"Industrial systems, installations and equipment and industrial products – Structuring principles and reference designations," this standard is what’s known as a horizontal standard
What is the object doing? (e.g., "The cooling system") iec 61346-1 pdf
Many factories and power plants built in the late 90s and early 2000s were designed strictly according to IEC 61346. Maintenance Documentation: iec 61346-1 pdf