long-welded
Of rails for railway track, welded into longer lengths, usually before they are laid, to help eliminate jointed track.
long-welded: rails fused into continuous lengths before installation
Long-welded rail is ordinary steel rail that has been joined end-to-end by welding, rather than bolted together with fishplates and bolts at joints. Standard rail sections arrive at the plant in lengths of 12 to 13 metres. These are thermit-welded or electric-arc-welded into continuous strings of 200 to 500 metres or longer before being transported to the track and laid in position. The result is rail with far fewer mechanical joints per kilometre of track.
The advantage lies in ride quality and maintenance. Each bolted joint creates a discrete weak point where rail ends can move independently, causing the characteristic clacking sound on jointed track and accelerating wear in wheels, axleboxes, and the track bed itself. Long-welded rail, laid in continuous stretches, distributes loads more evenly and eliminates hundreds of these stress concentrations. Modern mainline railways almost universally prefer it.
Thermal stress and restraint
The major challenge with long-welded rail is thermal expansion and contraction. A 300-metre continuous rail will expand and contract by roughly 300 to 450 millimetres across a seasonal temperature swing of 60 degrees Celsius. If the rail is rigidly held at both ends, internal stress builds to dangerous levels. Track must be laid with some degree of freedom, using elastic fastenings and careful attention to neutral temperature, the temperature at which the rail is held mechanically neutral so that it can move slightly under thermal stress.
If restraint is insufficient, the rail may buckle sideways on a hot day, a failure mode called sun kink. If restraint is excessive, the rail can fracture in cold weather. Modern practice uses elasticated clips and pandrol fastenings that allow controlled lateral and longitudinal movement, calibrated to the prevailing season and geography.
Quality of the welds is critical. Weld defects, inclusions, or poor penetration become stress concentrators themselves and can trigger fatigue fractures. Rail is typically ultrasonically inspected after welding to detect internal flaws. Long-welded rail also demands better ballast quality and more frequent tamping than jointed track, because the continuous structure is less forgiving of uneven support.