United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 83-80: Use of Specialized "Stiff" Pipe Clamps

                                                            SSINS No.: 6835 
                                                            IN 83-80       

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF INSPECTION AND ENFORCEMENT
                           WASHINGTON, D.C. 20555
                                     
                              November 23, 1983

Information Notice No. 83-80:   USE OF SPECIALIZED "STIFF" PIPE CLAMPS 

Addressees: 

All nuclear power reactor facilities holding an operating license (OL) or 
construction permit (CP), nuclear steam system suppliers, and 
architect-engineers. 

Purpose: 

This information notice is provided as a notification of a potential 
significant problem in the use of specialized "stiff" pipe clamps. These 
pipe clamps may result in significant localized stresses in the piping. It 
is expected that recipients will review the information for applicability to 
their facilities. No specific action or response is required. 

Description of Circumstances: 

As a result of a staff evaluation of allegations concerning Class 1 piping 
design deficiencies, it has become apparent that certain loadings induced by
specialized "stiff" pipe clamps can result in significant localized stresses
in the piping that should be considered in the piping design. These "stiff" 
pipe clamps have been developed by several pipe clamp vendors to meet some 
recent design specification requirements that the clamps be designed to 
provide total system stiffness compatible with the shock suppressor 
stiffness. In developing these stiff pipe clamps, clamp vendors have 
incorporated several innovative design concepts that can detract from the 
piping integrity when they are not properly considered by piping designers: 

1.   Several types of "stiff" clamps require, during clamp installation, a 
     preloading of the clamp U-bolts or straps to achieve the desired 
     stiffness properties and to prevent the clamp from lifting off the 
     piping during design load application. The bolt preload value is 
     determined analytically by the clamp vendors and its magnitude can be 
     extremely large. Typically, the clamp vendors qualify only the clamp 
     stresses and do not test or evaluate the effect of the preload on the 
     piping stresses. Some clamp vendors specify the preload value in field 
     installation procedures that are not usually reviewed by piping 
     designers. This may result in clamp preload forces not being 
     appropriately considered in the piping design. 



8311010020 
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                                                          IN 83-80         
                                                          November 23, 1983 
                                                          Page 2 of 3      

2.   Certain types of "stiff" clamps provide a small contact area of the 
     clamp onto the pipe wall, apparently to facilitate easier clamp 
     installation and to ensure a positive controlled clamping onto the 
     pipe. However, a condition exists for inducing significant localized 
     stresses in the piping during design loadings. 

3.   Some pipe clamps are available for mounting on piping components other 
     than straight pipe (e.g., pipe elbows). However, when attachments are 
     placed on elbows, the Class 1 piping stress indices and flexibility 
     factors provided in the ASME Boiler and Pressure Vessel Code are not 
     applicable per NB-3683.2. 

The above identified clamp design features represent a significant change 
from the design of conventional pipe clamps that have been used for years in
both nuclear and nonnuclear high pressure piping application. These 
relatively new design features can result in localized piping stresses 
significantly higher than the stresses from conventional pipe clamps. Piping
designers who are accustomed to neglecting these localized stresses, because
of the low magnitude stresses associated with conventional pipe clamps, 
might incorrectly assume that such stresses can be neglected with these new 
clamps. The NRC staff does not believe that the clamp design is deficient. 
However, the NRC staff does believe that potential safety concerns could 
exist if the piping designers are not aware of the conditions under which 
high stress can be induced by the clamp or do not properly evaluate piping 
stresses for the installed condition of the clamp. The applicant/licensee 
(and its piping designers) should be cognizant of the effect of the 
clamp-induced pipe loadings. Furthermore, the applicant/licensee should be 
aware that post-installation control of the clamp preload may be necessary 
when the clamp stiffness is required to assure total piping system 
restraint. 

The staff has identified the following vendors as the major suppliers of 
"stiff" clamps. Their respective "stiff" pipe clamps models are also 
identified: 

     1.   E-Systems, Inc. (all models)
     2.   Western Piping (all models)
     3.   ITT Grinnell   (Figure 215 Stiff Clamp)
                         (Figure 315 Stiff Clamp
                         (Figure 214 Mini-Stiff Clamp)
                         (Figure 314 Mini-Stiff Clamp)
     4.   Bergen-Paterson (Part 6175)
     5.   Paul Munroe/Remco Synkrotherm Pipe Clamp

It is suggested that holders of operating licenses or construction permits 
review this information for applicability at their facilities. 
.

                                                          IN 83-80         
                                                          November 23, 1983 
                                                          Page 3 of 3      

No written response to this information notice is required. If you need 
additional information about this matter, please contact the Regional 
Administrator of the appropriate NRC Regional Office or this office. 


                                   Edward L. Jordan Director 
                                   Division of Emergency Preparedness 
                                     and Engineering Response 
                                   Office of Inspection and Enforcement 

Technical Contact:  D. Terao, NRR
                    (301) 492-4421

                    J. R. Fair, IE
                    (301) 492-4509

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