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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