E-Journal of Advanced Maintenance Vol.2 (2010/2011) 14-24
Japan Society of Maintenology

A Review: Japanese Pipe Wall Thinning Management Based on
JSME Rules and Recent R&D Studies Performed to Enhance the Rules
Isoharu NISHIGUCHI 1,*, Fumio INADA2, Makoto TAKAHASHI3, Bunji OGAWA4,
Tetsuhiko INAGAKI5, Taku OHIRA6, Kotaro IWAHARA7, Katsuhiko YAMAKAMI8
1

Kanagawa Institute of Technology. 1030, Shimo-ogino, Atsugi, Kanagawa 243-0292, Japan
Central Research Institute of Electric Power Industry (CRIEPI), 2-11-1, Iwado-kita, Komae-shi,
Tokyo 201-8511, Japan
3
Tokyo Electric Power Co., 1-1-3, Uchisaiwai-cho, Chiyoda-ku, Tokyo 100-0011, Japan
4
Kansai Electric Power Co., 8 Yokota, 13 Go-shi, Mihama-cho, Mikata-gun, Fukui 919-1141, Japan
5
Chubu Electric Power Co., 1, Higashi-shinmachi, Higashi-ku, Nagoya 461-8680, Japan
6
Japan Atomic Power Co., 1-1, Kanda Mitoshiro-cho, Chiyoda-ku, Tokyo 100-0053, Japan
7
Hitachi-GE Nuclear Energy Co. 3-1-1, Hitachi-shi, Ibaraki, 317-0073, Japan8
Mitsubishi Heavy Industries Ltd., 2-1-1, Nihama, Arai-cho, Takasago-shi, Hyogo 652-8585, Japan
2(Received; April 1st, 2010)
Abstract.
In summer 2004, a large-bore carbon steel pipe of a PWR secondary system ruptured at the Mihama Unit 3,
Japan, with some fatalities. The Main Committee on Power Generation Facility Codes (MC-PGFC) of the Japan
Society of Mechanical Engineers (JSME) established technical rules for PWRs and BWRs, which wererequested by the nuclear power industry as well as the regulatory bodies. In Japan, different wall-thinning
management rules have been established for PWR plants and BWR plants because of the difference in their
management, such as water chemistry and inspection points. For example, in BWR plants, the wall-thinning rate
is relatively small at the condensation system and the feed water system after oxygen injection point. The rules
for each type of plant are based on data obtained by wall-thinning measurement. The endorsement of these rules
by Nuclear and Industry Safety Agency (NISA) was completed in summer 2008. A special feature of the
management of pipe wall thinning in Japan is that Japanese utilities have a large amount of field data for wall
thinning. Regarding BWR plants, there are data for 26,000 locations obtained from above two inspections of 29
plants, and for PWR plants, there are data for 20,000 locations obtained from above three inspections of 23
plants.
Moreover, MC-PGFC have produced a roadmap for R&D studies to support and enhance the rules, andmany subjects of R&D studies are contained in the roadmap on methods of predicting pipe wall thinning,
phenomenological screening procedures for parts whose management is necessary, new methods of measuring
pipe wall thickness, improved methods for evaluating the wall-thinning rate, and repair methods. In this paper, thewall-thinning management rules, summary of the roadmap, and trends in recent R&D studies in Japan are outlined.
KEYWORDS: Pipe Wall Thinning, Flow Accelerated Corrosion, Liquid Droplet Impingement Erosion,
Structural Integrity, Piping System, Codes and Standards, Nuclear Power Plant

1.

Introduction

Pipe wall thinning is one of the major degradation phenomena in the piping systems in nuclear
power plants. In 1986, an accident due to pipe rupture occurred in a secondary system at Surry Unit 2,
USA. After that, a management procedure for pipe wall thinning was established in the US under thecooperation of the nuclear power industry and the Nuclear Regulatory Commission. In Japan, aguideline for managing pipe wall thinning was established by PWR utilities in 1990. Pipe wall*

Corresponding author, E-mail: nishiguc@sd.kanagawa-it.ac.jp
ISSN – 1883 – 9894/10/11 © 2010/2011 – JSM and the authors. All rights reserved.

14

I. Nishiguchi et al./ Japanese Pipe Wall Thinning Management Based on
JSME Rules and Recent R&D Studies Performed to Enhance the Rules

thinning in thermal power plants as well as in BWR plants was also managed by their own
management plan. However, in summer 2004, a large-bore carbon steel pipe of a PWR secondary
system ruptured at Mihama Unit 3, Japan, with some fatalities.
On the other hand, the Atomic Energy Commission of Japan recently completed the Nuclear
Energy Policy Outline, which included essential future tasks such as aging management, theimprovement of maintenance and inspection, plant power uprate, and so forth. Roadmaps for R&D
were established by Atomic Energy Society of Japan (AESJ) and Japan Society of MechanicalEngineers (JSME). Many R&D studies have now started with support from the Ministry of Economy,
Trade and Industry (METI) and industry groups.
Regarding pipe wall thinning, which is an issue of aging management, the Main Committee on
Power Generation Facility Codes (MC-PGFC) of JSME has established technical rules for PWRs [1],BWRs [2], and thermal plants [3], which were requested by the nuclear power industry as well as byregulatory bodies. The objective of establishing these rules is to reduce the risk of pipe rupture causedby pipe wall thinning. In these rules, technical knowledge regarding pipe wall-thinning phenomena
including flow-accelerated corrosion (FAC), liquid droplet impingement erosion (LDI), and cavitation
erosion was also accumulated [4][5]. The endorsement of the rules by the Nuclear and Industry Safety
Agency (NISA) was completed in summer 2008.
Moreover, MC-PGFC completed a roadmap for R&D studies to support the above rules in September
2007. Since then, many R&D studies supported by the government and industry have been started.
In this report, the technical rules and recent R&D studies at CRIEPI and other organizations inJapan are outlined.
2.

Overview of Technical Rules

JSME is one of the organizations operating the codes & standards committee in Japan, that is,
MC-PGFC, which was established in 1997, as shown in Fig. 1. MC-PGFC established the technicalrules for the types of power plants in Japan, that is, PWRs, BWRs, and thermal power plants. These
technical rules can serve as a guide when managers of each utility and vender draft constructing,operating, and maintaining procedures. MC-PGFC analyzed plant data, which were used to devise thetechnical rules.
Japan Society of Mechanical Engineers (JSME)
Board of Directors
About 20 Research Divisions
Code & Standard Center
The Main Committee on Power Generation Facility Codes(MC-PGFC)
Nuclear Power Plant Sub-committee
Thermal Power Plant Sub-committee
Fusion Plant Sub-committee
Special Task Group for Pipe Wall Thinning Issues
Sub-Task Group of Thermal power Plants
Sub-Task Group of Nuclear Power Plants
Sub-Task Group of Technical Consideration
Standard & Business Committee

Fig. 1. Structure of JSME Codes & Standards Center.

The outline and objectives of the rules are described in paragraph A as “general rules”. The quality
assurance management specifications are described in paragraph B as “duties of top management”. A
technical description is given in paragraph C. The procedures for each types of power plant differ
slightly from each other because the water chemistry, current management, and other factors dependon the types of power plant.

15

I. Nishiguchi et al./ Japanese Pipe Wall Thinning Management Based on
JSME Rules and Recent R&D Studies Performed to Enhance the Rules

3.

Description of Each Technical Rule

3.1 Basic philosophy of technical rules
PWR [1], BWR [2], and thermal power plant [3] management rules incorporate the new knowledge
that has been gained in recent years, and now provide processes that enable operators to manage pipe
wall thinning by determining pipe wall thickness using ultrasonic testing (UT) techniques and othermethods. Specifically, the rules specify the following processes for developing an examination program:
‑
‑
‑
‑
‑

How to select the piping systems to be inspected
How to determine when to implement the UT technique
Performing thickness measurement using the UT technique (routine and detailed measurement)
Evaluating the wall thinning rate and the remaining period of service
Determining what actions to take (repair or replacement).

In the following sections, we discuss how these issues are dealt with in the technical rules.
The newly developed technical rules provide guidelines for the effective use of accumulated
measurement data to ensure further improvements in pipe-wall-thinning management. This means that
it is very important that facility owners promote continuing and voluntary efforts to expand theirknowledge and that they reevaluate the procedures (determining the scope of examination,measureing wall thinning rates, etc.) on the basis of new insights obtained. JSME will incorporate
new knowledge and findings in future revisions of the rules, as appropriate.
3.2 Rules for PWR [1][6][7]3.2.1 Outline of the rules
In 1990, Japanese PWR utilities established an industry guideline for the management of
secondary piping wall thickness (hereafter, the 1990 industry guideline), and they had followed theguideline until the accident at Mihama unit 3 occurred. In the course of JSME’s work to establish a
new set of rules, measurement data obtained from various plants were reviewed and JSME revised therequirements in the 1990 industry guideline, mainly in terms of the examination scope.
The rules also address pipe wall thinning caused by FAC and LDI including flashing erosion.
Cavitation erosion was excluded because it is a wall-thinning phenomenon that should be addressedby the design process and/or operation management. A detailed technical basis for these rules is given
in references [6] and [7].
In the following sections, we outline how JSME revised the scope and time interval between pipe
thickness examinations.
3.2.2 Management of FAC
The 1990 industry guideline specified the piping systems subject to examination, focusing on
temperature, wetness, and velocity. The initial thinning rate to determine the first inspection timing
was investigated by analyzing the measurement data at that time.
JSME reviewed measurement data obtained from 23 PWRs in Japan. Then, using the data as astatistical population, the range of conditions under which significant wall thinning was observed andthe piping systems that had experienced wall thinning in the past were identified.
The parameter used to determine whether or not there is significant wall thinning is the thickness,tm, given by eq.(1). This parameter is also used to determine whether it is necessary to expand themeasurement scope from a normal grid to a fine grid (with squares of side 20 mm, See Fig. 2).
t m = t sr +2
(t n − t sr )3(1)

tn = minimum manufacturing thickness
tsr = minimum required thickness

16

I. Nishiguchi et al./ Japanese Pipe Wall Thinning Management Based on
JSME Rules and Recent R&D Studies Performed to Enhance the Rules

Flow Direction

Normal grid

Fine gridFig. 2. Normal grid and fine grid used in the inspection [1].

Moreover, locations in piping systems where relatively high wall-thinning rates were observed
were also reviewed to determine whether the measurement data were valid as shown in Fig. 3.
All measured data

Check initial wall thickness
data for unusual data valuel

Check wall thinning rate
for unusual data value

Check measured data for
accuracy of linearity

Evaluate the resultsfrom above

Unusual value found

All Usual
Valid data

Unusual data

Fig. 3. Validation of measurement data [1].

Consequently, the examination scope of the 1990 industry guideline was revised to that shown in
Fig. 4. The previous guideline was changed, and wall thickness measurement is required for someconditions in the new rules where it is not required in previous guideline. Additionally, wall thickness
measurement is required for specific piping systems and for similar piping systems where obvious
wall thinning has been observed.
The JSME rules thus specify that thickness measurement using the UT technique should be
performed at the following components within the selected piping systems:‑‑‑‑

Downstream of an orifice
Downstream of a valve (control valve, flow-regulating valve, globe check valve, swing
check valve, globe valve)
Elbows, tees, reducers, bent pipes
Outlet pipes of heat exchanger, turbine, and pump17

I. Nishiguchi et al./ Japanese Pipe Wall Thinning Management Based on
JSME Rules and Recent R&D Studies Performed to Enhance the Rules
Flowvelocity

Temperature
50-100 100-150 150-200 200-250

Two-phase < 30 m/sec
flow with
30-50m/sec
the wetness≥50m/sec< 5%
Two-phase < 30 m/sec
flow with
30-50m/sec
the wetness≥50m/sec< 5-15%

≥250
deg C

No change from the 1990 guideline
Inspect all the components
Change from the 1990 guideline
Inspect all the components
Inspect all the components
in the specific piping systems

Two-phase < 30 m/sec
flow with
30-50m/sec
the wetness≥50m/sec>15%

Added pipng system(Example)
Single phase:< 30 m/sec
Sigle-phase30-50m/sec
water flow
≥50m/sec

・ Condenser System piping#1HTR-#2HTR
Two phase:・ #2,3HTR Drain pipng
・ HTR Vent line

Fig. 4. Inspection scope in the JSME rule [1].

The 1990 industry guideline also required that the time to performing the first wall thickness
inspection is determined using the wall-thinning rates obtained by the statistical analysis oftemperature, wetness, and flow velocity. The JSME rules applies the same approach for determining
the timing of the first measurement using the UT technique and it specifies the use of wall-thinning
rates established separately for temperature, wetness, and flow velocity conditions. To obtainconservative values for the initially established thinning rates, the maximum valid thinning rates
obtained from 23 PWRs are used. Thinning rate data for areas near welding lines are excluded,
because a slight difference in the measurement point may induce a large error in the thinning rate. In
evaluating the data, measurement data were validated by previously mentioned procedure (see Fig. 3).
3.2.3 Management of liquid droplet impingement erosion
Incidents at PWRs and BWRs in Japan were reviewed to determine which of them caused by LDI.
It was found that this phenomenon mostly occurred in high-velocity two-phase flow pipes connected
to a subatmospheric-pressure component such as a condenser, where there is a rapid pressure
reduction downstream of an orifice or a control valve. JSME has thus identified piping systems wherea high-velocity two-phase flow can be generated, and specified them as requiring examination in the
new rules. Within these piping systems, pipe components such as elbows, which are susceptible todamage caused by LDI and components where a rapid pressure reduction can cause flashing must be
examined in accordance with the JSME rules.
3.3 Rules for BWRs [2][8]3.3.1 Outline of the rules
Technical basis for these rules is given in reference [8]. The rules were developed withconsideration of the following concepts:‑‑‑‑

Wall thinning caused by FAC and erosion are to be separately treated.
Wall thinning caused by FAC in the pipes downstream of oxygen injection and that in thepipes upstream of oxygen injection are to be treated differently.
LDI including flashing is considered as erosion. Cavitation was excluded because it
requires a broader consideration of design and other factors.
The subsystems are categorized into FAC-1, FAC-S, FAC-2 and LDI-1, LDI-2 dependingon the location to the oxygen injection and whether or not connected with the condenser.

3.3.2 Management of FAC
Bearing in mind the above concepts, we categorize the scope of inspections as follows:18

I. Nishiguchi et al./ Japanese Pipe Wall Thinning Management Based on
JSME Rules and Recent R&D Studies Performed to Enhance the Rules

FAC-1
‑
‑
‑

Downstream of oxygen injection and small effects of turbulence
Condensation system, feed water system, low wetness region of main steam line and other systems.
Periodic measurement of wall thickness to confirm the low wall thinning rate at representative points‑

Downstream of oxygen injection and large effects of turbulence (particular points with highwall-thinning rates in FAC-1 subsystems (where the thinning rate is more than 0.2 mm/ 104hr))
Elbows and other components downstream of feed water pumpRemaining period of service to be determined by wall thickness measurements

FAC-S

‑
‑
FAC-2
‑
‑
‑

Upstream of oxygen injection
Two-phase flow region of main steam line, heater vent systems, extraction steam systems,
and other systems
Remaining period of service to be determined by wall thickness measurements.

3.3.3 Management of erosion
Subsystems are categorized for LDI as:
LDI-1‑ Particular points downstream of control valves, check valves, etc.
‑ Extraction steam systems, and other systems‑ Remaining period of service to be determined by wall thickness measurements
LDI-2‑ Elbows in piping downstream of orifices, check valves connected to condenser where
high-velocity two-phase flow is induced, and so forth.
‑ Remaining period of service to be determined by wall thickness measurements.
3.3.4 Technical basis of the rules obtained from operational data
Some typical examples of the data obtained are illustrated in Figs. 5 and 6. Figure 5 showswall-thinning rates upstream and downstream of oxygen injection in the condensation and feed water
systems. Though the wall-thinning rate upstream of oxygen injection is expected to be higher thanthat downstream, the wall thinning rate of both subsystems is not so large because the temperature isrelatively low in the subsystem upstream of oxygen injection. The results obtained in the laboratory
suggest that the wall-thinning rate is small when the temperature is low. Figure 6 shows the effect oftemperature on the wall-thinning rate. The laboratory data suggests that the wall-thinning rate is
greatest at approximately 150 ºC, but the operational data show neither a peak nor an increase there. It
is believed that the thinning rate in plants is small enough because of the injection of oxygen.
Wall thinning rate
(mm/10kh)

Dissolved oxygen
concentration >15ppb
Dissolved oxygen
concentration <15ppb
Fig. 5. Wall-thinning rate upstream and downstream of oxygen injection [2].

19

I. Nishiguchi et al./ Japanese Pipe Wall Thinning Management Based on
JSME Rules and Recent R&D Studies Performed to Enhance the Rules
Wall thinning rate
(mm/10kh)

Dissolved oxygen
concentration >15ppb
pH=7
0 ≤ ≤ 5050 ≤ ≤ 100
100 ≤ ≤ 150
150 ≤ ≤ 200
200 ≤ ≤ 250
Total

231
63
530
766
151
1741

Temperature ºC
Fig.6. Temperature dependence of wear rate [2].

4.

JSME Roadmap for R&D to Support Technical Rules

MC-PGFC completed the roadmap for R&D studies to support and enhance the technical rules in
September 2007. This roadmap recommends studies to develop methods for predict pipe-wallthinning, procedures for the phenomenological screening of parts for which management is necessary,
new methods of measuring pipe wall thickness, improved methods for evaluating the wall-thinning
rate in the case of the change of operation condition or water chemistry condition, criteria of the wall
thinning, repair methods, and so forth. MC-PGFC plans to revise the technical rules in 2012, andR&D studies will be conducted on many of these issues.
5.

Special Features of Management of Pipe Wall Thinning in Japan

Japanese electric utilities have a large amount of field data. Regarding BWR plants, there are data for
26,000 locations obtained from above two inspections of 29 plants, and for PWR plants, there are datafor 20,000 locations obtained from above three inspections of 23 plants. On the other hand, prediction
models such as CHECWORKS and BRT-CICERO are currently not used in the management of utilities
in Japan. This does not mean that prediction models are unnecessary since they can be used as follows:
‑
‑
‑
‑

6.

To evaluate inspection data where the thinning rate is highTo alter management program controlling operating conditions, pipe-wall-thinningmitigation measure such as controlling water quality, and so forth.
Making predictions where inspection is difficult.
Making predictions where data are insufficient.

Examples of Studies on FAC in Japan

Many R&D studies on FAC have now started with support from METI (Ministry of Economy,
Trade and Industry) and industry. These studies are divided into two categories based on their aims.
One is to clarify the elementary processes, and the other is to develop integrated evaluation methods
that combine models of elementary processes.

20

I. Nishiguchi et al./ Japanese Pipe Wall Thinning Management Based on
JSME Rules and Recent R&D Studies Performed to Enhance the Rules

The main objective of the latter studies is to modify Sanchez-Caldera’s model [9] to evaluate thelocal thinning rate.
Sanchez-Caldera’s model assumes a single oxide layer, as shown in Fig. 7, and can be divided into
three processes:‑‑‑

Process (1): Fe2+ is produced from the metal surface due to oxidation with water
Process (2): The Fe2+ produced in process (1) moves through the porous oxide film
Process (3): Fe2+ diffuses from the oxide surface to the bulk water.
Oxide film ofporosity

Process (2)Process (3)Metal

Process (1)Water flow along theoxide film surface

Interface of
metal andOxide film

Interfaceof
oxide film
and water

Figure 7 Sanchez-Caldera’s model of FAC [9].

From the model, the following equation to evaluate the wall-thinning rate can be obtained:
RT =(Ceq − C∞ )θ
⎛δ 1⎞+ (1 − f )⎜ + ⎟
K*
⎝D k⎠
1

,

(2)

where RT is the wall-thinning rate, K* is the reaction-rate constant for the generation of Fe2+, k is the masstransfer coefficient, C is the solubility, D is the diffusion coefficient of Fe2+ in water, δ is the thickness of theoxide film, f is the rate at which oxidized iron becomes magnetite, and θ is the porosity of the oxide layer.
A model to predict the local thinning distribution has been developed in CRIEPI [10][11], in which
the effect of the mass transfer coefficient as a hydraulic factor as well as that of the water chemistry
and material factors are taken into account. Regarding the mass transfer coefficient,
Chilton-Colburn’s analogy of heat and mass transfer [12] is often used because of its broad
applicability to evaluate the mass transfer in a pipe or a duct with fully developed turbulence. Using
this analogy, the mass transfer coefficient k in a straight pipe is obtained as
2

⎛U ⎞
D
k = ⎜⎜ τ ⎟⎟ Re⋅ Sc 1 / 3 ⋅ ,
d
U
⎝ m⎠

(3)

where Uτ is the friction velocity defined as⎡ dU ⎤
Uτ = ν ⎢⎥⎣ dy ⎦ wall(4)

and Um is the mean velocity, Re is the Reynolds number, Sc is the Schmidt number, d is the hydraulicdiameter, and ν is the kinematic viscosity.
In the case of a fluctuating flow such as that downstream of an orifice, in an elbow, at a T-junction,and so forth, CRIEPI has proposed a formula for the effective friction velocity Uτe by considering the
turbulent velocity at the wall so as to obtain the local mass transfer coefficient near a wall as follows:21

I. Nishiguchi et al./ Japanese Pipe Wall Thinning Management Based on
JSME Rules and Recent R&D Studies Performed to Enhance the Rules⎡ d (U + Cu ′) ⎤U τe = ν ⎢⎥dy⎣⎦ wall(5)

w/o consideration of u'with consideration of u'corr. factor R =0.367

corr. factor R =0.664

2

1.0

2

Velocity
V=4.5m/s
V=3.0m/s
V=1.5m/s

TR∝k

FAC rate TR (mm/year)

where u’ is the local turbulent velocity.
Figure 8 shows that the correlation between the FAC rate and the mass transfer coefficient was
greatly improved when the turbulent velocity was considered, and the qualitative validity of the local
mass transfer model was suggested [10].

0.1

0.1
1
0.1
1
Mass transfer coefficient（mm/s）

Fig.8. Correlation of FAC rate and mass transfer coefficient with and without
considering the turbulent velocity (u’) in the FAC experiment condition.

Regarding the effect of the water chemistry and material factors, the FAC model was constructedby assuming the following processes:
1)
2)

The saturated layer of iron and the diffusion layer are located on the surface of thematerial. The rate-determining step of FAC is the diffusion of the soluble iron species
between the bulk solution and the saturated layer through the diffusion layer.
The stability of the surface oxide is affected by the chemical conditions in the saturated
layer, which are determined by the diffusion of oxygen from the bulk solution and theconsumption of oxygen due to corrosion.

The thermodynamic solubility of iron, the major factor related to the water chemistry affecting thethinning rate, was evaluated using the model. The effect of the dissolved oxygen concentration was
also taken into consideration in the model. The model reproduces the experimental results, whichindicate a marked decrease in the FAC rate with increasing dissolved oxygen concentration.
In the NISA projects, Sanchez-Caldera’s model is mainly assumed; however, Uchida et al. [13]used a double-oxide-layer model.
Regarding studies on clarifying the elementary processes, CFD and PIV downstream of parts
generating turbulence are being studied in NISA projects, and the relation between the friction factor
and the thinning rate is also being considered at Institute of Nuclear Safety System, Incorporated(INSS) in Japan.
7.

Examples of Studies on LDI in Japan

This authors were unable to find commercial codes for evaluating LDI, which is normallyevaluated by first obtaining the velocity distribution using CFD code, and then predicting the wallthinning rate using a model equation for the droplet-material interaction, where the input data arevelocity, wetness of steam, sonic velocity, and other parameters.
An integrated system for the evaluation of LDI has been developed at CRIEPI. First, they
considered the target piping system and the target elements [14][15]. LDI easily occurs in piping witha high-speed and wet steam flow. Hence, they focused on piping containing wet steam with an orifice22

I. Nishiguchi et al./ Japanese Pipe Wall Thinning Management Based on
JSME Rules and Recent R&D Studies Performed to Enhance the Rules

or valve, such as a vent line, as the target piping system. Also, droplets easily collide with elements
where the flow direction changes, such as elbows, because of fluid inertia. Therefore, they set the
elbow as the target element for the system. Figure 9 shows an overview of the LDI evaluation system.
The procedure of use of the system is separated into four steps:
Step1. Input: The piping layout and boundary flow conditions at the inlet and exit are input.
Step2. Flow evaluation: Using the information in step 1, the mass flow rate, the flow
distributions, and the droplet behavior are calculated.
Step3. LDI evaluation: Using the information in steps 1 and 2, the LDI sensitivity or thethinning rate due to LDI is evaluated.
Step4. Output: The order of priority of the measurement points (relative evaluation) or thethinning rate (absolute evaluation) is output.

Fig.9. Overview of LDI prediction system.

In step 2, based on the results of the step 1, their in-house codes are applied for the steam flow calculations.
One of the codes is a three-dimensional one that enables the evaluation of a wet steam flow and is usuallyapplied to evaluate the mass flow rate and droplet behavior. The other is a one-dimensional one used to calculate
the average flow in a section of piping. This code can evaluate flow distributions about 1,000 times fasterthan the three-dimensional code because of its simplicity and also gives the flow conditions at every point ina shorter CPU time. Consequently, this code is usually applied for the evaluation of flow distributions.
In CRIEPI’s system, Sanchez-Caldera’s model [9] is used for the droplet-material interaction:
m& =Cρm& tot (1 − x )V 4 Fe Fh(6)2

p 2ε C AC

where m& is the wall thinning rate, V is the liquid droplet velocity, x is the quality of fluid, Ac is theattack area of a droplet, Fe is the entrainment of droplet, Fh is the hitting factor, p is the elasticity
coefficient of the metal or oxide layer, and εc is the fracture distortion of the metal or oxide layer.
Recently, several studies have been conducted as part of the NISA project, including those on the effect ofthe velocity and critical velocity on erosion by a water jet, and a simulation of stress propagation in a material.
8.

Conclusions

The recent management and R&D of pipe wall thinning in Japan has been outlined. In 2006,
MC-PGFC of JSME established the rules to manage pipe wall thinning due to FAC and LDI for
PWRs and BWRs. The endorsement of these rules by NISA was concluded in summer 2008.
MC-PGFC completed the roadmap for R&D studies to support the technical rules in September 2007.
Many R&D projects supported by the government and industry have been started including those on
developing methods of evaluating FAC and LDI.

23

I. Nishiguchi et al./ Japanese Pipe Wall Thinning Management Based on
JSME Rules and Recent R&D Studies Performed to Enhance the Rules

Acknowledgement
The first chairperson of the special task group for dealing with issues related to pipe wall thinningin MC-PGFC of JSME was the late Dr. Yasuhide Asada, Professor Emeritus of the University ofTokyo, and the chairperson of the group when the rules were established was Prof. Sekimura, theUniversity of Tokyo. The authors are grateful to the members of the special task group as well as themembers of the sub-task groups for useful discussions.
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[3] “Codes for Thermal Power Generation Facilities – Rules on Pipe Wall Thinning Management for
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