It's the "Recommended Practice for Instrumentation and Control Systems for Fired Heaters and Steam Generators." It provides guidelines for safe and reliable burner management systems.
Disclaimer: This post is for informational purposes. Always refer to the latest official API publication for engineering decisions. api rp 556 pdf
Petroleum production units, refineries, and chemical processing plants. What is API RP 556
The document is structured to cover the complete lifecycle of fired heater systems, specifically: Target Facilities: Petroleum production units
Applies to gas-fired heaters but specifically excludes steam reformers, pyrolysis furnaces, and standard boilers .