Partial Stroke Testing Device (PSTD)
Partial Stroke Actuators insure reliable performance of Emergency Shutdown Valves
Vinyl Chloride Monomer (VCM) is the precursor to PVC Plastic and is made from Ethylene Dichloride which is “cracked” in a furnace to form VCM. The Quench Column tied in with each furnace requires a set of Emergency Shutdown Valves for fire safety.
The cracking furnace produces an output of product and coke fines which can collect in the butterfly valves used for isolation. Over time the coke fines will affect valve operability which creates uncertainty about their ability to function in a real emergency.
Working with Plant Engineering and Instrumentation staff CHEMFLOW Products and QTRCO developed a safety solution incorporating Hobbs Triple Offset Butterfly Valves coupled to QTRCO’s FD Series Flat Yoke® Actuator with XRCISER® Partial Stroke Testing and custom on-board controls.
After start-up the valves were held in the normally open position for about 6 months. This allowed for an accumulation of coke fines in the valves to the point where valve operation could be adversely affected. Using the QTRCO on-board controls, operations ran the partial stroke test. A 15 degree rotation had been engineered into the XRCISER® pneumatic travel stops. Upon engagement of the stops air was released from the primary pistons allowing 100% of the spring force to rotate the valve stem. The valve discs were able to break the crust of coke fines and move to the partial stroke position thus verifying the functionality of the Emergency Shutdown System.