ML082340114
| ML082340114 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee  |
| Issue date: | 08/31/2004 |
| From: | Mills W, Wire G Bechtel-Bettis |
| To: | NRC/SECY/RAS |
| SECY RAS | |
| References | |
| 06-849-03-LR, 50-271-LR, Entergy-Intervenor-NEC-JH_66, RAS M-231 | |
| Download: ML082340114 (11) | |
Text
LPAE KS K NEC-JH_66 Fatigue Crack Propagation Rates for Notched 304 0Stainless Steel 4_ Specimens In Elevated Temperature Water Fatigue crack propagation (FCP) ratesfor304 stainless steel (304 SS) were dejermined in 24'C and 288'C"air and 288"C water with 20-60 cc 1-1,/kg 1-1,0 using double-edged Gary L. Wire notch (DEN) s.pecimens. Tests perforniedat matched loading conditions in air and water provided a direct comparison of the relative crack growth rates over a wide range of test William J. Mills conditions. Crack growth rates of 304 SS in water were about 12 times the air ratefor both short cracks (0.03-0.25 num) and long cracks up to 4.06 nin beyond the notch, A Bechtel Petis, Inc.. which are consistent with conventional deep crack tests. The large environmentol degra-AWeslMitflin, PA15122-0079 dationfor 304 SS crack growth is consistent with the strong redertion of ftiigue life in high hydrogen wa/e: Further.very similar enviromnpental efl'cts were reported in finigue U.S. NUCOLEARl REGULAIORY 00WS~ crack growith tests in hydrogen water chemisot, (HWC). Priorto the recent tests reported by Wire and Mills Il/ and Evats and Wire 12]. most literature data in high hrdrogen water showed only a mild environmental 4ffect for 304 SS. of order 2.5 times air or less.
Cket No. Otcal M EAMbi No. -
However, the tests were predominanllv perforned (t high cyclic stress intensities or hiegh frequencies where environmental elfects are saall. The environmental effmct in low oxygen fERED by: Applhant~Icensee Intle environments at low stress intensir, depends strongly on both the stress ratio. R, and the NP staff Other load rise time. T, . Fractographic.exatmitations were pemJi.'rmed on specimens tested in both air and water to understand the operative cracking inechoaisntis associated with environmental effects. In 288°C water, the fractnre setafces were crispy fiaceted with a S Witro essPanel crystallographiic appearance, and showed striations under high magnificarion. The clean age-like facets suggest that hydrogen enibrittlententis the primary coause *f acceler-ated cracking. [DOl: 10.1115/1.767959]
I Introduction The double-edge notched uniaxial specimen provides two sites Fatigue crack propagation data for Ty'pe 30 4 stainless steel (304 for crack initiation. It provides an advantage over compact tension SS) were obtained in air and an elevated termperature aquseous specimens itn that it can be tested in both tensionienlsion and environment. The data were developed from instrumented fatigue tension-compression loading conditions. Tests were performed On-tests on double-edged notched (DEN) fatigue specimens with two der load control it) fully reversed (R = -- I) and tension-tension different notch root radii p of 0.38 and 1.52 r san,reported by Wire loading (R=0). Alignment was achieved by manually adjusting ei at. [3]. The fatigue tests were primarily de signed to determine the pull rod to minimize bending stresses, which were monitored the effect of notch radius oil fatigue crack iniitiation but also pro- by strain gages attached to the specimen (Fig. I). Once a satisfac-vide fatigue crack growth data for both shall ow and long cracks. tory alignment was achieved, the strain gages were removed and Direct comparison of crack growth rates obtaiined in air and water the EPD leads were attached. For the tests in water, the assembly under identical loading condilions.and for eq tiivalent crack sizes was then enclosed in an autoclave, which was filled with water 0
demonstrates that 304 SS experiences a larg e environmental ef- and heated to 288 C. Deaerated water containing 20 to 60 cc 0
feet, and the. detailed analysis below shows that this trend was H /kg H2 was used.in this study. The room temperature pl- was 4 supported by all tests. 10.1 to 10.3. and the oxygen concentration was less than 20 ppb47g The specimen was cycled until crack initiation was detected,.
based on the electrical potential drop reading corresponding to crack growth of 0.13 mm. Following an interim visual inspection.l4-2 Experimental cycling was continued to obtain crack extension data.
The DEN specimens (Fig. 1) were siachinned front a 127 aun The crack growth rate da/dN was calculated using the secant diameter bar forging with an L-C orientation per ASTM E 8231 method applied to the average extension -curves, as discussed by with yield and Ultimate strength of 288 and 5446 MPa. The chemi- Wire [I]. Crack growth rates were obtained at extensions as low cal composition of the 304 SS material is p rovided in [1]. The as 0.013 .nm in order to investigate possible short crack effects.
rincrostructure consists of nonssensitized grains with a grain size of For. conventional deep cracks, rates were calculated over larger ASTM 2. increments of crack extension.
Load-controlled cyclic fatigue tests were performed in air at For shallow cracks, of depth L<p from the notch, the stress roots) temperature and 288'C and in deaerAle d 288'C water. The intensity factor solution developed by Schijve [4.1 for a crack ernia-electric potential drop (EPD) technique with ccurrent reversal was nating from an edge notch was used to compute K. When the P
1 lised to monitor crack initiation and growth, as detailedin 1. crack depth exceeded the notch root radius, the conventional stress intensity factor solution developed by Tada et al. [5] for
-Contnibuted by the Prssure, Vessels and Piping
. in the JOURNAL o0' PRESSURE VESSEL Mialoscript "TECnNOLOGy. Divisino fr received publicatioby DEN specimens, which is based on the total crack depth including
- "the PVP Division May 29, 2003; revision received Dee .nber 23, 2004. Editor: the notch depth, was used to calculate K. The transition between S. Y. Lameik." the two formulations was made at L=p. It is noted that an inde-6
- 318 oý . 3 6, AUGUST 2004 Copyright © 2004 by ASME Transactions of the'ASME USNRC August 12, 2008 (11:00am) i RULEMAKINGS AND AJADJUDICATIONS STAFF
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OG/01/2008 19:59 3817623511 NOVERFLO PAGE 01 0 2T608B,71M Pa, 1.52n*"
S20 0 1T605A,6B6.MPa,0.38mm V 2T610-1 ,93MPa,1.52tun A 1T601A,5uMPa.0.3arm 10o 00J 00 0.0 0.2 0.4 0.6 0.o 1.0 e/rho Fig. 2 Short crack growth rates from DEN specimens. Rates normalized by deep crock rates using positive AK, Eq, 2 FIg. 1 Double-edge notehod fatigue specimen with EPD (Grip details not shown, all dimensions in mam) the ratio in Fig. 2 then decreased to values near unity at large crack depths. The figure shows that the short crack growth rates can exceed the deep crack rates by a factor of tbiry, but that the p endent K solution for a double-edge notched plate by Yamamoto ratio quickly approaches a stable value as the crack depth be-L6] provided results within 4% for shallow and intermediate crack comes significant compared to the notch radius. The value of the lengths over the range of the present test$. For both the fully ratio at larger crack depths ranged from approximately one to four reversed and tensiofi-tenpion tests, the stress intensity factor range for the tests shown, implying that the tensile portion of the loading (AK) is defined as the difference between K at maximum and is largely responsible for the crack propagation at large crack minimum loads (i.e., AK=K,ý,-Kmi)'. Crack asymmetry is a depths. For the particular notch depths studied here, short crack potential problem with the DEN specimen. However, the largest effects are only important below Lip of order 0.2. Therefore, shal-difference observed between the two cracks was 2 mm out of an low crack effects can produce an order of magnitude increase in K overall crack length (D + L) of about 9 mm. The 2 mm difference is less than 5% of the specimen width of 38 mina, indicating crack asymmetry is not a problem for this data.
Broken specimen halves were examined on a scanning electron microscope (SEM) to characterize the fatigue fracture surface crack growth rates under fully reversed loading conditions, but this acceleration is confined to very small crack extensions, on the order of 0.1 to 0.3 trm. For longer cracks, conventional test data for deeply cracked specimens can be used to predict cracking behavior.
morphology. The crack length associated with each fractograph The increased rates observed for short cracks near notches is was detenrmined so fracture surface features could be correlated consistent with increased effective stress intensity, as reviewed in with crack growth rates and applied 6X levEls. Relative amounts depth by Lalor, Sehitoglu, and McClung [9]. They observed that of a' maxtensite on fracture faces were estimated using a com- the crack opening stress. increased rapidly with increasing crack mercial ferrite measurement instrument (Feritscope MP3C). depth and leveled out for crack depths above approximately 40%
While fracture surface roughness and the presence of only a thin of the notch radius. They were able to explain the observed crack layer of rnartensite precluded precise measurements, relative opening stresses on the basis of finite element analysis of crack amounts of martermitc were readily determined. closure effects.
. 3.2 Environmental Effects by Comparisox to Controls.
3 Test Results The effect of environment on fatigue crack gowth can be seen by 3.1 Short Crack Effects. Before examinifng envii0nMetttal directly comparing the data from 288"C air and water testS, as effects, it is appropriate to evaluate the cracking behavior for ahort controls were run in air at the same or very similar loading con-versus long cracks. Crack growth rates for short cracks can be ditions to the tests in water. This allows a direct assessment of much larger than long crack data due to differences in crack clo- environmental effects down to the smallest detectable crack ex-sureaccording to Newman [7). Crack closure in the crack wake tensions, while avoiding the treed for an explicit treatment of short reduces the portion of the load that is effective in growing a crack. crack effects. Hence, the daldN values in air and water are com-However, short cracks have little or no crack wake, and closure is pared directly at the same crack extension and cyclic stress. This subsequently reduced. To examine for such closure effects, the assures that crack driving forces are the same, without having to growth rates in air for the DEN at R = - I were compared directly explicitly calculate them.
to growth rates from conventional deep crack tests in air at 288'C, Figure 3 shows conclusively that the crack growth rates in wa-R = 0 per James and Jones 8.]: ter are much enhanced over rates in air. The ratio of crack growth rates in water' over air is called the environmental ratio (ER), for daldN= l.40X 10- 9 AK" 7 , mm/cycle, AK in MPaIm convenience. At a stress amplitude of 69 MPa and lowest fre-(2) quency tested of 0.0033 Hz, the BR is 15 (Fig. 3(a)). The large ER The ratio of the DEN rates to rates for long cracks from Eq. (2) in water observed in Fig. 3(s) pcrsjsttd to the end of the test, are shown in Fig. 2. It was convenient to use only the positive where the crack extension was 4.1 mm. Hence, large environmen-portion of the loading to calculate the air rates for long cracks, as tal effects continue to crack depths of engineering significance, Journal of Pressure Vessel Technology AUGU5T 20o4, Vol. 126 / 319
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- 2O1611, AirT.1-"mMO. 0UP, R-10 0.01 0.1 1 10 D11" 0.0 I1 0.1 1 IQ CrookFXt .. 10.. Mal CrmakEat.nWin, Mm Fig. 3 Environmental effects in DEN tests. Stress amplitude and other test parameters on plots and are not just a short crack phenomenon. Figure 3 shows that for low alloy steel fatigue crack growth data. This vatiable was the ER was large at the smallest detectable crack extensions of used successfully to correlate environmental effects on low alloy about 0.025 nun. Hence, the increases in crack growth rate 6x- steels in water. The time-based crack growth in air (daldt), is plain the reductions in fatigue life reported in the literature [10], defined as Several other trends are worthy of note. Higher frequency led to (da/dt),=(dc/dN)6, 1 IT, where T, is the load rise time a smnaller ER of IOX, as shown by comparing Mig, 3(b) and Fig. (3a) 3(a). The apparent increase in ER with decreasing frequency is consistent with the reduction of fatigue life at low strain rate noted and the time based environmental rate (daldr), in water is by Cbopra and Smith [10]. The ER for a higher sttres amplitude (Fig. 3(c)) is only about a factor of 8X compared to 15X in Fig. (da~dt),= (daldN),1T, (3b) 3(a) at the same low freqbuency, indicating a reduction. in ER at Eq. (3) is appropriate for fatigue crack growth tests with continu-high stress amplitude and crack growth rates. The ER at R = 0 is ous cycling, which produce a tineindelen1ent rate such as seen also smaller, as shown in Fig..3(d), This may be further evidence of an effect of higher effective loading for a given stress ampli- in the present tests. In the event that stress corrosion crAcking or tude provided by R=0 compared to R-= - 1, which has a com- other time-dependent behavior is operative, the total time would be more appropriate- in Eq. 3, pressive half cycle, Also, the ER in Fig. 3(c,d) decreases at the The strong environmental effects observed on 304 SS are cor-largest crack extensions. which correspond to the highest stress intensity. Such an effect is consistent with the gq.neral notion that related reasonably well by utilizing a time-based plot, as shown in at high loading, mechanical effects will dominate. Fig. 4, although data variability is large. The air rates for DEN specimens were determined directly from the control tests in air, 3.3 Environmental Effects Using 'Time-Based Plots and as shown in Fig. 3. The 304 SS DEN data (diamonds) show a Comparison to Literature. From a fundamental point of view, clear increase in crack growth rates relative to those in air at low the crack tip strain rate is the appropriate crack driving parameter air rates, and are consistent with the degradation of fatigue ife of to correlate environmentally assisted crack propagation tate data, up to 15X reported by Chopra and Smith [10] and 13X reported as reviewed by Scott [11]. However, a unique method of crack-tip by Leax [13]. As noted above. the large ER did not diminish in
.J strain-rate calculation could not be establilshed and variability in one test up to a crack depth of 4.1 mm. This depth iS greater than calculated values was over a factor of ten between various mod- associated with "hourt crack" effects and is significant from an els. Shoji at al. (12] suggested using the time-based rate in air as engineering standpoint. Subsequent tests on conventional compact a practical correlating parameter representing crack tip strain-rate tension specimens at this laboratory, represented by the circles in 320 / Vol. 126, AUGUST 2004 Transactions of the ASME M.
30176233511 NOVERFLO NO\I~iRFLOPA~GE03 2002 19:59 HWC Water at 288'C 125-150ppb H,. I Sppb 0, E 1 4 I e 10-7
,o-Air Rate, ARI0 DENData.
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Air rate, mrnPi FIg. 4 304 SS DEN crack growth rates In water vs air- Torend shows decroeaed ER at high alr rate. Air rates Ere caleulaetdi Fig. i Comparison o? DEN to CT data in H1WC Largo environ-directly from control tetat Mental effeets extend to low air rates Fig. 4, verify that the environmental effect continue3 unabated to eraturc average about 14 times the air rate, very sbrilar to DEN a crack growth of 17 mam, as reported by Evans and Wire [2). For data. Indeed, crack growth rates in HWC at frequencies between 304 SS CT data. the baseline crack growth rate in air, (daldN)r,, 1.67X 10-2 and 5.56X 10-4Hz are identical to those obtained in was determined Via [8] for the appropriate test conditions (ie., this study. The fact that the stainless steel studied by Prater was AK, R, and temperature). It is also noted that the agreement be- sensitized does not appear to be important, as tlh cracking mode tween short crack and long crack results indicates that there is no was transgranular. Gordon et al. (17] indicatedl that the fatigue "chemical" enhancement of crack growth of short cracks, such as crack growth rates in HWC water were the same for solution reported by Gangloff [14) for high strength steel in a NaCl solu- annealed and sensitized 304 SS. and )ewett em al. [18) reported tion. very similar rates in these materials as well as welds.
A review of fatigue crack propagation of austenitic stainless A comparison of crack growth data trends from DEN tests and steels was performed recently by Shack and Kassner [15). Data selected conventional compact tension test data in HWC is pro-from surface crack tests performed in low oxygen "bydrogen wa- yided in Fig. 6. The DEN and CT data are in good agreement in ter chemistry" (HWC) environments by Prater et a]. [ [6] are com- the intermediate growth rate regimes where bomb specimen types pared with DEN data in Fig. 5. HWC is BWR water chemistrv were evaluated. Moreover, the data by Ljunberg [19] show even with hydrogen added to cootrol the electrochemical potential, The greater enhancement in the low crack growth rate regime. These literature tests on surface crack spccimens tested in HWC water results provide further support for the observation that environ-confirm that the large environmental effects shown here have been mental effects tend to increase in the lower stress intensity regime observed previously. Overall, the surface crac.k tests from the bt- whore crack growth rates In air are reduced.
The tests by Andresen and Campbell [20] show evidence for a transition to reduced environmental effects at Ifgh equivalent air rates, and more limited data by Gordon et al. (117] are consistent with such an effect. It is noteworthy that the DEN data agree qualitatively with HWC data in Fig. 6, including evidence of a transition to substantially lower environmental offects at equiva-tent air rates above 10-i rm/s, The hydrogen level for the HWC test data mu Figs. 5 and 6 is 2 150 ppb ox less, much less than several ppm in :the current DEN tests and in PWR water. Although the corrosiou potential in HWC is typically about 0.3 V SHE higher than that in water with higher hydrogen used in the present tests, according to Oilman [21], the overall crack growth rate response in the two environments ap-pears to be similar.
'5 " *...... 3.4 Effects Of Stress Ratio, Stress Intensity,, nod Rise Time.
V 1.*6XI-1-z Fvans and Wire [2) performed a series of tests on a 1.9T CT 1l.t DEN ecimieu (thilckness=24.1 mm) of the same heat and water eon-
- p57)1OH ditions used it the DEN tests. The CT teats sihowed that large cnvirotproental effects occurred in conventional, deeply cracked lo'* *o~s*o" '
- = 0"* attendant lower potential.
compact tension with high specimensResults fromhydrogem and the tests and the DEN'levels the I
Air rate, mm/3 compact tension tests by Evans and Wire (2002) are showrn in Fig.
- 7. For DEN data represented in Figs. 7-8, the full cyclic Stress FIg. 5 Consparlson of DEN to surface crack datp, Surface range and crack extensions increments of 0. 32 man or larger were crack data tiested In HWC [S] employed.
JournAl of Pressure Vessel Technology AUGUST 2004, Vol. 126 / 321
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AK, MPa-m " 6K, MPa-mo' Fig. 7 304 SS crack growth rates In water at 28) °C.Rise time Fig. 9 Normalized 304 SS CT FCP Data at Low Potential. Nor-1 (T,) is In seconds malization: (1-R)-R' , "T.ý-O to R0,T,-1SO a This formulation indicates a strong role of T, and R, consistent The results in Fig. 7 indicate a strong effect of both T, and A. with results described above in low oxygen water. It is noted that The environmental effects can be rationalized in terms of a com- the present crack growth rates are similar to those reported by bined mean stress effect on closure or R ratio and a ri.e time or Itatani et al. t25] in BWR water in the few cases where data are freqtuency effect, consistent with the literature. Bamford [22] ava*l table at similar T,., R, and AK, Figure 8 shows that the crack noted larger environmental effects at higher R ratios. He incorpo- growth rates in Fig. 7 can be reasonably well normalized by T11'31 05 rated an effective AKo*=K,,*(I--R) , which shifted the high R and 1/(J -IR)"., Hence, the form of the correlation developed by data more in line with low I? data. Cullen [23] reported strongly Itatani et al, for tension-tension appears to be promising for increased FCP rates for cast stalrness steel at higher R in PWR tension-compression. Further, the presetot rise time and stress ratio uater. Thedata by Bernard et al. [24] on Z3 CNDI17-12, similu to R ratio dependence are consistent with all but the very high R
.,jl 6 SS, showed a clear rise time effect in PWR water. Recently, a (0.95) BWR water data utilized by Itatani et al. [251. Figure 9 correlatiork for FCP of austeoitic stainless steels in BWR water shows that normalization in Pig. 8 worked successfully on data was developed by ttatani et al. [25]. The correlation was of the from compact tension tests at high R by Evans and Wire [2] and form at low R by Bernard et al. [24]. Both data sets include long rise times (450-500 s) where envirotimentaI effects are substantial.
da/dN=A(AK)"T/,1(I - R)P with m=3.0, The plot shows that ER reduces to about 2X at larex &K. While (4) the selected parameters values correlate these limited data sets, n= 0.5, aidand p=2.12 much ruore data would be required to obtain- a definitive coorelation.
4 Characterization of Fatigue Crack Propagation Data N6rmallzod tD ROD. T"=150*
Mechanisms Air Curv, Rv-O 0 Nomalized Watar Data Frecture surface features for specimens tested in air and water were evaluated to correlate operative cracking mechanisms with environmental cracking behavior, The fracture surface appea-race 0 for specirne1ns tested in roora temperature air was found to be dependent on loading conditions. A faceted morphology (Fig.
0 10(a)) was observed at crack growth rates less than I X10- t4nV/cyCee, vast fields of well-defined striations were gen-1W i erated betwveen I X 10-4 and I X 10-3 ram/cycle, and a combina-E tion of fatigue striations and dimples (Fig. 10(b)) was observed above I X Ia0-) m/cycle. The nature of striated fracture surfaces in the intermediate and high crack growth rate regimes resrnbles that typically observed in FCC materials, but the facets formed at 10-6 I low crack growth rates are rather unique, as discussed below, Evidence of rubbing and ftetting (Fig. 11) due to repeated contact between mating fracture surfaces was observed in specimens 10 tested under fully reversed cyclic loading conditions.
Facets generated at low crack growth rates had an irregular Normalls'edK e v MfA w -M. appearance that was associated with a quasi-cleavage mechanism
--. . -- 1 -, a* 4XrJ. Norwnaulzaxion; miat was opaerative tor both shallow and deep cracks, as long as (I-R)-' 7'3to R=O, T(.Il50 9 crack growth rates were less than I X 10-4 turn/cvcie. Bccause 322 / Vol, 126, AUGUST 2004 TransactIons of the ASME
I Fig. 11 Repeated contact between crack surface, (R=-1). (a)
Rlub mark*s at low AK ltvels in 288C aIr. (b) Striations our-Fig. 10 Fractogtaphs of 304 St tested In 241C air. (a) Irregular rounded by severely rubbed regions (240C air).
quaei-cleavage facets at da/dN=ex10-' nam/cycle. Arrow de-notes failed twin boundary- (b) Striations and dimples at i Xi0-2 ramtcycle son of Pigs. 12(a) und 12(b) shows that the high temperature facets had more of a cystallographic nature with some evidence of" river patterns, in contrast with the irregular facets generated in 304 SS is a metastable alloy at room temperature, the material room temperature air. The lack of quasi-cleavage facets indicates directly ahead of an advancing crack undergoes a strain-itdueed that 288'C is above the critical temperature where cold working transformation to a' martensite. Therefore, cracks propagate induces a martensrite transformation (i.e., MU, temperature), Based through martensite, which results in a quasi-cleavage morphology on the composition of 304 SS, the MD temperature associated that re.*embles the quasi-cleavage fracture surface appearance in with 30% cold work is on the order of 100-C (Lacombe [293).
martensitic steels. Forritescope measurements showed that all fa-tigue fracture surfaces generated at room temperature contained Indeed, Ferriteseope measurements showed no detectable 0
a' martensite, with the amount of martensite increasing at higher a'-martensite on fatigue fracture surfaces generatod at 288 C, stress intensity factor levels due to larger plastic zone sizes. At crack growth rates slightly above I X 10-4 mm/cycle, facets The morphology of the quasi-cleavage facets was consistent formed in 289'C air were poorly defined and parallel fracture with the fracture surface appearance for 304 SS (Gao et al. [261) markings associated with slip offsets were often superimposed on and high purity Fe-lSCr-I2Ni SS (Wei ct al. [27]) tested in room them, The transition to poorly defined facets is believed to be temperature air, 3.5% NaCI solutions and hydrogen. Strain- associated with a transition from beterogeneous-to-homogeneous induced a' martcnsite forrncd ahead of fatigue cracks in both slip. Fracture surfaces generated in 288'C water were remarkably alloys, which caused a quasi-cleavage mechanisin. Unlike 304 SS, different than those generated in air. Facets formed in water had a 316 SS fatigue tested in room temperature air (Mills (283) exhib- crystallographic appearance with well-defined river patterns, as ited more conventional, cleavage-like facets. Because 316 SS is a shown in Fig. 12(c). The sharp, cleavage-like facets formed im-more stable alloy due to its higher nickel content, cc' martensite mediately adjacent to machined notches and well away from the transformation does not occur at room temperature; hence, it ex- notclhes, indicating that the same faceted growth mechanism was hibits classic, cleavage-like faceted growth as cracks propagate operative for shallow and long cracks. Moreover, well-defined through stable austenite, crystallographic facets persisted over the entire range of crack In the tow crack growth rate regime, 304 SS also exhibited growth rates generated in this program, including crack growth localized cracking along annealing twin boundaries, but no evi- rates as high as 8)X 10-4 mm/cycle where fracture surfaces gener-dence of intergranular cracking. Localized separation along favor- ated in air exhibited poorly defined facets and vast fields of fa-ably oriented twin boundaries produced fiat, featureless facets that tigpe striations. There was no evidence of either intergranular appear as dark islands, surrounded by quasi-cleavage facets. Gao cracking or annealing twin boundary cracking in 288°C water.
0 et al. [263 and Wei et at. [27] also reported twin boaindary crack- Although fracture surfaces generated in 288 C water exhibited ing in 304 SS and high purity Fe-ISCr-l2Ni SS, crisp cleavage-like facets, high magnification of facet faces re-'
Facets formed in 288°C air had a different morphology. as they vealed the presence of fatigue striations (Fig, 13). At crack growth' took on a more conventional cleavage-like appearance. Compari- rates from I X 10- to 3 X 10"' 'nm/cycle, parallel fracture mark-Journal of Pressure Vessel Technology AUGUST 2004, Vol. 126 / 323 6S:61 BOOZ/TO/90 0-1Jd3GAON T19EZ9LI13E t7o 17393Vd
Fig. 13 Fractographs of 304 8S fatigus tested In 288"C water.
4 (a) Highly angular fasts persist to 3X10- mm cycle. (b) High magnification of (a) shows fatigue striations superimposed on facet faces occurred in the most Susceptible regions, which left ligaments in the wake of the %dvancing crack front. As the overall crack con-tinued to extend, local stress intensities within the mote resistant ligaments increased to the point where cracking reinitiated and propagated across the ligaments. As a result, local cracking direc-tions within these ligaments were often normal to the overall cracking direction. The rapid crack advance in the more suscep-tible regions is believed to be a significant contributor to the en-vironmental acceleration observed in high temperature water. Spe-Fig. 12 FRactographs of 304 SS tatigue tested In (a) 24"C air cifically, this rapid cracking not only increased the overall crack showing Irregular facets (b) 2M8C air showing cleavage-lIke length, it increased local stress and provided alternate paths for facets (c) 288WC water with crystallographic facets that nre reinitiating local cracks along the more resistant ligaments.
sharp, cleavage-like, and highly angular. The role of active path dissolution versus hydrogen embrittle-ment in. causing accelerated cracking of stainless steel in high temperature water remains an issue because of the coupled nature illg. on the facets wer very straight, but their spacing was iden- of these processes, as electrochemical reactions near the crack tip tical to macroscopic crack growth rates indicating that they were involve both anodic dissolution of the metal and a cathodic reac-fatigue striations. At growth rates above 3 X 10-4 mtl/ycle, Stria- tion that produces hydrogen. The presence of well-defined crys-tiaras had a ductile or wavy appearance, as shown in Vig- 13(b). tallographic features indicates the absence of significant metal dis-Pacet and striation orientations on fracture surfaces generated in solution, thereby suggesting that slip/dissolution is not the 2889M water revealed that local cracking directions. were often primary cause of accelerated cracking. This observation is consis-very different from the overall cracking direction. Although facets tent with findings by Chopra and Smith [101 that crack growth were usually aligned iia the cracking direction, some were aligned rates for 304 SS are greater in low dissolved oxygen water than in .$.L normal to the macroscopic cracking direction (Figs. 12(c) and high dissolved oxygen water. This observation cannot be recon-
"j(a)). LLkewise, most striations were oriented normal to overall ciled with a slip/dissolution mechanism. L:
W08stg direction, but in some regions striations had different The presetnce of sharp, crystallographic facets suggests that a tations, and in some cars were even parailel to the macro- hydrogen ernbrittlemcnt mechanism is responsible for accelerated scopic craclkng direction, These observations indicate that crack cracking in 288*C water. This is supported by fractorg,- pbic find-advance in water involved a very uneven process, as cracking first ings by 14aoninea and Hakarainen [30) where hydrogen-324 / Vol. 126, AUGUST 2004 Transactions of the ASME
19:59 3el7623511 NVRL NOVERFLO PAGE cG 05 l
I precharged 304 SS exhibited cleavage-like facets without any dc- Much of literature data in hydrogenated water chemistry shows tectable e tx' martensite formation. The facet morphology for the an apparently mild environmental effect for 304 SS, with an ER of hydrogen-precharged specimens is very similar to that observed in 2.55 or less. However, based on the current test results, larger 288gC water, thereby implicating hydrogen in promoting acceler- environmental effects occur in) bydrogenated water in the low AK ated cracking in high temperature water. Moreover, Gao et al. [26] regime at long rise times and high R-ratio conditions.
K) and Wei et al. [27] demonstrated that a hydrogen embrittlerment mechanism was responsible for accelerated fatigue crack growth The high crack growth rates in 2880C deaerated water were associated with a faceted growth mechanism. The hightly angular, rates in stainless steel alloys tested in room temperature aqueous cleavage-like appearance of the facets suggests that a hydrogen environments. Although r'pmartensite formation occurred in.these embnittlement mechanism was the primary cause of accelerated 4 *. specimens, Gao and Wei determined that this transformation did cracking in this environment, not have a critical role in controlling crack growth rates and it was not a prerequisite for hydrogen embrittlement. Acknowledgment Although hydrogen embrittlement is believed to be the primary cause of environmental cracking in 2881C water, it is possible that This work was performed under U.S. Department of Energy oxide film formation at the crack tip also affects cracking behavior Contract with Bechtel Bettis, Inc. The authors wish to acknowl-by restricting slip reversals during the unloading portion of fatigue edge the efforts of H, K. Shen, A. L. Bradfield, J. T. Kandra, and J.
cycles. The importance of oxide film formation in affecting frac- I. Chasko in performance of these experiments.
ture surface morphology is apparent when comparing fracture sur-faces generated in air and vacuum. Fatigue fracture surfaces gen- References erated in air possessed crystallographic facets. whereas those [1I Wire. G. _..and Mills. W. .- 2001. "antigue Crack Propagation From Notched generated in vacuum had a nondescript, nonfaceted appearance Specimens of 304 Stainless Steel In An Slcvatod Temperature Aqueous Envi-(Wire [1]). Apparently, the thin oxide hikes that forms in 24'C air roYn rat.'"PVP-Vol. 439. Prexaune Vessjel and Piping Coes and Srandaftb-serves as a dislocation barrier that impedes slip reversals during 2002, PVP'2002.1232,A*SMO. New York, pp. 15 t-164.
[2] Evans, W. M.. and Wire, G. L.. 2001, "Fatigue Crack Propagatioyi,Beabvioe of unloading cycles. Hence, damage tends to be concentrated along 304 Stainless Stool From Compaet Týnerion Specimens in An Elavat~d Tcm-particular slip bands, and eventually local separation along these pcratorc Aqueous PnvironmenL" PVP-Vol. 439. Pr*ssure Vesil and Pipi*g slip bands produces crystallographic facets, In vacuum, the ab- Codes and Jtnuldurt,-2Op2. PVP2002- 1226* ASME, New YCrk, pp. 91-98.
sence of an oxide film promotes more effective slip reversals that (3) Wire, G. L.. Leax, T. R.. and Kandra, J. T_. 1999, "Mean Strets and EnviTon, mental E'fects on Fatigue In vyp. 304 Stainess Steel," Probabillsile and minimizes local damage along any particular slip band. As a re- Em'ironmneptt Aspects of Fracture and Fatigue.PVP-VoI. 386. ASME. Now suit, crystallographic facets do not develop in vacuum. Oxide film I Yorl, pp. 213-228.
formation in water is also expected to restrict slip reversals and [4] Schijvc. .. 1982. "Thc Sirns Intensity Factor of Small Cracks at Notcht.-,
Fatigc F'rac. Eng, Mater. Strct, 5(t), pp. 77-90.
promote facet formation and higher crack growth rates; however,
[5] Tqad, H.. Paris, P. C., and Irwin, G. R., 2000, The Stress Amohysts of Creark the degree of acceleration is expected to by much less than that[ Hoadbeuk, ASME.
associated with hydrogen erobrittlement. [61 Yamamoto, Y., Sumi. Y.. and AP. K., 1974. "StreS tIntensity Factors of Cracks In summary, it is unlikely that slip/dissolution is a primaryl Emanatng Prxom Semi-Elliptical Side NotcheS ill Plates." tnt. J. FraCL. 11)4).
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[7) Newman,. . C., 1992,' Frctux Mechanips Parameters for the Small Fati5 uc because of the presence of crisp crystallographic features and an Cracks," Small-Crock Test Method.v, ASIM STP 1149, pp. 6-33.
increase in crack growth rates with decreasing dissolved oxygen [a] James. L. A.. and Jones. D. R. 1985. "Fatigue Crtak Growth Correlations for levels (Chopra and Smith, (10]). The cleavage-like facets on the Aua(ernitic 3tabileos Stecls in Air," PredicrN'e Capcabilttes litn v2trosritntuily fracture surface, which are very similar to facets found in Ass'is ed Cracking, PVP Vol. 99, pp. 3(y13-414.
[9) Lator, P., Selitoglu. H., and McCtvng, R, C., 1986, "Mehhoira Aspects of hydrogen-precharged 304 SS (Harninen and Hakatainen [30]), Small Crack Growth From Notches-the Role of Crack Colaare." The fteha"ip, suggest that hydrogen embrittlement is the primary cause of ac- of Short Fatigues CracO:s", EGF Piub. 1. K. 1. Miller and B. R. de los Kino. eda..
celerated cracking in high temperature water. It is also likely that M.ehanical Eagincrit,& Publicatlons, London. pp. 369-386.
[10] Chopra. 0. K.. and Srmth. J. L., 1998, "Eati-abion of Fatiguc Strta-LitU the formation of crack tip oxides restricted slip reverials which Curves roear Auenitic Stainljes Steels in Ligh't Water Reactor anviroemclts."
also contributed to increased crack growth rates, although this Foti~ue. Envlronmeantal FaaOrs. and New Materials, PVP VOt. 374. ASKE effect is expected to be much smaller effect than that associated New York, pp. 249-259.
with hydrogen embrittlemcnt, I I') Scott. P. M.. 1938, "A Review of BAvlrotenushtal effects oa Pretssure Vesnel tIntegrity." Proceedings of'the Third Enviropmeaatof ODgradoatonof Motlriols in Nuclear Power 5.vstrmat-Watrr Reactors. TMS. pp. 15-29.
[121 Shoji. T. Takahawi. H.. Suzuki, M., and Kond0. T.. 1981, "A New Parameter 5 Summary and Conclusions for Characte'ir.ins Comrosion Fatigue Crack Growth," ASME J. Hog. Mater.
Instrumented corrosion fatigue tests on 304 SS DEN specimens Tacheol., 103. pp. 298-304.
[13) Leas. T. R-., 1999, "Statistical Modols of Mean Strns ansdWater Euvironment provided fatigue crack growth rate data in 249 and 2ý88C air and Effects on the Fatigue Oehavior of 304 Stlailess Steel." Pralrabilistic and 288°C water Over a wide range of crack growth rates. Results in EnWironmental Aspect.s of Frat-ure and Fatidgi. pVP Vol. 386. ASME. New air and water at the saree mechanical parameters allowed direct York. pp. 229-239, assessment of environmental effects, avoiding any concerns for [14) Gaogloff, F.. 1915, "Crack Sive Effraec on the Chemical Driving Force for pt Aqucoua Corrosion Fatigue." Metall. Trans, A. l6A, pp. 953-969.
data variability due to materials, test technique, and data correla-lJ (15) Shack, W, J.. and Kassner, T. F. 1994. 'Revirw or Enaoviroaon al Effacta on tion, Crack growth rates in water are about 12x times the air rate Fatitue Crack Growthb of Auatenitlc Stainless Steels," NUREGICR-6176, at low speeds where the environmental effects are largest. The ANL-94/l.
large environmental degradation in crack growth is consistent (16] Prater. 'C.A.. Catoin, W. R., and Coffin, L F.. 1985. "Effect of Hydrogen Additions to Water on the Cotrosion Fatigue Behavior of Nuclear Structural with the strong reduction of fatigue life in commercial PWR wa- MatiDAsi1." Proceedlngs' of the $econd ntmernoatinalSytnqsimm on Environ.
ter Further, very similar crack growth rate data were reported in fental Degrodation of Uoyerilab irt Nuclear Power Systes-WalZer Reactort.
low oxygen HWC. in both s5urface crack and conventional deep NACB. pp. 615-623.
eeok tests. The large environmental enhancement in 304 SS 171 Gordon. 5. M., Jndha, M. E., Davis, R. H., Piekart. A. E., and J.wesu, C. W.,
1985. "Environmentally Assisted Cracking Resistanse of OWR Structural Ms.
(12X) persisted to crack extensions up to 4.1 tmim. Far outside the tcrials in Hydrogen Watcr Chemistry," Psreedings of the Second nternea.
range associated with short crack effects. The same large environ- tional Synposaitrn on Ettvltoanental Degradation of MateralsD In Nuclea, mental effects observed in the DEN tests were reproduced in CT PowerSysremns-ter Reactors. NACE. pp. 583-592.
upecimens at a high stress ratio and low AK. The overall results [181 Jewett. C. W., and Piclati, A. F.. 1996. "The Benmfit of Hydrogen Addition to the Boiling Water Reactor Environmem on Stress Corrosion Crack Initiatinoa can be normalized successfully by incorporating the combined and Growth in Type 304 Staialtin Steel," ASME L E.I. Matet Tecbhol.. 108.
effects of stresS ratio and rise time, qualitatively similar to the pp. 10-19.
formulation developed by Itatani et al. to describe test results in [19] Ljuogbersr, L G.. 1989. "Effect of Water taipurilies in BWR on Environanm-tat Crack Orowth Under ReaSatie Load Conditions," Praceedings of the BWR water.
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Four*I Intenmational SY'ymposjium on Ez iror.otia), Dro'-rdolio'r of Materials [25] Itaani. K,, Aofno, M., Kik=u), M.. SuZuki, S,. and Uda, X.. 200t. "Fatigue
!it Nac1kar Power Systemi-Wktuer Reaclorr. NACE, pp 4-59are45n Crack Growth Curve foy Auilehijd Stainle&4 Stcele in BWR Envirovtmenl,"
(201 Andiresen. P. L..,and CAmpball, F. G..O,9. "The Ffflcinf of CrackClsrei ASME ), Pressure Vessel Technol,, 123. pp. 166-172.
N~ight Iraftcrattnrc Wator and Ili; Role in Influctiiing Cinek Closne Data," (265] Goo, M., Clhen, S., and Wei, R. P, 1992, -Crack Paths. Mtoinaetre, and Proceeiniigy of the Fout iabI natalionl Si~mposiyph on lD rrnnnuI aro- Fatigue CTrick Growth in Annealed and Cold-Roltad AISI 304 Swleaes dalimon fMareaixa~ I" Nuclear Power .Systeni~s-WiurerRraciors. Je~kyllIslijwd.
Steel.'" NKetall. Trais. A, 23A. pp. M55-37t.
[21) Wet, R. P, and Gao, M.. 1993. "Mierooeehaniat for Corronina Fatigue CrAck
[21] Giman. 1. D., 1988, "Corrosiioa.Ptiguc CiaAh-Growlh Rntwsill Atietenitic Growth ih Meatlaetle Auslratiec Stainkits Steels," Ca(r$.l'4n-beforat 1,4-Stailess Stecia in Light Water Reator eavco~tim~twn," [tot.1, Prctreýr Vhseiwk Piping, 31. pp. 55-68. eraclaoiv. Les Feditiuns d* Physique. Lzs Ulis, France, pp, 619-629.
C22] Bantford, W.'H.. 1979, '1 ianpCrack Gr..th of Stainlnss SWed Piping !nia (28] Willa, W. I., and' Jztm*, L. A., O98N. "'atigue Crack Propagation Behavinr of t
Preseiizcd Water Reacinir Erevirxonetict. ASME J. Piesatirc /coscl Tcchnooi. Type 316 Staina.x Steel at Bley*ted 7Thrnpcratot in a Vacuum, Inlt. . IN-101. pp. 7.3-71). tigu. 10. pp. 33-30.
(23] Cul~rn. W. UI.,1985, *i'aquoeCrnelt Growth Rule%of'Low-Cafrbort and Stit'it. [29] Lacombe, P.. and glemrrtgr, G., 1993, "Structvre -andEquilibrium Dliagrama of lensPiping Stcels in PWR (?reilifized Water Kcae.tor) trcnet, Vaiorin Stainless Steel Grades," ,Staihlow Rterl. L.s Editions de Physique, NURECitlt.-3045, MP-A,2055, Les Ulls, France, pp. 15-58.
[243 Ocmrnii4 .IL.. Slam&. G., andRabl;4. P,. 1979, nluetaece of PW1t Envilan.
nitint on Fatigute Crckc]Growth lOnhavicir or Stainless Sleis1," 7mirnand load (30] **iniltocn, .W,and litakAnrairtr, T.. 980, "'On the effetLsOf a' Martansite: in Depenldent Dre-adiornt of PrxracituBowidary Mopaixlor IWO.RRPC-79/2, Hydrogen F-mtrittlemcnt of a CathodlcaIly Charged AIST Type 304 Auntec Intareatiottal Atomic Energy Agency, pp. 2? -36, Sa*dsnlea Steal," Corrosion (Houstoaj, 36. pp. 47-5 I.
it
326 / Vol. 126, AUGUST 2004 Transaction, of the ASME Iý