Arc- Part of the circumference of a curve. The curved portion of a bend.
Arc Length- The curved distance along a circumferential line. The length of the curved portion of a member.
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 between two points on a curve.
Cold Bending- Any bending process where curvature is induced by load application at room temperature.
Compound Bend- A curve made up of two or more arcs in the same plane, joined tangentially without reverse curvature.
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 deviation from the original cross section shape.
Ductility- The ability of the material to deform without fracture. This is measured by elongation of reduction of area in a tensile test.
Easy-Way- The orientation of a member relative to the plane of curvature where bending occurs about the weak principal axis.
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).
Flattening- The distortion of the cross section of pipe or tube from its normal (round) shape.
Gag Pressing- A cold bending method that uses hydraulic rams to simultaneously apply bending forces at discrete, widely-spaced, locations along the member. Also known as point-bending.
Hard-Way- The orientation of a member relative to the plane of curvature where bending occurs about the strong principal axis.
Hot Bending- Any bending process where curvature is induced by load application at an elevated temperature.
Hump- A rounded bulge on the backwall or heel of the material.
I.D.- Inside Diameter of the material.
Incremental Step Bending- A cold-bending method that uses hydraulic rams to apply bending forces at several discrete, closely-spaced, locations along the member.
Induction Bending- A hot-bending method that utilizes an electric induction coil to heat a short section of the member before it is curved by force.
In-Plane Flexure- Bending a curved member where moment is applied about the axis of curvature. The primary flexural stresses and deflections are in the plane of curvature.
Intrados- The inside arc of the bend.
A type of potential cross-sectional distortion that is caused by compression stresses in the member induced during the bending operation.
Local buckling can be in the form of a single half-wave or a series of wrinkles along the entire bend length.
Mandrel- A tool that can be inserted into a HSS member to support the walls and minimize cross-sectional distortion during the bending process.
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.
Multi-Axis Bend- A bend with curvature about more than one axis. Also known as a multi-plane bend.
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.
Normalizing- A thermal treatment where the member is heated to a suitable temperature above the upper transformation temperature, followed by cooling in still air room temperature.
O.D.- Outside Diameter of the material.
Off-Axis Bend- A bending orientation where the member is curved about a non-principal or non-geometric axis. Also known as conical rolling.
Out of Plane Flexure- Bending of a curved member where moment is applied in the plane of curvature. The primary flexural stresses and deflections are in perpendicular to the plane of curvature.
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.
Pyramid Roll Bending- A cold-bending operation where a member is bent progressively by repeatedly passing it through a set of three adjustable rolls in pyramid arrangement.
Radius- A line segment that joins the center of a circle with any point on the materials circumference (see Center-Line Radius).
Reverse Compound Bend- A curve made up of two or more arcs in the same plane, joined tangentially with reversal of curvature. Also know as an s-curve or an offset bend.
Rise- The distance, perpendicular to the chord, between the mid-point of a chord and an arc. Also known as the mid-ordinate.
Rotary Draw Bending- A bending method where the member is clamped to a form and bent by rotating it around a bend die with a given radius.
Slope- The angle of an inclined member designated using the vertical (rise) and the horizontal (run) distances between two points. Also known as bevel or pitch.
Spiral- A three-dimensional curve with an arc in one plane and a constant slope in a perpendicular plane. Also known as helix, or helical curve. The curving process is often called sloped rolling or pitched rolling.
Springback- The deformation of a bent member immediately after a bending load is released, where a portion of the curvature is partially lost.
Synchronized Incremental Cold Bending- A bending process where pressure is applied in a highly synchronized fashion at several locations along the steel member.
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).
Variable-Radius Bend- Parabolic, elliptical and other non-circular bends with variable radii. Also known as multi-radius and non-circular bends.
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.