Which failure mode is a direct result of a solenoid failure in SIS design?

• A. Receipt of incorrect solenoid from manufacturer
• B. Valve stuck in position
• C. Lost communications with DCS
• D. Accidental bypassing of valve during maintenance

Answer: (B)

The failure mode resulting from a solenoid failure in Safety Instrumented System (SIS) design is best represented by the scenario where the valve becomes stuck in position. This situation occurs because solenoids are responsible for actuating the valve; if the solenoid fails to operate, it may prevent the valve from opening or closing as intended. Consequently, this can disrupt the normal functioning of the safety system, leading to potential safety risks.

In contrast, the other options represent different issues not directly stemming from solenoid failure. For example, receiving an incorrect solenoid from the manufacturer pertains to procurement and quality control issues, while lost communications with the Distributed Control System (DCS) relates to data transmission or network failures. Similarly, accidental bypassing of a valve during maintenance is related to operational procedures rather than a direct failure of the solenoid mechanism. Thus, the situation where the valve is stuck in position accurately describes a direct consequence of solenoid failure in the context of SIS design.