ML20058F299
| ML20058F299 | |
| Person / Time | |
|---|---|
| Issue date: | 07/08/1982 |
| From: | Bell M NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Steindler M ARGONNE NATIONAL LABORATORY |
| References | |
| REF-WM-1 NUDOCS 8207300389 | |
| Download: ML20058F299 (7) | |
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3109.6 JBMartin REBrowning Bell Dr. M. J. Steindler, Chairman FRCook & r/f Materials Review Board HJMiller Argonne National Laboratory J0 Bunting 9700 South Cass Avenue PDR Argonne, Illinois 60439
Dear Dr. Steindler:
The purpose of this letter is to respond to your request of June 15, 1982 to vote on the adequacy of the May 26, 1982 Revision of MCC-103S Stress Corrosion Cracking Susceptibility Test Method.
I vote against approval on a provisional basis, since the method by itself appears inadequate even as a screening test for the materials considered by DOE as candidate metallic barriers.
My main concern is that the testing does not appear to address two major phenomena associated with stress corrosion cracking of titanium and titanium alloys, those being hydrogen effects and galvanic cell effects.
My concerns and a number of additional comments are enclosed.
Sincerely, Orfcirs..;f;
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MICW C J.B Q Michael J. Bell, Chief High-Level Waste Licensing Management Branch Division of Waste Management Enclosute:
As stated
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3109.6/FRC/82/07/06/1 M. J. Bell Comments on MCC-1035 1.
Stress corrosion cracking susceptibility in which hydrogen concentrations and/or hydride phases play a role may not be determined by the MCC-103S test method.
For those alloys for example, Ti and Ni base alloys susceptible to hydrogen embrittlement and/or hydrogen enduced stress corrosion cracking, both low-temperature, low-strain rate tests and cyclic strain tests are more appropriate to determine susceptibility to the subject failure mode.
For T1 alloys these concerns are well stated in a report prepared by T. F. Archbold and D. H. Polonis for PNL, dated September, 1980, entitled, Assessment of Delayed Failure Modes In Titanium and Titanium Alloys.
Also, MCC-1035 is carefully designed to remove potential galvanic effects between dissimiliar metals.
However, there is a possibility that HLW containers will be placed in contact with or close to metal emplacement sleeves or guide rails.
The evaluation of potential galvanic effects on stress corrosion should be tested in a separate screening test.
This could be carried out through the use of double U-bend type specimens in which dissimilar metals are placed in contact or by other methods of establishing the potentially detrimental electrochemical interactions.
Hence, Scope, Section 1.0, should be modified to include a statement that the subject test is not sufficient to determine susceptibility to stress corrosion cracking under the influence of hydrogen and under galvanic cell reactions.
I 3109.6/FRC/82/07/06/1
, Separate screening tests should be developed to assess susceptibility under these conditions since these are likely limiting conditions for some candidate alloys.
2.
In order to emphasize the screening aspect of the subject test, in Section 4.0, Uses and Limitations, the last two sentences of the 4
section should be modifed as follows:
" Data from this test are not sufficient to predict or extrapolate performance under the stress and environment conditions in a waste repository.
Additional SCC testing will be required to qualify materials."
In addition to make this point more prominent these two sentences should be added to Section 1.0, Scope.
3.
In Section 4.0, there should be guidance as to what would disqualify i
a particular alloy as a candidate for further testing.
For example, would one single failure be sufficient to disqualify an alloy?
Without clear guidance, the MCC-103S screening tests may serve no practical purpose.
l 4.
Under item 3 of Section 5.0, there is a requirement to eliminate galvanic couples and stray electrical currents between specimens.
This may be difficult if more than one sample or varying materials are used within the test set-up.
As an alternative MCC may consider specification of maximum allowable currents in the procedure with a provision to record electrical currents and solution conditions.
Oxygen concentration in solution during electrical monitoring is of i
3109.6/FRC/82/07/06/1 obvious importance and could be determined along with the pH.
Electrical monitoring could be performed at the conclusion of testing and at other intervals as were practical to assure conditions were not changed, or, if they were changed, would be determined.
S.
Section 7.0 allows the test solutions to be left to the discretion of the experimenter; however, there is a requirement that test solutions must effectively simulate actual repository site solution characteristics.
This flexibility is inappropriate for a screening test.
Later, Qualification tests should include possible ranges of site specific conditions, however, the screening test should include a decidedly harsh stress corrosion environment for each of the three candidate site (i.e., salt tuff and basalt).
6.
Solution Control should include a tight control on Eh, for example, 110mV, in order to assess this very important parameter.
This would require additional control of 0 and pH, beyond that suggested in 2
Section 7.2.
7.
In Section 8.1, the test material characterization with respect to heat treatment is not definitive.
It leaves open the possibility that tests could be run on as-received material so long as the mill heat treatment schedules are specified.
Section 8.1 should be modified so that it is mandatory for test materials to be re-heat-treated in order to remove residual stresses.
This will ensure that calculated or measured stresses in C-ring samples are accurate.
Appropriate controls on the heat treatment must be I
specified.
l
3109.6/FRC/82/07/06/1 8.
In Section 8.2.1 and 8.2.2 it is necessary that all materials being used to retain and/or insulate "U" bend and "C" bend specimens be of specified materials.
Variation of materials may cause inconsistent results because of varying galvanic couples existing in the test vessel.
In addition, the material for the test vessel should be specified.
This contrasts to the allowance to use NACE-TME-01-71 as a guideline for apparatus design, per item 7 under Section 5.0.
These sections should be revised to resolve these issues.
9.
The test specimen cleaning procedures of Section 8 are inadequate to assure consistent results, since surface contamination may well influence stress corrosion cracking.
To obtain a more consistent screening test, an acid cleaning technique which will remove oxide films should be specified.
10.
Section 8.0 should require a copy of heat treating procedures and test results monitoring the heat (s) during production.
Requirements for keeping extra material should be included to allow additional testing at a later date if desired.
For example, for every heat tested at least 3 times the number of specimens tested (or sufficient material to make the specimens) should be saved.
Test specimen characterization should include determination of the texture and require a description of the mechanical history of the material.
If the mechanical history is not provided by the heat treatment procedures a process description should be obtained for i
each heat of material tested.
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l 3109.6/FRC/82/07/06/1 11.
In Section 9.4, Item 4, fluorescent liquid penetrant inspection techniques should be specified as opposed to normal red dye penetrant inspection because of the additional sensitivity of the fluorescent inspection technique.
Section 9.4 should include a requirement to compare the expected springback with the actual springback to assure anticipated stresses existed during the test.
t 12.
There are few mandatory requirements for characterizing weld material prior to testing.
Since such material is highly variable because of weld parameters used, this material should receive the same comprehensive analyses as those specified in Seciton 8.1 for base metal.
These should include full metallurgical characterization using optical microscopy, XRD, TEM, hardness, and also compositional and mechanical property determinations.
13.
There is no discussion on how weld-induced stresses might compromise stress calculations in C-rings.
If stress relieving of welded C-rings is not desirable, it would be desirable to perform only U-bend tests on welded material.
14.
The 250 C test temperature may, based on some DOE reports, represent a realistic HLW barrier temperature.
Since the stress levels achieved in U-bend and C-ring samples might be anticipated in HLW water components due to inadvertent mechanical damage or general handling and emplacement, and since the test requires the use of simulated repository water chemistries, the actual test conditions specified in MCC-103S are probably close to those expected in the
3109.6/FRC/82/07/06/1 6-repository.
Thus, one would not expect to see any stress corrosion cracking in carefully-selected candidate HLW barrier metals.
For the purposes of screening tests more aggressive test conditions i
should be used to determine the more corrosion resistant metals.
This is the case particularly for Ni-based alloys.
15.
The use of a small number of specimens may not yield statistically 3
significant data.
It is recommended that 10 specimens be adopted I
for each heat of test material and test condition.
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