United States Nuclear Regulatory Commission - Protecting People and the Environment

IE Circular No. 81-05, Self-Aligning Rod End Bushings for Pipe Supports


                                                           SSINS No: 6830  
                                                           Accession No.:  
                                                           8011040282      
                                                           IEC 81-05       

                               UNITED STATES 
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF INSPECTION AND ENFORCEMENT 
                           WASHINGTON, D.C. 20555 
                                     
                               March 31, 1981 

IE Circular No. 81-05: SELF-ALIGNING ROD END BUSHINGS FOR PIPE SUPPORTS 

Background: 

By letter dated July 24, 1980, Bechtel Power Corporation notified NRC of 
generic deficiencies in pipe support sway struts furnished by Corner & Lada,
Inc., to the Callaway and Wolf Creek sites. The specific deficiencies 
identified involved the clamp end of the sway strut becoming loose and 
possibly being disengaged from the bushing. This could result in a large gap
in the support system not accounted for in the original analysis. This 
deficiency was reported to NRC pursuant to 10 CFR Part 21 on May 14, 1980. 

In another letter dated October 8, 1980, Bechtel Power Corporation notified 
NRC of generic deficiencies in pipe support end bushings at Midland Units 1 
and 2 and at Palisades. In this report, self-aligning rod end bushings on 
the ends of sway struts and snubbers furnished by ITT Grinnell, Pacific 
Scientific, NPSI, and Corner & Lada were found to be partially or totally 
disengaged from the structural component. This report was identified as a 10
CFR Part 21 notification. 

Discussion: 

The problem of loose bushings in snubber and sway strut assemblies is 
potentially generic to all sizes of all manufacturers' assembles. However, 
the potential for complete disengagement of the bushing from the assembly is
limited to those cases in which the assembly is attached to a clamp where 
the gap is sufficiently large to permit the paddle to slide completely over 
the bushing. 

The consequences of complete disengagement of the bushing would be to 
invalidate the original analytical assumptions used in the piping analysis, 
potentially creating an overstress condition in the piping or overloading 
the supports. This would be more significant for the seismic event since the 
gap would change the dynamic characteristics of the system and lead to 
impact loads that could damage the piping or supports. 

The corrective actions taken by licensees have been to replace the defective
struts or to "stake" the loose bushing in place. However, some of the staked
bushings subsequently became loose and had to be reworked. Another potential
corrective action would be to shim the clamps where the potential for 
complete disengagement of the assembly from the bushing is possible. This 
method would prevent total disengagement even if the bushing became loose. 
If shims are used, consideration should be given to preventing any 
interference with required rotation of the assembly. 
.

                                                          IEC 81-05       
                                                          March 31, 1981  
                                                          Page 2 of 2     

Recommended Actions for Holders of Operating Licenses or Construction 
Permits: 

1.   Determine whether your facility uses pipe strut or snubber assemblies 
     using bushings that could potentially become loose. 

2.   Identify from design drawings or field inspections those supports using
     the strut or snubber assemblies identified in item 1 above where 
     sufficient gap exists in the clamp attachment for complete 
     disengagement of the bushing and the assembly. 

3.   Inspect where practical the snubber or strut assemblies identified in 
     item 2 above to determine if any bushings are loose or disengaged. If 
     a large number of supports are involved in this inspection, a 
     statistical sampling may be appropriate to determine if your facility 
     has a problem with loose or disengaged bushings. 

4.   If loose or disengaged bushings are found at your facility, take 
     appropriate corrective actions to ensure that complete disengagement of
     the assembly from the bushing cannot occur. 

No written response to this circular is required. If you need additional 
information with regard to this subject, please contact the Director of the 
appropriate NRC Regional Office. 

Attachments: 
1. Sway Strut Assembly: Figure 211 
2. Recently issued IE Circulars  

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