SIS-TECH”s Diamond-SIS is a non-programmable logic solver for ensuring Coker drum switching and de-heading operations are safely and reliably performed. SIS-TECH engineers, working in cooperation with Coker unit experts from several major companies, set out to find an alternative to using limit switches to avoid the inappropriate operation of valves used in the switching/decoking cycles. The team identified the following in-service and open-drum events that could lead to dangerous hydrocarbon incidents during Coker drum switching and de-heading operations:
• Vent valve opening
• Blowdown valve opening
• Drain valve opening
• Top head opening
• Bottom head opening
• Overhead to Fractionator valve opening
• Inlet feed valve opening

SIS-TECH engineers analyzed these events and determined that the most reliable, simplest, and most cost-effective solution was to design a solution that protects each Coker drum individually, thus eliminating the complexities associated with multiple Coker drum applications and at the same time addressing valve limit switch reliability issues. The Diamond-SIS Coker drum switching solution continuously monitors three key process variables to accurately and reliably detect when a Coker drum is in service. The system uses hardwired logic to monitor and control movement of five valves based on specific combinations of three process variables. Inputs include: overhead pressure; overhead temperature; inlet temperature. Outputs include: vent drain valve; top/bottom head valves; blowdown valve; overhead to fractionator valve; inlet feed valve. What makes SIS-TECH’s solution different than simply implementing the above logic using conventional relays is that the Diamond-SIS is designed and built as a certified safety instrumented system (SIS) suitable for applications requiring up to SIL 3 (Safety Integrity Level) and flexible enough to accommodate 1oo1 (read as one out of one), 1oo2, 2oo2, or 2oo3 voting schemes.