Project Subjects
Integrated Maintenance Technology for
Inspection, Prediction and Monitoring
Background and Objective
It is recently reported that creep damage preferentially accumulates in welded portions of high chromium
steels at ultra super critical thermal power plants, which are in service for less than 100,000 hours. Creep damage
also occurs in welded portions at aged super critical power plants which are operated for more than 200,000 hrs.
Therefore, trouble free operation of the plants is an important issue for the maintenance section of the thermalpower generation division, referring to damage assessment result of structural components.
In this project, to prevent damage and loss which are caused by accidents at power plants, we developed
advanced non-destructive inspection technology, analytical damage prediction technology and monitoring technology of damage in service. Furthermore, by integrating these technologies, we constructed a new system of themaintenance technologies for power stations, which we call the “Maintenance Triangle”.

Main results
1. Damage assessment system for welded joint based on stress analysis of boiler piping
We developed a ﬁnite element program which is able to analyze the stress generated in the entire piping
system, and constructed a damage assessment system for welded joints (Fig. 1) by combining the FE programwith a void growth simulation program developed in previous work. Since the entire piping between boilers andturbines is modeled in an FE mesh, system load can be evaluated in the FE analysis. Inner pressure was also able
to be considered owing to using three dimensional elements. Conducting the stress analysis and void growthsimulation, we were able to predict creep damage to welded portions of the boiler piping with high accuracy[Q09005].
2. Advanced non-destructive inspection technology for welded joint of boiler piping
In order to detect damage inside materials of piping with sound precision, we have developed an advanced
ultrasonic phased array nondestructive inspection (NDI) system. Optimizing inspection conditions based on an
ultrasonic wave propagation simulation, it was demonstrated that the system was able to detect a state of damage
where the creep void was overcrowded in the heat-affected zone of welded joints (Fig. 2). By introducing signal
processing technology to the NDI system, we could apply the modiﬁed inspection system to welded components
with complex surface geometry, which were hard to do with conventional ultrasonic NDI systems [Q09016].
3. Damage monitoring technology with optical ﬁber acoustic emission sensors
A monitoring system with optical ﬁber acoustic emission (AE) sensor was developed to examine damageof structural materials at high temperatures under service conditions, which was difﬁcult for existing systems sofar. We were able to detect AE signals caused by the propagation of creep cracks and fatigue cracks in the laboratory using the developed monitoring system. Further, it was installed to a high temperature equipment of an actual
boiler to monitor the propagation of thermal fatigue cracks (Fig. 3). It was conﬁrmed that the system works undera real operation environment.
Other reports

40[H09003], [H09004], [H09012], [Q09011]

Stable Power Supply Technology
Grainboundary

StressLowHigh

Void

10μm

Weldment

BoilerTurbine
20cm
50μm

Stress analysis of piping

Stress analysis of weldment

Void growth simulation

Fig. 1 Flow of damage evaluation in welded joints of piping
It became possible to evaluate system load accurately by analyzing entire piping system, and to consider inner pressure
with steam in piping by using three dimensional elements.

Phased array transducer（5MHz 、16 elements）

Arrival time interval

Scanning direction

Indication of damage
A2A side
B sideVoltage

20mm

Weldmetal

ch1
ch2
ch3

VoidTime
Optical fiber

Insulator

Magnet for
fixation

A1

Weld metal
B1

40μm

Inspection result

Observation result

B2Piping

InterferometerAE sensor

Fig. 3 Installation of AE sensor to real piping
An online monitor became possible with the optical ﬁber
AE sensor for high temperature equipment.

Fig. 2 Inspection result of creep damage
It was demonstrated that the NDI system was able todetect creep damage prior to the small cracks stage inthe welded joints specimen.

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