of Terms : Metal Stringers : Bend Tube : Albina Pipe Bending Co., Inc.

Arc: The curved portion of a bend.
Arc Length: The length of a bent/rolled surface. Measured in feet and inches.

Backwall or Pipe Heel: The outer half or the half of the pipe undergoing tension during bending (see Extrados).
Bend Radius: The arc of the bend itself, usually taken at the centerline. The distance from the center of curvature to the center-line (axis) of the pipe, expressed as a number multiplied by the pipe or tube size. For example, the bend radius of a 5 x D bend for a 2-inch nominal pipe size (NPS) pipe or a 2-inch tube is 10 inches (see Center-Line Radius).
Bender: 1. A mechanical device capable of forming a bend in a straight length of material. 2. A commercial or industrial company engaged in the business of making bends.
Bending Moment: The amount of force, required to initiate a change of direction in a straight length of material about the center of curvature.
Bending Procedure: A written procedure containing all of the essential parameters and information necessary to guide the operator in producing bends.

Center to Center: The distance between the theoretical or calculated centers of two adjoining bends on the same plane. Also used for diametric measurement between the center lines of two tangent points of a bend (i.e. 180° bend, for which the Center to Center distance will be equal to twice the Center-Line Radius).
Center-Line Radius: The distance from the center of the curvature to the center-line (axis) of the pipe.
Chord: The straight distance measured between the centerline points of any two points of a bend.
Cold Bending: The bending of pipe or shapes by cold working methods.
Compression: The forces which thicken the inside wall of the bend.

Degree of Bend: The angle to which the bend is formed.
Diameter: A straight line passing through the center of a circle.
Distance Between Bends: The actual length of the straight section between the tangent points of two adjoining bends (see Tangent).
Distortion: A change from original shape and dimension. Note: Occurs in every rolled part to some degree.
Ductility: The ability of the material to deform without fracture. This is measured by elongation of reduction of area in a tensile test.

Elongation: The increase in length of material fibers during bending, expressed as a percentage of the original length.
Extrados: The outside arc of the bend (see Backwall).

Flat Plane: The deviation of the horizontal plane of a single bend between its tangent points, based on the theoretical center-line of the bend.
Flattening: The distortion of the cross section of pipe or tube from its normal (round) shape.

Minimum Wall Thickness: The wall thickness specified on the fabrication drawing or computed in accordance with the applicable specification as the minimum acceptable for temperature and pressure application.

Neutral Axis: The area where there is neither compression nor tension during bending.
Nominal: Usually refers to pipe sizes up to and including 12 inch. Also used in reference to wall thickness, generally as a "mean" or average measurement.

O.D.: Outside Diameter of the material.
Out of Plane: (see Flat Plane).
Ovality: The distortion of the cross section of pipe or tube from its normal (round) shape usually expressed as a percentage of the difference between major and minor axis (Pipe Fabrication Institute (PFI) Standard is 8%).

Plane of Bend (POB): Is referred as the rotation from a neutral axis. It is specifically used for changes of plane in successive bends.

Radius: A line segment that joins the center of a circle with any point on the materials circumference (see Center-Line Radius).

Tangent: Straight section of material on either side of the bend or arc. May be any length. Notes: In order to make the bend itself, there has to be sufficient material at each end during the bending process. Excess may be trimmed after.
Tangent Point: The point at which the bend is started or ended.
Tensile Strength: The strength of material stretched to the point at which it will rupture.
Throat: The inner half of the pipe or the half undergoing compression during bending (see Intrados).

Wall: The thickness of tubular material, usually expressed as "nominal" or "minimum".
Wall Thickness: The thickness of the material usually stated in "schedule" for pipe or "guage" for tube.
Wall Thinning: The amount of reduction from original wall thickness of pipe or tube to the amount of wall thickness remaining in the extrados of a bend after forming (see Extrados).
Wrinkles: Definite folds, creases or ripples formed on the surface of the pipe during bending operation.

Yield Point: The point at which material will deform permanently during bending.
Yield Strength: The stress at which a material exhibits a specified deviation.

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Glossary of Terms