API 579-1/ASME FFS-1(API 579)

An engineering assessment methodology used to determine whether equipment with identified flaws, damage, or degradation can continue to operate safely and reliably for a defined future period. FFS evaluations quantify the remaining structural capacity of degraded equipment using the procedures in API 579-1/ASME FFS-1, considering the specific type and extent of damage relative to the design margins.

The estimated time from the present until an equipment item reaches a condition where it can no longer perform its intended function safely and must be repaired, replaced, or retired. For static equipment, RUL is typically calculated from the current measured wall thickness, the minimum required thickness, and the corrosion rate. For rotating equipment, RUL may be estimated from degradation models fitted to condition monitoring data.

The minimum wall thickness required by the applicable design code to safely contain the operating pressure at the design temperature, considering the allowable stress of the material, weld joint efficiency, and applicable code margins. This is the absolute minimum thickness for pressure containment — below this value, the equipment exceeds its design basis and must be retired, repaired, or de-rated.

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.

Piping Inspection Code — provides requirements for the inspection, repair, alteration, and rerating of in-service metallic and fiberglass-reinforced plastic piping systems. It covers inspection practices for maintaining the mechanical integrity of process piping, including determination of corrosion rates, remaining life, and inspection intervals.