Issue link: https://onenorgren.uberflip.com/i/1505207
Process Fluid Control 27 3. Safety instrumented system 4. SIL certification » The reduction of the evaluated risk is performed by a safety instrumented system (SIS). The plant manufacturer needs to ensure that all components meet the requirements of the IEC61508 for the respective SIL. » The SIS needs to be independent from the standard loop and consists of sensor, logic and actuator (see picture 2). Control valves are part of the actuator. » Norgren developed control valves that are evaluated and certified according to the requirements of the IEC61508. » These control valves are successfully used in safety instrumented applications since many years. » All components of the SIS will be evaluated by manufacturer according to the requirements of the IEC 61508 and certified by independent organizations (e.g. TÜV). » The certification according to SIL covers aspects of systematic and statistical suitability. » Systematic suitability is proved by a certified product development and quality management process. Potential faults are identified and avoided by FMEAs. » Statistical suitability is done by confirmation of a low failure probability of the components. This evidence was provided by a long- term test under worst-case conditions and confirmed by field data. » In the Low Demand Mode (LDM; Safety requirements < 1 operations / year) the probability of failure is stated as Probability of Failure on Demand (PFD). The calculation is based on the failure rate (λ) and the test interval (T). » In the High Demand Mode (HDM; Safety requirements > 1 operations / year) the probability of failure is stated as Probability of Failure per Hour (PFH). PFH corresponds to the failure rate (λ). » The achievable level of risk reduction (SIL 1 … 4) is based on systematic and statistical suitability. » The control valves developed by Norgren can be used in both LDM and HDM. » They are certified for service life up to 12 years and meet the requirements for SIL2 as a single-channel design and SIL3 in a multi-channel design of the SIS. SIS example: Overfill safety device Logic controller Actuator Actuator Logic controller Sensor Sensor Safety loop Standard loop Sensor Sensor