Rail Head Wear, Combined Limit, and Tonnage to Replacement

Vertical wear reduces the section and the bending strength, and it lowers the running surface relative to the joint bars and the fastenings. Gauge face wear is the more consequential one on a curve: as the high rail's gauge face wears back, the track gauge widens and the contact geometry between wheel flange and rail moves toward the angle at which a flange can climb. That is why the common combined criterion weights the two together, vertical plus half the gauge face, rather than treating either alone. A 136 lb high rail measured with a wear gauge at 6/16 in vertical and 8/16 in gauge face gives 10/16 in combined against a 12/16 in railroad limit -- inside, with 2/16 in left. Then comes the half that turns an inspection into a program: if that curve wore 10/16 in over 180 MGT, the rate is 0.0035 in per MGT and the remaining 0.125 in is about 36 MGT, which on a route handling 30 MGT a year is a little over a year. That is a budget line and a rail order rather than an emergency, and it is visible only because the wear was measured twice. The measurement is a comparison against the NEW rail section, not against a nominal dimension, so the original weight and section have to be known, and wear rates differ enormously between the high and low rail of a curve and between curves and tangent. Wear limits are railroad-specific and vary by section, class of track, curvature, and traffic, the combined-wear formula itself differs between railroads, and the head-area figure here is a rectangular screen rather than a section property. It does not evaluate the many other conditions that condemn rail independently of wear: internal defects found by ultrasonic testing, shelling, spalling, head checks and squats, corrugation, engine burns, batter at joints, bolt hole cracks, and broken or defective welds -- most rail is removed for one of those rather than for wear. It does not measure gauge, which is a separate geometry parameter with its own limits, and it does not assess remaining bending strength under a specific axle load. The FRA Track Safety Standards at 49 CFR 213, the railroad's engineering instructions, and the track owner govern.

combined wear = vertical + gauge face / 2; remaining = entered limit - combined; head area removed (rectangular screen) = vertical x head width + gauge face x (head height - vertical), over the new head area; wear rate = combined / tonnage since installation; tonnage to the limit = remaining / rate.

The vertical and gauge-face wear criteria and the common combined form, by name, with 49 CFR 213 and the track owner's engineering instructions named as the source of the limits. The limits are entered because they are railroad-specific. The track owner governs.

Arithmetic on the user's own wear-gauge readings against a limit they supply; no railroad's wear-limit table is reproduced.

Estimate. AHJ and licensed professional govern.

Field names used by the API: new_head_height_in, new_head_width_in, new_head_area_in2, vertical_wear_in, gauge_face_wear_in, combined_limit_in, tonnage_mgt, combined_wear_in, remaining_in, wear_rate_in_per_mgt, remaining_mgt

• Gauge face is weighted at half the common combined form is vertical + gauge face / 2, but the formula differs between railroadstrack owner engineering instructions
• Measured against the new section not against a nominal dimension; the original weight and section must be knownrail wear gauge practice
• Wear is not the usual reason rail is removed internal and surface defects and defective welds condemn far more rail than wear does49 CFR 213