ML20150C907

Safety Evaluation Re Employee Concern Element Rept EN 232.8, Criteria for Min Pipe Wall Thickness

ML20150C907
Person / Time
Site:	Sequoyah
Issue date:	03/11/1988
From:	NRC OFFICE OF SPECIAL PROJECTS
To:
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References
NUDOCS 8803220411
Download: ML20150C907 (2)

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UNITED STATES NUCLEAR REGULATORY COMMISSION g

g WASHINGTON, D. C. 2C555

,e SAFETYEVALUATIONBYTHEOFFICEOFSPECIALP!0JECTS FCR EMPLOYEE CONCERNS ELEMENT REPORT EN 232.8.,

"CRITERIA FOR MINIMUM PIPE WALL THICKNESS"

' TENNESSEE VALLEY AUTHORITY SEQUOYAH NUCLEAR POWE'R PLANT, UNITS 1 AND 2 DOCKET HOS. 50-327 AND 50-328 I.

SUBJECT Category:

Engineering-Subcategory:

Piping and Valve Design Element:

Criteria for Mininum-Pipe Wall Thickness Concern:

IN-85-545-X06:

"12-1/2% was the criteria established by Engineer Design for minimum wall thickness since 1978.

One Engineer was found to be using the less stringent formula contained in Code Section NB.

The above applies-to QA Class 2, and some Class 1, stainless steel pipe in Units 1 and 2.

II. JUMMARY OF ISSUE (as stated by TVA)

The ASME Section III code formula for calculating required minimum wall thickness of stainless steel Class 1 and 2 pipbg may be less cons'ervative than the 12-1/2 percent critarion established for WBN Units I and 2 in 1978.

III. EVALUATION 4

The employee concern as expressed in the X Form is confusing.

The 12-1/2%

minimum wall thickness is a manufacturing tolerance and not a criterion or specification for the design of pipe minimum wall thickness.

The formulas contained in the ASME Code, Section NB for Class 1, Section NC for Class 2, and ASME B31.1, paragraph 104.1 are for calculating the minimum pipe wall thickness required for containinq a fluid at a given temperature, pressure, material, diameter.

After these calculations are performed, the code defines bcw piping is to be specified to assure that the minimum design wall thickress is present b tolerances. y consideration of pipe manufacturing pipe wall thickness The concern does nnt express how the ASME Code formulas were misapplied.

That an engineer had used the ASME code formulas to compute pipe wall thickness is the regulatory requirement.

The use of the 12-1/2% wall thickness manufacturing tolerance is a subordirate and supplemental requirement compared to the pressure design calculations in determining the code recuired pipe wall thickness.

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, i The evaluation by TVA's Employee Concern Task Group as presented in Elerrent Report 232.2(B) consisted of a review of TVA's Division of Engineering design criteria established for the Sequoyah site, comparison with the ASME Boiler and Pressure Vessel Code (BAPV) for minimum pipe wal.1 thickness calculation requirements, review of the FSAR sections pertaining to piping classifications and design, and review of draft Sequoyah site carbon steel piping wa}l thick-ness calculations to verify, confornance with the code.

The TVA reviewer confirmed, for itens procured after April 2,1973 at the Sequoyah site, the ASME B&VP Code had been used; and prior to this date, the ASME Power Piping Code, B31.1 was used.

TVA's internal documents for piping design at the Sequoyah site (Sequoyah Plant Design Criteria SQN-DC-V-3.0, "General Design Criteria for the Classification of Piping, Pumps, Valves and Vessels") were reviewed and were found to neet the applicable code requirements for deter-mining minimum wall thickness, including addressing the wall thickness j

manufacturing tolerances.

TVA has confirned to the staff by copy of a letter from Bechtel Western Power Compny to TVA, dated January 29, 1988, that in addition to the carbon steel pipinq calculations that were reviewed and documented in the Element Report i

232.8(B), stainless steel pipe wall thickness calculations were reviewed for

)

proper calculation of wall thicknesses.

The concern also mentinns a time frame of 197S, well after the design of Class 1 and 2 piping systems were completed and construction of these systems was also completed at the Sequoyah site.

We believe that this concern has little probability of beir.g applicable to the Seoucyah site, and the limited review of stainless stael Class 1 and 2 piping systens demerstrates stainless steel piping systens have correct minimum wall thickress calculations.

The staff believes that the investigations described abnve are sufficient to confirm that this concern does not appear applicable to the Sequoyah site.

IV.

CONCLUSIONS We concur with TVA's conclusion that this concern is not valid for safety class pipirg systems installed at the Sequoyah site.

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