The valve stem for a funnel valve to a solution neutralization tank was found to be separated from the body of the valve. This valve is used for purging hydrogen gas from the vessel. The functional classification of this valve is safety-significant. The "as-found" condition of the affected valve prevented the valve from performing its intended design function.
The affected valve is a one-half inch polyvinyl chloride (PVC) ball valve. The valve has an extension shaft coupled to the valve body, and the valve handle is coupled to the extension shaft, allowing the valve to be operated outside the process panel cover. The valve stem is cross-drilled and the extension shaft is pinned through the stem.
With this occurrence, engineering evaluated the one-half inch PVC ball valve design, and redesigned the extension rod and handle, which will be installed when the affected valve is replaced. The redesign will allow replacement of the extension rod and handle without requiring removal of the valve itself. The redesigned extension and valve handle will apply lower operating stresses to the valve stem, minimizing the likelihood of recurrence.
This occurrence demonstrated the use of data by engineering to evaluate equipment problems. As the data changed, highlighting a problem with one-half inch PVC ball valves, the facility redesigned the valve extension and valve handle to prevent recurrence.
Valves for compressed gas service and for cryogenic liquid service are discussed in the Hydrogen Safety Best Practices Manual.