SAFETY-INSTRUMENTED SYSTEMS: Control Valves As Final Elements

摘要

History is a constant reminder that accidents and catastrophic events can and do occur in process environments. As processes become more complex and existing basic process control systems (BPCS) and safety systems age, risk reduction becomes more challenging. Notable international standards addressing process safety include IEC 61511 and ISA 84.01. These standards cover the design and management requirements for a safety-instrumented system (SIS) from cradle to grave. Since the final control element is often the weakest link of an SIS, the proper valve and actuator must be selected to improve reliability and availability and to minimize risk. When designing an SIS, the use of a control valve can be considered in three potential configurations: 1. single control valve used only for on-off safety, 2. single control valve used for both safety and control, and 3. control valve used as a redundant final control element.