United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 79-02: (Revision No. 1), Pipe Support Base Plate Designs Using Concrete Expansion Anchor Bolts

                               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
.

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):  
.

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.
     
.

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.  
.

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 
.

                                 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. 
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