Development of a flaw evaluation handbook of the high pressure institute of Japan

Development of a ¯aw evaluation handbook of thehigh pressure institute of Japan

Hideo Kobayashia, Shinsuke Sakaib, Masayuki Asanoc,*, Katsumasa Miyazakid,Takeharu Nagasakie, Yoshiaki Takahashif

aTokyo Institute of Technology, Tokyo, JapanbThe University of Tokyo, Tokyo, Japan

cMetal and Ceramics Technology R & D Department, Power and Industrial Systems R & D Center, Toshiba Corporation, 2-4 Suehiro-cho,

Tsurumi-ku, Yokohama 230-0045, JapandHitachi Limited, Mechanical Engineering Laboratory, Hitachi, Kobe, Japan

eMitsubishi Heavy Industry Limited, Nuclear Plant Designing Department, Kobe, JapanfNuclear Power Engineering Department, Tokyo Electric Power Company, Tokyo, Japan

Received 28 April 2000; revised 2 January 2001; accepted 2 January 2001

Abstract

This paper introduces a handbook, which is edited by the High Pressure Institute of Japan to support engineers who evaluate ¯aws detected

in nuclear power components according to the Japanese ®tness-for-service code. The handbook is written in Japanese and contains basic

information on fracture mechanics as well as the speci®c ¯aw evaluation procedures and material properties data stipulated in the code. The

main features of the handbook are summarized in the paper. q 2001 Elsevier Science Ltd. All rights reserved.

Keywords: Nuclear power components; Japanese ®tness-for-service code; Inservice inspection; Flaw evaluation; Fatigue crack growth; Stress corrosion

cracking; Failure assessment diagram

1. Introduction

In Japan, a new ®tness-for-service code on nuclear power

components has just been published in 2000 by the Japan

Society of Mechanical Engineers (JSME). This code speci-

®es ¯aw evaluation rules for ¯aws detected by inservice

inspections (ISI) of nuclear power components.

Most engineers are not suf®ciently familiar with fracture

mechanics, so that they cannot easily perform a ¯aw evalua-

tion according to the code. Therefore, a committee on

improvement of fracture mechanics techniques for ¯aw

evaluation of the High Pressure Institute (HPI) of Japan

has edited a ¯aw evaluation handbook to support such engi-

neers. The handbook is composed of the main text and nine

appendices. The authors have intended the handbook to be

simple and self-contained. Hence, it includes the founda-

tions of fracture mechanics, procedures for crack growth

and fracture analyses as well as the solutions of fracture

mechanics parameters and materials data. The appendices

contain a large amount of solutions of stress intensity factor,

J-integral and limit load and wide ranging material, data

obtained in Japan such as fatigue crack growth and stress

corrosion cracking (SCC) growth rates of austenitic stain-

less steels in high temperature water and fracture toughness.

Users can easily perform a ¯aw evaluation in accordance

with the ¯owchart and the procedures given in the handbook

with the accompanying appendices. Computer software is

being developed to assist application of the ¯aw evaluation

procedure. This paper describes the main text, appendices of

the handbook, the computer software and the future work of

the committee.

2. Main text

2.1. Contents of main text

The ¯aw evaluation handbook comprises a total of 400

pages, including 213 tables and 157 ®gures, and is

composed of introduction, fundamentals of fracture

mechanics, ¯aw evaluation procedures and nine appendices.

In the fundamentals of fracture mechanics, fracture para-

meters and criteria are explained referring to fracture

modes such as elastic fracture, elastic±plastic fracture and

International Journal of Pressure Vessels and Piping 77 (2000) 929±936

0308-0161/00/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved.

PII: S0308-0161(01)00015-1

www.elsevier.com/locate/ijpvp

* Corresponding author. Tel.: 181-45-510-6656; fax: 181-45-500-2542.

E-mail address: [email protected] (M. Asano).

plastic collapse. The failure mode depends on the

toughness of materials and crack geometry, so that a

proper criterion must be used to evaluate the failure

condition of cracked components. These criteria are

summarized with fracture parameters for each mode as

follows: elastic fracture

K $ KIC; �1�elastic±plastic fracture

J $ JIC �for ductile initiation�; �2a�

2J

2a$

dJR�Da�da

�for unstable transition�; �2b�

plastic collapse

P $ PC�a;sf�; �3�where K is the stress intensity factor, KIC, the plane strain

fracture toughness, J, the J-integral, JIC, the elastic±plastic

fracture toughness, JR(Da), the J-resistance curve, a, the

crack length, P and PC are the applied and plastic collapse

loads. Here, s f is the ¯ow stress, which is usually de®ned as

the average of the yield strength and the tensile strength of

the material.

The handbook adopts the failure assessment diagram

(FAD) approach [1] as a main fracture criterion, so that

the user can easily perform ¯aw evaluation without any

knowledge of the failure mode. The basic concept of the

deformation plasticity failure assessment diagram (DPFAD)

approach is also stated such as the reason why the failure

assessment curve Lr � �Je=J�1=2 could be the boundary of

failure and non-failure regions. The user can progress

through the individual steps of the ¯aw evaluation proce-

dure according to the ¯owchart with the corresponding

appendices. Further, examples of the structural integrity

assessment of cracked components are described to enable

an understanding of the usefulness and the limitation of

fracture mechanics.

The handbook contains nine appendices, which cover

over 300 pages and describe detailed rules, procedures

and a large body of data. For example, the rules on ¯aw

characterization are given in Appendix A, J-integral solu-

tions in Appendix J, stress intensity factor solutions in

Appendix K, limit load solutions in Appendix L. Example

problems with solutions are given in Appendix X, with

suf®cient detail to be helpful to engineers to understand

the ¯aw evaluation schemes and to con®rm their calculation

programs.

H. Kobayashi et al. / International Journal of Pressure Vessels and Piping 77 (2000) 929±936930

Fig. 1. Flaw evaluation procedure of the HPI handbook: (a) ¯owchart; (b) ¯aw characterization; (c) modeling of crack; (d) growth analysis; (e) ¯aw assessment

on FAD.

2.2. Flaw evaluation procedure

Fig. 1 de®nes the ¯aw evaluation procedure in the hand-

book. The user can perform each step according to the

accompanying appendices.

First, the user characterizes and models detected ¯aws as

crack geometries, which can be evaluated by fracture

mechanics (Appendices A and G). Then the crack growth

analysis will be performed after de®ning the stress state

(Appendix E) and material properties (Appendix M). SCC

can be dealt with in addition to fatigue crack growth. SCC

crack growth rate data are given in Appendix M for auste-

nitic stainless steel in normal and hydrogen injected boiling

water reactor (BWR) chemistries. To enable users to

perform the crack growth analysis in complicated stress

®elds, such as welding residual stress, Appendix K provides

stress intensity factor solutions based on the in¯uence func-

tion method for many cases [3]. In the analysis, two neigh-

boring cracks are judged to be one when the crack tips

contact with each other.

The ®nal crack obtained by the growth analysis will be

assessed for stability against the maximum load during the

plant operation by the FAD approach. The assessment

point (Lr, Kr) can be obtained according to Appendices

L and K. Then the point is plotted on the FAD to assess

the safety margin. The option 1 failure assessment curve

of the R6 method [1] is conservatively used. J-integral

solutions for typical geometries are given in Appendix J

to de®ne the R6 option 3 curve for more sophisticated

analyses. The crack is allowable if the assessment point

is located within the failure assessment curve and has a

safety margin that is larger than the required value in

the new Japanese code. The details of each appendix

are discussed in Section 3.

3. Appendices

3.1. Contents of appendices

The ¯aw evaluation handbook contains nine appendices

to help users both with understanding and carrying out the

H. Kobayashi et al. / International Journal of Pressure Vessels and Piping 77 (2000) 929±936 931

Fig. 2. Characterization of planar ¯aw in cladding components in Appendix A.

¯aw evaluation procedure. The appendices occupy 88% of

the total volume of the handbook, and are

Appendix A Characterization of ¯aw

Appendix B Procedure of crack growth analysis

Appendix E Residual stress distribution

Appendix G Crack geometry treated in the handbook

Appendix J J-integral solutions

Appendix K Stress intensity factor solutions

Appendix L Limit load solution

Appendix M Material data

Appendix X Example calculations

The relationships between these appendices and the ¯aw

evaluation steps are shown in Fig. 1. As the outline of the

appendices has been described in Section 2.2, only typical

appendices are selected and are explained in more detail

here.

3.2. Characterization of ¯aw (Appendix A)

Appendix A describes the rules on ¯aw characterization

for actual ¯aws detected at an ISI. In order to perform a ¯aw

characterization, users must have some information on the

¯aw, such as location, direction and size. The classi®cation

of ¯aws into planar, linear or laminar ¯aws is similar to that

of the ASME B and PV Code Sec. XI, IWA-3000.

One of the unique points of the new Japanese code is the

characterization procedure for planar ¯aws in a vessel wall

with a cladding such as at the bottom of pressure vessels.

The detected ¯aws are classi®ed into ®ve categories as

shown in Fig. 2. A surface ¯aw in the cladding layer and

a surface ¯aw extending through the cladding layer are

classi®ed into categories 1 and 2, respectively. A subsurface

¯aw existing beyond the interface between the cladding

layer and base metal, an interface ¯aw at the boundary of

the cladding and base metal and a subsurface ¯aw in the

base metal are classi®ed into categories 3, 4 and 5, respec-

tively. These last categories are characterized as surface

¯aws if s is smaller than 0.4d, where s is the distance

from the outside crack tip to the surface and d is the half

depth of the crack, Fig. 2.

3.3. Crack growth analysis (Appendix B)

Appendix B describes the rules for crack growth analysis

with an example for a surface ¯aw. Crack growth under

combined fatigue and SCC can be dealt with in addition

to fatigue or SCC acting alone. The analytical procedure

for a surface crack is shown in Fig. 3. The stress intensity

factors can be calculated by the solutions in Appendix K

both at the surface and the deepest points of a surface crack.

The fatigue crack growth and the SCC crack growth proper-

ties are shown in Appendix M with the reference crack


Fig. 3. An example of analytical procedure for crack growth by fatigue and SCC for a surface crack in Appendix B.

growth curves of the new Japanese code for both air and

high temperature water environments.

Crack coalescence criteria adopted in the handbook are

based on the experimental results obtained by Iida [2] and

shown in Fig. 4. Multiple ¯aws in parallel planes are treated

as ¯aws in the same plane, if the ligament between the inner

tips of planar ¯aws, S, is less than 5 mm and the distance of

the planes, H, is less than 10 mm, or if S is larger than 5 mm

and H is less than 2S. Or, the ¯aws are treated as multiple

¯aws in the separated parallel planes. Multiple ¯aws in the

same plane are treated as separated ¯aws if S is greater than

zero. On the other hand, these ¯aws must be treated as a

single large ¯aw if S decreases to zero during the crack

growth analysis. These unique ¯aw coalescence criteria

have been con®rmed by the technical background work

to maintain appropriate margins in the crack growth

analysis.

3.4. Stress intensity factor, J-integral and limit load

solutions (Appendices K, J and L)

Using these Appendices, users can simply calculate frac-

ture mechanics parameters such as the stress intensity

factor, J-integral and limit load. The solutions for each frac-

ture mechanics parameter are listed in Table 1. Wide

ranging solutions of 48 stress intensity factors, 18 J-inte-

grals and 28 limit loads are collected in these appendices for

various geometries and loadings from published papers.

Appendix K involves many stress intensity factor solu-

tions based on the in¯uence function method proposed by

Shiratori et al. [3]thus enabling crack growth analyses to be

performed in complex non-linear stress ®elds such as weld-

ing residual or thermal stresses. Simpli®ed stress intensity

factor solutions are also included in Appendix K for the

fracture analysis.

3.5. Material data (Appendix M)

In this appendix, material properties, such as mechanical

properties, fatigue and SCC crack growth rates and fracture

toughness are given with the reference data of the code.

These data have been obtained for Japanese materials

used in nuclear power plants such as ferritic steels, austeni-

tic stainless steels and nickel base alloys.

In particular, wide ranging crack growth data are given

for austenitic stainless steels in the BWR environment, as


Fig. 4. Coalescence criteria for crack growth evaluation in Appendix B: (a) example of parallel planar surface ¯aws; (b) example of parallel planar subsurface

¯aws.

shown in Fig. 5 [4]. The ®gure also shows the reference

curve given by the ASME Boiler and Pressure Vessel

Code Section XI for comparison. SCC crack growth

curves of the stainless steels in the BWR environment are

also given for the normal and the hydrogen injected water

chemistries. Users can select one of these for their own

purposes.

Also, a large amount of J-resistance curves are provided

for carbon steels as well as fracture toughness JIC, since the

elastic±plastic fracture mode is assumed for carbon steel

pipes. These resistance curves are expressed by second-

order polynomials for ductile crack growth analysis.

3.6. Example calculations (Appendix X)

The handbook includes simple examples on the ¯aw

evaluation procedure to assist the user to understand the

procedure and to check his computer programs.

One example is the fracture load estimation for a cracked

pipe. The user is asked to evaluate the fracture loads both by

the limit load approach and by the J-integral method, and to

compare the results with standard solutions. This makes the

users familiar with fracture mechanics. Another example on

a stability analysis by the R6 method [1] is given as a higher

level problem.

4. Development of ¯aw evaluation system

Windows based computer software is being developed to

assist application of the ¯aw evaluation procedure. The

main purposes of the development are twofold: (1) to

perform the ¯aw evaluation based upon the handbook

procedure; (2) to provide a fundamental library for the

development of the user's unique system. The principal

features of the system are summarized in Table 2. The

graphical user interface (GUI) system and the class library

are developed independently so that the class library can be

applied easily for general-purpose applications.

The system is being developed using object-oriented

language. The structure of class inheritance for ¯aw evalua-

tion is designed to enable general-purpose usage. The

fundamental class controls the interface to the GUI and is

inherited to second class, which controls the geometry of the

investigated component, such as plate, pipe, nozzle, etc.

The role of the ®nal inheritance class is to control the

geometry of the ¯aw and the type of loading. By adding

only the net property in the ®nal class, a new class can easily

be added to the library. In one class, the calculation of stress

intensity factor K, limit load L and J-integral are realized.

Fig. 6 shows a typical window image of the developed


Table 1

Crack geometries collated in the handbook

Component Crack geometries

Plate Semi-elliptical surface crack

In®nite surface crack

Elliptical embedded crack

Through-wall crack

Cylinder with an

axial ¯aw

Semi-elliptical surface crack at inner side

In®nite surface crack at inner side

Semi-elliptical surface crack at outer side

In®nite surface crack at outer side

Through-wall crack

Cylinder with a

circumferential ¯aw

Semi-elliptical surface crack at inner side

Rectangular surface crack at inner side


Through-wall crack

Through-wall crack and surface cracks

Elbow Through-wall crack at the crown

Through-wall crack at the outer arc

Tee-junction Semi-elliptical surface crack at the joint

Axial through-wall crack at the shoulder

Sphere Through-wall crack


Nozzle 1/4 corner crack

Corner crack at the cylinder

Corner crack at the sphere

Circumferential in®nite surface crack

Two-dimensional crack

Others 1/4 corner crack at a circle

(both side)

1/4 corner crack at a circle

(one side)

Fig. 5. Fatigue crack growth rate of austenitic stainless steel in BWR water

environment.

¯aw evaluation system. The left part is the tree-view struc-

ture from which the geometry of the component, the geome-

try of the ¯aw and the type of loading are selected using the

mouse pointer. After inputting the required data value such

as the geometry, load and material property from the menu

part, the ¯aw evaluation is performed by pushing the R6

toolbar. Then, the evaluated point is drawn on the FAD in

the right part as shown in the ®gure. Depending on whether

the evaluated point is plotted inside the limit curve or not,

safety can be examined easily. The safety margin is calcu-

lated automatically and the value is also shown on the

right part. Thus, the R6 evaluation can be performed in an

extremely simple manner using the developed system.

5. Future plans

The following items are considered to be necessary for

the establishment of ¯aw evaluation, in addition to the

enhancement of the computer software, for the handbook

to be self-contained and widely used, and are being studied

now.

1. Development of a simpli®ed ¯aw evaluation procedure

for a pipe with an axial crack.

2. Determination of allowable ¯aw sizes without detailed

analysis for cracks in class 2, 3 pipes and at a nozzle

corner.

3. Accumulation of fatigue and SCC crack growth data of

low carbon stainless steels and nickel based alloys in high

temperature water to ensure a proper margin in the crack

growth analysis.


Fig. 6. Typical window image after ¯aw evaluation.

Table 2

Principal features of the developed system

Operating system Windows 98, Windows NT

Program language Visual C11

Integrity assessment R6 method, option 1

Calculation of stress intensity

factor

Evaluation for brittle fracture

Calculation of limit load

Evaluation for plastic collapse

Fundamental functions Calculation of J-integral

Flaw evaluation based on J

Evaluation of safety margin

Evaluation of fatigue crack

growth

Evaluation of SCC

6. Conclusions

The HPI of Japan has edited a ¯aw evaluation handbook

to support engineers who evaluate detected ¯aws according

to the Japanese ®tness-for-service code. This paper has

summarized the main features of the handbook, the accom-

panying software and the future works.

Acknowledgements

This work was performed by a committee on improve-

ment of fracture mechanics techniques for ¯aw evaluation.

The committee was organized in the HPI of Japan and

composed of 48 members from 24 universities, national

institutes, fabricators and utilities. The authors would like

to thank members of the committee for their contribution

and the sponsorship of Tokyo Electric Power Company.

References

[1] Ainsworth RA. The assessment of defects of strain hardening material.

Engng Fracture Mech 1984;19(4):633±42.

[2] Iida K. Shapes and coalescence of surface cracks. Proceeding of ICF

International Symposium on Fracture Mechanics, Beijing, China,

1983:679±93.

[3] Shiratori M, Miyoshi T, Yu Q, Terakado T, Matsumoto M. Develop-

ment of a software system estimating stress intensity factors and

fatigue crack propagation for three dimensional surface cracks by an

in¯uence function method. ASME PVP 1999;385:299±309.

[4] Asano M et al. Effect of long-term thermal aging on the material

properties of austenitic stainless steel welded joints. Proceedings of

the Fourth JSME/ASME Joint International Conference on Nuclear

Engineering, vol. 5, 1996:183±8.


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Development of a flaw evaluation handbook of the high pressure institute of Japan