SIS-TECH”sDiamond-SIS is a non-programmable logic solver for ensuring Coker drumswitching and de-heading operations are safely and reliably performed.SIS-TECH engineers, working in cooperation with Coker unit experts fromseveral major companies, set out to find an alternative to using limitswitches to avoid the inappropriate operation of valves used in theswitching/decoking cycles. The team identified the following in-serviceand open-drum events that could lead to dangerous hydrocarbon incidentsduring 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 engineersanalyzed these events and determined that the most reliable, simplest,and most cost-effective solution was to design a solution that protectseach Coker drum individually, thus eliminating the complexitiesassociated with multiple Coker drum applications and at the same timeaddressing valve limit switch reliability issues. The Diamond-SISCoker drum switching solution continuously monitors three key processvariables to accurately and reliably detect when a Coker drum isin service. The system uses hardwired logic to monitor and controlmovement of five valves based on specific combinations of three processvariables. Inputs include: overhead pressure; overhead temperature;inlet temperature. Outputs include: vent drain valve; top/bottom headvalves; blowdown valve; overhead to fractionator valve; inlet feedvalve. What makes SIS-TECH’s solution different than simplyimplementing the above logic using conventional relays is that theDiamond-SIS is designed and built as a certified safety instrumentedsystem (SIS) suitable for applications requiring up to SIL 3 (SafetyIntegrity Level) and flexible enough to accommodate 1oo1 (read as oneout of one), 1oo2, 2oo2, or 2oo3 voting schemes.