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Information Notice No.79-36 - Computer Code Defect in Stress Analysis of Piping Elbow
UNITED STATES SSINS No.: 6870 NUCLEAR REGULATORY COMMISSION Accession No: OFFICE OF INSPECTION AND ENFORCEMENT 7910250519 WASHINGTON, D.C. 20555 December 31, 1979 Information Notice No. 79-36 COMPUTER CODE DEFECT IN STRESS ANALYSIS OF PIPING ELBOW Description of Circumstances: The NRC was informed on December 17, 1979 that a computer code, NUPIPE, used in the stress analysis of piping systems contained a defect which could result in incorrect stress values at one end of piping elbows. This defect was identified from discussions with a user of NUPIPE and the NUPIPE code developers. The stress calculation error can occur when a flexible joint is modeled at the end of an elbow (ELBOW-ELASTOJT connection in NUPIPE terminology). This defect in the NUPIPE code is in the transformation of the loads in the ELASTOJT coordinate axis to the piping ELBOW coordinate axis. The incorrect coordinate axis transformation may incorrectly interchange the torsion and bending moment loads on the piping elbow. This can result in the incorrect assignment of the stress intensification factor for the individual moments. The correct stress may be higher or lower than calculated by NUPIPE, depending on the loading condition. Four conditions must exist for the possibility of the calculation of an incorrect stress in the NUPIPE code: 1. an USAS B31.1.0 - 1967 Code analysis is being done, and 2. an ELBOW-ELASTOJT connection exists, and 3. an absolute sum of two load cases is being calculated, and 4. the ELBOW torsional moment axis does not align with the ELASTOJT local x-axis. Possible users of the NUPIPE code include the code developer, Stone and Webster, EG&G (Idaho Falls), and those using the Cybernet system. The NRC is currently reviewing the extent of usage of the NUPIPE code and the generic implications for other facilities. There is a potential for a similar defect to occur in other piping analysis computer codes. This Information Notice is provided as early notification of a possible significant matter. It is expected that recipients will review the information for possible applicability to their facilities. No specific action is requested in response to this Information Notice. If NRC evaluations so indicate, further licensee actions may be requested or required. If you have any questions regarding this matter, please contact the Director of the appropriate NRC Regional Office. No written response to this Information Notice No. is required.
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