Integrity Circuit

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.

A specific process or phenomenon that causes degradation of material properties, leading to eventual failure of equipment. Damage mechanisms include corrosion (uniform, localized, galvanic), erosion, fatigue, creep, hydrogen damage, stress corrosion cracking, embrittlement, and other metallurgical or environmental attack modes. API 571 catalogues over 60 damage mechanisms relevant to refining and petrochemical equipment.

The comprehensive plan that defines what to inspect, how to inspect, when to inspect, and what to look for on each equipment item. An inspection strategy integrates the RBI risk ranking, the identified damage mechanisms, the appropriate NDE techniques, the CML locations, the inspection interval, and the acceptance criteria into a coherent plan that can be executed in the field.

A methodology that uses risk assessment to prioritize and plan inspection activities for pressurized and other equipment. RBI combines Probability of Failure (driven by damage mechanisms and equipment condition) with Consequence of Failure (driven by process hazards and safety impact) to rank equipment by risk and allocate inspection resources where they will have the greatest impact on risk reduction.