Information Notice No. 85-59: Valve Stem Corrosion Failures

                                                            SSINS No.: 6835 
                                                            IN 85-59       

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

                                July 17, 1985

Information Notice No. 85-59:   VALVE STEM CORROSION FAILURES 

Addressees: All nuclear power reactor facilities holding an operating 
license (OL) or a construction permit (CP). 

Purpose: 

This information notice is provided to alert recipients of a potentially 
significant problem pertaining to stress corrosion failures of valve stems 
and shafts; items that are not routinely examined. It is suggested that 
recipients review the information for applicability to their facilities and 
consider actions, if appropriate, to preclude a similar problem occurring at
their facilities. However, suggestions contained in this information notice 
do not constitute NRC requirements; therefore, no specific action or written
response is required. 

Description of Circumstances: 

There have been four instances where cracks were found in 410 stainless 
steel valve stems. These instances involved different licensees and 
different manufacturers. Such cracks cannot be observed without the 
disassembly of the valves, and the valve operability test programs do not 
provide a means of early detection. In three of these instances, the cracks 
grew until the stem sheared when the valve was activated. Such failures can 
prevent the system from performing its safety function. 

Uncontrollable leakage from the stem packing of several Velan globe valves 
was reported by Oconee 1 in December 1971. Disassembly and examination 
revealed cracks for the entire length of the stems and more than half of the
diameter in depth. In order to prevent cracking, 410 stainless steel needs 
to be tempered immediately after hardening, but several batches were not 
tempered. Ultimately, 2600 stems were replaced in the 1-1/2-, 1- and 
1/2-inch valves, using 17-4PH and 300-series stainless steel materials. 

A 20 inch Anchor/Darling gate valve stem snapped while being manually opened
at Brunswick 2 on August 4, 1982. There was pitting of the 410 stainless 
steel in the gland packing section and the crack had initiated from one of 
these pits. The cross-section area of the stem of the suppression pool 
suction valve had been reduced by 70% by intergranular stress corrosion 
cracking (IGSCC). The material had a higher hardness than specified as a 
result of improper heat treatment. 



8507120320 
.

                                                             IN 85-59     
                                                             July 17, 1985 
                                                             Page 2 of 3  

Excessive hardness is associated with cracking and corrosion. The 
manufacturer replaced five lots of valve stems with proper heat-treated 410 
stainless steel, and there have not been any further problems. 

An injection valve in the low-pressure coolant injection (LPCI) system broke
in two places during disassembly at Browns Ferry 3 on February 28, 1984. One
break was below the stem packing area and the other was at the gate 
connection. Over 50% of the cross-section of the stem of these 24-inch 
Walworth valves had been lost in these areas by IGSCC. The stem had higher 
hardness than specified. New stems made from 17-4 PH stainless steel were 
installed. 

Linear indications were discovered on three main steam isolation valve 
(MSIV) shafts at Farley 1 on February 29, 1984. The indications were from 1 
to 13 inches, long, contained thick oxides, and were located in the packing 
gland area. The MSIVs were Atwood-Morrill 32-inch swing check valves and the 
shaft hardness exceeded specifications. 17-4 PH stainless steel also was 
used as the replacement material for the shafts. 

Although 410 stainless steel is defined as a stainless steel because of its 
alloy content, it is really a high chromium, very hardenable steel. Cooling 
this material in air from the 1700-to-1900F temperature range results 
in a surface hardness of up to HRC 45 and high internal stresses. Tempering 
the hard and brittle martensite produces a softer and more ductile 
composition that has much less chromium available for intergranular 
corrosion resistance. Tempering in the 700-to-1050F range is not 
recommended because it results in low and erratic impact properties and poor 
resistance to corrosion and stress corrosion. 

The following conclusions were reached: 

1.   The actual hardness of the 410 stainless steel valve stems and shafts 
     was higher than specified and higher than documented. 

2.   The excessive hardness is associated with intergranular stress 
     corrosion cracking. 

3.   The cracking occurred in internal areas where there could be 
     concentrations of corroding chemicals, such as at the gland packing. 

4.   The oxides found in the cracks showed that the cracks occurred during 
     service and grew slowly. 

5.   The cracks were not detected by the routine valve operability test 
     programs, but were only discovered by actual failures or after 
     disassembly during refueling outages. 

6.   Failure of these valves would make the specific safety system 
     inoperable. 
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                                                             IN 85-59     
                                                             July 17, 1985 
                                                             Page 3 of 3  

No specific action or written response is required by this information 
notice. If you have any questions about this matter, please contact the 
Regional Administrator of the appropriate regional office or this office. 


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

Technical Contact:  P. Cortland, IE
                    (301) 492-4175

Attachment: List of Recently Issued IE Information Notices