Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
June 21, 1979
IE Bulletin No. 79-02
(Revision No. 1)
PIPE SUPPORT BASE PLATE DESIGNS USING CONCRETE EXPANSION ANCHOR BOLTS
Description of Circumstances:
Since the issuance of IE Bulletin 79-02 on March 8, 1979, IE inspection
experience and many inquiries from licensees indicate that additional
information and clarification is needed. This revision is intended to serve
that purpose. None of the requirements of the original Bulletin have been
deleted, and the due date for completion of the requested actions (July 6,
1979) has not been changed. The following text supersedes the text of
Bulletin 79-02. Changes from the original text are identified by lines in
the margin. The purpose of this revision is to identify acceptable ways of
satisfying the Bulletin requirements.
While performing inservice inspections during a March-April 1978 refueling
outage at Millstone Unit 1, structural failures of piping supports for
safety equipment were observed by the licensee. Subsequent licensee
inspections of undamaged supports showed a large percentage of the concrete
anchor bolts were not tightened properly.
Deficiency reports, in accordance with 10 CFR 50.55(e), filed by Long Island
Lighting Company on Shoreham Unit 1, indicate that design of base plates
using rigid plate assumptions has resulted in underestimation of loads on
some anchor bolts. Initial investigation indicated that nearly fifty percent
of the base plates could not be assumed to behave as rigid plates. In
addition, licensee inspection of anchor bolt installations at Shoreham has
shown over fifty percent of the bolt installations to be deficient.
Vendor Inspection Audits by NRC at Architect Engineering firms have shown a
wide range of design practices and installation procedures which have been
employed for the use of concrete expansion anchors. The current trends in
the industry are toward more rigorous controls and verification of the
installation of the bolts.
The data available on dynamic testing of the concrete expansion anchors show
fatigue failures can occur at loads substantially below the bolt static
capacities due to material imperfections or notch type stress risers. The
data also show low cycle dynamic failures at loads below the bolt static
capacities due to joint slippage.
* Lines indicate changes to previous edition
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IE Bulletin No. 79-02 (Revision No. 1) June 21, 1979
Page 2 of 6
Action to be Taken by Licensees and Permit Holders:
This Bulletin addresses those pipe support base plates that use concrete
expansion anchor bolts in Seismic Category I systems as defined by
Regulatory Guide 1.29, "Seismic Design Classification" Revision 1, dated
August 1973 or as defined in the applicable FSAR. For older plants where
Seismic Category I requirements did not exist at the time of licensing it
must be shown that piping supports for safety related systems, as defined in
the Final Safety Analysis Report, meet design requirements.
The revision is not intended to penalize licensees who have already
completed some of the Bulletin requirements. In those instances in which a
licensee has completed action on a specific item and the Bulletin revision
provides more conservative guidance, the licensee should explain the
adequacy of the action already performed. It should be reiterated that the
purpose of the Bulletin actions are to assure operability of Seismic
Category I piping systems in the event of a seismic event.
1. Verify that pipe support base plate flexibility was accounted for in
the calculation of anchor bolt loads. In lieu of supporting analysis
justifying the assumption of rigidity, the base plates should be
considered flexible if the unstiffened distance between the member
welded to the plate and the edge of the base plate is greater than
twice the thickness of the plate. It is recognized that this criterion
is conservative. Less conservative acceptance criteria must be
justified and the justification submitted as part of the response to
the Bulletin. If the base plate is determined to be flexible, then
recalculate the bolt loads using an appropriate analysis. If possible,
this is to be done prior to testing of anchor bolts. These calculated
bolt loads are referred to hereafter as the bolt design loads. A
description of the analytical model used to verify that pipe support
base plate flexibility is accounted for in the calculation of anchor
bolt loads is to be submitted with your response to the Bulletin.
It has been noted that the schedule for analytical work on base plate
flexibility for some facilities extends beyond the Bulletin reporting
time frame of July 6, 1979. For those facilities for which an anchor
bolt testing program is required (i.e., sufficient QC documentation
does not exist), the anchor bolt testing program should not be delayed.
2. Verify that the concrete expansion anchor bolts have the following
minimum factor of safety between the bolt design load and the bolt
ultimate capacity determined from static load tests (e.g. anchor bolt
manufacturer's) which simulate the actual conditions of installation
(i.e., type of concrete and its strength properties):
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IE Bulletin No. 79-02 (Revision No. 1) June 21, 1979
Page 3 of 6
a. Four - For wedge and sleeve type anchor bolts,
b. Five - For shell type anchor bolts.
The bolt ultimate capacity should account for the effects of
shear-tension interaction, minimum edge distance and proper bolt
spacing.
If the minimum factor of safety of four for wedge type anchor bolts and
five for shell type anchors can not be shown then justification must be
provided.
3. Describe the design requirements if applicable for anchor bolts to
withstand cyclic loads (e.g. seismic loads and high cycle operating
loads).
4. Verify from existing QC documentation that design requirements have
been met for each anchor bolt in the following areas:
(a) Cyclic loads have been considered (e.g. anchor bolt preload is
equal to or greater than bolt design load). In the case of the
shell type, assure that it is not in contact with the back of the
support plate prior to preload testing.
(b) Specified design size and type is correctly installed (e.g. proper
embedment depth).
If sufficient documentation does not exist, then initiate a testing
program that will assure that minimum design requirements have been met
with respect to sub-items (a) and (b) above. A sampling technique is
acceptable. One acceptable technique is to randomly select and test one
anchor bolt in each base plate (i.e. some supports may have more than
one base plate). The test should provide verification of sub-items (a)
and (b) above. If the test fail all other bolts on that base plate
should be similarly tested. In any event, the test program should
assure that each Seismic Category 1 system will perform its intended
function.
The preferred test method to demonstrate that bolt preload has been
accomplished is using a direct pull (tensile test) equal to or greater
than design load. Recognizing this method may be difficult due to
accessibility in some areas an alternative test method such as torque
testing may be used. If torque testing is used it must be shown and
substantiated that a correlation between torque and tension exists. If
manufacturer's data for the specific bolt used is not available, or is
not used, then site specific data must be developed by qualification
tests.
Bolt test values of one-fourth (wedge type) or one-fifth (shell type)
of bolt ultimate capacity may be used in lieu of individually
calculated bolt design loads where the test value can be shown to be
conservative.
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IE Bulletin No. 79-02 (Revision No. 1) June 21, 1979
Page 4 of 6
The purpose of Bulletin 79-02 and this revision is to assure the
operability of each seismic Category I piping system. In all cases an
evaluation to confirm system operability must be performed. If a base
plate or anchor bolt failure rate is identified at one unit of a
multiunit site which threatens operability of safety related piping
systems of that unit, continued operation of the remaining units at
that site must be immediately evaluated and reported to the NRC. The
evaluation must consider the generic applicability of the identified
failures.
Appendix A describes two sampling methods for testing that can be used.
Other sampling methods may have used but must be justified. Those
options may be selected on a system by system basis.
Justification for omitting certain bolts from sample testing which are
in high radiation areas during an outage must be based on other testing
or analysis which substantiates operability of the affected system.
Bolts which are found during the testing program not to be preloaded to
a load equal to or greater than bolt design load must be properly pre-
loaded or it must be shown that the lack of preloading is not
detrimental to cyclic loading capability. If it can be established that
a tension load on any of the bolts does not exist for all loading cases
then no pre-load or testing of the bolts is required.
If anchor bolt testing is done prior to completion of the analytical
work on base plate flexibility, the bolt testing must be performed to
at least the original calculated bolt load. For testing purposes
factor's may be used to conservatively estimate the potential increase
in the calculated bolt load due to base plate flexibility. After
completion of the analytical work on the base plates the conservatism
of these factors must be verified.
For base plate supports using expansion anchors, but raised from the
supporting surface with grout placed under the base plate, for testing
purposes it must be verified that leveling nuts were not used. If
leveling nuts were used, then they must be backed off such that they
are not in contact with the base plate before applying tension or
torque testing.
Bulletin No. 79-02 requires verification by inspection that bolts are
properly installed and are of the specified size and type. Parameters
which should be included are embedment depth, thread engagement, plate
bolt hole size, bolt spacing, edge distance to the side of a concrete
member and full expansion of the shell for shell type anchor bolts.
If piping systems 2 1/2-inch in diameter or less were computer analyzed
then they must be treated the same as the larger piping. If a chart
analysis method was used and this method can be shown to be highly
conservative, then the proper installation of the base plate and anchor
bolts should be verified by a sampling inspection. The parameters
inspected should include those described in the preceding paragraph. If
small diameter piping is not inspected, then justification of system
operability must be provided.
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IE Bulletin No. 79-02 (Revision No. 1) June 21, 1979
Page 5 of 5
5. All holders of operating licenses for power reactor facilities are
requested to complete items 1 through 4 within 120 days of date of
issuance of the Bulletin. No extension of time to complete action
requested in Bulletin 79-02 is granted by issuance of this revision of
the Bulletin. (Due Date - July 6, 1979) A reactor shutdown is not
required to be initiated solely for purposes of this inspection above.
However, it, is expected that testing of otherwise inaccessible
supports will be performed during the earliest extended outage
following Bulletin issuance. It is also expected that testing of anchor
bolts in accessible areas in operating plants will be performed within
the reporting interval. In the event the required testing is not
completed at the time of the initial report, on or about July 6, 1979,
the licensee should justify system operability and therefore continued
plant operation based upon the results of testing completed.
Maintain documentation of any sampling inspection of anchor bolts
required by item 4 on site and available for NRC inspection. Report in
writing within 120 days of date of Bulletin issuance, to the Director
of the appropriate NRC Regional Office, completion of your verification
and describe any discrepancies in meeting items 1 through 4 and, if
necessary, your plans and schedule for resolution. For planned action,
a final report is to be submitted upon completion of your action. A
copy of your report(s) should be sent to the United States Nuclear
Regulatory Commission, Office of Inspection and Enforcement, Division
of Reactor Operations Inspection, Washington, D.C. 20555. These
reporting requirements do not preclude nor substitute for the
applicable requirements to report as set forth in the regulations and
license.
6. All holders of construction permits for power reactor facilities are
requested to complete items 1 though 4 for installed pipe support base
plates with concrete anchor bolts within 120 days of date of issuance
of the Bulletin. No extension of time to complete action requested in
Bulletin 79-02 is granted by issuance of this revision of the Bulletin.
For pipe support base plates which have not yet been installed,
document your actions to assure that items 1 though 4 will be
satisfied. Maintain documentation of these actions on site and
available for NRC inspection. Report in writing within 120 days of date
of Bulletin issuance, to the Director of the appropriate NRC Regional
Office, completion of your review and describe any discrepancies in
meeting items 1 though 4 and, if necessary, your plans and schedule for
resolution. A copy of your report should be sent to the United States
Nuclear Regulatory Commission, Office of Inspection and Enforcement,
Division of Reactor Construction Inspection, Washington, D.C. 20555.
Approved by GAO B180225 (R0072); clearance expires 7/31/80. Approval was
given under a blanket clearance specifically for identified generic
problems.
Enclosures:
1. Appendix A
2. List of IE Bulletins Issued
in Last Twelve Months
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APPENDIX A
SAMPLING METHODS
Item 4 of this Bulletin states that for anchor bolt testing purposes a
sampling program is acceptable. Two sampling methods are discussed below,
but other methods may be used if justified.
a. Test one bolt on each plate as originally recommended in Bulletin
No.79-02. If the test fails, all other bolts on that base plate should
be similarly tested. A high failure rate should be the basis for
increased testing.
b. Randomly select and test a statistical sample of the bolts to provide
a 95 percent confidence level that less than 5 percent defective
anchors are installed in any one seismic Category I system. The
sampling program should be done on a system by system basis.
