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).
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).
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.
Hot Bending- The bending of pipe or shapes through hot methods.
Hump- A rounded bulge on the backwall or heel of the material.
I.D.- Inside Diameter of the material.
Intrados- The inside arc of the bend.
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).
Slope- Is calculated as the rise/run of a segment.
Springback- Memory of the material to return to its original condition.
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.