We are entering detail design for our interlock project for a 6 drum Coker. The scope of the project includes the switch valves, vapor valves, isolation valves etc… Delta Valves have been previously installed. My question to this forum is what do others do to prevent valve movement on valves with modern digital Limitorque actuators (MX w/ Modbus)? Intercepting power is not a good option as in our case it would take power from the communication circuit – causing our logic to get hosed up when the position signal is lost. Our current plan is to use the ESD signal through Modbus to prevent the valve from moving out of sequence. For the more severe consequences, the additional hardwired ESD contacts will be used with input from independant process transmitters (ie: drum temp/pressure) through a SIL rated PLC.
There is underlying concern from the operators that without intercepting power the valves are still at risk of moving (voodoo event…..). I’m being reassured by our I&E folks that this is not a concern – but am not getting 100% closure. Unfortunately, we had an incident in the past caused by a valve being closed out of sequence. Investigation summary was that the valve was moved by op’s…but operator did not admit to it. Some tough issues ahead for me…..
Your feedback / wisdom is appreciated.
Regards,
Craig Catton
