ML19291C130

Deficiency Rept:On 780404,design Change Issued Permitting Wall Thickness Variations W/Potential for Localized Pipe Stresses.Piping Found in Violation of Original Requirements. Design Changes Rescinded

ML19291C130
Person / Time
Site:	Comanche Peak
Issue date:	01/14/1980
From:	TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC)
To:
Shared Package
ML19291C129	List: ML19291C128 ML19291C130
References
TXX-3088, NUDOCS 8001220435
Download: ML19291C130 (2)

Text

S TXX-3088 ATTACHMENT January 14, 1980 Page 1 VIOLATION OF PIPING MINIMUM WALL THICKNESS Description of Deficiency On April 4,1978, a design change was issued defining permissible variations from the specified minimum wall thickness requirements for ASME Section III, Code Class piping fabricated on site. Subsequently, similar design changes were made to the shop fabrication and piping erection specifications. The criteria established for the above design changes were based on minimum wall calculations considering temperature and pressure only.

In the process of performing stress analysis on piping systems, Engineering identified that the permissible variations in wall thickness could result in overstress conditions in the piping. Without the specific location and magnitude of the variation, the impact could not be assessed. As a result, the design changes were rescinded on May 16, 1979, and all piping which violated the originally specified minimum wall thickness was required to be documented. In September 1979, additional changes were made requiring all future welds below the specified minimun be repaired or evaluated for acceptability.

Action was taken to review the impact of thin wall piping. It was established that 1010 welds had mechanical measurements documenting the wall thickness.

These measurements were forwarded to Engineering for review. The remainder of the welds had no documentation. A program was established with Southwest Research to ultrasonically measure these welds for Engineering review. As of December 13, 1979, a total of 3778 welds were identified as requiring ultrasonic testing and subsequently examined. Further investigation is now underway to review documentation of base metal repairs to determine if addi-tional wall thickness violations exist and require review.

Safety Implications Had this situar'an gone unde"_cted or unresolved it is conceivable that localized pi p stresses wou. have affected the postulated pipe break locations and potentially could have rc :ulted in a pipe rupture.

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e TXX-3088 ATTACHMENT January 14, 1980 Page 2 Corrective Action The following action has been taken:

1. The design change documents defining permissible variations from specified minimum wall thickness requirements have been rescinded.

Additional changes have been implemented requiring that future welds violating the specified minimum wall thickness be repaired.

2. All welds made during the period that variations from minimum wall thickness were allowed, have been ultrasonically or mechanically measured to determine actual wall thickness.

3. Welds violating minimum wall requirements made prior to the imple-mentation of the above changes were documented on nonconformance reports which were subsequently dispositioned and accepted "as is" on the authority of the original design change. These nonconformance reports have been reopened and are under evaluation.

4. Base metal repair documentation is under review to determine areas of piping which violated the specified minimum wall.

5. Welds identified in 2, 3, and 4, as being below the specified minimum wall requirements will be reviewed by Engineering. Repairs or replace-ments will be made as determined by the Engineering review.

6. The above activities will be accomplished by Hot Functional Testing.

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