IR 05000456/1986008
| ML20214E201 | |
| Person / Time | |
|---|---|
| Site: | Braidwood  |
| Issue date: | 02/26/1986 |
| From: | Danielson D, Jeffrey Jacobson, Muffett J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| To: | |
| Shared Package | |
| ML20214E198 | List: |
| References | |
| 50-456-86-08, 50-456-86-8, 50-457-86-07, 50-457-86-7, NUDOCS 8603070195 | |
| Download: ML20214E201 (6) | |
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U.S. NUCLEAR REGULATORY COMMISSION
REGION III
Reports No. 50-456/86008(DRS); 50-457/86007(DRS)
Docket Nos. 50-456; 50-457 Licenses No. CPPR-132; CPPR-133 Licensee:
Commonwealth Edison Company Post Office Box 767 Chicago, IL 60690 Facility Name: Braidwood Station, Units 1 and 2 Inspection At:
Braidwood Site, Braidwood, IL Inspection Conducted: August 8-10, 21,'27, and October 24-26, 1985, and February 18, 1986.
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4 Inspectors /tJ. W. Muffett Date (
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J. M. Jacobson
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Date
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'hb Approved By:
D. H. Danielson, Chief
Materials and Processes Section Date Inspection Summary Inspection on August 8-10, 21, 27, and October 24-26, 1985, and February 18, 1986 (Report No. 50-456/86008(DRS); 50-457/86007(DRS))
Areas Inspected:
Unannounced safety inspection of licensee action on previous inspection findings related to the engineering evaluation of corroded small bore piping and procedural control of piping materials.
The inspection involved a total of 96 inspector-hours by two NRC inspectors.
Results: No violations or deviations were identified.
8603070195 860303 PDR ADOCK 05000456 O
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DETAILS 1.
Persons Contacted Connonwealth Edis_onlC_EC_oj
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- M. J. Wallace, Project Manager
- D L. Shamblin, Project Construction Superintendent
- L. O. De1 George, Assistant Vice President Engineering and Licensing
- D. Skoza, Project Field Engineer Sargent & Lundy Engin_cers (S&L)
A. Dermenjian, Assistant Head, Engineering Mechanics Division C. S. Lim, Project Engineer Phillips Getschow Co_mpany_(_PG_C_o)_
J. R. Stewart, Project Engineer National Board Audit Team
- S. Lindbeck, Audit Team Member
- Denotes those attending the final exit interview at the Braidwood Station on February 18, 1986.
2.
Licensee Action on Pre _vi_ou_s_ Inspection _ Fin _ dings a.
(Closed) Open Item (456/84017-03; 457/84017-03); (Closed) 50.55(e)
(456/84-10-EE; 457/84-10-EE): As discussed in NRC Inspection Reports No. 50-456/84017; No. 50-457/84017 it was discovered that some small bore piping which may have violated minimum wall thickness requirements due to corrosion or manufacturing defects (ribbon grooves) was installed. The licensee connitted to perform an investigation of the significance of the installation of the potentially deficient pipe and to take the necessary actions determined by the results of the investigation. The purpose of this report is to document the NRC inspections of these activities. The licensee initiated Nonconformance Report (NCR) 633 to address this issue. The program to address NCR 633 consisted of four parts.
They are, theoretical determination of maximum increase in stress due to pitting, physical and chemical testing, a program for statistically significant wall thickness measurements, and a final engineering evaluation.
Each of these activities are addressed as follows:
(1) Theoretical Increase in Stress:
The stress intensification factor (SIF) was developed to account for the potential increase in stress due to the pitting. This SIF was developed employing certain conservative
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assumptions. The first is that the worst pit depth measured was assumed to be in the same location on botil the inside diameter and the outside diameter. The second is that this depth of metal was assumed to be removed from the entire circumference of both the inside diameter and the.outside diameter. The third is that the pit shape was idealized to
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have sharp corners at the points at the beginning and end of the removed area. The SIF was then applied to the prior stress
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analysis results for all the piping systems in which the corroded pipe may have been installed.
It was determined that six locations on these piping systems were not within applicable ASME Code allowable stresses when the SIF due to the corrosion pitting was employed.
In addition, four locations which had stress levels close to the ASME Code allowable stress were also removed. The piping removed was as follows:
Six Overstressed Locations Systems Size / Schedule Safety-Related Component Cooling 2" Sch 80 Yes Component Cooling 2" Sch 80 Yes Steam Generator Blowdown 2" Sch 80 Yes
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Steam Generator Blowdown 2" Sch 80 Yes Chilled Water 3/4" Sch 80 No I
Chilled Water 3/4" Sch 80 No Four Additional Locations J
Systems Size / Schedule Safety-Related
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Component Cooling 2" Sch 80 Yes Steam Generator Blowdown 2" Sch 80 Yes Steam Generator Blowdown 2" Sch 80 Yes
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Steam Generator Blowdown 2" Sch 80 Yes These portions of the potentially affected (approximately a total of 30 feet) systems were removed and replaced with new sections of pipe. Based on this approach no piping remained in the plant which was not in compliance with ASME Code requirements for strength. The calculations which form a basis for this
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methodology have been reviewed by the NRC inspector and found to
be an acceptable technique for conservatively estimating the j
stress increase due to corrosion. The calculations were
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EMD-04966f4, " Stress Intensification Factors of 1/4"-2" Sch 80
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Pitted and Corroded Pipe" and EMD-049655, " Stress Check of 1/2" i
and 3/4" Sch 80 Corroded Pipe."
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(2) Chemical and Physica?_ Testing:
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A number of chemical and physical tests were performed to
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determine to what extent the pipe had been degraded by the j
corrosion. These tests were as follows:
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a) Tensile Test b) Chemical Analysis of Composition of the Piping c) Burst Test (Piping overpressurized to the point of.
bursting)
i (d) Bend Test i
(e) Fatigue Test i
(f) Macro Etch Examination
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I Metallographic Examination
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Outside Diameter Surface Deposit Analysis
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Pit Residue Analysis
(j) Residual Chemical Acidity Test l
Taussig Associates, the testing laboratory, reached the conclusion
based on their tests that all the samples met or exceeded the j
requirements for the specified materials l(ASTM A106, Gr.B).
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l addition, Taussig expects no degradation in service performance
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or lifetime.
It is important to note that Ceco states that the
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samples tested were judged to exhibit the worst examples of
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pitting and corrosion. The results of these tests were reviewed i
l by the NRC inspectors and the values for various mechanical
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properties were in compliance with the ASME code.
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(3) Wall Thickness _Me_asurements:
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A random sampling program was performed on the affected
I population of piping. The population of affected piping was r
28,723 pieces, of these 4,586 were installed in Unit 1 and j
common systems and 24,137 were in storage. The pieces were
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each uniquely identified by assigning sequential numbers. A
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random number generating process was used to determine 300 l
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pieces for detailed measurement. Over 28,000 wall thickness
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l measurements were made on the 300 piece sample. Of the sample
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of 300 segments of pipe, 218 contain no measurements below the
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minimum wall thickness allowed by the manufacturer's tolerance t
as stated in the ASTM specification A106. The remaining 82
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contained no minimum wall thickness violations which would
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have caused the piping to violate the ASME Code stress allowables in the affected installations. All of these samples were visually inspected by the NRC inspectors. None of the samples were found to exhibit unusual properties.
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(4) Final Engineering Evaluation The final evaluation of the pipe corrosion problem at the Braidwood Station is contained in Comonwealth Edison Report
"Braidwood Station - Units 1 and 2 Engineering Evaluation of the Pipe Corrosien Problem Identified in CECO NCR No. 633" dated January M86. The report was reviewed and found to be an acceptable evaluation of the corrosion problem. The report makes the following conclusions:
(a) Confirmatory testing and wall thickness measurements indicate all pipe locations would meet the ASME code allowable stress limits.
(b) The corroded pipe still has adequate strength to perform its intended design function.
(c) Chemical tests indicate no surface residue which would tend to cause additional corrosion in the future.
e (d) The corroded pipe is expected to perform in the same manner as a new pipe during its service life.
In addition to the NRC review of the results of this program, a National Board Audit Team member reviewed the disposition of Comonwealth Edison Nonconformance Report No. 633. This review determined that the report " Engineering Evaluation of Pipe Corrosion Problem Identified in CECO NCR 633," EMD-054247, complied to the ASME code requirements in the disposition of NCR 633. The test results were also reviewed by Steven Danylak Ph.D. a professor of Materials Science at University of Illinois at Chicago.
Dr. Danylak stated:
"There is no evidence to suggest that the chemical cleaning was overly aggressive. The surface morphology of the chemically cleaned pipe that had been corroded is not substantially different from the not chemically cleaned or new pipe. All pipe showed surface irregularities and depressions. The chemically cleaned and corroded pipe contained shallow pits not unexpected in carbon steel. Neither the pitted regions nor the corrosion products from these regions exhibit any unusual morphology based on the pit shape or chemistry, so there is no reason to expect that the chemically cleaned pipe would corrode more rapidly that the not chemically cleaned pipe.
I have also evaluated the general service conditions to which the steel pipe will be subjected and, in my opinion, these conditions are relatively mild as, for example, compared to those in the Chemical Process industry which routinely uses this grade of pipe. My field experience of corrosion problems in the Power and Chemical Process industries has shown that the chemically cleaned pipe may continue to be used when the design calls for A106 grade B steel pipe."
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In conclusion it appears that any segment of piping which had the potential to be adversely affected by the corrosion has been removed from the Braidwood Plant. Also it appears that based on the testing the corroded piping complied with applicable specification require-ments.
In addition there is no evidence that the installed corroded piping will behave in a substantially different manner than the non corroded piping, b.
(Closed) Violation (456/84017-02;457/84017-02): The NRC inspection which identified the corroded piping problem also found Ceco in violation of 10 CFR 50, Appendix B, Criterion XV (control of nonconforming material) and Criterion XVI (lack of adequate corrective action).
In response to this violation Phillips Getschow Procedure QCP B4, which governs this activity was revised to more tightly control storage of piping.
The NRC inspector has reviewed this procedure and has inspected the current manner of storing piping materials. Both items comply with applicable regulatory standards and are therefore acceptable.
4.
Exit Interview The Region III inspectors met with licensee representatives (denoted under Paragraph 1) at the conclusion of the inspection on February 18, 1986. The inspector summarized the scope and findings of the inspection. The licensee acknowledged this information. The inspector diso discussed the likely informational content of the inspection report with regard to documents or processes reviewed during the inspection.
The licensee did not identify any such documents / processes as proprietary.
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