Can a “fail open” valve fail closed?. Clearly the answer is YES or we would not have asked the question! On piping and instrumentation diagrams (P&IDs) or other process safety information (PSI), valves may be indicated as “fail open,” “fail closed,” or “fail in last position.” This indicates what the valve does in case of utility failure – usually instrument air or electric power failure.
In the batch reactor system in Figure 1, the reactor contents were initially heated with steam on the heat exchanger. When the batch reached the required reaction temperature, steam was shut off and chilled water was turned on to the heat exchanger to control the reactor temperature. The water flow was controlled by Valve 1, which was a “fail open” valve; it required instrument air pressure to close the valve.
On the day of the incident, the reactor temperature began to increase, causing a high temperature alarm. The operator observed the signal to Valve 1 as “full open”. The reactor temperature continued to increase, eventually triggering high temperature and low cooling water flow alarms. The operator was unable to troubleshoot the problem over a 7-minute period and did not open the Emergency Cooling Bypass to increase cooling water flow to the reactor. The emergency shutdown system intervened and dumped the reactor to a containment pit. There were no injuries, but an environmental release occurred.
What if that “fail open” valve fails closed?