Information Notice No. 94-61, Supplement 1: Corrosion of William Powell Gate Valve Disc Holders

UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C.  20555

May 25, 1995


NRC INFORMATION NOTICE 94-61, SUPPLEMENT 1:  CORROSION OF WILLIAM POWELL GATE
                                             VALVE DISC HOLDERS


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 supplement to alert addressees to problems caused by the corrosion of
carbon steel disc holders in William Powell (the vendor) gate valves and to
correct an error in Information Notice (IN) 94-61, "Corrosion of William
Powell Gate Valve Disc Holders."  After issuance of the IN, the vendor
investigation identified inaccuracies in the IN.  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 IN are not NRC requirements; therefore, no
specific action or written response is required.  

Background

In December 1991, maintenance personnel at Farley Nuclear Plant replaced a
gate valve stem and disc holder assembly and disc for the "Service Water (SWS)
to Component Cooling Water (CCW) System Room Cooler."  The stem assembly was
replaced because the disc holder had failed, causing the stem assembly and
disc to separate.  Southern Nuclear Operating Company (the current plant
licensee) evaluated the cause of the failure and determined that the carbon
steel disc holder had become corroded.  The disc holder is threaded and welded
to a martensitic stainless steel stem and engages the disc by means of a     
T-slot connection.  Localized galvanic corrosion of the holder was caused by
its submersion in service water (an electrolytic solution).

Description of Circumstances

IN 94-61 indicated that the valves in question had stainless steel bodies. 
Further investigation has shown that the valve bodies and disc holders were
ordered by the original plant licensee (Alabama Power Company) and supplied by
the vendor as carbon steel.  The vendor submitted to the NRC staff copies of
the drawing and material specification sheet approved by Alabama Power Company
at the time of purchase.  The current licensee verified that the valve bodies
in question were indeed carbon steel and also identified some corrosion of
these bodies.  The original belief that the valves were stainless steel 


9505190250.                                                            IN 94-61, Supp. 1
                                                            May 25, 1995
                                                            Page 2 of 3


resulted from the current plant licensee using as a reference the
documentation for replacement stainless steel valves during its investigation. 
In subsequent modifications to the SW system, the licensee eliminated the need
for the valves in question and removed them from the system.  Several larger
carbon steel SW valves have experienced corrosion of the internal components
as well as of the valve bodies.  The licensee is replacing these valves with
austenitic stainless steel valves containing stainless steel disc holders.     


Discussion

IN 94-61 indicated that a former Vice President of Engineering and Quality at
William Powell had stated that if a valve drawing shows that the body, stem,
and most other parts are stainless steel, and the disc holder material is not
specified, it cannot be assumed that the disc holder is also stainless steel. 
He stated that the only way to verify the material of the disc holder, other
than direct inspection, is to call William Powell, giving the individual valve
serial number and drawing number.

The current chief engineer at William Powell stated that, in the past, it has
been William Powell policy to provide disc holders constructed of material
equivalent to that used in the valve body.  Presently, for economic reasons
(i.e., minimization of different types of stock), the vendor has standardized
on a martensitic stainless steel disc holder to match the stem material for
carbon and alloy steel valves. 

In carbon steel valves, internal corrosion cannot be detected through external
visual inspection or valve performance.  Valve disc holders that are not
severely corroded will continue to function normally.  The only way to
determine the extent of corrosion before a complete failure is to remove the
valves from service, disassemble them, and inspect the valve internal
components.

The safety significance of disc holder corrosion is the potential for failure
of safety-related valves in corrosive/electrolytic environments to reposition
when demanded.

.                                                            IN 94-61, Supp. 1
                                                            May 25, 1995
                                                            Page 3 of 3


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.


                                      original signed by 

                                    Brian K. Grimes, Director
                                    Division of Project Support
                                    Office of Nuclear Reactor Regulation

Technical contacts:  Michael J. Morgan, RII
                     (334) 899-3386 or 3387

                     Geoffrey P. Hornseth, NRR
                     (301) 415-2756

Attachment:
List of Recently Issued NRC Information Notices