Industries Technical Review Vol. 55 No. 2 (June 2018)
5

time when water quality or operating conditions change, as well as the optimization of thewater quality and operating conditions for the reduction of wall thinning.
(2) Water level monitoring (Figure 6)
The thin-film UT sensor is installed in equipment where air pockets may exist to obtain
UT data at a given frequency, thereby enabling the monitoring of the water level. Through theearly detection of abnormal water levels, it becomes possible to prevent water hammer events,abnormal vibrations of the pump, etc., toward the improvement of the safety of the equipment.
This monitoring system can be also used for the verification of the air vent effect of a vent line.
In fact, in the corrosion wall thinning verification test implemented at an outside laboratory,
this monitoring system was applied and the wall thickness of a pipe which was heated to 200°C or
higher was continuously measured for over 1500 hours. The wall thickness measurement values
obtained by the pulsar receiver and the actual values measured after the test showed a similar wall
thinning state. It was verified that this system can monitor wall thinning during heating.

Figure 5 Wall thickness monitoring

Figure 6 Water level monitoring|6. Conclusion
As an alternative to regular wall thickness measurement using a portable measuringapparatus, which was conventionally conducted at power plants, MHI has developed the UT
monitoring system in which a thin-film UT sensor that can be permanently installed in a pipe to bemeasured and a pulsar receiver driven by a battery and that has a radio communication function arecombined. Through the application of this monitoring system, the accuracy of thickness evaluation
is improved by an increase in data acquisition frequency, and the wall thinning state can beobserved in real time. Therefore, it can be expected that inspection costs can be reduced throughthe reduction of included work. This monitoring system can be used not only for the monitoring ofpipe wall thinning, but also for the monitoring of air pockets by measuring the water level in a pipe.
In the future, we will further expand the application of this technology to actual plants andcontribute to the increased safety, reliability and economic efficiency of plants. Wide-ranging
application to UT monitoring needs other than the monitoring of pipe wall thinning and air pockets
will be also studied.

References
1.
2.

Yamamoto, Y. et al., Technology of Flexible Thin-film Ultrasonic testing Sensor with High TemperatureResistance, Mitsubishi Heavy Industries Technical Review Vol. 52 No. 4 (2015)
Kodaira, T. et al., Continuous monitoring system using high-temperature thin-filmUT sensor, Japan
Society of Maintenology 14th Annual Conference