RP 580 is a recommended practice document that is aimed at providing guidelines for risk-based inspection (RBI) of fixed equipment in the petroleum and chemical process industries. The primary audience for RP 580 includes both inspection and materials engineering personnel because these professionals are integral to implementing and managing risk-based inspection programs. Inspection personnel are responsible for executing the inspections and assessments, while materials engineering personnel bring expertise in the materials, corrosion, and degradation mechanisms affecting the equipment. Therefore, the correct answer is 'Inspection and materials engineering personnel'.