Glossary of Terms

A

Arc- The curved portion of a bend.

Arc Length- The length of a bent/rolled surface. Measured in feet and inches.

B

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.

C

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.

D

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.

E

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).

F

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.

H

Hot Bending- The bending of pipe or shapes through hot methods.

Hump- A rounded bulge on the backwall or heel of the material.

I

I.D.- Inside Diameter of the material.

Intrados- The inside arc of the bend.

M

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.

N

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

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%).

P

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

R

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

S

Slope- Is calculated as the rise/run of a segment.

Springback- Memory of the material to return to its original condition.

T

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).

W

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.

Y

Yield Point- The point at which material will deform permanently during bending.

Yield Strength- The stress at which a material exhibits a specified deviation.