NBBI Pressure Equipment Inspector (PEI) key terms

The highest internal pressure permitted at the coincident temperature specified for a boiler or pressure vessel, set by the original design or by a later rerating calculation accepted by the inspector.

The pressure used when sizing shell thickness, heads, and reinforcement during original construction; it must equal or exceed the maximum allowable working pressure under all expected operating conditions.

The lowest temperature at which a vessel may operate without risking brittle fracture, considering material toughness, thickness, and stress; impact testing requirements depend on it.

Extra thickness added to a component during design so that expected metal loss from corrosion or erosion over the service life will not reduce the wall below the minimum required thickness.

The least wall thickness that satisfies the applicable construction formula for pressure, plus corrosion allowance and any structural minimums; measured thickness must be compared against it during inspection.

A factor between 0 and 1 applied in shell and head formulas to account for the strength of a welded or riveted joint relative to seamless plate, based on joint type and extent of radiographic examination.

A pressure test using water or another liquid, typically held at a specified multiple of MAWP for a set time, to demonstrate structural integrity and tightness before initial service or after certain repairs.

A pressure test using air or another gas, permitted only where hydrostatic testing is impractical and with added safeguards such as remote gauging and exclusion zones because of stored energy and rupture risk.

The inlet pressure at which a pressure relief valve begins to open under operating conditions, established so the valve protects the equipment at or below its maximum allowable working pressure.

The pressure increase above maximum allowable working pressure permitted during relief device operation, usually expressed as a percentage and dependent on whether one or several devices are installed.

A device that automatically opens to discharge fluid when inlet pressure reaches its set point, then recloses to protect a boiler or vessel from overpressure during operation or fire exposure.

Flat or curved plate area of a boiler supported against pressure by stays, tubes, or ligaments; its thickness and stay spacing are governed by staybolt pitch and stress limits.

A threaded rod passing through and connecting opposite plates of a stayed surface, carrying tension to hold the plates at a fixed spacing against internal pressure.

The narrowest strip of plate remaining between adjacent openings, such as tube holes or staybolt holes, whose width determines the efficiency and stress in that region.

A notched-bar test, commonly Charpy V-notch, that measures a material's resistance to brittle fracture at a specified temperature and is required for certain materials, thicknesses, or low-temperature service.

Sudden failure with little plastic deformation, occurring when a combination of low temperature, high stress, thickness, and low-toughness material causes a crack to propagate rapidly through the component.

Piping carrying steam or water that is part of the boiler boundary and subject to boiler code rules, extending from defined connection points to the first valve or specified limit.

The code published by the National Board that governs in-service inspection, repair, alteration, and rerating of boilers and pressure vessels, and the accreditation of organizations performing that work.

A commissioned inspector holding a National Board commission who performs inspections required by the code and applicable jurisdiction, and who signs data reports to attest compliance.

A credential issued by the National Board after examination and experience requirements, authorizing an individual to act as an inspector for in-service, repair, and alteration work under the code.

Work that restores a boiler or pressure vessel to a safe condition without changing its design parameters, such as weld build-up, patch replacement, or tube replacement, and that requires documentation.

A change to a boiler or pressure vessel that affects its pressure-retaining capability, design temperature, or other design parameters, requiring engineering review and code-compliant documentation.

Changing the maximum allowable working pressure or temperature of existing equipment based on engineering calculations and inspection, with new nameplate marking and revised documentation.

A form, such as the NB-2 or R-1 series, on which the inspector and the performing organization record the scope of work, code compliance, and signatures for repairs, alterations, or new construction.

The form completed by the original manufacturer at construction, listing design data, materials, and test results, and serving as the baseline document for later inspection and repair records.

The permanent marking attached to a boiler or pressure vessel that shows the manufacturer, serial number, design pressure and temperature, capacity, and code stamp information.

A stamp applied to a nameplate or component indicating that the item was built, repaired, or altered under an accredited program and conforms to the applicable code rules.

The National Board symbol stamp issued to an accredited organization authorized to perform repairs and alterations to pressure-retaining items under the code.

National Board review and approval of an organization's quality system, facilities, and personnel, granting authority to hold a symbol stamp and perform covered work.

A written document describing an organization's procedures, responsibilities, and controls for code work, reviewed and accepted by the National Board as part of accreditation.

Filing of construction or repair documentation, including data reports, with the jurisdiction and the National Board so that the equipment is recorded in official records.

A nondestructive method using high-frequency sound to measure remaining wall thickness, commonly used to evaluate corrosion and erosion against minimum required thickness.

An estimate of how long a component can continue in service, based on measured thickness, corrosion rate, and minimum required thickness, used to set inspection intervals.

The time between required inspections, established by the jurisdiction or by risk-based and condition-based assessments, and shortened when corrosion rates or damage are significant.

A nondestructive method using penetrating radiation to reveal internal discontinuities in welds and castings; the extent of examination affects joint efficiency in design formulas.

Radiographic examination of the complete length of a weld joint, permitting the highest joint efficiency for that joint type in design calculations.

A test that demonstrates a component's ability to withstand a specified load or pressure, often used for unique or nonstandard items where design formulas alone cannot establish adequacy.

The governmental authority, such as a state or province, that adopts boiler and pressure vessel laws and regulations and may impose requirements in addition to the national code.