FRA Track Inspector Rail Defect Reference Manual July 2015
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The rail web is branded at least every 16 feet, and the branding will consist of the following information:• Weight per every 3 feet of rail: two- or three-digit number• Section: two-letter code• Type of process used for hydrogen elimination: two-letter code• Manufacturer: spelled out, letter code, or symbol• Year rolled: four-digit number• Month rolled: lines or roman numerals
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The web of each rail is “hot stamped” at least every 16 feet on the opposite side as the branding and should not be within a 2-foot proximity of a rail end. The data will contain the following information:• Heat Number• Rail Position Letter• Ingot or Strand/Bloom Number• Method of Hydrogen Elimination (Optional)
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The most common method in North American steel is controlled cooling. The methods used are identified by the following:• CC – Control Cooled• BC – Bloom Cooled• VT – Vacuum Treated• HH – Head Hardened• OH – Open Hearth Method
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Rail manufacturing can be grouped into four stages. They are (1) the production of molten steel from the necessary raw materials; (2) the casting of the liquid to form ingots or continuously cast blooms; (3) the rolling process to form cross sections of rail; and (4) finishing, which consists of cooling, straightening, cutting to the desired length, and final inspection
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Track maintenance programs – Track maintenance programs consist of any track maintenance procedure that can ensure the track can maintain adequate support to reduce the amount of rail flexing, provide proper friction control, and provide rail profile maintenance that will considerably influence the rail service life
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Wear – Lateral wear occurs primarily on the gauge face when the rail is located on the high side of a curve from the presence of high-wheel flange force. Vertical wear occurs on the rail head running surface from the wheel/rail interaction during cyclical loading and rail grinding patterns
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Plastic flow – Plastic flow or mechanical deformation of the rail head can occur on high or low rail, and is normally associated in curves that carry higher axle load operations. Plastic flow is a result of wheel/rail contact stress that is exceeding the material strength of the rail steel.
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Rail defects – Rail defects develop in any type of rail, or rail welds, as a result of several conditions. These conditions normally will originate from the rail manufacturing process; cyclical loading; and impact from rolling stock, rail wear, and plastic flow.
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Listed below is terminology that can be used to describe the planes of stresses in rail:• Vertical Plane – stresses progressing in a longitudinal direction normal to rail length• Horizontal Plane – stresses progressing horizontally along the rail• Transverse Plane – stresses progressing transversely along the cross section of the rail
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They are normally characterized into three components referred to as static load, dynamic load, and impact load
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Static load is the equivalent to the gross weight of the railcar divided by the number of wheels (i.e., 160-ton railcar with 8 wheels has a static load of 20 tons). The static loading can be influenced by track curve super-elevation.
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Dynamic loading is the increase of static load that results from train speed. This is a result of vertical dynamics associated with the car truck interaction with the track geometry.
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Impact loading is the additional increased loading over static and dynamic that occurs when a wheel travels over a significant rail head irregularity, or the wheel contains a flat spot
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Lateral Loading – The load forces applied by the wheel flange to the high rail in curved track. This is a result of wheel/truck curving forces. In sharp curves, lateral loading is normally stable throughout the curve. However, in a shallow curve or tangent track, lateral loading can occur as a result of truck hunting
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Creep – Load forces that are generated at the localized rail/wheel interface by the rolling action of the wheel. Longitudinal creep forces result from traction applied to the rail head by the wheel. Transverse creep forces result from lateral movement of the wheel during truck hunting.
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Bending Stress – Bending of the rail that occurs from vertical wheel loading and lateral wheel loading. Vertical wheel loading normally results from loading between the tie supports, and causes tensile longitudinal stresses in the rail base area and head/web fillet area. Lateral wheel loading applies tensile longitudinal stresses in the rail web area and head/web area of the rail field side
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Thermal Stress – These stresses occur in continuous welded rails due to thermal expansion and contractions that occur as the actual rail temperature increases above or reduces below the rail neutral temperature. When the rail temperature is above neutral temperature, compressive longitudinal stresses are established. When the rail temperature is below neutral temperature, tensile longitudinal stresses are established. These stresses can drastically influence rail flaw development.
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Residual Stress – These stresses are a result of the manufacturing process, particularly from roller straightening and head hardening. They can also result from the welding of rails because of the different expansion and contraction of the steel that occurs during the weld process. Residual stresses can be found in any location within the rail section and can exhibit high tensile stresses that can result in rail failure
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Defect development identification is determined by the type of defect, origin, and direction of development in relation to the planes of the rail section. These are identified as transverse, vertical and horizontal planes of development. The defects that develop in a transverse plane in relationship to the rail section are normally internal in origin and are not visibly identified until the defect progression penetrates the rail head
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Internal transverse defect size can only be identified visibly by breaking the cross-section of the rail in a press. After the rail is broken, a transverse defect is measured against the cross-sectional area of the rail head. If half of the rail head cross-section shows signs of defective growth, the defect is called a 50-percent fracture.
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Normal Growth – Defect development over a period of time in gradual stages. Normal development is typically progressive and can be uninterrupted. The defect will show a smooth and polished fracture with no granular structure. There may also be a number of identifiable smooth granular growth rings.
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Rapid Growth – Signifies recent development in numerous small stages. The small, polished, well-defined fracture is surrounded by a rough granular surface, which shows the outline of several growth rings of gradual increasing size.
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Sudden Growth – Signifies recent development in a few large stages. The small, polished, well-defined fracture is surrounded by a rough granular surface, which shows the outline of one or two growth rings. The distance between rings will increase directly with the rate of growth
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Defects that develop in an oblique, angular, or longitudinal direction in relationship to the rail section can also produce identifiable stages of development, referred to as multiple stage ruptures. This is often seen in bolt hole breaks, base breaks, and head and web separations
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There are two significant types of rail batter that an inspector will normally encounter during review of a rail defect. They are generally referred to as impact and friction batter. Impact batter is a result of a rail breaking exposing the fracture face to wheel impact from rolling stock. Friction batter is a result of sufficient rail section separation allowing the two fracture faces to make contact under load.
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A transverse defect is a type of fatigue that has developed in a plane transverse to the cross sectional area of the rail head.
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Compound fissure means a progressive fracture originating from a horizontal split head that turns up or down, or in both directions, in the head of the rail. Transverse development normally progresses substantially at a right angle to the length of the rail
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Detail fracture means a progressive fracture originating at or near the surface of the rail head. These fractures should not be confused with transverse fissures, compound fissures, or other defects, which have internal origins. Detail fractures may originate from shelly spots, head checks, or flaking.
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The reverse detail fracture is a progressive transverse fracture normally originating at the bottom corner of the gage side of the rail head
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Engine burn fracture means a progressive fracture originating in spots where driving wheels have slipped on top of the rail head.
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Ordinary break means a partial or complete break in which there is no sign of a fissure, and in which none of the other defects described in this section is found.
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Horizontal split head means a horizontal progressive defect originating inside of the rail head, usually one-quarter inch or more below the running surface and progressing horizontally in all directions, and generally accompanied by a flat spot on the running surface. The defect appears as a crack lengthwise of the rail when it reaches the side of the rail head
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Vertical split head means a vertical split through or near the middle of the head, extending into or through it. A crack or rust streak may show under the head close to the web or pieces may be split off the side of the head
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The origin is an internal longitudinal seam, segregation, or inclusion inherent from the manufacturing process. Vertical separation will progress longitudinally and vertically (parallel to side of head), and may gradually turn toward the gage or field side of the rail head. It is common for a portion of a vertical split head to develop toward the gage side of the rail head while the other end develops toward the field side.
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A shear break is a longitudinal separation of the rail head, resulting from the loss of significant rail head parent metal. The reduction of rail head parent metal results in the loss of the ability of the rail section to support loading, and is not typically associated with inherent conditions in the material. A shear break usually occurs when the rail is loaded off the center axis, causing rail head collapse, and can be associated with gaging problems, light weight rail, severely worn (vertical wear) rail, or off-center loads caused by worn rolling stock wheels
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Head and web separation means a progressive fracture longitudinally separating the head and web of the rail at the fillet under the head.
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Split web means a lengthwise crack along the side of the web, extending into or through it. The origin can be a seam or damage to the web, mechanical damage, or the split web can sometimes develop at locations where heat numbers are stamped into the web. Split webs can also develop as a result of high residual stresses from the roller straightening process, rail welding, and joint application
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Piped rail means a vertical split in a rail, usually in the web, due to failure of the shrinkage cavity in the ingot to unite in rolling.The origin of a piped rail is normally from the presence of a longitudinal seam or cavity inside the web that is inherent from the manufacturing process. Once development initiates, the seam will develop vertically toward the head and base of the rail. This type of defect is relatively uncommon in modern rail manufacturing technology
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Broken base means any break in the base of the rail. Broken base is generally categorized into two types of failure—broken base and base fracture
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Defective weld means a field or plant weld containing any discontinuities or pockets, exceeding 5 percent of the rail head area individually or 10 percent in the aggregate (oriented in or near the transverse plane) due to incomplete penetration of the weld metal between the rail ends, lack of fusion between weld and rail end metal, entrainment of slag or sand, underbead or other shrinkage cracking, or fatigue cracking. Weld defects may originate in the rail head, web, or base, and in some cases, cracks may progress from the defect into either or both adjoining rail ends. If the weld defect progresses longitudinally through the weld section, the defect is considered a split web for purposes of remedial action.
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Bolt hole crack means a crack across the web, originating from a bolt hole, and progressing on a path either inclined upward toward the rail head or inclined downward toward the base. Fully developed bolt hole cracks may continue horizontally along the head/web or base/web fillet, or they may progress into and through the head or base to separate a piece of the rail end from the rail. Multiple cracks occurring in one rail end are considered to be a single defect. However, bolt hole cracks occurring in adjacent rail ends within the same joint must be reported as separate defects
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Flattened rail means a short length of rail, not at a joint, that has flattened out across the width of the rail head to a depth of three-eighths inch or more below the rest of the rail and 8 inches or more in length. Flattened rail occurrences have no repetitive regularity and thus do not include corrugations, and have no apparent localized cause such as a weld or engine burn. Their individual lengths are relatively short, as compared to a condition such as head flow on the low rail of curves.
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Damaged rail means any rail broken or injured by wrecks, broken, flat, or unbalanced wheel, wheel slipping, or similar causes
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Crushed head means a short length of rail, not at a joint, which has drooped or sagged across the width of the rail head to a depth of three-eighths inch or more below the rest of the rail head and 8 inches or more in length. Unlike flattened rail, where the depression is visible on the rail head only, the sagging or drooping is also visible in the head/web fillet area.
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Portable Test Process – The portable test process consists of an operator pushing a test device over the rail at a walking pace, while visually interpreting the test data on a flaw detector. When a suspect defect is identified, the operator will stop and manually verify the defect type and location. The defect is then logged and reported to the railroad for remedial action. Presently, no permanent record of the test is stored for future analysis.
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Start/Stop Test Process – The start/stop process is a vehicle-based test at a slow speed, usually not in excess of 35–40 km/h. The vehicle travels along gathering data that is presented to the operator in real time for interpretation. Once a suspect equipment response is identified by the test operator, the vehicle is stopped and proceeds back to the suspect location. The location is verified by the operator and, if determined defective, classified and reported for immediate remedial action. This process produces a permanent record of test for future analysis.
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Chase Car Test Process – The chase car process is a variation of the start/stop process. This process consists of a lead test vehicle performing the flaw detection process in advance of a chase car. Once the lead test vehicle encounters an equipment response that represents a suspect defective condition, a copy of the test data is electronically transmitted back to the chase car for verification. The location is verified by the chase car operator, allowing the lead detector car to continue with the test. The purpose of this process is to increase production while maintaining the ability to report a defective condition for remedial action to the railway. A permanent record of the test is produced by the detector and chase car for future analysis.
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Continuous Test Process – The continuous test process consists of operating a high-speed vehicle-based test system nonstop along a designated route, sometimes covering in excess of 150– 300 km per shift. The test data is then analyzed according to defined standards at a centralized location. Once analyzed, reports are sent out to a verification staff via the Internet. They verify “suspects” to confirm as “defects” using a portable test unit or a portable hand-held flaw detector. Verification reports are transmitted back to the railroad over the Internet for records and proper remedial action. This process also produces a permanent record of test for future analysis
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Rolling contact fatigue (RCF) conditions develop in rails at the wheel/rail interface in most railroad systems
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Shells are identified as progressive horizontal separations, generally on the gauge side of the rail head, which may crack out at any level, usually at the upper gauge corner. Shelling may turn down to form a transverse separation and, once detected, is classified as a detail fracture. Uncapped or gutted shells will result in the dislodgement of parent metal from the rail section.
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Flaking originates at the surface of the rail and is commonly found near the stock rail area of a switch where concentrated loading cold works the steel. Flaking can be identified on the rail head surface as a horizontal separation with scaling or chipping of small segments of parent metal
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Burned rail is a rail head condition that is the result of friction from slipping locomotive drivers. The damaged area can gradually chip out and roughen under repeated traffic. Potential transverse defects can develop from thermal cracks associated with the burned area. Once the surface condition reaches a critical stage of displacement of the rail head surface material, the detection of an underlying rail flaw is obstructed.
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Head checking is identified as a slight separation of metal on the gauge side of the rail head, normally found in the high side of curves. It is also common in switch areas, due to the lateral force induced on the rail head from wheel displacement through turnouts. Head checking can turn down and develop into a transverse separation
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Spalling is generally referred to as the displacement of parent metal from the rail head from high contact stresses associated with cyclical loading. This may also be referred to as a slight flaking in the minimal stage of severity. Further deterioration of the rail head can increase the amount of metal displacement, resulting in a significant spalling condition
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The flash butt rail welding process is a method of forging two separate rails together by generating electrical heat until sufficient flashing of the parent metal takes place
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Gas pressure welding is a solid phase welding technique that uses the mixture of oxygen and acetylene gases for heating the rail ends to reach a temperature of approximately 2400 ºF and then applying high pressure to bond the rail ends. This process is normally done in a welding plant but also has mobile in-track capabilities.
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The steps used in the aluminothermic weld process consist of:• Preparing rail ends for welding• Rail end separation• Setting the weld gap and alignment• Rail clamp application• Applying the mold assembly• Placing weld material into the crucible• Preheating the rail ends• Igniting the weld material• Removing mold assembly• Shearing excess head weld material• Rough grinding the excess material• Final grinding of the weld material
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The primary benefits of rail grinding could be categorized by these four areas:1. Remove existing rolling contact fatigue to prevent development to a more severe condition that can result in additional damage or weakening of the rail section.2. Reprofile the rail head to the desired transverse shape and improve performance at the wheel/rail contact patch.3. Correct surface defects such as engine driver burns, dipped welds, etc.4. Improve rail inspection system capabilities
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