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HomeNRC LibraryDocument CollectionsGeneric CommunicationsInformation Notices1992

# Information Notice No. 92-15: Failure of Primary System Compression Fitting

```
                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF NUCLEAR REACTOR REGULATION
                           WASHINGTON, D.C.  20555

                              February 24, 1992


NRC INFORMATION NOTICE 92-15:  FAILURE OF PRIMARY SYSTEM COMPRESSION FITTING


Addressees

All holders of operating licenses or construction permits for nuclear power 
reactors.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information 
notice to alert addressees to problems that could result from the inadequate 
installation of compression fittings.  It is expected that recipients will 
review the information for applicability to their facilities and consider 
actions, as appropriate, to avoid similar problems.  However, suggestions 
contained in this information notice are not NRC requirements; therefore, no 
specific action or written response is required.

Description of Circumstances

On November 23, 1991, operators at the Oconee Nuclear Station, Unit 3, 
detected unidentified leakage of approximately 70 gallons per minute (gpm) 
from the reactor coolant system (see licensee event report 50-287/91-008).  
The licensee shut down the reactor in an orderly manner.  The licensee 
observed a maximum leak rate of approximately 130 gpm and found that a total 
of 87,000 gallons of reactor coolant was discharged to the containment 
before the reactor coolant system could be depressurized.  On November 25, 
1991, personnel entered the Unit 3 containment building and determined that 
the source of the leak was a separated compression fitting on a 3/4-inch 
diameter instrument line.  The instrument line is part of the reactor vessel 
level indication system (RVLIS).  The leak occurred where the line connects 
to the top of the "A" steam generator hot leg.  The tubing separated from 
the fitting next to a 3/4-inch flow restriction valve.

The licensee inspected the fitting and determined that the probable cause of 
the tubing separating (or pulling out) was that the nut had not been suffi-
ciently tightened onto the compression fitting.  The nut on the fitting 
appeared to have been tightened approximately 1/2 turn less than was recom-
mended by the fitting manufacturer, the Parker-Hannifin Corporation.  The 
gap between the nut and the fitting was greater than the maximum nominal 
value furnished by the vendor.  The licensee inspected the tubing at the 
failed fitting and determined that the diameter reduction at that location 
was much less than the diameter reduction for the tubing in another fitting 
that had not failed.  Based on these inspections the licensee determined 
that the ferrule 

9202190038 
.

                                                       IN 92-15
                                                       February 24, 1992
                                                       Page 2 of 3


was not adequately compressed into the tubing.  The licensee reconfigured 
the instrument line and replaced the valve, the 3/4-inch instrument tubing, 
and the fittings on the hot legs of both steam generators.

The licensee inspected all of the fittings on instrument tubing connected to 
the Unit 3 primary system.  The licensee examined the 264 Parker-Hannifin 
fittings in the primary system using nominal expected gap values furnished 
by Parker-Hannifin as an acceptance criteria.  However, Parker-Hannifin does 
not consider the gap to be a critical dimension.  The licensee also 
inspected the 191 Swagelock fittings in the primary system using gap 
inspection gages furnished by Swagelock.  The licensee found that 
approximately 27 percent of both types of fittings appeared to have gaps 
outside of the nominal range.  The licensee attempted to tighten these 
fittings to reduce the gaps to the values recommended by the manufacturers.  
However, a small percentage of the Parker-Hannifin fittings could not be 
tightened to meet the vendor's nominal gap values.  The licensee accepted 
these fittings as-is based on the judgement of the instrument technicians 
that the connections could not be tightened further without damaging the 
tubing or connections, and on an engineering evaluation made after 
disassembling and inspecting one of the questionable fittings.

Discussion

This event reemphasizes the importance of making successful connections in 
instrument tube lines.  Fitting nuts on compression fittings must be 
tightened sufficiently to ensure that the fitting has been adequately 
seated.  According to the licensee, they have previously experienced 
problems with inadequate assembly of 3/4-inch fittings due to the high 
torque required to properly seat the fittings.  The licensee's modifications 
to the RVLIS eliminated the use of 3/4-inch fittings on these lines.

While conducting inspections at other facilities, the NRC and licensees have 
noted other problems with the installation of compression fittings, 
including the following:

�    Interchanging hardware from different manufacturers

�    Installing the ferrules backwards in fittings, or omitting the ferrules

�    Failing to bottom the tubing on the shoulder of the fitting

�    Using tubing that is not cut square or that is burred, scratched, de-
     formed, or contaminated with dirt, oil, or other contaminants

�    Failing to adequately tighten the fitting to the finger-tight position 
     before making additional turns from the finger-tight position

�    Failing to ensure that the tubing has not moved back out of the fitting 
     when the nut is tightened

These problems indicate that licensees' procedures for installing 
compression fittings may not provide adequate guidance to avoid improper 
assembly of the 
.

                                                       IN 92-15
                                                       February 24, 1992
                                                       Page 3 of 3


fittings.  Procedures may also fail to address the vendor's installation 
recommendations, not only for the initial installation of connections, but 
also for disconnecting and retightening fittings during normal maintenance 
activities.  In addition, personnel who make compression fitting connections 
may not be adequately trained.

Related Generic Communications

The NRC staff has previously issued Information Notice 84-55 (including 
Supplement 1), "Seal Table Leaks at PWRs," to address problems associated 
with compression fitting failures.

This information notice requires no specific action or written response.  If 
you have any questions about the information in this notice, please contact 
one of the technical contacts listed below or the appropriate Office of 
Nuclear Reactor Regulation (NRR) project manager.




                                   Charles E. Rossi, Director
                                   Division of Operational Events Assessment
                                   Office of Nuclear Reactor Regulation


Technical contacts:  Joseph J. Lenahan, RII
                     (404) 331-4190

                     John R. Fair, NRR
                     (301) 504-2759


Attachment:  List of Recently Issued NRC Information Notices
.
```

*Page Last Reviewed/Updated Friday, May 22, 2015*

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