Int. J. Pres. Ves. & Piping 31 (1988) 55-68

Corrosion-fatigue Crack-growth Rates in Austenitic Stainless Steels in Light Water Reactor Environments

J. D. G i l m a n

Electric Power Research Institute, 3412 Hillview Avenue, Palo Alto, California 94303, USA

R. Rungta, P. Hinds and H. Mindlin

Battelle, Columbus Division, 505 King Avenue, Columbus, Ohio 43201, USA

(Received 9 June 1987; accepted 2 July 1987)

A B S T R A C T

Widespread intergranular stress corrosion cracking has occurred at welds in B WR piping systems. A S M E Section X I requires that these serviceflaws be .fully evaluated against fatigue crack growth. This paper discusses a data analysis model aimed at developing a correlation for available crack-growth data for stainless steel in P W R as well as B W R environments.

Useful presentations o f fatigue crack-growth data are obtained by plotting the time rate of crack growth for water environments as a function of the predicted time rate for air environments. The analysis suggests that fatigue crack growth in some stainless/water systems is a time-dependent, corrosion- related phenomenon. However, data for deoxygenated water environment do not indicate time-dependent characteristics.

The data also indicate that the A S M E Section X I Task Group recommendation for estimating corrosion fatigue crack-growth rates in austenitic piping materials may be unreasonable under certain loading conditions. Additional data are needed to confirm this conclusion.

1 I N T R O D U C T I O N

Stress cor ros ion c rack ing o f austeni t ic stainless steels has been s tudied extensively in recent years, as a result o f the widespread inc idence o f

55 Int. J. Pres. Ves. & Piping 0308-0161/88/$03"50 © Elsevier Applied Science Publishers Ltd, England, 1988. Printed in Great Britain

56 J.D. Gilman et al.

intergranular stress corrosion cracking (IGSCC) at welds in BWR piping systems. Fatigue crack growth in these same materials and environments has received less research emphasis because cyclic loading is not considered a fundamental cause or contributor to the IGSCC problem.

Nevertheless, there are some incentives for examining fatigue crack- growth rates in stainless steels for reactor environments. Some IGSCC repair techniques leave existing cracks in place, with added reinforcement or reduced stress, and these flaws must be fully evaluated against several criteria, including fatigue crack growth (ASME Section XI Task Group 1986). When piping is replaced with more crack-resistant materials, a crack- growth analysis is useful to show flaw tolerance of the improved material. Finally, reliable flaw assessment methods are needed generally, for both BWR and PWR applications, to perform flaw evaluations in support of the in-service inspection program.

The purpose of this paper is to present available corrosion fatigue data in a format suggested by other investigators, to answer several questions:

(1) Does this format for presentation aid data interpretation and correlation?

(2) Does the corrosion fatigue behavior exhibit strong time-dependent or frequency-dependent effects which should be considered in flaw assessments?

(3) Is a conventional Paris-law approach applicable? (4) Are there enough data to answer these questions?

2 B A C K G R O U N D

In the case of austenitic stainless steels, the predominant view is that environmentally assisted cracking occurs by the anodic dissolution process. 1 But whether the mechanism of cracking i s anodic dissolution or hydrogen embrittlement, the rate of cracking is believed to depend upon the rate at which flesh surface is exposed at the crack tip. Based on a dislocation emission rate at the crack tip, Shoji e t al. 2"3 suggested that the time based crack-growth rate in an inert environment could be chosen as a parameter quantifying fresh metal surface creation rate at the crack tip. A comparison of time based crack-growth rate in the inert environment and in an aggressive environment, for identical loading conditions, will then provide a measure of the acceleration in crack-growth rates due to the environment. Shoji e t al. a further suggested that the time based crack-growth rate in air (a relatively inert environment) could also be used as a descriptor of the crack tip strain rate which governs surface exposure through oxide film rupture.

Corrosion-fatigue crack-growth rates 57

Using this approach, Ford e t al. 1 have proposed that environmentally assisted crack-growth rates are a single function of the crack tip strain rate for static load, cyclic load, and constant extension rate tests. In cyclic loading, the crack tip strain rate is proportional to the time based crack- growth rate in air. Using Ford's approach, there should be a relationship of the form ti e = 6a + AN between the crack-growth rates in air, tia, and in the water environment, fie- This study seeks such a correlation for available crack-growth data for stainless steels.

3 EFFECTS OF E N V I R O N M E N T

Figure 1 shows expected relationships between crack-growth rate and crack tip strain rate, based on Ford e t aL, t for four different reactor environments. Figure 2 defines those environments, again consistent with Ford e t aL, 1 as a function of the electrochemical potential (ECP) and the room-temperature conductivity. The ECP depends on oxidizing species in the water (primarily dissolved oxygen) and the conductivity is an indication of ionic species which may accelerate crack growth. Sulfate and chloride are known to be detrimental.

Currently, BWR operators seek to control water purity to maintain conditions in the upper left box in Fig. 2. Typical operating conditions are

Fig. I.

Jl _ Static Stress ~ C y c l i c ~ Stress -I'J o - 3 , - _ . . . . . . .

i0 - 4 _ I i n . / d o y

I

~ tO -6 - - Environ I in./year

I0 -e Undetectable

K)-00 ~-,, lo-~ ~9 ~s io-7 io-e io-5 io-4 io-3

Crack Tip Strain Rate per Second Crack growth in weld sensitized stainless steel depends on the crack tip strain rate and water chemistry, according to the model developed by Ford et al. 1

58 J.D. Gilman et al.

2OO

0

E

o ~-~o

-6O0

0 .1 .2 .3 .4 .5

Fig. 2. BWR water chemistry is characterized by the corrosion potential (usually controlled by dissolved oxygen) and the conductivity (which may indicate harmful ionic species).

close to the 'clean' line. Conditions on the 'nominal' line are typical of past practice without these controls. Some plant owners are adopting hydrogen water chemistry (HWC) to reduce oxygen levels and maintain conditions in the lower left-hand box. Figure 1 shows the expected benefits of these water chemistry improvements for weld sensitized Type 304 stainless steel.

The PWR primary system operates normally at a very low ECP; typically - 6 0 0 mV she (standard hydrogen electrode), for which very little influence of environment on crack growth is predicted by the model just described.

4 DATA SOURCES

A large number of fatigue crack-growth data have been compiled in EDEAC (EPRI Database for Environmentally-Assisted Cracking), a computerized database developed and maintained by Battelle. 4 Data in EDEAC were solicited directly from numerous laboratories, or were obtained in some cases through the MPC-PVRC Task Group on Crack Propagation Technology. A few data not in EDEAC are also included in this study.

These laboratory data generally do not include measured ECP and water conductivity. For this reason, the only variable characterizing environment in the present study is the dissolved oxygen content. It is quite possible that these data are influenced by variations in conductivity and ECP. Unfortunately, there is not presently a large body of fatigue crack-growth data for stainless steels in which the water environment has been controlled

Corrosion-fatigue crack-growth rates 59

and characterized with respect to ECP and with respect to very low levels of impurities.

5 D A T A A N A L Y S I S M E T H O D

The fatigue crack-growth rate for stainless steel in air, which is the key parameter for this data correlation, has been presented by James and Jones 5 in the form

do d N - C°Sr AK" (1)

where Co is a temperature-dependent constant and S r depends on the stress ratio, R. For 288°C,

Co = 3"428 × 10- 9

n = 3"30 (2)

S r = 1"0 + l '80R 0 < R < 0"79

S r = --43"35 + 57"97R 0"79 < R < 1"0

n, Sr and R have no units. The value of C O corresponds to units of mm/cycle for fatigue crack growth rate, da/dN and M P a ~ / m for applied stress intensity factor range, AK.

The time-dependent crack growth rate is defined as

da 1 - - - (3)

d N T r

where T r is the load rise time in seconds. This is based on the assumption that the environmental influence occurs predominantly during rising load conditions.

In the data plots to follow, the ordinate 6 e is the observed value ofda/dN, divided by Tr. The abscissa 6a is the calculated value ofda/dN for air divided by T~.

5.1 Crack growth rates in high-oxygen water

Figure 3 presents crack-growth data for sensitized stainless steel in air- saturated water containing 8 p p m of oxygen. 6'7 A l though- the re is considerable scatter, the upper bound of the data can be fitted by a curve of the form ti e = d a + A~ . In this case, A = 0.0025 and n = 0"446. Under

50 J .D . Gilman et al.

10-41

.g®

~ l0 - s

(.9

o

o I0- e

6e:a a + 0.0025 (a

orn

O

0

O

o=Oe

io -7 W8 W r ~C 6 W 5 W 4 i~ 3

Air Rate, %, mm/sec

Fig. 3. Time based presentation of corrosion-fatigue crack-growth data for sensitized (650°C, 2 h) Type 304 stainless steel in high purity water at 290°C containing 8 ppm oxygen. A

curve has been fitted near to the upper bound of the data.

R f Hz Wave,form

O 0.1 0-2 Positive saw tooth /k 0.1 0"02 Positive saw tooth [] 0'1 0.002 Positive saw tooth

0-1 0.0002 Positive saw tooth • 0.5 0.002 Triangular • 0' 1 0.002 Triangular

Data from Refs 6 and 7.

slow-cycling conditions, for d, = 2 x 10 -a m m s -1, the observed fatigue crack-growth rate in water exceeds the predicted rate in air by a factor of about 50. Predictions based on extrapolation of the curve lead to higher factors at slower cyclic rates.

Figure 4 presents additional data reported by Shack e t al . s for high-R loading, and for material and environment similar to those for the data in Fig. 3. The extrapolated curve from Fig. 3 also bounds the high-R fatigue data, except that high-K data (above 60 MPax/m) are well above the curve. Crack growth rates under static load are at least as high as those for high-R cycling at similar values of Kma x.

EE 10_4

.o" % : 0 a + 0 . 0 0 2 5 (6 o)

Io -5

64 55 Y ~ ~ I ~ • • ,o-. "%=°o

-- +39 ~ ~ - / ~ - 37 3g r ~

2 a ~ l l l l I I l l l t I l t l I I l l t...) 3 3 ~ 56

~ 7 ~ , ~ • io-iO 10 -9 10- 8 10 -7 10- 6 i0 -5 10 -4 iO -3

Air Rote, ~1~ mrn/sec

Fig. 4. A comparison of high- R fatigue crack-growth data with the low- R data and curve-fit of Fig. 3, for Type 304 stainless steels in 8 ppm oxygenated water at 290°C. Numbers indicate Kma~ (MPax/m) for R of 0'94 and higher. The uncorrelated high K data may reflect quasi- static IGSCC or invalid linear elastic fracture mechanics conditions (test specimens are 1TCT). R-values: • , ©, 0-1; I I , [], 0.54).6; O, 0-74)-8; • , 0.94-0.95; + , 1.0 (static). Closed

symbols, static, data from Ref. 8; open symbols, data from Refs 6 and 7.

10-4 I ~ 33

_ -

O7'5

_,- o, / ' 7 I0 _--- . . . 0.632652 e/'/• , o, oo.oo .oo.o

,0-. / -%°0° --- / eo.9 /

~ Oo.6 7 -,Eoo /

o .v E~,~jc,-uo.4 .o~ /

If °7 % o;

,0-el i IJLI/'t t l t l j II t l t I ,Jl I ~t,I , , , I jO-9 life ~o-r io-~ t0-~ ~-4 10-3

Air Rote, %, mm/sec

Fig. 5~ Fatigue crack-growth data for low-carbon grades of Type 316L and 316NG stainless steel in high purity water at 290°C. Numbers indicate R-values. The outlier at R = 0"75 represents 0-03 mm of extension following a drop in loading rate. The outlier at

R = 0"95 also represents only 0"03 mm of crack growth according to Andresen. 9

02, ppb* Conductivity, #S/cm Reference

• 200 0"5 9 • 250 0-8 "~

• 2 0.81 8 A 250 O" 1 V 2 0.1 [] 200 <0.1 11

15 <0.2 10

* In this paper, 'billion' is taken to be 10 9.

62 J . D . Gilman et al.

5.2 Crack growth rates in Type 316 stainless steel

The effects of environment on crack growth in Type 316NG or 316L stainless steel are shown in Fig. 5. Data from four laboratories 8- 11 are bounded by the indicated curve. Filled points indicate relatively high water conductivi ty due to the presence of sulfate ions. The influence of conductivity is not apparent, but crack-growth rates at R = 0-95 dropped to near the air line when oxygen was reduced to near zero. 8

5.3 Crack growth rates in oxygenated water

Figure 6 shows data for sensitized Type 304 stainless steel in water containing 200 ppb or less of dissolved oxygen. There is considerable scatter and no apparent correlation with sensitizing heat treatment. A few data are as high as the curve fitted to the 8 ppm data (Fig. 4) and several data are as low as the curve fit to the Type 316NG data (Fig. 5).

Figure 7 includes all of the data from Fig. 6 (open circles) plus additional data (triangles) for solution-annealed Type 304 stainless steel. There are not enough low-rate data to establish a trend for solution-annealed material in 200ppb oxygenated water. However, three recent data for 15 ppb oxygen (and low conductivity) fall on the curve fitted previously to the 316NG data. These three points include weld sensitized, furnace sensitized and solution- annealed Type 304 stainless steels. 1 o, 13

10 - 4

E E

• t:~ 10-5

.ic

e 10- 6

L )

10 - 7

oS/ 0.:0o+OOO2S,0o -v

0.:0o + 0.0,8,0o,O

J ° / ' . / o o~e. ~.~ // 304 Stoinless Steel

I , . ( , I ~ , , l V ~ ~ ~ J l i i H I i J J l i0 - 9 t0 - 8 10 - 7 10 - 6 10 - 5 10- 4

Air Rate, %, mm/sec

Fig. 6. Time based comparison of crack-growth data for Type 304 stainless steel in oxygenated water at 288°C containing 0"2 ppm oxygen, with varying degrees of sensitization: ©, 621°C, 40h; I-1, 621°C, 16h;/k, 621°C, 2h; <>, 621°C, 1 h (data from Ref. 12); O, 650 °C, 2h (data from Ref. 6). Curves derived from the 8ppm oxygen data (upper) and 316 NG

(lower) are shown for comparison.

Corrosion-fatigue crack-growth rates 63

Fig. 7.

E E

n -

. E

o ( .9

¢.3

IO - 4

- o Z / - . . + . 0 4 4 6 ( ~ o ~ , , ' ~ O O 1 ~

ae=aa 0-0025 (a a)~6..~ o o~U"

°.:°o+ o.o,

_ .....~_ .>~, / "o.=Oa

io-6__ / %." ~,,, / o y 9,,,o,,," 0 /

/ ..-~ o / j S

,0-. . . 4 " , 1 , . . , / , , , I j I i l l I I I=1 10 -9 I0 - 8 10 - 7 10 - 6 10 - 5 iO - 4

Air Rote, 60, mm/sec

A compar ison of" data for solut ion-annealed materials to the data of" Fig. 6 for sensitized Type 304 stainless steel in oxygenated water at 288°C.

Oxygen Material Reference

C) 200 ppb Sensitized \ 1 2

A 200 ppb Solution annealed J • 15 ppb Sensitized

1 3 • 15 ppb Solution annealed J

io-4 Bounds of data for cast 316 Stainless / , ~ ~ Steel and forged 304 Stainless S tee l /A~ - -H~ v in PWR environment, R=0.7 at / ' ~ - / / ~ ¢

~' 10_ 5 20 cpm (Bamford, 1977) J / . , ~ = /

/ / . Z .

22 u mit s o frequency effect / / in low-oxygen water

10-8 / I t t [ / t I t t l I i I I I I I I I I I I I I I I I I I , 10 -9 10 -8 10 -7 10- 6 10- 5 10_ 4 10 -3

Air Rote, %, ram/see

Fig. 8. Crack-growth data for deoxygenated water, compared to the curve derived f rom data for 316 NG in oxygenated water. The frequency-independent parallel line bounds the low-oxygen data (open points). Sensitized Type 304 stainless steel: ©, 150t)pb H2; • , 200ppb 02 (data from Ref. 15). Type 316 stainless steel: r-l, PWR, 0"06cpm, R = 0.2 (data

from Ref. 14).

64 J .D. Gilman et al.

5.4 Crack growth rates in deoxygenated water

Data for stainless steels in the PWR primary environment were reviewed by Bamford? 4 Figures 8 and 9 show some of these data plus more recent low frequency data for oxygen-free water. Prater e t al . ~5 conducted low frequency tests in high purity water containing 150ppb of hydrogen. Measured electrochemical potentials were - 400 mVshe or less in these tests.

~o o _

io-i

El! /S" - - - ~ o , , , i F , ' / \ a ~ + + o.oo2s (a3 ~ " o , ,

° I ~ i I ~ " - - - _

F ~ Stoinless Steel

i0- 6 io -5 1o -4 10- s 1o -2 10-'

Air Rote, %, rnm/sec

Fig. 9. Fatigue crack-growth data {'or cast stainless steels in deoxygenated (PWR) water at 288C, compared to the curve derived for wrought 316 NO in oxygenated water. PWR data for Type 316 are consistent with the curve, suggesting that the unusually high crack-growth rates in castings are not a result of the PWR environment but of the product form.

Material R .£ Hz Reference

• Cast 351-CF8A 0.2 0-017 16 © Cast 316 SS 0.7 0.017 17 [] Cast 316 SS 0-2 0.33 "1

• Cast 316 SS 0.25 1.0 t 14 /~ 316N SS 0.24 10 • Cast 316 SS 0-2 0.017

Corrosion-fatigue crack-growth rates 65

The open points in Fig. 8 constitute all of the available low frequency data for such low ECPs. The data are bounded by a line parallel to the air line, supporting Bamford's conclusion that crack growth in the deoxygenated PWR environment is not frequency dependent.

6 DISCUSSION

The data trend exhibited by Fig. 4 is qualitatively consistent with expectations based on the more general crack growth model (Fig. 1). The corrosion-assisted fatigue crack growth rate is well represented by the curve except for high-R, high-K conditions approaching static loading, where the stress-dependent IGSCC rate will overwhelm the contribution due to cyclic loading. As a practical matter, crack growth in IGSCC-susceptible reactor components is likely to be dominated by sustained-load stress corrosion cracking rather than by fatigue crack growth.

The data for Type 316NG or 316L materials (Fig. 5), fit a lower trend line than those for sensitized Type 304. Still, a time-dependent effect of frequency is apparent when oxygen is present.

Andresen 9 correlated the Fig. 5 data from his laboratory using a different algorithm for the abscissa. The most significant difference is in the effect of R on the 'air rate'. Use of the James and Jones formulation 5 in the present work has the effect of moving high-R points to the right. The result is that Shack's data 8 for R = 0.95 now correlate with the low-R data, both here and in Fig. 4.

Data for the PWR environment are scarce in the loading regime where time-dependent effects are observed in oxygenated water. Limited data reveal no evidence of time-dependent effects. Data for cast stainless steels exhibit unusual excursions to high rates (Fig. 9) but there are insufficient data to establish a trend with decreasing 6 a.

Hydrogen water chemistry conditions for the BWR are defined by upper limits on ECP and on ionic impurities, as shown in Fig. 2. No fatigue crack- growth data are available for conditions precisely at the limits of water purity, but the low-oxygen data of Fig. 8 may also be representative of HWC crack growth behavior at somewhat higher potentials. The 15 ppb oxygen data in Figs 5 and 7 were obtained at an unspecified ECP which could have been well above the maximum ECP currently specified for HWC controls.

The basis for HWC controls is prevention of intergranular cracking, which is a key characteristic of service cracks that have occurred in welded BWR piping. The fatigue cracks represented by data in this paper include both transgranular and intergranular modes. No significance has been attached to cracking mode in correlating these data. Other investigators

J. D. Gilman et al.

ve discussed the dependence of cracking mode on material, environment d loading conditions in cyclic loading. Shack et al. s concluded that Type 6NG is susceptible to environmentally enhanced transgranular cracking impure environments, partly on the basis of high-R tests included in

g. 5. It is important to remember in examining Figs 3 through 9 that specific ta for water environments are being compared to the mean of data for the " environment. Because the mean of the water data has not been Lablished, the effect of water versus air is not represented quantitatively by ese plots. However, it is clear that the mean of water data is higher than the Jan of air data for all of these material/environment systems. An ASME Task Group is has recommended corrosion-fatigue crack- owth rates in austenitic piping materials that are higher than the air rate by nstant factors. A multiplier of 10 is recommended for the BWR vironment, and 2 for the PWR environment. Figures 4 and 5 show that ack-growth rates in the normal BWR environment may exceed the mean " rate (the 45 ° line) by factors greater than 10 when the rate of cycling is ~, such that the air rate is less than about 10- v mm- t s. This is true even r unsensitized material in high purity, low oxygen (0.015 ppm) water. Many PWR data exceed the mean air rate by factors greater than 2, cording to Fig. 9. As noted previously, these data are for cast materials lich may have different characteristics than wrought material. Such erratic haviour could result from residual stress in the cast test specimens.

7 CONCLUSIONS

seful presentations of fatigue crack-growth data are obtained by plotting e time rate of crack growth ( d a / d N divided by load rise time) for water vironments, as a function of the predicted time rate for air environments. Data thus presented suggest that fatigue crack growth in some stainless .-el/water systems is a time-dependent, corrosion-related phenomenon. owever, data for deoxygenated systems with low oxidation potentials do ~t indicate time-dependent characteristics. Data trends have been represented by curves of a form suggested in the 3rk of Ford et al.1 but in a simplified form which does not reflect stress ,rrosion cracking under quasi-static loading. As a practical matter, the contribution of stress corrosion cracking la is :ely to dominate that of fatigue crack growth in systems susceptible to the rmer.

Corrosion-fatigue crack-growth rates 67

R E F E R E N C E S

1. Ford, F. P., Taylor, D. F., Andresen, P. L. and Ballinger, R. G., Environmentally-controlled cracking of stainless and low-alloy steels in light- water reactor environments, Electric Power Research Institute Report NP- 5064M, Palo Alto, CA, 1986.

2. Shoji, T., Takahashi, H., Suzuki, M. and Kondo, T., A new parameter for characterizing corrosion fatigue crack growth, J. Eng. Mater. Technol., 103 (1981), 298-304.

3. Shoji, T., Takahashi, H., Nakajima, H. and Kondo, T., Role of loading variables in environment enhanced crack growth of water-cooled nuclear reactor pressure vessel steels, Proc. of the IAEA Specialists Meeting on Subcritical Crack Growth, US NRC Report NUREG-CP-0044, Washington, DC, 1983.

4. Mindlin, H., Rungta, R., Koehl, K. and Gubiotti, R., EPRI database for environmentally-assisted cracking (EDEAC), Electric Power Research Institute Report NP-4485, Palo Alto, CA, 1986.

5. James, L. A. and Jones, D. P., Fatigue crack growth correlation for austenitic stainless steels in air, Proc. of the Conference on Predictive Capabilities in Environmentally-Assisted Cracking, R. Rungta, ed., PVP Vol. 99, American Society of Mechanical Engineers, New York, 1985, pp. 363-414.

6. Kawakubo, T., Hishida, M., Amano, K. and Katsuta, M., Crack growth behavior of type 304 stainless steel in oxygenated 290C pure water under low frequency cyclic loading, Corrosion, 36 (1980), pp. 638-47.

7. Kawakubo, T. and Hishida, M., Toshiba Corporation, Yokohama, Japan EDEAC files 96, 176 and 190. Battelle Columbus Division, Columbus, OH, 1987.

8. Shack, W. J., Kassner, T. F., Maiya, P. S., Park, J. Y. and Ruther, W. E., BWR pipe crack remedies evaluation. Proc. of the US Nuclear Regulatory Commission Fourteenth Water Reactor Safety Information Meeting, NUREG/CP-0082, Vol. 2, Washington, DC, 1987, pp. 101-17.

9. Andresen, P. L., Environmentally assisted growth rate response of non- sensitized 316 grade stainless steels in high temperature water, Corrosion~87, Paper 85, National Association of Corrosion Engineers, Houston, TX, 1987.

10. Gordon, B. M., Jewett, C. W. et aL, Hydrogen water chemistry of BWRs, Electric Power Research Institute Report NP-5064M, Palo Alto, CA, 1985.

11. Schmidt, C. G., Caliguiri, R. D. and Eiselstein, L. E., Stress corrosion susceptibility of type 316 nuclear grade stainless steel and XM-19 alloy in simulated BWR water, Electric Power Research Institute Report NP-5177-LD, Palo Alto, CA, 1987.

12. Hale, D. A., Yuen, J. L. and Gerber, T. L., Fatigue crack growth in piping and RPV steels in simulated BWR water environment, USNRC Report NUREG/ CR-0390, Washington, DC, 1978.

13. Jewett, C. W. and Pickett, A. E., The benefit of hydrogen addition to the boiling water reactor environment on stress corrosion crack initiation and growth in type 304 stainless steel, J. Engng Mater. TechnoL, 108 (1986), pp. 10-19.

14. Bamford, W. H., Fatigue crack growth of stainless steel reactor coolant piping in a pressurized water reactor environment, Westinghouse Report WCAP- 8953, Pittsburg, PA, 1977.

68 J.D. Gilman et al.

15. Prater, T. A., Catlin, W. R. and Coffin, L. F., Influence of dissolved hydrogen and oxygen on crack growth in LWR materials, Electric Power Research Institute Report NP-4183, Palo Alto, CA, 1985.

16. Cullen, W. H., Taylor, R. E., Torronen, K. and Kemppainen, M., The temperature dependence of fatigue crack growth rates of a 351-CF8A cast stainless steel in LWR environment, USNRC Report NUREG/CR-3546, Washington, DC, 1984.

17. Landerman, E. I. and Bamford, W. H., Westinghouse Electric Corporation, EDEAC File 121. Battelle Columbus Division, Columbus, OH, 1987.

18. Section XI Task Group for Piping Flaw Evaluation, ASME Code, Evaluation of flaws in austenitic steel piping, J. Pres. Ves. Technol., 108 (1986), pp. 352-66.