NCCER Pipefitter key terms

A standard size designation for pipe that is used for reference but does not exactly match any actual dimension; for sizes 14 inches and larger it equals the outside diameter.

The measured distance across the outer surface of a pipe through its center; used with wall thickness to calculate the true inside dimension of the pipe.

The measured distance across the inner bore of a pipe through its center; it equals the outside diameter minus twice the wall thickness.

A standardized designation that groups pipe wall thicknesses for a given nominal size, with higher schedule numbers indicating thicker walls and greater pressure ratings.

The thickness of the pipe metal between the inner and outer surfaces, usually stated in thousandths of an inch or as a decimal fraction; it determines pressure capacity.

A designation identifying the material strength and composition of metal pipe, such as A106 Grade B carbon steel, which affects allowable pressure and welding requirements.

The maximum internal pressure a pipe, fitting, or valve is designed to withstand under stated temperature and service conditions without failure or permanent deformation.

A component such as an elbow, tee, reducer, or coupling used to connect pipe sections, change direction, branch flow, or alter pipe size within a piping system.

A fitting that changes the direction of a pipeline, commonly available in 45-degree and 90-degree configurations, with long-radius and short-radius variations affecting flow resistance.

A fitting with three openings that branches flow from a main run into a perpendicular outlet; equal tees keep the same size while reducing tees change the branch size.

A fitting that connects two pipes of different nominal sizes, either concentrically or eccentrically, to transition the line to a smaller or larger diameter.

A ring-shaped fitting attached to pipe ends to allow bolted connections to valves, equipment, or other pipe sections, commonly classified by facing type and pressure class.

The machined surface of a flange that contacts the gasket, such as raised face, flat face, or ring-type joint, and must match the mating flange for a proper seal.

A sealing material placed between flange faces or other mating surfaces to prevent leakage of fluids or gases under pressure and temperature changes.

A joint type in which two pipe ends are aligned and joined by a full-penetration weld around the circumference, providing strong, leak-resistant connections for high-pressure service.

A joint type in which the pipe is inserted into a recessed socket in a fitting or flange and fillet-welded around the outside, commonly used on smaller-diameter, high-pressure lines.

The angled edge machined on a pipe end to allow full penetration during a butt weld; the bevel angle and root face must meet the applicable specification.

The small space left between the beveled ends of two pipes before welding, which allows the root pass to penetrate fully and fuse both pipe walls.

The first weld bead deposited in a multi-pass joint, made at the root of the groove to fuse the pipe ends and form the foundation for subsequent passes.

A weld of roughly triangular cross section joining two surfaces that meet at an angle, commonly used for socket welds and attaching flanges or branches.

A pictorial piping drawing that shows the layout in three dimensions, including pipe sizes, fittings, valves, dimensions, and flow direction, used for fabrication and installation.

A schematic drawing that shows the functional relationships of piping, equipment, instruments, and controls in a process system, using standard symbols and line types.

A prefabricated section of pipe with fittings and flanges assembled off-site or in a shop, sized for transport and later joined to other spools in the field.

A weld made at the installation site rather than in a fabrication shop, typically joining spools or connecting piping to equipment and often marked on drawings.

An identifying code on piping drawings that specifies size, service, sequence, material class, and insulation, allowing the fitter to trace a line through the system.

The distance a fitting extends along the pipe, measured from the centerline or face to the end of the fitting, subtracted from center-to-center dimensions when calculating pipe lengths.

The measured distance between the centerlines of two fittings or pipe runs; take-outs are subtracted from it to determine the actual length of straight pipe needed.

In an offset layout, the diagonal distance between two points measured along the angled pipe, calculated from the offset and the fitting angle using trigonometric relationships.

A piping configuration that changes the line's elevation or horizontal position and then returns it to a parallel path, commonly built with two elbows and a connecting pipe.

An offset that changes both elevation and horizontal direction at once, requiring the fitter to calculate true lengths using the combined rise, run, and fitting angle.

A device such as a hanger, shoe, or anchor that carries pipe weight, controls movement, and maintains spacing; support type must match the design's thermal and load requirements.

A support that suspends pipe from above using rods, clamps, or springs, allowing controlled vertical movement while carrying the weight of the pipe and its contents.

A rigid support that restrains pipe movement in one or more directions, used to control thermal expansion and direct movement toward expansion loops or joints.

A deliberate bend or loop built into a piping system to absorb thermal expansion and contraction, preventing excessive stress on anchors, equipment, and joints.

A pressure test in which a piping system is filled with water and pressurized above its design pressure to verify strength and check for leaks before service.

The field practice of pressure-testing a completed piping system with liquid, typically water, held at a specified pressure for a set duration while joints are inspected for leakage.

The process of cutting tapered external threads on pipe ends, usually with a die head, so they can be joined to threaded fittings and valves with sealant applied.

A standardized tapered thread cut on pipe ends and fittings, such as NPT, that tightens and seals as it is engaged, with sealant or tape used on the threads.