What are the common lengths of rails?

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What are the common lengths of rails?

July 18, 2019, 2:31 PM

The most common length for BG rails is 13m (42’8”) although double-length rails (26m, 85’4”) are seen in some places. MG rails are usually 12m (39’4”) in length. NG rails vary, but the commonest length is 9m (29’6”). Much earlier (before the metric system was adopted!), rails were generally produced in sizes of 11, 12, or 14 yards (33′, 36′, 42′), less commonly 13 yards (39′) or 10 yards (30′ – NG).

Welded rail sections are of two types: Short Welded Rail or SWR which consists of just two or three rails welded together, and Long Welded Rail or LWR which covers anything longer. (In the past, there was a distinction made between LWR and Continuously Welded Rail, or CWR, based on the length — in CWR, the total length was 0.75km or more. The term ‘CWR’ is no longer used although you may still find it in old documents or painted signs.)

LWR is typically any length larger than twice the breathing length, which is the length allowed at the end of the welded rail section which is free to expand or contract as the temperature changes. (Beyond the breathing length, the rails do not move because of the resistance of the fasteners and the sleepers and ballast.) The breathing length varies with the temperature range, the sleepers, and the type of rails, but is typically 10m or less with concrete or steel sleepers. The expansion range of the rails is reduced with the steels of higher tensile strength, such as the 90UTS and 110UTS steels, allowing longer welded sections to be built.

With welded sections, the maintenance and safety problems of having rail joints with fishplates, etc., are reduced, but welded rail also calls for more precise provisioning of destressing/pretensioning to account for thermal expansion, etc. SWR with three-rail welded panels results in 28-30 fishplated joints over the distance of a kilometer, which is the source of the commonly heard (and beloved of railfans) clackety-clack rhythm of the wheels.

LWR is usually formed from panels of 10-rail or 20-rail length welded using flash butt welding at specialized plants (Meerut, Gonda, etc.). The welded rails are transported on special rail flat wagons which have end unloading chutes. LWR and CWR are also formed by in situ welding of the rails using alumino-thermic welding (also known as thermite (thermit) welding). In this, the highly exothermic reaction of aluminium with ferric oxide (provided as a paste called thermite) results in temperatures of around 2500C and the reduction of the ferric oxide to elemental molten iron that then helps form a weld. More details on thermit welding here. Also see the item below on welding.

There have been proposals from some rail manufacturers to supply long rails (65m, 78m) to reduce the number of welds required for LWR/CWR. Bhilai Steel Plant makes 80m rails as its basic design at the plant, however, usually these are cut to form the 13m and 26m rails to allow proper degassing and controlled cooling. Initially, only 13m rails could be produced — Bhilai Steel Plant was unable to make rails to the right specifications at longer lengths, and IR also did not have facilities for transporting longer rails. An experiment in the mid-1990s to produce 26m rails was unsuccessful. However, more recently, rail production technology has improved, and longer rails can be produced by Bhilai Steel Plant with the requisite low levels of hydrogen gas and conformance to other specifications. Lengths of 78m have been supplied from September 2004, and more recently some 130m rails have been supplied to IR.

[2003] The Steel Authority of India Ltd. (SAIL) will be producing, at the Bhilai plant, extra-long pre-welded rail panels (260m long, which is 10x the length of normal rails, and also 240m panels — this is a convenient multiple of the 80m manufactured length of rails from the Bhilai plant). [2/09] The Bhilai Steel Plant began supplying these 260m rails in February of 2009.

Source – IFRCA.org

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