Api Rp 556 Pdf __full__ May 2026

API RP 556, “Instrumentation, Control, and Protective Systems for Gas-Fired Heaters” (2nd ed., 2011; reaffirmed R2024), is an industry recommended practice that consolidates best practices for measuring, controlling, alarming, and protecting fired heaters and related steam-generation equipment in refineries and hydrocarbon-processing plants. It fills the gap between heater mechanical design documents and plant-level control/safety philosophies by describing practical instrumentation arrangements, control strategies, alarm/shutdown criteria, and commissioning/maintenance considerations specific to gas-fired heater service.