ML18153B583

Forwards Summary of Recent Insp of Secondary Pipe Thinning, Per Commitments Made at 881026 Meeting

ML18153B583
Person / Time
Site:	Surry
Issue date:	01/19/1989
From:	Cartwright W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
88-689C, NUDOCS 8901260218
Download: ML18153B583 (9)

Text

e VIBGJNIA ELECTRIC AND PowEB CoMPANT RICH]!;IOND, VJBGINJA 23261 W. R. CAKTWJ!lIODT VICJI P*J16IDJ1l'IT January 19, 1989 NUOLJIA.

United States Nuclear Regulatory Commission Serial No. 88-689C Attention: Document Control Desk NO/DAS:vlh Washington, D. C. 20555 Docket Nos. 50-280 50-281 License Nos. DPR-32 DPR-37 Gent 1emen: -

VIRGINIA ELECTRIC AND POWER COMPANY SURRY POWER STATION UNITS 1 AND 2 CONFIRMATION OF ACTION LETTER SECONDARY PIPE THINNING

SUMMARY

'OF RECENT INSPECTIONS Our letter (Serial No.88-689) of October 19,

• 1988~ in conjunction with commitments made during a meeting on October 26, 1988, identified- several items which required investigation and appropriate corrective action prior to plant restart. One of those items was to complete NOE inspections of secondary piping consistent with our existing program. This letter forwards for your information a summary of those inspections.

Should you have any questions concerning this investigation summary, please do not hesitate to contact us.

Very truly yours,

'.~Jswe_

J,,..~ R. Cartwright Attachment Secondary Pipe Inspection Program -

Summary of Recent Inspections 890~260218 890119 PDR ADOCK 05000280 P PDC E?~ o 1d- 66 ~, a

cc: U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, N. W.

Suite 2900 Atlanta~ Georgia 30323 Mr: W. E. Holland NRC Senior Resident Inspector Surry Power Station Mr. B. C. Buckley NRC Surry Project Manager Project Directorate II-2 Division of Reactor Projects - I/II

SURRY FCl'ER STATICE UNITS 1 AND 2 ffiloKZ\RY OF REX:ENT INSPEX:1.'ICR; UNIT 1 1988 FORCED oumGE UNIT 2 1988 REFUELING CXJ'.mGE JANUARY 19, 1989 hl34-MWH-193-l

January 19, 1989 1.0 INTRODUcrION The feed.water pump suction pipe rupture at the Surry Power Station, Unit 2 ~on December 9, 1986, was. detennined to have been caused by flow-assisted corrosion canmonly referred to as single phase erosion/corrosion (E/C). Subsequently, we began an investigation into E/C and its effects on secondary piping systems. From this investigation, a Secondary Pipe Inspection Program has been developed that inspects piping canponents which are considered to be susceptible to E/C wear in both single and two phase piping systems.

The purpose of this report is to provide results of the ongoing secondary piping system inspection program conducted at the Surry Power Station during the Unit 2 1988 Refueling Outage and the Unit 1 1988 Forced Outage.

2.0 PRE-OUTAGE INSPEcrION PLAN The Unit 2 inspection plan was developed prior .to the refueling outage and 156 piping components were selected to be inspected based on the following:

a. Previous outage inspections indicated that the ccrnponent should be inspected

b. To obtain actual wear rates or obtain baseline infonna~ion. for individual canponents

c. The canponents were classified as a priority point either by previous Surry or North Anna inspections or by computer analysis using "CHEC".

3.0 IMPLEMENTATION OF INSPECTION PROGRAM 3.1 Canponent Evaluations The detennination of E/C pipe component degradation is made by measuring the current wall thickness U:sing ultrasonic testing (UT).

methods. Each piping canponent is inspected by a*zone layout which is specifically designed for the cc:rnponent based on its size, type, orientation, and whether it is subject to single or two phase flow.

Within each zone, there. is a grid pattern (i.e., 1-inch x 1-inch pattern with alternating rows being offset) which locates each UT inspection point. The number of UT inspection points for each component can range from approximately 180 to over 1,000 points depending on canponent size and type. After a piping component has been inspected by UT methods, the data is evaluated by Engineering.

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For canponents which have been previously inspected and baseline UT data is available. which can be correlated to the current data, an estimated wear rate .is calculated for the time period between inspections. If a canponent is being inspected for the first time or data cannot be accurately correlated, an evaluation of the current data is performed to determine an estimated wear rate. Once the canponent wear rate is determined, the project¢ canponent life is calculated based on allowable minimum wall thickness. The piping canponents are then categorized into the follCMing four groups for further action bas~ on remaining canponent life: irrrnediate replacement, potential next outage replacement, inspect next outage, and future inspection. Refer to T~les I and II for specific criteria.

3.2 Expansion of Pre-Outage Inspection Plan As previously noted, the Unit 2 Inspection Plan selected 156 piping components for inspection. During the inspection, the inspection scope was expanded due to the identification of unexpected high pipe wear rates and associated unexpected canponent replacements. The inspection scope was expanded by inspecting additional -piping components upstream and downstream of the canponents experiencing unexpected high wear. Piping canponents of similar configuration on the same system were also added to this expanded scope. This information was also factored into the expanded inspection program for the other unit.

Higher than expected wear rates were encountered on canponents which were replaced during the 1986/1987 forced outage. This finding resulted in an expansion of the Unit.2 inspection prograITI to include all canponents replaced during .the 1986/1987 forced outage.

Likewise in Unit 1, previously replaced canponents on that unit which had not been inspected during the earlier 1988 refueling outage were also added to the inspection scope. Because of the above, the inspection program was expanded fran an initial 156 components to 368 canponents for Unit 2 and an additional 103 canponents for Unit 1 ..

4.0 PIPING COMPONENT INSPECTION AND REPLACEMENT

SUMMARY

Canponent inspection and replacement results are tabularized belCM:

Unit 2 Unit 1 Unit 1 1988 R.O. 1988 F.O. 1988 R.O.

OOMPONENTS EVALUA'IED 368 103 285

'IDTAL REPLACEMENTS 100* 42** 27

• 31 Components are being replaced due to construction convenience; 81 Replaced canponents are located in single-phase piping systems and 19 replaced canponents are located in two-phase piping systems.

• • 12 Canponents are being replaced due to construction convenience; All replaced canponents are located in single-phase piping systems.

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e 5.0 OUTAGE INSPECI'ION OBSERVATIONS 5.1 Engineering Canponent Evaluations Several observations were made by Engineering during the evaluations of the.inspected pipe canponents. They are as follCMs:-

a. For original piping canponents, the measured wear was a "local" area phenanenon.

b. For replaced piping canponents, the measured wear was a "general" area phenanenon due to a lack of a protective oxide layer on the interior of the canponent.

c. The measured wear, in sane canponents, was as much as 2 to 3 times the projected wear which was based on previous inspection data.

5.2 Metallurgical Examination Due to the higher than anticipated E/C wear rates, a detailed metallurgical examination (i.e., surface morphology, micro-structure, chemistry, hardness, etc.) was. initiated. Preliminary results of the metallurgical examination of the pump suction elbCMs is as follows:

a. The elbCMs have been subjected to single phase E/C wear.

b. The elbows had been blast cleaned prior to installation in order to insure maximum levels of cleanliness. Materials Engineering examined the surface profile* of piping which had been blast cleaned. It has been determined that the surface profile (i.e.,

depth and contour) is similar to the "dimpled appearance" of the carbon steel piping which has active E/C. From this examination, it has been concluded that blast cleaning removes the protective oxide layer and also creates a surface profile which can irmnediately enhance the piping canponent's sensitivity to E/C. Therefore, blast cleaning is now prohibited for cleaning the interior portions of secondary piping canponents.

The only piping canponents which received a blast cleaning and were installed this outage are those canponents used for extraction steam piping. These canponents will be monitored in the future per the inspection program to determine wear rate and effective life.

c. The elbows were found to have an extremely low trace chrane content, in the range of 0.006 to 0.007 weight percent chrcme.

The carbon steel material specification for these elbows (i.e.,

A234 WPB) does not specify a weight percent chrane content.

a. The pipe flanges welded to the E/C thinned pump suction elbows showed no wear due to E/C. This has been attributed to the higher trace chrome content in the flange material (i.e., 0.14 to 0.22 weight percent chrome).

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e 5.3 Plant Chemistry Since the 1986/1981 forced outage, the Surry units have operated at pH levels between 8.8 and 9.1 and Oxygen levels between 1 to 4 ppb.

Research has shown that E/C is significantly curtailed when the pH can be raised above 9.4 and oxygen levels maintained above 10 ppb.

However, Westinghouse's Guide for Secondary Water Chemistry and EPRI's Secondary Side Water Chemistry Guidelines specifies less than or equal to 5 ppb of dissolved oxygen in order to mitigate steam generator tube denting. Likewise, at this time, the pH level is restricted to an upper limit of 9.2 because of a concern with the transport of copper corrosion products to

• the steam generators.

There is an ongoing study which is evaluating how to raise the pH level in the secondary water chemistry.

6.0 CCMPONENT REPLACEMENT Based on the metallurgical examinations, current industry research, and the limitations associated with raising the pH levels at this time, replacement of secondary piping will be with 2!% chranium - 1%

molybdenum material (P22) wherever practical. The 1!% .chranium - ;%

molybdenum material (Pll) will be used when P22 is not available. Carbon steel is being utilized only for a wear test case on the feedwater pump suction side and in areas where the canponents had already been installed prior to the decision to use P22 material.

7.0 CONCLUSION

S Our conclusions from the current inspection data are as follows:

(a) *unexpected high wear of previously replaced pipe canponents was due to:

blast cleaning of interior pipe surfaces which removes the protective oxide layer and creates a surface profile sensitive to E/C.

the extremely low trace chrane content of the replacement pipe material which we now believe caused the material to be more sensitive to E/C.

uncertainty in determining when the "accelerated" E/C process actually began .. Current methodology had not accounted for plant chemistry changes since the beginning of unit operation.

(b) For canponent replacement, 2!% chranium - 1% molybdenum material will be used wherever practical.

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e e TABLE I PIPING COMPONENT CATEGORIZATION NON-SAFETY RELATED COMPONENTS ACCEPTANCE CATEGORY CRITERIA REMARKS A. Imnediate Replacement .. L < 1.65 years 1.65 years represents the time to the next outage plus 10%

B. Potential .Next outage 1.65 ~ L < 3.3 years 3.3 y~ars represents two fuel cycles Replacement of plus 10%. Canponent Canponent will be inspected at the next outage to verify the wear rate in order to confirm the need for future replacement.

• C. Inspect Next Outage 3.3 ~ L < 4.95 years 4.95 years represents three fuel cycles plus 10%. Component will be inspected at the next outage to verify the wear rate. Future inspection will be based on this second evaluation.

D. Future Inspection L ~ 4.95 years Future inspection intervals for ccmponent will be established based on Engineering evaluation.

L = projected time until code minimum wall.

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e* e

• TABLE II PIPING COMPONENT CATEGORIZATION SAFETY-RELATED COMPONENTS ACCEPTANCE CATEGORY CRITERIA REMARKS A. Irrmediate Replacement LC::: 2.2 years 2.2 years represents the time to the next outage plus 47% '

B~ Potential Next outage 2 . 2 :S L < 4

• 4 years 4.4 years represents two Replacement of fuel cycles plus 47%.

Canponent Canponent will be inspected at the next outage to verify the wear rate in order to confinn the need for future replace-ment.

c. Inspect Next outage 4.4 ~ L < 6.6 years 6.6 years represents three fuel cycles plus 47%. Component will be inspected at the next outage to verify.the wear rate. Future inspections will be based on this second evaluation.

D. Future Inspection L '> 6 . 6 years Future inspection intervals for canponent will be established based on Engineering evaluation.

L = projected time until code minimum wall h134-MWH-193-7