ML20234D911
| ML20234D911 | |
| Person / Time | |
|---|---|
| Site: | Beaver Valley |
| Issue date: | 09/15/1987 |
| From: | Sieber J DUQUESNE LIGHT CO. |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| 2NRC-7-200, IEB-87-001, IEB-87-1, NUDOCS 8709220230 | |
| Download: ML20234D911 (14) | |
Text
M:-
$YL "3$1p0C M
(412) 393 6000 j
one oxford centre 2NRC-7-200 301 Grant street -
September 15, 1987 Pittsbur@, PA 15279 i
l q
1 U.
S. Nuclear Regulatory Commission
, Attn:
Document Control Desk Washington, DC 20555
Reference:
Beaver Valley Power Station, Units No. l'and No. 2 BV-1-Docket No. 334, License No. DPR-66 BV-2 Docket No. 50-412, License No. NPF-73 IE Bulletin 87-01 Gentlemen:
We have reviewed IE Bulletin 87-01 " Thinning of Pipe Walls in Nuclear Power Plants".
Attached is the information requested by Items 1 thru 5 of the Bulletin.
If there are any questions concerning this response, please contact my office.
Very truly yours, j
1 6
. Sieber Vice President, Nuclear Attachment cc:
Mr.
P. Tam, Project Manager Mr. J. Beall, NRC Sr. Resident Inspector Mr. F.
I. Young, NRC Site Resident Inspector Mr. W. T. Russell, NRC Region I Administrator VEPCO 8709220230 870915 PDR ADOCK 05000334 I
G PDR~
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COMMONWEALTH OF PENNSYLVANIA)
)
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COUNTY OF BEAVER
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On this
/((I
' day of
/ M74a/L/
, 1987,
[44/4 /7/, Y/[1fMtv,:
Nota'ry Public'in and for_'said before me, a
q 4
Commonwealth and County, personally-appeared J. D. Sieber, who being J
duly sworn,. deposed, and said that (1) he is Vice President of-Duquesne
- Light, (2) he is duly authorized to execute and file the foregoing submittal on behalf of said Company, and (3).the statements
,'I set forth in the Submittal are true and correct to the best of-his knowledge, information and belief.
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DUQUESNE LIGHT COMPANY Beaver Valley Power Station, Units No. 1 and 2 Reply to IE Bulletin 87-01
" Thinning of Pipe Walls in Nuclear Power Plants" l
Letter dated July 9, 1987 I
i ITEM 1 Identify the codes or standards to which the piping was designed and j
fabricated.
j 1
1
Response
The construction code to which the piping systems were designed was ANSI B31.1.0 1967; the material codes were ASTM A-106 GRB & ASTM A-155 GR CMS-75 for the pipe and ASTM A234 WPA & WPB for the elbows.
ITEM 2 Describe the scope and extent of your programs for ensuring that pipe wall thicknesses are not reduced below the minimum allowable thickness.
Response
The scope of the Duquesne Light Company erosion / corrosion program for the Beaver Valley Power Station Units #1 and #2 consists of selected portions of single and two phase high energy systems.
This scope is further defined by the following. criteria:
- 1) Portions of single phase carbon steel piping systems which have an operating temperature of greater than or equal to 190*F and which have an operating pressure of greater than or equal to 275 psi gage; 2) Portions of two-phase carbon steel piping systems which have an operating temperature of greater than or equal to 190*F and which have a moisture content of greater than 5 percent; and 3) The failure of a portion of a
system contained in either of the above parts must directly or indirectly present a challenge to a safety system.
ITEM 2a Describe the criteria that you have established for selecting points at which to make thickness measurements.
Response
For single-phase piping systems the selection criteria includes system characteristics such as velocity and piping geometry,.and has relied heavily on industry failure experiences (i.e., steam generator J-Tube failures and the Surry condensate line rupture).
The EPRI computer program CHEC or a similar computer code, as well as industry failure experience is intended to be utilized in the formulation of selection criteria for future examinations.
. Reply to IE Eulletin 87-01 Page 2 Selection criteria for two-phase systems include system characteristics such as material composition, moisture
- content, velocity, and piping geometry which enables determination of those portions of application systems which will exhibit the greatest propensity for erosion / corrosion damage.
In. addition, the guidance and industry failure experience detailed in various NRC Information
- Notices, INPO Significant Event Reports and EPRI report NP-3944 were utilized in' the process for selection of locations to be examined.
Prior Beaver Valley Power Station operating and inspection experience were other considerations factored into the selection criteria.
ITEM 2b Describe the criteria that you have established for determining how' frequently to make thickness measurements.
Response
The EPRI Computer program CHEC or similar computer code and industry experience is intended to be utilized in determining the frequency of examination for single-phase systems.
EPRI report NP-3944 coupled with previous inspection data has been used as guidance in determining the frequency of inspections and=the need to re-inspect for two-phase systems.
ITEM 2c Describe the criteria that you have established for selecting the methods used to make thickness measurements.
Response
Duquesne Light Company has selected manual UT thickness measurement technique for obtaining data based upon its. versatility, portability, and economics.
Other NDE techniques may be evaluated for utilization on a
case by case basis as warranted by examination location design, configuration, and/or previous examination results.
ITEM 2d Describe the criteria that you have established for making replacement / repair decisions.
Reply to IE Bulletin 87-01 Page 3
Response
j Repair and/or replacement is initially assessed based upon the design condition minimum wall thickness required by the system design code.
Further assessment of a
degraded component may include other considerations and evaluation techniques such as those contained in EPRI Report No. SIR-87-010, Revision 2, titled, " Acceptance Guideline for Structural Evaluation of Erosion / Corrosion Thinning in Carbon Steel Piping".
ITEM 3 For liquid-phase
- systems, state specifically whether the following factors have been considered in establishing your criteria for selecting points at which to monitor piping thickness (Item 2a):
Response
For future single phase erosion / corrosion evaluations, Duquesne Light Company intends to use CHEC:
the EPRI computer program or similar computer code to rank components in order of susceptibility, predict the time to reach minimum required wall thickness, and to choose the most susceptible locations based on several criteria.
See responses to items 3a - 3f below for details on the criteria.
ITEM 3a l
Piping material
Response
Piping material is a factor in selecting points at which to monitor piping thickness and is inherent in the evaluation process of the i
CHEC computer program, and is supplied as an input thereto.
ITEM 3b Piping configuration
Response
Detailed piping isometrics will be used to evaluate piping configuration and its effect on susceptibility to erosion / corrosion.
Piping geometry is widely believed to be a major contributing factor to the occurrence of erosion / corrosion.
Piping geometry is an input to the CHEC computer program.
ITEM 3c pH of water in the system
___..__-._.._______w
1 R ply to IE Bulletin 87-01 Pago 4
Response
pH of the water is considered to be a factor in the determination of inspection
- points, is inherent in the design of the CHEC computer program, and is supplied as in input thereto.
ITEM 3d System temperature
Response
Temperature is used as part of the initial screening criteria to define the scope of the Duquesne Light Company erosion / corrosion program (i.e.,
temperature greater than or equal to 190*F) and, is also used as one of the criteria for selecting individual components for inspection.
System temperature is inherent in the evaluation process of the CHEC computer program and is an input thereto.
ITEM 3e Fluid bulk velocity l
l
Response
Macroscopic fluid velocity is a criteria for determining inspection points and is an input to the CHEC computer program.
ITEM 3f Oxygen content in the system
Response
l oxygen content is a factor in determining inspection points and is an l
input to the _ HEC computer program.
ITEM 4 i
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Chronologically list and summarize the results of all inspections that have been performed, which were specifically conducted for the i
purpose of identifying pipe wall thinning, whether or not pipe wall thinning was discovered, and any other inspections where pipe wall thinning was discovered even though that was not the purpose of the l
inspection.
i
' Reply to IE Bulletin 87-01 Page 5
Response
Attachment A provides a summary of'all-previous inspections of piping systems dealing with. the erosion / corrosion phenomenon for: Beaver Valley. Unit 1.
To date, only a wet steam piping baseline examination.
has been performed at Beaver. Valley Unit 2
which has recently
. received an operating license.
ITEM 4a Briefly ' describe the inspection program and' indicate whether it was specifically. intended to measure wall thickness or. whether wall thickness measurements were an incidental determination.
Response
The Beaver Valley inspection' program to date was formulated to investigate the. potential for 'and presence of erosion / corrosion degradation in single and two-phase piping systems.
The inspection
-portion of the program was designed specifically for wall thickness-determination.
For a
more detailed discussion of the erosion / corrosion program at Beaver'
- Valley, please refer to Attachment A which contains a summary of previous inspections.
ITEM 4b Describe what piping was examined and how..
Response
The portions of single-phase systems which were examined for erosion /corrosior damage were the steam generator ~ J-tubes in all three steam gc.
xtorc and portions of the condensate, heater drain, and feedwater systems.
The portions of two-phase systems which were examined were the
" wet steam" piping which consisted of extraction
- steam, MSR drains, and turbine cross-under piping.
See Attachment A for a
summary of the scope and extent of the piping examination and subsequent results.
_ ITEM 4c Report thickness measurement results and note 'those that were identified as unacceptable and why.
Response
See Attachment A for summary reports of thickness measurement results and the conclusions based on those measurements.
Reply to IE Bulletin 87-01 Page 6 ITEM 4d i
Describe actions already taken or planned for piping that has been found to have a nonconforming wall thickness.
If you have performed a
failure analysis, included the results of that analysis.
Indicate whether the actions involve repair or replacement, including any change of material.
Response
All examinations to date except for one location on the heater drain system have' not identified degradation beyond design condition minimum wall thickness.
Further investigation of the heater drain location for potential degradation beyond design condition minimum wall thickness is being pursued.
While evaluation based upon operating conditions indicates adequate I maining wall thickness, this plant area has been roped off to control personnel access, j
1 ITEM 5 Describe any plans either for-revising the present or for developing new or additional programs for monitoring pipe wall thickness.
Response
Duquesne Light Company is currently developing a detailed engineering standard that will formalize the Beaver Valley Unit
- 1 and #2 erosion / corrosion monitoring program.
It is intended to utilize the l
EPRI computer program CHEC or similar computer code for future single l
phase erosion / corrosion evaluation.
Past and newly evolving industry failure experience as well as the recommendations of the NUMARC Technical Subcommittee Working Group on Piping Erosion / Corrosion will be considerations in the development of the engineering standard.
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l ATTACHMENT A
Summary of Previous Erosion / Corrosion Inspections at Beaver Valley Unit 1 and 2 i
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Beaver Valley Unit 1 Steam Generator J Tube Examinations During the Beaver Valley Unit 1 third refueling outage (3R) in
- 1983, an inspection of Steam Generator (S/G) J tubes was performed to i
detect wall thinning.
The inspection entailed ultrasonic wall thickness measurements of all accessible J tubes in the "A" and "B"
The ultrasonic wall thickness measurements were performed at eight (8) cross-sections along each J tube with three (3) measurements on each cross section.
The results of the sample J tube inspection indicate that a large percentage of the thinning found in the J tubes can be attributed to the bending process employed at the time of J tube manufacture.
This conclusion was validated by the manufacture of five (5) sample J tubes to the original design specification by the original manufacturer.
The inspection of these samples indicated an average reduction of 0.037 inches in J tube wall thic < ness due to the bending process.
Using the sample J
tube data for establishment of new outside radius nominal wall thickness, the worst case degradation found during the inspection was 22.6%.
A re-inspection of J tubes during the fourth refueling outage was recommended as follow-up action.
During the Beaver Valley Unit 1 fourth refueling outage (4R) in 1984 an inspection of S/G J tubes was performed to detect additional wall thinning.
The inspection entailed ultrasonic wall thickness measurements of all accessible J
tubes in all three S/Gs.
The ultrasonic wall thickness measurements were performed at eight (8) l cross sections along each J tube with three (3) measurements on each cross section.
l The worst percentage decrease of average outside radius thickness j
was 15.2%.
Many of the decreases were below 5% when compared to 3R i
data.
While comparison of 4R and 3R "A" S/G data indicates a small degree of further wall thinning, the percentage increase in thinning was not considered significant enough to prevent continued operation.
No degradation was evident on the feedrings at the J tube penetration or effluent impingement areas.
A re-inspection of J tubes during the fifth refueling outage was recommended as follow-up I
action.
l The Beaver Valley Unit #1 J-tubes in all three steam generators (S/Gs) were ultrasonically examined during the fifth refueling outage (5R) in 1986 for determination of wall thickness.
This examination was the third iteration of the inspections for the "A" and "B" S/Gs which commenced during the third refueling outage (3R).
The "C" S/G J-tubes were examined during the fourth refueling outage (4R) in addition to the latest effort thus providing comparative data for all S/Gs.
The SR examination closely paralleled previous inspection methodology.
The wall thickness measurements were performed at eight (8) cross sections along each accessible J-tube with three measurements on each cross section being recorded.
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l This examination differed from those performed previously in regards to the ultrasonic equipment.
In the past, digital thickness instruments were utilized that provided a three-digit reading.
The SR examination utilized oscilloscope presentation equipment which required interpolation of the third significant figure.
Comparison of data for the "A"
S/G reveals a gradual loss of average wall thickness since the initial examination in 1983.
The outside radius thickness shows less consistency in its
- trend, however, at many "A"
S/G J-tube locations this parameter closely follows the average thickness decline.
The greatest wall loss of any J-tube has occurred at location A-15 which has exhibited a.088 inch
{
(40.37%)
worst point loss from the originally specified nominal wall of
.218 inches.
The average thickness at location A-15 was j
calculated at
.150 inches, a reduction of.034 inches (18.52%) from j
the average wall thickness calculated from the 4R inspection data.
j The average thickness of the outside radius of A-15 decreased.013
)
inches to a
value of.144 inches.
This represents an 8.27% decline during the fifth fuel cycle.
Eleven (11) other J-tube locations in the "A"
S/G showed significant
(>10%)
loss of wall thickness as compared to 4R results.
j The "B"
and "C" S/G data does not display the consistency as the "A"
S/G.
The "B" S/G data remains difficult to correlate due to the a
i possible misnumbering of J-tube locations during one of the first two examinations.
Nonetheless, the average J-tube wall thickness in the "B"
S/G is substantially greater than that in the "A".
The same condition is true for the "C" S/G.
The declining trend established
)
in the "A" S/G is not apparent in the "B" S/G and not as encompassing l
I in the "C" S/G.
A limited ultrasonic examination of selected J-tubes and a visual examination of all J-tubes in the "A" S/G was recommended for the sixth refueling outage currently scheduled to begin in December, 1987 as a
short term action.
Since the trend for J-tube wall thickness, at least in the "A" S/G is downward, long term remedial action of the systematic replacement of J-tubes commencing at the seventh refueling outage has been recommended.
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Beaver Valley Unit 1 Wet Steam Piping Examinations During the Beaver Valley Unit 1 third refueling outage (3R) in
- 1983, an inspection of selected areas on extraction steam lines and l
Moisture Separator Reheaters (MSR) drain lines was conducted to i
detect possible erosion / corrosion. degradation of wall thickness.
j Degradation of Wall thickness had been reported at other plants in NRC Information Notice 82-22 and INPO Significant Operating j
Experience Report 82-11.
A total of eighteen (18) fittings on the extraction steam lines and MSR drain lines were inspected with ultrasonic thickness measurements.
The measurements were taken along the outer radius of the fittings with grid spacing of one (1) inch for 12" and smaller piping and two (2) inches for 18" and larger piping.
A pass / fail criteria for thickness measurements of 0.875 of nominal was used, I
which was based on ANSI B16.9 criteria for fitting manufacturers.
The results of the inspection, revealed five (5) fittings suffering possible erosion / corrosion _ degradation.
Only one (1) of these fittings (MSR drain fitting) was below the 0.875 nominal criteria used.
Four (4) of the fittings'were MSR drain line elbows and the other fitting was an elbow on the extraction steam line downstream of a
valve.
The extraction. steam fitting exhibited the largest wall loss of 0.162 inches from nominal, however, this fitting was well above minimum wall thickness required since an extra strong weight fitting was installed where only standard weight was required.
All of the above fittings were substantially above the minimum thickness required for design temperature and pressure conditions as calculated by ANSI B31.1 methods.
A re-inspection of fittings during the fourth refueling outage was recommended as follow-up action.
During Beaver Valley Unit 1 fourth refueling outage (4R) in 1984, the fittings found with erosion / corrosion degradation during 3R were re-examined.
The re-examination of all five of these fittings indicated minimal further degradation for the four (4) MSR drain line fittings while the extraction steam line fitting exhibited additional wall loss as high as 0.082".
Since this fitting is located immediately downstream of a valve, turbulent flow conditions may be enhancing erosion / corrosion.
The remaining wall thickness of this l
fitting was more than adequate for continued safe operation since an j
extra strong schedule fitting was originally installed.
Eleven (11) additional fittings were subjected to an initial examination during 4R.
Three (3) of these fittings were found with 1
thickness below the manufacturer's minimum wall thickness (0.875 x nominal wall).
These fittings were evaluated to the guidelines of EPRI-NP-3944
" Erosion / Corrosion in Nuclear Plant Steam Piping: Causes and Inspection Program Guidelines" and found safe for continued l
operation.
Re-inspection and possible replacement was recommended j
for the fittings exhibiting significant erosion / corrosion rates i
during the fifth refueling outage as follow-up action.
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S The examination conducted during the fifth refueling outage (SR) consisted of a
re-examination of four fittings previously examined during the fourth refueling outage (4R).
These fittings were located i
in the extraction steam and MSR drain systems.
One 12" fitting in the first point extraction steam system exhibited further degradation of
.018" during the fifth operating cycle but remains substantially i
above the design minimum wall thickness.
The other locations l
examined did not reveal significant increased degradation.
One (1)
I MSR drain fitting which exhibited erosion / corrosion degradation in previous examinations was replaced with a
chrome alloy fitting l
without further examination in SR.
Re-inspection of the other fittings was recommended as follow-up action.
Beaver Valley Unit 2 Wet Steam Piping Examinations i
A wet steam piping baseline examination was performed at Beaver l
Valley Unit 2
prior to initial startup.
Twenty six (26) fittings l
were examined ultrasonically on the downstream 2/3 of the elbows, I
with respect to circumference and length.
The baseline provides results for comparison to future inservice examinations.
Beaver Valley Unit 1 Condensate Examinations l
Shortly after the surry piping failure
- event, an at power examination of the Beaver Valley Unit 1 condensate suction line was conducted on eight (8) fittings.
These fittings were selected on the basis of adverse geometry (i.e.,
conductive to the possible l
establishment of high localized fluid velocities and/or turbulence).
l The measurement was taken on a typical grid pattern on a "best effort l
basis" due to piping temperature conditions.
l The results of the examinations conducted did not reveal any l
indication of appreciable erosion / corrosion degradation.
In no case l
was the measured wall thickness less than the calculated permissible minimum wall thickness per ANSI B31.1.
In order to more accurately assess the condition of the condensate suction
- piping, a
more i
extensive and comprehensive examination was recommended for the next l
outage of sufficient duration.
During an outage in May, 1987 ultrasonic thickness measurements were taken on forty one (41) fittings of the Beaver Valley Unit 1 secondary systems.
These fittings were located in the condensate, l
feedwater, and heater drain systems.
In addition, four locations in the extraction steam system which were previously examined were re-examined during this midcycle outage.
A total of 25,196 measurements were recorded in the course of this examination.
There was no obvious evidence of erosion / corrosion degradation on any of the fittings in the condensate and feedwater
, systems.
One 12 x
16 reducer in the heater drain piping revealed significant wall loss.
This plant area was " roped off" to limit personnel access until permanent corrective measures can be implemented.
The extraction steam fittings that were re-examined did not reveal any significant increase in wall loss degradation.
The data from this examination is being further analyzed in order to plan future examinations.
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