NRC Bulletin 79-02, Pipe Support Base Plate Designs Using Concrete Expansion Anchor Bolts

• Issue date::March 8, 1979

• URL::https://www.nrc.gov/reading-rm/doc-collections/gen-comm/bulletins/1979/bl79002.html

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{{#Wiki_filter: Bulletin 79-02: Pipe Support Base Plate Designs Using Concrete Expansion Anchor Bolts

                              UNITED STATES 
                       NUCLEAR REGULATORY COMMISSION
                   OFFICE OF INSPECTION AND ENFORCEMENT
                          WASHINGTON, D.C. 20555
                                    
                               March 8, 1979

                                                     IE Bulletin No. 79-02 

PIPE SUPPORT BASE PLATE DESIGNS USING CONCRETE EXPANSION ANCHOR BOLTS Description of Circumstances:

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.

Action to be Taken by Licensees and Permit Holders:

For 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.

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 

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IE Bulletin No. 79-02 March 8, 1979

    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. If the base plate is determined 
    to be flexible, then recalculate the bolt loads using an appropriate 
    analysis which will account for the effects of shear - tension 
    interaction, minimum edge distance and proper bolt spacing. This is to 
    be done prior to testing of anchor bolts. These calculated bolt loads 
    are referred to hereafter as the bolt design loads. 

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): 

    a.   Four - For wedge and sleeve type anchor bolts, 

    b.   Five - For shell type anchor bolts. 

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 fails, 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. 

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IE Bulletin No. 79-02 March 8, 1979

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 this Bulletin. A reactor shutdown is not required to be 
    initiated solely for purposes of this inspection above. 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 1 support 
    base plates with concrete anchor bolts within 120 days of date of 
    issuance of this 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 (ROO72); clearance expires 7/31/80. Approval was given under a blanket clearance specifically for identified generic problems.

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