API 570

Pressure Vessel Inspection Code — covers in-service inspection, repair, alteration, and rerating of pressure vessels. It establishes requirements for maintaining the integrity of pressure vessels after they have been placed in service, including inspection intervals based on corrosion rates and remaining life calculations.

The rate of material loss due to corrosion or erosion, typically expressed in millimeters per year (mm/yr) or mils per year (mpy). Short-term corrosion rate is calculated between the two most recent thickness measurements; long-term corrosion rate is calculated from the original (or earliest) thickness to the most recent measurement. The more conservative (higher) rate is typically used for remaining life calculations.

The calculated time until the wall thickness at a CML or the minimum measured thickness on a component reaches the retirement thickness, based on the current measured thickness and the applicable corrosion rate. Remaining life is the inspection-data-driven equivalent of Remaining Useful Life (RUL), specifically calculated from thickness data for static equipment.

A group of equipment items and piping segments that are exposed to the same process environment and are therefore expected to experience the same corrosion or degradation mechanisms at similar rates. Corrosion circuits (also called corrosion loops or integrity circuits) group equipment for efficient inspection planning — representative CMLs in the circuit can provide condition data applicable to all items in the circuit.

Process Piping Code — prescribes requirements for materials, design, fabrication, assembly, erection, examination, inspection, and testing of piping systems for process plants, including refineries, chemical plants, pharmaceutical operations, and related processing installations. It covers pipe, fittings, flanges, bolting, gaskets, valves, and pressure-relieving devices.