API 570 key terms

An assembly of interconnected piping components-pipe, fittings, flanges, bolting, gaskets, valves, and the pressure-containing parts of other components-that shares the same design and operating conditions and can be isolated as a unit.

A section of a piping system that shares common characteristics such as material, service, and operating conditions, so that a single representative set of monitoring locations and one corrosion rate can be applied to the whole section.

The organization that owns or operates the piping system and is responsible for its safe operation, including setting inspection intervals, providing qualified inspectors, and approving repairs and alterations.

A person employed by the owner/user or by an authorized inspection agency who is certified under the API 570 program, or otherwise qualified to the satisfaction of the jurisdiction, and assigned to inspect piping systems.

An organization acceptable to the jurisdiction, such as an insurer's inspection department or a recognized inspection body, that supplies qualified inspection personnel and services to the owner/user.

The governmental or regulatory authority that has adopted the inspection code and holds legal responsibility for enforcing its requirements at a particular facility or location.

Any person or company that performs repairs, alterations, or rerating of piping, and that must be acceptable to the owner/user and work under an approved quality system with qualified procedures and personnel.

The speed at which wall thickness is lost to corrosion or erosion, usually expressed in mils per year or millimeters per year and calculated by dividing measured thickness loss by the elapsed time between measurements.

Extra wall thickness provided beyond the thickness needed to contain pressure, so that expected deterioration during service can occur before a component reaches its retirement thickness.

External corrosion of piping beneath insulation or fireproofing, most often on carbon steel operating roughly between 10 degrees F and 350 degrees F, where moisture can enter and remain trapped against the metal.

Cracking produced by the combined action of sustained tensile stress and a specific corrosive environment, such as chlorides acting on austenitic stainless steel, often with little or no visible metal loss.

A location where chemicals, water, or another stream is injected into or mixed with the main process flow, creating locally higher corrosivity that normally calls for closer inspection and dedicated monitoring locations.

A portion of piping that normally carries no flow, such as an unused branch or bypass, allowing corrosive fluids to stagnate and concentrate and making the area prone to accelerated localized attack.

Accelerated metal loss caused by flowing fluid wearing away protective oxide scale while fresh metal underneath continues to corrode, typically found at elbows, tees, reducers, and downstream of control valves.

Slow, time-dependent permanent deformation of metal held under sustained stress at elevated temperature, which can lead to bulging, cracking, or rupture in high-temperature piping services.

Progressive cracking caused by repeated or cyclic stresses such as vibration, thermal cycling, or pressure swings, which initiate and grow cracks at welds and other stress concentrations.

The highest internal pressure permitted at the design temperature for a piping system, established so that the allowable stress of the weakest component in the system is not exceeded.

Work required to restore a piping system to a safe operating condition that does not amount to an alteration, such as replacing a corroded section with like material, weld buildup, or patching.

A physical change in a piping system that affects its pressure-containing capability or design conditions and is not a replacement in kind, such as changing line size, adding a branch, or changing material.

A change to the pressure or temperature limits of an existing piping system, or to its service fluid, carried out through engineering evaluation and documented so the system stays safe at the new conditions.

Replacement of a component with another of the same configuration, pressure rating, and material, requiring no design change and therefore not treated as an alteration.

The maximum time permitted between inspections of a piping system, set by the owner/user from corrosion rate, remaining life, service risk, and any limits imposed by the code or jurisdiction.

The estimated time a component can continue operating at current conditions before its wall thickness reaches the retirement thickness, calculated by dividing usable thickness by the corrosion rate.

The wall thickness at which a piping component is considered unfit for continued service and must be rerated, repaired, or replaced, normally taken as the minimum required thickness calculated for the design conditions.

The thinnest wall that can safely contain the design pressure at design temperature, computed from pressure, diameter, allowable stress, and the weld joint and corrosion allowances required by the applicable code.

A structured method of prioritizing and scheduling inspection according to the likelihood and consequence of failure, so that inspection effort is concentrated where risk is highest.

A designated step in a repair or inspection activity at which work must stop so the authorized inspector can examine and approve the work before the job is allowed to continue.

A pressure test in which piping is filled with water or another liquid and pressurized above its operating pressure to verify strength and leak tightness before being returned to service.

Inspection methods such as ultrasonic, radiographic, magnetic particle, liquid penetrant, and visual testing that reveal flaws, cracks, or thickness loss without damaging the component being examined.

A technique that determines remaining wall thickness by timing sound pulses reflected from the far surface or an internal interface, providing data used to calculate corrosion rates and remaining life.

A specific point or area on a piping circuit designated for repeated thickness measurements or other examination, selected because it is expected to represent the worst deterioration in that circuit.

Inspection carried out while the piping system remains in operation, using external visual checks, thickness measurements, and other nonintrusive techniques without shutting down or opening the system.

Examination of the inside surfaces of piping, normally performed during a shutdown when the system is opened, cleaned, and inspected visually or by nondestructive methods.

Examination of the outside of piping, insulation, supports, and appurtenances to find leaks, corrosion, coating damage, misalignment, vibration, and hot spots while the system is operating.

A device such as a relief valve, rupture disk, or rupture pin installed to protect piping and equipment from overpressure by relieving fluid when the set pressure is reached.

A drawing showing the piping, equipment, valves, instruments, and control loops of a process, used as a reference for tracing lines, identifying boundaries, and planning inspections.

Documented results of inspections, including measurements, findings, calculated corrosion rates, remaining life, and recommendations, kept for the life of the system and used to plan future inspection intervals.

A pictorial drawing of a single piping line showing its routing, fittings, valves, and coordinates, commonly used to identify inspection locations, define repair scope, and record line configuration.