United States Nuclear Regulatory Commission - Protecting People and the Environment

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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