ML19326B687
| ML19326B687 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 01/22/1975 |
| From: | Cavanaugh W, Phillips J, Reuter D ARKANSAS POWER & LIGHT CO. |
| To: | |
| Shared Package | |
| ML19326B653 | List: |
| References | |
| NUDOCS 8004170527 | |
| Download: ML19326B687 (39) | |
Text
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- 1. Abnormal Occurrence Report No.
50-313/74-11A
- 2. Report Date: January 22, 1975 3. Occurrence Date: November 7, 1974
- 4. Facility:
Arkansas Nuclear One-Unit 1 Russellville, Arkansas
. S. Identification of Occurrence:
See AOR 50-313/74-11 dated 11/18/74
- 6. Cond_itions Prior to Occurrence:
Steady-State Power Reactor Power o NWth Hot Standby Net. Output 0 MWe Cold Shutdown x Percent of Full Power 0 %
Refueling Shutdown Routine Startup Operation Routine Shutdown Operation ~ .
Load Changes During Routine Power Operation " .
Other (Specify)
- 7. Description of Occurrence: -
.3 See AOR 50-313/74-11 s
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8004170 July 5, 1974 ,
NSP-10, Rev. O Page 1 of 3
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Abnormal Occurrence Report No. S0-313/74-11A Sheet 2
- 8. Designation of Apparent Cause of Occurrence:
Design Procedure Manufacture Unusual Service Condition Including Installation / Environmental Construction Component Failure Operator !
Other (Specify) X
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Not determined at this time. See attached report. l i
- 9. Analysis of Occurrence: !
See attached report. -
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- 10. Corrective Action:
See attached repart. 2 "N .
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} July S, 1974 NSP-l'D, Rev. O Page 2 of 3 l
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Abnormal Occurrence Report No. 50-313/74-11A Sheet 3
- 11. Failure Data:
See AOR 50-313/74-11
- 12. Reviews and Approvals: !
Reviewed and Approved by: Plant Cafety Committee Yes (X) No ( )
O Plant Superintendent
Reference:
JNA-825 Yes (X) No ( )
Date: 1/29/75 Reviewed by: /)e # Date: 7
' J'
/ Licensing' Supervisor /
Approved byl f}/' */, *. ,, / i .- Date: & ~ '/- ? T
/ afet 'Re$tfe'
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ihee '
Approved by: q)~ M [ Date: O 3 [
h nager of Nuc, lear Ser M s ' /
Approved by: .///lrEs '-
si i ./ Date: S ~ *l .7 \
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Director of Power Production' l
Approved by: . . -
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Date: 7-Y'74 3
,j Senior Vice Pre'sident D .
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. July S, 1974 NSP-10, Rev. O Page 3 of 3 *
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' ATTAClefENT TO AOR 50 313/74-11A On November 7,1974, a leak was discovered in a Reactor Building Spray System pipe of Arkansas Nuclear One-Unit ,1. The plant was being shut down following hot functional test of the primary coolant drain line, and was going into decay heat mode at the time the leak was detected.
The leak was located adjacent to a weld in line HCB-6-1. A segment of the system, including the leak, was replaced and the plant returned to operation. On November 13 a second leak was detected adjacent to a new weld which was made in.the original pipe as part of the original repair.
Subsequent leaks were also discovered in the spray pumps suction cross-over line between valves BW7A and BW7B. These leaks (labeled #3, #4 and #5 in this report) were not considered to be abnormal occurrences since that section of the pipe is isolated under normal modes required --
for spray system operation. Leak #4 was found in the weld made for the repair. of leak #3. Figure 1 is a simplified isometric showing the loca-tion of the first 4 leaks and figure 2 of leak #5. Samples of the pipe containing each of the first three pipe leaks have been forwarded to Bechtel's Materials, Fabrication .and Quality Control Services Laboratory for Metallurgical Analysis.
The following discussion describes the investigations made to date and the results. All failures except ' cracks #4 and #5 have been repaired by '
replacing a section of.the pipe. Cracks #4 and #5 have not been repaired
\s. because they are located in the non-essential crossover line and plans -
have been made to eliminate this line. The crossover line is currently
, isolated. '
Upon examination, the three leaking pipe sections showed very similar crack morphologies. All three exhibited intergranular cracking roughly parallel to circumferential butt welds in the continuous sensitized 3:
region of the Heat Affected Zone (HAZ). In all cases the cracking began
- on ID surfaces, approximately 1/4 inch from the root of the weld. The 9, microstructure of the pipe showed carbide precipitation. Both surfaces -
l exhibited a continuous network of intergranular attack approximately j 0.001 inch deep.
Intergranular stress-assisted corrosion cracks (IGSACC) of -TP-304 stain- 2l 1ess steels-at temperatures near atmospheric ambient are rare. Very j specific conditions and chemical specie. are generally required to provide !
IGSACC in sensitized TP-304 at ambient temperature. Sensitized stainless '
.s teels are. susceptible to IGSACC in nitric, sulphuric, phosphoric, hydro- ~ l chloric, hydrofluoric and naphthenic acids, in addition to certain ratios
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of. SO4 "/C1~, aqueous ammonium chloride solutions and dissolved 02 Most -
of the chemical species mentioned are outside the range of water chemistry expected in the containment spray system. Pickling is known to have a detrimental effect on the intergranular stress-assisted corrosion cracking l
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The various factors in this investigation are discussed below with an estimation of their probable effect in the cracking of pipe sections.
- 1. Pipe bhterial:
The piping material is ASTM A-3S8, TP-304. By specification, "all pipe shall be furnished in the heat treated condition.
The heat treatment procedure shall consist of heating the material to a minimum of 1900*F and quenching in water or rapidly cooling by other means." Extensive microstructural examination of the cracked pipe sections revealed some sensitization. The '
heat treat condition is a significant contributor to the inter- ,,
granular stress-assisted corrosion cracking. The examination also revealed a continuous network of intergranular attack on both ID and OD surfaces of the piping. The attack was on the order of 0.001 to 0.002 inches deep and was probably caused by pickling after heat treatment. The fact that the attack on the outside and inside surfaces is the same is significant in that it indicates the attack existed prior to installation and was not caused by the service environment. This type of intergran-ular attack is believed to hasten cracking of sensitized stain 1
} 1ess steels and to provide retention of fluoride ions -from the pickling solution. Fluoride ion in very small concentrations,
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1 to 400 ppm, . is known to cause IGSACC in sensitized TP-304 stainless at or near atmospheric ambient temperature.
- 2. Stress:
It is assumed that the stress component for IGSACC was due to fit-up and welding because the cracking observed has all been near >
welds, s
- 3. Water Chemistry:
The chemistry of the water to which the piping was exposed during normal operation and prior to failure will be presented in our ~
~
final report. The fluid is primar'ily borated water of varying concentrations .
The investigations included visual observations, microstructural examina-tions, sca'nning electron microscope examination of fracture surface and chemical analysis.
The results of the investigations are summarized here without reference to specific photomacrographs or photomicrographs. A pictorial review of the three cracks is presented in Appendices 1, 2 and 3. The photomacro-
,_ graphs and photomicrographs of the appendices are supported by commentary.
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- 1. Visual Observations:
The three pipe sections which leaked were examined visually with -
magnification aid to 30X. The three sections contained cracks parallel to the circumferential butt welds. The cracks were approximately 1/4" from the root of the weld. All cracks were within the HAZ as determined by the welding heat tinting. The cracks were longer, with wider openings on the ID' surfaces, ,
indicating that they originated on these surfaces. Three addi-tional cracks originated on the ID surface which did not go all the way through the wall. Examination of both ID and OD surfaces at 30X revealed a " dried mud cracked" appearance. At crack #1, the pipe had been deformed to match the adjacent pipe fitting.
Visual examination of all three pipe sections revealed that there was a similarity of location (in HAZ), orientation (parallel to ~
weld), appearance (intergranular) and origin (ID surface).
The cracks on the' pipe perimeters are located as follows:
Looking into the pipe from the circumferential butt weld side, crack #1 was located at 12:00 o' clock, crack #2 at 7:00 o' clock, and cracks on pipe #3 were located at 1:00 o' clock, 5:00 o' clock, 7:00 o' clock and 9:00 o' clock. Those at 5:00, 7:00 and 9:00
% o' clock did not penetrate the wall.
- 2. Microstructural Analysis: '
Cross sections of all cracks and pipe base metal away from the circumferential welds were examined on a metallurgical micro-scope with magnifications up to 1000X., The results were very similar for all three pipe sections examined.
- a. He cracks originated on the ID surfaces and progressed
.1 through the pipe thickness in an intergranular manner, s here was no evidence of transgranular or mixed mode cracking.
- b. He cracking occurred in the heat-affected zone of con- __
tinuous carbide precipitation at the grain boundaries. ~
- c. The cracking was branched with secondary cracking.
- d. . De weld appeared sound with no suggestion of any object-ionable features.
- c. The longitudinal welds on all pipe sections appear to have been solution treated after planishing. H ere was no evi-dence of a heat-affected zone near these welds.
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- f. The base metal of all pipo sections contained continuous and semi-continuous carbide precipitation at the grain boundaries, indicating an inadequate cooling rate from the solution heat treating temperature. The carbide precipita-tion was heavier in the center of the pipe thickness than at either' surface.
-g. On both ID and OD surfaces throughout the pipe lengths, there was a network of intergranular attack at the grain boundaries. This intergranular attack extended to a depth of 0.001 to 0.002 inch. This attack was most probably caused by pickling subsequent to heat treating.
- 3. Fractog'raphic Analysis:
The fracture surface of crack #1 was examined on a scanning electron microscope. 'Ihis examination confirmed the inter-granular mode of fracture. The fracture features were sharp, indicating fracture was accompanied by very little corrosion.
- 4. Chemical Analysis:
A sample from pipe containing crack #1 was subjected to chemical analysis to specification requirements.- The analysis shows all i specification requirements for chemistry were met, although the N_ / carbon content is near the maxinum permitted. The rare earth -
metals, Cesium, Cerium and Lanthanum were present in small quantities.
- 5. Water Analysis:
A chemical analysis of water from the containment spray and decay >
heat systems will be presented in our final report.
i
- 6. Deposit Analysis:
A wipe sample of the ID surface of pipe section containing crack
- 2 was obtained before the line was decontaminated. The analysis ,
of this sample is not complete. -
~
. Field Investigation:
g A random sampic of areas adjacent to 46 welds in the building "
i spray and' decay-heat systems was examined by ultrasonic and '
! radiographic methods. Of these areas, five showed crack-like -
indications in the radiographs. It was concluded that ultrasonic testing was not a satisfactory method of examining pipe for the suspected defect and that radiography was the more satisfactory method of examination.
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The following work remains to be done:
- 1. Obtain a chemical analysis of water samples and crud from the system.
- 2. Perform modified Strauss tests on samples of the pipe to determine the effect of carbide precipitation.
- 3. Field investigation of all schedule 10 stainless steel piping to identify pipe with excessive pickling attack.
- 4. Metallurgical examination of cracks #4 and #5 and RT indications f'ollowing removal of crossover pipe.
Item 1. has been delayed due to non-availability of legal shipping con- ~~
tainers. No date is available for completion. Items 2. through 4. depend on removal of the section of crossover pipe. This removal will be accom-plished during a planned shutdown in the spring of this year. The exact date of the planned shutdown is not yet known.
In addition to the above work, Southwest Research Institute has been retained to do the following:
- a. Review the analysis performed in the Bechtel Lab and issue a report on their findings;
\_ -
- b. Perform, by microprobe technique, an analysis to identify any corrodent; l
- c. Establish a program to examine, in the field, pipe surface con-
. ditions to identify pipe that has. experienced chemical attack l due to excessive pickling; -
- d. Perform an independent metallurgical examination of cracks #4 and ,
- 5 and RT indications following removal of the crossover pipe l
- e. Examination of the surface of the pipe in the field for carbide l precipitation by a surface replica technique; _
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- f. Propose additional investigations they believe would be advisable.
Item c has been completed. Our review of the program has not been com- '
pleted at this time. The other items depend.on the planned shutdown this spring.
In the interim, we have increased our surveillance of this system to I include a once-a-shift walk thorough examination for leaks.
Final results, conclusions and corrective action will be reported when all investigations are complete. The schedule for this final report necessarily f( ,)s depends on the planned spring shutdown for which an exact date is impossible to determine at this time.
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1 APPENDIX 2 PICTORIAL REVIEW OF CRACK No. 2 . 1 e l 3 l 4
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. Fig. 2-1 Sketch showing the locations of the samples received and the lccationr for the metallographic specimens.
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APPENDIX 3 i PICTORIAL REVIEW OF CRACK No. 3 - O T
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