Difficulties were experienced with two solenoid-operated globe valves in a charging system. When shut, the valves could not be reopened without securing all charging pumps. During a refueling outage, the two valves were disassembled and examined to determine the cause of the malfunction. It was found that disc guide assembly springs in both valves had undergone complete catastrophic failure. The springs, which initially had 25 coils, were found in sections of only 1-2 coils. Metallurgical analysis of the failed springs attributed the probable cause of failure was due to hydrogen embrittlement. The springs are made of 17-7 PH stainless steel.
Discussion with the valve manufacturer revealed that similar failures occurred on three previous occasions. These spring failures were also attributed to hydrogen embrittlement.
The above described events are an indication of a potential licensee/vendor interface problem. Based on the information received, the vendor was not completely informed via the purchase specifications regarding the service condition to which the valve would be exposed. Further, all users of these valves were not notified of the initial problem through either oversight by the vendor or as a result of the valves being supplied through an intermediate source. To avoid similar incidents in the future, onsite personnel need to ensure that their vendors receive comprehensive specifications relating to the application, use and service conditions associated with all of the stainless steel valves implemented in applications susceptible to hydrogen embrittlement.
A web-based resource developed by Sandia National Laboratories to provide data on hydrogen embrittlement of various materials is available at Technical Reference for Hydrogen Compatibility of Materials.