Refinery Valves and Accessories for Control and Safety Instrumented Systems

How to Apply Refinery Valves and Accessories for Control and Safety Instrumented Systems

Mastering the selection, installation, and maintenance of valves and their accessories for control and safety instrumented systems (SIS) is paramount for ensuring operational integrity, process efficiency, and personnel safety in refinery environments. This guide, derived from API Recommended Practice 553, will equip you with the practical knowledge to effectively implement its principles, directly enhancing your project outcomes and contributing to a safer, more reliable refinery.

Before You Begin

Prerequisites:

• •Knowledge: Foundational understanding of refinery processes, process control principles, and the fundamental concepts of Safety Instrumented Systems (SIS) including SIL ratings and functional safety. Familiarity with common valve types and their operational characteristics.
• •Tools/Resources: Access to API RP 553, relevant P&IDs, process design specifications, equipment datasheets, and vendor documentation.
• •Time Required: 2-4 hours for initial review and application planning, depending on project complexity.

Step-by-Step Implementation

Step 1: Define System Requirements and Valve Functionality

Clearly identify the specific role of each valve within the control loop or Safety Instrumented Function (SIF). Determine whether the valve is for modulating process flow, on/off service, or a critical safety shut-down function. This dictates the required performance characteristics, such as response time, accuracy, and fail-safe position.

Step 2: Select Appropriate Valve Type and Trim Design

Based on the functional requirements, choose the most suitable valve body style (e.g., globe, ball, butterfly) and trim design. For control applications, consider factors like flow characteristic (linear, equal percentage), rangeability, and cavitation/flashing potential. For SIS, prioritize reliability, rapid actuation, and leak-tight shutoff as per IEC 61508/61511 requirements.

Step 3: Specify Actuator and Accessory Compatibility

Determine the appropriate actuator type (pneumatic, electric, hydraulic) based on available utilities, required torque/thrust, and fail-safe action (fail-open, fail-closed, fail-in-place). Ensure compatibility with the valve and specify necessary accessories like positioners, solenoid valves, volume boosters, and limit switches, ensuring they meet the demands of the control or safety function.

Step 4: Account for Material and Environmental Considerations

Select valve and accessory materials that are compatible with the process fluid's chemical properties, temperature, and pressure. Consider potential erosion, corrosion, and coking. For SIS, ensure materials meet stringent reliability and longevity requirements in potentially harsh refinery environments.

Step 5: Plan for Installation and Accessibility

Ensure valves are installed in locations that allow for safe and efficient maintenance, calibration, and testing. Consider accessibility for personnel, lifting equipment, and alignment during installation. For critical valves, manifold designs might be beneficial for isolation and bypass during maintenance.

Step 6: Integrate with Instrumentation and Control Systems

Verify that the valve's instrumentation (positioner, switches) is correctly integrated with the control system or SIS logic solver. Ensure proper signal transmission, loop tuning parameters, and diagnostic capabilities are established to maintain system performance and safety.

Step 7: Establish Inspection, Testing, and Maintenance Protocols

Develop a robust plan for initial inspection and testing, including seat leakage tests and functional checks. Implement regular preventive maintenance schedules to ensure continued reliable operation. For SIS valves, periodic proof testing is critical to maintain the required Safety Integrity Level (SIL).

Common Pitfalls to Avoid

• • Undersizing or Oversizing: Selecting a valve that cannot adequately control the process or shut off flow, or one that is excessively large and leads to poor control at low flow rates, resulting in inefficient operation and potential damage.
• • Ignoring Process Conditions: Failing