ML20032A939
| ML20032A939 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 09/30/1981 |
| From: | Kassner T, Kupperman D, Shack W ARGONNE NATIONAL LABORATORY |
| To: | Muscara J NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| References | |
| CON-FIN-A-2212 NUDOCS 8111020602 | |
| Download: ML20032A939 (14) | |
Text
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.v PRELIMINARY Accession No.
Contract Program or Project
Title:
Environmentally Assisted Cracking in LWR Systems to A
Subject of this Dcrument:
Same as above.
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OCT2 6193g s Type of Document: Monthly Progress Report u.s. %~ _ %
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L, Author (s), Affiliation and Address:
W. J. Shack, T. F. Ka s h
rman ',
F. A. Nichols, J. Y. Park and R. W. Weeks - Argonne Nationa a oratory Argonne, IL 60439 Contract No.: 60-19-01-30 (NRC), 4C 01-06-1 (DOE), 8M443 (ANL)
Date of Documer,t: 9-1-81 thru 9-30-81 Date Transmitted to NRC: 10-21-81 NRC Individual and NRC Of fice or' Division to Whom inquiries Should be Addressed:
Dr. Joe Muscara l
Office of Nuclear Regulatory Research l
Materials Engineering Branch l
This document was prepared primarily for preliminary or internal use. It has not received full NRC review and approval. Since tl ere may be substantive changes, l
this document should not be considered final.
1 This Document may be made Publicly Available:
O Signature (NRC Program or Project Sponsor or Authorized Contractor Official)
U.S. Nuclear Regulatory Commission Washington, D. C. 20555 PRELIMINARY e.
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USDipeud Enay ARCONNE NATIONAL LABORATORY WOOSOuttiCAssAtNtt ARC 0NV,llh0is604I9 Tdtpixx 312/972-4931 4
October 21, 1981 Dr. J. Muscara Office of Nuclear Regulatory Research Materials Engineering Branch U.S. Nuclear Regulatory Commission Mail Stop 1130SS Washington, D.C. 20555
Dear Joe:
A copy of the September monthly report for our progran on " Environmentally Assisted Cracking in LWR Systems" is enclosed.
If you have any questions regarding this report, please contact either myself or any of the Principal Investigators.
Sincerely yours,
- D D I Lt_.
W. J. Shack Materials Science Division WJS:ph xc:
B. Elliott H. Conrad K. Wickman R. Silver W. Hazelton W. J. Collins Distribution Services Branch /NRC f
~
Tiit LMtRsiTyof Odexp ARC [M (MERsiTIEs AssociviON
g e
. Monthly Progress Reporj Contractor: Argonne National Laboratory Program:
Environmentally Assisted Cracking in LWR Systems 189a:
A2212 B&R No:
60-19-01-30 (NRC)
Reporting Period:
40-10-01-06-1 (DOE) 9-1-81 thru 9-30-81 8M443 (ANL)
Task Manager:
W. J. Shack Financial Summary:
Monthly Cumulative Baseline Actual Variance Variance Oct.-March
$ 421K 421K April 1.29K 129K May 135K 101K 34K 34K June 148K 131K 17K 51K July 160K 120K 40K 91K August 160K 123K 37K 128K Sept.
336K*
133K 203K*
331K*
FY 81 TOTAL 1489K
- Variance: The positive cummulative variance has been carried over into FY 82 and will be used largely to fund the subcontracts that have been established.
1 Administrative Report Due to scheduling conflicts the meeting date with members of EPRI to discuss areas of mutual interst in this program has been postponed to December 15-16, 1981. The meeting will be held at ANL.
Dr. W. J. Shack will discuss this program at the NRC Annual Information Meeting on October 30, 1981. Prior to this, he and Dr. T. F. Kassner will attend the International Corrosion Fatigue Crack Growth Meeting in Charlotte, North Carolina.
Technical Progress Subtak A: Leak Detection and NDE (D. S. Kupperman)
Work on the acoustic leak detection facility has progressed. All heaters have been installed. The system has been proof-tested at 2035 psi with room-temperature water and heated to 550*F with nominal pressure.
Steam has been generated employing the 20-mil-dia artificial leak.
The subcontract with GARD for data acquistion and analysis has been completed rod should be signed off soon.
Contact has been made with PNL to acquire some cast SS samples for the ultrasonic NDE effort. Further discussions with NBS personnel (Linzer and Fortunko) on the use of EMATs for ultrasonic flaw detection have been made.
Subtask B: Analysis of Sensitization (J. Y. Park)
Sensitization tests on the Type 316NG SS (Heat N. P915676) plate o
weldment have been carried out.
EPR measurements were made on five different cross-sections in the RAZ at 0 - 3.6 mm distance from weld fusion line.
No i
detectable level of sensitization was observed. This result is consistent with the test results by ASTM A262-A and -E.
Two load cells and load cell amplifiers for the constant load SCC test facility with the small diameter pipe autoclaves were calibrated for a range of load 0 - 5000 lb.
These units are now operational.
Subtask C:
Crack Growth Rate Studies (J. Y. Park and W. J. Shack)
The constant load crack growth rate test on the IT compact test specimen (Tygg304stainlesssteel)withanappliedstressintensityofK=17ksi is continuing.
It is now clearly evident that the crack is growing in i
under constant load, although the crack has not yet propagated far enough to permit accurate growth rate measurements. Efforts are also continuing to set up an A.C. potential measurement system as an alternative to the present compliance techniques. The potential measurements permit continuous monitoring without the need to interrupt the losiing cycle.
w m
4 ww-
2 Subtask D:
Non-Environmental Corrective Actions (P. S. Maiya and W. J. Shack)
The CERT stands are now calibrated and pressure checked and the initial screening tests on the Type 316NG weldment materials are now underway. Strain gauge measurements have been completed on two of the three mock-up weldments prepared by PNL. The third weldment is now being instrumented. The test equipment for the stress-relaxation tests is now operating. The initial tests will focus on the behavior of Type 304 stainless steel at room temperature since the data currently available suggest that there should be relatively small differences between the behavior at room temperature and at 288'C.
Subtask E:
Evaluation of Environmental Corrective Actions (W. E. Ruther and T. F. Kassner)
During this reporting period, two CERT experiments were performed in the slow-strain-rate Instron testing system with the large autoclave.
One specimenofType304sgainlesssteelwasfurnacesensitizedfor24nat600*C (EPRvalueof8.8g/cg)t288'C strain rate of 10~ -
and tested in high purity water (0.2 ppm oxygen) at a The other specimen was sensitized for 0.25h s
a at 700*C plus 2gh at 500*C to produce a lesser degree of sensitization (EPR value of 2 C/cm ) and tested in deoxygenated ester (<0.C5 ppm oxygen) at the same temperature and strain rate.
No intergranular stress-corrosion-cracking was evident from examination of the fracture surfaces of the specimens. The results of the four CERT experimegts performed to date are consistent with data reported by Clarke and Cowan for specimens with equivalent EPR values.
Thus, we believe that the reference heat of Type 304 stainless steel will be adequate for the more sophisticated and time consuming crack growth measurements under different water-chemistry conditions.
A titanium and a Type 316 stainless steel autoclave for evaluation and calibration of high-temperature pH sensors and reference electrodes and for electrochemical measurements on materials in simulated BUR quality water have arrived. The autoclaves are being coupled with recirculating water loops.
The assembly and checkout of the second MTS system for crack growth studies in the high-temprature water environment is progressing on schedule.
Subtask F: Mechanistic Studies (F. A. Nichols) icw of the literature to date reveals that, after many years of inve gation, there remains considerable controversy over the specific mechanism (s) by which cracks propagate under stress-corrosion conditions. On the other hand, a great deal has been learned about what seem to be general charactertstics of stress-corrosion cracking (SCC).
These developments have in turn enabled more rational use and extrapolation of experimental test results as well as providing the framework for the development of predictive models for specific systems of material and environment. Since such approaches will no doubt be increasingly applied in the near future, it behooves to NRC to conduct independent mechanistic studies and confirmatory research in order to properly assess any future proposals.
- W.
L.
Clarke and B.
L.
Cowan, "The EPR Method for the Detection of Sensitization in Stainless Steels", EPRI-WS-79-174, vol.
2_,
May, 1960.
1
3 Most all investigators seem to agree that SCC occurs under a specific range of relative rates of straining (leading to fracture of protective films) and repassivating (i.e., re-forming the protective film). Most controversy centers around the specific physical mechanism by which crack advance occurs in between film rupture and re-formation. There are two principal proposals.
The anodic dissolution of metal at the crack tip is significantexperimentalsupportexistsforthisconcept.{avoredbysome,and Correlations of anodic currents from rapidly strained electrodes with measure crack growth rates, coupled with the many examples showing SCC at potentials far above the value for equilibrium hydrogen production, have causedsometocgneludethathydrogenisnotanimportantfactor.
- However, studies by Brown using medium-strength steel in 0.6 M Nacl at various bulk pH's and various imposed currents, showed that the bulk potential (as usually measured, at the surface of a specimen) may differ draatically from that existing at the crack tip itself. More specifically, Brown reports, for his system of study, that the pH/ potential conditions obtaining at the crack tip were consistently below the line at which hydrogen discharge is theoretically possible (assuming equilibrium conditions). Of course, the possibility (even the certainty) of hydrogen production does not necessarily imply that hydrogen either enters the specimen or, if it does, that it in fact causes the crack advance. A complicating fact is that acid conditions may often exist at the.
crack tip even when not present in the bulk solution, and thus anodic dissolution may well occur. Studies similar to Brown's in other systems would be welcome, as would further analytical work to enable the prediction of gradients in potent al, pH and ion concentrations along a crack. The work of Oldfield and Sutton is an example of such work for crevices, whereas the work of Doig and Flewitt is an attempt to analyze actual stress-corrosion cracks in simi~ar manner.
In the context of deciding between hydrogen embrittlement (HE) and dissolutionasthephysicalcauseofcgackadvance,twotypesofexperiments have been performed. In one approach, Wilde and Kim measured the rate of hydrogen entry into (and permeation through) a thin membrane of 304 SS as a function of applied current densities both anodic and cathodic. Their results were obtained at 146*C in a saturated lithium chloride solution with and without the addition of Ig/l of Na3 s0. Although the Na3 s03 A
A addition 3
greatlyenhancedhydrogenabsorptionundercathodiccuryents,2n vidence for SCC was observed for cathodic currents arcater than 10~ A/cm These results seemclearlytoindicatethathydroganabsorptionperse_isigsufficientto cause SCC of 304 SS in chloride solutions. However, Thompson has argued that the absence of acidic conditions (which may exist at an actual crack tip) may have enabled sufficient tip blunting to obviate the HE process, thus suggesting that a combination of dissolution (at least to keep the crack sharp)andHEmaybeoperativeundersomeconditions,forthemorepuctile alloys such as 304 SS.
(Hydrogen charging has of course been shown to enhance cracking in less ductile, high-strength steel.)
A second type of experiment to distinguish between HE and dissolution processes as crack-advance mechanisms utilizes the effect of hydrostatic tension. All current models for HE in some manner require hydrostatic tension in order to concentrate the hydrogen atoms in a critical region. On the other hand, the dissolution rate is thought to depend primarily on the local
4 pH/ potential condition at the crack tip and not on the state of stress. Thus, studies have been made which compare Mode I (uniaxial tensile loading) with Mode III (pure shear loading).
With 70 - 30 brass thetwomodesgaveequivalentcgackingpropensity,8"hichseemstoruleout w
HE.
With a 7075 aluminum alloy in aqueous chloride-chromate environment, susceptibility was considerably reduced in Mode I, indicating but not exclusive role for HE.
For several titanium alloys,8 lbE essentially no susceptibility has been reported in Mode III, indicating a dominant HE contribution. Apparently, such studies have not yet been reported for austenitic stainless steels.
The concept of a critical range of strain rates at the crack tip to obtain susceptibility in a given material / environment system has been strongly supported by the widespread use of the c (CERT) for bothfundamentalandscreeningpurposes.ppstant-extension-ratetest The concept also provides a rational method for correlating SCC under fixed load, stress relaxation, or cyclicloadconditions,i.e.thecriticalrequirement{gtoattainthecorrect strain-rate regime, independent of how it is attained.
Ihere is evidence that below the critical strain rate regime, SCC does not This is consistent with apparent " threshold" stresses or stress occur.
intensities as often reported. However, it is known that application of a cyclic component of load can significantly increse the amount of plastic deformation. This implies that cyclic loads can reduce these apparent thresholds, and this has been reported for a number of systems.
If the cyclic amplitude is large, the fracture mechanisms or mode may change, e.g. ICSCC may change to TG corrosion fatigue, but for sufficiently small-amplitude this should not occur.
Also, significant strain-rate dependence might be expected as creep deformation is typically strongly temperature (and hence strain-rate) dependent.
Fessler.pgpecially striking example of such effects is seen in work by An The material was a ferritic steel in a carbonate solution at 82*C and an imposed potential of -650mV (S.C.E.).
The imposition of a sinusoidal component of magnitude 11.5% was sufficinet to greatly reduce the apparent (nominal ligament) threshold stress for precracked cautilever besms and the effect is much greater at very low frequencies. At the lowest frequency (about 2 cycles per month) the apparent threshold stress is only about one-thirdofitsvalueunderstaticloadingconditions(whichwasggightlygreater than the yield stress).
It has also been shown by Berry et al that cyclic loadgng{0.5510.05 of the yield stress) which resulted in a strain rate of
_ at 288C produced IGSCC in sensitized 304 SS in oxygenated (8 pmm) s10 s
BWR quglity water.
The frequency of the trapezoidal loading waveform was 42 x 10 Hz.
It can be seen from Fig. 5 that the Fessler results showed for that system much larger ef fects at much lower f requencies, but such f requencies have apparently not been explored with 304 SS for LWR conditions.
t Finally, the entire question of a critical strain-rate requirement in the vicinity of the crack tip brings in the question of how the local stress-strain-strain rate behavior relates to the applied loading conditions.
Determination of the mechanical properties of solution-annealed and sensitized 304 SS is covered in another section of this program, but a matter of interest here is the local dislocation structure and slip pattern near the crack tip, l
5 including the possible relationship between " striations" on the crack surface and the gpacing of dislocation sources. Such a correlation was noted by Neilson for 304 SS, but not under LWR conditions.
Based upon the survey outlined above, plans are being developed for applying similar techniques to elucidate operative mechanisms in 304 SS under LWR conditions.
References 1.
R. N. Parkins, British Corrosion J. 1;((1975)5.
2.
B. F. Brown, NATO Conf. on "The Theory of Stress Corrosion Cracking in Alloys", Ed J. C. Scully, Brussels, NATO, 1971, p. 186.
3.
J. W. Oldfield and W. H. Sutton, Br. Corr. J. 1][ (1978) 15.
4.
P. Doig and P. E. J. Flewitt, in " Mechanisms of Environment Sensitive Cracking of Materials", Ed. P. F. Swann, F. P. Ford and A. R. C.
Westwood, The Metals Soc., London, 1977, p. 113.
5.
B. E. Wilde and C. D. Kim, Corrosion j2[ (1972) 350.
j 6.
Anthony W. Thompson, Mater. Sci. & Eng. 4j[ (1980) 41.
7.
C. F. Barth, E. A. Steigerwald and A. R. Troiano, Corrosion Jt5, (1969) 353.
8.
J. A. S. Creen, H. W. Hayden and W. C. Montague, in "Effect of Hydrogen on Behavior Materials", Ed. A. W. Thompson and I. M. Bernstein, The Htallurgical Society of AIME, New York,1976, p. 200.
9.
J. A. S. Creen and H. W. Hayden, in " Hydrogen in Metals", Ed. I. M.
Bernstein and A. W. Thompson, Amer. Soc. Metals, Metals Park, OH,1974,
- p. 235.
10.
C. F. St. John, Scripta Met. j)_ (1974) 141.
11.
" Stress-Corrosion Cracking - the Slow Strain Rate Technique", Ed. C. M.
Ugiansky and J. H. Payer, STP 665, Amer. Soc. Test & Materials, 1979.
12.
T. L. Cerber and Y. S. Carud, S. Levy & So., Campbell, CA,1981 (private communication).
13.
Raymond R. Fessler, The Oil and Gas Journal, February 16, 1976, p. 81.
I 14.
Warren E. Berry, Earl L. White and Joe H. Payer, in " Proceedings: Seminar on Countermeasures for Pipe Cracking in BWRs", Vol. 2, Electric Power Res. Inst. Report WS79-174, 1980, Paper No. 30.
15.
N. A. Neilson, in " Stress-Corrosion Cracking and Hydrogen Embrittlement of Iron-Base Alloys", Ed. R. W. Stachle, J. Hechmann, R. D. McCright and J. E. Slater, NACE, Houston, 1977, p. 1108.
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