Rail Terms

Base
The part of the rail lying below the web area, also referred to as the foot or flange.

Bleeding
Reddish-brown streak indicating internal rusting.

Bonds
Short wires used to bridge gaps in electrical circuits, usually at track circuit joints or between rails.

Break
A complete separation of one or more pieces of rail.

Broken rail
A term commonly used to describe any rail that has been completely broken through the entire rail section.

Cant
The angle of an individual rail relative to vertical. Rail is canted by the inclination of the tie plate in order to match the conical wheel profile. Cant is usually expressed as a rate of inclination, such as 1 in 40.

Cold work
Plastic deformation of the rail material at low temperatures. Also known as cold rolled.

Continuous welded rail (CWR)
Rail sections that are welded end-to-end into rail strings that result in a rail without rail joints, also referred to as welded rail or ribbon rail.

Corrugation
A series of wave-like variations of the rail head running surface, identified by an uneven head wear pattern.

Crack
A separation of metal extending partially, but not completely, through the rail section.

Creep
The longitudinal movement of rail produced by the passage of trains over it.

Defect
A term generally used to refer to an identifi able imperfection internal to the rail section or rail section geometrical surface.

Detected defect
A defective rail detected by a rail flaw detection (RFD) vehicle or visual means by the operator of a RFD vehicle.

Fatigue
Irreversible damage to a material caused by cyclic loading, normally leading to the formation of a crack.

Field side
The side of the rail head away from the wheel flange.

Flaking
Usually refers to small pieces of parent rail material becoming detached from the rail running surface - a type of minute spalling sometimes associated with a faulty manufacturing process.

Flaw
A general term often associated with cracks originating from rail defects.

Fracture
Usually the complete separation of one or more portions of the rail.

Gage corner
The smaller upper rail head radius region that makes contact with the flange of the wheel.

Gage side
The side of the rail head closest to the wheel flange.

Gage line
The location on the gage side of the rail head 5/8 inch below the rail tread that is used to establish track gauge.

Hairline crack
A fine and usually shallow crack.

Head checks
Transverse surface cracks on the gage corner of rails, resulting from cold working of the rail surface. Often these are controlled by preventive rail grinding.

Head-hardened rail
A rail that has only the rail head hardened to provide a harder steel for locations where excessive loading forces may increase head wear, such as the high side of a curve.

Heat
One batch of metal from a steelmaking furnace at the steel mill. All rails rolled from ingots or cast blocks from one heat.

Heat treatment
The process of altering the properties of the rail material by a specific heating and cooling process. Heat-treated rail is good in locations that require a rail section of higher strength and durability.

High carbon rail
A rail with extra carbon added during the manufacturing process to increase hardness.

Inclusion
An impurity, normally an oxide or a sulfide. The inclusion can be generated by the steelmaking process or by in-track thermite welding processes.

Lip
A length of material, usually towards the lower edge of the rail head, which as undergone severe plastic deformation to form a folded layer.

Nucleus
A term often used by metallurgists to refer to the origin or starting point of a defect.

Origin
The cause of a defect, the initial location of a defect, the point of initiation of a crack.

Outside joint area
The part of the rail that is not located within the prescribed confines of the “rail end.”

Percent size
Percentage of rail head cross-sectional area that is weakened by the defect (transverse defects only).

Piped rail
Term assigned to defects that originate from ingot casting procedures.

Pressure butt welding
A welding technique used to connect parts which are nearly parallel and don’t overlap.

Progressive fracture
Term usually used to describe the gradual propagation of a crack over a period of time.

Rail defect
May be a defect detected visually, ultrasonically, by other NDT methods, or may be exposed by an in-service rail failure that may render the rail unfit for normal operations.

Rail end
The part of the jointed rail covered by the angle bar or a similar linear length in welded rail. Rail flaw imperfections on the surface or interior of the rail section.

Rail failure
Rail that is broken while in service. An internal defect may be present. However, a rail failure can result from conditions other than an internal defect, e.g. load impact or stress failure.

Rail lip
A length of rail steel material that has undergone severe plastic deformation to form a folded layer overhanging at the lower corner of the rail head. This condition is typically found on the high side of curves.

Rail neutral axis
The point in the rail web where internal pressure is compressive (pushing) above and tensile (pulling) below during vertical loading of the rail section.

Rail neutral temperature
The rail temperature at which there are no axial thermal forces in the rail section.

Rail surface irregularities
Rail surface irregularity is deformation or damage to the running surface of a rail which can include flaking, spalling, shelling, corrugation, localized rail head surface collapse, and crushed head and crack-out under the rail head.

Rail wear
A reduction of the rail head as a result of abrasive action between the steel wheel on the steel rail.

Relayed rail
Worn, but still usable, rail taken from track and reused in another location (often referred to as secondhand or used rail).

Rolling contact fatigue
A form of rail fatigue originating primarily from cyclic loading in the wheel/rail interface zone.

Running surface
A longitudinal band on the rail head where the wheels make contact with the rail - also referred to as the “bright band” or “rail tread”.

Rupture
A synonym for fracture or break.

Seam
An internal rail longitudinal pocket that is inherent from the manufacturing process.

Section modulus
The bending strength of a particular rail section.

Segregation
A result of an improper steel manufacturing process that can be identified by a separated or partially separated steel microstructure, mostly associated with the rail web.

Service failure
An undetected rail that breaks in service.

Shatter crack
Discontinuous, internal cracks formed in steel due to stresses produced by localized transformation and decreased solubility of hydrogen during cooling after hot working.

Shelling
A term associated with cracks originating from sub-surface defects or at the rail running surface that can result in considerable dislodgment of the rail parent metal.

Slag
Fused glassy material that is produced when a metal is separated from its ore during smelting.

Spalling
A term used to refer to the dislodged parent material area of the rail head that results from rolling contact fatigue.

Streak
Dark line seen on the running surface of the rail head. Stress relief normally referred to as post-weld heat treatment.

Tangent track
Straight track. Thermal cracking
a rail defect identified as fine cracks across the rail head, caused by excessive heat generated at the wheel/rail interface.

Transposed rail
Rail that is removed from one side of the track to the other side, without turning the rail, so gauge and field sides are interchanged. Also known as turned rail.

Tread
Path of wheel contact with running surface of the rail. Work-hardened rail
Rail that has a hardness greater than when manufactured, as a result of the cold working of the steel by cyclical traffic loading.

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