To ensure that it will function on demand, an EBV must be tested routinely. Safety shutdown systems are normally dormant, and many faults in the system are not apparent. Testing the whole system uncovers covert faults; 30 percent of which may involve valves, according to one study.
As part of procurement, require that knowledgeable representatives of the operating facility witness a Factory Acceptance Test (FAT) on the assembled EBV.
During shutdowns and turnovers, treat EBVs as safety relief valves. Have shop personnel inspect them thoroughly, and run a leak test.
During the plant operations the testing should include the:
• Actuated valve
• Sensor or initiating inputs (transmitter, switch, push button… )
• Control system components and logic
• Pneumatic or electrical power sources or both
• Control room alarms and displays
Conduct a full test of each EBV and its associated actuation system on a regular schedule (at least every three months). If the EBV is meant to close, it is common practice to provide a means by which to bypass, block-in, and pressure test the EBV to verify that it closes tightly.
Provide customized test procedures for each individual EBV function. Document in the procedures the set points at which the EBV is to activate. In test procedure documentation, detail a step-by-step process, leaving space for testing personnel to initial and date each step and to record results. In this way, the procedure becomes a comprehensive record of the integrity of the emergency system. Store completed test procedures in a secure location to be available for possible review.
The EBV testing process also provides a means by which to log changes made to the EBV system. As changes are made, they must be verified by testing and incorporated formally into the testing process.
During testing, the EBV should be fully stroked and actuated from all possible locations; such as, local pushbuttons, remote pushbuttons, and the automatic safety shutdown system.
For an EBV on spared equipment, such as a pump, this requirement is easily fulfilled: one pump is shut down and its valve tested while the other pump is running. An EBV on unspared equipment can be tested easily if the equipment can be shut down for the short test period.
If the equipment cannot be shut down during normal operation, then a duplicate EBV can be installed (see Figure 1300-10), allowing one valve to be tested while the other valve is in service. Although duplicate valves may seem costly, they allow the routine testing necessary to ensure that the EBV functions on demand.
Around the fuel EBV on fired equipment, install a full-flow, hand-operated, bypass valve so that the EBV can be tested fully. Provide a means to verify full, tight closure with a downstream pressure gage (see Figure 1300-11). EBV testing by partial stroking is not recommended for fired equipment. This bypass valve should be car-sealed in the closed position, equipped with position switches, and connected to alarms and lights to warn the operator when the manual bypass valve is not fully closed.
Occasionally, process requirements make partial stroking preferable to full stroking and the addition of a bypass valve. For HF Mitigation, some of the EBVs cannot be fully stroked without interrupting critical process streams.
Partial stroking is preferable because:
• There is a strong potential for plugging the bypass line in this service.
• The past performance of the monel plug valves is excellent.
• The bypass valve increases the risk of external leakage.
• Some through-valve leakage can be tolerated.
The cold flow properties of the TFE sleeve mean that monthly testing is essential to unseat the plug for all of the EBVs in HF service.